MXPA98009665A - Method and apparatus for measuring the duradirigida transfer in a c system - Google Patents

Abstract

In a communication network, a user of the network communicates with another user (30), using a remote unit (125) through at least one base station (B1A). The network is comprised of mobile switching control stations, first (MSC-I) and second (MSC-II), respectively, which control communications through a first set of base stations (B1A-B1E) that includes a first base station B1A and through a second set of base stations (B2A-B2E) that includes a second base station B2A. To direct communications between the remote unit (125) and the base stations, first (B1A) and second the first base station (B1A) measures a round trip delay of an active communication signal between the first base station (B1A) and the remote unit (125). The remote unit (125) measures a first phase shift of a pilot signal received from a first candidate base station (B1A) and reports it to the first mobile switching center (MSC-I) through the first base station ( B1A). The first mobile switching center (MSC-I) calculates a round trip delay candidate between the remote unit (125) and the first candidate base station (B1A). The first mobile switching center (MSC-I) calculates a round trip delay candidate between the remote unit (125) and the first candidate base station (B1A) based on the first phase shift and the round trip delay of the active communication signal. An active communication control unit accesses the directed hard transfer measurement table to determine a location of the remote unit based on the round trip delay corresponding to the first active communication signal and the round trip delay of candida

Description

METHOD AND APPARATUS FOR MEASURING HARD TRANSFER DIRECTED IN AN CDMA SYSTEM BACKGROUND OF THE INVENTION I Field of the Invention The present invention relates generally to cellular communication systems, in which multiple base stations are placed. More particularly, the present invention relates to a new and improved technique for transferring communication between base stations of different cellular systems. II. Description of the Related Art The use of multiple access modulation techniques by code distribution (CDMA) is one of several techniques to facilitate communications, in which a large number of users of the system are present. Although other techniques are known such as multiple time distribution access (TDMA) and multiple frequency distribution access (FDMA), the CDMA has significant advantages over these other modulation techniques. The use of CDMA techniques in a multiple access communication system is described in U.S. Patent No. 4,901,307, entitled "MULTIPLE DISTANCE SPECTRUM ACCESS COMMUNICATION SYSTEM USING TERRESTRIAL OR SATELLITE REPEATER" ("SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION"). SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS ", assigned to the assignee of the present invention, the description of which is incorporated herein by reference In the already mentioned patent, a multiple access technique is described, in which a large number of mobile telephone system users, each having a transceiver (also known as a remote unit), communicate through satellite repeaters or terrestrial base stations (also known as base stations or cell sites), using communication signals of diffused spectrum of CDMA.When using CDMA communications, the frequency spectrum can be It can be reused multiple times. The use of CDMA techniques results in a much higher spectral efficiency than can be achieved using other multiple access techniques, thus allowing an increase in the capacity of the system user. The conventional FM cellular telephone systems used in the United States are commonly called Advanced Mobile Telephone Service (AMPS), and are detailed in the Electronic Industry Association Standard EIA / TIA-533"Terrestrial Station Compatibility Specification - Mobile Station "(" Mobile Station -Land Station Compatibility Specification "). In such a conventional FM cellular telephone system, the available frequency band is divided into channels, typically 30 kilohertz (Khz) in bandwidth. The service area of the system is geographically divided into coverage areas of the base station that may vary in size. The available frequency channels are divided into sets. The sets of frequencies are assigned to the coverage areas in such a way as to reduce the possibility of interference in the co-channel. For example, consider a system in which there are seven sets of frequencies and the coverage areas are equally sized in hexagons. The set of frequencies used in a coverage area is not used in the six closest nearby coverage areas. In conventional cellular systems, a transfer scheme is used to allow a communication connection to continue when a remote unit crosses the boundary between the coverage areas of two different base stations. In the AMPS system, the transfer from one base station to another is initiated when the receiver at the active base station handles call alerts, that the received signal strength from the remote unit has dropped below a value of predetermined threshold. An indication of low signal strength implies that the remote unit should be close to the boundary of the coverage area of the base station. When the level of the signal falls below the predetermined threshold value, the active base station questions the system controller to determine if a nearby base station receives the signal from the remote unit with better signal strength than the current base station. The system controller in response to the question of the active base station sends messages to the neighboring base stations with a transfer request. Each of the base stations near the active base station uses a special scanning receiver, which searches for the signal coming from the remote unit in the channel, in which it is operating. If one of the next base stations reports an adequate signal level to the system controller, a transfer to that base station is attempted, in which the target base station is now marked. Then, the transfer is started by selecting an inactive channel from the set of channels used in the target base station. A control message is sent to the remote unit, which commands it to switch from the current channel to the new channel supported by the target base station. At the same time, the system controller switches the connection of the call from the active base station to the target base station. This process is referred to as hard transfer. The term hard is used to characterize the quality of "interrupt before doing" the transfer. In the conventional system a call connection is dropped (i.e., discontinued), if the transfer to the target base station is not successful. There are many reasons why a hard transfer failure may occur. The transfer may fail if there is no inactive channel available in the target base station. The transfer may also fail if one of the nearby base stations reports receiving a signal from the remote unit, when in fact the base station is currently receiving a different signal from the remote unit that uses the same channel to communicate with a station. distant base. This reporting error results in the transfer of the call connection to an erroneous base station, typically one in which the signal strength from the current remote unit is insufficient to maintain communications. Also, if the remote unit fails to receive the command to switch the channels, the transfer fails. Current operating experience indicates that transfer failures occur frequently, which significantly reduces the operating reliability of the system. Another common problem in the conventional AMPS telephone system occurs when the remote unit remains for an extended period of time near the edge between the two coverage areas. In this situation, the level of the signal tends to fluctuate with respect to each base station as the remote unit changes position or as other reflective or attenuating objects within the coverage area change position. Fluctuations in the level of the signal may result in an "alternation" situation, in which repeated requests are made to transfer the call from one side to the other between the two base stations. Such unnecessary additional transfers increase the probability that the call was inadvertently discontinued. In addition, repeated transfers, even if successful, can adversely affect the quality of the signal. In U.S. Patent No. 5,101,501, entitled "METHOD AND SYSTEM FOR PROVIDING A FLEXIBLE TRANSFER IN COMMUNICATIONS IN A CDMA CELLULAR TELEPHONE SYSTEM" ("METHOD AND SYSTEM FOR PROVIDING TO SOFT HANDOFF I? COMMUNICATIONS IN A CDMA CELLULAR TELEPHONE SYSTEM"), Issued on March 31, 1992, which is assigned to the assignee of the present invention, a method and system for providing communication with the remote unit through more than one base station during the transfer of a CDMA call is described. Using this type of transfer, the communication within the cellular system is uninterrupted by the transfer from the active base station to the target base station. This type of transfer can be considered as a "flexible" transfer in which the current communications are established with the target base station, which becomes a second active base station before communication with the first active base station is terminated. An improved flexible transfer technique is described in U.S. Patent No. 5,267,261, entitled "FLEXIBLE TRANSFER ASSISTED BY THE STATION MOBILE IN A CDMA CELLULAR COMMUNICATIONS SYSTEM " ("MOBILE STATION ASSISTED SOFT HANDOFF IN A CDMA CELLULAR COMMUNICATIONS SYSTEM"), issued on November 30, 1993, hereinafter referred to as the '261 patent, which is also assigned to the assignee of the present invention. In the system of the '261 patent, the flexible transfer process is controlled based on the measurements in the remote unit of the intensity of the "pilot" signals transmitted by each base station within the system. These pilot intensity measurements assist the flexible transfer process by facilitating the identification of viable base station transfer candidates.

More specifically, in the patent system 261 the remote unit monitors the signal strength of the pilot signals from the neighboring base stations. The coverage area of the nearby base stations does not really need the area of the base station with which active communication is established. When the intensity of the given signal from the pilot signal of one of the next base stations exceeds a given threshold, the remote unit sends a message of the signal strength to a system controller through the active base station. The system controller commands a target base station to establish communication with the remote unit and instructs the remote unit through the active base station to establish contemporary communication through the target base station while maintaining communication with the active base station. This process can continue for the additional base stations. When the remote unit detects that the signal strength of a pilot corresponds to one of the base stations, through which the remote unit communicates, has fallen below a predetermined level, the remote unit reports the intensity of the measurement signal of the base station corresponding to the system controller through the active base stations. The system controller sends an order message to the identified base station and to the remote unit, to terminate communication through the identified base station while communications are maintained through the other base station or active base stations. Although the above techniques are well suited for call transfers between base stations in the same cellular system, which are controlled by the same system controller, a more difficult situation is presented by the movement of the remote unit towards a coverage area served by a base station of another cellular system. A complicating factor in such "intersystem" transfers is that each system is controlled by a different system controller and typically there is no direct link between the base stations of the first system and the system controller of the second system and vice versa. Thus, the two systems are excluded from executing simultaneous communication of the remote unit through more than one base station during the transfer process. Even if the existence of an intersystem link between the two systems is available to facilitate the flexible transfer of the intersystem, often the dissimilar characteristics of the two systems further complicate the flexible transfer process.

When resources are not available to conduct flexible intersystem transfers, the execution of a "hard" transfer of a connection from one system call to another becomes critical if it is to keep the service uninterrupted. The intersystem transfer must be executed at the probable time and location to result in the successful transfer of the inter-system call connection. The next thing is that the transfer should only be attempted when, for example: (i) an inactive channel is available in the target base station. (ii) the remote unit is within the range of the target base station and the active base station, and (iii) the remote unit is in a position in which it is assured of receiving the command to switch channels. Ideally, each hard transfer of the intersystem should be conducted in a manner that reduces the potential for "alternation" transfer requests between the base stations of different systems. These and other deficiencies of existing intersystem transfer techniques impair the quality of cellular communications, and can be expected to further degrade performance as competing cellular systems continue to proliferate. According to the above, there is a need resulting from an intersystem transfer technique capable of safely executing the transfer of a call between the base stations of different systems. SUMMARY OF THE INVENTION The present invention is a means for using the round trip delay between the remote unit and the base stations, which are members of the Sets, Candidate and Active, to identify the location of a remote unit. One use of the present invention is to facilitate the hard transfer of a first base station controlled by a first system controller to a second base station controlled by a second system controller. The round trip delay between the remote unit and the base stations in the Active Set is measured directly by the corresponding base stations. The round-trip delay of the base stations in the Candidate Set is not directly measured and must be calculated based on the perception of the remote unit of the pilot signal from the candidate base station. Once the round trip delay is determined, it can be used in conjunction with the hard drive measurement directed by the remote unit (MDHO) to determine if the remote unit is located in a region within the coverage area where it is both necessary as the hard transfer is likely to be carried out successfully, and to determine to which of the base stations the hard transfer should be attempted. When the remote unit enters the MDHO state, an active communication control unit, which handles the connection of the remote unit, sends a set of round trip delay and designation measurements of the corresponding base station, system controller. The system controller accesses an MDHO table, which contains a series of rows of information. Each row contains a list of base station identification numbers and corresponding round trip delay ranges, to define -specific regions and the appropriate transfer action for each region. If the location of the remote unit is matched to one of the regions designated by the rows in the MDHO table, the system controller initiates the action specified in the MDHO table. The parameters that control the flexible transfer process can be increased to increase the number of members of the Sets, Candidate and Active. The pause of the base station can also be increased for the appropriate operation. The hard transfer measurement concept managed by the remote unit can be combined with the physical configurations of the coverage area, which provides both spatial, intrasystem and intersystem hysteresis. It can also be combined with other network planning configurations to provide maximum benefit, such as the use of CDMA for frequency transfer other than CDMA. BRIEF DESCRIPTION OF THE DRAWINGS The features, objectives and advantages of the present invention will be more apparent from the detailed description set forth below, when taken in conjunction with the drawings in which: Figure 1 provides an exemplary illustration of a PBX system Wireless, PCS, or cellular LL; Figure 2 shows a cellular communications network comprising a first and second cellular system respectively, controlled by, mobile switching centers, first (MSC-I) and second (MSC-II); Figure 3 shows a cellular communication system placed with a microwave link from point to point between two directional microwave antennas; Figure 4A shows a highly idealized representation of the hard transfer region of an FM system; Figure 4B shows a highly idealized representation of the hard, flexible, transfer region of a CDMA system; Figure 4C shows a highly idealized representation of the transfer region corresponding to a CDMA for a frequency transfer different from CDMA; Fig. 5 shows an indoor transition set and the base stations of the second system, and is used to illustrate the function of the hard drive transfer measurement table of the remote unit; Figure 6 shows an antenna pattern for a base station divided into three sectors; Figure 7 illustrates the use of the detection rule in a CDMA for the similar frequency transfer of CDMA; Figure 8 illustrates the use of the detection rule in a CDMA for frequency transfer different from CDMA; Figure 9 illustrates the two base stations placed in a configuration that provides CDMA for frequency transfer different from CDMA; Figure 10 illustrates the transfer of a CDMA system to a system that provides the service, using a different technology; Figure 11 illustrates an alternative configuration that provides a CDMA for a frequency transfer different from CDMA, using a single base station divided into multiple sectors; Figure 12 is a block diagram of a prior art base station comprising reception diversity; Figure 13 is a block diagram of a boundary base station having transmission diversity to produce path diversity; Figure 14 represents the use of base stations placed to execute the hard transfer; Fig. 15 depicts the use of proximally located base stations that have a significant portion of the cover area coverage to perform the hard transfer; Figure 16 illustrates the use of a "Cone of Silence" in a CDMA system crossed by a microwave link from point to point; and Figure 17 illustrates the use of a "Cone of Silence "in a CDMA system crossed by a microwave link from point to point, in which the area of coverage of the cone of silence and the coverage area of the microwave link are substantially equal DESCRIPTION OF THE PREFERRED MODALITY In the Figure 1 is provided an exemplary illustration of a cellular telephone system, a wireless system of the private telephone exchange (PBX), a wireless local cycle (WLL), a system of the personal communication system (PCS) or other analogous wireless communication systems. In an alternative embodiment, the base stations of Figure 1 may be satellite based The system illustrated in Figure 1 may use various multiple access modulation techniques to facilitate communications between a large number of remote units and a plurality of stations A number of techniques of the multiple access communication system are known in the art. or, multiple time distribution access (TDMA), multiple frequency distribution access (FDMA), multiple code distribution access (CDMA) and amplitude modulation (AM) schemes, such as the band lateral single compressor-amplitude expander. However, the spread spectrum modulation technique of CDMA has significant advantages over these modulation techniques for multiple access communication systems. The use of CDMA techniques in a multiple access communication system is described in U.S. Patent No. 4,901,307, issued February 13, 1990, entitled "MULTIPLE SPECTRO ACCESS COMMUNICATION SYSTEM SPREADED BY TERRESTRIAL REPEATER OR BY SATELLITE "(" SPREAD SPECTRUM MULTIPLE ACCESS COMMU? ICATIO? SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS ", assigned to the assignee of the present invention, which is incorporated herein by reference.) Many of the ideas described herein may be used with a variety of communication techniques, although through the preferred embodiments described herein are described with reference to a CDMA system. In the American Patent? O. 4,901,307 mentioned above, a multiple access technique is described wherein a large number of users of the mobile telephone system having a transceiver, communicates through satellite repeaters or terrestrial base stations using broadcast spectrum communication signals of CDMA. When using CDMA communications, the same frequency spectrum can be reused several times to communicate a plurality of different communication signals. The use of CDMA results in a much higher spectral efficiency than can be achieved using other multiple access techniques, thus allowing an increase in the capacity of the system user. In a typical CDMA system, each base station transmits a unique pilot signal. In the preferred embodiment, the pilot signal is a broadcast signal, direct sequence, unmodulated, continuously transmitted by each base station, using a common pseudo-random noise (PN) broadcast code. Each base station or each sector of the base station transmits the common displacement of the pilot sequence in time from the other base stations. The remote units can identify a base station, based on the phase shift of the code of the pilot signal that is received from the base station. The pilot signal also provides a phase reference for coherent demodulation and the basis of the intensity measurements of the signal used in the transfer determination. Referring again to Figure 1, the system controller and the switch 10, also referred to as a mobile switching center (MSC), typically includes the processing and interface circuitry to provide control of the system to the base stations. The controller 10 also controls the routing of calls from the public switched telephone network (PSTN) to the appropriate base station for transmission to the appropriate remote unit. The controller 10 also controls the routing of calls from the remote units, through at least one base station to the PSTN. The controller 10 can direct calls between remote units through the appropriate base stations. A typical wireless communication system contains some base stations that have multiple sectors. A base station divided into multiple sectors comprises multiple independent transmit and receive antennas, as well as some independent processing circuitry. The present invention applies equally to each sector of a base station divided into sectors and to each of the independent base stations divided into a single sector. The term base station can be assumed to refer to any sector of a base station or a base station divided into a sector. The controller 10 may be coupled to the base stations by various means such as dedicated telephone lines, fiber optic links or microwave communication links. Figure 1 illustrates the exemplary base stations 12, 14, 16 and the exemplary remote unit 18. The remote unit 18 can be a vehicle-based telephone or a portable unit, a PCS unit, or a wireless local loop unit Fixed location or any other data communication or voice setting device. The arrows 20A-20B illustrate the possible communication link between the base station 12 and the base station 18. The arrows 22A-22B illustrate the possible communication link between the base station 14 and the base station 18. Similarly, the arrows 24A-24B illustrate the possible communication link between the base station 16 and the base station 18. The base station locations are designed to service the remote units located within their coverage areas. When the remote unit is inactive, that is, no call is in progress, the remote unit constantly monitors the transmissions of the pilot signal from each nearby base station. As illustrated in Figure 1, the pilot signals are transmitted to the remote unit 18 by the base stations 12, 14 and 16 in the communication links 20B, 22B and 24B, respectively. Generally speaking, the term forward link refers to the connection from the remote unit to the base station. In the example illustrated in Figure 1, the remote unit 18 may be considered to be in the coverage area of the base station 16. As such, the remote unit 18 tends to receive the pilot signal from the base station 16 at a time. level higher than any other pilot signal that it monitors. When a remote unit 18 initiates a communication of the traffic channel (ie, a telephone call), a control message is transmitted to the base station 16. The base station 16, upon receipt of the call request message, signals the controller 10 and transfer the called telephone number. The controller 10 then connects the call through the PSTN to the planned receiver. If a call is initiated from the PSTN, the controller 10 transmits the call information to a set of base stations located near the location at which the remote unit most recently registered its presence. The responding base stations transmit a paging message. When the planned remote unit receives its page message, it responds with a control message that is transmitted to the nearest base station. The control message notifies the controller 10 that its particular base station is in communication with the remote unit. The controller 10 initially routes the call through this base station to the remote unit. If the remote unit 18 moves outside the coverage area of the initial base station, for example, the communication from the base station 16 is transferred to another base station. The process of transferring the communication to another base station is referred to as a transfer. In the preferred embodiment, the remote unit initiates and assists the transfer process. According to "Mobile Station Compatibility Standard-Base Station for the Dual-Mode Broadband Broadcast Spectrum System" ("Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System"), TIA / EIA / IS-95, generally referred to simply as IS-95, a transfer "assisted by the remote unit" can be initiated by the remote unit itself. The remote unit is equipped with a search receiver that is used to examine the transmission of the pilot signal from the nearby base stations, in addition to performing other functions. If a pilot signal from one of the base stations, for example the base station 12, is found to be more intense than a given threshold, the remote unit 18 transmits a message to the current base station, the base station 16. The information is communicates through the base station 16 to the controller 10. The controller 10 upon receipt of this information can initiate a connection between the remote unit 18 and the base station 12. The controller 10 requires the base station 12 to allocate resources to the call. In the preferred embodiment, the base station 12 allocates a channel element to process the call and reports such allocation back to the controller 10. The controller 10 informs the remote unit 18 through the base station 16, to search for a signal from the base station 12 and informs the base station 12 of the parameters of the traffic channel of the remote unit. The remote unit 18 communicates through both base stations, 12 and 16. During this process, the remote unit continues the identification and measurement of the signal strength of the pilot signals it receives. In this way, assisted transfer is achieved by the remote unit. The above process can also be considered a "flexible" transfer, in which the remote unit communicates simultaneously through more than one base station. During a flexible transfer, he can combine or choose between the signals received from each base station, with which the remote unit is in communication. The MSC retransmits the signals from the PSTN to each base station, with which the remote unit is in communication. The remote unit combines the signals it receives from each base station to produce a total result. In reviewing the flexible transfer process, it is clear that the MSC provides centralized control of the process. The transfers assisted by the remote unit tend to be more complex if it happens that the remote unit is located within the same cellular system, that is, they are not controlled by the same MSC. Figure 2 shows a cellular communications network 30 comprising cellular systems, first and second, under control of the mobile switching centers, first and second, MSC-I and MSC-II, respectively. The MSC-I and the MSC-II are respectively coupled to the base stations of the cellular systems, first and second, by means of various means such as, dedicated telephone lines, fiber optic links or microwave communication links . In Figure 2, five such exemplary base stations B1A-B1E respectively are shown illustrated, being provided within the coverage areas C1A-C1E of the first system, and five of the base stations B2A ~ B2E respectively, being provided within the coverage areas C2A-C2E of the second cellular system. For convenience of illustration, the coverage areas C ^ -C ^ and C2A-C2E of Figure 2, and the coverage areas shown in Figure 3 introduced subsequently in the present, are shown circular or hexagonal and highly idealized. . In the current communication medium, the coverage areas of the base station may vary in size and shape. The coverage areas of the base station may tend to be covered with the boundaries of the coverage area, defining shapes of the coverage area other than the ideal circular or hexagonal shape. In addition, the base stations can also be divided into sectors, such as into three sectors, as is known in the art. In what continues to the coverage areas C1A-CIE and C2A-C2E, they can be referred to as limiting or transitional coverage areas, because these coverage areas are close to the boundary between the cellular systems, first and second. The rest of the coverage areas within each system are referred to as the internal or internal coverage area. A quick review of Figure 2 reveals that the MSC-II does not have direct access to communicate with the base stations B ^ -B- ^., And the MSC-1 does not have direct access to communicate with the B2A-B2 base stations as shown in Figure 2, the MSC-I and MSC-II can communicate with each other. For example, the EIA / TIA / IS-41, entitled "Cellular Radio Telecommunications Intersystem Operations Operations", and the subsequent revision thereof, define a standard for communication between different commutations. regions of operation, as shown by the data link of the intersystem 34 in Figure 2. To provide flexible transfer between one of the base stations B1C-B1E and one of the B2C-B2E base stations, a large volume of the Power control and call signal must pass between the MSC-I and MSC-II. The long-term nature of the switch-to-switch connection and the large volume of energy control and call signal information can cause undue delay and can sacrifice undue resources. Another difficulty in providing flexible transfer is that the architecture of the system controlled by the MSC-I and the system controlled by the MSC-II can be vastly different. As well, the method of energy control used by the two systems can be very different. Therefore, the present invention relates to providing a hard transfer mechanism between two systems to avoid the complications and expense of flexible intersystem transfer. A hard transfer mechanism can be used in several situations. For example, the system controlled by the MSC-II may not use a CDMA to communicate the signals, but may instead use FM, TDMA or another method. In such a case, hard transfer is still required if a flexible transfer mechanism of the system is provided in the system controlled by the MSC-I, because flexible transfer is only possible if both systems operate using CDMA. In accordance with the above, this invention could be used for remote transfer units between two systems that employ different interfaces by air. It may be necessary for the second system to be modified to transmit a pilot signal, or another CDMA signal emitter, to assist in the initiation of the hard transfer process. A system employing a pilot signal emitter is detailed in the co-pending US Patent Application Serial No. 08 / 413,306 entitled "CDMA METHOD AND APPARATUS ASSISTED BY THE MOBILE UNIT FOR HARD TRANSFER OF THE ALTERNATIVE SYSTEM" ("METHOD AND APPARATUS FOR MOBILE UNIT ASSISTED CDMA TO ALTERNATIVE SYSTEM HARD HANDOFF "), filed on March 30, 1995. An alternative system is detailed in the US Patent Application, Copending Serial No. 08 / 522,469 entitled" DOUBLE REPEATER FOR DISTRIBUTION IN TIME, AT THE SAME FREQUENCY "(" SAME FREQUENCY, TIME-DIVISION-DUPLEX REPEATER "), filed on August 31, 1995, both of which are assigned to the assignee of the present invention. A system that can use a pilot signal emitter unit is detailed in the co-pending US Patent Application Serial No. 08 / 322,817 entitled "TRANSFER METHOD AND APPARATUS BETWEEN DIFFERENT CELLULAR COMMUNICATIONS SYSTEMS" ("METHOD AMD APPARATUS FOR HANDOFF BETWEEN DIFFERENT CELLULAR COMMUNICATIONS SYSTEMS "), filed on October 13, 1995 and assigned to the assignee of the present invention.

Another situation in which a hard transfer may be useful is the case where the remote unit must change the frequency in which it operates. For example, within the PCS band, point-to-point microwave links can operate in co-existence with the CDMA communication system. In Figure 3, the point-to-point microwave link 140 is shown between the directional microwave antenna 130 and the directional microwave antenna 135. The base stations 40, 100, and 110 may need to avoid using the frequency band used by the antenna. microwave link from point to point 140 and thus avoid the interface between the two systems. Because the directional microwave antenna 130 and the directional microwave antennas 135 are highly directional, the point-to-point microwave link 140 has a very narrow field. In itself, the other base stations of the system such as the base stations 115, 120 and sectors 50 and 70 can operate without interference with the point-to-point microwave link 140. In this way, the remote unit 125 may be operating. in a CDMA channel in the same frequency band as the point-to-point microwave link 140. If the remote unit 125 moves to the base station 110, which does not maintain communication on the frequency at which the remote unit 125 is currently operating, it is not possible to complete a flexible transfer from the base station 115 to the base station 110. Instead, the base station 115 may instruct the remote unit 125 to perform a hard transfer to another frequency band, the which is maintained by the base station 110. Another situation in which a hard transfer may be useful is the case where a remote unit must change the frequency in which it operates for a more equal load distributed mind. For example, within the PSC band, the CDMA communicates with the traffic channel signals in a plurality of frequency bands such as, the frequency band fx and the frequency band f2. If the frequency band f2 is loaded more excessively with the active communication signals than the frequency band fx, it may be advantageous to download some of the active communication signal from the frequency band f2 to the frequency band fx. To effect the load distribution, one or more of the remote units operating in the frequency band f2 are ordered to start operating in the frequency band f2, when executing a hard transfer of the intersystem. The surest way to execute a hard transfer may be that the base station 115 executes a hard transfer to an alternative frequency within it. Thus, at some point when the remote unit 125 preferably receives more secure and large signals from the base station 115, the base station 115 instructs the remote unit 125 to operate at a different frequency supported by the base station 115. The base station 115 starts transmitting and tries to receive the signal transmitted by the remote unit on the new frequency. Alternatively, a hard transfer could occur between a first frequency of the base station 115 and a second frequency of the base station 110. Neither of the two types of hard transfer requires communication of the system. Referring again to Figure 2, the first mobile switching center (MSC-I) against routing telephone calls from the PSTN to the appropriate base station B1A-B1B for transmission to the designated remote unit. The MSC-I also controls the routing of calls from the remote units within the coverage area, through at least one base station, to the PSTN. The MSC-II operates in a similar manner to direct the operation of the B2A-B2E base stations. the control messages and the like can be communicated between the MSC-I and the MSC-II by a data link of the system 34, using an industry standard, such as IS-41 or the subsequent revision standard.

When a remote unit is located within the coverage area of an internal base station, the remote unit is programmed to monitor the transmission of pilot signals from a set of nearby base stations. Consider a case in which the remote unit is located within the coverage area C1D, but approaches the coverage area C2D. In this example, the remote unit could begin to receive usable signal levels from the base station B2D, which then could be reported to the base station B1D and. to any other base station (s) with which the remote unit is currently in communication. The time at which the usable signal levels begin to be received by a remote unit can be determined by measuring one or more quantifiable parameters (eg, signal strength, signal-to-noise ratio, degree of frame error, degree of frame erasure, degree of bit error, and / or relative time delay) of the received signal. In the preferred embodiment, the measurement is based on the intensity of the pilot signal, as it is received by the remote unit. After such detection of the signal levels usable in the remote unit, or of reporting them to the base station B1D using a message of quality or signal strength, then a hard transfer assisted by the remote frequency unit could be processed. similar, as follows: (i) The base station B1D retransmits the level of the reported signal of the remote unit received from the base station B2D to the MSC-I, which is aware that the base station B2D is controlled by the MSC -II; (ii) The MSC-I requests the resources of the channel and the facilities of the connection line of the system between the two systems in the base station B2D to the MSC-II, by the data link of the intersystem 34; (iii) The MSC-II responds to the request by supplying the information for MSC-I through the data link of the Intesystem 34, which identifies the channel in which the communication is to be established, as well as other information. In addition, the controller reserves within the B2D base station, the designated channel for communication with the remote unit and the resources of the junction line; (iv) The MSC-I provides the new channel information to the remote unit through the base station B1D, and specifies a time at which the remote unit begins to communicate with the base station B2D; (v) The communication is established through the hard transfer between the remote unit and the base station B2D at the specified time; (vi) The MSC-II confirms to the MSC-I the successful transition of the remote unit in the system. One difficulty with this proposal is that the MSC-I is not aware of whether the signal coming from the remote unit is received by the base station B2D at a sufficient level to maintain communication at the moment. The MSC-II instructs the remote unit to establish communication with the base station B2D. Similarly, the base station B 2D may not yet receive a level of the usable signal coming from the remote unit. As a result, the call connection may fall during the process of transferring control to the MSC-II. If the connection of the call is dropped, an error message would be sent instead of an acknowledgment from the MSC-II to the MSC-I. Another difficulty in providing hard transfer is the nature of the boundaries of the coverage area of the CDMA system. In an FM system, such as the AMPS, the covering regions of the coverage area preferably extend. The coverage region of the coverage area is the area in which communication can be maintained between a remote unit and either one of the two different base stations alone. In the FM system such covering regions of the coverage area must be extended, because hard transfers only occur successfully when the remote unit is located in a covering region of the coverage area. For example, Figure 4A is a highly idealized representation of an FM system. The base station 150 and the base station 165 are capable of providing forward link and reverse link FM communication to the remote unit 155. (The forward link refers to the connection of the base station to the remote unit. refers to the connection of the remote unit to the base station). Within region 160, the signal strength of both the base station 150 and the base station 165 is a sufficient level to maintain communication with the remote unit 155. Note that due to the nature of the FM system, the stations base 150 and 165 can not communicate simultaneously with the remote unit 155. When a hard transfer occurs from the base station 150 to the base station 165 within the region 160, a new frequency is used for communication between the base station 165 and the remote unit 155 that was used between the base station 150 and the remote unit 155. The base station 165 never transmits on any frequency used by the base station 150, and thus the base station 165 does not nominally provide interference to the base station. the communication between the base station 150 and any remote unit with which it is in communication. The boundary 182 indicates the location beyond which the communication from the base station 165 to the remote unit 155 is not possible. Similarly, the boundary 188 indicates the location beyond which communication from the base station 150 to the remote unit 155 is not possible. Obviously, Figure 4A as well as Figs. 4B and 4C, are not drawn in scale and in reality the coverage regions of the coverage area are relatively narrow compared to the total coverage area of each base station. With the flexible transfer of CDMA, the existence of a covering region of the coverage area, in which communication can be completely maintained by precisely one of the two base stations, is not critical. In the region where the flexible transfer occurs, it is sufficient that reliable communication can be maintained if the communication is established simultaneously with two or more base stations. In the CDMA system, typically the base stations, active and close, operate on the same frequency. In this way as the remote unit approaches a coverage area of a nearby base station, the signal levels of the active base station fall and the interference levels of the base station are increased. Due to the increased interference from nearby base stations, if the flexible transfer is not established, the connection between the active base station and the remote unit can become dangerous. The connection is especially risky if the signal vanishes with respect to the active base station and not with respect to the next base station. Figure 4B is a highly idealized representation of a CDMA system. The CDMA base station 200 and the CDMA base station 205 are capable of providing reverse link CDMA communication and forward to the remote unit 155. Within the darkest region 170, the signal strength of both the station base 200 as of the base station 205 is a sufficient level to maintain communication with the remote unit 155, even if the communication is established with only one of, the base station 200 or the base station 205. Beyond the limit 188 communication only through the base station 205 is not reliable. Similarly, beyond the limit 186 communication only through the base station 200 is not reliable. The regions 175A, 170 and 175B represent the areas in which it is likely that a remote unit will be in flexible transfer between the base stations 200 and 205. When establishing communication through both base stations, 200 and 205, total security improves of the system even if the communication link with a remote unit within the region 175A to the base station 205 is not reliable alone to maintain communication. Beyond the limit 180, the signal levels of the base station 205 are not sufficient to maintain communication with the remote unit 155, even in flexible transfer. Beyond the limit 190, the signal levels of the base station 200 are not sufficient to maintain communication with the remote unit 155, even in flexible transfer. Note that Figs. 4A and 4B are drawn with reference to one another. The reference numbers used to designate the limits 180, 182, 184, 186, 188 and 190, increase in value with the increase in distance from the base station 150 and the base station 200. In itself, the flexible transfer region between limits 180 and 190 is the largest region. The region of coverage of the coverage area between limits 182 and 188 lies within the flexible CDMA transfer region. The "flexible transfer" region of CDMA is the narrowest region between limits 184 and 186. Note that if the base station 200 belongs to a first system and the base station 205 belongs to a second system, the base station 200 and the base station 205 may not be capable of simultaneous communication with the remote unit 155. Thus, if the communication needs to be transferred from the base station '200 to the base station 205, a hard transfer from the base station 200 to the base station needs to be executed. base station 205. Note that the remote unit should be located in the flexible CDMA transfer region between limits 184 and 186 in region 170 so that the hard transfer has a high probability of success. The difficulty lies in the fact that the hard transfer region 170 can be severely narrow and the time it takes for the remote unit 155 to move in and out of the hard transfer region 170 can be very small. Furthermore, it is difficult to discern whether the remote unit 155 is within the hard transfer region 170. Once it has been determined that the remote unit 155 is in the hard transfer region 170, a decision can be made as to whether, a which base station and when the hard transfer could occur. The present invention addresses these problems. The first aspect of the present invention is a system and method for determining the regions within the coverage area, where it is both necessary and probable that the hard transfer be carried out successfully and for which of the base stations the hard transfer should be attempted . The hexagonal cover installation shown in Figure 3 is highly idealized. When the systems are currently deployed, the resulting coverage area takes many different forms. Figure 5 shows a more real representation of a set of base stations. The base stations Tx-T3 and the base stations I1-I3, are part of a first communication system controlled by the controller 212 of the system 1. The base stations I ^ .- ^ are indoor base stations, which only limit with other base stations of the same system. The Tx-T3 base stations are base, edge or transition stations, which have coverage areas that border the coverage areas of the base stations that belong to a different operating system. The base stations S- ^ Sj are part of a second controller system by the controller 214 of the system 2. The last thick concentric circles surrounding the base station S3, the base stations l! -I3 and the base stations? 1-T3, they indicate the idealized coverage areas of the base stations, in which it is possible to establish communication with the corresponding base station. The last thick wavy lines surrounding the base stations S-L-S3 and T1 show more realistic coverage areas of the corresponding base stations. For example, the wavy line 228 represents the coverage area of the base station S1. The shape of the coverage area is effected mostly by the terrain in which the base station resides, such as the height at which the antennas are mounted., the number, reflection and height of tall buildings in the coverage area as well as trees, hills and other obstacles within the coverage area. The actual coverage areas are not shown for each base station to simplify the drawing. In a current system, some of the base stations can be divided into sectors, such as into three sectors. Figure 6 shows an antenna pattern for a base station divided into three sectors. No base station divided into three sectors is shown in Figure 5 in order to simplify the drawing. The concepts of the present invention apply directly to base stations divided into sectors. In Figure 6, the coverage area 300A is represented by the thinnest line width. The 3OOB coverage area is represented by the medium-width line. The coverage area 300C is represented by the thickest line. The shape of the three coverage areas shown in Figure 6 is the shape produced by the standard directional dipole antennas. The edges of the coverage areas can be considered as the location in which a remote unit receives the minimum signal level, necessary to maintain communication through that sector. As a remote unit moves towards the sector, the intensity of the signal received from the base station is increased as perceived by the remote unit. A remote unit at point 302 can communicate through sector 3OOA. A remote unit at point 303 can communicate through sector 3OOA and sector 3OOB. A remote unit at point 304 communicates through sector 3OOB. As the remote unit moves beyond the edge of the sector, communication through that sector can degrade. It is likely that a remote unit operating in the flexible transfer mode between the base station in Figure 6 and a nearby non-shown base station is located near the edge of one of the two sectors. The base station 60 of Figure 3 represents a base station divided into three more idealized sectors. The base station 60 has three sectors, each of which covers more than 120 degrees of coverage area of the base station. The sector 50, which has a coverage area indicated by the solid lines 55, covers the coverage area of the sector 70, which has a coverage area indicated by the thick dashed lines 75. The sector 50 also covers the sector 80, which it has a coverage area as indicated by thin scratched lines 85. For example, location 90, as indicated by X, is located both in the coverage area of sector 50 and sector 70. In general, a station The base is divided into sectors to reduce the total interference energy for the remote units located within the coverage area of the base station while increasing the number of remote units that can communicate through the base station. For example, sector 80 would not transmit a proposed signal for a remote unit at location 90 and thus does not significantly interfere with the remote unit located in sector 80, by communicating a remote unit at location 90 with the base station 60. For a remote unit located at location 90, the total interference has contributions from sectors 50 and 70 and from base stations 115 and 120. A remote unit at location 90 can be found in more flexible transfer with the sectors 50 and 70. A remote unit at location 90 can be simultaneously in flexible transfer with either or both of the base stations 115 and 120. The flexible transfer assisted by the remote unit operates based on the strength of the pilot signal from various sets of stations. base stations, as measured by the remote unit. The Active Set is the set of base stations, through which active communication is established. The Next Set is the set of base stations surrounding an active base station comprising base stations that have a high probability of having a signal strength of sufficient level to establish communication. The Candidate Set is a set of base stations that have an intensity of the pilot signal at a signal level sufficient to establish communication. When communications are initially established, a remote unit communicates through a first base station, and the Active Set only contains the first base station. The remote unit monitors the signal strength of the base stations of the Active Set, the Candidate Set and the Close Set. When a pilot signal from a base station in the Next Set exceeds a predetermined threshold level, the base station is added to the Candidate Set and removed from the Next Set on the remote unit. The remote unit communicates a message to the first base station that identifies the new base station. The system controller decides whether to establish communication between the new base station and the remote unit. If the system controller decides to do so, the system controller sends a message to the new base station with the identification information about the remote unit, and an order to establish communications with it. A message is also transmitted to the remote unit through the first base station. The message identifies a new Active Set that includes the base stations, first and new. The remote unit searches for the information signal transmitted by the new base station and communication is established with the new base station without terminating the communication through the first base station. This process can continue with additional base stations. When the remote unit communicates through multiple base stations, it continues to monitor the signal strength of the base stations of the Active Set, the Candidate Set and the Close Set. If the intensity of the signal corresponding to the base station of the Active Set falls below a predetermined threshold for a predetermined period of time, the remote unit generates and transmits a message to report the event. The system controller receives this message through at least one of the base stations, with which the remote unit communicates. The system controller may decide to terminate communications through the base station having a weak pilot signal strength. The system controller in the decision to terminate communications through the base station generates a message identifying a new Active Set of base stations. The new Active Set does not contain the base station through which the communication is terminated. The base stations through which communication is established, send a message to the remote unit. The system controller also communicates the information to the base station to terminate communications with the remote unit. In this way, communications from the remote unit are routed only through the base stations identified in the new Active Set. When a remote unit is in flexible transfer, the system controller receives decoded packets from each of the base stations that are members of the Active Set. From the set of signals, the system controller must create a single signal for transmission to the PSTN. Within each base station, the signals received from a common remote unit can be combined before they are deciphered, thus taking full advantage of the multiple signals received. The decoded result of each base station is provided to the system controller. Once the signal has been decoded it can not be 'easily' and advantageously 'combined' with other signals. In the preferred embodiment, the system controller must select among the plurality of decoded signals corresponding one to one to a base station with which communication is established. The most advantageous decoded signal is selected from the group of signals of the base stations and the other signals are simply discarded. In addition to flexible transfer, the system can also use "more flexible" transfer. Generally, the most flexible transfer refers to the transfer between sectors of a common base station. Because the sectors of a common base station are connected much more intimately, the transfer between the sectors of a common base station can be done by combining data without decoding instead of selecting decoded data. The present invention applies equally whether or not a more flexible transfer is used within any system. The more flexible transfer process is described in U.S. Patent Application No. 08 / 405,611 entitled "METHOD AND APPARATUS FOR EXECUTING TRANSFER BETWEEN SECTORS OF A COMMON BASE STATION" ("METHOD AND APPARATUS FOR PERFORMING HANDOFF BETWEEN SECTORS OF A COMMON BASE STATION "), filed on March 13, 1995, which is a continuation in part of US Patent Application No. 08 / 144,903, filed on October 10, 1993, now abandoned, each of which is assigned to the assignee of the present invention. In the preferred embodiment, the selection process is executed by the system controller within a subsystem of the selector bank (SBS). The SBS is comprised of a set of selectors. Each selector handles active communication for a remote unit. At the termination of a call connection, the selector can be assigned to another active remote unit. The selector provides all kinds of control functions for both the remote unit and the base stations. The selector sends and receives messages from the base stations. An example of such a message is the message sent by the base station each time the round trip delay between the base station and the remote unit changes by a threshold amount. The selector can also command the base station to send a message to the remote unit. An example of such a message is a message sent to the base station that commands it to order the remote unit to provide a Pilot Intensity Measurement Message (PSMM). The use of both signals is explained more fully below. In the most general mode, it does not need to be a selector that controls the transfer process and any kind of communication control unit can execute the functions that in the preferred modality are delegated to the selector. When a remote unit has established communication with a base station, the base station can measure the round trip delay (RTD) associated with the remote unit. The base station aligns its transmission to the remote unit in time based on universal time. The signal is transmitted from the base station to the remote unit by the wireless air link. The transmitted signal requires some time to travel from the base station to the remote unit. The remote unit uses the signal it receives from the base station to align the transmission it sends back to the base station. By comparing the time alignment of the signal received by the base station from the remote unit with the alignment of the signal sent by the base station to the remote unit, the base station can determine the round trip delay. The round trip delay can be used to estimate the distance between the base station and the remote unit. According to the preferred embodiment, the base station reports the round trip delay to the selector each time the delay changes by more than a predetermined amount. One aspect of the present invention utilizes the round trip delay between the remote unit and the base stations, which are members of the Assets and Candidates, to identify the location of a remote unit. Obtaining the round trip delay between the remote unit and a base station that is a member of the Candidate Set is somewhat more complicated than determining the round trip delay of a member of the Active Set. Because the base station that is a member of the Candidate Set does not demodulate a signal from the remote unit, the round trip delay can not be measured directly by the Candidate base stations. The message sent from the remote unit to the base station comprising the information of the pilot signal of the members of the Sets, Candidate and Active, is referred to as a Pilot Intensity Measurement Message (PSMM). A PSMM is sent by the remote unit either in response to a request from the base station, or because the signal strength of a base station in the Next Set has exceeded a threshold, or the signal strength of a station base in the Candidate Set has exceeded the intensity of one of the Active Set's base stations by a predetermined amount, or due to the expiration of a transfer drop regulator. Four parameters control the flexible transfer process. First, the pilot detection threshold, T_ADD, specifies the level that the signal strength of the pilot of a base station, which is a member of the Next Set, must exceed to qualify as a member of the Candidate Set. The pilot drop threshold, T_DR0P, specifies the level below which the intensity of the pilot signal from a base station, which is a member of the Active Set or Candidate, must fall in order to activate a regulator. The duration of the activated regulator is specified by the T_TDR0P. After the time specified by the T_TDR0P has passed, if the intensity of the pilot signal is still below the level of the T_DR0P, the remote unit initiates the withdrawal of the corresponding base station from the set to which it currently belongs. The comparison threshold of the Active Set against the Candidate Set, T_COMP, establishes the amount by which the intensity of the pilot signal of a member of the Candidate Set must exceed the intensity of the pilot signal of a member of the Active Set to activate a PSMM . Each of these parameters can be reprogrammed to a new value by means of a message sent from the base station. The PSMM includes two pieces of information that are relevant to the present invention. The PSMM comprises a record for each pilot signal corresponding to a base station, which is a member of the Set, Active or Candidate. First, the PSMM comprises a measurement of the intensity of the signal. Second, the PSMM comprises a measurement of the phase of the pilot signal. The remote unit measures the phase of the pilot signal for each pilot signal in the Candidate Set. The phase of the pilot signal is measured at the remote unit by comparing the phase of the usable multiple-path component that arrives first from a member of the Active Set. The phase of the pilot signal can be measured in relative PN chips. The pilot signal of the base station in the Active Set that provides the signal that arrives first is referred to as the reference pilot signal. The system controller can translate the phase of the pilot signal into a round-trip delay estimate using the following equation: RTD, RTDref + 2 * (PilotCannel Phase - ChannelCanal * Scroll * IncPilot)? G. l where: RTDcanl = the calculated estimate of the round trip delay of a base station that has an entry in the Candidate Set; RTD. the reported round-trip delay for the reference pilot signal; PhasePilotocanl = the phase relative to the perceived universal time of the remote reporting unit in the PSMM in PN chip units; DisplacementCanalcanl = the channel offset of the candidate base station, which is a number less than unity; and IncPilot = increment of the index of displacement of the wide pilot sequence of the system in PN chip units per channel. The round trip delay reported by the reference pilot signal, RTDref, is provided by the base station corresponding to the selector. The round trip delay for the reference pilot signal serves as the basis for stimulating the round trip delay between the remote unit and the base station that is a member of the Candidate Set. Recall that in the preferred embodiment, each base station transmits the same displacement of the pilot sequence in time, such that the remote unit can identify a base station based on the code phase shift of the pilot signal. The increment of the index of displacement of the pilot sequence, IncPilot, is the increase of the displacement of the code phase by means of which the pilot signals of the base station displace. The displacement of the channel, Displacement Canalcan, from the candidate base station, designates which of the code phases is assigned to the candidate base station. The relative phase of the candidate base station, Pilotcanal Phase, is the displacement of the code phase of the candidate base station as measured by the remote unit as compared to the reference pilot signal in PN chip units. The Pilotcanal Phase is reported to the base station in the PSMM. The Canalcan Displacement and the IncPilot are known to the selector. If there was no delay in the transmission in the system, the phase of the candidate base station would be the product of the displacement of the channel, Changing Channel, and the increase of the index of displacement of the wide pilot sequence of the system, IncPilot. Because there is a delay in transmission in the system, the remote unit senses both the reference pilot signal and the pilot signal of the candidate base station with different and variable delay. The subtraction of PN displacement induced by the system (= the product of the CanalDeplazamientocanl and the IncPiloto) of the perceived PN displacement (= PhasePilotocanl), produces the relative displacement between the reference pilot signal and the pilot signal of the candidate base station. If the difference is negative, the RTD between the reference base station and the remote unit is larger than the RTD between the candidate base station and the remote unit. The difference perceived by the remote unit alone reflects the delay relative to the forward link. The delay relative to the reverse link is doubled to explain the total round trip delay. For the sake of the example, it is assumed that the increase of the index of displacement of the wide pilot sequence of the system is 64 PN chips and that the following information is used for the base of a measurement of the round trip delay. Pilot Phase £ = O RTD = 137 (Base Station Id = 12) Pilot Phase14 = 948 RTD = 244 (Base station Id = 14, relative displacement 52 P?) Pilot Phase16 = 1009 (Base station Id = 12) relative displacement - 15 P?) . Because in the preferred embodiment each base station or sector of the base station transmits the same displacement of the pilot sequence in time, the identification of the base station can be considered as the displacement P? of the channel used by the base station to transmit the pilot signal. It is further assumed that the base stations 12 and 14 (which, it may be assumed, refer to the base stations shown in Figure 1), are members of the Active Set and that the RTD measurements measured by the base stations 12 and 14 they are reported as 137 and 244 PN chips, respectively. Note that to the right of the round trip delay data and of the pilot phase for the base station 14 is the calculated relative displacement. The measured pilot phase of the base station 14 is 948 PN chips. The fixed displacement of the base station 14 is equal to the base station ID, (14) times the increment of the displacement of the pilot sequence (64), which is equal to 896 PN chips. The difference between the measured pilot phase and the displacement of the pilot phase of the base station is the relative displacement between the base station and the remote unit, which in this case is 52 PN chips (= 948-896). It is not necessary to use these numbers to calculate the round trip delay between the base station 14 and the remote unit, because the base station 14 makes a direct measurement of the round trip delay, because the base station 14 is a member of the Active Set. However, because the base station 16 is a member of the Candidate Set, no round trip delay measurement is made directly by the base station 16 and Equation 1 above should be used to determine the one way delay and return. For the base station 16 the parameters are: RTDref = 137 PN chipsPilot phase, 1009 PN chips; Displacement Canalcanl = 16; and IncPilot = 64 PN chips per channel By entering these numbers directly in Equation 1 there is a round trip delay between the remote unit and the base station 16 of 107 PN chips. As noted above, to find the absolute displacement of the candidate base station, the product of the CanalDeplazamientocanl and the IncPiloto is subtracted from the Pilotcanal Phase, which in this case produces -15 PN chips. An interesting note is that the round trip delay between the base station 16 and the remote unit is less than the round trip delay between the base station 12. A first method to identify the location of the remote unit depends on the use of a hard transfer state driven by the measurement of the special remote unit (MDHO). In order to minimize the processing impact, the system accesses the MDHO status only when any member of the Active Set is marked as a transition base station. In an alternative mode, the system accesses the MDHO state only when all members of the Active Set are transition base stations. In still a third embodiment, the system accesses the MDHO state only when there is a single base station in the Active Set and that base station is a transition base station. In a fourth mode, there are sufficient processing resources, such that the MDHO status is always active. while in the MDHO state, the selector monitors the round trip delay of the members of the Active Set and computes the complete delay for the members of the Candidate Set. After the conditions that activate the MDHO status have changed, you can exit the MDHO state. The state of MDHO is based on the use of an MDHO table. In the MDHO table, each row represents a section of the coverage area, which is a covering region of the coverage area. As defined above, a coating region of the coverage area is an area, in which communication could be maintained between a remote unit and any one of two different base stations alone. Each row contains a list of pairs of identification numbers of the base station and round-trip delay ranges. The round trip delay range is specified in terms of a minimum and maximum round trip delay. In order to use the MDHO table, either a network planning tool or empirical data is used to identify a set of regions and the corresponding appropriate action for each region. Alternatively, a rule based or an expert system could be used to generate the MDHO table. As seen above, Figure 5 shows a set of base stations of the second, transitional, indoor system and is used to illustrate the function of the hard transfer measurement table driven by the remote unit. The dashed lines around the base stations indicate a round trip delay measurement threshold. For example, the dashed line 222 surrounding the base station S2 represents the location at which a direct path from the base station S2 to a remote unit located on the dashed line 222 shows a round trip delay of 200 PN chips. The dashed line 220 surrounding the base station S2 represents the location at which a direct path from the base station S2 to the remote unit located on the dashed line 222 shows a round trip delay of 220 PN chips. Therefore, any remote unit located between the dashed line 220 and the dashed line 222 could exhibit a round trip delay between 200 and 220 PN chips. Similarly, the dashed line 226 surrounding the base station Tx represents the location in which a direct path from the base station x to the remote unit located on the dashed line 226, shows a round trip delay of 160 PN chips . The dashed line 224 surrounding the base station Tx represents the location at which a direct path from the base station T-L to the remote unit located on the hatched line 224, shows a round trip delay of 160 PN chips. Therefore, any remote unit located between the dashed line 224 and the dashed line 226 could exhibit a round trip delay between 160 and 180 PN chips. Also, the dashed line 232 surrounding the base station S1 represents the location at which a direct path from the base station S? to the remote unit located on the dashed line 232, shows a round trip delay of 170 PN chips. The dashed line 230 surrounding the base station S1 represents the location at which a direct path from the base station S to the remote unit located on the dashed line 230, shows a round trip delay of 180 PN chips. Therefore, any remote unit located between the dashed line 230 and the dashed line 232 could exhibit a round trip delay between 170 and 180 PN chips. As noted above, multiple path signals that take a direct path between the remote unit and the base station are produced by the reflective elements within the medium. If the signals do not take a direct path, the round trip delay increases. The signal that arrives first is the signal that took the shortest path between the remote unit and the base station. S the signal that arrives first which is measured in conjunction with the present invention to estimate the round trip delay. Note that the specific regions can be identified by complete delays between the various stations. For example, coverage regions 240 and 242 can be identified by the fact that the round trip delay between the remote unit and the base station T1 is at 160 and 180 PN chips and the round trip delay between the unit remote and the S2 base station is between 200 and 220 PN chips. The coverage area 242 is further defined by the fact that a pilot signal from the base station S1 can be perceived as complete, regardless of the round trip delay. Assume that the proper action for a remote unit located within the region 240 and currently in communication with the base station Tl f is to execute a similar frequency hard transfer for the CDMA base station S2. Assume further that in the region 242 the total interference is too high that the only alternative is to execute a hard transfer for the AMPS system supported by the base station Sx. Table I illustrates a portion of an exemplary MDHO table. The first column indicates which coverage regions of the coverage area correspond to the row in the MDHO table. For example, coverage area 242 corresponds to coverage region N in Table I and coverage area 240 corresponds to coverage area N + l in Table I. Note that a remote unit located in the coverage area 242 matches the given parameters for the coverage area 240. In the illustrative mode, the MDHO table is examined in numerical order, and the first region that matches the given parameters is selected. such that the only way that a given set of given parameters is compared to the region N + l is if the region N has already been eliminated as a possible location. The second column contains a first base station ID. The third column contains the range of complete delays that correspond to the coverage region designated by the row. The columns, fourth and fifth, show a second base station ID and the pair of full delays as the columns, sixth and seventh. More columns designating the base station ID and the full delay pairs can be added as necessary. In the preferred embodiment, the MDHO table is' stored in the selector bank subsystem controller (SBSC). The SBSC easily stores the pilot database that provides the next lists and the pilot displacement and other data necessary for the standard operation. In the preferred embodiment the selector requires the SBSC to enter the MDHO table each time a new PSMM is received and each time the RTD measurement for any of the active base stations changes by a significant amount.

Table I The column marking the action describes the action to be taken when the location of the remote unit correlates one of the coverage regions. There are several types of exemplary actions that can be taken such as: CDMA of the base station of the Intersistema for hard transfer of AMPS; CDMA of the Intersistema base station for hard CDMA transfer; CDMA of the Intersistema for hard transfer of CDMA of different frequency; and CDMA of the Intersistema for hard transfer of CDMA of similar frequency. If more information on the round trip delay is needed to identify the location of the remote unit, the thresholds, T_ADD and T_DROP, can be modified when a remote unit is in the MDHO state. By increasing both thresholds, T_ADD and T_DROP the lower intensities of the pilot signal classify the corresponding base stations as members in the Sets, Candidate and Active, and the low signal intensities stay longer in the Sets, Candidate and Active, before let them fall The increased number of base stations listed in the Candidate Set and Active Set increases the number of round trip delay data points, which can be used to locate the remote unit. By reducing T_ADD and T_DROP, the amplitude of the system can have a negative effect in that each remote unit in the transfer uses system resources from the two base stations. It is desirable to reduce the number of remote units in the transfer in order to conserve resources in each base station and increase capacity. Therefore, in the preferred embodiment T_ADD and T_DROP are only reduced in value in the transition base stations. Also the length of time designated by the T_TDROP may be increased to increase the amount of time a base station remains in the Active Set after falling below the T_DROP. In the preferred embodiment if the second system does not transmit a CDMA pilot signal from the base stations limits on the frequency used in the first system, the second system is modified to transmit a pilot signal or other CDMA signal emitter for assist in the initiation of the hard transfer process as described in U.S. Patent Application Serial No. 08 / 413,306 and U.S. Patent Application Serial No. 08 / 522,469. In an alternative embodiment, even if the system does not transmit a CDMA pilot signal from the boundary base station, the boundary base stations in the second system do not produce pilot signals and there are no entries in the column of the base station ID of the table of MDHO corresponding to the base stations S1-S3. The emitting units of pilot signals can also be used in the indoor base stations to help identify the regions that are effected by microwave links from point to point. In some cases, it may be possible to eliminate the use of the candidate base stations as a means to identify the location of the remote unit, thus leaving only the information of the active base station to determine the location of the remote unit. For example, with more skilful network planning, it can happen that the coverage regions of the coverage area can be effectively identified using only the round-trip delay of the members of the Active Set. As noted above, no base stations divided into sectors are shown in Figure 5 in order to simplify the drawing. In fact, the presence of division in sectors helps the process of location, by narrowing the regions in which the remote unit can be located. Note, for example, the geometry of the base station 60 of Figure 3. Before the round-trip delays are considered, the coverage area of the base station 60 is divided into 6 different regions: the area covered only by the sector 50, the area covered by sector 50 and sector 70, the area covered only by sector 70, the area covered by sector 70 and sector 80, the area covered only by sector 80 and the area covered by sector 80 and sector 50. If network planning is used to orient the base stations divided into three sectors along the edge between the two systems, it may be possible to eliminate the use of the pilot signal emitters in the boundary base stations of system 2 and the use of the round-trip delay determination of the candidate base station. Each base station in the system is initially calibrated in such a way that the sum of the path noise of the receiver without charging measured in decibels and the desired pilot energy measured in decibels is equal to some constant. The calibration constant is consistent throughout the base station system. As the system is loaded (ie, the remote units begin to communicate with the base stations) the reverse link transfer limit moves effectively to the base station. Therefore, to mimic the same effect on the forward link, a compensation network maintains the constant relationship between the reverse link energy received at the base station and the pilot energy transmitted from the base station, by reducing the pilot energy to as the load increases. The process of balancing the forward link transfer limit with the reverse link transfer limit is referred to as base station expansion, and is detailed in U.S. Patent No. 5,548,812 entitled "METHOD AND APPARATUS FOR BALANCING THE TRANSFER LIMIT LINK IN PROGRESS WITH THE INVERSE LINK TRANSFER LIMIT IN A CELLULAR COMMUNICATION SYSTEM "(" METHOD AND APPARATUS FOR BALANCING THE FORWARD LI? K HANDOFF BOUNDARY TO THE REVERSE LINK HANDOFF BOU? DARY IN A CELLULAR COMMUNICATIO? SYSTEM "), issued on August 20, 1996 and assigned to the assignee of the present invention. The expansion process can adversely effect the operation in the MDHO state. Referring again to Figure 4B, if the energy transmitted by the base station 200 is reduced compared to the energy transmitted by the station 205, the coverage limits of the coverage area move closer to the base station 200 and move away from the base station 205. The signal level does not perform the round-trip delay between the remote unit at any location and the base station. Therefore, the MDHO table continues to identify the same locations as appropriate for the transfer, when the current limits may have changed. There are several ways to carry out the concept of expansion. One way is to sufficiently narrow the coating regions of the defined coverage area as stored in the MDHO table, such that the coating regions of the coverage area remain independent of the present expansion state. A second way to carry out the expansion concept of the base station is to limit or disable the expansion in the boundary base stations. The expansion mechanism operates on the forward link signal to force the execution of the forward link to mimic the natural reaction of the reverse link for the load level. Therefore, the elimination of the expansion does not eliminate the risk that the limits change with the load on the reverse link, and in this way the load maintains a factor even if a system does not use expansion. A third way of carrying out the concept of expansion of the base station is through network planning. If the boundary base stations of the second system do not transmit the traffic channel signals (i.e., the specific signals of the active remote unit) at the frequencies used by the boundary base stations of the first system, the expansion effect is reduced. If the limit base stations transmit a pilot signal from a pilot signaling unit, the effects of expansion are also reduced due to the fact that traffic channel signals are not generated when a unit transmitting pilot signals is used. The output of energy by a unit emitting pilot signals remains constant for extra time. A fourth way to carry out the concept of expansion of the base station is through the use of a system based on a standard. If the boundary base stations are expanded, an expansion parameter is sent from each base station to the system controller. The system controller updates the MDHO table based on the current expansion value. Typically, the system controller will increase the round trip delay values in the MDHO table to reflect the effects of the expansion. The effects of expansion may not be an issue in most situations. Because these boundary areas have traditionally been a source of business and technical issues, network planning typically seeks to place boundaries between the two systems in low traffic areas. The lower amounts of traffic correspond to smaller effects of the expansion. In some cases it may be desirable to avoid storage and access of the MDHO table. In that case, other methods may be used to effect the transfer. For example, in an alternative embodiment, two means are used to activate a transfer. The first method is called the detection standard. Certain base stations (or sectors of the base station) are designated as reference base stations, R. If a remote unit is within the coverage area of a reference base station and reports the detection of a pilot activation signal, PB , the selector activates a transfer with a target base station determined by the data set (R, PB). The detection standard is typically used but not always with a pilot signal emitting unit. The second method is called the descent rule.

Certain base stations are marked as boundary base stations. The selector activates a transfer if the Active Set of the remote unit contains only one base station and that base station is a boundary base station and the round trip delay of the reference pilot signal exceeds a threshold. Alternatively, the selector activates a transfer if the Active Set of the remote unit only contains base stations that are boundary base stations and the round trip delay of the reference pilot signal exceeds a threshold. Typically, the threshold varies between base stations and is independent of the rest of the Active Set. The downward action is determined by the current pilot reference signal. The descent rule may be the first of a set of standards for the measurement of directed transfer. Note that it is not necessary for a base station designated as a boundary base station to have a coverage area, which borders a coverage area of a base station of another system. The descent rule can be used both for the transfer of the intersystem and the transfer of the intrasystem. Both the detection standard and the descent rule may depend on the characteristics of the system. The use of these two rules can oppress the design of the network such as the placement of the base stations, the orientation of the sectors within a base station divided into multiple sectors and the physical placement of the antennas. If a remote unit or base station attempts to initiate a call at the boundary base station, the remote unit and the base station exchange a source message on the access channel. In the preferred mode, the Upper Channel Manager resides at the base station and controls the access channel. The Upper Channel Administrator examines the computerized round trip delay estimate from the source message. If the round trip delay exceeds the threshold, the Upper Channel Manager notifies the mobile switching center that it can instruct the base station to send a redirect message to the remote unit. The service redirection message may direct a remote unit capable of AMPS to an AMPS system or to another CDMA system or frequency. The re-dispatch message also depends on the type of service requested by the remote unit. If a data connection is requested instead of a voice connection, the AMPS system may not be able to maintain the connection. For this reason, the action taken should generally depend on the capabilities and status of the remote unit. Typically, each remote unit in the system has a class designation, which designates its capabilities. The current state of the remote unit can be consulted by the base station and a decision can be made based on the information received. Figure 7 illustrates the use of the detection standard in a CDMA for the similar frequency transfer of CDMA. Assume that a remote unit passes from system S ± to system S2 in region C1A / C2. As the remote unit approaches C2, it begins to perceive the pilot signal transmitted by it. When using the detection standard, if C1A is the reference base station the selector requests a transfer to an AMPS base station that is located within the coverage area C1A. As noted above, the hard transfer from an FM AMPS system to another FM AMPS system can be achieved over a physical region much larger than a hard transfer from one CDMA system to another CDMA system operating in the same system. frequency. Note that there must be a one-to-one or at least a substantial overlap between the coverage areas of the CDMA base station and the coverage areas of the AMPS base station in the boundary base stations. Once the FM AMPS operation has been switched, the probability of a successful hard transfer of the intersystem between the FM system is high. Figure 8 illustrates the use of a detection standard in a CDMA for a frequency transfer different from CDMA. In Figure 8, the area corresponding to the system S2 is shaded to indicate that the system S2 is in communication with the traffic channel signals at the frequency f2, but is not in communication with the traffic channel signals at the frequency fx. In Figure 8, the area corresponding to the system S1 is not shaded to indicate that the system S1 is in communication with the signals of the traffic channel at the frequency fx, but is not in communication with the signals of the traffic channel in the frequency f2. There may or may not be a pilot signal emitting unit operating in the boundary base stations of either the S ± or S2 system or both. If there is a unit emitting pilot signals, the detection standard can be used. Alternatively, if C1A and C1B become the only base stations in the Active Set the downgrade rule can be applied once the measurement of the round trip delay exceeds the threshold. In any case, a transfer may be made to an AMPS base station located within C1A or C1B. The configuration of Figure 8 has a greater advantage over the configuration of Figure 7. Figure 4C illustrates the advantage of the transfer using two different CDMA frequencies. Figure 4C is a highly idealized representation of a transfer region employing two different CDMA frequencies, following the same format as in Figures 4A and 4B. In Figure 4C, the base station 205 does not transmit traffic channel signals on the same frequency as does the base station 200, as represented by the striped transmission arrows that come from the base station 205 and the remote unit 155. The limit 189 represents the point at which reliable communication can be established between the remote unit 155 and the base station 200 at the frequency f1. The region 176 between the boundary 180 and the boundary 189 represents the area where the remote unit 155 can detect a pilot signal from the base station 205, if the base station 205 is equipped with a pilot signaling unit, while communicates through the base station 200. A comparison between Figures 4B and 4C reveals the advantage of the different frequency transfer. If the base station 205 is not transmitting a pilot signal there is no interference from the base station 205 for a signal between the base station 200 and the remote unit 155. If the base station 205 is transmitting a pilot signal, the amount of interference due to the pilot signal from the base station 205 for the signal between the base station 200 and the remote unit 155 is significantly less than the interference produced if the base station 205 is transmitting signals from the traffic channel. Therefore, boundary 189 is much closer to base station 205 than boundary 186. Boundary 181 represents the point at which reliable communication between remote unit 155 and base station 205 at frequency f2 can be established. . The region 178 between the boundary 181 and the boundary 190 represents the area where the remote unit 155 can detect a pilot signal from the base station 200 if the base station 200 is equipped with a pilot signal emitting unit operating on the frequency f2, while communicating through the base station 205. Again, note how close the boundary 181 is to the base station 200 to the boundary 184. The region 174 between boundary 181 and boundary 189 represents the area wherein a communication transfer can be carried out from the base station 200 at the frequency fx to the base station 205 at the frequency f2 or vice versa. Note how large the region 174 is that the region 170 in Figure 4B. The largest size of region 174 is very advantageous for the hard transfer process. The fact that two different frequencies are used, does not effect much the hard transfer process because either in the case of different frequency or of similar frequency, the transfer of communication has the characteristic of the hard transfer 'interrupt before doing'. The only insignificant disadvantage of the case of different frequency may be that the remote unit requires some amount of time to switch the operation from the first frequency to the second frequency. In the preferred embodiment, both the base station and the remote unit use a different frequency for transmission than for reception. In Figure 4C and other Figures and in the text describing the transfer between the two different CDMA operating frequencies, it can be assumed that both the frequency of reception and transmission are different after the transfer is made, even if the text and drawings are referred to for simplicity at a single frequency (such as frequency fj to designate the use of a set of reception and transmission frequencies.

Referring again to Figure 8, it is not necessary that each base station in system S2 refrain from operating at frequency f. It is only necessary that the boundary base stations and possibly the next layer of the interior base stations in the S2 system refrain from operating on the frequency f1. Indoor base stations can use frequency f1 for CDMA or FM or TDMA or point-to-point microwave links or any other function. Figure 9 still shows another alternative mode for a transition area between the two systems. The configuration of Figure 9 requires cooperation between the systems service providers, first and second, and should be more applicable where the two systems belong to the same service provider. Figure 9 illustrates two base stations located or substantially located, B and B2, which provide CDMA to the frequency transfer different from CDMA. Both the base station Bx and the base station B2 are base stations divided into two sectors that provide coverage to the coverage area 310. The base station BL of the Si system provides CDMA service on the frequency f ± both in sector a and in the sector ß, and base station B2 of the Sx system provides CDMA service in both sector a and sector ß at frequency f2.

Note that the coverage area 310 is crossed by the path 312. As the remote unit passes into the coverage area 310 of the system S? using the fx frequency a flexible transfer of the standard intrasystem is used to transfer the control of the call to the base station Bx, sector ß. As the remote unit continues down the path 312, flexible or more flexible transfer is used to transfer communication from the base station B ^ sector ß to the base station B? sector a. When sector a of base station B becomes' the only sector in the Active Set, the drop rule applies the activation of the transfer to sector β of system S2 of base station B2 at frequency f2. The transfer for the remote unit that passes from the system S2 to the system S? it happens in a similar way, between the sector of the base station B2 and the sector ß of the base station B1. Because the sector a of the base station B1 is located with the sector ß of the base station B2 and the sector a of the base station B2 is located with the sector ß of the base station Bl t in each case it can compete successfully with a Hard transfer without concern that the remote unit is not in the coverage area of the target base station.

The configuration of Figure 9 has several advantages. Because the area in which the transfer is executed from the system S? to the system S2 is not the same as the area in which the transfer is executed from the system S2 to the system Sl f the probability of an alternation situation is reduced. For example, if the area in which the transfer is executed from the S- system. to the system S2 is substantially equal to the area in which the transfer is executed from the system S to the system S? r a remote unit that accesses the transfer area and then stops moving or moves within the region can be continuously transferred to one system and then returned to the other. The configuration of Figure 9 introduces spatial hysteresis. Once the remote unit has passed the control from the system S1 to the system S2 in the lower half of the coverage area 310, the remote unit will not transit the control back to the system S1? unless it changes direction and completely accesses the upper half of the coverage area 310 in such a way that the base station B2 sector a is the only member of the Active Set of the remote unit. As with the configuration of Figure 8, the configuration of Figure 9 is not necessary for each base station in the S2 system to refrain from using the frequency f1. It is only necessary that the boundary base stations and possibly the next layer of the indoor base stations in the S2 system refrain from using the frequency f1. The indoor base stations in the S2 system can use the frequency f1 to transmit CDMA or FM or TDMA or microwave links from point to point or for any other function. Also in Figure 9, it is not necessary that the base station comprises exactly two sectors and a greater number of sectors can be used. Figure 10 shows a situation in which a CDMA system limits a system that provides the service using a different technology. This situation can be handled in a similar manner as in Figure 8. Figure 10 shows the special topology of Detroit, Michigan, E.U.A. Detroit borders Canada on one side. A river defines the boundary between Detroit and Canada.

Few bridges cross the river to connect the two cities. On the side of the river E.U.A. The CDMA S1 system is deployed. On the Canadian river side, the TDMA S2 system is deployed. Both sides, E.U.A. and Canadian are operating in AMPS systems in addition to the chosen digital technologies. A remote unit that passes on the Detroit side of the system is continuously in CDMA coverage, possibly in flexible and more flexible transfer. However, when it is found that the remote unit is exclusively in the coverage area of sector a of the coverage area CA or sector a of the coverage area Cc, a transfer is activated to the base station of AMPS located, respectively, once that the round trip delay exceeds a predetermined threshold, using the descent rule. The remote units in the water may or may not remain within the CDMA coverage areas depending on the chosen RTD threshold. Network planning should ensure that the antennas are properly oriented and that the base stations are located in such a way that an AMPS base station can be determined only based on the transition sectors, and that the call does not fall when these sectors are return the only sectors in the active set. Figure 14 illustrates one embodiment of the present invention, wherein the transmitters operating the two systems are capable of locating the two base stations. Figure 14 is a graphic representation. The coverage area C1A corresponds to an indoor base station in the Sx system operating on the frequency f 1. The coverage area C1B corresponds to a transition base station in the S-L system operating on the frequency f 1. The pilot signal emitter P1 is a pilot signal emitter unit operating at the frequency t1 located with the coverage area C2A. The coverage area C2A corresponds to an indoor base station in the system S2 operating on the frequency f2. The coverage area C2B corresponds to a transition base station in the system S2 operating on the frequency f2. The pilot signal emitter P2 is a pilot signal emitter unit operating at the frequency f2 located with the coverage area C1A. Note that in the configuration of Figure 14, a hard transfer between the base station C1B and the base station C2B must be executed as a remote unit passes between the Sx system and the S2 system. Because the base stations are not transmitting the signals of the traffic channel at the frequencies from which a hard transfer is made, the communication reliability between the base station C1B, at the frequency f and the remote unit located at the coverage areas C1B and C2B, is high. In the same way, the communication reliability between the base station C2B, at the frequency f2 and the remote unit located in the coverage areas C1B and C2B, is high. One issue with the configuration of Figure 14 is the co-location of the coverage areas C1B and C2. The location of the base stations typically requires some amount of coordination between the two operators of the system. If the two systems are operated by different transmitters, the transmitters may not want to share a physical facility. Also the location can formulate regulatory issues. Figure 15 is similar to Figure 14 except that the coverage area C1B and the coverage area C2B are not completely located. The principles of this modality apply to the case where the coverage areas of the two base stations are substantially covered. The region of spatial hysteresis is contracted approximately by the amount that the two coverage areas are displaced from one another. With either Figure 14 or Figure 15 the operation is the same and very simple. A remote unit that passes in the Sx system to the S2 system is initially in communication with the coverage area C1A using the frequency f1. As the remote unit approaches the two coverage areas located, the flexible transfer on the frequency fx is used to transfer the communication to the coverage area C1B. If the remote unit continues to the system S2, the remote unit begins to detect the pilot signal from the pilot signal emitter Px. When the active set contains only the base station corresponding to the coverage area IB? / ° the intensity of the pilot signal of the pilot signal Px exceeds a certain threshold, a hard transfer is executed from the base station corresponding to the coverage area C1B to the base station corresponding to the coverage area C2B. As the remote unit continues to the system S2, the flexible transfer is used for the transition of the communication between the base station corresponding to the coverage area C2B and the base station corresponding to the coverage area C2A. The reciprocal operation is used to complete a transfer from the S2 system to the Sx system. The configurations of Figures 14 and 15 are similar to the configuration of Figure 9 in that they introduce some measure of spatial hysteresis. For example, the connection of a remote unit that passes from the Sx system to the system S2 is represented by the dashed line 356. Note that until the remote unit reaches the location indicated by the arrow 350, it remains served with the Sx system in the frequency fx by the base station corresponding to the coverage area C1B. Likewise, the connection of a remote unit that passes from the system S2 to the system Sx is represented by the grated line 354. Note that until the remote unit reaches the location indicated by the arrow 352, it remains served with the base station which corresponds to the coverage area C2B. Therefore, between the arrow 350 and the arrow 352 the service providing the communication to the remote unit depends on which system provided the communication when the remote unit entered the region. The remote unit can move around within the region between arrow 352 and 350 without transfer between the two systems. Referring again to Figure 4B, another solution to the hard transfer dilemma is to increase the size of the hard transfer region 170. One of the reasons why the region is too narrow is due to the fading effects. Because a remote unit located within the hard transfer region 170 can only communicate with either the base station 200 or the base station 205, if the signal fades with respect to the active base station but does not fade with respect to to the inactive base station, the interference from the inactive base station becomes significant. One method to increase the size of the region and the reliability of communication within the region is to minimize the amount of fading experienced by the remote unit in this area. Diversity is a proposal to mitigate the harmful effects of fading. There are three main types of diversity: diversity of time, diversity of frequency and diversity of space. Frequency and time diversity is inherently present in a spread spectrum CDMA system.

The diversity of space, which is also called trajectory diversity, is created by multiple signal paths in a common signal. Path diversity can advantageously be exploited through broadcast spectrum processing, by receiving and processing separately arriving signals with different propagation delays. Examples of the use of path diversity are illustrated in U.S. Patent No. 5,101,501, issued March 31, 1992, entitled "FLEXIBLE TRANSFER IN A CDMA CELLULAR TELEPHONE SYSTEM" ("SOFT HANDOFF I? CDMA CELLULAR TELEPHO? E SYSTEM "), and the United States Patent? O. 5,109,390 issued April 28, 1992, entitled "DIVERSITY RECEIVER AND A CDMA CELLULAR TELEPHONE SYSTEM" ("DIVERSITY RECEIVER IN A CDMA CELLUALR TELEPHONE SYSTEM"), both assigned to the assignee of the present invention. The existence of a multi-path environment can provide path diversity to a broadband CDMA system. If two or more signal paths with a differential path delay greater than a duration chip are created, two or more receivers can be used to separately receive the signals in a single base station or remote receiving unit. (The path delay of a differential chip is a function of the means by which the tracking time is carried out on the receiver). After the signals are received separately, they can be combined for diversity before the decoding process. Multipath signals typically show an independence in the fading, that is, usually the different multipath signals do not fade together. In this way, if the output of the two receivers can be combined by diversity, a significant loss in execution occurs only when both multipath signals vanish at the same time. Referring again to Figure 4B, suppose that the base station 200 is the active base station. If there are two signal components other than the base station 200 that are received by the remote unit 155, the two different signals vanish independently or almost independently. Therefore, the total signal of the base station 200 does not experience the deep devades that occur when only a different signal is received. As a result, the probability that signals from the base station 205 dominate the signal from the base station 200 to the remote unit 155 is lower.

The multiple trajectory can be introduced artificially, instead of depending on the multiple trajectory signals developed statically and naturally. A typical base station has two receiving antennas and a transmitting antenna. Frequently, the transmitting antenna is the same as one of the receiving antennas. Such a configuration of the base station is shown in Figure 12. In Figure 12, the transmitter 330 supplies a transmit signal to the diplexer 332, which in turn supplies a signal to the antenna 334. The antenna 334 supplies a first signal of reception to port 1 of receiver 338 and antenna 336 supplies a second reception signal to port 2 of receiver 338. Within receiver 338 the reception signals of port 1 and port 2 are received separately and then combined before the decoding for a maximum advantage. The antenna 334 and the antenna 336 are configured in such a way that the signals received from each antenna vanish independently of the signals received by the other. Because the reception signals of the antennas 334 and 336 are supplied to different receivers, and are not combined until after the signals have been demodulated within the receiver 338, it is not critical that the signals received in the antenna 334 are displaced of the signals received from the antenna 336 by an address of at least 1 PN chip. To introduce diversity into the system of Figure 12, a second diplexer can be used to couple the transmission signal to the antenna before receiving only through a delay line. Such configuration is shown in Figure 13. In Figure 13, the transmitter 330 supplies a transmit signal to the diplexer 332, which in turn supplies a signal to the antenna 334. In addition, the transmitter 330 supplies a transmit signal ( which in the most basic mode contains the same signals as in the original transmission signal) to the delay line 340 and to the diplexer 342 and to the antenna 336. As in Figure 12, the antenna 334 and the antenna 336 are configured of such that the signals as they are received from each antenna in the remote unit vanish independently. Because both signals are received through a single antenna in the remote unit, in addition to the independence in the fading, the two signals must be sufficiently separated in time in such a way that the remote unit can separately distinguish the signals. The delay line adds enough delay so that the signal radiated by the antenna 336 reaches the remote unit with a greater delay than a chip relative to the signal of the antenna 334, so that the remote unit can distinguish the signals and separate and demodulate them separately. In the preferred embodiment, the configuration of the diversity base station of Figure 13 is only used in the boundary base stations. In an alternative embodiment, the delay line 340 comprises a gain adjustment element. The gain adjustment element can be used to adjust the level of the signal transmitted by the antenna 336 relative to the signal transmitted by the antenna 334. The advantage of this configuration is that the signal of the antenna 336 does not interfere significantly with other signals in the antenna. the system. However, the level of the signal of the antenna 336 relative to the signal level of the antenna 334 becomes significant when the signal of the antenna 334 vanishes. Thus, in the preferred embodiment, if the antenna signal 334 experiences a deep fading with respect to the remote unit, the signal of the antenna 336 is sufficiently long to provide reliable communication for the duration of the fading. It may be advantageous to provide an antenna signal 336 only when at least one remote unit is located in the hard transfer region. This technique can also be applied to any of the following alternative modalities. Still a different embodiment can create a separate signal path carrying a different set of signals for transmission by the antenna 336. In this mode, the base station determines which remote units need diversity (ie, which remote units are located in the hard transfer region). The set of signals transmitted by the antenna 336 can only comprise the traffic channel signals for the remote units in the hard transfer region and a pilot signal. Alternatively, synchronization and paging channel transmissions could also be included. As seen directly above, it may be advantageous to supply the pilot signal and others of the antenna 336 only when at least one remote unit is located in the hard transfer region. The remote unit that needs diversity could identify, for example, by detecting remote units that require more transmission power than some threshold or based on the round trip delay. The use of two transmitters reduces interference to the system, including interference for the remote units within the hard transfer region 170, which is in communication with the base station 205. In Figure 13, the dashed line 348 illustrates the second mode where two separate signal paths are used carry a different set of signals. It is assumed that any delay between the two signals is necessary, is induced within the transmitter 330. It should be noted that the second radiator does not need to be located with the base station. It could be separated by a great distance and could be located near the hard transfer limit. Alternatively, instead of using the antenna just before receiving to transmit the diversity of the signal, the signal could be transmitted from a different antenna. The different antenna could be a highly directional randomly selected antenna, which focuses the energy in the hard transfer region. A particularly advantageous configuration can be achieved by using a separate signal path in conjunction with a different antenna. In this case, more diversity can be achieved by assigning the signal to be transmitted by the different antenna to a different PN shift than the PN displacement nominally assigned to the transmitter 330. In this way, the base station executes a more flexible transfer when the remote unit enters. to the coverage area of the different antenna. The use of a different PN offset is useful in identifying when the remote unit is located in the hard transfer region. The above modalities can be implemented with a variety of different topologies to provide the same results. It is also observed that there are various methods by which diversity is introduced into the system. For example, the effects of fading can also be reduced by wavering the signal phase of the diversity antenna. The hesitation of the phase interrupts the alignment of the amplitude and phase of the multipath signals that can create a deep fading in a channel. An example of such a system is described in U.S. Patent No. 5,437,055, entitled "ANTENNA SYSTEM FOR MULTIPLE PATH DIVERSITY IN AN INTERNAL MICROCELLULAR COMMUNICATION SYSTEM") ("ANTENNA SYSTEM FOR MULTIPATH DIVERSITY IN AN INDOOR MICROCELLULAR COMMUNICATION SYSTEM") , which was issued on July 25, 1996, and which is assigned to the assignee of the present invention. The noxious effects of fading can also be controlled for some extension in a CDMA system, by controlling the transmission energy. A fading that reduces the energy received by the remote unit of the base station can be compensated by increasing the energy transmitted by the base station. The energy control function operates according to a time constant. Depending on the time constant of the energy control cycle and the duration of the fading time, the system can compensate for fading by increasing the transmit power of the base station. The nominal power level transmitted from the base station to the remote unit could be increased when the remote unit is in the region in which a hard transfer can be executed. Again, the remote unit in need of increased power could be identified, for example, on the basis of full delay or by reporting a pilot signal that exceeds a threshold. By increasing only the energy transmitted for those remote units in need, the net amount of energy transmitted is reduced, thus reducing the total interference in the system. As seen in conjunction with Figure 3, a situation in which a hard transfer may need to be executed is a situation in which a remote unit must change the frequency at which it operates within a single system. For example, such a transfer can be made to avoid interference with point-to-point microwave links, which operate in co-existence with the CDMA communication system or for the transition of all signals from the traffic channel to a single frequency , such that a CDMA to a frequency transfer different from CDMA may occur at the system boundary. In Figure 3, the point-to-point microwave link 140 is shown between the directional microwave antenna 130 and the directional microwave antenna 135. Because the directional microwave antenna 130 and the directional microwave antenna 135 are highly directional, the point-to-point microwave link 140 has a very narrow field. In itself, the other base stations of the system such as the base stations 115, 120 and sectors 50, 70 and 80 can operate without interference with the point-to-point microwave link 140. In the example of the preferred embodiment, CDMA signals are transmitted at microwave frequencies and therefore the point-to-point microwave link that crosses the system only interferes if it also operates at a microwave frequency. The point-to-point link in the most general mode can operate at frequencies higher or lower than those generally designated as microwave frequencies. Although the previously described techniques can in the present be applied to such hard handover, hard handover typically has an advantage over hard intersystem transfers in that the two base stations, among which the transfer is to be completed, are controlled by the same controller. Figure 11 illustrates an alternative configuration for providing a CDMA for frequency transfer different from CDMA using a single base station divided into multiple sectors. Both the base station B1A and the base station BXB have two directional sectors marked as sectors a and ß. In the base station B1A, sectors a and ß operate at frequency fx. In the base station B1B sectors a and ß operate on frequency f2. Both the base station B1A and the base station BXB have an omnidirectional sector,?, Which operates at a frequency different from the directional sectors in this base station. For example, in the base station BXA the sector? operates on the frequency f2 and on the BXB base station the sector? operates on the frequency fx. Figure 11 uses the descent rule. The omnidirectional sectors? are marked as boundary sectors with a round trip delay threshold of 0 which means that if any of the sectors? is the only base station in the Active Set, a transfer is immediately activated regardless of the round trip delay. Observe that the sectors? they are not currently boundary sectors between two systems, but from the perspective of the remote unit the action taken is the same. As the remote unit passes to the base station B1A from a coverage area bordering the Sx system at the fx frequency, the flexible transfer is used to establish communication with sector a of the base station BXA, and the flexible and more flexible transfer to transfer the connection to the sector ß of the base station B1A. The flexible transfer is then used to transfer the connection to the sector? from a base station B1B, which is marked as a boundary base station. As soon as the sector? from the base station B1B becomes the sole member of the Active Set, is a flexible transfer made from the sector? from the base station B1B to the sector ß of the base station B, Note that this configuration also introduces spatial hysteresis in that once the operation has been transferred to the frequency f2, the operation is not transferred back to the frequency fx at less than the remote unit between the coverage area of the sector? of the BXA base station, for such an extension that it becomes the only member of the Active Set. Also note that the choice to use three different sectors is based on the fact that most base stations divided into multiple sectors are comprised of three sectors and therefore the available base station equipment typically supports three sectors. In itself, a design that uses all three sectors creates practicality. Of course, a greater or lesser number of sectors may be used. There are two different types of situations, in which such a configuration can be used. The configuration of Figure 11 can be used at the location where all traffic must change frequencies. In that case, the base stations to the left of the base station B1A do not use the frequency f2 and the base stations to the right of the base station BXB do not use the frequency fx. In such a case, all remote units that enter on one side and exit on the other side must transit the frequencies. In an alternative situation, the base stations to the right of the base station B1B only use the frequency f2, such as for example because the microwave link prohibits the use of the frequency fx in that area. However, the base stations to the right of the BXA base station can operate on either the fx frequency or the f2 frequency. In such a case, either all, some or none of the remote units that pass from the base station B1B to the base station B1A may transit from the frequency f2 to the frequency fx. A second very different method for dealing with point-to-point microwave links or other areas where a piece of the spectrum needs to be cleared is illustrated in Figure 16. In Figure 16 a "Cone of Silence" is constructed around the link microwave from point to point 140, as shown by beams 364 and 366. The silent cone is a pilot signal that acts as a reference signal for the remote units that detect it. When a remote unit reports the detection of a pilot signal corresponding to the silent cone, the system controller knows that the pilot signal is an indication of the silent cone instead of a viable candidate pilot signal. The system controller uses the reception of the pilot signal that corresponds to the silent cone as a stimulus to initiate a hard transfer. Typically the executed transfer is an intrasystem CDMA for frequency transfer different from CDMA, although other types of transfers can be executed. An interesting aspect of the cone of silence is that the pilot signal of the cone of silence is not associated with any particular base station. Typically, the pilot signal of the silence cone is generated by a pilot signal emitting unit located with the directional microwave antennas 130 and 135. There are two different topologies of the silence cone, which can be used. In the first topology shown in Figure 16, beams 364 and 366 are currently narrow transmission bands that protect either side of the microwave link from point to point 140. In the second topology shown in Figure 17, beams 360 and 362 define the edges of the transmission coverage area of the pilot signal. In Figure 17, the coverage area of the pilot signal and the coverage area of the microwave point-to-point link 140 currently cover the same region. Typically, beams 364 and 366 are produced by two separate antennas other than the microwave antenna. The beams 360 and 362 can be created by the same antenna as the microwave signal, a different antenna but identical to an antenna that defines a slightly wider coverage area than said microwave antenna. The first topology of Figure 16 has the advantage that the pilot signals of the cone of silence do not interfere with the microwave link from point to point even if the microwave link from point to point operates on the same frequency as in the pilot signal of the cone of silence. The first topology has the disadvantage that if the remote unit passes through the beams of the pilot signal of the cone of silence without detecting the signals and without changing the frequency, the connection may fall or the connection may continue and cause interference to the signal. Microwave link from point to point. Also if the power is applied to the remote unit while it is located within beams 364 and 366, the remote unit will be unable to detect the pilot signals and may cause interference to the microwave link. The microwave link can be bidirectional and such link operation may require two CDMA frequency channels. In a modality, two CDMA reverse link channels are cleared to accommodate the microwave link from point to point. Two different pilot signals of the forward link silence cone are transmitted in the area of coverage of the silent cone that corresponds to each of the two reverse link channels cleared for the microwave link from point to point. In this way, the two pilot signals can cover the two coverage areas of the microwave link from point to point without interfering with the current communication between the two directional antennas due to the frequency diversity. In still a third embodiment, the pilot signal may be able to coexist on the same frequency with the microwave link from point to point without causing a significant amount of interference to the microwave link from point to point. The CDMA pilot signal is a broadband, low energy spread spectrum signal. This type of signal is perceived as simple Gaussian noise for other types of communication systems. The properties of the inherent CDMA signal make it capable only of coexisting with other communication systems without inducing significant interference. The distance between two point-to-point microwave link antennas can be much greater than the distance between a typical base station and the edge of the coverage area it defines. Therefore, the delay in which the remote unit perceives the pilot signal of the silent cone can be significantly greater than the delay typically associated with a cellular system. In itself, it may be necessary that the pilot signal of the cone of silence be recognized as one of a set of displacements of the consecutive pilot signal. For example, the induced delay in the pilot signal of the silent cone is greater than the normal shift between the pilot signals causing the displacement of the perceived pilot signal to correlate with the next displacement of the consecutive pilot signal. This type of operation is typically not a problem because the typical system only uses each eighth or seventh PN displacement. The set of displacements in which the pilot signals of the silent cone are expected can be added to the next set so that the remote unit looks for these signals in the same way that it searches for the other entries in the next list. In the detection of the pilot signal of the silent cone the action taken depends on the base stations with which it establishes the active communication. Because the pilot signal of the silent cone can cross many coverage areas of the base station, the pilot signal itself provides very little information regarding the location of the remote unit or the action that needs to be taken. The base station and the frequency at which the transfer should be made is based on the members of the Active Set at the time in which the pilot signal is perceived. Also the action to be taken could be determined by the members of the groups, Active and Candidate. In addition, the action to be taken could be based on the perceived PN displacement of the pilot signal of the silent cone. Also, it may be advantageous to postpone the action to be taken until the intensity of the pilot signal of the silence cone exceeds a second higher threshold. Because the pilot signal of the silent cone provides very little information, the same displacement of the pilot signal can be used throughout the system to protect a plurality of different microwave links from point to point. In Figure 16, all beams 364 and 366 can operate on the same or on four different PN offsets. If the distance between the two microwave link antennas from point to point becomes too large. It may be necessary to use a repeater to extend the coverage of the pilot signal. A method and apparatus for providing a repeater in a CDMA system is described in co-pending US Patent Application No. 08 / 522,469 entitled "Repeated Double by Time Distribution, of Similar Frequency" ("Same Frequency, Time-Division-Duplex Repeater") filed on August 31, 1995 and assigned to the assignee of the present invention. Alternatively, a series of antennas that provide the same or different pilot displacement sequences can be installed along the microwave length path to define more narrowly and accurately and safely and reliably the area of the mute cone. Many of the concepts of the present invention can be combined. For example, the detection and descent rules can be used in conjunction with the physical configurations of the coverage area that provide both the spatial hysteresis of the intrasystem and the intersystem. The standards can also be combined with other network planning configurations to provide a maximum benefit such as the use of CDMA for frequency transfer other than CDMA. The parameters that control the flexible transfer process can be increased to increase the number of Sets, Active and Candidate. The pause of the base station can also be increased. The concept of hard transfer guided by the measurement of the remote unit can be combined with the physical configurations of the coverage area that provide both the spatial hysteresis of the intrasystem and the intersystem. It can also be combined with other network planning configurations to provide the maximum benefit such as the use of CDMA for frequency transfer other than CDMA. The prior description of the preferred embodiments is provided to allow any person skilled in the art to make or use the present invention. The various modifications to these modalities will be readily apparent to those skilled in the art and the generic principles defined herein may be applied to other modalities without the use of the inventive faculty. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be in accordance with the broader scope consistent with the principles and novel features described herein.

Claims (90)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and therefore the property described in the following claims is claimed as property. 1. In a communication network in which a user of the network communicates through a remote unit with another user through at least one base station, said network including mobile switching centers, first and second to control respectively the communications through a first set of base stations including a first base station and through a second set of base stations including a second base station, a method for directing communications between said remote unit and said base stations, first and second comprising the steps of: measuring in said first base station a round trip delay of an active communication signal between said first base station and said remote unit; measuring in said remote unit a first phase shift of a pilot signal received from a first candidate base station; reporting by said remote unit to said first mobile switching center through said first station, said first phase shift; and calculating in said first mobile switching center a candidate round trip delay between said remote unit and said first candidate base station based on said first phase shift and said round trip delay of said active communication signal. The method according to claim 1, characterized in that it further comprises the step of transmitting from each of said first set of base stations a common pilot sequence wherein each of said first set of base stations transmits said common pilot sequence in a displacement of identification channel. The method according to claim 2, characterized in that said step of calculating said candidate round trip delay is computed as: RTDcanl = RTDref + 2 * (Pilotocanl Phase - Canalciml Displacement * IncPilot) where: RTDcanX = said round trip delay candidate; RTDr said round trip delay of said active communication signal; PhasePilotocanX = said first phase shift; and Offset of CanalcanX * IncPilot an identification channel offset corresponding to said first candidate base station. The method according to claim 1, characterized in that said first candidate base station is controlled by said first mobile switching center. The method according to claim 1, characterized in that said first candidate base station is controlled by said second mobile switching center. The method according to claim 1, characterized in that said first candidate base station is controlled by said second mobile switching center and said pilot signal from said first candidate base station is generated by a pilot signal emitter unit. The method according to claim 3, characterized in that said first candidate base station is controlled by said second mobile switching center and said pilot signal from said first candidate base station is generated by a pilot signal emitter unit. The method according to claim 1, characterized in that it further comprises the steps of: storing in said remote unit a list of active base stations comprising an entry corresponding to each base station with which the active communication is established; storing in said remote unit a list of candidate base stations comprising an entry corresponding to each base station through which active communication may be possible but not established and said list of candidate base stations has an entry for said first base station candidate and storing in said remote unit a list of nearby base stations, from which said list of candidate base stations is chosen. The method according to claim 8, characterized in that it comprises the step of: measuring in said remote unit an energy level of a pilot signal corresponding to a first input in said list of nearby base stations, and if said energy level exceeds a added threshold said first entry in said list of nearby base stations is added to said list of candidate base stations; and wherein if said remote unit communicates with one of a first set of base stations controlled by said first mobile switching center, each of the base stations of said first boundary set having a coverage area bordering a coverage area corresponding to a base station controlled by said second mobile switching center, said remote unit has a lower value of said aggregate threshold than the other remote units communicating with at least one base station of said first set of base stations. The method according to claim 8, characterized in that it further comprises the step of: measuring by said remote unit an energy level of said first base station and if said energy level is less than, a fall threshold is removed an input in said list of active base stations corresponding to said first base station; and wherein if said remote unit communicates with one of a first limit set of base stations controlled by said first mobile switching center, each of said base stations of the first limit set having an area of coverage bordering a corresponding coverage area. to a base station controlled by said second mobile switching center, said remote unit has a lower value of said drop threshold than the other remote units communicating with at least one base station of said first set of base stations. The method according to claim 8, characterized in that it further comprises the step of: measuring in said remote unit an energy level of said first base station and if said energy level is less than a fall threshold by more than a quantity of predetermined time, an entry is removed from said list of active base stations corresponding to said first base station; and wherein if said remote unit is in communication with one of a first limit set of base stations controlled by said first mobile switching center, each of said base stations of the first boundary set having a coverage area bordering an area of coverage corresponding to a base station controlled by said second mobile switching center, said remote unit has a larger value of said predetermined amount of time than the other remote units communicating with at least one base station of said first set of base stations . The method according to claim 1, characterized in that it further comprises the step of accessing a hard transfer measurement state addressed by an active communication control unit in said first mobile switching center, wherein said measurement state of hard directed transfer allows this calculation step. The method according to claim 12, characterized in that said active communication control unit is a selector. The method according to claim 12, characterized in that a first limit set of base stations controlled by said first mobile switching center each having a coverage area bordering a coverage area corresponding to a base station controlled by said second center of mobile switching, further comprising the steps of: storing in said remote unit a list of active base stations comprising an input corresponding to each base station with which active communication is established; and executing the step of accessing said measurement state of the directed hard transfer only when said list of active base stations comprises an input corresponding to one of said first limit set of base stations. The method according to claim 12, characterized in that a first limit set of base stations controlled by said first mobile switching center each having a coverage area bordering a coverage area corresponding to a base station controlled by said second center of mobile switching, further comprises the steps of: storing in said remote unit a list of active base stations comprising an input corresponding to each base station with which active communication is established; and executing the step of accessing said measurement state of the directed hard transfer only when each entry in said list of active base stations corresponds to said first limit set of base stations. The method according to claim 12, characterized in that a first limit set of base stations controlled by said first mobile switching center each having a coverage area bordering a coverage area corresponding to a base station controlled by said second center of mobile switching, further comprising the steps of: wherein said remote unit stores a list of active base stations comprising an input corresponding to each base station with which active communication is established; and executing the step of accessing said measurement state of the directed hard transfer only when said list of active base stations comprises a single entry and said single entry corresponds to one of said first limit set of base stations. The method according to claim 12, characterized in that it further comprises the step of: accessing by means of said active communication control unit a hard transfer measurement table directed to determine based on said delay of a location of said remote unit based on said round trip delay corresponding to said first active communication signal and said candidate round trip delay. The method according to claim 12, characterized in that it further comprises the step of accessing by means of said active communication control unit to a hard transfer measurement table directed to determine, based on said round trip delay corresponding to said first active communication signal and said candidate round trip delay, if the location of said remote unit corresponds to an area where a transfer is desired. The method according to claim 18, characterized in that said hard transfer measurement table comprises an input designating a type of action that must be taken based on the location of said remote unit. The method according to claim 19, characterized in that said type of action to be taken is a transfer from said first base station communicating with said remote unit using code distribution multiple access (CDMA) to said second base station that operates using an alternative modulation technology. 21. The method according to claim 20, characterized in that said alternative modulation technology is frequency modulation (FM). 22. The method according to claim 20, characterized in that said alternative modulation technology is multiple access by time distribution (TDMA). The method according to claim 19, characterized in that said type of action to be taken is a transfer from said first base station communicating on a first frequency with said remote unit using CDMA to said second base station communicating on a second frequency that CDMA uses. The method according to claim 19, characterized in that said type of action to be taken is a transfer from said first base station communicating on a first frequency with said remote unit using CDMA to said first base station communicating with said base station. remote unit that uses an alternative modulation technology. 25. The method according to claim 19, characterized in that said type of action to be taken is a transfer from said first base station communicating at a first frequency with said remote unit using CDMA to said first base station communicating at a second frequency that CDMA uses. The method according to claim 1, characterized in that said active communication signal is comprised of a set of multiple path signals each having a different delay and wherein said round trip delay of said active communication signal is the delay round trip corresponding to the multipath signal arriving first from said first set of multipath signals. The method according to claim 18, characterized in that said access stage is executed when said round trip delay of said active communication signal changes by a predetermined amount. The method according to claim 18, characterized in that said access step is executed each time said report step is repeated by said remote unit. The method according to claim 1, characterized in that said active communication signal is a broadcast spectrum signal which is broadcast by a pseudorandom (PN) noise sequence and wherein said round trip delay of said active communication signal it is measured in PN chips. The method according to claim 3, characterized in that said active communication signal is a broadcast spectrum signal which is broadcast by a pseudorandom (PN) noise sequence and wherein said round trip delay of said active communication signal it is measured in PN chips, said ID channel offset is measured in PN chips and said candidate round trip delay is also measured in PN chips. The method according to claim 1, characterized in that said first base station defines a first coverage area and wherein said first coverage area shrinks in size when the number of the remote unit communicating with said first base station increases. . 32. The method according to claim 1, characterized in that it comprises the step of deploying in said first base station a pause function of the base station to balance an advancing link coverage area for a reverse link coverage area. The method according to claim 1, characterized in that a first limit set of base stations controlled by said first mobile switching center each having a coverage area bordering a coverage area corresponding to a base station controlled by said second mobile switching center further comprises the step of deploying in said first base station, if said first base station is one of said first boundary set of base stations, a pause function of the boundary base station to balance a link coverage area in advance for a reverse link coverage area that is different from a pause function of the base station deployed by other base stations of said first set of base stations. 34. In a communication network in which a user of the network communicates through a remote unit with another user through at least one base station, said network including mobile switching centers, first and second to control respectively the communications through a first set of base stations that includes a first base station and through a second set of base stations that includes a second base station, a method to direct communications between said remote unit and said first and second base stations comprising the steps of: measuring in said first base station a round trip delay of an active communication signal between said first base station and said remote unit; accessing a hard transfer measurement state addressed by an active communication control unit located in said first mobile switching center; and access by said active communication control unit to a hard transfer measurement table directed to determine based on said round trip delay corresponding to said first active communication signal if a location of said remote unit corresponds to a area where a transfer is desired. 35. The method according to claim 34, characterized in that it further comprises the step of: transmitting from each of said first set of base stations a common pilot sequence wherein each of said first set of base stations transmits said common pilot sequence in a displacement of the identification channel. 36. The method according to claim 34, characterized in that said active communication control unit is a selector. 37. The method according to claim 34, characterized in that said table of hard directed transfer measurement comprises an input specifying a type of action to be taken based on said location of said remote unit. 38. The method according to claim 37, characterized in that said type of action to be taken is a transfer from said first base station communicating with said remote unit using code distribution multiple access (CDMA) to said second base station that operates using an alternative modulation technology. 39. The method according to claim 38, characterized in that said alternative modulation technology is frequency modulation (FM). 40. The method according to claim 38, characterized in that said alternative modulation technology is multiple access by time distribution (TDMA). 41. The method according to claim 37, characterized in that said type of action to be taken is a transfer from said first base station communicating at a first frequency with said remote unit using CDMA to said second base station communicating at a second frequency that CDMA uses. 42. The method according to claim 37, characterized in that said type of action to be taken is a transfer from said first base station communicating on a first frequency with said remote unit using CDMA to said first base station communicating with said base station. remote unit that uses an alternative modulation technology. 43. The method according to claim 37, characterized in that said type of action to be taken is a transfer from said first base station communicating on a first frequency with said remote unit using CDMA to said first base station communicating in a second frequency that CDMA uses. 44. The method according to claim 34, characterized in that said active communication signal is comprised of a set of multiple path signals each having a different delay and wherein said round trip delay of said active communication signal is the delay round trip corresponding to the multipath signal arriving first from said set of multipath signals. 45. The method according to claim 34, characterized in that it further comprises said step of executing said access step when said round trip delay of said active communication signal changes by a predetermined amount. 46. A communication network comprising: a remote unit through which a user of the network communicates with another user through at least one base station where said remote unit measures a first phase shift of a received pilot signal of a candidate base station; a first set of base stations including a first base station wherein said first base station measures a round trip delay of an active communication signal between said first base station and said remote unit; and a first mobile switching center for controlling communications through said first set of base stations wherein said first mobile switching center receives a message from said remote unit comprising said first phase shift and receives said forward delay and return of said active communication signal from said first base station and calculates a candidate round trip delay between said remote unit and said first candidate base station thereof. 47. The apparatus according to claim 46, characterized in that it further comprises: a second set of base stations including a second base station; and a second mobile switching center for controlling communications through said second set of base stations. 48. The apparatus according to claim 46, characterized in that each of said first set of base stations transmits a common pilot sequence and wherein each of said first set of base stations transmits said common pilot sequence in a displacement of the identification channel. 49. The apparatus according to claim 48, characterized in that said first mobile switching center calculates said round trip delay as: RTDcanl = RTDref + 2 * (PhasePilotocanl - Canalcanl Displacement * IncPilot) where: RTD "said round trip delay candidate; RTDref = said round trip delay of said active communication signal; PhasePilotocanX = said first phase shift; y Offset of CanalcanX * IncPilot = an identification channel offset corresponding to said first candidate base station. 50. The apparatus according to claim 46, characterized in that said first base station is controlled by said first mobile switching center. 51. The apparatus according to claim 47, characterized in that said first base station is controlled by said second mobile switching center. 52. The apparatus according to claim 47, characterized in that said first candidate base station is controlled by said second mobile switching center and said pilot signal from said first candidate base station is generated by a pilot signal emitter unit. 53. The apparatus according to claim 47: characterized in that said remote unit stores a list of active base stations comprising an entry corresponding to each base station with which the active communication is established; wherein said remote unit stores a list of candidate base stations comprising an entry corresponding to each base station through which active communication may be possible but not established and said list of candidate base stations has an entry for said base station candidate and wherein said remote unit stores a list of nearby base stations, from which said list of candidate base stations is chosen. 54. The apparatus according to claim 53: characterized in that said remote unit measures an energy level of a pilot signal corresponding to a first input in said list of nearby base stations, and if said energy level exceeds an aggregate threshold said first input in said list of nearby base stations is added to said list of candidate base stations; and wherein if said remote unit communicates with one of a first set of base stations controlled by said first mobile switching centereach of said first boundary set of the base stations having a coverage area bordering a coverage area corresponding to a base station controlled by said second mobile switching center, said remote unit has a lower value of said aggregate threshold than the other remote units communicating with at least one base station of said first set of base stations. 55. The apparatus according to claim 53: characterized in that said remote unit measures an energy level of said first base station and if said energy level is less than a fall threshold an entry is removed in said list of active base stations corresponding to said first base station; and wherein if said remote unit communicates with one of a first limit set of base stations controlled by said first mobile switching center, each of said base stations of the first limit set having a coverage area bordering a corresponding coverage area. to a base station controlled by said second mobile switching center, said remote unit has a lower value of said drop threshold than the other remote units that communicate with at least one of said first set of base stations. 56. The apparatus according to claim 53, characterized in that said remote unit measures an energy level of said first base station and if said energy level is lower than a fall threshold by more than a predetermined amount of time, a entry into said list of active base stations corresponding to said first base station; and wherein if said remote unit is in communication with one of a first limit set of base stations controlled by said first mobile switching center, each of said base stations of the first boundary set having a coverage area bordering an area of coverage corresponding to a base station controlled by said second mobile switching center, said remote unit has a larger value of said predetermined amount of time than the other remote units communicating with at least one base station of said first set of base stations . 57. The apparatus according to claim 46, further characterized in that an active communication control unit in said first mobile switching center, which accesses a measurement state of the directed hard transfer in which said active communication control unit calculates said round trip delay candidate. 58. The apparatus according to claim 57, characterized in that said active communication control unit is a selector. 59. The apparatus according to claim 57, characterized in that said remote unit stores a list of active base stations comprising an entry corresponding to each base station with which the active communication is established, also comprising a first set of base stations controlled by said first mobile switching center, each having a coverage area bordering a coverage area corresponding to a base station controlled by said second mobile switching center, wherein said active communication control unit accesses said measurement state of the directed hard transfer only when said list of active base stations comprises an entry corresponding to one of said first limit set of base stations. 60. The apparatus according to claim 57, characterized in that said remote unit stores a list of active base stations comprising an entry corresponding to each base station with which active communication is established, further comprising a first set of base station limits controlled by said first mobile switching center, each having a coverage area bordering a coverage area corresponding to a base station controlled by said second mobile switching center, wherein said active communication control unit enters said measurement state of the transfer hard directed only when each entry in said list of active base stations corresponds to said first limit set of base stations. 61. The apparatus according to claim 57, characterized in that said remote unit stores a list of active base stations comprising an entry corresponding to each base station with which active communication is established, further comprising a first set of base stations controlled by said first mobile switching center, each having a coverage area bordering a coverage area corresponding to a base station controlled by said second mobile switching center, wherein said active communication control unit accesses said measurement state of the directed hard transfer only when said list of active base stations comprises a single entry and said single entry corresponds to one of said first limit set of base stations. 62. The apparatus according to claim 57, characterized in that it further comprises a table for measurement of the directed hard transfer that is accessed by said active communication control unit to determine a location of said remote unit based on said round trip delay. corresponding to said first active communication signal and said candidate round trip delay. 63. The apparatus according to claim 57, characterized in that it further comprises a table for measurement of the directed hard transfer that is accessed by said active communication control unit to determine, based on said round trip delay corresponding to said first signal of active communication and said candidate round trip delay, if the location of said remote unit corresponds to an area where a transfer is desired. 64. The apparatus according to claim 63, characterized in that said table of the directed hard transfer measurement comprises an input designating a type of action to be taken based on a location of said remote unit. 65. The apparatus according to claim 64, characterized in that said type of action to be taken is a transfer from said first base station communicating with said remote unit using code distribution multiple access (CDMA) to said second base station that operates using an alternative modulation technology. 66. The apparatus according to claim 65, characterized in that said alternative modulation technology is frequency modulation (FM). 67. The apparatus according to claim 65, characterized in that said alternative modulation technology is multiple access by time distribution (TDMA). 68. The apparatus according to claim 64, characterized in that said type of action to be taken is a transfer from said first base station communicating on a first frequency with said remote unit using CDMA to said second base station communicating in a second frequency that CDMA uses. 69. The apparatus according to claim 64, characterized in that said type of action to be taken is a transfer from said first base station that 5 communicates on a first frequency with said remote unit using CDMA to said first base station communicating with said remote unit using an alternative modulation technology. 70. The apparatus according to claim 64, • characterized in that said type of action to be taken is a transfer from said first base station communicating on a first frequency with said remote unit using CDMA to said first base station communicating on a second frequency using CDMA. 71. The apparatus according to claim 46, • characterized in that said active communication signal is comprised of a set of multiple path signals each having a different delay and wherein said round trip delay of said communication signal 20 is the round trip delay corresponding to the multipath signal arriving first from said set of multipath signals. 72. The apparatus according to claim 63, characterized in that said measured hard transfer measurement table is accessed when said round trip delay of said active communication signal changes by a predetermined amount. 73. The apparatus according to claim 63, characterized in that said measured hard transfer measurement table is accessed each time said first mobile switching center receives said message from said remote unit comprising said first phase shift. 74. The apparatus according to claim 46, characterized in that said active communication signal is a broadcast spectrum signal which is broadcast by a pseudorandom (PN) noise sequence and wherein said round trip delay of said active communication signal it is measured in PN chips. 75. The apparatus according to claim 48, characterized in that said active communication signal is a broadcast spectrum signal which is broadcast by a pseudorandom (PN) noise sequence and wherein said round trip delay of said active communication signal it is measured in PN chips, said ID channel offset is measured in PN chips and said candidate round trip delay is measured in PN chips. 76. The apparatus according to claim 46, characterized in that said first base station defines a first coverage area and wherein said first coverage area shrinks in size as the number of the remote unit communicating with said first base station increases. 77. The apparatus according to claim 46, characterized in that said first base station displays a pause function of the base station to balance an advancing link coverage area for a reverse link coverage area. 78. The apparatus according to claim 46, characterized in that it further comprises a first limit set of base stations controlled by said first mobile switching center having each of said first set of base stations a coverage area that abuts a coverage area that corresponds to a base station controlled by said second mobile switching center, and wherein said first base station is one of said first boundary set of base stations, and said first base station displays a first pause function of the base station to balance a forward link coverage area for a reverse link coverage area that is different from a pause function of the base station deployed by other base stations of said first set of base stations. 79. In a communications network characterized in that it comprises: a remote unit through which a user of the network communicates with another user through a base station; mobile switching centers, first and second to control respectively the communications through a first set of base stations and through a second set of base stations includes a second base station; a first base station that is a member of said first set of base stations, which measures a round trip delay of an active communication signal between said first base station and said remote unit; an active communication control unit located in said first mobile switching center having a measurement state of the directed hard transfer in which said active communication control unit accesses a hard transfer measurement table directed to determine in base to said round trip delay corresponding to said first active communication signal if a location of said remote unit corresponds to an area where a transfer is desirable. 80. The apparatus according to claim 79, characterized in that each of said first set of base stations transmits a common pilot sequence and wherein each of said first set of base stations transmits said common pilot sequence in a displacement of the identification channel. 81. The apparatus according to claim 79, characterized in that said active communication control unit is a selector. 82. The apparatus according to claim 79, characterized in that said table of the directed hard transfer measurement comprises an input specifying a type of action to be taken based on said location of said remote unit. 83. The apparatus according to claim 82, characterized in that said type of action to be taken is a transfer from said first base station communicating with said remote unit using code distribution multiple access (CDMA) to said second base station that operates using an alternative modulation technology. 84. The apparatus according to claim 83, characterized in that said alternative modulation technology is frequency modulation (FM). 85. The apparatus according to claim 83, characterized in that said alternative modulation technology is multiple access by time distribution (TDMA). 86. The apparatus according to claim 82, characterized in that said type of action to be taken is a transfer from said first base station communicating at a first frequency with said remote unit using CDMA to said second base station communicating at a second frequency that CDMA uses. 87. The apparatus according to claim 82, characterized in that said type of action to be taken is a transfer from said first base station communicating on a first frequency with said remote unit using CDMA to said first base station communicating with said base station. remote unit that uses an alternative modulation technology. 88. The apparatus according to claim 82, characterized in that said type of action to be taken is a transfer from said first base station communicating at a first frequency with said remote unit using CDMA to said first base station communicating at a second frequency that CDMA uses. 89. The apparatus according to claim 79, characterized in that said active communication signal is comprised of a set of multi-path signals each having a different delay and wherein said round-trip delay of said active communication signal is the one-way delay and which corresponds to the multipath signal arriving first from said set of multipath signals. 90. The apparatus according to claim 79, characterized in that said active communication signal accesses said measurement table of the directed hard transfer when said round trip delay of said active communication signal changes by a predetermined amount. SUMMARY In a communication network, a user of the network communicates with another user (30), using a remote unit (125) through at least one base station (B1A). The network is comprised of mobile switching control stations, first (MSC-I) and second (MSC-II), respectively, which control communications through a first set of base stations (B1A-B1E) that includes a first station base BXA and through a second set of base stations (B2A-B2E) including a second base station B2A To direct communications between the remote unit (125) and the base stations, first (B1A) and second (B2A), the first base station (B1A) measures a round trip delay of an active communication signal between the first base station (B1A) and the remote unit (125). The remote unit (125) measures a first phase shift of a pilot signal received from a first candidate base station (BIA) AND 1st reports to the first mobile switching center (MSC-1) through the first base station (B ^). The first mobile switching center (MSC-I) calculates a round trip delay candidate between the remote unit (125) and the first candidate base station (B1A) based on the first phase shift and the round trip delay of the active communication signal. An active communication control unit accesses the directed hard transfer measurement table to determine a location of the remote unit based on the round trip delay corresponding to the first active communication signal and the candidate round trip delay.