WO1997005750A1

WO1997005750A1 - Method and apparatus for facilitating location tracking of a portable subscriber unit

Info

Publication number: WO1997005750A1
Application number: PCT/US1996/007531
Authority: WO
Inventors: Jyh-Han Lin; Richard T. Bennett; Jheroen Dorenbosch
Original assignee: Motorola Inc.
Priority date: 1995-07-31
Filing date: 1996-05-24
Publication date: 1997-02-13
Also published as: TW303559B

Abstract

A method and apparatus facilitates location tracking of a portable subscriber unit (122) in a radio communication system including a plurality of cells for providing radio communications with the portable subscriber unit (122). The plurality of cells are partitioned into subzones (402), a subzone (402) comprising at least one cell and utilizing at least one control channel. Each subzone (402) is assigned one of N subzone color codes (606). Adjacent subzones (402) have different subzone color codes (522), and same-valued subzone color codes (522) are reused in non-adjacent subzones (606). Control information is transmitted throughout each subzone (402) on the control channel (608) by a fixed portion (102) of the radio communication system. The control information includes the subzone color code (522) of the subzone (402). The portable subscriber unit (122) detects changes in the subzone color code (522), and thereafter, registers with the fixed portion (102) of the radio communication system in response.

Description

METHOD AND APPARATUS FOR FACILITATING LOCAΗON TRACKING OF A PORTABLE SUBSCRIBER UNIT

Related Applications

Application No. 08/131,243 filed October 4, 1993 by Simpson et al., entitled "Method and Apparatus for Identifying a Transmitter in a Radio Communication System."

Field of the Invention

This invention relates in general to registration in a radio communication system, and more specifically to a method and apparatus for facilitating location tracking of a portable subscriber unit.

Background of the Invention

A radio communication system with two-way communication capability between base stations and portable subscriber units provides an important means for the base stations to determine the reliability of message transactions with portable subscriber units. Such a system can thus inform a caller invoking a message intended for a portable subscriber unit of the reliability of the message transaction.

A cost effective implementation of a two-way radio communication system, as described above, requires efficient coverage zone management. In particular, the coverage zone management utilized by the base stations as well as the portable subscriber units must be cost effective, and should further provide minimal latency of message transactions.

Prior art two-way radio communication systems have supported coverage zone management by requiring the portable subscriber units to scan a plurality of control channels to determine zone crossings, as well as a need for zone registration. This technique, however, is costly to implement in the portable subscriber units, and impacts battery life performance. Moreover, the scanning process utilized by the portable subscriber units can under certain conditions affect the latency of portable subscriber unit registration, and as a result slow down message delivery to a portable subscriber unit. Thus, what is needed is a method and apparatus for facilitating location tracking of a portable subscriber unit. In particular, the tracking method must track quickly and efficiently the location of portable subscriber units in order to reduce the latency of message transactions between the portable subscriber units and the base stations.

Brief Description of the Drawings

FIG. 1 is an electrical block diagram of a radio communication system in accordance with the preferred embodiment of the present invention.

FIG. 2 is an electrical block diagram of elements of a fixed portion of the radio communication system in accordance with the preferred embodiment of the present invention. FIG. 3 is an electrical block diagram of a portable subscriber unit in accordance with the preferred embodiment of the present invention.

FIG. 4 is a coverage diagram of the radio communication system comprising a plurality of subzones with non-adjacent color codes in accordance with the preferred embodiment of the present invention. FIG. 5 is a timing diagram of elements of an outbound protocol and an inbound protocol of the fixed and portable portions of the radio communication system in accordance with the preferred embodiment of the present invention.

FIG. 6 is a flow chart depicting operation of the fixed portion of the radio communication system in accordance with the preferred embodiment of the present invention.

FIG. 7 is a flow chart depicting operation of the portable subscriber unit in accordance with the preferred embodiment of the present invention.

Description of the Preferred Embodiment

FIG. 1 is an electrical block diagram of a radio communication system in accordance with the preferred embodiment of the present invention. The radio communication system comprises a fixed portion 102 and a portable portion 104. The fixed portion 102 includes a plurality of base stations 116, for communicating with the portable portion 104, utilizing conventional radio frequency (RF) techniques, and coupled by communication links 114 to a controller 112 which controls the base stations 116. The hardware of the controller 112 is preferably a combination of the Wireless Messaging Gateway (WMG™)

Administrator! paging terminal, and the RF-Conductor!™ message distributor manufactured by Motorola, Inc. The hardware of the base stations 116 is preferably a combination of the Nucleus® Orchestra! transmitter and RF-Audience!™ receivers manufactured by Motorola, Inc. It will be appreciated that other similar hardware can be utilized for the controller 112 and the base stations 116.

Each of the base stations 116 transmits RF signals to the portable portion 104 comprising a plurality of portable subscriber units 122 via a transmitting antenna 120. The base stations 116 each receive RF signals from the plurality of portable subscriber units 122 via a receiving antenna 118. The RF signals transmitted by the base stations 116 to the portable subscriber units 122 (outbound messages) comprise selective call addresses identifying the portable subscriber unit 122, and data or voice messages originated by a caller, as well as registration acknowledgments as will be described below. The RF signals transmitted by the portable subscriber units 122 to the base stations 116 (inbound messages) comprise positive acknowledgments (ACKs) which indicate the message was received reliably by the portable subscriber unit 122, or negative acknowledgments (NAKs) which indicate the portable subscriber unit 122 did not receive the message reliably. The portable subscriber unit 122 can also transmit unscheduled messages such as subscriber unit registration messages, which will be described in more detail below. A detailed description of inbound acknowledge-back messaging is more fully described in U.S. Patent No. 4,875,038 issued October 17, 1989 to Siwiak et al., which is hereby incorporated herein by reference.

The controller 112 preferably is coupled by telephone links 101 to a public switched telephone network (PSTN) 110 for receiving selective call originations therefrom. Selective call originations comprising voice and data messages from the PSTN 110 can be generated, for example, from a conventional telephone 111 coupled to the PSTN 110. The outbound messages are preferably similar to Motorola's well- known FLEX™ digital selective call signaling protocol as described more fully in U.S. Patent No. 5,168,493 issued December 1, 1992 to Nelson et al., which is hereby incorporated herein by reference. This protocol utilizes well-known error detection and error correction techniques and is therefore tolerant to bit errors occurring during transmission, provided that the bit errors are not too numerous in any one code word.

Outbound channel transmissions of the digital message portion transmitted by the base stations 116 preferably utilize two and four-level frequency shift keyed (FSK) modulation, operating at sixteen hundred or thirty two hundred symbols-per-second (sps), depending on traffic requirements and system transmission gain. Inbound- channel transmissions from the portable subscriber units 122 to the base stations 116 preferably utilize four-level FSK modulation at a rate of eight hundred bits per second (bps). Inbound channel transmissions preferably occur during predetermined data packet time slots synchronized with the outbound channel transmissions.

The outbound and inbound channels preferably operate on separate carrier frequencies utilizing conventional frequency division multiplex (FDM) techniques. A detailed description of FDM techniques is more fully described in U.S. Patent No. 4,875,038 issued to Siwiak et al. It will be appreciated that, alternatively, the outbound and inbound channels can operate on a single carrier frequency using time division duplex (TDD) techniques as described more fully in U.S. Patent No. 5,168,493 issued to Nelson et al. It will be further appreciated that, alternatively, other signaling protocols, modulation schemes, and transmission rates can be utiUzed for either or both transmission directions.

FIG. 2 is an electrical block diagram 200 of elements of the fixed portion 102 in accordance with the preferred embodiment of the present invention. The diagram 200 comprises portions of the controller 112 and the base stations 116. The controller 112 includes a processing system 210 for directing operation of the controller 112. The processing system 210 preferably is coupled through a transmitter interface 204 to a transmitter 202 via the communication links 114. The communication links 114 preferably utϋize conventional means such as a direct wire line

(telephone) link, a data communication link, or any number of radio frequency links, such as a radio frequency (RF) transceiver link, a microwave transceiver link, or a satellite link, just to mention a few.

The transmitter 202 transmits two and four-level FSK data messages to the portable subscriber units 122 during outbound messaging. The processing system 210 is also coupled to at least one base receiver 206 through a receiver interface 208 via the communication links 114. The base receiver 206 demodulates four-level FSK and is preferably collocated with the base stations 116, as implied in FIG. 2, but can be positioned remote from the base stations 116 to avoid interference from the transmitter 202. The base receiver 206 is for receiving one or more acknowledgments (ACKs, NAKs, or registration requests) from the portable subscriber units 122.

The processing system 210 is also coupled to a telephone interface 218 for communicating with the PSTN 110 through the telephone links 101 for receiving selective call originations.

In order to perform the functions necessary in controlling the elements of the controller 112, as well as the elements of the base stations 116, the processing system 210 preferably includes a conventional computer system 212, and conventional mass storage media 214. The conventional mass storage media 214 includes subscriber user information such as, for example, portable subscriber unit 122 addressing, programming options, etc.

The conventional computer system 212 is preferably programmed by way of software included in the conventional mass storage media 214. The conventional computer system 212 preferably comprises a plurality of processors such as VME Sparc processors manufactured by Sun Microsystems, Inc. These processors include memory such as dynamic random access memory (DRAM), which serves as a temporary memory storage device for program execution, and scratch pad processing such as, for example, storing messages originated by callers using the PSTN 110, processing acknowledgments received from the portable subscriber units 122, and for protocol processing of messages destined for the portable subscriber units 122, just to mention a few. The conventional mass storage media 214 is preferably a conventional hard disk mass storage device. It will be appreciated that other types of conventional computer systems 212 can be utilized, and that additional computer systems 212 and mass storage media 214 of the same or alternative type can be added as required to handle the processing requirements of the processing system 210.

The processing system 210 is conventionally programmed for processing incoming messages from the PSTN 110, and for processing outbound and inbound messages transmitted to and from the portable subscriber unit 122.

The processing system 210 is further programmed for partitioning a plurality of cells, which include one or more base stations 116, into subzones. Each subzone comprises at least one cell and utilizes at least one control channel, transmitted throughout the subzone, for communicating with a plurality of portable subscriber units 122. The processing system 210 also assigns one of N subzone color codes to each of the subzones, where preferably N = 4 corresponding to four subzones assigned to four unique color codes. The processing system 210 assigns subzone color codes such that adjacent subzones have different subzone color codes, and wherein same-valued subzone color codes are reused in non-adjacent subzones. The processing system 210 controls the base stations 116 by way of the transmitter interface 204 to periodically transmit control information for each of the subzones on the control channel utilized by the subzone, the control information comprising the subzone color code assigned to the subzone.

The processing system 210 is also programmed for processing subzone registration requests transmitted by the portable subscriber units 122. In one embodiment, the processing system 210 assigns a registration control channel corresponding to each of the subzone color codes. The controller 112 transmits control information on the registration control channel to the portable subscriber units 122. During transitions between subzones the portable subscriber units 122 transmit registration requests on the inbound registration control.

In an alternative embodiment, the processing system 210 receives registration requests from portable subscriber units 122 on a first control channel. The processing system 210 chooses, in response to the registration request, a second control channel for the portable subscriber unit 122 to use while registered in the subzone. Consequently, the controller 112 transmits, by way of the base stations 116, over the first control channel a message assigning the portable subscriber unit 122 to the second control channel. The processing system selects the second control channel based on existing traffic loads carried by control channels utilized for the subzone. Referring to FIG. 3, an electrical block diagram of the portable subscriber unit 122 in accordance with the preferred embodiment of the present invention comprises a transmitter antenna 302 for transmitting RF signals to the base stations 116, and a receiver antenna 305 for intercepting RF signals from the base stations 116. The transmitter antenna 302 is coupled to a conventional transmitter 304. Similarly, the receiver antenna 305 is coupled to a conventional receiver 306. The RF signals received from the base stations 116 are received as two and four- level FSK signals. The RF signals transmitted by the portable subscriber unit 122 to the base stations 116 are transmitted as four-level FSK signals. Radio signals received by the receiver 306 produce demodulated information at the output. The demodulated information is coupled to the input of a processing unit 310, which processes outbound messages. Similarly, inbound acknowledgment messages are processed by the processing unit 310 and delivered to the transmitter 304 for transmission. A conventional power switch 308, coupled to the processing unit 310, is used to control the supply of power to the transmitter 304 and receiver 306, thereby providing a battery saving function.

To perform the necessary functions of the portable subscriber unit 122, the processing unit 310 includes a microprocessor 316, a RAM 312, a ROM 314, and an EEPROM 318. Preferably, the microprocessor 316 is similar to the M68HC08 micro-controller manufactured by Motorola, Inc. It will be appreciated that other similar processors can be utilized for the microprocessor 316, and that additional processors of the same or alternative type can be added as required to handle the processing requirements of the processing unit 310. It will be appreciated that other types of memory, e.g., EEPROM or FLASH, can be utilized for the ROM 314, as well as the RAM 312. It will be further appreciated that the RAM 312 and the ROM 314, singly or in combination, can be an integral portion of the microprocessor 316. The microprocessor 316 is programmed by way of the ROM 314 to process incoming messages on the outbound channel, and for creating acknowledgment messages on the inbound channel. During outbound message processing, the microprocessor 316 samples the demodulated signal generated by the receiver 306. The microprocessor 316 then decodes an address in the demodulated data of the outbound message, compares the decoded address with one or more addresses stored in the EEPROM 318, and when a match is detected, the microprocessor 316 proceeds to process the remaining portion of the message.

Once the microprocessor 316 has processed the message, it stores the message in the RAM 312, and a call alerting signal is generated to alert a user that a message has been received. The call alerting signal is directed to a conventional audible or tactile alerting device 322 for generating an audible or tactile call alerting signal. In addition, the microprocessor 316 is programmed to send the ACK or NAK depending on the quality of the received message. To send the acknowledgment, the microprocessor 316 controls the modulation circuit (not shown) of the transmitter 304 to send the FSK data corresponding to the acknowledgment message(s).

Outbound messages can be accessed by the user through user controls 320, which provide functions such as lock, unlock, delete, read, etc. More specifically, by the use of appropriate functions provided by the user controls 320, the message is recovered from the RAM 312, and then displayed on a display 324, e.g., a conventional liquid crystal display (LCD), or played out audibly, in the case of a voice message, by the combination of an audio amplifier 326 and a speaker 328.

The microprocessor 316 is further programmed to receive from the receiver 306 a first subzone color code. The microprocessor 316 proceeds to store the first color code in RAM 312. During transitions between subzones the receiver 306 generates a second subzone color code corresponding to a second subzone uniquely distinct from the first subzone. In one embodiment, the portable subscriber unit 122 detects a loss of reception on the control channel of the first subzone during a subzone crossing, and proceeds to scan from a list of registration control channels.

The list of registration control channels preferably comprises four registration control channels corresponding to four unique subzone color codes for each of four subzones, as described above for the fixed portion 102 of the radio communication system. Limiting the control channel list to four registration control channels provides the portable subscriber unit 122 a means for efficiently locating a control channel, and thereby reducing the latency of portable subscriber unit 122 registration. It will be appreciated that, alternatively, the four subzone color codes can utilize the same registration control channel.

In an alternative embodiment, the microprocessor 316 controls the receiver 306 to scan a predetermined set of control channel frequencies given by the fixed portion 102 of the radio communication system to obtain the control information in response to a loss of reception of the control information from the previously received subzone (i.e., the first subzone). In this embodiment, the portable subscriber unit 122 is programmed, by way of the EEPROM 318, with a list of the control channels utilized by the fixed portion 102 of the radio communication system. This list is typically large, and can result in registration latency of the portable subscriber unit 122.

Once the portable subscriber unit 122 has locked onto a control channel during a loss of reception, the microprocessor 316 checks for subzone color code differences by comparing first and second subzone color codes. When a mismatch is detected the microprocessor 316 proceeds to register the portable subscriber unit 122 with the second subzone corresponding to the second subzone color code in response to the first and second subzone color codes being different from one another. Under these conditions, the portable subscriber unit 122 transmits a registration request to the base stations 116 of the second subzone. When the portable subscriber unit 122 receives a registration acknowledgment from the base stations 116, the acknowledgment message indicates recognition by the controller 112 of the portable subscriber unit 122 as a registered unit in the second subzone. The acknowledgment message further can include information identifying a control channel different from the registration control channel chosen by the controller 112 to be utilized by the portable subscriber unit 122 while in the subzone. Consequently, the microprocessor 316 controls the receiver to switch to the control channel designated by the controller 112. The controller 112 preferably chooses the control channel based on traffic conditions present in the subzone. The microprocessor 316 is further programmed to recognize an out- of-range (OOR) condition by use of the subzone color codes. The portable subscriber unit 122 determines an OOR condition by a continuous loss of reception of subzone color codes. If no subzone color code is detected for a predetermined time period, then the portable subscriber unit 122 alerts the user of the portable subscriber unit 122 about the OOR condition via the display 324. The portable subscriber unit 122 continues to scan periodically for subzone color codes until a valid subzone color code is detected, and thereafter removes the OOR alert from the display 324. FIG. 4 is a coverage diagram of the radio communication system comprising a plurality of subzones 402 with non-adjacent color codes in accordance with the preferred embodiment of the present invention. In the radio communication system shown there are preferably only four color codes: red (R), yellow (Y), green (G), and blue (B). As can be seen, no subzone 402 is adjacent to a subzone with identical color code. This configuration allows for transitions between subzones to be uniquely identified by portable subscriber units 122, thereby providing the capability for subzone registration. It will be appreciated that, alternatively, more or fewer color codes may be utilized for subzone identification. In addition, in a configuration as in this example, only two binary bits are necessary to identify the four subzones 402. Limiting the color code information to a few bits provides for a more bandwidth efficient protocol, and further simplifies the processing needs of the portable subscriber units 122. As s a result, the cost of the portable subscriber unit 122 is reduced, and overall battery life performance is improved.

FIG. 5 is a timing diagram 500 of elements of an outbound protocol and an inbound protocol of the fixed portion 102 and portable portion 104 of the radio communication system in accordance with the preferred embodiment of the present invention. The signaling format operating on the outbound and inbound channels preferably operates on independent frequencies utilizing FDM as described above. Using FDM transmission both outbound and inbound RF channel transmissions are depicted during a time interval 501.

The elements of the outbound protocol comprise an outbound sync 507, a selective call address 512, a message vector 514 and an outbound message 516. The outbound sync 507 includes a syncl field 508, a frame information field 509, and a sync2 field 510. The syncl field 508 comprises a bit syncl field 518, an A word 520, a B word 522, and an inverted A word 524. The bit syncl field 518 provides the portable subscriber unit 122 a means for synchronization utilizing techniques well known in the art. The A word 520 identifies the protocol version used, that is, Flex™,

InFlexion™, or ReFlex™. The B word 522 comprises one of one hundred twenty eight possible sixteen bit color codes. The upper two bits of the color codes are preferably used by the controller 112 for designating four unique subzone color codes (00, 01, 10, and 11). The upper bits of the B word 522 are referred to herein as a subzone color code 522. The least significant bits can be used by the portable subscriber unit 122 to uniquely identify a transmitter 202. The inverted A word 524 is' used as redundant information for further verification of the integrity of the control channel information. The selective call address 512 identifies the portable subscriber unit

122 for which the outbound message 516 is intended. The message vector 514 points in time within the signal format to the position of the outbound message 516 to be received by the portable subscriber unit 122. The message vector 514 further provides information to the portable subscriber unit 122 identifying a scheduled time slot for acknowledging the message transaction. The outbound message 516 can comprise either a selective call message, or a registration acknowledgment transmitted by the base stations 116.

The elements of the inbound protocol comprise an inbound sync 526, scheduled time slots 528, and unscheduled time slots 530. The inbound sync 526 provides the base stations 116 a means for synchronization utilizing techniques well known in the art. Scheduled messages commence after the inbound sync 526 at a time boundary 503. A transmission time interval 502 depicts the time interval for scheduled transmissions on scheduled time slots 528 from the portable subscriber units 122. Unscheduled messages commence after a time boundary 505 which depicts the end of scheduled transmissions from the portable subscriber units 122. The duration of unscheduled transmissions on unscheduled time slots 530 is depicted by a transmission time interval 504. Unscheduled time slots 530 may be used by any portable subscriber unit 122 located in a subzone. For certain cases there may be more portable subscriber units 122 attempting to utilize unscheduled time slots 530 than available in the subzone. To overcome this limitation, the well-known ALOHA protocol is utilized for unscheduled messaging.

Scheduled inbound messages preferably can comprise ACKs, or NAKs, while unscheduled transmissions preferably can comprise registration requests. Scheduled and unscheduled inbound messages include a portable subscriber unit identification number (preferably the address of the portable subscriber unit 122). Registration request messages include the subzone color code of the subzone in which the portable subscriber unit 122 is located. The registration request along with known location information associated with the base receiver 206 allows the controller 112 to identify the subzone 402 in which the portable subscriber unit 122 is located.

FIG. 6 is a flow chart 600 depicting operation of the fixed portion 102 of the radio communication system in accordance with the preferred embodiment of the present invention. The flow chart 600 begins with step 602 where the controller 112 tracks a portable subscriber unit 122 by partitioning a plurality of cells into subzones 402, a subzone 402 comprising at least one cell. In step 604 the controller 112 provides at least one control channel and transmits the at least one control channel throughout the subzone 402. In step 606 the controller 112 assigns one of N (preferably N = 4) subzone color codes 522 to each of the subzones 402, wherein N is a predetermined integer greater than unity, and wherein the subzone color codes 522 are assigned such that adjacent subzones 402 have different subzone color codes 522, and wherein same-valued subzone color codes 522 are reused in non-adjacent subzones 402.

In step 608 the controller 112 periodically transmits control information for each of the subzones 402 on the at least one control channel utilized by the subzone 402, the control information comprising the subzone color code 522 assigned to the subzone 402. In step 610 the controller 112 waits for registration requests transmitted by portable subscriber units 122. In one embodiment the registration requests are received on a first control channel, where in an alternative embodiment the registration requests are received on a registration control channel assigned by color code to each subzone 402. When the controller 112 receives a registration request from a portable subscriber unit 122, the controller 112 proceeds to step 612 where it records the subzone location of the portable subscriber unit 122. In response, the controller 112 sends an acknowledgment in step 614 to the portable subscriber unit 122 acknowledging the registration of the subscriber unit. In one embodiment, the acknowledgment message transmitted to the portable subscriber unit 122 acknowledges the registration of the portable subscriber unit 122 in the subzone 402. In an alternative embodiment, the acknowledgment message also acknowledges the registration of the portable subscriber unit 122 in the subzone 402, and further assigns the portable subscriber unit 122 to a second control channel chosen by the controller 112 based on traffic conditions.

FIG. 7 is a flow chart 700 depicting operation of the portable subscriber unit 122 in accordance with the preferred embodiment of the present invention. The flow chart 700 begins with step 702 where the portable subscriber unit 122 receives a first subzone color code 522 from a first subzone, and stores the first subzone color code 522 in memory (RAM 312). In step 704 the portable subscriber unit 122 receives a second subzone color code 522, and compares the first and second subzone color codes 522. For the case when the subzone color code 522 remains unchanged, the portable subscriber unit 122 proceeds to step 702. When a mismatch is detected in the subzone color code 522, the portable subscriber unit 122 in step 708 registers with the second subzone corresponding to the second subzone color code in response to the first and second subzone color codes being different from one another. In step 710 the portable subscriber unit 122 transmits the registration request to the controller 112. In step 712 the portable subscriber unit 122 waits for an acknowledgment from the controller 112 acknowledging registration of the portable subscriber unit 122 in the subzone. The portable subscriber unit 122 waits for a predetermined period, if an acknowledgment is not received in this period the portable subscriber unit 122 proceeds to step 710 where the registration request is re-transmitted. If the re-transmissions attempted exceed a resend count (not shown) then the portable subscriber unit 122 ceases transmission of the registration request. When an acknowledgment is received from the base stations 116 within the predetermine period, then the portable subscriber unit 122 proceeds to step 704 where it continues to monitor subzone 402 transitions. Thus, it should be apparent by now that the present invention provides a method and apparatus for facilitating location tracking of a portable subscriber unit 122. In particular, the method and apparatus advantageously provides a novel method for detecting out of range and subzone transitions without sacrificing battery life of the portable subscriber unit 122. The subzone color codes 522, defined above, provide the portable subscriber unit 122 enough information to quickly determine out of range conditions as well as transitions between subzones 402. In addition, assigning a registration control channel to each subzone color code 522 allows the portable subscriber unit 122 quicker access to control channel information thereby improving battery life performance, and reducing latency for registration in a new subzone 402, Furthermore, the complexity of the firmware necessary to implement the above method in the portable subscriber unit 122 is simplified thereby reducing the overall manufacturing cost of the portable subscriber unit 122. What is claimed is:

Claims

1. A method of facilitating location tracking of a portable subscriber unit in a radio communication system including a plurality of cells for providing radio communications with the portable subscriber unit, the method comprising the steps of: partitioning the plurality of cells into subzones, a subzone comprising at least one cell and utilizing at least one control channel, the at least one control channel transmitted throughout the subzone; assigning one of N subzone color codes to each of the subzones, wherein N is a predetermined integer greater than unity, and wherein the subzone color codes are assigned such that adjacent subzones have different subzone color codes, and wherein same-valued subzone color codes are reused in non-adjacent subzones; and periodically transmitting control information for each of the subzones from a fixed portion of the radio communication system on the at least one control channel utilized by the subzone, the control information comprising the subzone color code assigned to the subzone.

2. The method of claim 1, wherein N = 4.

3. The method of claim 1, further comprising in the portable subscriber unit the steps of: receiving a first subzone color code from a first subzone; storing the first subzone color code; thereafter receiving a second subzone color code; comparing the first and second subzone color codes; and registering with a second subzone corresponding to the second subzone color code in response to the first and second subzone color codes being different from one another.

4. The method of claim 1, further comprising in the portable subscriber unit the step of scanning at least one predetermined control channel frequency to obtain the control information in response to a loss of reception of the control information from a previously received subzone.

5. The method of claim 1, further comprising the step of designating a registration control channel corresponding to each of the subzone color codes, wherein the transmitting step comprises the step of transmitting the control information on the registration control channel corresponding to the subzone color code assigned to the subzone.

6. The method of claim 5, further comprising in the portable subscriber unit the step of scanning only the registration control channel corresponding to each of the subzone color codes to obtain the control information in response to a loss of reception of the control information from a previously received subzone.

7. The method of claim 1, further comprising in the fixed portion the steps of receiving through at least one base receiver a registration request from the portable subscriber unit on a first control channel, the registration request comprising one of the subzone color codes; and identifying the subzone in which the portable subscriber unit is located from the one of the subzone color codes in combination with location information associated with the at least one base receiver.

8. The method of claim 7, further comprising in the fixed portion the steps of choosing, in response to the registration request,, a second control channel for the portable subscriber unit to use while registered in the subzone; and transmitting over the first control channel a message assigning the portable subscriber unit to the second control channel.

9. The method of claim 8, wherein the choosing step comprises the step of selecting the second control channel based on existing traffic loads carried by control channels utilized for the subzone.

10. A controller for facilitating location tracking of a portable subscriber unit in a radio communication system including a plurality of cells for providing radio communications with the portable subscriber unit, the controller coupled to a transmitter and a base receiver for communicating therewith, the controller comprising: a processing system for directing operation of the controller; a telephone interface coupled to the processing system for receiving a message intended for the portable subscriber unit from a telephone system; a transmitter interface coupled to the processing system for controlling a transmitter to transmit the message to the portable subscriber unit; and a receiver interface coupled to the processing system for receiving information transmitted from the portable subscriber unit to at least one base receiver, wherein the processing system is programmed for: partitioning the plurality of cells into subzones, a subzone comprising at least one cell and utilizing at least one control channel, the at least one control channel transmitted throughout the subzone; assigning one of N subzone color codes to each of the subzones, wherein N is a predetermined integer greater than unity, and wherein the subzone color codes are assigned such that adjacent subzones have different subzone color codes, and wherein same-valued subzone color codes are reused in non-adjacent subzones; and periodically transmitting control information for each of the subzones from a fixed portion of the radio communication system on the at least one control channel utilized by the subzone, the control information comprising the subzone color code assigned to the subzone.

11. The controller of claim 10, wherein N = 4.

12. The controller of claim 10, wherein the processing system is further programmed for: designating a registration control channel corresponding to each of the subzone color codes, and transmitting the control information on the registration control channel corresponding to the subzone color code assigned to the subzone.

13. The controller of claim 10, wherein the processing system is further programmed for: receiving through the at least one base receiver a registration request from the portable subscriber unit on a first control channel, the registration request comprising one of the subzone color codes; and identifying the subzone in which the portable subscriber unit is located from the one of the subzone color codes in combination with location information associated with the at least one base receiver.

14. The controller of claim 13, wherein the processing system is further programmed for: choosing, in response to the registration request, a second control channel for the portable subscriber unit to use while registered in the subzone; and transmitting over the first control channel a message assigning the portable subscriber unit to the second control channel.

15. The controller of claim 14, wherein the processing system is further programmed for selecting the second control channel based on existing traffic loads carried by control channels utilized for the subzone.

16. A portable subscriber unit for facilitating location tracking thereof in a radio communication system including a plurality of cells for providing radio communications with the portable subscriber unit, wherein the plurality of cells are partitioned into subzones, a subzone comprising at least one cell and utilizing at least one control channel, the at least one control channel transmitted throughout the subzone, and wherein one of N subzone color codes is assigned to each of the subzones, N being a predetermined integer greater than unity, and wherein the subzone color codes are assigned such that adjacent subzones have different subzone color codes, and wherein same-valued subzone color codes are reused in non-adjacent subzones, and wherein control information is periodically transmitted for each of the subzones from a fixed portion of the radio communication system on the at least one control channel utilized by the subzone, the control information comprising the subzone color code assigned to the subzone, the portable subscriber unit comprising: a microprocessor for directing operation of the portable subscriber unit; a receiver coupled to the microprocessor for receiving a first subzone color code from a first subzone; a memory coupled to the microprocessor for storing the first subzone color code; and a transmitter coupled to the microprocessor for sending registration information to the fixed portion, wherein the receiver is further for receiving a second subzone color code, and wherein the microprocessor is programmed for: comparing the first and second subzone color codes; and registering with a second subzone corresponding to the second subzone color code in response to the first and second subzone color codes being different from one another.

17. The portable subscriber unit of claim 16, wherein N = 4.

18. The portable subscriber unit of claim 16, wherein the microprocessor is further programmed for contiolling the receiver to scan at least one predetermined control channel frequency to obtain the control information in response to a loss of reception of the control information from a previously received subzone.

19. The portable subscriber unit of claim 16, wherein a registration control channel corresponding to each of the subzone color codes is designated, and wherein the control information is transmitted on the registration control channel corresponding to the subzone color code assigned to the subzone, and wherein the microprocessor is further programmed for scanning only the registration control channel corresponding to each of the subzone color codes to obtain the control information in response to a loss of reception of the control information from a previously received subzone.