JP2006287601A - Mobile communication system and base station device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mobile communication system which reduces control delay between a terminal and a base station and can perform high-speed radio communication. <P>SOLUTION: In the mobile communication system comprising a plurality of terminals for using one of first radio channel groups in a first frequency band and one of second radio channel groups in a second frequency band wider than the first frequency band to perform radio communication, a plurality of broadband base stations for using the second radio channel groups to transmit an information signal and a narrow-band base station for using the first radio channel groups to perform radio communication and performing communication with the plurality of broadband base stations, one of the first radio channel groups is associated with the second radio channel groups in advance, respectively. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a mobile communication system.

  When a conventional mobile communication system has a plurality of frequency bands, wireless transmission is performed for high-speed communication such as moving images in a relatively wide frequency band, and low speed such as voice in a relatively narrow frequency band. Wireless transmission for performing proper communication is performed. Furthermore, in order to efficiently perform high-speed communication, there are some that use a narrow frequency band to notify control data for high-speed communication (see, for example, Patent Document 1).

  Furthermore, there is a mobile communication system having a service form that makes use of each feature by applying each to different systems, for example, PHS and MMAC (Multimedia mobile Access Communication) (see, for example, Patent Document 2).

  In addition, when performing handover by site selection, the mobile communication terminal periodically observes reception characteristics of radio signals transmitted from a plurality of base stations, and requests for transmission of information signals to the base station determined to be the best, that is, Send a handover request. The base station that has received this transmits an information signal to the mobile communication terminal, thereby realizing a handover that follows the radio propagation path fluctuation. That is, a control method is disclosed in which a mobile communication terminal determines a base station that transmits an information signal (see, for example, Non-Patent Document 1).

  Further, the handover control method in which the mobile communication terminal notifies the observed reception characteristics to the base station control apparatus via the base station, and the base station control apparatus selects the base station that transmits the information signal to the mobile communication terminal. There is also. That is, this is a control method in which the base station control apparatus determines a base station that transmits an information signal (see, for example, Patent Document 3).

Further, the conventional radio resource control method has been studied for a mobile communication system in which radio transmission is performed in one frequency band.
JP-A-9-200825, pages 13 and 15 JP 2000-316178 JP, page 6, Fig. 1 JP-A-8-154269, pages 5, 8 3GPP Technical Specification TR25.848v4.0.0 (2001-03) chap.6

  In the conventional technology described above, in a conventional mobile communication system in which a plurality of frequency bands are applied to different systems (PHS and MMAC), in order to receive an information signal from each system, a control signal (information signal) is sent to each system. Destination, information signal format, and control data such as power control) are required. As a result, overhead occurs in each system, which causes a reduction in communication efficiency.

  In general, the reliability of control signals must be emphasized. This is because, for example, when an error occurs in the destination of the information signal, reception of the corresponding information signal is also erroneous, resulting in a decrease in system throughput. In order to prevent this, reliability is ensured by using a modulation system that is low speed but excellent in error tolerance or adding redundancy to the control signal. In other words, it is necessary to ensure the reliability of the control signal at the expense of the transmission speed, which causes the above-described overhead.

  In addition, when a mobile communication terminal selects a base station that transmits an information signal and transmits a transmission request for an information signal to the base station, the mobile communication terminal transmits another request before the mobile communication terminal. A radio channel is allocated to the mobile communication terminal, and the throughput of the mobile communication terminal is reduced. In addition, information signal transmission requests may be concentrated on a single base station, which may reduce the utilization efficiency of radio resources.

  In addition, conventionally, control and handover control for reducing interference between base stations was performed by communication between base stations and communication between a base station and a base station control device that is above it, causing a control delay. .

  As is well known, further speeding-up is desired for future mobile communication systems. This clearly makes the cell range formed by one base station narrower.

  Thus, while high-speed wireless communication is required, the conventional mobile communication system reduces control delay required for control of channel allocation to each terminal, handover, etc. applicable to a high-speed mobile communication system. There was no effective technique for. In addition, there has been no effective method for efficiently allocating radio resources to each terminal while considering interference.

  Therefore, the present invention has been made in view of the above problems, and provides a mobile communication system capable of reducing a control delay between a terminal and a base station and performing high-speed wireless communication.

  (1) The present invention relates to one of the first radio channel groups in the first frequency band and the second radio channel group in the second frequency band that is wider than the first frequency band. Wireless communication is performed using a plurality of terminals that perform wireless communication using one, a plurality of broadband base stations that transmit information signals using the second wireless channel group, and the first wireless channel group In addition, in a mobile communication system including a narrowband base station that communicates with the plurality of broadband base stations, one of the first wireless channel groups is preliminarily set for each of the second wireless channel groups. It is characterized by being associated.

  A frequency band (first frequency band) that is different from a wideband frequency band (second frequency band) for transmitting and receiving information signals, for transmitting and receiving control signals necessary for transmitting and receiving information signals between broadband base stations and terminals By using this, all wide frequency bands can be used for transmission of information signals. The first radio channel group for performing communication between the terminal and the narrowband base station in the first frequency band includes a first radio channel group for transmitting information signals in the second frequency band from a plurality of wideband base stations. Since one of the two radio channel groups is associated with each other in advance (since a wideband channel and a narrowband channel can be assigned to a terminal at the same time), a request for an information signal occurs A broadband-side channel can be reliably secured without a control delay until the information signal is transmitted to the terminal.

  (2) The narrowband base station associates, in advance, an assigning unit that assigns one of the second radio channel groups to a plurality of terminals, and each of the assigned second radio channels. And transmitting means for transmitting a control signal including information necessary for receiving an information signal from a wideband base station using the first radio channel, wherein each terminal transmits the control signal. Is used to receive information data from the second radio channel assigned by the assigning means.

  Since the wideband channel and the narrowband channel are allocated to the terminal at the same time, it is possible to reduce the influence of overhead for securing the wideband channel.

  Control delay between terminals and base stations can be reduced and high-speed wireless communication can be performed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 shows a configuration example of a mobile communication system of the present invention.

  The mobile communication system of the present invention has a control-BTS (hereinafter referred to as C-BTS) 100 that is a base station (narrowband base station) that controls the mobile communication system as a main function, and a base station that performs data transmission as a main function ( Broadband base stations) (for example, three in this case) Data-BTS (hereinafter referred to as D-BTS) 101a to 101c and a plurality (for example, four in this case) of mobile communication terminals (hereinafter simply referred to as terminals) 102a to 102d. The C-BTS 100 forms a communication area (cell) 103, and the D-BTSs 101a to 101c form communication areas (cells) 104a to 104c, respectively.

  In the following description, when it is not necessary to distinguish between Data-BTS (hereinafter referred to as D-BTS) 101a to 101c, these are collectively referred to as D-BTS 101, and it is not necessary to distinguish between communication areas 104a to 104c. In this case, these are collectively referred to as a communication area 104. Further, when it is not necessary to distinguish the terminals 102a to 102d, they are collectively referred to as the terminal 102.

  The C-BTS 100 transmits and receives signals to and from the terminal 102 through the radio channels 105 and 106 in the first frequency band. The D-BTS 101 transmits a signal to the terminal 102 through the radio channel 107 in the second frequency band that is different from the first frequency band.

  The C-BTS 100 and D-BTS 101 are connected by a communication line 108. Here, the communication line 108 may be a wired line or a wireless line, but is preferably a wired line from the viewpoint of reliability. Further, the C-BTS 100 is connected to a network (a network unique to a communication carrier or a backbone network such as the Internet) 110 via a communication line 109.

  The C-BTS 100 transmits a control signal to the terminal 102 via the radio channel 105 and transmits a similar control signal to the D-BTS 101 via the communication line 108. Further, the terminal 102 transmits a signal to the C-BTS 100 using the radio channel 106. The D-BTS 101 transmits an information signal to the terminal 102 in accordance with the control signal transmitted from the C-BTS 100.

  The control signal includes the destination of the information signal transmitted from the D-BTS 101 (the identifier USERID of the terminal that should receive the information signal), data related to the format of the demodulation method / decoding method of the information signal, other power control, etc. Including control data used for. Further, the terminal 102 receives the control signal transmitted from the C-BTS 100, and receives the information signal transmitted from the D-BTS 101 according to the content of the control signal.

  Usually, since transmission of an information signal requires high-speed transmission, a broadband wireless channel is required. Therefore, the second frequency band is wider than the first frequency band. As a result, considering the characteristics of the radio signal, the communication area (cell) 103 formed by the C-BTS 100 is larger than the communication area (cell) 104 formed by the D-BTS 101. As shown in FIG. 1, a plurality of communication areas 104 (formed by the D-BTS 101) are included in the communication area 103 formed by the C-BTS 100.

  FIG. 2 shows a first modification of the mobile communication system shown in FIG. Here, only a different part from FIG. 1 is demonstrated. That is, in FIG. 1, the radio signal transmitted from the terminal 102 via the uplink radio channel 106 is received by the C-BTS 100, but in FIG. 2, it is transmitted from the terminal 102 via the uplink radio channel 106. The radio signal is (also) received by the D-BTS 101. When the D-BTS 101 receives a signal from the terminal 102, the D-BTS 101 transmits the signal to the C-BTS 100 via the communication line 108. That is, in FIG. 2, a signal from the terminal 102 to the C-BTS 100 is relayed by the D-BTS 201 and reaches the C-BTS 100.

  The configuration example illustrated in FIG. 2 has an effect of reducing the transmission power of the terminal 102 as compared to the configuration example illustrated in FIG.

(DL and UL between C-BTS and D-BTS and terminal)
Next, a channel configuration in the mobile communication system of FIG. 1 will be described with reference to FIGS.

  The bandwidth of the first frequency band 301 used for bidirectional communication between the C-BTS 100 and the terminal 102 is Wc, and the bandwidth of the second frequency band 302 used for downlink communication from the D-BTS 101 to the terminal is Assuming Wd, there is a relationship of Wc << Wd as described above. Here, the first frequency band 301 is used for transmission of a control signal from the C-BTS 100 to the terminal 102 and transmission of a radio signal including both the control signal and the information signal from the terminal 102 to the C-BTS 100. The second frequency band 302 is used for transmission of information signals from the D-BTS 101 to the terminal 102.

  In the first configuration example of FIG. 3, an FDD (Frequency Division Duplex) method is applied to the first frequency band 301. That is, the first frequency band 301 is divided into two frequency bands, which are used for downlink (DL) transmission from the C-BTS 100 to the terminal 102 and uplink (UL) transmission from the terminal 102 to the C-BTS 100, respectively. To do. All the terminals 102 existing in the communication area 103 can use the radio channel in the first frequency band 301.

  In the second configuration example of FIG. 4, a TDD (Time Division Duplex) method is applied to the first frequency band 301. That is, the first frequency band 301 is divided in time and used for DL and UL wireless transmission. Also in this case, all the terminals 102 existing in the communication area 103 can use the radio channel in the first frequency band 301.

  In the third configuration example of FIG. 5, the FDD scheme is applied to the first frequency band 301. Furthermore, the frequency band applied to DL is further divided into a plurality of frequency bands, and assigned to a plurality of D-BTSs 101, respectively. That is, for each terminal 102 in each communication area 104, one of the plurality of frequency bands corresponding to the D-BTS 101 to which the terminal belongs is assigned to the downlink, and the control signal is transmitted. . In this case, with respect to UL, all the terminals 102 existing in the communication area 103 can use the radio channel in the first frequency band 301.

  In the fourth configuration example of FIG. 6, the FDD scheme is applied to the first frequency band 301. Furthermore, the frequency band applied to DL and UL is each divided | segmented into plurality. Each of the plurality of D-BTSs 101 is assigned one of a plurality of DL frequency bands and one of a plurality of UL frequency bands. That is, the C-BTS 100 transmits a control signal to each terminal 102 in each communication area 104 using one of a plurality of downlink frequency bands. Each terminal 102 transmits a signal to the C-BTS 100 using one of a plurality of uplink frequency bands.

(DL between C-BTS and D-BTS and terminal)
Next, the DL radio channel transmitted from the C-BTS 100 and the D-BTS 101 to the terminal 102 in the mobile communication system of FIG. 1 will be described with reference to FIGS.

  7 and 8, the signal transmitted from the C-BTS 100 is divided at a predetermined time Tc. This block of time Tc is referred to herein as a time slot (TS). A signal transmitted from the D-BTS 101 is divided at a predetermined time Td. Here, this block of time Td is referred to as a frame (FR). One frame always has one time slot corresponding to the frame. That is, each downlink radio channel 107 (frames FR-0, FR-1,...) Is associated in advance with each downlink radio channel 105 (time slots TS-0, TS-1,...) ( Assigned). In other words, each downlink radio channel 105 (time slots TS-0, TS-1,...) Is associated with each downlink radio channel 107 (frames FR-0, FR-1,...) In advance. (Assigned).

  Information indicating the correspondence between each downlink radio channel 105 (time slots TS-0, TS-1,...) And each downlink radio channel 107 (frames FR-0, FR-1,...) Is stored in advance in the C-BTS 100. Are stored in the management table 503a (see FIG. 12).

  The frame length Td is determined by, for example, an information signal interleaving cycle. The time slot length Tc needs to satisfy the relationship of Tc <= Td in order to reliably notify the terminal of a control signal for transmitting a frame corresponding to the time slot.

  In FIG. 7, there is a time offset (T_offset) between the radio channel 105 transmitted from the C-BTS 100 and the radio channel 107 allocated to the radio channel 105 transmitted from the D-BTS 101, and T_offset < The case of Tc is shown.

  In FIG. 8, there is a time offset (T_offset) between the radio channel 105 transmitted from the C-BTS 100 and the radio channel 107 allocated to the radio channel 105 transmitted from the D-BTS 100, and Tc < The case where T_offset <2Tc is shown.

  Considering that a control signal including information such as a destination of an information signal transmitted from the C-BTS 100 through the wireless channel 107 is notified to the terminal 102 through the wireless channel 105, the terminal 102 is notified through the wireless channel 105. If the destination of the received information signal does not indicate its own terminal, it is possible not to receive the associated radio channel 107, so the case shown in FIG. it is conceivable that.

(Control signal transmitted from C-BTS to terminal)
Next, information included in the control signal transmitted by the C-BTS 100 in the mobile communication system of FIG. 1 will be described with reference to FIGS.

  FIG. 9 shows a first example of the control signal. The control signal transmitted from the C-BTS 100 to the terminal 102 includes a D-BTSID for identifying the D-BTS 101, and a USERID for identifying the terminal 102 existing in the communication area 104 formed by the D-BTS. In addition, MCSID for identifying a modulation scheme and a coding scheme applied to an information signal corresponding to the control signal, control data used for power control, and the like are included. The terminal 102 that has received a control signal including information as shown in FIG. 9 determines whether or not an information signal addressed to the terminal 102 exists, and if so, from which D-BTS 101 the information signal is transmitted. It is possible to receive the information signal by the corresponding modulation format or the like.

  FIG. 10 shows a second example of the control signal. The control signal transmitted from the C-BTS 100 to the terminal 102 is applied to the USERID for identifying the terminal 102 existing in the communication area 104 formed by the D-BTS 101 and the information signal corresponding to the control signal. MCSID for identifying the modulation method and coding method being used, control data used for power control, and the like are included. When the C-BTS 100 transmits a control signal including information as shown in FIG. 10, the terminal 102 needs to recognize the D-BTS 101 (identifier) to which the terminal 102 belongs. There is. In this case, there is an effect that the amount of control signal transmitted by the C-BTS 100 can be reduced.

  FIG. 11 shows a third example of the control signal. The third example is applied when the DL frequency band is divided into a plurality of frequency bands and allocated to the plurality of D-BTSs 101 as shown in FIGS. In this case, a set of control signals is transmitted from the C-BTS 100 to the terminal 102 in each of a plurality of DL frequency bands. Each control signal identifies the USERID for identifying the terminal 102 existing in the communication area 104 formed by the D-BTS 101, and the modulation scheme and coding scheme applied to the information signal corresponding to the control signal. Control data used for MCSID, power control, and the like.

  When the C-BTS 100 transmits a control signal including information as illustrated in FIG. 11, the terminal 102 does not necessarily need to recognize the D-BTS 101 to which the own device belongs. For example, the terminal 102 receives control signals in all frequency bands in which the control signal is transmitted. If there is a control signal including the USERID of the own device in the received control signals of all frequency bands, the terminal 102 recognizes that an information signal addressed to the own device exists. Further, from the frequency of the control signal including the USERID of the own device, the terminal 102 can determine which D-BTS 101 transmits the information signal. And it becomes possible to acquire MCSID from the said control signal, and to receive an information signal from D-BTS101 which transmits an information signal to an own apparatus. In addition, when the terminal 102 recognizes the D-BTS 101 to which the terminal 102 belongs, it is only necessary to receive the control signal in the frequency band assigned to the D-BTS 101, and the reception processing of the terminal 102 is simplified. be able to.

(Configuration example of C-BTS 100)
FIG. 12 shows a configuration example of the C-BTS 100, which is roughly composed of a wireless communication processing unit 501, a control unit 502, and a storage unit 503.

  The radio communication processing unit 501 transmits a radio signal transmitted from each terminal in the uplink of the first frequency band 301 and a transmission system for transmitting radio signals to each terminal in the downlink of the first frequency band 301. It has a receiving system for receiving. In the transmission system, first, the transmission data generation unit 501b generates transmission data in a predetermined format for transmitting a signal (control signal) addressed to each terminal via the narrowband downlink radio channel 105, and performs encoding processing. Output to the unit 501c. The transmission data is encoded by the encoding processing unit 501c, further modulated by the modulation processing unit 501d, converted from a digital signal to an analog signal, frequency converted, and the like by the wireless processing unit 501a. Sent through. A radio signal transmitted from each terminal via the radio channel 106 is received by the radio processing unit 501a via an antenna, and frequency conversion or conversion from an analog signal to a digital signal is performed. The received signal is demodulated by the demodulation processing unit 501e and further decoded by the decoding processing unit 501f. The reception data separation unit 501g separates and extracts the decoded reception signal as necessary.

  The storage unit 503 includes a management table 503a for managing terminals existing in the communication area of the D-BTS 101, a handover management table 503b used for handover control, A priority table 503c, a cell management table 503d, and other various data for storing the priority are stored.

  The transmission data generation unit 501a refers to the management table 503a and outputs the control signals addressed to each terminal, for example, in the order of the time slots in which the control signals are to be transmitted, to the encoding processing unit 501c. The reception data separation unit 501g refers to the management table 503a and separates and extracts the reception signal decoded from each time slot as necessary.

  The control unit 502 includes a terminal control unit 502a, an external network (NW) control unit 502b, a broadband base station (D-BTS) control unit 502c, a standby control unit 502d, and a radio resource control unit 502e.

  The terminal control unit 502a is for communicating with each terminal through the narrowband uplink / downlink radio channels 106 and 105. For example, a control signal addressed to each terminal 102 is generated and output to the transmission data generation unit 501b. In addition, it receives a signal output from the received data separator 501g.

  The external network (NW) control unit 502 b is for performing communication with the external network 110 via the communication line 109.

  The broadband base station control unit 502 c is for communicating with each D-BTS 101 under the C-BTS 100 via the communication line 108.

  The standby control unit 502 d is for performing control processing when the terminal 102 is on standby via the D-BTS 101. Control processing during standby will be described in a fifth embodiment to be described later.

  The radio resource control unit 502e assigns radio resources such as the wideband downlink radio channel 107 and the narrowband downlink radio channel 106 to each terminal, and records the result in the management table 503a. The control processing in the radio resource control unit 502e will be described in second to fourth embodiments described later.

(Configuration example of D-BTS 101)
FIG. 13 shows an example of the configuration of the D-BTS 101, which is roughly composed of a wireless communication processing unit 511, a control unit 512, and a storage unit 513.

  The non-communication communication processing unit 511 transmits a radio signal to each terminal on the downlink of the second frequency band 302 and a radio signal transmitted from each terminal on the uplink of the first frequency band 301 ( A receiving system for receiving a broadcast signal including a terminal identifier (see the fifth embodiment).

  In the transmission system, first, in the transmission data generation unit 511b, transmission data in a predetermined format for transmitting a signal (information signal) addressed to each terminal 102 via each broadband downlink radio channel 107 is generated and encoded. The data is output to the processing unit 511c. The transmission data is encoded by the encoding processing unit 511c, modulated by the modulation processing unit 511d, converted from a digital signal to an analog signal, frequency converted, and the like by the wireless processing unit 511a, and then the antenna. Sent through. A radio signal transmitted from the terminal 102 via the radio channel 106 is received by the radio processing unit 511a via the antenna, and frequency conversion and conversion from an analog signal to a digital signal are performed. The received signal is demodulated by the demodulation processing unit 511e and further decoded by the decoding processing unit 511f. The reception data separation unit 511g separates and extracts the decoded reception signal as necessary.

  The control unit 512 includes a terminal control unit 512a, a narrowband base station (C-BTS) control unit 512b, and a standby control unit 512c.

  The terminal control unit 512a is mainly for transmitting an information signal to the terminal 102 via the broadband downlink radio channel 107. That is, an information signal addressed to the terminal 102 is generated and output to the transmission data generating unit 511b. Further, the measurement value of the reception characteristic of the broadcast signal transmitted from the terminal via the narrowband uplink radio channel 106 is temporarily stored in the reception characteristic table 513a.

  The narrowband base station control unit 512b is for communicating with the C-BTS 100 via the communication line 108.

  The standby control unit 512c is for performing a control process during standby of the terminal 102 via the D-BTS 101. Control processing during standby will be described in a fifth embodiment to be described later.

  The storage unit 513 stores the reception characteristic table 513a and other various data.

(Configuration example of terminal 102)
FIG. 14 shows a configuration example of the terminal 102, which is roughly composed of a wireless communication processing unit 521, a control unit 522, and a storage unit 523.

  The non-communication communication processing unit 521 transmits a radio signal to the C-BTS 100 and the D-BTS 101 in the uplink of the first frequency band 301, and the C-BTS 100 in the downlink of the first frequency band 301. A first reception system for receiving the transmitted radio signal and a second reception system for receiving the radio signal transmitted from the D-BTS 101 in the downlink of the second frequency band 302 are provided.

  In the transmission system, first, in the transmission data generation unit 521b, transmission data in a predetermined format for transmitting a signal addressed to the C-BTS 100 or the D-BTS 101 via the narrowband uplink radio channel 106 is generated and encoded. The data is output to the processing unit 521c. The transmission data is encoded by the encoding processing unit 521c, modulated by the modulation processing unit 521d, converted from a digital signal to an analog signal, frequency converted, and the like by the wireless processing unit 521a, and then the antenna. Sent through.

  A radio signal transmitted from the C-BTS 100 on a narrow-band downlink is received by the radio processing unit 521a via an antenna, and frequency conversion and conversion from an analog signal to a digital signal are performed. The received signal is demodulated by the demodulation processing unit 521e, and further decoded by the decoding processing unit 521f. The reception data separation unit 521g separates and extracts the decoded reception signal as necessary.

  A radio signal transmitted from the D-BTS 101 via a broadband downlink is received by the radio processing unit 521a via an antenna, and frequency conversion and conversion from an analog signal to a digital signal are performed. The received signal is demodulated by the demodulation processing unit 521h and further decoded by the decoding processing unit 521i. The reception data separation unit 521j separates and extracts the decoded reception signal as necessary.

  The control unit 512 includes a narrowband base station (C-BTS) control unit 522a, a wideband base station (D-BTS) control unit 522b, a radio resource control unit 522c, and a standby control unit 522d.

  The narrowband base station controller 522a is for communicating with the C-BTS 100 via narrowband uplink / downlink radio channels 106 and 1058. Each signal separated by the reception data separation unit 521g is output to the narrowband base station control unit 522a. In addition, a signal to be transmitted to the C-BTS 100 or the D-BTS 101 is generated and output to the transmission data generation unit 521b.

  The broadband base station controller 522b is for receiving an information signal via the D-BTS 101 and the broadband downlink radio channel 107. Each signal separated by the reception data separation unit 521j is passed to the broadband base station control unit 522b or stored in the storage unit 523 under the control of the broadband base station control unit 522b.

  The radio resource control unit 522c performs handover control described in the third embodiment.

  The standby control unit 522d is for performing control processing during standby of the terminal 102 via the D-BTS 101. Control processing during standby will be described in a fifth embodiment to be described later.

  The storage unit 513 stores a management table 523a that stores resources allocated to the terminal 102, a reception characteristic table 523b that stores reception characteristics of signals arriving from the D-BTS 101 around the terminal 102, and other various data. Is done.

  When the terminal 102 is on standby, the terminal 102 transmits a notification signal at a predetermined cycle, whereby the C-BTS 100 assigns a radio channel 107 (D-BTS 101) for transmitting an information signal to the terminal 102. (Refer to the fifth embodiment). The C-BTS 100 transmits a control signal or the like to the terminal using the narrow band downlink radio channel 105 previously associated with the broadband downlink radio channel (D-BTS 101) allocated to the terminal.

(Operation of terminal 102)
FIG. 15 is a flowchart for explaining the processing operation of the terminal 102 in the mobile communication system of FIG.

  When the terminal 102 starts communication, the terminal 102 receives a downlink signal of the first frequency band 301 having a narrow band through the radio processing unit 421a, the modulation processing unit 521e, the decoding processing unit 521f, and the reception data separation unit 521g. Each control signal separated from the reception signal by the reception data separation unit 521g is passed to the narrowband base station control unit 522a. The narrowband base station control unit 522a checks whether the received control signal includes a control signal (including the identifier USERID of the terminal 102) addressed to itself. In the case of a control signal addressed to the own apparatus, the time slot position where the control signal is inserted in the received signal is stored in the management table 523a. This time slot is a narrowband downlink radio channel 105 assigned to the terminal 102 for transmission of a control signal by the C-BTS 100.

  Thereafter, the terminal 102 receives a control signal addressed to itself from the wireless channel 105 according to a predetermined cycle (steps S1 and S2). The period in this case depends on the notification period of the control signal, that is, the time slot length Tc, and the shortest period is the time slot length Tc.

  The terminal 102 that has received the control signal confirms in the narrowband base station control unit 522a whether the control signal includes information related to transmission of the information signal addressed to itself (step S3). When the control signal includes information related to transmission of the information signal addressed to its own device, information notified by the control signal (information related to the format such as USERID, D-BTSID, and demodulation method / decoding method of the information signal) (MCSID) etc.), the information signal transmitted from the D-BTS 101 is received (step S4). That is, under the control of the broadband base station control unit 522b, the D-BTSID notified by the control signal (or the terminal 102 should receive the information signal) from the D-BTS 101 via the broadband downlink radio channel 107 The transmitted information signal is received through the antenna, the wireless processing unit 521a, the demodulation processing unit 521h, and the reception data separation unit 521j. The information signal addressed to the own device is passed to the broadband base station control unit 522b or stored in the storage unit 523.

  When the control signal does not include information related to transmission of the information signal addressed to the own device, the process returns to step S1 and waits again until a predetermined period elapses. While the communication with the C-BTS 100 is continued, the terminal 102 repeatedly performs the operations of Step S1 to Step S4 (Step S5).

(DL between C-BTS and D-BTS and terminal)
Next, another example of a DL channel configuration transmitted from the C-BTS 100 and the D-BTS 101 to the terminal 102 will be described with reference to FIG. Here, a different part from FIG. 7, FIG. 8 is demonstrated. That is, FIG. 16 is different from FIGS. 7 and 8 in that each time slot of time length Tc is further divided into a plurality of blocks. In FIG. 16, each time slot of time length Tc is further divided into a plurality of (for example, n in this case) blocks, and the block length is Tb. Further, each block is assigned in advance to n D-BTSs 101 (for example, D-BTS1, D-BTS2, D-BTS3,..., D-BTSn in this case). -A control signal corresponding to the BTS 101 is transmitted.

  As a result, when the terminal 102 recognizes the D-BTS 101 to which the own device belongs, it is only necessary to receive the control signal of the block corresponding to the D-BTS 101 to which the own device belongs, and the reception processing of the terminal 102 is simplified. There is an effect to be. Also, unused blocks can be used for other purposes, and more efficient radio resource allocation can be performed.

  Next, still another example of a DL radio channel configuration transmitted from the C-BTS 100 and the D-BTS 101 to the terminal 102 in the mobile communication system of FIG. 1 will be described with reference to FIG. Here, a different part from FIG. 7, FIG. 8 is demonstrated. That is, FIG. 17 is different from FIGS. 7 and 8 in that a plurality of control signals assigned in advance to each of the plurality of D-BTSs 101 are multiplexed in each time slot of the time length Tc. In FIG. 17, in each time slot of time length Tc, each D-BTS 101 is assigned to each D-BTS 101 using a plurality of codes (for example, spreading codes) pre-assigned to each of a plurality (eg, n in this case) of D-BTSs 101. Corresponding control signals are code-spread and multiplexed.

  Thereby, when the terminal 102 recognizes the D-BTS 101 to which the own device belongs, only the control signal corresponding to the D-BTS 101 using the spreading code corresponding to the corresponding D-BTS 101 to which the terminal 102 belongs is used. The reception processing of the terminal 102 can be simplified. In addition, an unused spreading code can be used for multiplexing signals other than the control signal, and more efficient radio resource allocation can be performed.

  According to the first embodiment, by transmitting and receiving a control signal through a narrow band radio channel, it is possible to use all the wide band radio channels for transmission of information signals. This means that the influence of overhead due to the application of a wireless channel capable of broadband transmission, that is, high-speed transmission, to control signal transmission is reduced.

  In addition, for each frame on the wideband radio channel 107, a time slot of each control signal on the narrowband downlink radio channel 105 (a divided time slot when a plurality of control signals are time-division multiplexed, a plurality of controls) When a signal is code division multiplexed, a spread code is associated in advance (that is, a radio channel of a control signal including information necessary for transmitting an information signal from a base station to a terminal is secured in advance. It is possible to prevent a communication request from being rejected or waiting without acquiring a radio channel for transmitting a control signal. In addition, by reliably using a radio channel having a wide frequency band capable of high-speed transmission, it is possible to prevent a decrease in communication efficiency as a result.

  Note that the narrowband uplink radio channel 106 and the narrowband downlink radio channel 105 are the uplink / downlink time slots, frequencies, and codes (spreading codes) of the first peripheral frequency band 301 allocated to the terminal 102. At least one of the following. The broadband downlink radio channel 107 is at least one of downlink time slots (frames), frequencies, and codes (spreading codes) in the second frequency band 302 allocated to the terminal 102. Thus, the channel is at least one of a frequency, a time slot (frame), and a code that can be used when each terminal communicates with the C-BTS 100 and the D-BTS 101.

  Hereinafter, for simplicity of explanation, one downlink radio channel 107 corresponds to one D-BTS 101, and the C-BTS 100 assigns a wideband downlink radio channel 107 by assigning the D-BTS 101 to each terminal 102. Shall. Actually, the downlink radio channel 107 corresponding to each D-BTS 101 can accommodate a plurality of user channels. Each terminal 102 is assigned to each user channel. The C-BTS 100 assigns a D-BTS 101 having a vacant user channel to a terminal 102, and sends control information to the terminal 102 together with information indicating the vacant user channel and identification information of the D-BTS 101 assigned to the terminal 102. Send with.

(Second Embodiment)
In the second embodiment, an operation in the case where an information signal is transmitted using not only the wideband downlink radio channel 107 but also the narrowband downlink radio channel 105 in the mobile communication system of FIG. 1 will be described.

  FIG. 18 is a diagram for explaining the operation of the mobile communication system according to the second embodiment. In FIG. 18, the same parts as those in FIG. 1 are denoted by the same reference numerals, and only different parts will be described. That is, in FIG. 18, two D-BTSs 101 a and 101 c form communication areas 104 a and 104 c in the communication area 103 formed by the C-BTS 100, respectively, and three terminals 102 (102 a to 102 c) communicate with the communication area 103. The case where it exists in is shown.

  Here, the D-BTS ID of the D-BTS 101a is "ID1", the D-BTS ID of the D-BTS 101b is "ID2", the D-BTSID of the D-BTS 101c is "ID3", and the USERIDs of the terminals 102a, 102b, and 102c are respectively “A”, “B”, and “C”.

  In FIG. 18, the terminals 102b and 102c exist in the communication area 104c of the D-BTS 101c. The terminal 102c receives the information signal from the D-BTS 101c via the broadband wireless channel 107. On the other hand, no terminal exists in the communication area 104b of the other D-BTS 101a. Alternatively, even if a terminal (for example, the terminal 102a) exists in the communication area 104b, no information signal is transmitted to the terminal. That is, the downlink radio channel 105 of the C-BTS 100 assigned to the D-BTS 101a is not currently used. In such a case, consider a case where an information signal is transmitted to another terminal 102b other than the terminal 102c existing in the communication area 104c of the D-BTS 101c. In the second embodiment, in such a case, when the communication speed with the terminal 102b is low, an information signal is transmitted from the C-BTS 100 using the free resources of the narrowband radio channel 105.

  Since the wireless channel 105 has a narrower frequency band than the wireless channel 107, in this case, relatively low-speed communication such as voice communication is provided.

  FIG. 19 is a diagram for explaining a first usage method of the first frequency band 301 used for bidirectional communication between the C-BTS 100 and the terminal 102 in the mobile communication system according to the second embodiment. It is. Here, the FDD scheme is applied, and the first frequency band 301 is divided into two frequency bands. The downlink (DL) from the C-BTS 100 to the terminal 102 and the uplink (DL) from the terminal 102 to the C-BTS 100 ( UL) for wireless transmission. The frequency band applied to the DL is further divided into a plurality of (for example, three in this case) frequency bands 311 to 313 and assigned to different D-BTSs 101. Here, it is assumed that the frequency band 312 is assigned to the D-BTS 101a and the frequency band 313 is assigned to the D-BTS 101c in advance.

  At this time, as described above, even if there is no terminal in the communication area 104b of the D-BTS 101a, or even if a terminal (for example, the terminal 102a) exists in the communication area 104b, the information signal is transmitted to the terminal. Since no transmission is performed, the downlink radio channel 105 assigned to the D-BTS 101a, that is, the frequency band 312 is not currently used.

  In this state, when a relatively low-speed voice communication is to be started with a terminal 102b existing in a D-BTS 101c different from the D-BTS 101a, the D-BTS 101c is used using this empty frequency band 312. An information signal (in this case, an audio signal) is transmitted to the terminal 102b existing in the network.

  FIG. 20 is a diagram for explaining a second usage method of the first frequency band 301 used for bidirectional communication between the C-BTS 100 and the terminal 102 in the mobile communication system according to the second embodiment. It is. In FIG. 20, the FDD scheme is applied to divide the first frequency band 301 into two frequency bands, and the downlink (DL) from the C-BTS 100 to the terminal 102 and from the terminal 102 to the C-BTS 100, respectively. In the case of using for uplink (UL) wireless transmission, only the downlink is shown.

  A signal transmitted from the C-BTS 100 in the downlink is divided at a predetermined time Tc. That is, the time width of one time slot is Tc. Each time slot is further divided into a plurality of blocks B1 to Bn having a time width Tb. Each block is assigned to a plurality of different D-BTSs 101.

  For example, the block B2 is assigned to the D-BTS 101a, and the block B3 is assigned to the D-BTS 101c.

  At this time, as described above, even if there is no terminal in the communication area 104b of the D-BTS 101a, or even if a terminal (for example, the terminal 102a) exists in the communication area 104b, the information signal is transmitted to the terminal. Since the transmission is not performed, the block B2 allocated to the D-BTS 101a is not currently used.

  In this state, when a relatively low speed voice communication is to be started with the terminal 102b existing in the D-BTS 101c different from the D-BTS 101a, the empty block B2 is used in the D-BTS 101c. An information signal (in this case, an audio signal) is transmitted to the terminal 102b existing in the network.

  FIG. 21 is a diagram for explaining a third usage method of the first frequency band 301 used for bidirectional communication between the C-BTS 100 and the terminal 102 in the mobile communication system according to the second embodiment. It is. In FIG. 21, the FDD scheme is applied to divide the first frequency band 301 into two frequency bands, and the downlink (DL) from the C-BTS 100 to the terminal 102 and from the terminal 102 to the C-BTS 100, respectively. In the case of using for uplink (UL) wireless transmission, only the downlink is shown.

  A signal transmitted from the C-BTS 100 is divided at a predetermined time Tc. That is, the time width of one time slot is Tc. Further, in each time slot of the time length Tc, a plurality of codes (for example, spreading codes) assigned in advance to each of a plurality of (for example, n in this case) D-BTS 101 are used to correspond to each D-BTS 101. Control signals are multiplexed and transmitted.

  For example, among the plurality of spreading codes, the control signal spread by the first spreading code assigned to the D-BTS 101a is D2, and the control signal spread by the second spreading code assigned to the D-BTS 101c is D3. To do.

  At this time, as described above, even if there is no terminal in the communication area 104b of the D-BTS 101a, or even if a terminal (for example, the terminal 102a) exists in the communication area 104b, the information signal is transmitted to the terminal. Since the transmission is not performed, the first spreading code assigned to the D-BTS 101a is not currently used. Therefore, in the downlink, there is a free capacity (empty channel) corresponding to the control signal D2 spread using the first spreading code.

  In this state, when a relatively low speed voice communication is to be started with the terminal 102b existing in the D-BTS 101c different from the D-BTS 101a, this free capacity (empty channel) is used. An information signal (in this case, an audio signal) is transmitted to the terminal 102b existing in the D-BTS 101c.

  Next, the operation of the C-BTS 100 (radio resource control unit 502e) will be described with reference to FIG.

  When starting communication with the terminal 102, the radio resource control unit 502e of the C-BTS 100 refers to the management table 503a according to a predetermined cycle (step S11). The period in this case is preferably a control signal notification period, that is, an integral multiple of the time slot length Tc, n * Tc (n is an arbitrary integer).

  Here, the main part of the management table 503a to be referred to is shown in FIG. In the management table, the D-BTSID for identifying each D-BTS forming the communication area in the communication area 103 formed by the C-BTS 100, the number of terminals (USERNUM) belonging to the communication area 104 formed by the D-BTS 101, USERID for identifying each terminal and the communication speed (RATE) of wireless communication with the terminal are stored. The management table 503a is updated when wireless communication is started with the terminal or when wireless communication is ended.

  By referring to the management table 503a, the C-BTS 100 confirms whether there is an unused radio resource (step S12). In the management table shown in FIG. 23, since there is no terminal belonging to the D-BTS 101a whose D-BTSID is “ID1”, the radio channel assigned to the D-BTS 101a is free.

  As described above, when there is a radio resource that is not used, the management table 503a further checks whether or not there is a terminal performing low-speed radio communication (step S14). In FIG. 23, among the three terminals belonging to the D-BTS 101c with the D-BTSID “ID3”, the communication speed of the terminal 102b with the USERID “B” is “L”, and low-speed wireless communication is performed. Is shown. In this case, the radio channel assignment is changed so that the information signal transmitted from the D-BTS 101c with the D-BTSID “ID3” to the terminal 102b is transmitted from the C-BTS 100 (step S15). Then, the management table is updated as shown in FIG. 24 in accordance with the changed contents (step S16).

  FIG. 24 shows that the information signal is transmitted from the C-BTS 100 to the terminal 102b whose USERID is “B”. The ID for identifying the C-BTS 100 is “cont”, and this identifier is written in the “D-BTSID” column.

  The C-BTS 100 repeats the operations of Steps S11 to S16 while the use of radio resources continues (Step S17). Further, when there is no radio resource being used (step S13), and when there is no terminal performing low-speed radio communication (step S14), the radio channel assignment is not changed.

  In FIG. 22, when there is a radio resource (radio channel 105) that is not used for the downlink of the first frequency band 301, the empty space is used when the radio communication speed between the terminal and the base station is low. A case of using the wireless channel 105 of FIG. Not only in this case, an empty wireless channel 105 may be allocated according to the communication type between the terminal and its communication partner. The communication type is, for example, the type of the backbone network to which the terminal is connected via the base station (for example, the type of a circuit switching network or a packet switching network), the type of the communication partner of the terminal (for example, a telephone number or an IP address, etc.) And the type of QoS (Quality of Service) of communication between the terminal and the communication partner of the terminal (communication priority, allowable delay time, etc.).

  When the radio channel assignment is changed based on such communication type, a new “communication type” column is provided in the management table 503a (or the “RATE” column is replaced with a “communication type” column). And register the type of communication performed by each terminal. Then, in step S14 of FIG. 22, a terminal that performs communication belonging to the category of low-speed communication (for example, having a QoS with a low minimum guaranteed speed) is searched with reference to the “communication type” column of the management table.

  According to the second embodiment, by transmitting and receiving a control signal through a narrow band radio channel, it is possible to use all the wide band radio channels for transmission of information signals. This means that the influence of overhead due to the application of a wireless channel capable of broadband transmission, that is, high-speed transmission, to control signal transmission is reduced.

  Further, the narrow band downlink radio channel 105 (for example, a time slot when a plurality of control signals are time-division multiplexed) is associated with each wide band radio channel 107 in advance (that is, a base station). (A radio channel for a control signal including information necessary for transmitting an information signal from a terminal to a terminal is secured in advance), a radio channel for transmitting a control signal cannot be acquired, It is possible to prevent waiting. In addition, by reliably using the radio channel 107 having a wide frequency band capable of high-speed transmission, it is possible to prevent a decrease in communication efficiency as a result.

  Further, when high-speed transmission is not required for transmission of information signals to terminals, wireless resources can be made more efficient by transmitting information signals not using the wideband wireless channel 107 but using a narrow band free downlink radio channel 105. It can be used well and communication efficiency can be improved.

(Third embodiment)
It is well known that further higher speed is desired for mobile communication systems in the future. Accordingly, it is assumed that a higher frequency band and a wider band radio channel are applied to each D-BTS performing data transmission. This means that the communication area 104 formed by each D-BTS becomes narrower. When the communication area 104 becomes narrow, as shown in FIG. 25, the area where the plurality of communication areas 104 overlap increases. When the terminal 102 exists in a region where a plurality of communication areas overlap, the terminal 102 can communicate with the plurality of D-BTSs 101, and handover between D-BTSs increases.

  Therefore, in the third embodiment, a handover control method for the mobile communication system according to the first embodiment will be described.

  Here, the case where the narrow band first frequency band 301 and the wide band second frequency band 302 are used as shown in FIG. 3 or FIG. 4 will be described as an example.

  FIG. 26 is a diagram for explaining a handover state of the mobile communication system according to the first embodiment. In FIG. 26, the terminal 102a exists in an area 401 where two communication areas 104a and 104b formed by two D-BTSs 101a and 101b respectively overlap. In this case, the terminal 102a can receive information signals from the D-BTSs 101a and 101b via the broadband wireless channels 107a and 107b. Here, such a state is called a handover state.

  Next, a handover control procedure according to the third embodiment will be described with reference to FIG. Note that handover control by site selection is performed in consideration of radio resource utilization efficiency and the like.

  When the radio processing unit 521a or the demodulation processing unit 521h of the terminal 102a receives a radio signal transmitted from each D-BTS 101 existing in the vicinity thereof, the reception characteristics (for example, received signal strength indicator (RSSI)) are received. , At least one of a signal to interference ratio (SIR) and a propagation loss is measured. The measurement result is passed to the radio resource control unit 522c.

  The radio resource control unit 522c of the terminal 102a can perform radio communication with the D-BTS 101 that is the transmission source of the radio signal when the reception characteristics of the received radio signal are good (for example, RSSI is equal to or greater than a predetermined threshold). The identifier (D-BTSID) of the D-BTS 101 included in the received signal is stored. A handover state is assumed when the number of D-BTSs 101 capable of wireless communication reaches a predetermined value (for example, “2”). For example, as illustrated in FIG. 26, the terminal 102a detects the handover state because the reception characteristics of the radio signals transmitted from the D-BTSs 101a and 101b are good.

  When detecting the handover state (step S21), the radio resource control unit 522c of the terminal 102a transmits a handover request message to the C-BTS 100 using the narrowband uplink radio channel 106 (step S22). The handover request message includes an identifier of the D-BTS 101 capable of wireless communication. In the case of FIG. 26, identifiers (D-BTSIDs) of the D-BTSs 101a and 101b, that is, “ID1” and “ID2” are included.

  The radio resource control unit 502e of the C-BTS 100 that has received the handover request transmits either the narrowband downlink radio channel 105 or the D-BTS 101a or 101b having the identifier included in the handover request message in the case of FIG. A handover request response message is transmitted to the terminal 102a using the broadband downlink radio channel (the radio channel 107a or the radio channel 107b) (step S23).

  Through the negotiation in steps S22 to S23, the C-BTS 100 and the terminal 102a can reliably share the change in the handover state. Thereafter, the radio resource control unit 522c of the terminal 102a includes a handover control parameter such as a reception characteristic value measured for each D-BTS 101a and 101b in the handover state with the terminal 102a for each handover control period (HO_INT). The message is transmitted to the C-BTS 100 using the narrowband uplink radio channel 106 (step S24).

  The radio resource control unit 502e of the C-BTS 100, based on the handover control parameter notified from the terminal 102a and the availability of the wideband downlink radio channel 107 of the D-BTS 101a and 101b, every data transmission cycle (DT_INT), The D-BTS 101 that transmits the information signal to the terminal 102a and the signal format at that time are determined. The radio resource control unit 502e of the C-BTS 100 selects, for example, the D-BTS 101 having the best reception characteristics at the terminal 102a from among the D-BTSs 101 having the wideband free downlink radio channel 107.

  When the radio resource control unit 502e determines, for example, a base station that transmits an information signal to the terminal 102a as the D-BTS 101b and determines a signal format or the like when transmitting the information signal, the radio base station control unit 502c A control signal for notifying this is transmitted to the D-BTS 101b via the communication line 108 (step S26). The control signal includes an identifier of the D-BTS 101 that transmits and receives the information signal, an identifier of the terminal, information on a format such as a demodulation method and a decoding method of the information signal, and the like. The radio resource control unit 502e transmits the control signal including the same information to the terminal 102a from the terminal control unit 502a using the narrowband downlink radio channel 105 (step S27).

  In the D-BTS 101b, the narrowband base station control unit 512b receives the control signal. Then, the terminal control unit 512a of the D-BTS 101b transmits an information signal according to the information included in the control signal to the terminal 102a specified by the information included in the control signal (step S28). ). In addition, the terminal 102a that has received the control signal receives the information signal transmitted from the D-BTS 101b using the modulation scheme and decoding scheme specified by the control signal under the control of the broadband base control unit 522b. Receive (step S29).

  Note that a relationship of HO_INT> = DT_INT is established between the handover control cycle HO_INT and the data transmission cycle DT_INT.

  According to the handover control procedure as shown in FIG. 27, the terminal 102a has a wide band downlink radio channel 107 among a plurality of D-BTSs 101 in the handover state, and has good reception characteristics at the terminal 102a. -The information signal transmitted from the BTS 101 is received.

  Next, another example of the handover control procedure will be described with reference to FIG. In FIG. 28, the same parts as those in FIG. 27 are denoted by the same reference numerals, and only different parts will be described. That is, in FIG. 28, the radio resource control unit 522c of each terminal 102 can receive an information signal at each terminal 102 at each handover control period (HO_INT) (the reception characteristic is greater than or equal to a predetermined threshold). And a handover control parameter including a reception characteristic value measured for the D-BTS 101 is transmitted to the C-BTS 100 using the narrowband uplink radio channel 106 (step S24). ).

  The radio resource control unit 502e of the C-BTS 100 detects a handover state for each terminal from the handover control parameter transmitted from each terminal 102 (step S24 '). That is, whether or not each terminal is in the handover state is determined from the number of identifiers of the D-BTS 101 included in the handover control parameter transmitted from each terminal. After detecting the terminal that is in the handover state, the same processing operation as in steps S25 to S29 in FIG. 27 is performed.

  In the procedure shown in FIG. 27, the reliability is improved by negotiating the transition of the terminal 102 to the handover state. However, due to the time spent in the negotiation, it is not possible to immediately respond to the change to the handover state. On the contrary, in the procedure shown in FIG. 28, since the negotiation for the change to the handover state is not performed, it is possible to immediately cope with the change of the handover state. However, not negotiating leaves a problem with its reliability. Therefore, it is effective to appropriately combine these according to the movement status of the terminal 102, the service type received by the terminal 102, and the like.

  Next, the processing operation of the terminal 102 will be described with reference to the flowchart shown in FIG.

  When the communication is started, the radio processing unit 521a and the demodulation processing unit 521h of the terminal 102 measure reception characteristics of radio signals arriving from nearby D-BTSs in a predetermined cycle (steps S31 and S32). The measured reception characteristic is stored in the reception characteristic management table 523b of the storage unit 523 by the radio resource control unit 522c (step S33).

  FIG. 30 shows an example of the reception characteristic table 523b of the terminal 102. In FIG. 30, the reception characteristic table stores the identifier D-BTSID, reception characteristics, and the like for each D-BTS that is the transmission source of the radio signal arriving at the terminal 102. With regard to the reception characteristics on this reception characteristic table, the reception characteristic table may be updated with the measurement value every time it is measured, or the reception characteristic table is updated with an average value of the past measurement values. May be.

  Each time the handover control period elapses, the terminal 102 compares the reception characteristic value of each D-BTS on the reception characteristic table with a predetermined threshold value HO_Th (steps S34 and S35). Different threshold values are provided depending on the type of reception characteristic (for example, RSSI, SIR, propagation loss, etc.).

  The radio resource control unit 522c of the terminal 102 detects a D-BTS having a reception characteristic value exceeding the threshold value HO_Th, or has detected a D-BTS that has been a reception characteristic value exceeding HO_Th so far but is lower than HO_Th this time. If the number of D-BTS having a reception characteristic value exceeding the threshold value HO_Th exceeds a predetermined number (for example, “2”), it is determined that the handover state has changed (step S36), Is notified to the C-BTS 100 by a handover request message (step S37). In addition, the identifier of each D-BTS having a reception characteristic value exceeding the threshold HO_Th and the handover control parameter including the reception characteristic value of the D-BTS are notified to the C-BTS (step S38). The terminal 102 repeats steps S31 to S38 while continuing communication (step S39).

  Next, an example of a processing operation in which the radio resource control unit 522c of the terminal 102 dynamically changes the reception characteristic threshold value HO_Th will be described with reference to the flowchart illustrated in FIG.

  This threshold value changing process is executed, for example, between step S34 and step S35 in FIG. That is, every time the handover control period elapses, it is executed in the preceding stage of step S35 in FIG.

  When the handover control period elapses (step S34), the radio resource control unit 522c exists at a position where it can communicate with the terminal 102, and the communication state of the information signal transmitted from the D-BTS currently communicating with the terminal 102 (Step S41). The communication state is represented by parameter values such as throughput, error rate, number of information signal allocations, and the like. The communication state is measured by the decoding processing unit 521i, the broadband base station control unit 522a, and the like.

  If it is determined that the communication state is good (for example, the error rate is less than a predetermined threshold value), the threshold value HO_Th is increased by a predetermined value (step S43). Thereafter, the process proceeds to step S35 of FIG. Conversely, if it is determined that the communication state is bad, the threshold value HO_Th is decreased by a predetermined value (step S44). Thereafter, the process proceeds to step S35 of FIG.

  According to the processing operation as shown in FIG. 31, when the communication state between the terminal 102 and the D-BTS 101 that is currently communicating is good (for example, when the terminal 102 is not moving), The probability of maintaining the communication with the D-BTS that is currently transmitting the information signal is increased. Conversely, when the communication state is poor (for example, when the terminal 102 is moving), the threshold value HO_Th is lowered, and the opportunity for executing the handover is expanded. In this way, the terminal 102 is changed by changing the threshold value HO_Th, which serves as a measure for improving and deteriorating the reception characteristics, based on whether the communication state between the terminal 102 and the D-BTS 101 communicating with the terminal 102 is good or bad. Can always communicate with the D-BTS 101 in a good communication state.

  Next, another example of another change processing operation of the threshold value HO_Th in the radio resource control unit 522c of the terminal 102 will be described with reference to the flowchart shown in FIG.

  This threshold value changing process is executed, for example, between step S34 and step S35 in FIG. That is, every time the handover control period elapses, it is executed in the preceding stage of step S35 in FIG.

  When the handover control period elapses (step S34), the radio resource control unit 522c exists at a position where it can communicate with the terminal 102, and the communication state of the information signal transmitted from the D-BTS currently communicating with the terminal 102 (Step S41). The communication state is represented by parameter values such as throughput, error rate, number of information signal allocations, and the like.

  Here, instead of classifying the communication state into two, good and bad, the two thresholds CS_Th1 and CS_Th2 are used to classify the communication state into, for example, one of upper, middle, and lower.

Here, for simplicity of explanation, CS_Th1> CS_Th2.

  First, the communication state parameter is compared with the first threshold value CS_Th1 to check whether or not the communication state is “up” (step S51). When the communication state is larger than CS_Th1, the threshold value HO_Th is set to HO_Th1 (step S53). When the communication state is equal to or less than CS_Th1, the communication state parameter is further compared with the second threshold value CS_Th2 to check whether the communication state is “medium” (step S52). When the communication state is larger than CS_Th2, the threshold value HO_Th is set to HO_Th2 (step S54). When the communication state is CS_Th2 or less, the threshold value HO_Th is set to HO_Th3 (step S55).

  Here, for simplicity of explanation, HO_Th1> HO_Th2> HO_Th3.

  According to the processing operation as shown in FIG. 32, in the terminal 102, when the communication state with the D-BTS 101 that is currently communicating is good, the D-BTS that is currently transmitting the information signal. The probability of maintaining the communication with is increased. Conversely, when the communication state is poor, the threshold value HO_Th is lowered, and the opportunity for executing the handover is expanded. In this way, the terminal 102 is changed by changing the threshold value HO_Th, which serves as a measure for improving and deteriorating the reception characteristics, based on whether the communication state between the terminal 102 and the D-BTS 101 communicating with the terminal 102 is good or bad. Can always communicate with the D-BTS 101 in a good communication state.

  In FIG. 32, two threshold values CS_Th1 and CS_Th1 are used. However, the present invention is not limited to this, and three or more threshold values may be used. Accordingly, although three types of threshold values for reception characteristics are used in FIG. 32, three or more types of threshold values for reception characteristics may be provided.

  Next, the processing operation of the C-BTS 100 will be described with reference to the flowchart shown in FIG. FIG. 33 shows a processing operation when a handover control parameter is transmitted from the terminal 102.

  Here, for the sake of simplicity of explanation, the case where the terminal 102 measures the SIR as the reception characteristic of the signal transmitted from the D-BTS 101 as the reception characteristic will be described as an example.

  Every time the handover control parameter is notified from the terminal 102 (step S61), the terminal control unit 502a of the C-BTS 100 updates the handover management table 503b of the storage unit 503 based on the content (step S62).

  FIG. 34 shows an example of the handover management table 503b of the C-BTS 100. This management table 503b includes an identifier D-BTSID of each D-BTS under the umbrella of the C-BTS 100, and a USERID that identifies terminals belonging to each D-BTS (can receive signals coming from the D-BTS). The handover control parameter (for example, SIR here) transmitted from the terminal is stored. For the handover control parameter notified from the terminal 102, the management table 503a may be updated with the notified parameter value, or the update table 503b may be updated with the average value in consideration of the past notification result. Also good.

  Thereafter, the radio resource control unit 502e of the C-BTS 100 refers to the changed management table and changes the allocation of terminals to each D-BTS (step S63). Regarding the change of allocation, the C-BTS 100 is determined in consideration of the number of terminals belonging to each D-BTS, the handover control parameter of each terminal, the priority of each terminal, and the like. The processes in steps S61 to S63 are continued until all communications are completed (step S64).

  Here, the operation of assigning terminals to each D-BTS in step S63 will be described with reference to FIGS. Here, three allocation methods as shown in (1) to (3) below will be described.

  FIG. 35 is a table 503c indicating the priority of each terminal, and this table may be stored in the C-BTS 100 in advance. A value “1” means the highest priority.

  The priority is, for example, the type of the backbone network to which the terminal is connected via the base station (for example, the type of a circuit switching network or a packet switching network), the type of the communication partner of the terminal (for example, a telephone number or an IP address) Such as the type of information indicating the communication partner, etc.), and the QoS (Quality of Service) type (communication priority, allowable delay time, etc.) of communication between the terminal and the communication partner of the terminal. .

  Further, the “handover state” column is provided in the handover management table 503b illustrated in FIG. 34, and the terminal 102 in which “1” is registered in this column indicates that it is in the handover state.

  (1) First, a case will be described where terminals are assigned to each D-BTS in consideration of the number of terminals belonging to the D-BTS with the highest priority.

  As shown in FIG. 34, first, a terminal is allocated to a base station (D_BTS) whose D-BTSID is “ID4”. Since only the terminal with USERID “E” belongs to the base station “ID4”, the terminal “E” is assigned to the base station “ID4” as it is.

  Next, the terminal is allocated to the base station (D-BTS) whose D-BTSID is “ID2”. Although the terminals of USERID “A”, “E”, “F” belong to the base station “ID2”, since the terminal “E” has already been assigned to the base station “ID4”, here, Among these three terminals, the terminal “A” having the largest SIR value is assigned to the base station “ID4”.

  Next, the terminal is allocated to the base station (D-BTS) whose D-BTSID is “ID3”. Terminals with USERID “A” and “B” belong to the base station “ID3”, but since the terminal “A” is already assigned to the base station “ID2”, the terminal “B” is here. Assigned to base station “ID3”.

  Finally, the terminal is allocated to the base station (D-BTS) whose D-BTSID is “ID1”. The base station “ID1” includes terminals having USERIDs “A”, “B”, “C”, and “D”, but the terminals “A” and “B” have already been connected to other base stations (D− In this case, of the remaining two terminals “C” and “D”, the base station “ID1” is assigned to the terminal “C” having the largest SIR value.

  According to this method, it is possible to assign terminals equally to all D-BTSs 101 without allocating many terminals to some D-BTSs 101 in a concentrated manner.

  (2) Next, a case will be described in which a terminal is allocated to each D-BTS in consideration of the handover control parameter transmitted from each terminal with the highest priority.

  On the table shown in FIG. 34, first, the terminal “C” having the largest SIR value is assigned to the base station “ID1”. Next, the terminal “A” having the largest SIR value is assigned to the base station “ID2”. Although the terminals “A” and “B” belong to the base station “ID3”, the terminal “A” has already been assigned to another D-BTS (base station “ID2”). B "is assigned to base station" ID3 ". Finally, since only the terminal “E” belongs to the base station “ID4”, the terminal “E” is directly assigned to the base station “ID4”.

  (3) Next, a case will be described in which a terminal is allocated to each D-BTS in consideration of the priority of each terminal with the highest priority.

  On the table shown in FIG. 35, the terminal “A” has the highest priority. Therefore, the terminal “A” is assigned to the base station “ID1” having the largest SIR value measured by the terminal “A”. The terminals with the next highest priority are the terminals “B”, “D”, and “F”. Similarly to the above, the terminal “B” is assigned to the base station “ID3”, and the terminal “F” is assigned to the base station “ID2”. Finally, since only the terminal “E” belongs to the base station “ID4”, the terminal “E” is directly assigned to the base station “ID4”.

  The allocation methods shown in (1) to (3) above can be used in appropriate combination.

  If an allocation method as shown in the above (1) to (3) is used, terminals are allocated to all D-BTSs. On the other hand, in the conventional handover control method, the terminal side determines a counterpart base station (a base station from which the terminal requests data transmission) based on the reception characteristics of the signal transmitted from the base station. When the base station D-BTS 101 is assigned to each terminal by such a conventional method, it is easily imagined that the state shown in FIG. 36 is obtained. That is, a state in which terminals are assigned only to some D-BTSs 101 and terminals are not assigned to base stations “ID3” and “ID4” easily occurs. When such a state occurs frequently, the utilization efficiency of radio resources is reduced.

  In contrast to such a conventional method, according to the method according to the third embodiment, the C-BTS 100 is connected to each terminal 102 existing in the communication area of the C-BTS 100 (via a narrow-band uplink radio channel). And a plurality of D-BTSs 101 under the control of the C-BTS 100 are allocated to each terminal on the basis of the reception characteristics with respect to the signals arriving from the transmitted D-BTSs 101. That is, it follows the radio propagation path fluctuation between the terminal 102 and the D-BTS 101, and the information signal from the base station (D-BTS 101) having the optimum propagation environment at that time among the plurality of base stations (D-BTS). Since the base station D-BTS 101 is assigned to each terminal so that the terminal can be transmitted to the terminal, the throughput of the terminal can be improved. In addition, it is possible to effectively allocate radio channels to terminals and improve the utilization efficiency of radio resources.

  Then, since handover control for switching the D-BTS 101 that transmits an information signal to the terminal 102 is performed via a narrowband radio channel between the C-BTS 100 and the terminal 102, the terminal 102 performs handover control. It is not affected by the required control delay.

(Fourth embodiment)
As described in the third embodiment, when the communication area 104 formed by each D-BTS 101 is narrowed, an area where a plurality of communication areas 104 overlap is increased as shown in FIG. When the area where a plurality of communication areas overlap increases, handovers do not only increase. A state in which radio signals transmitted from the plurality of D-BTSs 101 arrive at the terminal 102 and interference between the D-BTSs occurs increases.

  Therefore, in the fourth embodiment, a method for reducing interference between D-BTSs in the mobile communication system according to the first embodiment will be described.

  Here, the case where the narrow band first frequency band 301 and the wide band second frequency band 302 are used as shown in FIG. 3 or FIG. 4 will be described as an example.

  FIG. 37 is a diagram for explaining interference between base stations D-BTS of the mobile communication system according to the fourth embodiment. In FIG. 37, a terminal 102b exists in an area 401 where two communication areas 104a and 104b formed by two D-BTSs 101a and 101b respectively overlap, and a terminal 102a exists in the communication area 104a.

  The C-BTS 100 transmits a control signal for notifying the terminal 102a that the D-BTS 101a transmits an information signal to the terminal 102a using the narrowband downlink radio channel 105a, and also transmits to the terminal 102b. Then, the control signal for notifying that the D-BTS 101b transmits the information signal to the terminal 102b is transmitted using the narrowband downlink radio channel 105b. Further, the C-BTS 100 transmits a control signal for notifying the terminal 102a that an information signal is transmitted to the D-BTS 101a via the communication line 108, and also transmits a control signal to the D-BTS 101b. A control signal for notifying that the information signal is transmitted to 102b is transmitted.

  As a result, the terminal 102a receives an information signal from the D-BTS 101a via the broadband downlink radio channel 107a, and the terminal 102b receives an information signal from the D-BTS 101b via the broadband downlink radio channel 107b.

  In this state, since the terminal 102b exists in the area 401 where the communication area 104a of the D-BTS 102a and the communication area 104b of the D-BTS 102b overlap, an information signal transmitted from the D-BTS 101a also arrives. In this case, at the terminal 102b receiving the radio channel 107b, the signal from the D-BTS 101b (the signal to be received) interferes with the signal from the D-BTS 101a, resulting in the reception characteristics of the signal from the D-BTS 101b. Adversely affect. Here, such interference is referred to as inter-base station interference.

  In addition, since the terminal 102b exists at the end of the communication area 104b of the D-BTS 101b, it is easily imagined that the reception characteristic of the signal arriving from the D-BTS 101b in the terminal 102b is poor. That is, interference between base stations is superimposed on a state in which reception characteristics are originally inferior, so that the effect becomes very large.

  Next, with reference to FIG. 38, the processing operation for allocating radio resources so as to reduce the interference between base stations will be described.

  Here, the two D-BTSs 101a and 101b in FIG. 37 are represented as D-BTS (1) and D-BTS (2), respectively, and the two terminals 102a and 102b are represented as terminal (1) and terminal (2), respectively. Represents. Further, the C-BTS 100 is simply represented as C-BTS. It is assumed that the terminal (1) and the terminal (2) exist in the D-BTS (1) and the D-BTS (2).

  The C-BTS, D-BTS (1), and D-BTS (2) transmit a known signal (known signal) between the base station (C-BTS100, D-BTS101) and the terminal 102 at a predetermined period PI_INT. is doing. The known signal includes identification information (for example, D-BTID and the like) of the transmission source of the known signal. For example, the D-BTS (1) and the D-BTS (2) transmit a known signal using a predetermined frequency or a predetermined time slot in the downlink of the wideband second frequency band 302, The C-BTS also transmits a known signal using a predetermined frequency or a predetermined time slot in the downlink of the narrow first band 301 (step S71).

  When the terminal (1) and the terminal (2) receive a known signal transmitted from each base station, the reception characteristics (for example, RSSI and SIR) are measured (step S72), and information including the measurement result (step S72). Reception state information) is transmitted to the C-BTS 100 using the narrowband uplink radio channel 106 (step S73).

  The reception status information includes, for example, the identification information of each D-BTS measured by each terminal (that is, the measurement was possible) and the RSSI value of the known signal. The C-BTS (terminal control unit 502a thereof) stores the reception state information transmitted from each terminal (step S74). The processing operations in steps S72 to S74 are performed every predetermined time RS_INT.

  The radio resource control unit 502e of the C-BTS determines radio channel allocation at predetermined time intervals DT_INT in consideration of reception status information transmitted from each terminal, priority and throughput of each terminal (step S75). ). Here, the assignment of the radio channel is to determine a D-BTS that transmits an information signal, a terminal that receives the information signal, a demodulation method / decoding method of the information signal, and the like. Note that when the D-BTS 101 (wideband downlink radio channel) is determined for each terminal, the narrowband downlink radio channel for the terminal is naturally determined. This is because the two are associated in advance as described above.

  When the allocation of the radio channel is determined, a control signal for notifying the determined content is transmitted to each terminal using the narrowband downlink radio channel 105. In addition, a control signal for notifying the determined content is transmitted to each D-BTS via the communication line 108 (step S76).

  Each D-BTS transmits an information signal via the broadband downlink radio channel 107 to the terminal assigned to the D-BTS based on the information included in the received control signal (step S77). . Each terminal receives an information signal transmitted from the D-BTS assigned to the terminal via the broadband downlink radio channel 107 based on the information included in the received control signal (step S78).

  Normally, a relationship of RS_INT> = DT_INT is established between the cycle time RS_INT and the cycle time DT_INT.

  In FIG. 38, as a typical control example, when the radio channel assignment is determined in step S75, it is determined that the terminal (2) is subject to interference from the signal from the D-BTS (1), that is, the base station A case where it is determined that there is inter-interference (Case 1) and a case where it is determined that there is no inter-base station interference (Case 2) are shown.

  (Case 1) For example, when it is determined in step S75 that D-BTS (1) transmits an information signal to terminal (1) and D-BTS (2) transmits an information signal to terminal (2), When it is determined that the terminal (2) receives interference due to the signal from the D-BTS (1), the C-BTS does not allocate a radio channel to the D-BTS (1). That is, the control signal is not transmitted to the D-BTS (1) and the terminal (1). As a result, no information signal is transmitted from the D-BTS (1).

  (Case 2) For example, when it is determined in step S75 that D-BTS (1) transmits an information signal to terminal (1) and D-BTS (2) transmits an information signal to terminal (n) (not shown) If it is determined that there is no inter-base station interference in the terminal (1) and the terminal (n) based on the reception state information transmitted from each terminal, the C-BTS transmits the control signal to each D-BTS. To each terminal. As a result, terminal (1) and terminal (n) receive information signals transmitted from D-BTS (1) and D-BTS (2).

  According to the basic procedure shown in FIG. 38, the C-BTS that determines the allocation of radio channels manages the reception status of all terminals, so that radio resources in consideration of inter-base station interference without causing a control delay. Assignment can be done easily.

  Next, the processing operation of the C-BTS will be described with reference to the flowchart shown in FIG.

  The terminal control unit 502a of the C-BTS 100 receives the reception state information transmitted from each terminal every time RS_INT, and updates the management table 503a using it (steps S81 to S83).

  FIG. 40 shows a main part of the management table 503a stored in the C-BTS 100. Here, it is assumed that the reception status information includes the identifier (D-BTSID) of the D-BTS 101 that is the source of the known signal received by each terminal and the RSSI measured from the known signal. 40, in the management table 503a, D-BTSIDs of all D-BTSs 101 under the control of the C-BTS 100, USERIDs that are identifiers of terminals belonging to the respective D-BTSs 101, and receptions transmitted from the terminals. The D-BTSID, RSSI, and the like included in the status information are stored in the “reception status” column. In addition, the “reception status” column also stores a flag I_ob indicating a D-BTS that may be subject to inter-base station interference among D-BTSs that can measure RSSI of known signals at each terminal. ing.

  In addition, the measurement result of the reception characteristic stored on the management table may be updated with a value included in the notified reception state information, or an average value thereof may be added in consideration of a value notified in the past. The management table may be updated.

  Here, with reference to the flowchart shown in FIG. 41, the processing operation for determining the presence or absence of inter-base station interference will be described.

  The radio resource control unit 502e of the C-BTS measures a known signal from the D-BTS to which the terminal belongs using the reception state information transmitted from each terminal recorded in the management table as illustrated in FIG. The received RSSI (reception level) is compared with a predetermined first threshold Th_ob1 (step S91). If the reception level is greater than Th_ob1, a predetermined second threshold Th_ob2 is set to a separately stored value Param1 (step S92). If the reception level is equal to or lower than Th_ob1, the second threshold Th_ob2 is set to a separately stored value Param2 (step S93). Here, it is assumed that Param1 <= Param2.

  Subsequently, the difference between the reception level of the radio signal from the D-BTS to which the terminal belongs and the reception level of the radio signal from the other D-BTS is calculated and set as a reception state offset (Offset) (step) S94). When the value of Offset is larger than the second threshold Th_ob2, it is determined that there is no inter-base station interference (step S95, step S96), and when the value of Offset is equal to or smaller than the second threshold Th_ob2, It is determined that there is inter-station interference, and the flag I_ob on the management table is set to “1” (steps S95 and S97). Steps S91 to S97 are performed for all terminals that have notified the reception state information (step S98).

  For example, taking the case where Th_ob1 = −65 dBm, Param1 = 3 dB, and Param2 = 5 dB as an example, the inter-base station interference determination processing operation of FIG. 41 will be specifically described. Here, it demonstrates using FIG. Since this processing is performed for a terminal that can receive signals from a plurality of D-BTSs (that is, the reception level of a plurality of D-BTSs is notified), the USERID in FIG. Is performed on the terminal.

  Since the terminal “A” belongs to the base station whose D-BTSID is “ID1”, the reception level (−60 dBm)> Th_ob1 (−65 dBm) is satisfied (step S91), and Param1 (3 dB) is set in Th_ob2 ( Step S92). Further, when the offset with another base station is calculated, the offset between the base station “ID1” and the base station “ID2” is 3 dB, and the offset between the base station “ID1” and the base station “ID3” is 5 dB. (Step S95). Since Th_ob2 is 3 dB, in this case, it is determined that the base station “ID2” receives inter-base station interference (step S97), and the base station “ID3” is determined not to receive inter-base station interference (step S97). S96).

  Since the terminal “C” belongs to the base station “ID2”, the reception level (−70 dBm) <= Th_ob1 (−65 dBm) is set (step S91), and Param2 (5 dB) is set in Th_ob2 (step S93). Further, when calculating the offset with another base station, the offset is 5 dB between the base station “ID2” and the base station “ID3” (step S94), and this value is within Th_ob2 (5 dB). It is determined that inter-base station interference is received from the base station “ID3” (step S97).

  By performing the inter-base station interference determination process of FIG. 41, it is determined that interference between base stations is also received from adjacent D-BTSs where the difference in reception level is somewhat large in an environment with originally poor reception characteristics. As a result, the effect of alleviating the influence of inter-base station interference on the reception characteristics of information signals is added.

  Returning to the description of FIG.

  The radio resource control unit 502e of the C-BTS takes into account the management table 503a as shown in FIG. 40, the priority (priority table 503c) of each terminal, the throughput, and the like every time DT_INT (step S84). Is determined (step S85). As described above, the radio channel allocation refers to the combination of the D-BTS that transmits the information signal and the terminal that receives the information signal, and determines the demodulation method and decoding method of the information signal for each combination. That is.

  At this time, if there is a terminal that may receive interference from another base station among the terminals to which the base station (D-BTS 101) is assigned (step S86), there is a possibility of receiving the interference. One of the assignment of the radio channel to a certain terminal and the assignment of the terminal to the base station that causes interference to the terminal is canceled (step S87). Information signals from the base station are not transmitted to terminals whose assignment has been canceled.

  For example, the processing operation in step S87 in the case where the priority of the terminal that receives interference and the priority of the terminal that gives interference is used as a criterion will be described with reference to FIG.

  As shown in FIG. 42, it is assumed that the terminal “A” is assigned to the base station (D-BTS) “ID1” and the terminal “C” is assigned to the base station (D-BTS) “ID2”. When the terminal “A” receives interference from the base station (D-BTS) “ID2” and the priority of the terminal “C” is higher than the priority of the terminal “A”, in step S87, the terminal “A” The assignment of the base station “ID1” to “is canceled ((a) of FIG. 42). That is, the base station “ID1” is prevented from transmitting an information signal.

  On the other hand, it is assumed that the terminal “A” is assigned to the base station (D-BTS) “ID1” and the terminal “B” is assigned to the base station (D-BTS) “ID2”. When the terminal “A” receives interference from the base station (D-BTS) “ID2” and the priority of the terminal “B” is lower than the priority of the terminal “A”, in step S87, the terminal “B” "(2) in FIG. 42. That is, the base station" ID2 "is prevented from transmitting an information signal.

  When transmitting an information signal from a base station to a terminal, if the information signal transmitted from another base station may cause interference, the information signal from the other base station should not be transmitted. Thus, occurrence of interference between base stations can be prevented.

  A control signal is transmitted from the C-BTS 100 to the base station to which the terminal is assigned and the terminal to which the base station is assigned (step S88). Note that the processes in steps S81 to S88 are repeated until all communication via the broadband wireless channel between the terminal and the D-BTS 101 is completed (step S89).

  Next, another operation example of the C-BTS will be described with reference to the flowchart shown in FIG. 43, the same parts as those in FIG. 39 are denoted by the same reference numerals, and only different parts will be described. That is, FIG. 43 shows a case where the radio channel assignment is changed in consideration of the presence or absence of inter-base station interference. Therefore, step S87 in FIG. 39 is replaced with steps S101 to S103 in FIG.

  The C-BTS determines the radio channel allocation for each time DT_INT in consideration of the management table, the priority and throughput of each terminal (steps S84 and S85). Here, when a terminal to which a radio channel is assigned is a terminal that is likely to receive interference between base stations (a terminal that receives interference), the priority of the terminal and the base that interferes with the terminal If the priority of the terminal receiving the interference is higher than the priority of the terminal that is the other party to which the station transmits the information signal (the terminal that gives interference), The assignment of the terminal to the base station is canceled (step S101, step S102). on the other hand. When the priority of the terminal on the interference side is higher, the base station assigned to the terminal on the interference side (the base station on the interference side) is different from the terminal on the interference side. Then, a terminal that does not receive interference from the base station on the interference side is assigned (step S103).

  In this way, the control signal is transmitted from the C-BTS 100 to the base station to which the terminal is assigned and the terminal to which the base station is assigned (step S88).

  FIG. 44 shows a priority table 503c that stores the priority of each terminal. The priority “1” is the highest priority.

  Here, the processing operation of the C-BTS 100 shown in FIG. 43 will be described more specifically with reference to the management table of FIG.

  In step S85, the terminal “A” is assigned to the base station (D-BTS) “ID1”, the terminal “C” is assigned to the base station (D-BTS) “ID2”, and the terminal “A” is assigned to the base station “ID3”. Assume that “E” is assigned. The terminal “A” receives interference from the base station (D-BTS) “ID2”, but at this time, the base station “ID2” is assigned the terminal “C” having a higher priority than the terminal “A”. ing. Accordingly, the process proceeds from step S101 to step S103, and not the terminal “A” but the terminal “B” that does not receive interference from other base stations D-BTS is assigned to the base station “ID1”.

  Further, the terminal “C” receives interference from the base station “ID3”. At this time, the base station “ID3” is assigned the terminal “E” having a lower priority than the terminal “C”. Accordingly, the process proceeds from step S101 to step S102, and the assignment of the terminal “E” to the base station “ID3” is canceled.

  According to the processing operation shown in FIG. 43, a broadband downlink radio channel can be preferentially allocated to a terminal with high priority due to the influence of inter-base station interference.

  Next, still another operation of the C-BTS will be described with reference to the flowchart shown in FIG. 45, the same parts as those in FIG. 39 are denoted by the same reference numerals, and only different parts will be described. That is, FIG. 45 shows a case where the radio channel assignment is changed in consideration of the presence or absence of inter-base station interference. Therefore, step S87 in FIG. 39 is replaced with steps S104 to S105 in FIG.

  The radio resource control unit 502e of the C-BTS decides radio channel allocation every time DT_INT in consideration of the management table as shown in FIG. 40, the priority of each terminal as shown in FIG. 44, the throughput, and the like. (Step S84, Step S85). Here, when the terminal to which the radio channel is allocated is a terminal that is likely to receive inter-base station interference (a terminal that receives interference) (step S86), the process proceeds to step S104, and interference is caused to the terminal. It is checked whether a terminal is assigned to the base station of the providing side. When a terminal is assigned to the base station, the process proceeds to step S105, and the terminal assigned to the base station assigned to the terminal on the interference side (the base station on the interference side) is changed. That is, a terminal that does not receive interference from other base stations is assigned to the base station that receives the interference.

  In this way, the control signal is transmitted from the C-BTS 100 to the base station to which the terminal is assigned and the terminal to which the base station is assigned (step S88).

  According to the processing operation shown in FIG. 45, it is possible to prevent a wideband downlink radio channel from being vacant due to the influence of inter-base station interference, that is, a decrease in radio resource utilization efficiency.

  Next, still another example of the C-BTS processing operation will be described with reference to the flowchart shown in FIG. 46, the same parts as those in FIG. 39 are denoted by the same reference numerals, and only different parts will be described. That is, step S87 in FIG. 39 is replaced with step S106 in FIG.

  The radio resource control unit 502e of the C-BTS decides radio channel allocation every time DT_INT in consideration of the management table as shown in FIG. 40, the priority of each terminal as shown in FIG. 44, the throughput, and the like. (Step S84, Step S85). Here, when the terminal to which the radio channel is allocated is a terminal that is likely to receive inter-base station interference (a terminal on the side receiving the interference) (step S86), the process proceeds to step S106, and the terminal In order to reduce the transmission power of the base station on the interference side by an arbitrary predetermined value ΔP “dB”, this fact is notified to the base station on the interference side using a control signal.

  According to the processing operation shown in FIG. 46, even if a base station on the side that interferes with a terminal transmits an information signal, the influence of the interference on the terminal is reduced. In addition, it is possible to prevent a radio channel from being vacant due to the influence of inter-base station interference, that is, a reduction in radio resource utilization efficiency.

  Next, still another example of the C-BTS processing operation will be described with reference to the flowchart shown in FIG. 47, the same parts as those in FIG. 39 are denoted by the same reference numerals, and only different parts will be described. That is, step S87 in FIG. 39 is replaced with step S107 in FIG.

  In step S106 of FIG. 46, the transmission power of the base station on the side that interferes with the terminal is reduced. However, in step S107 of FIG. 47, it is assigned to a terminal that may receive interference. In order to increase the transmission power of the base station (base station on the side of interference) by an arbitrary predetermined value ΔP “dB”, this is notified to the base station on the side of interference using a control signal.

  According to the processing operation shown in FIG. 47, even if a base station on the side that interferes with a terminal transmits an information signal, the influence of interference at the terminal is reduced. In addition, it is possible to prevent a radio channel from being vacant due to the influence of inter-base station interference, that is, a reduction in radio resource utilization efficiency.

(Fifth embodiment)
In a conventional mobile communication system, when a terminal is in a standby state, the terminal normally measures reception characteristics of radio signals coming from a plurality of base stations, selects a base station having the best reception characteristics, and Establish synchronization with Also, periodically monitor the reception characteristics of radio signals coming from all base stations that can receive radio signals at the terminal, and if it is determined that the reception status of signals from other base stations is excellent, Resynchronization with other base stations is performed, but frequent resynchronization increases the power consumption of the terminal.

  As described in the third embodiment, when the communication area 104 formed by each D-BTS 101 is narrowed, an area where a plurality of communication areas 104 overlap is increased as shown in FIG. When the area where a plurality of communication areas overlap increases, radio signals transmitted from the plurality of D-BTSs 101 arrive at the terminal 102. Therefore, when the terminal 102 of the mobile communication system according to the first embodiment exists in a dense communication area as shown in FIG. 25, a base station with a good signal reception state is selected as in the conventional case. If the operation of establishing synchronization is repeated frequently, the load on the terminal increases.

  Therefore, in the fifth embodiment, a cell management method for reducing the load on the terminal 102 in the mobile communication system according to the first embodiment will be described.

  Here, the case where the narrow band first frequency band 301 and the wide band second frequency band 302 are used as shown in FIG. 3 or FIG. 4 will be described as an example.

  FIG. 48 is a diagram for explaining the cell management method of the mobile communication system according to the fifth embodiment. In FIG. 48, the terminal 102a exists in a region 402 where three communication areas 104a, 104b, and 104c formed by the D-BTSs 101a, 101b, and 101c respectively overlap.

  In this case, the terminal 102a can receive the information signal via the broadband downlink radio channels 107a to 107c transmitted by the D-BTSs 101a to 101c. At this time, the C-BTS 100 needs to grasp the communication area where the terminal 102a exists. This is because it is necessary to determine a D-BTS for transmitting an information signal (allocate a broadband wireless channel) when transmission of an information signal to the terminal 102a is started. In addition, since the C-BTS 100 starts transmission of an information signal with high reliability and high speed to the terminal 102a, the reception characteristics of the radio signal at the terminal 102a among the three D-BTSs are: It is necessary to grasp a relatively good D-BTS.

  Here, managing the reception characteristics at the terminal 102a of the D-BTS 101 forming the communication area where the terminal 102 exists and the radio signal transmitted by the D-BTS 101 is called cell management.

  Next, a cell management method according to the fifth embodiment will be described with reference to FIG. FIG. 49 shows a case where the terminal 102a exists in an area 402 where three communication areas 104a, 104b, and 104c formed by the D-BTSs 101a, 101b, and 101c overlap each other, as in FIG.

  As shown in FIG. 49, the terminal 102a uses a first frequency band, for example, at a predetermined timing and a predetermined transmission power, for example, a signal 440 (here, a notification signal) including the identifier (USERID) of the terminal 102a. Is called). When the D-BTS 101a to 101c receives the broadcast signal via the narrowband uplink radio channel 106, the D-BTS 101a to 101c receives the broadcast signal (received signal strength indicator (RSSI), signal to interference power ratio (SIR)). interference ratio) and at least one of propagation loss) are measured, and the measurement result is notified to C-BTS 100 using communication lines 108a to 108c.

  In this way, each D-BTS 101 that has received the notification signal periodically transmitted by the terminal 102a measures the reception characteristics of the notification signal, and notifies the C-BTS 100 of the measurement result. Can recognize the D-BTS 101 forming the communication area in which the terminal 102a exists, and can recognize the transmission path state between the D-BTS 101 and the terminal 102a.

  Next, with reference to FIG. 50, the operation at the time of terminal standby between the base stations C-BTS 100 and D-BTS 101a to 101c of FIG. 49 and the terminal 102a will be described.

  In FIG. 50, the three D-BTSs 101a to 101bc in FIG. 49 are represented as D-BTS (1), D-BTS (2), and D-BTS (2), respectively, and the terminal 102a is represented as terminal (1). ing. Further, the C-BTS 100 is simply represented as C-BTS.

  The standby control unit 522d of the terminal (1) transmits the notification signal with a predetermined transmission power (for example, notified from the C-BTS 100) on the uplink of the first frequency band 301 at every predetermined time LR_INT. (Step S201). For example, when the terminal 102 (1) is in a standby state, the terminal (1) can perform battery saving by stopping the operation clock until the time LR_INT elapses. Longer is desirable. However, if the time LR_INT is long, the accuracy of cell management is lowered. Therefore, the time LR_INT is determined by a trade-off between the two.

  Here, the radio processing unit 511a of each D-BTS (1) to (3) receives the broadcast signal transmitted by the terminal (1) every time LR_INT, and displays the RSSI, RSSI, and other reception characteristics. Is also measured (step S202). The reception characteristic measurement result including RSSI is passed to the standby control unit 512c. The standby control unit 512c stores the reception characteristic notified from each terminal in the reception characteristic table 513a and notifies the C-BTS via the communication line 108 of the measured reception characteristic (step S203). Note that the standby control unit 512c measures the reception characteristics of the received notification signal only when the RSSI at the time of reception of the notification signal transmitted from the terminal exceeds a predetermined threshold.

  The C-BTS stores the measurement result notified from each D-BTS in the management table 503a (step S204).

  In such a state, when the transmission of the information signal to the terminal (1) is started, the C-BTS refers to the management table 503a and determines the D-BTS that transmits the information signal to the terminal ( Step S205). For example, a D-BTS that can be assumed to have the best reception characteristics at the terminal (1) is selected. For example, it is assumed that D-BTS (2) is selected. The C-BTS transmits a control signal to instruct the D-BTS (2) to transmit an information signal to the terminal (1) via the communication line 108b (step S206). Also, the control signal similar to the above is transmitted to the terminal using the narrowband downlink radio channel 105 (step S207). Thereafter, the D-BTS (2) transmits an information signal to the terminal (1) using the broadband downlink radio channel 107b (step S208).

  According to the procedure shown in FIG. 50, the terminal 102a can receive an information signal from a D-BTS with relatively good reception characteristics without performing any complicated control in order to receive the information signal. It becomes possible.

  Here, transmission power when the terminal 102 transmits the notification signal will be described. The transmission power value itself is determined for each mobile communication system.

  The communication area in which the terminal exists and the base station D-BTS to be allocated to the terminal are determined based on the reception characteristics of the notification signal measured by the D-BTS 101. Therefore, the reception characteristic must satisfy the minimum necessary condition for guaranteeing the fact that the terminal 102 exists in the communication area of the base station D-BTS 101. That is, when the notification signal transmitted from the terminal 102 can be received by the D-BTS 101, it must be ensured that the terminal 102 exists in the communication area 104 of the D-BTS 101.

Here, it is assumed that the transmission power of the information signal transmitted from the D-BTS 101 via the broadband downlink radio channel 107 is P_dt. Also, let P_mr be the received power required in the vicinity of the boundary of the communication area, which is determined as a range that guarantees that the reception characteristics of the information signal satisfy the necessary minimum conditions. At this time, the propagation loss Pathloss is: Pathloss = P_dt−P_mr (1)
Is defined.

Also, assuming that the power required to receive the broadcast signal transmitted from the terminal 102 in the D-BTS 101 is P_dr (this is a value specific to the mobile communication system), the transmission at the terminal 102 from the above conditions. The power P_mt is
P_mt = P_dr + Pathloss (2)
Can be determined.

  The P_dr and Pathloss can be notified from the C-BTS 100 to the terminal 102 via the narrowband downlink radio channel 105, for example.

  The value of Pathloss may be changed by the C-BTS 100 according to the cell management status. For example, when the number of terminals 102 managed by the C-BTS 100 increases and the cell management load increases, by setting the Pathloss value to be small, a plurality of communication areas formed by each D-BTS 101 can be set. The case where it is determined that the terminal 102 exists is reduced, and as a result, the load of cell management can be reduced.

  Next, the notification signal transmitted by terminal 102 will be described with reference to FIG. The broadcast signal is preferably a signal specific to the mobile communication system or a signal specific to the terminal. Further, as the signal sequence, a pseudo-noise sequence having excellent autocorrelation characteristics is desirable. Accordingly, the D-BTS 101 that has received the notification signal can easily measure the reception characteristics.

  Since broadcast signals transmitted from a plurality of different terminals arrive at the D-BTS 101, the broadcast signals must be able to be received separately while suppressing the influence of mutual interference. For this reason, as shown in FIG. 51, the broadcast signal of each terminal is transmitted by TDMA (Time Division Multiple Access).

  FIG. 51 shows a frame configuration of a channel (in this case, referred to as a broadcast channel in distinction from a channel that transmits a control signal) through which a broadcast signal of each terminal is transmitted in a narrowband downlink. One frame is divided into n time slots (slots), and one broadcast signal is transmitted in each slot. In FIG. 51, the notification signal transmitted from the terminal 102a is assigned to the slot TS1, and the notification signal transmitted from the terminal 102b is assigned to the slot TS3. In addition, each terminal transmits a notification signal with a period LR_INT. In FIG. 51, LR_INT corresponds to a time length of N frames.

  In FIG. 51, the transmission timing of the notification signal of the terminal 102a is (Frame No. mod N) +4 slots, and the transmission timing of the notification signal of the terminal 102b is (Frame No. mod N) +2 slots. A notification signal is transmitted.

  Thus, the D-BTS 101 receives broadcast signals transmitted from the terminals at different timings, and can easily measure the reception characteristics of the broadcast signals transmitted from a plurality of terminals.

  As shown in FIG. 52, the broadcast signal of each terminal may be transmitted by CDMA (Code Division Multiple Access).

  FIG. 52 shows a frame configuration of a channel through which a notification signal of each terminal is transmitted. One frame consists of n time slots (slots), and a plurality of broadcast signals multiplexed by spreading codes assigned in advance to each terminal are transmitted in each slot.

  In FIG. 52, the notification signal transmitted from terminal 102a, the notification signal transmitted from terminal 102b, and the notification signal transmitted from terminal 102c are multiplexed and transmitted in slot TS0. In addition, each terminal transmits a notification signal with a period LR_INT. In FIG. 51, LR_INT corresponds to a time length of N frames.

  In this case, the plurality of terminals assigned to the same slot all transmit the notification signal at the same transmission timing. In addition, this transmission timing is defined uniquely for the mobile communication system and the C-BTS. In this case, the broadcast signal of each terminal is separated by a signal sequence. That is, an orthogonal sequence typified by a WH code is applied to a broadcast signal transmitted by each terminal. As a result, the D-BTS 101 receives the broadcast signal transmitted from each terminal 102 at the same timing, but easily measures the reception characteristics of the broadcast signal transmitted by each terminal due to the orthogonality of the signal sequence. It becomes possible to do. In addition, when the broadcast signal of each terminal is multiplexed in an orthogonal sequence, it is preferable that the period at which each terminal transmits the broadcast signal is relatively longer than in the case of FIG.

  Next, with reference to FIG. 53, the transmission method of the notification signal of terminal 102 will be described. FIG. 53 shows the timing at which the terminal 102 transmits a notification signal.

  In FIG. 53, the terminal 102 can not only transmit the notification signal in the cycle LR_INT but also set LR_INT_N that is an integer multiple of LR_INT to a predetermined cycle. Further, LR_INT_N can be changed dynamically and always. Thereby, the frequency | count that the terminal 102 transmits an alerting signal decreases, and there exists an effect which reduces the power consumption of a terminal as a result. Note that LR_INT_N can be changed by the terminal 102 itself, or the C-BTS 100 can instruct the terminal 102 to change the LR_INT_N.

  When the terminal 102 itself changes, for example, it is possible to use a change in reception characteristics of a radio signal transmitted by the C-BTS 100 or whether or not the terminal 102 is moving. Also, FIG. 56 shows the operation of the C-BTS 100 when the C-BTS 100 instructs the terminal 102 to make a change (described later).

  Next, the operation of the C-BTS 100 that performs the cell management method according to the fifth embodiment will be described with reference to the flowchart shown in FIG.

  In FIG. 54, the standby control unit 502d of the C-BTS 100 performs the following processing operation for each terminal LR_INT at each time LR_INT. That is, the reception characteristic of the notification signal transmitted from the terminal 102 notified from the D-BTS 101 is acquired (step S212), and the management table 503a is updated (step S213).

  The main part of the management table 503a is shown in FIG. Here, the reception characteristic notified from the D-BTS 101 to the C-BTS 100 is the RSSI of the notification signal of each terminal that can be received by the D-BTS 101. The management table shown in FIG. 55 includes a D-BTSID that is an identifier of each D-BTS 101 under the management of the C-BTS 100 and a USERID that is an identifier of a terminal that has transmitted a receivable notification signal in each D-BTS. In addition, for each D-BTS, an allocation flag is stored for the reception characteristic notified by each D-BTS, and for each terminal to which the D-BTS transmits an information signal. When the allocation flag is “1”, this indicates that the D-BTS is allocated to the terminal.

  As for the reception characteristics on the management table, the management table may be updated with the notified value every time it is notified, or the management table is updated with the average value of the past values. May be.

  Once the management table is updated, the C-BTS next updates the allocation flag (step S214). This is to cope with, for example, a case where the D-BTS 100 having the best reception characteristics for an arbitrary terminal 102 changes.

  Next, another operation of the C-BTS 100 for carrying out the cell management method according to the fifth embodiment will be described with reference to the flowchart shown in FIG. In FIG. 56, the same parts as those in FIG. 54 are denoted by the same reference numerals, and only different parts will be described. That is, in FIG. 56, a process (step S222 to step S228) for changing the period time LR_INT_N at which the terminal transmits a notification signal is added between step S221 and step S214.

  In step S213 of FIG. 56, when the standby control unit 502d updates the management table (first management table) 503a illustrated in FIG. 55, the update of the second management table (cell management table) 503d is performed next. (Step S221).

  An example of the second management table is shown in FIG. In the second management table, the best reception characteristics are notified in the USERID for identifying each terminal 102 under the management of the C-BTS 100 and the notification results of the reception characteristics for the past several times for each terminal 102. The identifier D-BTSID of the base station is stored. FIG. 57 shows a case where the past four times are stored.

  When the second management table is updated, the standby control unit 502d determines whether or not the past N (N is a predetermined positive integer) D-BTSIDs are the same for each terminal 102 (step S102). S222). If they are the same, the time LR_INT is added to the time LR_INT_N (step S223). On the other hand, if the past N D-BTSIDs are different, it is further determined whether the past M (M is a predetermined positive integer and M <N) D-BTSIDs are all different (step S225). ). If all are different, the time LR_INT is subtracted from the time LR_INT_N (step S226).

  Note that a constraint condition is added to LR_INT_N so as not to exceed a predetermined range LR_INT_Min <LR_INT_N <LR_INT_Max. Therefore, when LR_INT_N is updated in step S223, it is checked in the next step S224 whether the above constraint conditions are satisfied. If it satisfies, the process proceeds to step S228, and the terminal 102 is notified of the changed time LR_INT_N. If not, the changed time is not notified. Also, when LR_INT_N is updated in step S226, it is checked in the next step S227 whether or not the constraint condition is satisfied. If it satisfies, the process proceeds to step S228, and the terminal 102 is notified of the changed time LR_INT_N. If not, the changed time is not notified.

  For example, when N = 4 and M = 3, the transmission cycle LR_INT_N of the terminal “A” and the terminal “E” is subtracted by the time LR_INT from the second management table of FIG. 57, and the transmission cycle of the terminal “D” The time LR_INT is added to LR_INT_N.

  Next, the operation of the D-BTS 101 for carrying out the cell management method according to the fifth embodiment will be described with reference to the flowchart shown in FIG.

  In FIG. 58, the standby control unit 512c of the D-BTS 101 performs the following processing operation at each time LR_INT for each terminal 102 that will exist in the communication area. That is, the reception characteristic of the notification signal transmitted by the terminal 102 is acquired (step S232). Furthermore, the acquired reception characteristic is compared with a predetermined threshold Th_P (step S233), and the acquired reception characteristic is notified to the C-BTS 100 only when the reception characteristic exceeds the threshold (step S234). The threshold value Th_P is a value predetermined for the mobile communication system and is defined as a reception characteristic necessary for receiving a broadcast signal from a terminal in the D-BTS.

  When the D-BTS 101 performs the operation shown in FIG. 58, the reception characteristic of the notification signal (transmitted from the terminal 102) measured by the D-BTS 101 is insufficient to receive the information signal. The terminal 102 as judged is not notified to the C-BTS. As a result, the number of terminals 102 to be managed for each D-BTS 101 is reduced on the management table 503a of the C-BTS 100. Therefore, the cell management load in the C-BTS 100 can be reduced.

  According to the fifth embodiment, the D-BTS 101 measures the reception characteristics of the broadcast signal periodically transmitted from each terminal 102, and sets the reception characteristics and the USERID of the transmission source of the broadcast signal as the C-BTS 100. To notify. The C-BTS 100 can reduce the load on the terminal 102 during standby by recognizing the D-BTS 101 to which each terminal belongs based on the reception characteristics and USERID notified from each D-BTS 101 under its control. it can.

  Also, by assigning a broadband downlink radio channel (D-BTS 101 that transmits an information signal) to each terminal 102 based on the reception characteristics and USERID notified from each D-BTS 101, each terminal 102 An information signal can be received from the D-BTS 101 that provides the best reception characteristics for the terminal.

  Furthermore, the transmission cycle of the notification signal is dynamically changed according to the movement situation of the terminal (when the terminal 102 is almost stationary, the transmission cycle is lengthened, and the communication area 104 is frequently When moving, the transmission cycle is shortened), and the power consumption of the terminal 102 can be reduced.

  Note that the present invention is not limited to the first to fifth embodiments as they are, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The figure which showed the structural example of the mobile communication system of this invention. The figure which showed the other structural example of the mobile communication system. The figure for demonstrating the 1st frequency band of a narrow band, and the 2nd frequency band of a wide band. The figure for demonstrating the 1st frequency band of a narrow band, and the 2nd frequency band of a wide band. The figure for demonstrating the 1st frequency band of a narrow band, and the 2nd frequency band of a wide band. The figure for demonstrating the 1st frequency band of a narrow band, and the 2nd frequency band of a wide band. The figure for demonstrating the radio channel of DL transmitted to a terminal from C-BTS and D-BTS. The figure for demonstrating the radio channel of DL transmitted to a terminal from C-BTS and D-BTS. The figure which showed the information contained in the control signal which C-BTS transmits. The figure which showed the information contained in the control signal which C-BTS transmits. The figure which showed the information contained in the control signal which C-BTS transmits. The figure which showed the structural example of C-BTS. The figure which showed the structural example of D-BTS. The figure which showed the structural example of the terminal. The flowchart for demonstrating operation | movement of a terminal. The figure for demonstrating the downlink between C-BTS and D-BTS, and a terminal. The figure for demonstrating the downlink between C-BTS and D-BTS, and a terminal. The figure for demonstrating operation | movement of the mobile communication system concerning 2nd Embodiment. The figure for demonstrating the 1st usage method of the 1st frequency band used for the bidirectional | two-way communication between C-BTS and a terminal. The figure for demonstrating the 2nd utilization method of the 1st frequency band used for bidirectional | two-way communication between C-BTS and a terminal. The figure for demonstrating the 3rd usage method of the 1st frequency band used for bidirectional | two-way communication between C-BTS and a terminal. The flowchart for demonstrating operation | movement of C-BTS. The figure which showed the principal part of the management table of C-BTS. The figure which showed the principal part of the management table of C-BTS. The figure for demonstrating the mobile communication system which concerns on 3rd Embodiment. The figure for demonstrating the hand-over state of the mobile communication system concerning 3rd Embodiment. The figure for demonstrating a handover control procedure. The figure for demonstrating the other example of a handover control procedure. The flowchart for demonstrating the hand-over control operation | movement of a terminal. The figure which showed an example of the reception characteristic table of a terminal. The flowchart for demonstrating the process sequence for changing the threshold value of the receiving characteristic used for the handover control in a terminal. The flowchart for demonstrating the other process sequence for changing the threshold value of the receiving characteristic used for the handover control in a terminal. The flowchart for demonstrating the handover control operation | movement of C-BTS. The figure which showed an example of the handover management table of C-BTS. The figure which showed an example of the priority table of C-BTS. The figure for demonstrating the case where a terminal is allocated to D-BTS using the conventional handover control method. The figure for demonstrating the interference between base station D-BTS of the mobile communication system which concerns on 4th Embodiment. The figure for demonstrating the processing operation | movement for allocating a radio | wireless resource so that interference between base stations may be reduced. The flowchart for demonstrating operation | movement of C-BTS. The figure which showed the principal part of the management table of C-BTS concerning 4th Embodiment. The flowchart for demonstrating the interference determination process between base stations in C-BTS. The figure for demonstrating the allocation method of the radio | wireless resource which considered the interference between base stations. The flowchart for demonstrating the other operation example of C-BTS. The figure which showed the other example of the priority table of C-BTS. The flowchart for demonstrating the further another operation example of C-BTS. The flowchart for demonstrating the further another operation example of C-BTS. The flowchart for demonstrating the further another operation example of C-BTS. The figure for demonstrating the cell management method of the mobile communication system concerning 5th Embodiment. The figure for demonstrating the cell management method of the mobile communication system concerning 5th Embodiment. The figure for demonstrating the operation | movement at the time of the terminal standby between C-BTS, D-BTS, and a terminal. The figure for demonstrating the alerting | reporting signal which a terminal transmits. The figure for demonstrating the alerting | reporting signal which a terminal transmits. The figure for demonstrating the transmission method of the alerting | reporting signal of a terminal. The flowchart for demonstrating operation | movement of C-BTS. The figure which showed the principal part of the management table of C-BTS concerning 5th Embodiment. The flowchart for demonstrating other operation | movement of C-BTS. The figure which showed an example of the cell management table of C-BTS. The flowchart for demonstrating operation | movement of D-BTS.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Narrowband base station (C-BTS100), 101 ... Broadband base station (D-BTS), 102 ... Mobile communication terminal (terminal), 103, 104 ... Communication area, 105, 106, 107 ... Radio channel, 108, 109 ... communication line, 110 ... network, 301 ... first frequency band, 302 ... second frequency band.

Claims (17)

Wireless communication using one of the first radio channel groups in the first frequency band and one of the second radio channel groups in the second frequency band wider than the first frequency band A plurality of broadband base stations that transmit information signals using the second radio channel group, and a plurality of broadband base stations that perform radio communication using the first radio channel group In a mobile communication system consisting of a narrowband base station that communicates with
A mobile communication system, wherein one of the first radio channel groups is associated with the second radio channel group in advance. The narrowband base station is
Allocating means for allocating one of the second radio channel groups to a plurality of terminals,
A control signal including information necessary for receiving an information signal from the broadband base station using the first radio channel previously associated with each of the assigned second radio channel groups Transmitting means for transmitting to each terminal;
Comprising
Each of the terminals uses the control signal transmitted via the first radio channel previously associated with the second radio channel allocated by the allocating unit, and uses the control signal transmitted through the first radio channel. 2. The mobile communication system according to claim 1, wherein an information signal from the broadband base station is received through a radio channel.   The mobile communication system according to claim 1, wherein one of the first radio channel groups is associated with the plurality of broadband base stations in advance.   The narrowband base station uses the allocating unit to determine the information signal to be transmitted to the first terminal, which is one of the plurality of terminals, according to a predetermined communication rate and communication type. A radio channel for transmitting the information signal is selected from one of the second radio channel groups allocated to one terminal and an unused radio channel of the first radio channel group. The mobile communication system according to claim 2, wherein:   Each of the plurality of terminals notifies the narrowband base station of reception characteristics of a signal received by the terminal among signals transmitted from the plurality of broadband base stations and identification information of a transmission source of the signal The mobile communication system according to claim 2, further comprising:   The allocating unit allocates one of the second radio channel groups to each of the plurality of terminals based on at least the reception characteristics and the identification information notified from each terminal. The mobile communication system according to claim 5.   Each of the plurality of terminals notifies the narrowband base station of the reception characteristics of the signal and the identification information of the transmission source only for a signal having a reception characteristic equal to or greater than a predetermined threshold among the received signals. 6. The mobile communication system according to claim 5, wherein the threshold is changed based on a state of a signal received from one of the allocated second radio channel groups.   The assigning means is configured to send the plurality of terminals out of the second radio channel group based on the priority of each of the plurality of terminals and the reception characteristics and the identification information notified from each of the plurality of terminals. The mobile communication system according to claim 5, wherein one of each is assigned.   The assigning means assigns one of the second radio channel groups to each of the plurality of terminals so that the number of terminals transmitting information signals from each broadband base station is equalized. The mobile communication system according to claim 6. The assigning means includes
Based on the reception characteristics of the signal from the first broadband base station and the reception characteristics of the signal from the second broadband base station notified from the first terminal belonging to the communication area of the first broadband base station, Determining the presence or absence of interference from signals from the second broadband base station;
The first and second terminals based on the determination result of the presence / absence of interference and the priority predetermined for the second terminal belonging to the communication area of the first terminal and the second broadband base station The mobile communication system according to claim 5, wherein one of the first radio channel groups is assigned to at least one of the first radio channel groups. The narrowband base station is
Based on the reception characteristics of the signal from the first broadband base station and the reception characteristics of the signal from the second broadband base station notified from the first terminal belonging to the communication area of the first broadband base station, Determining the presence or absence of interference from signals from the second broadband base station;
6. The mobile communication system according to claim 5, wherein when it is determined that there is interference, transmission power when the second broadband base station transmits a signal is reduced. The narrowband base station is
Based on the reception characteristics of the signal from the first broadband base station and the reception characteristics of the signal from the second broadband base station notified from the first terminal belonging to the communication area of the first broadband base station, Determining the presence or absence of interference from signals from the second broadband base station;
6. The mobile communication system according to claim 5, wherein when it is determined that there is interference, the transmission power when the first broadband base station transmits a signal is increased. Each of the plurality of terminals comprises means for transmitting a notification signal including identification information of the terminal at a predetermined period,
Each of the plurality of broadband base stations transmits to the narrowband base station the reception characteristics of the broadcast signal received by the broadband base station among the broadcast signals transmitted from the terminals and the identification information of the transmission source of the broadcast signal. Comprising means for notification,
The narrowband base station is
The mobile terminal according to claim 2, wherein, for each of the plurality of terminals, the broadband base station to which the terminal belongs is recognized based on the reception characteristics and the identification information notified from the plurality of broadband base stations. Communications system.   The assigning means assigns each of the first radio channel groups to the plurality of terminals based on the reception characteristics and the identification information notified from the plurality of broadband base stations. The mobile communication system according to claim 13, wherein The narrowband base station is
The mobile communication system according to claim 13, wherein a transmission cycle of the broadcast signal of each terminal is changed based on the reception characteristics and the identification information notified from the plurality of broadband base stations. Wireless communication using one of the first radio channel groups in the first frequency band and one of the second radio channel groups in the second frequency band wider than the first frequency band A plurality of broadband base stations that perform wireless communication using the first wireless channel group and perform wireless communication that transmits information signals using the second wireless channel group; A base station apparatus that performs communication between
Allocating means for allocating one of the second radio channel groups to a plurality of terminals,
Contains information necessary for receiving an information signal from the broadband base station using the first radio channel previously associated with each of the second radio channels allocated by the allocating means Transmitting means for transmitting a control signal;
A base station apparatus comprising:   The assigning means assigns one of the second radio channel groups to each of the plurality of terminals based on reception characteristics measured at each terminal for signals transmitted from the plurality of broadband base stations. The base station apparatus according to claim 16.

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