WO1999037110A1

WO1999037110A1 - Tdma mobile communication system

Info

Publication number: WO1999037110A1
Application number: PCT/JP1999/000085
Authority: WO
Inventors: Shuichi Miyazaki; Hiroshi Usami
Original assignee: Hitachi, Ltd.
Priority date: 1998-01-14
Filing date: 1999-01-13
Publication date: 1999-07-22

Abstract

A TDMA communication system in which additional time slots of radio channels are assigned to base stations according to traffic. Occupied frequencies, without duplication between adjacent cells, are fixedly assigned to radio base stations (102-104), which calculate the usage of occupied frequency time slots assigned to them and send the calculated usage to a base station control system (101). In response to the usage of time slots received from the radio base stations, the base station control system (101) provides the base stations with additional frequencies slots that are shared among base stations.

Description

Specification

TDMA mobile communication system technical field

The present invention relates to a mobile communication system using a TDMAC Time Division Multiple Access (TDMAC) method, and more particularly to traffic control when sharing a radio frequency between different radio communication areas. Background art

In cellular mobile communications, the same occupied radio frequency is repeatedly allocated between different cells in order to increase the frequency utilization efficiency of the entire system. This allocation is fixedly allocated to each base station when constructing the base station, and occupied radio frequencies fi (i = l, 2, 3, ..., so that the base stations do not interfere with each other. I) is assigned in repeat units. Initially, it was common to assign one occupied radio frequency to one cell. FIG. 10 shows an example of a 7-cell repetition pattern in which 7 waves on the occupied radio frequency are allocated in repetition units. In recent years, when the traffic of a cell has increased due to an increase in the number of subscribers, etc., measures have been taken by adding another occupied radio frequency to one cell. That is, two occupied radio frequencies are fixedly assigned to one cell. Also in this case, an occupied radio frequency is assigned so that the base stations do not interfere with each other. For example, f8 which does not interfere with fl to f7 is assigned to the cell fl in FIG.

By the way, in Japanese Patent Application Laid-Open No. 62-197844, the same radio frequency is allocated to all radio zones in TDMA, and the channel in the TDMA frame of that frequency is allocated to each radio. Divide into zones A method for shortening the instantaneous interruption caused by frequency switching at the time of hand-off is described.

Traffic may be concentrated in a specific cell due to a sudden increase in new subscribers or events. As described above, in the conventional digital car telephone system, the traffic capacity is increased by increasing the occupied radio frequency allocated to each cell in the service provider. In the conventional TDMA system, one occupied frequency is allocated to several slots.

However, considering a TDMA system that divides into a very large number of time slots such as 64 time slots per radio frequency wave, the conventional method of adding channels in frequency units is fixed every time one radio frequency wave is added. As a result, 64 time slots increase. For example, as shown in Fig. 12, even if the traffic condition requires only one slot increase, if 64 time slots are fixedly added to one radio base station, 63 time slots will be required. The first problem is that resources also waste resources.

Further, in the conventional technology of allocating the same radio frequency to all the radio zones and dividing and allocating the channel in the TDMA frame of the frequency to each radio zone, it is necessary to allocate a time slot according to an increase in traffic. There is a second issue that has not been taken into account.

The purpose of the present invention is to appropriately increase the time-out at each base station according to the increase in traffic even when traffic is concentrated on a specific cell due to a sudden increase in new subscribers or events. By doing so, the resources can be used effectively. Disclosure of the invention

In order to solve the above problems, the present invention divides a service area into a plurality of cells. In a TDMA mobile communication system including a radio base station arranged at least one in the cell and a base station controller controlling the radio base station, radios that do not overlap between adjacent cells A frequency is fixedly allocated to the radio base station, and the radio base station calculates a utilization rate of a time slot of the occupied frequency allocated to the radio base station, and calculates the calculated time slot utilization rate by: The base station controller transmits to the base station controller, and the base station controller compares the time slot utilization rate received from each radio base station with a threshold value. It is characterized in that at least one of the time slots of the shared radio frequency shared by a plurality of cells is supplemented to the radio base station determined to require the allocation of the mouth.

Further, according to the present invention, in order to solve the above-mentioned problem, in the TDMA mobile communication system according to claim 1, the time slot utilization rate is determined based on a time slot of an occupied frequency assigned to the radio base station. It is characterized in that it is calculated based on the ratio of those used for mobile stations that communicate with.

Further, in order to solve the above problem, the present invention is characterized in that the base station control device has a database that stores an identifier indicating the radio base station and a time slot utilization rate corresponding to the radio base station. .

Further, in order to solve the above problem, the present invention fixedly assigns an occupied frequency that does not overlap between adjacent cells to the radio base station, and the radio base station reduces the time slot of the occupied frequency assigned to itself. Calculating a utilization rate, transmitting the calculated time slot utilization rate to the base station controller, the base station controller based on the respective time slot utilization rates received from the plurality of radio base stations, The wireless base station is supplemented with a time slot of a shared radio frequency shared by a plurality of cells. Further, according to the present invention, in order to solve the above-mentioned problems, the base station control device is configured to reduce a time slot of the shared radio frequency in proportion to a time slot utilization rate received from each of the plurality of radio base stations. It is characterized by replenishment. Further, according to the present invention, in order to solve the above problems, a radio base station calculates a time slot utilization rate of a shared radio frequency allocated to the radio base station, and calculates a time slot utilization of the calculated shared radio frequency. The base station controller compares the time slot utilization rate of the shared radio frequency received from each radio base station with a threshold value, and further transmits a time slot of the shared radio frequency. If it is determined that allocation of a slot is necessary, at least one of the time slots of another shared radio frequency is supplemented to the radio base station. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram showing an embodiment of a network configuration according to the present invention. FIG. 2 is a diagram showing a configuration example of a base station control device according to the present invention. FIG. 3 is a diagram showing a configuration example of a mobile station according to the present invention. FIG. 4 is a diagram showing a configuration example of a base station according to the present invention. FIG. 5 is a diagram showing a time slot configuration of a TDMA radio frame format of the shared radio frequency fx; j (j = 1, 2, 3,..., J) according to the present invention. FIG. 6 is a flowchart for explaining a time slot allocation method according to the present invention. FIG. 7 is a diagram showing a time slot management table of occupied radio frequencies according to the present invention. FIG. 8 is a diagram showing a time slot management table of a shared radio frequency according to the present invention. FIG. 9 is a diagram showing the relationship between the number of time slots and the number of radio frequencies when the present invention is applied. FIG. 10 is a diagram showing an example of a 7-cell repetition pattern in which seven waves on an occupied radio frequency are allocated in a repetition unit. FIG. 11 shows the frequency allocation according to the present invention. It is a figure showing an application example. FIG. 12 is a diagram showing the relationship between the traffic capacity and the number of occupied radio frequencies in the case of the 6-multiplex TDMA system. BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described with reference to the drawings. In the present invention, the radio frequency band allocated to the mobile communication service is distributed to the occupied radio frequency band and the shared radio frequency band for use. FIG. 11 is a diagram showing an example of frequency allocation according to the present invention. In the figure, Fi indicates the occupied radio frequency band, and FXj indicates the shared radio frequency band. Here, the occupied radio frequency band refers to a group of occupied radio frequencies, and most of them are a group of radio frequencies fixedly assigned when the base station is installed. Also does not change its assignment. On the other hand, a shared radio frequency band refers to a group of shared radio frequencies, and a shared radio frequency refers to a frequency that is commonly allocated among a plurality of cells. Is also good. In the present invention, this shared radio frequency is divided into, for example, 64 time slots and the like, and this time slot is shared between adjacent cells according to the traffic.

FIG. 1 is a diagram showing a network configuration according to the present invention. In the present embodiment, cells 110, 111, and 112 indicate cells (wireless communication areas) formed by the base stations 102, 103, and 104, respectively. Each cell is assigned a frequency so that they do not interfere with each other. For example, occupied radio frequencies fi (i = 1, 2, 3,...) Are assigned to each cell 110, 111, 112 according to the frequency repetition shown in FIG. The mobile stations 105 to 109, when present in an arbitrary cell, communicate with the base station forming this cell through a time slot on the occupied radio frequency. There is no time slot on the occupied radio frequency In this case, communication is performed using the time slot on the shared radio frequency. In other words, by allocating the vacant time slot of the shared radio frequency to the base station where traffic is concentrated and there is no vacant time slot on the occupied radio frequency, the occurrence of the vacant time slot is minimized. It is possible to increase the traffic capacity.

Here, the shared radio frequency f _x] '(]' = l, 2, 3,..., J) is shared by the base stations 102, 103, 104 in the service area. Although the shared radio frequency fxj is shared by three base stations in the embodiment shown in FIG. 1, it may be shared by more base stations. Alternatively, a plurality of shared radio frequencies may be prepared and used repeatedly in the system by the service provider.

In the embodiment shown in FIG. 1, the connection between the base stations 102 to 104 and the base station controller 101 is star-shaped with respect to the digital transmission line 114, but it is apparent that the connection can be applied to other connection forms such as a bus-shaped connection. It is. The transmission clock between the base stations 102 to 104 and the base station controller 101 is synchronized with one of the digital transmission lines 114.

The base station control apparatus 101 manages several base stations, that is, cells 110 to 112 formed by the base stations 102 to 104 collectively. The cell unit managed by the base station controller 101 is called a group cell 113 here. In each of the cells C1 to C3 managed by the base station controller 101, the time slots of the occupied radio frequencies fi (i = 1, 2, 3) individually allocated to the respective cells are shared by the present invention. Wireless communication is performed using the time slots of the radio frequency ixj (j = 1, 2, 3) as necessary. The number of cells to be managed as the group cell 113 is determined when the base station is arranged (at the time of designing the station), taking into account the topography, population density, etc. of the area forming the cell. Specifically, in urban areas with high population density, the number of cells managed as group cells is increased and cells are densely arranged. In rural areas with low population density, group cells are managed as group cells. Measures such as reducing the number of cells to be managed and arranging the cells roughly are taken. Next, a configuration example of each device according to the present invention will be described. FIG. 2 is a diagram showing a configuration example of the base station control device 101. As illustrated, the base station control device 101 includes a communication processing unit 200 and a control unit 201. In FIG. 2, for the sake of explanation, only base stations 102 and 103 are shown, and other base stations are omitted. The communication processing unit 200 has a multiplex processing unit 201 that processes communication information from each of the base stations 102 to 104, and an interface unit 203 that transmits communication information to the mobile switching network via the digital transmission path 115. . On the other hand, the control unit 201 controls the occupied radio frequencies fi (i = l, 2, 3, ..., 1) and the shared radio frequencies fxj (; i = l, 2, 3, ...) used by each base station. , J) and a resource management / assignment unit 204 that manages the assignment status with each time slot and assigns the time slot, and stores a resource management table (time slot management tables 206 and 207). It has a DB unit 205.

FIG. 3 is a diagram showing a configuration example of a mobile station. As shown in the figure, mobile stations 105 to 109 include a transmitting / receiving section 301 having a transmitting section 305 and a receiving section 306, an antenna 300 connected to the transmitting / receiving section 301, a switch section 302 having switches 307 and 308, and a predetermined It includes a control unit 304 for controlling the transmission / reception unit 301 and the switch unit 302 so that communication is performed in a time slot, and a human interface unit 303.

FIG. 4 is a diagram showing a configuration example of the base stations 102 to 104. As shown in the figure, the base station includes a transmission / reception unit 401 having a transmission unit 410 and a reception unit 411, an antenna 400 connected to the transmission / reception unit 401, and a communication having switches 412, 413, and an interface unit 405. A processing unit 402; a control unit 403 that controls the transmission / reception unit 401 and the communication processing unit 402 so that communication is performed at a predetermined time slot; a global positioning system (GPS) 406 and a GPS antenna 407 And Here, the control unit 403 As shown in the figure, a transmission quality detection unit 414 and a reception timing control unit 415 are provided. In addition, the Global Positioning System GPS 400 is provided to synchronize between base stations by absorbing the delay time difference of the digital transmission line 114 connected to each base station due to the difference in transmission line length. It is something that can be done. The base station establishes a clock in accordance with the GPS 400 time signal, thereby synchronizing between the base stations.

Next, the TDMA wireless frame format used in the present embodiment will be described. Fig. 5 is a diagram showing the time slot configuration of the TDMA radio frame format of the shared radio frequency fxj (j = 1, 2, 3, .., J) commonly used by the base stations 102 to 104. It is. The numbers 1 to 64 shown in the figure indicate time slot numbers. Each of the 64 slots can be used as either a communication time slot assigned to each user or a control time slot commonly used by many users. In this embodiment, for simplicity of description, all 64 slots are allocated to communication time slots. Here, the communication time slot refers to a time slot for transmitting user information such as voice, and corresponds to a conventional communication channel. Once allocated to a mobile station, the communication time slot is occupied by that mobile station until communication is terminated.

Next, the operation of the present embodiment will be described. The method for allocating a time slot according to the present invention is as follows.

(1) In the mobile station, the signal from the human interface unit 303 is modulated by the transmission unit 305 via the switch 307, and transmitted from the antenna 300.

(2) At the base station, the signal received by antenna 400

The signal is demodulated and sent to the switch 413. (3) The transmission quality detection unit 415 calculates the time slot utilization rate of the occupied radio frequency based on the reception signal from each mobile station processed by the communication processing unit 402.

FIG. 6 is a flowchart for explaining a method of allocating a time slot according to the present invention. The time slot utilization rate Ua (%) is calculated from the ratio of the total number of time slots in the occupied radio frequency allocated to each base station to the number of time slots used for communication as shown in the following equation (Step 1). ). (Time slot utilization rate Ua (%) 703) =

(Number of used time slots 704) / (Total number of time slots in occupied radio frequency 705) x lOO

That is, the transmission quality detection unit 415 of each base station regards a slot that is considered to be a low-power, no-signal slot as an idle time slot, obtains the number of time slots used for communication, and registers a previously registered occupied radio. It is determined by the ratio with the total number of time slots in the frequency.

(4) In FIG. 6, the time-slot utilization rate Ua (%) calculated by the transmission quality detection unit 415 is transmitted from the interface unit 405 to the base station control device 101 via the digital transmission path 114. Can be

(5) In the base station control apparatus 101 of FIG. 2, the time slot utilization rate Ua () transmitted from each base station is transmitted to the resource management Z allocating section 204 in the control section 201. The time slot utilization rate Ua (%) is stored in the time slot management table 206 of the occupied radio frequency in the DB unit 205 (Step 2).

The occupied radio frequency time slot management table 206 is configured, for example, as shown in FIG. The occupied radio frequency time slot management table 206 includes an occupied radio frequency 701, a base station number 702, a time slot utilization rate Ua (%) 703, a used time slot number 704, and a total time slot in the occupied radio frequency. The number of lots, such as 705, is stored. Fig. 7 shows the calculation results of the time slot utilization rate Ua () as an example. The time slot utilization rate Ua (¾) is stored, for example, by rounding up decimal places.

(6) In FIG. 2, the resource management Z allocating section 204 stores in the DB section the cells in which the time slot utilization rate Ua is 90% or more, that is, the base station numbers in which there is a lot of traffic and the number of available slots is insufficient. The time slot management table 206 for the occupied radio frequency in 205 is searched and the base station number is stored. If there is no base station with an insufficient number of available slots, the traffic is not enough to allocate a shared radio frequency, and the processing shifts to processing (13) (step 3).

(7) The resource management allocating section 204 obtains the required number of time slots S to be added to each base station based on the occupied radio frequency time slot management table 206, and obtains the occupied radio frequency time slot management table 206. To memorize. In Fig. 7, the time slot utilization rate Ua) of base station number 1 is 90% or more. Therefore, four time slots are allocated from the shared radio frequency. As described above, S may be a predetermined constant value, or the number of time slots to be allocated may be dynamically varied in consideration of the time variation of traffic in the cell. For example, it is well known that there is a time zone where congestion is expected empirically, but it is conceivable that the number of allocated slots is set to be larger than usual during that time. Further, a value proportional to Ua may be set as S.

(8) Resource management The Z allocating unit 204 performs time slot management of the occupied radio frequency in the DB unit 205 by dividing the total number of time slots S allocated to the cell units (group cells) managed by the base station controller 101. Determined from table 206 (step 4).

(9) Next, the resource management / allocation unit 204 allocates The total number of available time slots of the shared radio frequency fxj (; i = 1, 2, 3, .., J)) Tb is obtained from the shared radio frequency time slot management table 207 in the DB unit 205. (Step 5).

FIG. 8 shows an example of the configuration of the time-to-mouth management table 207 of the shared radio frequency. The shared radio frequency time slot management table 207 stores a shared radio frequency 801, the number of used time slots 802, the total number of time slots in the shared radio frequency 803, the number of available time slots 804, and the like. . The number of empty time slots is calculated by the following formula.

(Number of free time slots 804) =

(Total number of time slots in shared radio frequency 803) — (Number of used time slots 802)

The number of used time slots is always grasped for each base station by the resource management / allocation unit 204 and is stored in the time slot management table 207 of the shared radio frequency.

(10) Next, the resource management Z allocating unit 204 compares ∑S and ∑Tb, and if there is a shortage of free slots for the shared radio frequency fxj to be allocated to the cell (新しい Tb∑S), a new shared Add the radio frequency fx (j + l) to the group cell. Specifically,; fxj (j = 1, 2, 3, .., J), the shared radio frequencies are assigned to the group cells in order, and when the number of free time slots of the shared radio frequency becomes, for example, four, It is conceivable that fx (jU) is newly added as a shared radio frequency (step 6).

(11) If there is no vacant time slot in all shared radio frequencies (fxl to fxJ), call loss will occur. However, it is necessary to avoid a process in which some time slots can be assigned and all calls are lost. For this reason, the procedure for determining which call is to be blocked as “blocking process” is determined. For example, the following can be considered as a method of determining the procedure. (a) Calls with a long communication duration are utilized, and short calls are regarded as call losses.

(b) Priority is given to calls from base stations with high time slot utilization Ua, and call losses are made from base stations with low time slot utilization.

(1 2) In FIG. 2, the shared radio frequency fx] ′ (j = l) is assigned in order from the base station with the highest time-to-mouth utilization rate Ua stored in the time slot management table 206 of the occupied radio frequency of the DB unit 205. , 2, 3, .., J) free time slots (step 7).

(13) Update the time slot management tables 206 and 207. After the timer is activated, the process from (1) is repeated after a certain period of time (for example, when 120 seconds have elapsed assuming a normal voice call time) (Step 8).

(14) The resource management Z allocating section 204 of the base station control apparatus 101 sends the allocation signal of the evening mouth to each base station via the digital transmission line 114. The time slot assignment signal includes an identifier indicating one of the shared radio frequencies and an identifier indicating the time slot.

(15) The base station that has received the time slot assignment signal sends a time slot to the mobile station based on the shared radio frequency specified by the time slot assignment signal of the base station controller 101 and the time slot. Send an assignment signal of.

(16) In FIG. 3, the signal from the base station received by the antenna 300 of the mobile station is sent to the receiving section 306, where it is demodulated and passed through the switch 304 to the human interface section 303. Processing such as images or voices is performed within the system to exchange information with the user. Here, the control unit 304 controls the transmission / reception unit 301, the switch unit 302, and the human interface unit 303.

The present invention has been described in detail based on the embodiments. However, the present invention is not limited to this. For example, in the embodiment, the time slot utilization rate is measured in each base station, but may be collectively measured in the base station controller. In this example, the number of TDMA multiplexes is 64, but it is not necessary to be 64. It can also be applied to the TD-CDMA system that performs code division multiplexing within each time slot.

FIG. 9 shows the relationship between the number of time slots and the number of radio frequencies when the present invention is applied. In the past, radio resources were fixedly allocated to one cell, which caused many idle time slots. For example, in the example shown in Fig. 12, 63 timeslots became empty timeslots, and the efficiency of frequency utilization was reduced.

According to the present invention, since the radio resource of the shared radio frequency is shared by a plurality of base stations, an empty time slot not used in the cell C 1 is allocated to the other cells C 2 and C 3 in the service area. Free time slot can be reduced. This effect increases as the number of shared cells increases. For example, if the shared radio frequency is shared by 10 cells, the idle time slot can be reduced to 1/10. That is, in the example of FIG. 12, the empty timeslot of 63 timeslots can be suppressed to an average of 6 timeslots. As a result, the problem can be solved, and as a result, it is possible to promote effective use of wireless resources and increase traffic capacity. Industrial applicability

In a TDMA mobile communication system in which the number of time slots within one radio frequency is relatively large, the present invention uses a plurality of timeslots of a shared radio frequency that does not interfere with the existing occupied frequency in accordance with the traffic fluctuation of each cell. By allocating to cells, it is possible to promote effective use of available time slots and frequencies.

Claims

The scope of the claims

1. A TDMA mobile unit comprising: a radio base station, which divides a service area into a plurality of cells, and is arranged at least one "" 3 in the cell; and a base station control device δ controlling the radio base station. In communication systems,

An occupied frequency that does not overlap between adjacent cells is fixedly assigned to the radio base station,

The radio base station calculates a time slot utilization rate of the occupied frequency assigned to the radio base station, and transmits the calculated time slot utilization rate to the base station controller.

The base station controller compares the time slot utilization rate received from each radio base station with a threshold value, and determines that time slot allocation is necessary, and determines the time slot of a shared radio frequency shared by a plurality of cells. A TDMA mobile communication system, characterized in that at least one of them is supplemented to the five radio base stations determined to require the time slot allocation.

2. The TDMA mobile communication system according to claim 1, wherein the time slot utilization rate is a mobile station in which a time slot of an occupied frequency allocated to the radio base station communicates with the radio base station. TDMA mobile communication system, characterized in that it is calculated based on the ratio of those used for mobile communication.

3. The TDMA mobile communication system according to claim 1, wherein the base station control device has a database storing an identifier indicating the radio base station and a time slot utilization rate corresponding to the radio base station. A TDMA mobile communication system, comprising:

5 4. A service area is divided into a plurality of cells, and at least one radio base station is arranged in the cell, and a base station control device that controls the radio base station. In a TDMA mobile communication system comprising

The radio base station calculates a utilization rate of a time slot of an occupied frequency assigned to the radio base station, and transmits the calculated time slot utilization rate to the base station control device.

The base station control device may supplement the radio base station with a time slot of a shared radio frequency shared by a plurality of cells based on the respective time slot utilization rates received from the plurality of radio base stations. Features # 0 DMA mobile communication system.

5. The TDMA mobile communication system according to claim 4, wherein the base station control device performs a time slot of the shared radio frequency in proportion to a time slot utilization rate received from each of the plurality of radio base stations. A TDMA mobile communication system characterized by replenishing data.

56. The TDMA mobile communication system according to claim 4, wherein the radio base station calculates a time slot utilization rate of a shared radio frequency allocated to itself, and calculates the calculated shared radio frequency. Transmitting the time slot utilization rate to the base station controller,

The base station control device compares the time slot utilization rate of the shared radio frequency 0 received from each radio base station with a threshold value, and when it determines that it is necessary to allocate a further time slot of the shared radio frequency, the other shared radio frequency slot is used. A TDMA mobile communication system, wherein at least one of radio frequency time slots is supplemented to the radio base station.

7. TDMA consisting of a radio base station that divides the servicer into a plurality of cells and does not overlap between adjacent cells 5 a radio base station to which an occupied frequency is fixedly allocated and a base station controller that controls the radio base stations Mobile communication system At

The wireless base station transmits to the base station control device a calculating device that calculates the time slot utilization rate of the occupied frequency allocated to itself, and the evening slot usage ratio calculated by the calculating device. The base station controller compares the time slot utilization rate received from each wireless base station with a threshold value, and determines that the time slot needs to be replenished. A TDM / mobile communication system, comprising: an allocation device that allocates at least one time slot of a shared radio frequency shared by a plurality of cells to a radio base station determined to need to be allocated.

8. A radio base station, which divides a service area into a plurality of cells and does not overlap between adjacent cells, is fixedly assigned an occupied frequency, and includes a base station control device that controls the plurality of radio base stations. In TDMA mobile communication systems,

The radio base station includes: a calculating device that calculates a time slot utilization rate of an occupied frequency allocated to the radio base station; and a transmission device that transmits the time slot utilization ratio calculated by the calculating device to the base station control device. The base station control device transmits a time slot of a shared radio frequency shared by a plurality of cells to the radio base station based on the time slot utilization rate received from each of the plurality of radio base stations. TDMA mobile communication system characterized by control of replenishment.

9. The TDMA mobile communication system according to claim 8, wherein the calculating device calculates a usage rate of a time slot of a shared radio frequency, and the transmitting device uses the calculated time slot of the shared radio frequency. δ rate is transmitted to the base station controller, and the base station controller receives a time slot utilization rate and a threshold value of the shared radio frequency received from each radio base station. TDMA mobile communication characterized by replenishing at least one of the time slots of other shared radio frequencies to the radio base station when it is determined that it is necessary to further allocate time slots of the shared radio frequency. system.