JP2641441B2 - Mobile radio communication method and mobile radio communication system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a mobile radio communication system suitable for use in a premises such as a building, among other mobile radio communication systems, and capable of connecting to a premises extension telephone.

[Conventional technology]

As a communication system that makes the most of the advantages of wireless communication, a car telephone system has been put to practical use. The basic concept of this method is described, for example, in the literature (Ito and Matsuzaka, "Overview of the Car Phone System", Research and Application Report, Vol. 26, No. 7 (1977))
Familiar with.

On the other hand, so-called on-premise mobile radio communication systems that can be used in premises such as buildings, underground shopping malls, and airports have been studied in various places in recent years in order to expand the car telephone system and make radio telephones available in a wider service area. I have.

Unlike the cordless telephone currently in practical use, the above-mentioned in-plant mobile radio communication system has a building or office premises as one callable area, and can talk from any place in the area, The feature is that it is possible to move while talking.

With the practical use of such wireless communication systems,
It is fully anticipated that all extension telephones on the premises will be wireless. For this reason, the terminal installation density of the private mobile radio communication system is expected to be much higher than that of the current mobile phone or the like.

From the background described above, in the design of a private mobile radio communication system, there is a demand for a technology that makes effective use of the allocated radio frequency resources to the utmost. Therefore, it is necessary to devise ways to shorten the reach of radio waves and increase the reuse rate of the same frequency.

Examples of specific system concepts include literature (Sasaki, Hattori, Kadoma: "Multi-Zone Cordless Telephone System Configuration", 1986 IEICE Communications Division National Convention,
438), as shown in the mobile station (subscriber radio)
By restricting the transmission power, the range of radio waves can be limited to about several tens of meters, and wireless base stations that communicate with mobile devices are arranged at intervals of about several tens of meters throughout the entire campus. It is thought that several tens of channels can be used as radio frequency channels, but when a mobile station communicates with a radio base station, a so-called multi-channel access method is used in which an unused channel is selected from those channels and used. Is used.

[Problems to be solved by the invention]

The technology required for the mobile radio system is basically similar to that of the conventional mobile phone system, but differs in the radio channel assignment, the tracking exchange technology, and the like described below.

One of the points that the private mobile radio communication system physically differs from the conventional mobile telephone system is the total number of radio base stations. As described above, in a private mobile radio communication system, it is necessary to install radio base stations at intervals of several tens of meters, and the total number is enormous.

For this reason, as seen in the conventional car phone system,
It becomes difficult to control the frequency management of all the radio base stations collectively by the radio control station provided at the center.

In addition, the propagation characteristics of radio waves are often unknown in the premises, and even if they are known, their characteristics are expected to change significantly due to changes in the layout of the room or the like. Therefore, it is difficult to provide a fixed cell structure as seen in a conventional car telephone system.

One method for solving the above-mentioned problems is to introduce a concept of autonomous distributed processing in which radio base stations arranged at appropriate intervals autonomously manage and assign radio frequencies.

In the autonomous distributed processing method, it controls all wireless base stations,
There is no radio control station to manage and therefore no fixed cell structure. Instead, since each radio base station selects and uses a radio channel independently, a dynamic cell structure is inevitably created.

One method of the autonomous distributed processing method is disclosed in, for example,
An autonomous decentralized channel assignment scheme as described in -244137 is known.

In this conventional method, each wireless base station independently determines which wireless channel can be used, and based on learning based on past history, gives priority to selection of a wireless channel to be used for communication with a subscriber wireless station. This is a simple but extremely effective method.

However, autonomous processing can be performed by this method only with respect to the operation of allocating wireless channels.
Elemental technologies that address issues before the assignment of wireless channels,
For example, for a "subscriber" to determine which radio base station a certain subscriber radio station should communicate with, and for a "tracking exchange" associated with the movement of a subscriber radio station, a separate radio control station is used. Requires control and cannot perform autonomous processing.

[Means for solving the problem]

In order to solve such a problem, according to the present invention, a radio base station arranged at an appropriate interval preliminarily communicates with a nearby radio base station with use status and availability status of the radio channel in its own station. In addition, information on the internal state of the own station is exchanged with each other, and each wireless base station autonomously manages the wireless channel based on the information transmitted and received.

Similarly, in the case of a tracking exchange and a call response from a subscriber radio station, each radio base station exchanges data with a neighboring radio base station with the reception status of a signal from the subscriber radio station, and exchanges data. , Each radio base station itself determines whether or not it should respond.

[Action]

In the mobile radio communication system of the present invention, since information on the internal state of the neighboring radio base station is obtained, the following processes are executed independently for tracking exchange and calling from the subscriber radio station. it can.

〔Example〕

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

FIG. 1 is a conceptual diagram of a mobile radio communication system according to the present invention. Each of the radio base stations 21 to 27 is a subscriber radio station 3
It has service areas 11 to 17 in which communication with a certain level or higher is possible when communicating with 1,32. The service areas are arranged so that they do not overlap with each other as much as possible in an automobile telephone system or the like so that a portion not included in any service area is generated. Has been determined.

However, in the premises such as buildings where the present invention is mainly applied, there are many objects such as walls and rockers that absorb and reflect radio waves. Therefore, the service area of each wireless base station cannot be an ideal circle. Instead, it has a three-dimensionally complicated shape. In addition, there are often layout changes indoors,
The radio wave propagation characteristics and the shape of the service area change with each change.

However, it is impractical to relocate the wireless base station every time the indoor layout is changed, so that each wireless base station has an average so that there is no place outside the service area with some layout change. It is necessary to arrange at a higher density than the size of the service area. Therefore, the service area of each wireless base station is characterized in that there are many overlapping parts.

In such a situation, the subscriber radio station can communicate with a plurality of radio base stations, but on the other hand, if an adjacent radio base station attempts to communicate with the subscriber radio station using the same frequency, Mutual interference will occur. Also, even in radio base stations whose service areas do not overlap, interference may occur if the distance is short. for that reason,
A method of determining a radio frequency used by each radio base station is one of important considerations.

Conventionally known radio frequency determination methods include, for example, (1)
A method in which radio channels that can be used in advance are divided into a plurality of groups, and a radio channel is fixedly allocated to each radio base station while considering that the same radio frequency is not allocated to neighboring radio base stations (automobile telephones). method),
(2) Before a radio base station starts communication, monitor a radio channel to be used, confirm that the radio channel is free, and use the radio channel. A method of searching for an empty channel (cordless telephone method),
(3) The same as (2) above, but each wireless base station assigns a priority to the channel to be used, and changes the priority by learning based on the past channel use history. To search for empty channels in ascending order (Japanese Patent Laid-Open No. 61-244)
137).

In this embodiment, unlike any of the above-described systems, when a certain radio base station starts communication with a subscriber radio station, the radio base station and a nearby radio base station in a range in which the radio base station may cause interference are set in advance. Data is exchanged, and the method is performed after learning and confirming that the wireless base station does not cause interference with neighboring wireless base stations by using the wireless channel.

FIG. 2 shows an embodiment of the configuration of the mobile radio communication system according to the present invention. In the figure, 21 to 27 are radio base stations RB
S and 31 are subscriber radio stations RMS, 41 is a radio exchange RXU, 51 is a private branch exchange PBX, and 61 to 63 are conventionally used wired telephones. FIG. 2 shows an example in which seven RBSs are installed. However, actually, the RBSs must be arranged at intervals of about several tens of meters within an area where communication is possible.

The wireless exchange 41 exchanges between a wireless line and a wired line or between a wireless line and a wireless line. Literature (Sasaki, Hattori, Kadoma: "Multi-zone cordless telephone system configuration",
In systems such as # 438), the radio switching center 41 is in charge of radio line frequency assignment, tracking exchange, and the like. In the present embodiment, however, the radio switching center is a unit that performs only exchanges. Management such as tracking exchange is performed autonomously by each wireless base station.

For these managements, the wireless base station needs to grasp the wireless channel use status of the neighboring wireless base station. Therefore, each wireless base station has a function of exchanging data such as the usage status of the wireless channel with each other. This data exchange may be performed using a dedicated wired line connecting the respective wireless bases or using a specific wireless channel. If a wireless channel is used, each wireless base can exchange data only with neighboring wireless bases within a range that affects each other, and there is no influence on the assignment of the wireless channel due to the relationship of the reach of radio waves. Data exchange with a distant wireless base can be easily prevented.

On the other hand, if a dedicated wired line is used, both the speed and reliability of data transfer can be improved, but it is necessary to use some method to prevent data from being exchanged with a distant wireless base. This is because if data is exchanged between all the radio base stations, the amount of data to be transmitted and received increases exponentially as the total number of radio base stations increases, making it difficult to expand the network. Therefore, the following method is considered as an example.

First, each radio base has a transceiver for transmitting and receiving data as described above. The transceiver transmits data addressed to the neighboring radio base, receives data transmitted by the neighboring radio base, and has a function of reproducing and relaying data. have. That is, it receives data sent from an adjacent wireless base, takes it in itself, and simultaneously sends the same data to another adjacent wireless base. At this time, if another adjacent radio base does not exist, that is, if the radio base is located at the end of the relay chain, no further relay is performed. If there are a plurality of adjacent wireless base stations, the relay is performed to all the corresponding wireless base stations.

However, with only the above functions, the data transmitted by a certain wireless base is transmitted to the wireless bases throughout the premises, causing the above-described inconvenience. Therefore, the number of times of regenerative relaying may be limited to a certain number or less, and a counter indicating the number of times of regenerative relaying may be provided in transmission data. Each time the base station performs regenerative relay, the counter value is incremented or decremented by a fixed amount and relayed. Therefore, during replay,
Only the counter part of the data changes each time it is relayed. Further, when each radio base receives the data relay from the adjacent radio base, it checks the value of the counter, and if it reaches a predetermined value, does not perform any further relay. By providing such a mechanism, it is possible to prevent the data transmission from being performed in a wide range.

Next, one embodiment of the configuration of the radio base is shown in FIG. FIG. 1 shows an example in which the above-described data exchange is performed using a wireless channel. In the figure, 201 to 204 are transmission / reception units TRX. In this figure, four transmission / reception units are built in one radio base. It does not matter. The number of transmission / reception units is the number of subscriber radio stations that can be used simultaneously in the service area of the radio base.

Reference numeral 205 denotes a controller in the wireless base, which manages the operation state of each transmitting / receiving unit, assigns a wireless channel, and exchanges data with a nearby wireless base. 206
Is a transceiver for data exchange with a nearby radio base. 207 is an antenna.

FIG. 4 shows an example of the configuration of the transmission / reception unit 201 built in the radio base. In the figure, 701 is a microprocessor unit, 702 is a modulator of an audio signal, 7
03 is a frequency converter, 704 is a high frequency amplifier, and it is desirable that the transmission output can be varied. 705 is a multiplexer / demultiplexer, 7
06 is a frequency synthesizer, 707 is a receiving amplifier, 708 is a frequency converter, 709 is a bandpass filter, 710 is a demodulator for audio signals, 711 is an envelope detector for received signals, and is used to measure signal strength and communicate. It is provided to measure the amount of interference. Reference numeral 712 denotes a modem for exchanging digital control signals with the subscribed radio station.

FIG. 5 is a block diagram of an embodiment of a subscribed radio station. In the figure, 801 is an antenna, 802 is a multiplexer / demultiplexer,
803 is a frequency converter, 804 is a bandpass filter, 805 is a detector, 806 is a low-frequency amplifier, 807 is a frequency synthesizer, 808 is a microphone amplifier, 809 is a modulator, 810 is a frequency converter, 811 is a bandpass filter, 812 is a high frequency amplifier,
813 is a micro computer unit, 814 is a modem for digital signals, 815 is a sound generator for notifying an incoming call such as a bell buzzer, 816 is a battery for powering the RMS, 817
Is a dial keypad and display unit, 818 is a microphone, and 819 is a speaker.

Next, the operation of the embodiment shown in FIGS. 2 to 5 will be described in detail.

The radio bases shown in FIG. 3 are appropriately arranged at intervals of about several tens of meters as described above. Each radio base group manages the radio channel autonomously without receiving any other instructions. When starting communication with the subscribing radio station, the communication channel includes whether or not the own station should respond. Assignment operation is performed by original judgment. However, since the service area of each radio base usually overlaps with that of other radio bases, each radio base communicates data (internal information) on the management status of radio channels with neighboring radio bases.
Must be exchanged with each other to grasp the state of the nearby wireless base in advance.

For this purpose, each radio base has a controller 205 and a dedicated transceiver 206, as shown in FIG. 3, and exchanges internal information through a predetermined specific radio channel. Since many radio base stations share the same frequency, a packet communication method using CSMA (Carrier Detection Multiple Access), which is well known in the art, will be appropriate for data transmission.

The wireless channel used for data transmission is a control wireless channel provided separately from the plurality of wireless channels used for communication. Similar control channels are provided for a conventional car telephone system and cordless telephone system for calling, receiving, tracking, and the like. Even in this method, a control channel (hereinafter, referred to as a common control channel) is necessary for making and receiving calls, but the above-mentioned wireless channel for data transfer between wireless base stations is the same as the common control channel. May be used. However, since data exchange between wireless base stations is frequently performed, it is one idea to provide a wireless channel independent of a common control channel.

The contents to be included in the internal information include (1) the ID number of each wireless base, (2) the number of the wireless channel that each wireless base is currently using for communication with the subscriber wireless station, and (3)
The number of a wireless channel that is not used by its own station but is in use by a nearby wireless station and cannot be used because of its interference.

In order to obtain the data of the above (3), each radio base station uses any available transmission / reception unit that is not communicating with the subscriber radio station among the transmission / reception units of its own station. The wireless channels are searched in order to determine whether there is any channel that is receiving interference. Conversely, if there is no empty transmission / reception unit in the local station, new frequency allocation cannot be performed until one of the units becomes empty due to the end of communication, etc.
There is no need to search for the channel that is interfering.

As other internal information, (4) if there is a transmitting / receiving unit currently communicating with the subscriber's radio station, the signal strength from the subscriber's radio station, and (5) the radio channel that cannot be used due to interference. It is more convenient if the degree of the interference is included.

Each wireless base exchanges the above-mentioned internal information constantly, at regular intervals and every time the internal state changes, and constantly grasps the state of the nearby wireless base. At this time, if the signal strength can be measured at the same time as the reception of the internal information, it is possible to know the approximate value of the distance to the nearby wireless base from the signal strength. It is natural that closer radio base stations influence each other, and it goes without saying that a certain weighting of the internal information data according to the received signal strength is more convenient for the management of the radio channel. No. Based on the information obtained, each radio base that has grasped the state of the neighboring radio bases can determine which channel to use when it needs to allocate a radio channel for a call response from a subscribing radio station or for tracking exchange. In order to determine whether or not to use, priorities are set for the available channels. Since the usage status of the channel of the nearby radio base is known, for example, the literature (COX, REUDIN
K: “A Comparison of Some Channel Assignment Strat
egies in Large-Scale Mobile Communications System
s ", IEEE Trans., vol. COM-20, No. 2, Apr., 1972).
If the Nearest Neighbors method is applied, it is possible to greatly reduce the call loss rate as compared with the conventional method of fixedly assigning wireless channels.

In addition, according to the present invention, the number of a wireless channel that cannot be used because a nearby wireless base station is receiving interference can also be obtained as information.
It would be possible to create a method to further reduce the blocking rate compared to ours method.

Next, with respect to the operation of the present embodiment, a specific operation procedure will be specifically described taking a call from a subscribing wireless station and a tracking exchange as an example.

(A) Calling from a subscriber radio station An example of a procedure when a subscriber radio station makes a call from any place where a call can be made is shown in FIG.

When the owner of the subscriber's radio station signals the intention to make a call from the dial keypad 817, the microcomputer unit
813 sets a synthesizer 807 to a frequency of a predetermined common control channel, modulates a call signal by a modem 814, a modulator 809 for a voice signal, a frequency converter 810, a band-pass filter 811, and a high-frequency amplifier. 812, the signal is transmitted through the multiplexer / demultiplexer 802 and the antenna 801.

On the other hand, if each wireless base has a free space in the transmitting / receiving unit,
It is used to monitor the common control channel. Therefore, the call signal will be successfully captured by the radio base having an available transmission / reception unit.

However, as already described, the service areas of the radio bases often overlap each other, and therefore the above-mentioned call signal may be captured by a plurality of radio bases.

However, since a plurality of wireless bases are not allowed to respond to the call signal, each wireless base that has captured the call signal transmits data (call capture signal) relating to a capture state such as the strength of the call signal between the wireless bases. Interact with each other. Further, based on the result, the call capturing state of the neighboring radio base station is compared with that of the local station, and it is independently determined whether or not the local station should respond to the call from the subscriber radio station. As the criterion, the received signal strength of the call signal is considered to be the most appropriate, but other than that, the number of available wireless channels, the availability of transmission / reception units, and the like may be added. However, all radio bases need to follow the same criteria.

When transmitting and receiving the call capturing signal, the wireless base of the other party to be exchanged cannot be specified. Therefore, the call capturing signal is subjected to error correction coding and broadcast to a nearby wireless base. Therefore, even if the above procedure is followed, a single radio base does not always respond to a call to a subscriber radio station due to a transmission error or the like.

Therefore, when each radio base station determines that it should respond to the subscriber radio station, it sends a call response signal including the number of the radio channel to be used to the subscriber radio station. Also, if a call response signal is received from the subscriber radio station or from a plurality of radio bases, a confirmation signal may be returned only to the radio base that first received the call response. If there is no call response from any of the radio bases, a call signal may be sent again after a predetermined time.

Next, the subscriber's radio station receiving the call response signal shifts to the radio channel specified in the signal. The radio base station also sets an empty transmission / reception unit to the specified radio channel, and connects the radio exchange and the subscriber radio station.

When a call is accepted, the wireless switching center does not perform any operation, but merely connects to the private branch exchange 51. The dial signal transmission process after the establishment of the communication line between the subscriber radio station and the radio base is omitted because it is not different from a conventional cordless telephone or the like.

(B) Tracking exchange After the subscriber radio station starts communication with the radio base according to the above-described procedure, the position of the subscriber radio station is changed by the movement of the user of the subscriber radio station. It may be possible to get out of the service area. At this time, the radio base constantly monitors the signal strength of the subscriber radio station, and when the signal strength decreases, requests another neighboring radio base to take over the communication with the subscriber radio station. For this purpose, first, the first wireless base currently communicating with the subscriber wireless station broadcasts a tracking exchange request signal to a nearby wireless base through a predetermined wireless channel (see FIG. 7).
The contents of the tracking exchange request signal include a radio channel number during communication with the subscriber radio station, a current signal reception strength of the subscriber radio station, an ID number of the subscriber radio station, and the like.

On the other hand, the second radio base receiving the tracking exchange request signal from the neighboring radio base monitors the subscriber's radio station by using the transmission / reception unit if there is a vacant transmission / reception unit in its own station. Etc., and returns the result as a tracking exchange response signal. If there is no empty transmission / reception unit, no response is made, or a signal indicating that no response can be made may be returned. Further, if the subscriber's wireless station is monitored using an available transmission / reception unit and it is determined that the signal strength is not sufficient for communication, the tracking exchange response signal need not be transmitted.

Next, the first wireless base station that has transmitted the tracking exchange request signal,
A tracking exchange response signal returned from a neighboring wireless base station is compared, and a wireless base station that best captures the signal of the subscriber station is selected and a tracking exchange control signal is transmitted. At the same time, the mobile station notifies the subscriber wireless station that the tracking exchange is to be performed through the wireless channel currently used for the call with the subscriber wireless station. Further, the first radio base transmits to the radio switch,
The identification number of the wireless base of the tracking exchange destination is notified, and a request for switching the wired line is made. Thus, the chase exchange is completed.

〔effect〕

As described above, if each wireless base station closely exchanges data with the neighboring wireless base stations regarding the usage status of the wireless channel, each wireless base station can autonomously manage the wireless channel. Therefore, there is no need to provide a radio control station that controls and manages all systems. In addition, when performing communication with the subscriber wireless station, each wireless base station can predict in advance the amount of interference given to other base stations, and efficient frequency allocation can be performed.

Further, since each wireless base station dynamically manages the wireless channel and the service area, it is not necessary to change the arrangement of the wireless base stations even when the radio wave propagation condition changes, such as a change in the indoor layout.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing how service areas of the present system overlap, FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention, and FIG. 3 is a block diagram of a radio base station according to an embodiment of the present invention. FIG. 4 is a block diagram showing a configuration of a transmission / reception unit in the radio base station, FIG. 5 is a block diagram showing a configuration of a subscriber radio station according to one embodiment of the present invention,
FIG. 6 is a flowchart showing a calling operation of one embodiment of the present invention, and FIG. 7 is a flowchart showing a tracking exchange operation of one embodiment of the present invention. 21-27 Radio base station (RBS), 31-32 Subscriber radio station (RMS), 41 Radio exchange station (RXU), 51 Private branch exchange (PBX).

Continuation of the front page (56) References JP-A-63-164722 (JP, A) JP-A-61-112443 (JP, A) JP-A-60-70835 (JP, A)

Claims (7)

(57) [Claims] 1. A mobile radio communication method in which a plurality of radio base stations selectively use a plurality of shared radio channels to communicate with a mobile radio device in a communication area, wherein each radio base station includes By exchanging internal information indicating the radio channel usage status of each station with another radio base station via a radio line, the radio channels that can be used by the own station are grasped, and the The radio base station that has received the call signal exchanges, via a radio line, a control signal indicating the reception strength of the call signal with another nearby radio base station, and compares the reception strength of the local station with other radio base stations. It is determined whether or not the own station should respond to the call signal from the relationship with the reception strength at the station. Sends a call response signal specifying a specific wireless channel, and The mobile radio device that has transmitted the call signal communicates with a radio base station that has determined to respond to the call signal through a specific radio channel specified by the call response signal. Mobile radio communication method. 2. The method according to claim 1, wherein each of the radio base stations communicates with other nearby radio base stations by identifying the own station, identifying the radio channel in use by the own station, and interfering with other stations. 2. The mobile radio communication method according to claim 1, wherein internal information including identification information of a radio channel in an unusable state is communicated via a radio line. 3. The radio base station sets priorities for the available radio channels, and allocates a radio channel specified according to the priorities to a mobile radio device that has transmitted the call signal. 3. The mobile radio communication method according to claim 1 or 2, wherein: 4. Each of the radio base stations includes, when reception strength from a mobile radio device during communication is reduced, an identification number of the mobile radio device during communication and identification information of a radio channel in use. A tracking request signal is sent out to the wireless line, and another wireless base station that has received the tracking request signal observes the reception strength from the mobile radio device during the call, and sends a tracking request response signal indicating the observation result. A wireless base station that has transmitted to the wireless line and transmitted the tracking request signal selects another neighboring wireless base station to be a takeover destination based on the reception strength observation result notified by the tracking request response signal. And
2. The wireless base station according to claim 1, wherein the communication with the communicating mobile wireless device is taken over.
4. The mobile radio communication method according to claim 3. 5. A non-response or tracking reject signal is transmitted when another neighboring radio base station receiving the tracking request signal cannot track or take over the communicating mobile radio device. The mobile radio communication method according to claim 4, wherein: 6. A radio base station in a mobile radio communication system comprising a plurality of radio base stations having a plurality of shared radio channels, a radio switching station connected to each of said radio base stations, and a plurality of mobile radios. A plurality of terminal transmitting / receiving units for wirelessly communicating with a mobile wireless device, a control transmitting / receiving unit for transmitting / receiving a control signal via a wireless line, and a control unit for controlling each of the transmitting / receiving units The control unit periodically transmits and receives internal information indicating a wireless channel usage state of each station to and from another nearby wireless base station via the wireless line by the control transmitting / receiving unit. Means for selecting and storing a wireless channel usable by the own station, and receiving a call signal from a mobile wireless device via the wireless line by the control transmitting / receiving unit. Means for exchanging a control signal indicating the reception strength of the call signal with another wireless base station in the vicinity, and a relation between the reception strength at the own station and the reception strength at another station. Determining whether or not the own station should respond to the call signal, and if it is determined that it should respond to the call signal, via the control transmission / reception unit, identifies the available After sending a call response signal specifying the wireless channel of
A radio base station comprising: a means for outputting a control signal for operating on a specific radio channel designated by the call response signal to one of the terminal transmission / reception units. 7. Each of the terminal transmission / reception units has means for measuring a signal reception intensity from a wireless mobile device, and the control unit is configured to control the mobile radio communication in any of the terminal transmission / reception units. When a decrease in the reception strength from the mobile station is detected, the control transmitting / receiving unit sends, via a radio circuit, a tracking request including the identification number of the mobile radio apparatus whose signal strength has decreased and the radio channel identification information in use. Means for transmitting a signal, and using one of the terminal transmission / reception units when receiving a control signal for a tracking request transmitted by another radio base station via the control transmission / reception unit. Means for observing the reception strength from the corresponding mobile radio, and transmitting a tracking request response signal indicating the observation result of the reception strength via the radio line by the control transmitting / receiving unit. When the above-mentioned tracking request signal is transmitted from the own station, based on the result of observation of the reception strength notified by the tracking request response signal from the other station received by the transmitting / receiving unit for the terminal, the other handover destination neighbors are taken over. Means for selecting one of the radio base stations and transmitting a control signal to the radio base station for taking over the communication with the mobile radio having the reduced reception strength. Item 7. The wireless base station according to item 6.