Radio communication system

A radio communication system includes a line controller, a plurality of base stations connected to the line controller and a plurality of mobile stations connected to each of the plurality of base stations by radio communication line having control channel and communication channel, and each of the plurality of base stations includes a control unit for monitoring idle slot in the communication channel within a communication area of the base station. The control unit transmits the monitored information of the idle slot to the mobile station within the communication area of the base station at predetermined intervals by using the control channel and each mobile station can use an idle slot in the base station or, if there is no idle slot in the base station, in another base station based on the monitored information of the idle slot to make communication.

INCORPORATION BY REFERENCE

The present application claims priority from Japanese application JP2005-277262 filed on Sep. 26, 2005, the content of which is hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

The present invention relates to a radio communication system and-more particularly to a radio communication method and apparatus for carrying out a channel notification in a digital mobile communication system.

As one of the digital radio communication systems being put to practical use currently, a mobile communication system is defined in “REGIONAL DIGITAL MOBILE TELECOMMUNICATION SYSTEM”, ARIB STD-T79, Ver. 1, Association of Radio Industries and Businesses, Jun. 6, 2001, pp. 1-24.FIG. 11illustrates a general mobile communication system having a plurality of base station zones. InFIG. 11, numeral1101denotes a line controller,1102-1and1102-2base stations and103-1and1103-2base station zones, that is, communication areas of the respective base stations. The mobile communication system is so configured that the base station1102-1makes communication connection service with a plurality of mobile stations1104-1,1104-2, . . . ,1104-N residing in the communication area1103-1between the base stations or between the mobile stations via base station or directly between the mobile stations or makes communication connection service between a mobile station outside the communication area1103-1and another mobile station within the communication area1103-1.

The mobile communication system is also so configured that the base station1102-2makes communication connection service with a plurality of mobile stations1105-1,1105-2, . . . ,1105-M residing in the communication area1103-2between the base stations or between the mobile stations via base station or directly between the mobile stations or makes communication connection service between a mobile station outside the communication area1103-2and another mobile station within the communication area1103-2. The mobile stations are named generically as the mobile station1104or1105.

The line controller1101makes communication connection between the base stations and the plurality of mobile stations, maintenance and management of the service area in the digital radio communication system and controls an originating call from a mobile station or setting of communication routes. The line controller1101may be installed integrally with the base station1102-1or1102-2or separately from the base stations as shown inFIG. 11. In the latter case, the line controller1101is generally connected to the base stations1102-1and1102-2via transmission paths1106-1and1106-2such as cable or microwave communication lines. Further, the mobile stations described here contain radios or radio transmitter-receivers mounted in vehicles, portable radios and information terminal stations. In this example, only two base stations are shown, although in general the system includes a plurality of base stations and a large number of mobile stations but description is made with reference toFIG. 11showing the most simple configuration for convenience of description.

FIG. 5shows an example of assignment of frequencies for radio carriers permitted to be used in the digital mobile communication system using the digital radio technique defined in the standard ARIB STD-T79. InFIG. 5, in the uplink direction, that is, in the direction of transmission from the mobile station to the base station,112waves (f1, f2, . . . ) having a bandwidth of 25 KHz have been authorized for radio carriers f of about 262 to 266 MHz. Further, in the downlink direction, that is, in the direction of transmission from the base station to the mobile station,112waves (F1, F2, . . . ) having a bandwidth of 25 KHz have been authorized for radio carriers F of about 271 to 275 MHz separated by 9 MHz from 262 MHz in the uplink direction. Accordingly, the frequencies f1, f2, . . . and F1, F2, . . . can be used in the uplink and downlink directions, respectively, in communication of the digital radio communication system. The systems can use one or a plurality of radio carriers in accordance with the respective system scale. Further, in the standard ARIB STD-T79, a radio carrier W has been authorized so that a mobile station1104positioned within the communication area1103can make direct communication with a mobile station1104positioned outside of the communication area1103. The radio carrier W also has a bandwidth of 25 KHz and over ten waves (W1, W2, . . . ) have been authorized. In the radio communication system shown inFIG. 11, for example, the base station1102-1makes communication using pair waves of f1in the uplink direction and F1in the downlink direction and the base station1102-2also makes communication using pair waves of f3in the uplink direction and F3in the downlink direction.

Further, each radio carrier is divided into frames as shown inFIG. 6and each frame is further divided into four slots, to which a control channel C and communication channels S1, S2and S3are assigned. The communication channels S1, S2and S3are named collectively as communication channel S. One frame is 40 ms, for example. The control channel C is used to make connection control of radio communication line and the communication channel S is used to make talking and data communication.

JP-A-5-191856 discloses a method in which a number-of-calls counter for counting the number of originating calls and the number of calls that cannot attain connection due to the fact that communication channel is busy is provided in the radio base station and the numbers are broadcast to portable terminals (radio terminals) at all times or when connection cannot be attained in origination of call by each portable terminal.

JP-A-2005-136779 discloses a mobile communication system including a plurality of base stations. The system includes retrieval means for retrieving idle channel for each base station periodically to obtain idle channel information, information sharing means for notifying the idle channel information to other base stations to share the idle channel information with each other, and idle channel information notification means for notifying the idle channel information of other base stations to mobile terminals on the basis of the shared idle channel information.

Reference may be further made to JP-A-2003-250176 and JP-A-6-303662.

SUMMARY OF THE INVENTION

Referring now to an operation sequence shown inFIG. 12, operation of the radio communication system shown inFIG. 11is described.FIG. 12shows the operation sequence in case where there are idle slot in the communication channel. The base station transmits an idle signal to the mobile stations periodically to make the base station and the mobile stations be in the synchronized state. The same thing applies even to the following operation sequences. When the mobile station1104-1makes call originating operation in order to make talking with the mobile station1104-2, a call origination request is transmitted from the mobile station1104-1to the base station1102-1(step1201). When the base station1102-1receives the call origination request, the base station detects the idle situation of the communication channel S. When the base station detects an idle slot, the base station transmits a reception permitting signal to the mobile station1104-1using the control channel C (step1202) and at the same time the base station designates an idle communication channel S, for example, an idle communication channel S1(CH designation) to notify the designated communication channel to the mobile stations1104-1and1104-2(steps1203and1204). Thus, the mobile stations1104-1and1104-2are set to the communication channel S1to make talking (steps1205and1206). In this state, the communication channels S2and S3are still idle and accordingly other mobile stations1104can make talking.

Referring now toFIG. 13, an example of the operation sequence in case where there is no idle slot in the communication channel is described. The like elements to those shown inFIG. 12are designated by the like reference numerals. InFIG. 13, the operation sequence in steps1201to1206in which the mobile stations1104-1and1104-2use the communication channel S1to make talking is the same as that ofFIG. 12. Subsequently, when the mobile station1104-3makes call originating operation in order to make talking with the mobile station1104-4, an call origination request is transmitted from the mobile station1104-3to the base station1102-1(step1301). When the base station1102-1receives the call origination request, the base station detects the idle situation of the communication channel S. When there are idle slots (communication channels S2and S3are idle), the base station transmits a reception permitting signal to the mobile station1104-3using the control channel C (step1302) and at the same time the base station designates an idle communication channel S, for example, an idle communication channel S2(CH designation) to notify the designated communication channel to the mobile stations1104-3and1104-4(steps1303and1304). Thus, the mobile stations1104-3and1104-4are set to the communication channel S2to make talking (steps1305and1306).

Further, when the mobile station1104-5makes call originating operation in order to communicate with the mobile station1104-6, the mobile stations1104-5and1104-6are set to the communication channel S3to make talking (steps1307and1308) by the same processing procedures as described above (detailed description is omitted) since the slot S3is idle in the same manner as above.

Furthermore, when the mobile station1104-N makes call originating operation in order to make talking with the mobile station1104-7, for example, a call origination request is transmitted from the mobile station1104-N to the base station1102-1(step1309). When the base station1102-1receives the call origination request, the base station starts the operation for detecting the idle situation of the communication channel S. However, in the radio communication system, three slots S1, S2and S3in the communication channel S are set as shown inFIG. 6and the three slots are already used. Accordingly, since the communication channel S cannot be permitted to the mobile station1104-N any more, the base station1102-1transmits a request rejecting signal for connection to the mobile station1104-N (step1310).

In the foregoing description, communication between the base station1102-1and the mobile stations1104within the communication area1103-1of the base station1102-1has been described, although the communication between the base station1102-2and the mobile stations1105within the communication area1103-2of the base station1102-2is also made similarly.

In the radio communication system described above, when the mobile station operating in the base station transmits the call origination request signal to the base station, the base station detects the idle slot situation in the communication channel in response to the call origination request signal and when there is an idle slot, the base station transmits the reception permitting signal to the mobile station. When there is no idle slot, the base station transmits the call origination request rejecting signal to the mobile station. Accordingly, in the conventional radio communication system, in order that the mobile station makes communication, the mobile station first makes call originating operation and the base station then makes detection operation as to whether there is any idle slot in the communication channel or not and returns a response. Hence, the mobile station cannot make judgment as to whether the mobile station can make communication with another mobile station or not until the response from the base station is received. Accordingly, it is inconvenient for the mobile station in case of emergency and the reliability is possibly deteriorated. The realization of the radio communication system in which the above defects are improved is desired.

As described above, in the radio communication system, in order that the mobile station make communication, the mobile station first makes call originating operation and the base station then makes detection operation as to whether there is any idle slot in the communication channel or not and returns a response. Hence, the mobile station cannot make judgment as to whether the mobile station can make communication with another mobile station or not until the response from the base station is received. Accordingly, it is inconvenient for the mobile station in case of emergency and the reliability is possibly deteriorated. The realization of the radio communication system in which the above defects are improved is desired.

Further, when there is no idle slot in the base station to which the mobile station originating a call is registered, it is desirable that the mobile station can originate a call from the base station having an idle slot automatically or manually.

It is an object of the present invention to provide a radio communication system having high reliability and contributing to improvement of communication service or expansion of communication area.

It is another object of the present invention to provide a radio communication system which can grasp whether an idle channel is present or not.

It is still another object of the present invention to provide a radio communication system which can switch the communication area in which communication can be made.

According to an aspect of the present invention, the radio communication system comprises a line controller, a plurality of base stations connected to the line controller and a plurality of mobile stations connected to each of the plurality of base stations by radio communication line having control channel and communication channel. Each of the plurality of base stations includes a first control unit for monitoring whether there is any idle slot or not in a plurality of slots of the communication channel of the base station, and the first control unit transmits first resultant monitored information containing information as to whether there is any idle slot or not in the communication channel of the base station to the plurality of mobile stations within a communication area of the base station at first predetermined intervals by means of the control channel.

In the radio communication system, preferably, the first control unit of the base station acquires information as to whether there is any idle slot or not in the communication channel of other base stations and transmits it to the plurality of mobile stations within the communication area of the base station by means of the control channel.

In the radio communication system, preferably, the line controller includes a second control unit for monitoring whether there is any idle slot or not in a plurality of slots of the communication channel for each of the plurality of base stations to produce second resultant monitored information and an interface for transmitting the second resultant monitored information to each of the plurality of base stations.

Preferably, the line controller transmits the second resultant monitored information to each of the plurality of base stations at second predetermined intervals. Alternatively, the line controller transmits the second resultant monitored information to each of the plurality of base stations when the second resultant monitored information is changed.

Preferably, the first control unit of each base station monitors an occupancy situation of slots in the communication channel of the base station to produce the first resultant monitored information.

Preferably, each of the plurality of mobile stations includes a display unit for displaying information as to whether there is any idle slot or not in the communication channel of the base station and other base stations.

Preferably, each of the plurality of mobile stations includes an operation unit for permitting an operator of the mobile station to manually select any base station having idle slot on the basis of the displayed information as to whether there is any idle slot or not in the communication channel of the base station and other base stations.

Preferably, each of the plurality of mobile stations includes a third control unit for providing information as to whether there is any idle slot or not in the communication channel of the base station and other base stations and when the mobile station which is registered in the base station having no idle slot originates a call, the mobile station is automatically registered in another base station having idle slot on the basis of the information as to whether there is any idle slot or not in the communication channel of other base stations.

Preferably, the information as to whether there is any idle slot or not in the communication channel of other base stations is transmitted to the plurality of mobile stations within the communication area of the base station at third predetermined intervals.

According to another aspect of the present invention, a radio communication method in a radio communication system including a line controller, a plurality of base stations connected to the line controller and a plurality of mobile stations connected to each of the plurality of base stations by radio communication line having control channel and communication channel, comprises the steps of monitoring by each of the plurality of base stations whether there is any idle slot or not in a plurality of slots of the communication channel of the base station to produce first resultant monitored information and transmitting by the base station the first resultant monitored information to the plurality of mobile stations within a communication area of the base station at first predetermined intervals by means of the control channel.

In the radio communication method, preferably, the line controller monitors whether there is any idle slot or not in a plurality of slots of the communication channel of each of the plurality of base stations to produce second resultant monitored information and transmits the second resultant monitored information to each of the plurality of base stations at second predetermined intervals or when the second resultant monitored information is changed, and each of the plurality of base stations transmits the received second resultant monitored information to the plurality of mobile stations of the base station at third predetermined intervals.

Preferably, each of the plurality of mobile stations of each base station receives the first and second resultant monitored information and each of the plurality of mobile stations displays information as to whether there is any idle slot or not in the communication channel of the base station and other base stations in a display unit of the mobile station and permits an operator of the mobile station to manually select any base station having idle slot on the basis of the displayed information as to whether there is any idle slot or not.

Preferably, each of the plurality of mobile stations of each base station receives the first and second resultant monitored information and when the mobile station which is registered in the base station having no idle slot originates a call, the mobile station is automatically registered in another base station having idle slot on the basis of the second resultant monitored information.

According to still another aspect of the present invention, a line controller in a radio communication system including the line controller, a plurality of base stations connected to the line controller and a plurality of mobile stations connected to each of the plurality of base stations by radio communication line having control channel and communication channel, comprises a control unit for monitoring whether there is any idle slot or not in a plurality of slots of the communication channel of each base station, a memory for storing the information as to whether there is any idle slot or not in the communication channel and an interface for connection with the plurality of base stations, and the information as to whether there is any idle slot or not in the communication channel of each base station is transmitted to relevant base station or the plurality of base stations.

In the line controller, preferably, the information as to whether there is any idle slot or not in the communication channel is transmitted to the relevant base station or the plurality of base stations at predetermined intervals or when the information is changed.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention are now described with reference to the accompanying drawings. The like reference numerals are given to the like elements throughout the whole drawings.

An embodiment of the present invention is now described with reference toFIGS. 1A,1B,2and3. The radio communication system described in the embodiment is the same as that ofFIG. 11and accordingly detailed description thereof is omitted.FIGS. 1A and 1Bare block diagrams schematically illustrating an embodiment of a line controller1101and a base station1102.FIG. 1Aillustrates the base station1102, which includes a radio apparatus101and a control apparatus102. The radio apparatus101includes a transmission unit103for transmitting a signal from the base station1102to the mobile station1104by a radio carrier F1, for example, and a reception unit104for receiving a signal from the mobile station1104by a radio carrier f1, for example. The controller102includes a control unit105, a memory106and an interface108for connection with other devices.FIG. 1Billustrates the line controller1101, which includes a control unit109, a memory110and an interface111for connection with other devices. Further, the base stations1102-1and1102-2have the same configuration and accordingly description is made as the base station1102.

FIG. 2is a block diagram schematically illustrating the mobile station1104. The mobile station1104is shown inFIG. 2, while the mobile station1105has the same configuration and accordingly description is made using the mobile station1104. The mobile station1104shown inFIG. 2shows a radio communication apparatus using the pair waves of the radio carrier f1in the uplink direction and the radio carrier F1in the downlink direction and capable of making simultaneous transmission and reception. InFIG. 2, numeral201denotes an antenna for making transmission and reception to the base station1102,202a high-speed switch for making simultaneous transmission and reception,203a receiving unit,204a received-signal processing unit including a demodulator,205a speaker unit,206a control unit,207a memory,208an operation/display unit,209a microphone,210a transmission signal processing unit, and211a transmitting unit including a modulator. The operation/display unit208includes an operation part and a display part.

Operation of the present invention is now described on the basis of the operation sequence shown inFIG. 3. Reference numerals inFIG. 3correspond to those shown inFIG. 11. InFIG. 3, when the mobile station1104-1makes call originating operation in order to make talking with the mobile station1104-2, a call origination request is transmitted from the mobile station1104-1to the base station1102-1(step301). When the base station1102-1receives the call origination request, the base station detects the idle situation of the communication channel S. When there is an idle slot, the base station transmits a reception permitting signal to the mobile station1104-1using the control channel C (step302) and at the same time the base station designates an idle communication channel S, for example, an idle communication channel S1to notify the designated communication channel to the mobile stations1104-1and1104-2(steps303and304). Thus, the mobile stations1104-1and1104-2are set to the communication channel S1to make talking (steps305and306). In this state, the communication channels S2and S3are still idle and accordingly other mobile stations1104can make talking.

In the present invention, the base station1102-1notifies the idle communication channel to each mobile station1104in this state. This operation is described in further detail.FIG. 4shows a format of the control channel transmitted by the radio carrier F1in the downlink direction defined in the standard ARIB STD-T79, that is, in the direction of transmission from the base station1102to the mobile station1104. InFIG. 4, R represents a guard time for burst transitional response, P a preamble, CAC a control signal (containing PCH, BCCH, SCCH), PCH a broadcast channel, BCCH an information channel, SCCH a signaling channel for individual zone, E a collision control bit, SW a synchronous word, CI carrier information, CC a color code (interference measure code), and I an idle bit. InFIG. 4, numerical values represent the number of bits and the control channel includes 320 bits in total.

The control unit105of the base station1102, for example, the base station1102-1always grasps the talking state in the radio communication system within its own communication area1103-1and also grasps the idle state of the communication channel S, so that the control unit105stores the grasped resultant monitored information into the memory106as a communication channel idle slot situation table as shown in Table 1. Needless to say, the memory format is not limited to the table format. It may be any format as far as it is understood whether respective slots are idle or not. The idle slot situation in the communication channel can be grasped by monitoring the communication channel by the base station. That is, the base station always monitors whether there is any idle slot or not in response to the call origination request from the mobile station and accordingly the base station can always grasp the idle slot situation in the communication channel. Further, since the line controller also monitors the idle slot situation in the communication channel in each base station, the base station can produce the idle slot situation in the communication channel in the base station itself and other base stations if necessary on the basis of the resultant monitored information transmitted from the line controller.

TABLE 1Base Station 1102-1Slot NumberSlot is Idle or NotS1NotS2IdleS3Idle

Table 1 is a communication channel idle slot situation table showing the idle situation of the communication channels S1, S2and S3of one frame shown inFIG. 6. This table is monitored by the control unit105and is always updated in response to the talking state in the radio communication system. In Table 1, slots S2and S3are idle. The control unit105makes reference to the communication channel idle slot situation table at predetermined intervals, for example, at intervals of several tens to several hundreds milliseconds and transmits the contents thereof to all the mobile stations1104using the control signal CAC of the downlink direction control channel shown inFIG. 4(step307).

Each mobile station1104which has received the control signal grasps the idle state of the slots indicated by the slot numbers S1, S2and S3by the received-signal processing unit204and stores the idle state in the memory207. In order that an operator makes talking, the operator operates the operation/display unit208to read out the idle slot state from the memory207, so that the idle slot state can be displayed in the operation/display unit208. In step307ofFIG. 3, since the communication channel S1is occupied, the communication channels S2and S3are displayed in the operation/display unit208as idle slots. Further, since the mobile stations1104-1and1104-2are in the talking state at this time, this information is not received by them.

Then, when the mobile station1104-3is to make talking with the mobile station1104-4, the base station1102-1notifies in advance to each mobile station1104that the slots S2and S3are idle in step307as described above and accordingly the operator can understand easily that the mobile station1104-3can make talking at this time. Therefore, when the mobile station1104-3makes call originating operation, a call origination request is transmitted from the mobile station1104-3to the base station1102-1(step308). The base station1102-1which has received the call origination request transmits a reception permitting signal to the mobile station1104-3using the control channel C since the communication channels S2and S3have idle slots at this time (step309) and at the same time the base station1102-1designates the idle communication channel S2(CH designation) to notify the designated communication channel S2to the mobile stations1104-3and1104-4(steps310and311). Thus, the mobile stations1104-3and1104-4are set to the communication channel S2to make talking (steps312and313). The control unit105makes reference to the updated communication channel idle slot situation table to transmit the idle slot situation to all the mobile stations1104(step314) in the same manner as described above.

Similarly, when the mobile station1104-5is to make communication with the mobile station1104-6, the same steps as described above (detailed description thereof is omitted) are executed, so that the mobile stations1104-5and1104-6are set to the idle communication channel S3to make talking (steps315and316).

The control unit105of the base station1102-1monitors the communication channel slots and accordingly when the communication channel S3is used, the control unit updates the communication channel idle slot situation table stored in the memory106of the base station as shown in Table 2.

TABLE 2Base Station 1102-1Slot NumberSlot is Idle or NotS1NotS2NotS3Not

Table 2 shows the state where the slots S1, S2and S3are not idle. Accordingly, the control unit105of the base station1102-1makes reference to the communication channel idle slot situation table stored in the memory106to transmit to all the mobile stations1104that the slots S1, S2and S3are occupied, using the control signal CAC of the down control channel shown inFIG. 4(step317). Consequently, the mobile stations1104which do not make talking currently understand that there is no idle slot in the base station1102-1. Accordingly, since the mobile stations can understand the talking state in the current system without requiring the operation that the mobile station makes call originating operation and receives a request rejecting signal from the base station1102-1as shown inFIG. 13, the extremely convenient radio communication system can be realized.

The line controller1101manages the base stations1102-1and1102-2collectively. In other words, the control unit109of the line controller monitors the idle slot situation in the communication channel for each base station and produces information as to whether there is any idle slot or not in each base station as the resultant monitored information to be stored in the memory110of the line controller1101as a table representing the idle slot situation in each base station1102as shown in Table 3.

Accordingly, each base station1102can get the idle slot situation of other base stations from the line controller and notify the idle slot situation to the mobile stations within its own communication area if necessary. An example for notifying the idle slot situation to the mobile stations is now described.

Referring first toFIGS. 14A and 14b, operation for transmitting the idle slot situation as shown in Table 3 from the line controller1101to the base stations is described. For simplification of description, as shown inFIG. 14A, it is supposed that three base stations1102-1,1102-2and1102-3are connected to the line controller1101. InFIG. 14A, it is also supposed that the idle slot information shown in the slot situation table ofFIG. 14Ais stored in the line controller1101. In the example of the table, the slots S1, S2and S3of the base station1102-1are all occupied (busy) and its situation is shown as the information number1. Similarly, the idle situation of the slots S1, S2and S3in the base stations1102-2and1102-3is shown as the information numbers2and3. Further, inFIG. 14A, it is supposed that the mobile stations1104-1,1104-2,1104-3. . . are positioned within the communication area of the base station1102-1. Similarly, a plurality of mobile stations are also positioned within the communication areas of the other base stations1102-2and1102-3, although not shown.

FIG. 14Bshows an example of the operation for transmitting the idle slot information from the line controller1101to each base station. InFIG. 14B, the line controller1101transmits the contents of the information numbers1,2and3to the base station1102-1,1102-2and1102-3at intervals of 10 milliseconds, respectively. Accordingly, the idle slot situation information of the base station1102-1is transmitted to the base station1102-1at intervals of 30 milliseconds (=10 milliseconds×3). When there are N base stations, the period is 10 milliseconds×N. The value of 10 milliseconds is a mere example and it may be decided properly in accordance with specifications or requirements of the radio communication system. Alternatively, only when the idle slot situation is changed, the changed idle slot situation may be transmitted to the related base stations instead of transmitting the idle slot situation information at predetermined intervals or the idle slot situation information may be transmitted in response to a request from the base station or the mobile station.

Each base station transmits the received information of the monitored idle slots in its own communication channel to the mobile stations within its own communication area at predetermined intervals. The predetermined interval is several tens to several hundreds milliseconds as described above.

In the above example, only the idle slot situation information (information number1,2or3) of each base station is notified to each base station at predetermined intervals, although the idle slot situation information (information numbers2and3) of other base stations (1102-2and1102-3) may be added to the idle slot situation information of the base station to be transmitted to each base station simultaneously or at another timing. Consequently, each base station can notify the idle slot situation information in other base stations except itself to all the mobile stations within its own communication area at predetermined intervals or at any timing. The operator of each mobile station can operate the operation/display unit208of each mobile station to display the idle slot situation information of the base station and/or other base stations into the display part, so that the operator can understand the idle slot situation information.

FIG. 7is a schematic diagram illustrating another embodiment of the present invention. The reference numerals given to the elements ofFIG. 7are the same as those ofFIG. 11. In the embodiment ofFIG. 7, it is understood from the foregoing description made in the preceding embodiment that there is no idle slot in the communication channel S of the base station1102-1when a mobile station within the communication area1103-1of the base station1102-1, for example, the mobile station1104-N is to make talking with another mobile station, for example, the mobile station1105-1within the communication area1103-2of the base station1102-2. On the other hand, as described above, the line controller1101understands that there are idle slots in the communication channel S of the base station1102-2as shown in Table 3. Accordingly, when the mobile station1104-N moves from the communication area1103-1into the communication area1103-2, the mobile station1104-N can make talking with the mobile station1105-1within the communication area1103-2of the base station1102-2since there are idle slots in the communication channel S of the base station1102-2.

Operation of the embodiment ofFIG. 7is now described with reference to the flow chart ofFIG. 8. InFIG. 8, first, the mobile station1104-N starts to move from the communication area1103-1of the base station1102-1into the communication area1103-2of the base station1102-2and at the same time measures electric field level for reception of peripheral base station (step801). Measurement of the reception field level of the peripheral base station can be made, for example, by monitoring a gain control voltage of a high-frequency amplifier (not shown) of the receiving unit203of the mobile station1104-N by the control unit206and displaying it in the operation/display unit208.

When the reception field level reaches a predetermined value or more (that is the level at which voice can be heard), the mobile station1104-N can make talking with the base station1103-2(step802) and accordingly the mobile station1104-N switches the frequency (step803). That is, the pair frequencies f1and F1for the communication area1103-1of the base station1102-1are switched to the pair frequencies f3and F3for the communication area1103-2of the base station1102-2. The switching of the frequencies can be made by operating the operation/display unit208to control the control unit206so that an oscillation frequency of a frequency synthesizer is switched, for example. When the switching of the frequencies is completed, the processing proceeds to step810. In step810, the base station1102-2is captured. The capture processing is similar to that in step1002or1002′ ofFIG. 10and description thereof is omitted. When the capture of the base station is completed, the processing proceeds to step804.

In step804, the mobile station1104-N transmits a registration request of ID, for example, of the mobile station1104-N to the base station1102-2of destination. When the base station1102-2receives the ID registration request, the base station1102-2transmits registration completion notification to the mobile station1104-N (step805). In the registration of the mobile station to the base station, when there are a plurality of base stations, a registration table for mobile station in each base station is properly updated in response to movement of the mobile station. The method of registering the mobile station within the communication area is well known heretofore and accordingly detailed description thereof is omitted. Further, the registration processing of the mobile station is similar to registration reception1007and1017inFIG. 10. Thus, the mobile station1104-N can make talking with the mobile station1105-1within the communication area1103-2of the base station1102-2. Accordingly, the mobile station1104-N starts talking operation (step806). The operation sequence of talking is the same as that shown inFIG. 3and detailed description thereof is omitted. As described above, when there is idle slot in the communication channel of other base stations even if there is no idle slot in the communication channel S of the base station, the mobile station can understand the idle slot in the communication channel of other base stations on the basis of the notification of the idle slot from each base station and accordingly the mobile station can move (roam) to the communication area of other base stations and can make talking with the mobile station positioned within the communication area of the other base stations.

Still another embodiment of the present invention is now described with reference toFIGS. 9 and 10.FIG. 9shows the distribution of electric field strength in the vicinity of the boundary of the communication area1103-1of the base station1102-1and the communication area1103-2of the base station1102-2. InFIG. 9, the abscissa axis represents distance and the ordinate axis represents an electric field level. Numeral901-1represents a curve of the electric field strength in the communication area1103-1of the base station1102-1and901-2a curve of the electric field strength in the communication area1103-2of the base station1102-2. The communication areas1103-1and1103-2partially overlap each other. In this state, for example, when the mobile station1104-N is positioned at place A, the mobile station is positioned within the communication area1103-1of the base station1102-1and can make talking through the base station1102-1. However, when the base station1104-N is positioned at place B or C, the communication areas1103-1and1103-2overlap each other at the place B or C and accordingly the mobile station1104-N can select any of the base stations1102-1and1102-2to make communication.

Operation in this case is now described with reference to the operation sequence ofFIG. 10. First, when the mobile station1104-N is positioned at place B, the power supply of the mobile station1104-N is turned on (step1001). When the power supply is turned on, the mobile station1104-N captures electric waves of the base station1102-1of which the electric field strength at the place B is stronger (step1002). At this time, the mobile station1104-N operates the operation/display unit208so that the mobile station1104-N requests the base station1102-1to register its own ID (step1003). When the base station1102-1receives the registration request, the base station transmits the registration request to the line controller1101(step1004). When the line controller1101receives the registration request, the line controller updates a mobile station information table stored in the memory110to register the mobile station1104-N (step1105) therein. An example of the mobile station information table is shown in Table 4.

In Table 4, the mobile stations1104-1,1104-2, . . . are registered in the base station1102-1before and the mobile station1104-N is registered in this table thereafter. Further, the mobile stations1105-1, . . . ,1105-P are registered in the base station1102-2.

Next, the line controller1101transmits registration reception notification to the base station1102-1(step1006). When the base station1102-1receives the registration reception notification, the base station transmits the registration reception notification to the mobile station1104-N (step1007). Thus, the mobile station1104-N is placed under control of the base station1102-1.

In step1008, the electric field level for reception of peripheral base station is measured. That is, the mobile station1104-N measures the reception field level of peripheral base station in the same manner as described above to judge whether the enough electric field strength to be able to make transmission and reception under control of the base station1102-1can be acquired or not and confirms that reception can be made normally.

In step1009, the base station1102-1always monitors the idle slot in its own communication channel S as described in the preceding embodiment and notifies the idle slot information to the mobile stations1104placed under control of the base station as described with reference toFIG. 3(step1010). Accordingly, the mobile station1104-N can also receives the information and confirm the idle slot situation in the communication channel S of the base station1102-1(step1011).

Next, if it is grasped that there is no idle slot in the communication channel S of the base station1102-1already as shown in Table 2 when the mobile station1104-N is to make communication with another mobile station, the mobile station1104-N can get the idle slot situation in the communication channel S of peripheral base station from the line controller1101as shown inFIG. 3. For example, in Table 3, it is grasped that there are idle slots S2and S3in the base station1102-2. Accordingly, the mobile station1104-N switches the frequency (step1012). In the switching of the frequency in step1012, since the mobile station1104-N is positioned at place B shown inFIG. 9, the operation/display unit208of the mobile station1104-N is operated to control the control unit206so that the oscillation frequency of the frequency synthesizer is varied manually or the control unit105of the mobile station1104-N varies the oscillation frequency of the frequency synthesizer automatically to make switching to the pair radio carriers f3and F3for the communication area1103-2of the base station1102-2. Consequently, the mobile station1104-N can make communication with the base station1102-2. The operation sequence in case where the base station is changed over manually is described later with reference toFIG. 15. Then, in step1002′, the base station1102-2is captured. This operation is the same as that of step1002, although it is made as follows.

The mobile station1104-N transmits a registration request of ID thereof to the base station1102-2(step1013). When the base station1102-2receives the registration request, the base station further transmits the registration request to the line controller1101(step1014).

When the line controller1101receives the registration request, the line controller updates the mobile station information table shown in Table 4 stored in the memory110as shown in Table 5 and registers the mobile station1104-N to be place under control of the base station1102-2.

The line controller1101transmits the registration reception information to the base station1102-2(step1016). When the base station1102-2receives the registration reception information, the base station transmits the registration reception information to the mobile station1104-N,(step1017). Consequently, the registration of the mobile station1104-N placed under control of the base station1102-1is changed so that the mobile station is placed under control of the base station1102-2(step1018). In step1008′, the electric field level for reception of peripheral base station is measured in the same manner as in step1008. That is, the mobile station1104-N measures the reception field level of peripheral base station in the same manner as described above to judge whether the enough electric field strength to be able to make transmission and reception under control of the base station1102-2can be acquired or not and confirms that reception can be made normally.

As described above, when the mobile station is positioned at place B or C where a plurality of communication areas overlap each other, an idle slot in the communication channel can be used to make communication only by changing the base station in which the mobile station is registered without movement of the mobile station and accordingly the radio communication system having the extremely high freedom degree and the spreadable communication area can be realized.

In the embodiment ofFIG. 10, the operation sequence for changing the registration of the mobile station from a base station to another base station manually by the operator of the mobile station is now described with reference toFIG. 15.

Processing operation inFIG. 15is the same as inFIG. 10with the exception that steps1020and1021are added between the steps1011and1012ofFIG. 10. InFIG. 15, when it is confirmed that there is no idle slot in step1011, the operator manually operates the operation/display unit208to display candidates for base stations of destination or the idle slot situation of other base stations in the display unit in step1020. The operator selects any base station of destination from the displayed information and depresses a switch not shown in the operation/display unit208to select the base station in step1021. Consequently, the frequency is switched in step1012. Thereafter, the same processing operation as in steps1002′,1013to1017is performed and registration of the mobile station into the base station of destination is completed. In step1008′, the mobile station measures the reception field level of peripheral base station to judge whether the enough electric field strength to be able to make transmission and reception under control of the base station1102-2can be acquired or not and confirms that reception can be made normally.

As described above, according to the embodiment, whether the idle slot in the communication channel is present in the base station or not can be easily grasped in the mobile station within a predetermined communication area in the radio communication system having a plurality of base station zones. Further, the operator of the mobile station can operate to move the mobile station from the communication area or the mobile station can switch the communication area automatically to thereby make talking even at place or time that talking cannot be made, so that the radio communication system having the extremely high reliability and contributing to improvement of communication service or expansion of the communication area can be realized.

The foregoing description has been made to the embodiments of the present invention in detail, although the present invention is not limitd to the embodiments of the radio communication system described above and it is needless to say that the present invention can be widely applied to the radio communication system of SCPC type or any other type than that.

It should be further understood by those skilled in the art that various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.