JP2002281557A - Digital mobile communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital mobile communication system with which a mobile station moved outside the communication area of a base station can perform direct communications with a mobile station inside the communication area of the base station. SOLUTION: When the mobile station located outside the communication area detects the receiving level of a frequency F2 from the base station with a receiving level detecting part 27 and judges that the level is lower than a reference level by using a first deciding part 34, the mobile station switches the frequency in a receiving demodulating part 26 to a frequency F1 for direct communications and performs transmission to the mobile station inside the area. Each of mobile stations periodically monitors the signal of the frequency F1 and when such a signal is received, the request signal of direct communications is transmitted to the base station by the frequency F1. Then, a direct communication mode is started. The mobile station out of the area receives transmitted signals from a plurality of mobile stations inside the area, and on the basis of such receiving level data, the mobile station of the best receiving level data is selected by a second discriminating part 35. Then, direct communications are performed with that mobile station by the frequency F1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a digital mobile communication system, and more particularly, to a digital mobile communication system comprising one base station and a plurality of mobile stations.
The present invention relates to a digital mobile communication system having a direct communication mode function in which an arbitrary mobile station that has moved out of the communication area of a base station directly communicates with a mobile station in the area without relaying the base station.

[0002]

2. Description of the Related Art In a digital mobile communication system including one base station and a plurality of mobile stations, a two-wave simplex system is adopted as a communication system. As shown in FIG. 5, in the two-wave simplex system, the base station 51 and each of the mobile stations 52, 53, and 54 communicate with each other at two types of carrier frequencies F1 and F2.
The transmission from the base station 51 to the base station 51 (uplink) uses the frequency F1, and the transmission from the base station 51 to the mobile stations 52, 53, 54 (downlink).
Uses the frequency F2. Each mobile station is a base station
Under the control of the base station 51, communication between mobile stations (relay communication mode) is established by relaying the base station 51.

Accordingly, when the mobile station 54 moves out of the communication area a of the base station 51, communication with the base station 51 becomes impossible, so that the communication between the mobile stations relaying the base station 51 as described above. Becomes impossible. As a countermeasure in this case, there is a method of manually switching to the direct communication mode.
Mobile stations that have moved out of the communication area a of the
To leave the control of 51, it is possible to communicate with each other in the direct communication mode using the frequency F1.

However, in the case of this method, for example, even if the mobile station 54 which has moved out of the area of the communication area a tries to communicate with the mobile station 53 which is in the communication area a of the base station 51, the mobile station 53 will , Under the control of base station 51,
Neither frequency F1 nor frequency F2 could be used arbitrarily, and as a result, communication with the mobile station 53 could not be performed.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and a mobile station having moved out of the communication area of a base station is
It is an object of the present invention to provide a digital mobile communication system that enables direct communication with a mobile station within a communication area of a base station.

[0006]

In order to solve the above-mentioned problems, the present invention provides a first mobile station transmitting means for transmitting data at a first carrier frequency F1, and a second carrier frequency F2.
A plurality of mobile stations comprising first mobile station receiving means for receiving and demodulating and decoding the transmission signal of the first and second base stations; and base station receiving means for receiving and demodulating and decoding the transmission signal of the first carrier frequency F1. A single base station including a base station transmitting means for transmitting data at the second carrier frequency F2, and a two-wave simplex signal for performing communication between the mobile stations by relaying the base station. In a digital mobile communication system of a system, a second mobile station receiving means for receiving, demodulating and decoding a transmission signal of the first carrier frequency F1, receiving the second mobile station receiving means, Switching means for switching between the first mobile station receiving means and a communication area determining means for determining, based on a received signal received by the mobile station, whether communication with a partner transmitting station is possible based on the quality of the received signal. ,
The mobile station communicates with the second carrier frequency F from a base station.
2 based on the received signal, the communication area determination means determines whether the mobile station is located within an area where communication with a base station is possible or outside the area where communication is not possible. The switching means switches from reception by the first mobile station receiving means to reception by the second mobile station receiving means, transmits a communication request to the mobile station within the service area by the first carrier frequency F1, and performs the mobile operation within the service area. The station periodically switches from the reception by the first mobile station reception means to the reception state by the second mobile station reception means by the switching means, and uses the first carrier frequency F1 transmitted by the mobile station outside the service area. Receiving the communication request, switching from reception by the first mobile station reception unit to reception status by the second mobile station reception unit by the switching unit, and A serial mobile station, and not out of range of the mobile station under management, and the first carrier frequency F1 to perform direct communication with the transceiver.

[0007] The communication area determination means is provided in the mobile station and detects a level of a received signal of the second carrier frequency F2 or the first carrier frequency F1; The first determination unit compares the reception level with the reference level, and determines that communication with the receiving station is impossible when the reception level is equal to or lower than the reference level.

Alternatively, the communication area determining means detects a bit error rate of a decoded signal in a received signal of the second carrier frequency F2 or the first carrier frequency F1 provided in the mobile station. Rate detection unit, comparing the detected bit error rate with a reference value,
When the bit error rate is equal to or more than the reference value, the first determining unit determines that communication with the receiving station is impossible.

The mobile station is capable of communicating with the mobile station outside the service area the data of the reception level of the communication request signal at the first carrier frequency F1 transmitted by the mobile station outside the service area by the first determination unit. If it is determined that communication is possible, an out-of-service-station detection notification signal for shifting to the direct communication mode is transmitted to the base station.

Alternatively, the mobile station transmits the bit error rate data of the communication request signal at the first carrier frequency F1 transmitted by the mobile station out of service to the mobile station out of service by the first determination unit. It is determined whether or not communication is possible, and if it is determined that communication is possible, an out-of-service-station detection notification signal for shifting to the direct communication mode is transmitted to the base station.

[0011] The mobile station is provided with a memory unit for storing data of the reception level detected by the reception level detection unit,
The first carrier frequency F transmitted by the mobile station out of range
The data of the reception level of the communication request signal according to 1 is stored in the memory unit, and the data of the reception level is read from the memory unit in response to a request from the base station, and the out-of-service area is read out by the first determination unit. It is determined whether communication with the mobile station is possible, and the result of the determination is transmitted to the base station.

[0012] Alternatively, the mobile station is provided with a memory unit for storing data of the bit error rate detected by the bit error detection unit, and the first mobile station outside the service area transmits the data.
The data of the bit error rate of the communication request signal at the carrier frequency F1 is stored in the memory unit, and the data of the bit error rate is read from the memory unit in response to the request of the base station, The determination unit determines whether communication with the mobile station outside the service area is possible, and transmits the determination result to the base station.

[0013] The mobile station receives the first carrier frequency F1 emitted by each of the plurality of mobile stations within the service area,
A second determining unit that determines a mobile station of the best data from among the respective reception level data, wherein the mobile station outside the service area is directly connected to the mobile station of the best data determined by the second determining unit; Perform communication.

Alternatively, the first carrier frequency F1 generated by each of the plurality of mobile stations within the service area is provided to the mobile station.
Is provided, and a second determination unit that determines the mobile station of the best data from among the data of the respective bit error rates is provided, and the mobile station out of the service area determines the best mobile station determined by the second determination unit. Communicates directly with the data mobile station.

The transmission signal of the first carrier frequency F1 issued by the out-of-service mobile station includes data designating the mobile station of the communication partner, and the specified data in the signal that has received the transmission signal is included in the transmission signal. The mobile station is provided with a third determination unit that determines whether the mobile station belongs to the mobile station, and the mobile station that determines that the data specifies its own station directly communicates with the mobile station outside the service area.

After the direct communication is started, when the communication area determining means determines that the communication area is within the service area, the switching means switches the reception from the second mobile station receiving means to the reception by the first mobile station receiving means. Switch to.

The shift to the direct communication is performed by an instruction from the base station using a base station transmitting means for transmitting data at the second carrier frequency F2.

A display unit is provided in each of the mobile stations, and when the communication area determination means determines that the mobile station is out of the service area, the fact is displayed.

Each of the mobile stations is provided with a voice section, and when the communication area determination means determines that the mobile station is out of the service area, a voice or alarm sound is generated to that effect.

The mobile station in the service area terminates the direct communication when the communication time of the direct communication elapses a predetermined time, and relays the base station to perform communication between the mobile stations. Return to.

The base station forcibly terminates the direct communication with the mobile stations within the service area at an arbitrary timing, and returns to the mode in which the mobile stations communicate with each other by relaying the base station.

[0022]

Embodiments of the present invention will be described below with reference to the drawings based on embodiments. FIG. 1 is a conceptual explanatory view of a digital mobile communication system according to the present invention, which is a two-wave simplex system composed of one base station 1 and three mobile stations (mobile station 2, mobile station 3, and mobile station 4). It is a system example.
FIG. 2 is a main block diagram showing one embodiment of a base station and a mobile station constituting a digital mobile communication system according to the present invention, and FIG. 3 is an operation flowchart for explaining FIG. FIG. 4 is an operation flowchart for explaining a second embodiment of the digital mobile communication system according to the present invention.

In FIG. 1, each of mobile station 2, mobile station 3 and mobile station 4 is under the control of base station 1;
(Mainly communication) between mobile stations by relaying (relay communication mode). In this case, a carrier of frequency F1 (first carrier frequency F1) is used for transmission (uplink) from each mobile station to base station 1, and a frequency (frequency) is used for transmission (downlink) from base station 1 to each mobile station. Use the carrier of F2 (second carrier frequency F2) (two-wave simplex). Here, mobile station 2 and mobile station 3
Since each is within the communication area a of the base station 1,
These mobile stations can perform communication relaying the base station 1.
On the other hand, since the mobile station 4 has moved out of the communication area a of the base station 1, it cannot communicate with the base station 1, and therefore cannot communicate with another mobile station that relays the base station 1. .
Thus, in the present invention, a communication function for temporarily using the frequency F1 for reception is newly added to each mobile station in addition to the original communication function using the frequencies F1 and F2. Thereby, the communication area a
The out-of-service mobile station 4 can directly communicate with the nearby mobile station 3 without isolation by using the frequency F1 for transmission and reception.

FIG. 2 is a block diagram showing the configuration of the present system, wherein (A) is a base station 1 and (B) is a mobile station (2, 3 or 4). 2A, an antenna 11 receives a transmission signal of a first carrier frequency F1 from a mobile station;
Reference numeral 12 denotes a reception demodulation unit that demodulates and decodes the signal of the first carrier frequency F1 from the antenna 11. Reference numeral 13 denotes a baseband processing unit which processes a signal from the reception demodulation unit 12 and a baseband signal such as mobile station control data. Reference numeral 14 denotes a modulator, which performs digital modulation processing of a predetermined system using the signal from the baseband processor 13 and the second carrier frequency F2. Reference numeral 15 denotes a transmission unit which sets the signal of the second carrier frequency F1 to a predetermined level and transmits the signal. 16 is a transmitting antenna.

In FIG. 2 (B), reference numeral 21 denotes a data generator which generates data to be transmitted to the communication partner mobile station, such as microphone sound and required data. Reference numeral 22 denotes a modulator, which processes a signal from the data generator 21 and digital modulation of a predetermined method at the first carrier frequency F1. The control unit 41 sets the first carrier frequency F1. 23 is a transmitter,
The signal of the first carrier frequency F1 is transmitted at a predetermined level. 24 is a transmitting antenna. An antenna 25 receives a signal of the second carrier frequency F2 or the first carrier frequency F1. Reference numeral 26 denotes a reception demodulation unit which demodulates and decodes a signal of the second carrier frequency F2 or the first carrier frequency F1 from the antenna 25 in accordance with an instruction from the control unit 41.
Reference numeral 27 denotes a reception level detection unit which detects the reception level of the signal of the second carrier frequency F2 or the first carrier frequency F1 based on the signal from the reception demodulation unit 26. Reference numeral 28 denotes a bit error rate detection unit which detects a bit error rate (BER) based on the decoded signal from the reception demodulation unit 26.

Reference numeral 33 denotes a memory unit, and a reception level detection unit 27
Alternatively, the data of the reception level or the bit error rate detected by the bit error rate detection unit 28 is temporarily stored. Reference numeral 34 denotes a first determination unit which compares the data of the reception level or bit error rate detected by the reception level detection unit 27 or the bit error rate detection unit 28 with a preset reference level or reference value, When the level is equal to or lower than the level or when the bit error rate is equal to or higher than the reference value, it is determined that communication with the opposite station that transmitted the received signal is impossible.

Reference numeral 35 denotes a second discriminating unit, which is a receiving level (receiving level detecting unit 27) or bit error rate (bit error rate) for each of the signals of the first carrier frequency F1 transmitted by a plurality of mobile stations in the service area. The detection unit 28) is compared, and the best mobile station is selected as a communication partner with the own station. Also, it is determined whether the reception level is equal to or higher than the reference level or the bit error rate is equal to or lower than the reference value, and whether the other mobile station can communicate with the own station is determined. Reference numeral 36 denotes a third determination unit, which determines whether a request for direct communication using the first carrier frequency F1 issued by a mobile station outside the service area specifies the own station, based on an ID or station identification data.

Reference numeral 38 denotes a display unit, which is used when the first determination unit 34 determines that communication with the base station 1 is impossible.
To indicate that you are out of service area. Reference numeral 39 denotes a voice unit, which emits a voice or an alarm sound when the first determination unit 34 determines that the communication area a is out of the service area a. 40 is an input unit,
When specifying a partner mobile station with which a mobile station outside the service area directly communicates, an ID or station identification data is input. Reference numeral 41 denotes a control unit, which controls each discrimination unit, memory unit, display unit, and the like based on each detection result.

Next, the operation of the present invention will be described for each embodiment. In the following description, initially, the mobile station 2, the mobile station 3, and the mobile station 4 are within the communication area a of the base station 1, then the mobile station 4 moves out of the service area, and then moves again into the service area. (Return). Further, since each mobile station has the same configuration, FIG. 2 will be described for each mobile station. ST numbers in parentheses in the description indicate steps in the operation flowchart (FIG. 3 or FIG. 4). First, a first embodiment will be described. First, the transition from the relay communication mode to the direct communication mode will be described with reference to FIGS. In the relay communication mode, another mobile station (mobile station 2
Alternatively, the mobile station 4 communicating with the mobile station 3) constantly detects the reception level of the signal of the second carrier frequency F2 transmitted from the base station 1 (ST1). This detection is detected by the reception level detection unit 27 based on the signal from the reception demodulation unit 26. The detected data is compared with a preset reference level in the first determination unit 34, and if the reception level exceeds the reference level, the relay communication mode is maintained (ST2).
-Y), when it is below the reference level (ST2-N), the fact that it is out of the area is displayed (display section 38) or voice (voice section 39) is issued (ST11), and directly through the processing described later. Move to communication mode.

As a criterion for determining the shift to the direct communication mode, a bit error rate (BER) of demodulated data may be used in addition to the reception level. In this case, the bit error rate detection unit 28 detects the same bit error rate based on the signal from the reception demodulation unit 26, and the detected bit error rate is compared with a preset reference value by the first determination unit 34. If the bit error rate is smaller than the reference value, the relay communication mode is maintained (ST2-Y). If the bit error rate is equal to or larger than the reference value (ST2-N), the mode shifts to the direct communication mode as described above.
The indication to that effect is the same as above (ST1
1).

The present system is a digital mobile communication system in which all data including voice is transmitted and received. Therefore, to determine whether or not communication with the partner station is possible, a method using both the reception level and the bit error rate or both can be considered as described above. The method of determining the reception level has a simple circuit and can be realized at low cost. The method using the bit error rate requires a complicated circuit and is more expensive than the method using the reception level.

The shift to the direct communication mode will be described in detail. The control of the control unit 41 changes the reception frequency of the reception demodulation unit 26 from the second carrier frequency F2 to the first carrier frequency F2.
Switch to 1. Then, it is confirmed that the first carrier frequency F1 is not used (ST12). Therefore, under the control of the control unit 41, the antenna 25 and the reception demodulation unit 26
And the received level is detected by a received level detecting section 27, and the detected data is compared with a preset reference level in a second determining section 35. Here, the bit error rate of the demodulated data may be used as the data to be determined by the determination unit 35 in addition to the above-described reception level. If the reception level exceeds the reference level, or if the bit error rate is less than the reference value, it means that there is a mobile station using the first carrier frequency F1 in the vicinity. In this case, The switching to the direct communication mode is temporarily suspended (ST12-N), otherwise (ST12-Y), which means that there is no mobile station using the first carrier frequency F1. , The out-of-service mobile station 4 transmits a request to shift to the direct communication mode (ST1).
3). Specifically, an ID corresponding to a communication partner specified by a key operation on the input unit 40 or an ID not specifying a specific communication partner is generated in the data generation unit 21 and the first carrier frequency F1 is used. After adding information data (voice and the like) from the data generation unit 21 and own station ID (identification code data), the digital modulation process is performed, and the data is transmitted from the antenna 24 via the transmission unit 23 (ST13).

As described above, since a communication partner can be designated in advance, unnecessary voice / information is not generated / displayed at a station which is not a communication target, so that unnecessary confusion can be avoided.

On the other hand, each mobile station within the service area in the relay communication mode periodically switches from the normally received second carrier frequency F2 to the first carrier frequency F1 and transmits from the out-of-service mobile station 4. The presence or absence of reception of the first carrier frequency F1 is monitored (ST3). Therefore, the request for transition to the direct communication mode by the signal of the first carrier frequency F1 transmitted by the mobile station 4 is received by another mobile station within the service area. here,
The received mobile stations are referred to as mobile station 2 and mobile station 3. Based on the signal from the reception demodulation unit 26, each of the received mobile stations 2 and 3 detects the reception level at the reception level detection unit 27 or detects the bit error rate at the bit error rate detection unit 28. Detected, one or both of the detected data, the ID of the transmitting station and the ID of the communication partner of the transmitting station are temporarily stored in the memory unit 33, and the reception frequency is returned to the second carrier frequency F2 from the base station. . On the other hand, the base station uses the second carrier frequency F2 for each mobile station within the service area to determine whether or not a request for transition to a direct communication mode of a mobile station outside the service area has been received.
I make regular inquiries (ST4). Each mobile station within the service area that has received this inquiry reads the reception level and bit error rate stored in the memory unit 33, the ID of the out-of-service station, the ID of the communication partner of the out-of-service station, and the like, and uses the first determination unit 34. To determine the presence or absence of a communicable out-of-service station, and uses the first carrier frequency F1 for modulation processing (modulation unit).
22) Thereafter, the data is transmitted from the antenna 24 to the base station 1 via the transmitting unit 23 as out-of-service-station presence / absence response data (ST5).

The base station 1 receives the out-of-service-station presence / absence response data, confirms whether at least one of the mobile stations in the service area has received the direct communication mode shift request of the out-of-service station, and if so, directly. Data indicating the approval of the communication mode transition is transmitted to each mobile station. Receiving data indicating this acknowledgment (S
T7) Each mobile station within the service area switches to the direct communication mode.
(ST8), the transmission to the base station 1 using the first carrier frequency F1 is prohibited except for the transmission of the relay communication mode return request from the area station until the base station 1 instructs to return to the relay communication mode. I do. Thereafter, each mobile station within the service area directly communicates with the mobile station 4 outside the service area in the direct communication mode (ST9). As described above, the base station 1 periodically inquires the mobile stations within the service area whether or not the mobile station outside the service area has received the request for transition to the direct communication mode, and the mobile stations within the service area respectively reply to the request. Therefore, the mobile station 4 outside the service area can easily grasp the reception levels of all the mobile stations by intercepting the answer.

On the other hand, the mobile station 4 intercepts the transmission of the out-of-service-station presence / absence response data transmitted by each of the mobile station 2 and the mobile station 3 (receiving demodulation unit 26) (ST14). The received signal is measured as data for each mobile station and stored in a memory unit.
It is stored in 33 (ST15). This data is data indicating the level or bit error rate of a signal transmitted by the mobile station 2 or 3 and received by the mobile station 4, and is data indicating the reception quality of the partner mobile station. Therefore, this means that the mobile station with good reception quality exists near the mobile station 4, and
In particular, in the case of direct communication without specifying a partner, stable communication can be made possible by selecting this mobile station. Therefore, the data indicating the reception level or the bit error rate of the signal received by the mobile station 4 is stored in the second determination unit.
Compare with 35 and select the mobile station with the best data (ST1
9). After the selection, the mobile station communicates with the mobile station in the direct communication mode according to the result (ST21). Specifically, the control unit
Under the control of 41, the data generation unit 21 generates data (ID, etc.) for designating the mobile station to communicate with, and the modulation unit 22,
The signal is transmitted from the antenna 24 via the transmission unit 23. Here, when the communication partner is specified as described above, the ID of the partner station specified in advance is used instead of the ID for specifying the mobile station based on the selection result.

The transmission signal in the direct communication mode is received by the partner mobile station (mobile station 2 or mobile station 3) (reception demodulation unit 2
6), each partner mobile station determines the ID of the communication partner included in the received signal and the ID of its own station by the third determination unit 36,
If it is D, the received content can be reproduced from the audio unit 39, or the display unit
Display on 38. If it is not the ID of the own station, it is ignored. However, if the ID does not specify a specific communication partner, the ID of the own station
Process as Thereafter, the partner mobile station and the mobile station 4 perform communication under the direct communication mode (ST21). However, the partner mobile station periodically changes the reception frequency of the reception demodulation unit 26 from the first carrier frequency F1 even during the direct communication mode.
The signal is switched to the second carrier frequency F2 and received. For example, when the partner mobile station receives an instruction to return from the relay communication mode for emergency communication from the base station 1, it determines that the direct communication mode has ended (ST10-Y) and ends the direct communication mode.
In particular, if there is no instruction from the base station 1 (ST10-N), the direct communication mode is continued.

When the communication in the direct communication mode is completed, the mobile station 4 informs the other mobile station of the end. Upon receiving the notification, the partner mobile station determines that the direct communication mode has ended.
(ST10-Y), a relay communication mode return request is transmitted to the base station 1 using the first carrier frequency F1 (ST11). Base station 1
Then, upon receiving this, the mobile station in the range is transmitted using the second carrier frequency F2 to notify that the mobile station is to return to the relay communication mode. It returns to the relay communication mode that relayed (ST1).
Specifically, under the control of the control unit 41, the reception frequency of the reception demodulation unit 26 is switched from the first carrier frequency F1 to the second carrier frequency F2.

On the other hand, after switching to the direct communication mode, the mobile station 4
Periodically monitors the reception of the second carrier frequency F2 transmitted from the base station (reception demodulation unit 26), and monitors the reception level or bit error rate of the reception level detection unit 27 or bit error rate detection unit 28. Detected by. This detection may be based on both the reception level and the bit error rate.
The detection data is compared with a reference level or a reference value by the first determination unit 34 in the same manner as described above, and it is determined whether the mobile station 4 is out of the service area of the base station 1 (ST23). In the case of out of service area (out of standard), direct communication is maintained (ST23-N).
On the other hand, when it is determined that the area is within the service area (within the standard) (ST23-
Y), the mobile station 4 sends a return notification to the relay communication mode to the partner mobile station under the direct communication mode (ST24).
Upon receiving this, the partner mobile station determines that the direct communication mode has ended (ST10-Y), and issues a relay communication mode return request to the first mobile station.
To the base station 1 using the carrier frequency F1 (ST1).
1). Thereafter, the mode returns to the relay communication mode relaying the base station (ST1). Specifically, under the control of the control unit 41, the reception frequency of the reception demodulation unit 26 is changed from the first carrier frequency F1 to the second
To the carrier frequency F2.

As described above, since the out-of-service station constantly checks whether the position of the own station is out of service or in the service area, when the out-of-service station moves into the service area, the out-of-service station quickly returns to the relay communication mode and is under the control of the base station 1. it can. In addition, as described above, the transition to the direct communication mode requires the consent of the base station 1. Therefore, if there is an instruction in the base station 1 that gives priority to communication with an out-of-service station, the transition to the direct communication mode is performed. It can be temporarily delayed or stopped.

As described above, communication in the direct communication mode is performed by temporarily interrupting communication with the base station 1, so that long-time communication poses a problem in system operation. In order to solve this, in the mobile station, the control unit 41 is provided with a timer function for terminating the direct communication when a predetermined time elapses in the communication time of the direct communication.
The control unit 41 measures the time of the direct communication, and determines that the direct communication mode has ended when, for example, 10 minutes have elapsed (ST10).
A warning sound is issued from 39 to call attention, the direct communication (ST9) is terminated, and a relay communication mode return request is transmitted to the base station 1 using the first carrier frequency F1 (ST10).
With this function, mobile stations within the service area always return to the relay communication mode after 10 minutes elapse, and the system can be operated smoothly.

Also, even if 10 minutes have not elapsed in the direct communication mode, the base station forcibly terminates the direct communication with mobile stations within the service area at an arbitrary timing and relays the base station. To return to a mode in which mobile stations communicate with each other. As described above, since the mobile stations within the service area regularly receive the second frequency F2 even in the direct communication mode, when the mobile station receives the forcible interruption command data from the base station, It is determined that the communication mode has ended (ST10), a warning sound is generated from the voice unit 39 to warn the user, the direct communication (ST9) is ended, and a relay communication mode return request is made using the first carrier frequency F1. It transmits to base station 1 (ST10). With this function, when an emergency contact occurs, the base station 1 can forcibly return the mobile stations within the service area to the relay communication mode and make an emergency contact in the relay communication mode.

FIG. 4 is an operation flowchart for explaining a second embodiment of the digital mobile communication system according to the present invention. The operation of ST4 and ST5 is different from that of FIG. The other operations are the same as those in FIG. In the first embodiment, each mobile station in the service area responds to the presence or absence of the out-of-service station in accordance with the instruction of the out-of-service station presence inquiry from the base station 1 on a regular basis (ST4, ST5 in FIG. 3). In the second embodiment, as shown in FIG. 4, after the mobile station in the service area confirms the out-of-service station (ST3), the reception level or the bit error rate of the out-of-service station stored in the memory unit 33 is reduced. The first discrimination unit 34 discriminates and confirms whether there is an out-of-service station that requests the direct communication mode (ST4). Mobile stations in the area, if there is an out-of-service station that requests the direct communication mode (ST4-Y),
An out-of-service-station detection notification is spontaneously transmitted to the base station 1 (S
T5). If no out-of-service stations require direct communication mode
(ST4-N), the relay reception mode is maintained. On the other hand, the base station 1 that has received the out-of-service station detection notification (ST5) transmits an acknowledgment to all mobile stations as in the first embodiment, and shifts to the direct communication mode.

As described above, only when there is an out-of-service station requesting the direct communication mode, the base station 1 needs to instruct the out-of-service station presence inquiry by notifying the base station 1 from the mobile station in the service area. Therefore, the burden on the base station 1 can be reduced.

In the two embodiments described above, the reception demodulation unit 26, the bit error rate detection unit 28, and the reception level detection unit 27
Is used in common for receiving the first carrier frequency F1 and the second carrier frequency F2, but if they are independently provided, the same applies without providing the above-mentioned switching means. The effect of can be obtained.

[0046]

As described above, according to the present invention, the second mobile station receiving means for receiving and demodulating and decoding the transmission signal of the first carrier frequency F1 and the second mobile station are provided to the mobile station. Switching means for switching between the station receiving means and the first mobile station receiving means; and a communication area determination for judging, based on the received signal received by the mobile station, whether or not communication with a partner transmitting station is possible based on the quality of the received signal. Means, the mobile station, based on the received signal of the second carrier frequency F2 from the base station, the communication area determination means, the mobile station can be in the area where the mobile station can communicate with the base station or outside the area where communication is impossible It is determined whether or not the mobile station is located, and the out-of-service mobile station is switched by the switching means from reception by the first mobile station reception means to reception by the second mobile station reception means,
A communication request is transmitted to the mobile station within the service area by the first carrier frequency F1, and the mobile station within the service area is periodically switched by the switching means from the reception by the first mobile station receiving means to the reception state by the second mobile station receiving means. And accepts a communication request at the first carrier frequency F1 transmitted by a mobile station out of the service area,
Switching from the reception by the first mobile station receiving means to the receiving state by the second mobile station receiving means is performed by the switching means, so that the mobile station within the area under the management of the base station and the mobile station outside the area not under the management are Direct communication is performed using the first carrier frequency F1 for transmission and reception. For this reason, a mobile station that moves outside the communication area of the base station and cannot communicate with the base station communicates directly with a mobile station within the communication area of the base station, thereby indirectly isolating the base station without isolation. You can act according to instructions. In addition, when a mobile station outside the service area returns to the service area, the mobile station automatically returns to the relay communication mode in the service area, so that it can directly act upon receiving an instruction from the base station.

[Brief description of the drawings]

FIG. 1 is a conceptual explanatory diagram of a digital mobile communication system according to the present invention.

FIG. 2 is a main block diagram showing one embodiment of a digital mobile communication system according to the present invention.

FIG. 3 is an operation flowchart for explaining FIG. 2;

FIG. 4 is an operation flowchart for explaining a second embodiment of the digital mobile communication system according to the present invention.

FIG. 5 is an explanatory diagram of a conventional digital mobile communication system.

[Explanation of symbols]

 1 base station 2, 3, 4 mobile station 11, 16, 24, 25 antenna 12, 26 reception demodulation unit 13 baseband processing unit 14, 22 modulation unit 15, 23 transmission unit 41 control unit 34, 35, 36 discrimination unit 21 Data generator 27 Receive level detector 28 Bit error rate detector 33 Memory 38 Display 39 Audio 40 Input

Claims (16)

[Claims] 1. A first mobile station transmitting means for transmitting data at a first carrier frequency F1, and a second carrier frequency F2.
A plurality of mobile stations comprising first mobile station receiving means for receiving and demodulating and decoding the transmission signal of the first and second base stations; and base station receiving means for receiving and demodulating and decoding the transmission signal of the first carrier frequency F1. A single base station including a base station transmitting means for transmitting data at the second carrier frequency F2, and a two-wave simplex signal for performing communication between the mobile stations by relaying the base station. In a digital mobile communication system of a system, a second mobile station receiving means for receiving, demodulating and decoding a transmission signal of the first carrier frequency F1, a second mobile station receiving means, Switching means for switching between the first mobile station receiving means and a communication area determining means for determining, based on a received signal received by the mobile station, whether communication with a partner transmitting station is possible based on the quality of the received signal. The mobile station is based on The second carrier frequency F from station
2 based on the received signal, the communication area determination means determines whether the mobile station is located within an area where communication with the base station is possible or outside the area where communication is not possible. Switching from reception by the first mobile station receiver to reception by the second mobile station receiver by the first carrier frequency F1
A communication request to the mobile station within the service area, and the mobile station within the service area is periodically switched by the switching means from reception by the first mobile station receiving means to reception by the second mobile station receiving means. Receiving the communication request at the first carrier frequency F1 transmitted by the out-of-service mobile station, and switching from reception by the first mobile station reception means to reception by the second mobile station reception means by the switching means. The mobile station in the area under the management of the base station and the mobile station out of the area under the control of the base station perform direct communication using the first carrier frequency F1 for transmission and reception. Digital mobile communication system. 2. The communication area determination means, provided in the mobile station, for detecting a level of a reception signal of the second carrier frequency F2 or the first carrier frequency F1, a reception level detection unit, 2. The digital device according to claim 1, further comprising a first determination unit that compares the detected reception level with a reference level, and determines that communication with the receiving station is impossible when the reception level is lower than the reference level. Mobile communication system. 3. The communication area determination means detects a bit error rate of a decoded signal in a received signal of the second carrier frequency F2 or the first carrier frequency F1 provided in the mobile station. A rate detection unit, and a first determination unit that compares the detected bit error rate with a reference value and determines that communication with the receiving station is impossible when the bit error rate is equal to or greater than the reference value. The digital mobile communication system according to claim 1, wherein 4. The mobile station communicates the data of the reception level of the communication request signal at the first carrier frequency F1 transmitted by the mobile station out of service with the mobile station out of service by the first determination unit. 3. The digital communication device according to claim 2, wherein whether or not communication is possible is determined, and if it is determined that communication is possible, a signal of an out-of-service station detection notification for shifting to the direct communication mode is transmitted to the base station. Mobile communication system. 5. The mobile station according to claim 1, wherein the first discriminator is configured to transmit the bit error rate data of the communication request signal at the first carrier frequency F1 transmitted by the mobile station out of service to the mobile station out of service. 4. The communication device according to claim 3, wherein it is determined whether communication is possible, and when it is determined that communication is possible, a signal of an out-of-service-station detection notification for shifting to the direct communication mode is transmitted to the base station. Digital mobile communication system. 6. The mobile station is provided with a memory unit for storing data of a reception level detected by the reception level detection unit, and a communication request signal of the first carrier frequency F1 transmitted by the mobile station outside the service area is provided. The data of the reception level is stored in the memory unit, and in response to a request from the base station,
Reading the data of the reception level from the memory unit,
5. The digital mobile communication system according to claim 2, wherein the first determination unit determines whether communication with the out-of-service mobile station is possible, and transmits the determination result to the base station. 6. 7. A communication request signal based on the first carrier frequency F1 transmitted by the mobile station out of the service area, wherein the mobile station is provided with a memory unit for storing data of the bit error rate detected by the bit error detection unit. The bit error rate data is stored in the memory unit, and the bit error rate data is read from the memory unit in response to a request from the base station. 6. The digital mobile communication system according to claim 3, wherein it is determined whether communication is possible with the base station, and the result of the determination is transmitted to the base station. 8. The mobile station receives the first carrier frequency F1 emitted by each of a plurality of mobile stations within a service area, and determines the mobile station having the best data from the respective reception level data. 3. The mobile communication system according to claim 2, further comprising a second determination unit, wherein the out-of-service mobile station directly communicates with the mobile station having the best data determined by the second determination unit.
The digital mobile communication system according to claim 4 or claim 6. 9. The mobile station receives the first carrier frequency F1 emitted by each of a plurality of mobile stations within a service area, and selects a mobile station with the best data from among the data of the respective bit error rates. 6. A mobile communication system according to claim 3, further comprising a second determination unit for determining, wherein the mobile station outside the service area communicates directly with the mobile station of the best data determined by the second determination unit. The digital mobile communication system according to claim 7. 10. A transmission signal of the first carrier frequency F1 generated by the out-of-service mobile station includes data specifying a mobile station of a communication partner, and the specified data in a signal received from the transmission signal. Is provided in the mobile station, and the mobile station that determines that the data specifies the own station performs direct communication with the mobile station outside the service area. The digital mobile communication system according to claim 1, wherein 11. After the direct communication is started, when the communication area determining means determines that the communication area is within the service area, the switching means switches the reception from the second mobile station receiving means to the first mobile station receiving means. 2. The digital mobile communication system according to claim 1, wherein the digital mobile communication system is switched to reception by the digital mobile communication system. 12. The digital communication system according to claim 1, wherein the shift to the direct communication is performed according to an instruction of the base station using a base station transmitting means for transmitting data at the second carrier frequency F2. Mobile communication system. 13. The digital mobile communication system according to claim 1, wherein a display unit is provided in each of the mobile stations, and when the communication area determination means determines that the mobile station is out of the service area, the fact is displayed. 14. The digital mobile communication system according to claim 1, wherein a voice section is provided in each of said mobile stations, and when said communication area determination means determines that said mobile station is out of service area, a voice or an alarm sound is generated to that effect. . 15. The mobile station in the area terminates the direct communication when the communication time in the direct communication elapses a predetermined time, and relays the communication between the mobile stations by relaying the base station. 2. The digital mobile communication system according to claim 1, wherein the digital mobile communication system returns to a mode in which it is performed. 16. The base station forcibly terminates direct communication with the mobile station within the service area at an arbitrary timing,
2. The digital mobile communication system according to claim 1, wherein the mobile station returns to a mode in which the mobile stations communicate with each other by relaying the base station.