JPH04306924A - Mobile radio communication system - Google Patents

Abstract

PURPOSE:To allow the system to flexibly cope with a biased traffic by sending a reference synchronizing signal in terms of a radio signal to plural base stations and mobile stations from a control radio transmission station and establishing the synchronization of a time slot based on the synchronizing signal. CONSTITUTION:Control radio transmission stations DS1-2 to send a reference synchronizing signal in a radio wave to plural base stations BBS1-3 and mobile stations are provided in the system. The base stations BBS1-3 and mobile stations establish time slot synchronization of a digital radio line based on the reference synchronizing signal sent from the control radio transmission stations DS1-2. Thus, it is possible to select and use a different time slot in one radio frequency in the plural adjacent base stations BBS1-3 respectively, for example. That is, idle time slots of one radio frequency are used each other by the plural base stations BBS1-3 located close to each other without causing interference.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile radio communication system such as a portable radio telephone system or a car telephone system, and more particularly to a system employing a cellular system.

0002

2. Description of the Related Art FIG. 10 shows a schematic configuration of a conventionally known mobile/automobile radio telephone system employing a cellular system. This system includes a control station CS connected to a wired telephone network NW, a plurality of base stations BS1 to BSn connected to the control station CS via wired lines CL1 to CLn, and a plurality of mobile stations PS1 to PSn. PSm. Each of the above base stations BS1 to BSn has wireless zones E1 to E called cells in different areas.
form n. The mobile stations PS1 to PSm are connected via a wireless line to a base station in the wireless zone in which they are located, and further connected from this base station to a wired telephone network NW via a control station CS. In this state, it becomes possible to talk to a telephone connected to the wired telephone network NW. Furthermore, when the mobile stations PS1 to PSm move to another wireless zone during a call, the wireless line is switched to the wireless line of the destination base station under the control of the control station CS, and the call is continued.

FIG. 11 shows a sequence when a mobile station makes a call in this system. For example, assume that the hook switch is now turned on to make a call at mobile station PS3. Then, this mobile station PS3 first selects a radio frequency for control and generates a transmission signal containing its own identification code. Then, this transmission signal is transmitted to the wireless base station BS2 via the control radio frequency (control channel). On the other hand, the base station BS2 monitors the occurrence of a call using the control channel during standby, and when a call signal arrives from the mobile station PS3 in this state, the base station BS2 uses the identification code of the mobile station PS3 and its own station. A calling signal including the following is generated and transferred to the control station CS.

[0004] The control station CS determines whether the call is from its own system based on the identification code included in the call signal, and if it is from its own system, it specifies the radio frequency for the call. A call response signal including information for communication (communication channel designation information) is sent back to the base station BS2. base station BS
When the call response signal is returned from the control station CS, 2 generates a call response signal including communication channel designation information and the identification code of the calling mobile station PS3, and transmits this signal using the control channel. Transmit to mobile station PS3.

[0005] On the other hand, when the mobile station PS3 receives the call response signal, it performs a communication channel for establishing a communication channel using the radio frequency with the base station BS2 in accordance with the communication channel designation information included in this signal. Do some training. When a communication channel is established through this training, a calling signal is sent from the control station CS to the wired telephone network NW. When this calling signal is sent, the wired telephone network NW sends a signal requesting transmission of a dialing signal to the calling mobile station PS3 via the control station CS and base station BS2. In the mobile station PS3, when this dial signal transmission request arrives, a message indicating that the dialing operation is now possible is displayed.

[0006] When the speaker confirms this display and inputs the dial number of the other party using the dial keys, the mobile station P
S3 transmits a dialing signal corresponding to the dialed number to the base station BS2 via the wireless communication channel. When the base station BS2 receives the dial signal, it transfers the dial signal to the wired telephone network NW via the control station CS. For this reason, a switching operation is performed in the wired telephone network NW, whereby the telephone of the other party with whom the user desires to make a call is called. When the other party answers this call by going off-hook, a communication path is formed between the other party's telephone and the calling mobile station PS3, and from then on, communication between the other party's telephone and the mobile station PS3 is established via this communication path. It is possible to make calls between.

[0007] By the way, improving the capacity of mobile stations has become an important issue in mobile/vehicle radio telephone systems employing the cellular system, and for this reason, recently, communication content such as not only control signals but also call voice signals has become important. A method has been proposed in which the data is also digitized and the digitized signal is transmitted using the TDMA method. In this method, the transmission signal is configured into a frame for each radio frequency, one frame is time-divided into six time slots as shown in FIG. 12, and these time slots are each assigned as a communication channel to different mobile stations for communication. It was designed to do this. Using this method, the mobile station capacity can be increased six times compared to conventional systems.

[0008]

[Problems to be Solved by the Invention] However, in the current cellular radio telephone system, a radio frequency is fixedly assigned to each base station BS1 to BSn, and the same radio frequency is used between base stations separated by a certain distance or more to avoid interference. A method of repeated use is adopted. Therefore, even if the TDMA method described above is applied, the following problems still exist.

That is, in a system to which the TDMA method is applied, for example, as mentioned above, 6
Call channels are available. However, even if only one of these channels is used, this radio frequency will be occupied by the base station with low traffic. For this reason, for example, the traffic of an adjacent base station becomes high, and even if this base station wanted to use an empty channel of the radio frequency used by the base station with low traffic, it was unable to use it.

The present invention has focused on the above-mentioned circumstances, and enables base stations to mutually accommodate different time slots of the same radio frequency to flexibly respond to traffic imbalances, and to do this with simple equipment and control. The purpose is to provide a mobile radio communication system that can be realized.

Another object of the present invention is to maintain a stable radio frequency at all times without providing expensive oscillation circuits in base stations and mobile stations, thereby improving communication quality and improving the performance of base stations and mobile stations. An object of the present invention is to provide a mobile radio communication system that can be lowered in price.

0012

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a plurality of base stations each forming a wireless zone, and a digital radio line in which a plurality of time slots are time-division multiplexed to these base stations. In a mobile radio communication system comprising a plurality of mobile stations that are time-division multiple-connected via a mobile radio communication system, at least one integrated radio transmission for radio transmitting a reference synchronization signal to at least one of the plurality of base stations and the mobile stations. At least one of the plurality of base stations and the mobile station establishes time slot synchronization of the digital radio line based on a reference synchronization signal transmitted from the central radio transmitting station.

[0013] The present invention also provides an integrated radio transmitting station provided in a pager base station for transmitting a selective call signal to a selective call receiver, or a pager base station for transmitting a selective call signal to a selective call receiver. Another feature is that it also has the functions of a base station.

Further, the present invention provides, in addition to synchronization means for establishing time slot synchronization in at least one of a plurality of base stations and mobile stations based on a reference synchronization signal transmitted from a central radio transmitting station, a frequency variable control means. The present invention is also characterized in that the frequency variable control means performs frequency variable control for making the radio frequency for telephone calls constant based on the reference synchronization signal transmitted from the central radio transmitting station.

[0015]

[Operation] As a result, according to the present invention, time slot synchronization is always achieved between each base station. Therefore, for example, it becomes possible for a plurality of base stations adjacent to each other to select and use different time slots of one radio frequency. In other words, vacant time slots on one radio frequency can be shared among multiple nearby base stations without causing interference, thereby effectively reducing traffic imbalance between base stations. .

Moreover, in the present invention, time slot synchronization between base stations is established based on a reference synchronization signal transmitted from a central radio transmitting station, so there is an advantage that it can be implemented with relatively simple equipment and control. There is. By the way, it is also possible to supply a reference synchronization signal from the control station to each base station via a control line and thereby synchronize the time slots between the base stations, but in such a configuration, For each, a new control line must be laid, and it is also necessary to compensate for the amount of delay in the reference synchronization signal due to the difference in length of these control lines. Therefore, the equipment becomes large-scale, and complex control is required to match the timing of the reference synchronization signal reaching each base station. This becomes more noticeable as the number of base stations increases, and it becomes extremely difficult to implement the system.

Furthermore, if the central radio transmitting station and the pager base station are shared, there is no need to install a new transmitting station for time slot synchronization between the base stations. An integrated mobile radio communication system having a selective calling function can be easily constructed.

Furthermore, by including information regarding the radio frequency for telephone calls in the reference synchronization signal transmitted from the central radio transmitting station, each base station or mobile station automatically adjusts the frequency of the radio frequency based on the reference synchronization signal. This makes it possible to maintain the radio frequency of the communication channel at a constant value.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram of a mobile radio communication system according to an embodiment of the present invention. In this figure, the same parts as those in FIG. 10 will be described with the same reference numerals.

The service area of the system is divided into a large number of wireless zones E1, E2, E3, etc. called cells, and these wireless zones E1, E2, E3,...
... are installed with base stations BBS1, BBS2, BBS3, ..., respectively. These base stations BBS1, BBS2,
BBS3, ... are wired lines (not shown in Figure 10), respectively.
(corresponding to CL1, CL2, CL3, . . . ) to the control station CS. In addition, in the figure, for convenience of explanation, only base stations BBS1, BBS2, and BBS3 are illustrated, and illustration of other base stations is omitted.

[0021] Now, at any position in the service area where a large number of cells are formed, there is a central radio transmitting station DS1, D
S2 is installed. These integrated radio transmitting stations DS1,
DS2 forms large wireless zones EE1 and EE2 that cover the entire service area with these two stations, and sends slot synchronization signals to each base station and mobile station located within these large wireless zones EE1 and EE2. is constantly being sent. This slot synchronization signal has the same bit rate and frame structure as the communication transmission signal used between the base station and the mobile station, for example, as shown in FIG.
Each time slot TS1 to TS6 has a synchronization signal SYNC1, SYNC2, . . . unique to that time slot, respectively.
and identification signals CDVC of the central radio transmitting stations DS1 and DS2.
C1, CDVCC2 and control data DATA are inserted. For example, time data is inserted into this control data DATA. Furthermore, for the transmission of this slot synchronization signal, radio frequencies fB1 and fB2, which are different from the radio frequencies for control and communication used by each base station and mobile station, are used.

[0022] Also, each of the above-mentioned central radio transmitting stations DS1, DS2
are connected to the control station CS via wired lines DCL1 and DCL2, respectively. These wired lines DCL1,
DCL2 is controlled by the control station CS and is controlled by the radio transmitting stations DS1 and DS.
2 is used to transfer selective call signals to 2. When receiving a selective call signal from the control station CS, the central radio transmitting stations DS1 and DS2 insert this signal into, for example, the data area DATA of the slot synchronization signal and transmit it. On the other hand, FIGS. 2 and 3 are circuit block diagrams showing the configurations of a mobile station and a base station BBS used in this system, respectively. First, the mobile station PSS is roughly divided into a transmission system, a reception system, and a control system. Note that 40 is a battery as a power source.

The transmission system includes a transmitter 11 and a speech encoder (S
PCOD) 12 and error correction coder (CHCOD) 13
, a digital modulator (MOD) 14, an adder 15, a power amplifier (PA) 16, and a high frequency switch circuit (S
W) 17 and an antenna 18. The speech encoder 12 encodes the transmission signal output from the transmitter 11. The error correction encoder 13 performs error correction encoding on the digitized transmission signal outputted from the audio encoder 12 and the digitized control signal outputted from a control circuit 30, which will be described later. The digital modulator 14 generates a modulated signal according to the digitized transmission signal output from the error correction encoder 13. In the adder 15, this modulated signal is sent to the frequency synthesizer 32.
It is added to the carrier wave signal output from the carrier wave signal, and the frequency is converted by this. Then, in the power amplifier 16, the radio transmission signal output from the adder 15 is amplified to a predetermined transmission power. The high frequency switch 17 becomes conductive only during a transmission time slot specified by the control circuit 30, and during this period supplies the radio transmission signal output from the power amplifier 16 to the antenna 18, and sends the radio transmission signal output from the power amplifier 16 to the base station BBS. Send it towards.

On the other hand, the receiving system includes a receiver (RX) 21
, a digital demodulator (DEM) 22, an error correction decoder (CHDEC) 23, and a speech decoder (SPDEC) 2
4 and a receiver 25. In the receiver 21,
Frequency conversion of the radio reception signal received by antenna 18 and high frequency switch 17 is performed in a reception time slot of a predetermined radio frequency. In the digital demodulator 22, bit synchronization and frame synchronization are achieved with respect to the received signal output from the receiver 21, and the synchronization signal is supplied to the control circuit 30. Error correction decoder 23
Then, the digital demodulated signal output from the digital demodulator 22 is subjected to error correction decoding. The digitized reception signal obtained by this error correction decoding is output to the audio decoder 24, and the digitized control signal is supplied to the control circuit 30. The audio decoder 24 decodes the digitized call signal. Then, the analog reception signal restored by this decoding process is amplified and outputted from the receiver 25.

Further, the control system includes a control circuit (CONT) 30
For example, a display device (DISP) 31 made of a liquid crystal, a frequency synthesizer (SYN) 32, a received field strength detection circuit (RSSI) 33, and a transmission request switch (SW) 3.
4. Of these, the frequency synthesizer 32 generates local oscillation signals corresponding to each channel frequency for control, communication, and synchronization specified by the control circuit 30. The received field strength detection circuit 33 detects the received field strength of the radio wave transmitted from the base station BBS, and the detection signal is notified to the control circuit 30 for searching for an empty channel and monitoring out of communication range.

By the way, the control circuit 30 is equipped with, for example, a microcomputer as a main control section, and in addition to conventional control functions such as setting control of wireless communication channels and call control associated with making and receiving calls, it also has slot synchronization. signal reception control means 30a and time slot synchronization establishment means 30
b.

The slot synchronization signal reception control means 30a periodically receives the slot synchronization signal transmitted from the central radio transmitting station DS1 or DS2 during the standby period and during the call, and receives the synchronization signal SYNC. To detect. The time slot synchronization establishing means 30b establishes time slot synchronization based on the synchronization signal received and detected by the slot synchronization signal reception control means 30a, and stores and holds the established synchronization information.

Next, the base station BBS is also configured in substantially the same manner as the mobile station. That is, the transmission system includes a hybrid circuit 51, a speech coder (SPCOD) 52, an error correction coder (CHCOD) 53, and a digital modulator (MOD).
) 54, an adder 55, a power amplifier (PA) 56,
It is composed of a high frequency switch circuit (SW) 57 and an antenna 58. The voice encoder 52 encodes the speech signal sent from the wired telephone network NW side. Further, the error correction encoder 53 performs error correction encoding of the digitized speech signal outputted from the voice encoder 52 and the digitized control signal outputted from the control circuit 30, which will be described later. The digital modulator 54 generates a modulated signal according to the digitized transmission signal output from the error correction encoder 53. Adder 55 adds this modulated signal to the high frequency signal output from frequency synthesizer 72, thereby converting it into a radio frequency corresponding to the communication channel. Then, in the power amplifier 56, the radio transmission signal output from the adder 55 is amplified to a predetermined transmission power. The high frequency switch 57 becomes conductive only during a transmission time slot specified by the control circuit 71, and during this period supplies the radio transmission signal output from the power amplifier 56 to the antenna 58.
from the mobile station to the mobile station.

On the other hand, the receiving system includes a receiver (RX) 61
, a digital demodulator (DEM) 62 , an error correction decoder (CHDEC) 63 , and a speech decoder (SPDEC) 6
It consists of 4. Receiver 61 performs frequency conversion of the radio reception signal received by antenna 58 and high frequency switch 57 in the reception time slot of the communication channel. The digital demodulator 62 performs bit synchronization and frame synchronization with respect to the received signal output from the receiver 61, and the synchronization signal is transmitted to the control circuit 70.
supplied to In the error correction decoder 63, the digital demodulated signal output from the digital demodulator 62 is subjected to error correction decoding. The digitized speech signal obtained by this error correction decoding is output to the audio decoder 64, and the digitized control signal is supplied to the control circuit 70. The audio decoder 64 decodes the digitized call signal. The analog call signal restored by this decoding process is sent to the wired lines CL1 to CLn via the hybrid circuit 51.

Further, the control system includes a control circuit (CONT) 70
, a frequency synthesizer (SYN) 72, and a received field strength detection circuit (RSSI) 73. Frequency synthesizer 72 generates local oscillation signals corresponding to each channel frequency for control, communication, and synchronization designated by control circuit 70 . In the received electric field strength detection circuit 73,
The received electric field strength of a radio transmission signal transmitted from a mobile station is detected, and the detected signal is supplied to a control circuit 70 for searching for an empty channel and monitoring out of communication range.

The control circuit 70 has conventional control functions such as wireless communication channel setting control and call control associated with sending and receiving calls, as well as slot synchronization signal reception control means 70.
a, and time slot synchronization establishing means 70b.

The slot synchronization signal reception control means 70a periodically receives the slot synchronization signal transmitted from the central radio transmitting station DS1 or DS2 during the standby period and during the call, and receives the synchronization signal SYNC. To detect. The time slot synchronization establishing means 70b establishes time slot synchronization based on the synchronization signal received and detected by the slot synchronization signal reception control means 70a, and stores and holds the established synchronization information. In addition, base station BBS1~
BBSn is equipped with a plurality of communication units shown in FIG. 3. Next, the operation of the system configured as above will be explained.

[0033] The central radio transmitting stations DS1 and DS2 each correspond to the large radio zones EE1 and EE2 covered by their respective stations in FIG.
The slot synchronization signal shown in is constantly transmitted. At this time, the transmission frequency of this slot synchronization signal is fixed to a radio frequency fB1, fB2 that is different from each radio frequency for control and communication used by each base station BBS1, BBS2, ... and mobile station in the system. used. Therefore, by transmitting the slot synchronization signal, the base station BB
There is no risk of interference with communication between S and the mobile station. Furthermore, since the number of radio frequencies fB1 and fB2 used for transmitting slot synchronization signals is small, only two waves, the frequency utilization efficiency of the system is not reduced. on the other hand,
The following control is performed at each mobile station and each base station BBS in the system.

First, in the mobile station, in the standby state, the control circuit 30 monitors the elapsed time t1 and turns on the call request switch 3 in steps 4c, 4d, and 4e, respectively, as shown in FIG.
The operation monitoring at 4 and the progress monitoring at time t2 are repeatedly performed. The purpose of monitoring the progress of time t1 is to know the time to re-establish the time slot synchronization of the local station.
is set to 30 minutes, for example. Furthermore, the monitoring of the passage of time t2 is to set the intermittent reception operation timing of the receiver 21 for battery saving.

In this state, when t1 has elapsed and the time slot synchronization of the local station is re-established, the control circuit 30
The process moves to step 4a, where the receiver 21 is first set to an operating state in order to receive the slot synchronization signal, and its reception frequency is set to the radio frequency fB1 or fB2. Therefore, the receiving system of the mobile station receives the slot synchronization signal transmitted from the central radio transmitting station DS1 or DS2, and this received signal is subjected to error correction decoding by the error correction decoder 23 and then supplied to the control circuit 30. Ru. The control circuit 30 extracts the synchronization signal S from the received signal in step 4b.
When YNC is recognized and the synchronization signal SYNC is recognized, the start timing K of the time slot TS1 shown in FIG. 6 is calculated based on the synchronization signal SYNC and the position of the transmitting station identification information CDVCC recognized at the same time. Then, this calculated timing K is stored in the RAM in the control circuit 30 as slot synchronization establishment information. In this case, other time slots TS2 to TS other than time slot TS1
6 start timings may be stored, or all the start timings of each time slot TS1 to TS6 may be stored.

On the other hand, in each base station BBS, in the standby state, the control circuit 70 performs step 5 as shown in FIG.
While monitoring the arrival of an incoming signal from the wired telephone network NW in step d and monitoring the arrival of an outgoing signal from the mobile station in steps 5i and 5j, step 5c
The station monitors the time (time t1 = 30 minutes progress monitoring) in order to re-establish the time slot synchronization of its own station. Then, when the time comes to re-establish the slot synchronization of its own station in this state, the base station BBS sets the receiver 61 to receive the radio frequency fB1 or fB2 in step 5a, as in the case of the mobile station, and controls the A slot synchronization signal transmitted from radio transmitting station DS1 or DS2 is received. Then, in step 5b, the synchronization signal SYNC is recognized from this received signal, and when the synchronization signal SYNC is recognized, based on this synchronization signal SYNC and the position of the transmitting station identification information CDVCC recognized at the same time, time slot TS1
Calculate the start timing K of . Then, the control circuit 7 uses this calculated timing K as slot synchronization establishment information.
Store in RAM in 0. In this case as well, the mobile station may store the start timings of time slots TS2 to TS6 other than time slot TS1, or may store all the start timings of each time slot TS1 to TS6. You can do it like this.

[0037] Thus, each mobile station and each base station BBS
have a common central radio transmitting station DS1 or DS, respectively.
Common slot synchronization establishment information K based on the slot synchronization signal transmitted from No. 2 is stored respectively. That is, all the mobile stations and base stations BBS existing in the large radio zones EE1 and EE2 of the central radio transmitting stations DS1 and DS2 are in a state in which time slot synchronization is achieved with each other.

In this state, suppose that the call request switch 34 is pressed at any mobile station. Then, the control circuit 30 of this mobile station moves from step 4d to step 4l in FIG. 4, where it sets the transmission time slot of the control channel based on the previously stored slot synchronization establishment information, to send an outgoing signal to the nearest base station BBS.

On the other hand, at the base station BBS, the arrival of a transmission signal from a mobile station is monitored in steps 5i and 5j of FIG. That is, step 5
At i, a reception time slot of the control channel is set based on the previously stored slot synchronization establishment information, and a transmission signal transmitted from the mobile station is received in this reception time slot. In step 5j, it is determined whether the received signal is an outgoing signal. When reception of the transmission signal is confirmed, the control circuit 70 moves to step 5k, where it returns a transmission response signal to the mobile station that is the transmission source. In addition to mobile station ID information and the like, call channel designation information is inserted into this call response signal. This communication channel designation information consists of information representing the radio frequency for communication and information representing the position of the time slot, and these pieces of information are determined by an empty channel search based on the timing of the previously stored slot synchronization establishment information. Ru. And the control circuit 7
0 moves to step 5l after returning the above-mentioned call response signal, sets the radio frequency and time slot for the call, and then enters into a call state.

After transmitting the above transmission signal, the mobile station performs step 4m while monitoring the passage of time t3 in step 4n.
monitors the return of the outgoing response signal. And t3
If the call response signal is returned within the time limit, the process moves to step 4k, where the radio frequency and time slot for the call are set in accordance with the call channel designation information inserted in the response signal, and the call state is established thereafter. In addition, the above t3
If the outgoing response signal is not returned even after the elapse of time, it is determined that the time slot synchronization may be out of sync, and after displaying on the display 31 that connection is not possible in step 4o, the process returns to step 4o. Return to 4a and head over to the general radio transmitting station DS.
Based on the slot synchronization signal transmitted from DS1 or DS2, an operation is performed to re-establish slot synchronization.

Also in the call state, the base station calling the mobile station monitors the slot synchronization re-establishment timing in steps 4c and 5c, respectively. Then, when the slot synchronization is to be re-established, the slot synchronization is re-established in steps 4a and 4b and steps 5a and 5b. In this case, in order to avoid affecting the transmission and reception of call signals, the slot synchronization signals sent from the central radio transmitting stations DS1 and DS2 are received in the time slot used for the call. This is done using vacant time slots other than the above.

Next, when an incoming call occurs from the wired telephone network NW, the following control is performed. That is, when an incoming signal arrives from the wired telephone network NW via the control station CS, the base station BBS detects it in step 5d of FIG. 5, and proceeds to step 5e. Then, in step 5e, a transmission time slot of the control channel is set based on the previously stored slot synchronization establishment information, and the incoming signal is transmitted using this time slot. In addition to the code indicating the incoming call, this incoming signal contains the ID of the destination mobile station.
Information (telephone number) and call channel designation information are inserted. In this case, all time slots TS1 to T
An incoming signal may be inserted in S6 and transmitted. In this way, an incoming signal can be quickly detected no matter which time slot the mobile station is monitoring incoming calls. However, if multiple incoming calls occur at the same time, it is necessary to divide them into three slots and use them, for example.

On the other hand, in the standby state, the mobile station monitors the intermittent reception timing in step 4e of FIG.
At f, power is supplied to the receiver 21 and the receiver 21 is set to the receiving operation state. Then, based on the slot synchronization establishment information previously stored in step 4g, the reception time slot of the control channel is set to receive an incoming signal, and it is determined in step 4h whether this received signal is an incoming signal for the own station. Judge by. As a result of this determination, if no incoming signal is detected, step 4i
After cutting off the power supply to the receiver 21 and returning it to a non-operating state, it returns to a standby state.

On the other hand, when an incoming signal for the mobile station is detected, the mobile station moves to step 4j and returns an incoming response signal to the base station BBS using the transmission time slot of the control channel. After this return, in step 4k, the radio frequency and time slot for the call are set according to the call channel designation information inserted in the incoming signal, and the call signal is thereafter transmitted and received using this call channel.

After transmitting the incoming signal, the base station BBS performs step 5 while monitoring the elapse of time t4 in step 5g.
f monitors the return of the incoming call response signal from the mobile station. If the incoming call response signal is returned within t4, the process moves to step 5l, where the radio frequency and time slot for the call are set, and the call state is thereafter established. If the incoming call response signal is not returned even after the above-mentioned t4 has elapsed, it is determined that the time slot synchronization may be out of sync, and in step 5h, the control station CS is notified that connection is not possible. After the notification, the process returns to step 5a and performs an operation to re-establish slot synchronization based on the slot synchronization signal transmitted from the central radio transmitting station DS1 or DS2.

As described above, in this embodiment, each base station BBS and each mobile station are connected to the central radio transmitting stations DS1 and DS.
Time slot synchronization is periodically established based on the slot synchronization signal constantly transmitted from No. 2. Therefore, each base station BBS and the mobile station are in a state where the mutual time slot synchronization is consistent. Figure 7 is Figure 1
This shows the timing of time slots set at base stations BBS1, BBS2, and BBS3 shown in FIG. 2, and the time slots between the stations are synchronized. Therefore, these base stations BBS1, BBS2, and BBS3 use the common radio frequency time slots TS1 to T as shown in FIG.
S6 can be used without causing interference while accommodating each other, thereby increasing the effective utilization rate of the radio channel for communication. Furthermore, even if traffic imbalance occurs between base stations, this can be averaged and eliminated.

Incidentally, in a conventional system in which slot synchronization is not established between base stations, the time slot positions of base stations BS1, BS2, and BS3 are different, as shown in FIG. 8, for example. Therefore, when base station BS1 uses time slot TS1 and base station BS2 uses time slots TS2, TS3, and TS5, base station BS3 can use them since time slots TS4 and TS6 are normally empty slots. However, if these time slots TS4 and TS6 are used, they will interfere with the time slots TS2, TS3, and TS5 that are already in use, so they cannot be used. Therefore, the effective utilization rate of communication channels is low, and traffic imbalance cannot be effectively reduced.

[0048] Also, in this embodiment, the central radio transmitting station D
S1 and DS2 are provided to transmit a slot synchronization signal, and each base station BBS and mobile station establish time slot synchronization based on this slot synchronization signal.
Compared to the case where wired control lines are laid from the control station CS to each base station to supply synchronization signals, time slot synchronization can be achieved between each base station and with mobile stations with relatively simple equipment and control. be able to.

Furthermore, in this embodiment, the central radio transmitting station DS
1. Since the DS2 is shared with the base station of the selective call communication system, an integrated mobile radio communication system including a selective call function can be constructed with relatively simple equipment.

It should be noted that the present invention is not limited to the above embodiments. For example, in the above embodiment, slot synchronization is established at both the base station and the mobile station, but slot synchronization may be established only at the base station or only at the mobile station. In this case, the mobile station or base station on the side that does not establish slot synchronization may establish slot synchronization based on a signal sent from the base station or mobile station on the side that has established slot synchronization.

[0051] Furthermore, in the above embodiment, there are two central radio transmitting stations.
Although the case where a station is provided has been described, only one station may be provided, or three or more stations may be provided. Further, in the case where two or more stations are provided, the transmission frequencies of the respective central radio transmitting stations do not necessarily have to be different, and the same transmission frequency may be used for time-division transmission. In this case, if the identification code of the dominant radio transmitting station is inserted into the slot synchronization signal, the base station and mobile station can always re-establish slot synchronization based on the slot synchronization signal sent from the same dominant radio transmitting station. can. Further, the slot synchronization signal does not necessarily need to be transmitted all the time, and may be transmitted periodically or randomly intermittently.

Furthermore, the format of the slot synchronization signal may be configured as shown in FIG. 9, for example. In other words, since the synchronization signal SYNC is extremely short compared to the time slot length, the synchronization signal SYNC is placed after the synchronization signal SYNC.
For example, the data representing the position of the NC is
Data indicating how many bits apart the end bit of is from the start position K of the frame may be inserted. In this way, the position of K can be easily calculated from the above data at the base station and the mobile station.

Further, in the above embodiment, the central radio transmitting station was provided to cover the entire service area of the system, but it does not necessarily have to be provided to cover the entire service area; for example, if the traffic is average It may also be set up to cover only service areas in urban areas with high traffic rates.

Furthermore, automatic frequency control (AFC) means is provided in the base station and/or the mobile station,
The radio frequencies of the base station and mobile station may be controlled based on the transmission frequency of the central radio transmitting station. In this way, the radio frequencies of the base station and mobile station can be made extremely stable, and the crystal oscillation circuit of the frequency synthesizer can be made inexpensive. Also,
In addition to performing AFC based on the transmission frequency of the central radio transmitting station, for example, radio frequency reference information is inserted into the data area of the slot synchronization signal, and base stations and mobile stations perform self-transmission based on this reference information. The radio frequency may be stabilized.

Furthermore, the time slot of the control channel used when the mobile station transmits the outgoing signal may be randomly selected. For example, the telephone number of the mobile station may be divided by the number of time slots and the time slot corresponding to the remaining number may be selected and used. In addition, if a response signal cannot be received, it is preferable to randomly change the transmission time slot and transmit the signal again. This is effective in preventing collisions of transmitted signals with other mobile stations.

In addition, the shape and size of the area covered by one central radio transmitting station, the format of the slot synchronization signal, the means for establishing synchronization based on this slot synchronization signal, the base station and mobile station The configuration, the control procedure of the control circuit, the control contents, etc. can be modified in various ways without departing from the gist of the present invention.

[0057]

As described in detail above, according to the present invention, a central radio transmitting station is provided, from which a reference synchronization signal is wirelessly transmitted to at least one of a plurality of base stations and mobile stations,
By establishing time slot synchronization in at least one of a plurality of base stations and mobile stations based on this reference synchronization signal, the base stations can mutually use different time slots on the same radio frequency to reduce traffic. It is possible to provide a mobile radio communication system that can flexibly respond to bias and can achieve this with simple equipment and control.

According to another aspect of the present invention, at least one of each base station and mobile station is provided with frequency variable control means,
This frequency variable control means performs frequency variable control to keep the radio frequency for telephone calls constant based on the reference synchronization signal transmitted from the central radio transmitting station, which increases the cost for base stations and mobile stations. It is possible to provide a mobile radio communication system in which a radio frequency can be maintained stably at all times without providing an oscillation circuit, thereby improving communication quality and reducing the cost of base stations and mobile stations.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a mobile radio communication system according to an embodiment of the present invention.

FIG. 2 is a circuit block diagram showing the configuration of a mobile station in the system shown in FIG. 1.

FIG. 3 is a circuit block diagram showing the configuration of a base station of the system shown in FIG. 1.

FIG. 4 is a flowchart showing the control procedure and control contents of the control circuit of the mobile station shown in FIG. 2;

FIG. 5 is a flowchart showing the control procedure and control contents of the control circuit of the base station shown in FIG. 3;

FIG. 6 is a diagram showing an example of the format of a slot synchronization signal transmitted by a central radio transmitting station.

FIG. 7 is a timing diagram showing a state in which time slot synchronization is established between a plurality of base stations.

FIG. 8 is a timing diagram showing a conventional state in which time slot synchronization between multiple base stations is not achieved.

FIG. 9 is a diagram showing another example of the format of the slot synchronization signal transmitted by the central radio transmitting station.

FIG. 10 is a schematic configuration diagram of a conventional mobile/car radio telephone system.

FIG. 11 is a diagram showing an example of a transmission sequence of the system shown in FIG. 10;

FIG. 12 is a diagram showing an example of a signal format of a transmission signal.

[Explanation of symbols]

NW...wired telephone network, CS...control station, CL, CL1 to CL
n...wired line, DCL1, DCL2...wired line for selective calling, BBS1, BBS2,...base station, DS1, DS2
...Controlling radio transmitting station, EE1, EE2...Large wireless zone formed by the controlling wireless transmitting station, 11...Telephone, 12,5
2... Audio encoder, 13, 53... Error correction encoder, 14,
54... Digital modulator, 15, 55... Adder, 16,
56...Power amplifier, 17, 57...High frequency switch, 18
, 58... antenna, 21, 61... receiver, 22, 62...
Digital demodulator, 23, 63...Error correction decoder, 24
, 64... Audio decoder, 25... Receiver, 30, 70... Control circuit, 31... Display, 32, 72... Frequency synthesizer, 33, 73... Reception field strength detection circuit, 34... Transmission request switch, 40... Battery, 51...Hybrid circuit,
30a, 70a...Slot synchronization signal reception control means, 3
0b, 70b...Time slot synchronization establishment means.

Claims (3)

[Claims] Claim 1: A mobile station comprising a plurality of base stations, each forming a wireless zone, and a plurality of mobile stations connected to these base stations in a time-division multiplex manner via a digital radio line in which a plurality of time slots are time-division multiplexed. In the mobile radio communication system, at least one central radio transmitting station is provided for wirelessly transmitting a reference synchronization signal to at least one of the plurality of base stations and the plurality of mobile stations, A mobile radio communication system characterized in that at least one of the mobile stations is equipped with synchronization means for establishing time slot synchronization of a digital radio line based on a reference synchronization signal transmitted from the central radio transmission station. 2. The central radio transmitting station is provided at a pager base station for transmitting a selective call signal to a selective call receiver, or a pager base station for transmitting a selective call signal to a selective call receiver. The mobile radio communication system according to claim 1, characterized in that the mobile radio communication system has the function of a station. 3. A mobile station comprising: a plurality of base stations each forming a wireless zone; and a plurality of mobile stations connected to these base stations in a time-division multiplex manner via a digital radio line in which a plurality of time slots are time-division multiplexed. In the mobile radio communication system, at least one central radio transmitting station is provided for wirelessly transmitting a reference synchronization signal to at least one of the plurality of base stations and the plurality of mobile stations, At least one of the mobile stations includes a synchronization means for establishing time slot synchronization of a digital radio line based on a reference synchronization signal transmitted from the central radio transmitting station, and a synchronizing means for establishing time slot synchronization of a digital radio line based on a reference synchronization signal transmitted from the central radio transmitting station. 1. A mobile radio communication system comprising: variable frequency control means for variably controlling a radio frequency for telephone calls in order to keep it constant based on a signal.