JP2683678B2 - Mobile communication system - Google Patents

Description

TECHNICAL FIELD The present invention relates to a mobile communication system. In particular, it relates to switching of wireless channels for ensuring communication quality of mobile stations. According to the present invention, a signal to be transmitted is time-compressed and communicated with another station in a vacant time, so that a wireless channel is switched without disconnecting a line in communication.

[Conventional technology]

As a typical example of the mobile communication system, a car telephone system has been conventionally known. In the general car phone system,
A plurality of base stations are installed in the service area. A mobile station moving within the service area is wirelessly connected to one base station and is connected to a fixed telephone network via the base station. An exchange is installed between the base station and the fixed telephone network. The connection between the mobile station and the base station is controlled by the control station.

In such a mobile communication system, in order to maintain the communication quality of the mobile station in communication, control is performed to switch the radio channel in use due to zone shift, interference, or other reasons.

 FIG. 9 shows a conventional control procedure for switching wireless channels.

First, a new radio channel is designated from the control station to the mobile station and the transfer destination base station. The destination base station that has received the designation starts transmitting the downlink loop check signal. The loop check signal is a signal for confirming that the wireless line is connected. On the other hand, the mobile station that has received the designation of the radio channel switches the radio channel used by the mobile station and transmits the uplink loop check signal after receiving the downlink loop check signal. Upon receiving the uplink loop check signal, the transfer destination base station ends the transmission of the downlink loop check signal. After confirming the end of the downlink loop check signal, the mobile station ends the transmission of the uplink loop check signal. After confirming the end of the uplink loop check signal, the transfer destination base station further ends the wireless channel switching operation and starts communication.

In the wireless channel switching method by transmitting / receiving the loop check signal, the confirmation that the wireless channel designation has been accurately transmitted to the base station and the mobile station and the quality of the communication line are simultaneously confirmed.

[Problems to be solved by the invention]

The transmission quality in the wireless section is not always sufficient because it is affected by fading and other factors. Therefore, the signal from the source base station to the mobile station that specifies the wireless channel is
There is a possibility of making a mistake on the wireless section. Therefore, when switching the wireless channel by the loop check signal, it is not possible to confirm whether or not the correct wireless channel is designated for the mobile station until both the mobile station and the base station have completely switched the wireless channel. . For this reason, conventionally, the base station of the transfer source has to manage the radio channel so that the mobile station may return to the original radio channel at any time until the channel switching of the mobile station is completely completed. There was a drawback that the control load was large. Further, when switching the wireless channel again, it is necessary to disconnect the wireless line each time, which causes a problem that communication is interrupted.

In addition, it is difficult to confirm the quality of the assigned wireless channel at the time of switching the wireless channel unless the channel is actually switched to the designated wireless channel. Therefore, conventionally, a method of confirming with a loop check signal has been adopted. However, this method requires a temporary but complete disconnection of the line between the mobile station and the base station to confirm the new radio channel and radio line. The time required for this confirmation is relatively long, and there is a drawback that communication during that time is interrupted. In addition, as a result of confirmation, if the quality of the assigned wireless channel is poor, it is necessary to switch the wireless channel again, so that communication is interrupted again, and the control load increases. there were.

Furthermore, when switching the wireless channel between zones, the switching station switches the destination of the information signal from the migration source base station to the migration destination base station, but when transmitting the signal from the switching station to the mobile station via the migration source base station. In the case of transmitting a signal to a mobile station via the transfer destination base station, there is a drawback that the phase shifts when the signal is transmitted from the base due to the characteristics of the wired transmission path and other characteristics. The relationship between the transmission timing of the two base stations and the reception timing of the mobile station is shown in Fig. 10 and
Figure 11 shows.

If the signal of the transfer destination base station is transmitted earlier than the signal of the transfer source base station as shown in FIG. 10, before the mobile station finishes the signal from the transfer source base station and switches the receiver. , The signal from the transfer destination base station reaches the mobile station.
Therefore, the mobile station cannot receive a signal from the time when the transfer destination base station transmits the signal to the time when the mobile station switches the receiver. Therefore, the signal disappears.

Conversely, as shown in FIG. 11, when the signal of the transfer destination base station is transmitted later than the signal of the transfer source base station, the mobile station
Communication is interrupted between the end of the signal from the transfer source base station and the arrival of the signal from the transfer destination base station.
That is, a signal interruption occurs.

An object of the present invention is to solve the above problems and to provide a mobile communication system capable of switching a radio channel without disconnecting the line between a mobile station and a base station during communication.

[Means for solving the problem]

The mobile communication system of the present invention includes a plurality of base stations and a mobile station wirelessly connected to any one of the plurality of base stations, and each base station wirelessly communicates with a mobile station communicating with itself. In the mobile communication system, the base station includes means for switching the channel and designating to transmit / receive a signal to / from another base station, and the mobile station includes means for switching the wireless channel according to the designation of the designating means. And the mobile station includes means for time-compressing a signal to be transmitted so that an empty time slot occurs in a part of the radio channel allocated for communication, and the means for switching is the radio channel specified by the specifying means. Prior to switching to, the wireless channel can be used by transmitting and receiving signals on the specified wireless channel at the timing of the above free time slot. Characterized in that it comprises a means for confirming whether or not.

The signal to be transmitted and received is a digital signal, and the means for time compression writes the signal to be transmitted in accordance with the clock of the signal, buffer means for temporarily storing the signal, and reads out from the buffer means by a clock faster than the clock and sends it out. Means, buffer means for writing and temporarily storing the received signal in accordance with the clock of the received signal, and means for reading out in accordance with a clock having a speed equal to the clock of the signal to be sent from the buffer means.

(Operation)

A signal is time-compressed to create an empty time slot, and the empty time slot is used to transmit and receive a signal between the mobile station and another base station during communication between the mobile station and the base station. As a result, prior to switching the wireless channel, a new wireless channel can be assigned and a wireless channel can be checked without disconnecting the communication.

〔Example〕

FIG. 1 is a block diagram of an automobile telephone system according to an embodiment of the present invention.

In this system, a plurality of base stations 4 and a mobile station 5 wirelessly connected to any of the plurality of base stations 4 are provided. The base station 4 is connected to the fixed telephone network 1 via the exchange 2. The base station 4 is also connected to the control station 3, and the control station 3 controls the connection between the base station 4 and the mobile station 5.

The feature of the present embodiment is that the plurality of base stations 4 and mobile stations 5 each include means for time-compressing a signal to be transmitted, and the mobile station 5 has an idle time obtained by this time-compression means. It is to include means for switching a radio channel at the timing of a slot and transmitting and receiving a signal to and from a base station different from the base station of the communication partner.

FIG. 2 is a block diagram showing an example of the base station 4.

The base station 4 includes a multiplex / frame conversion circuit 21, a superframe conversion circuit 23, a transmission / reception circuit 24, a desuperframe conversion circuit 25, a separation / deframe conversion circuit 27, and a control circuit 28. The speed conversion circuits 22 and 26 are provided as means for compressing.

The speed conversion circuit 22 includes buffer means for temporarily storing a signal to be transmitted by writing the signal in accordance with a clock, and means for reading out the signal from the buffer means by a clock faster than the clock and transmitting the signal. The speed conversion circuit 26 includes a buffer means for writing and temporarily storing the received signal in accordance with the clock of the received signal, and a means for reading out in accordance with a clock having a speed equal to the clock of the signal to be sent from the buffer means.

The multiplexing / framing circuit 21 multiplexes a digital format information signal and control signal addressed to the mobile station, and outputs this in a frame format in synchronization with a frame synchronization signal. The speed conversion circuit 22 time-compresses the framed signal. The superframe conversion circuit 23 adds an empty time slot to the time-compressed frame to form a superframe synchronized with the superframe synchronization signal. Transmitter / receiver circuit 24
Transmits the superframe to the mobile station 5 and receives the superframe from the mobile station 5.

The de-superframe conversion circuit 25 extracts a free time slot portion from the received signal in the superframe format,
Detect superframe sync signal. Speed conversion circuit 26
Expands the desuperframed signal in time.
The separation / deframe conversion circuit 27 separates the time-expanded signal, and outputs the separated information signal and control signal.

The control circuit 28 supplies a signal to be inserted into a vacant time slot to the super framing circuit 23, sets a radio channel used by the transmitting / receiving circuit 24, and de-super framing circuit 25.
The inspection of the signal of the empty time slot taken out by the above and other control in the base station 4 are performed.

FIG. 3 is a block diagram showing an example of the mobile station 5.

The mobile station 5 includes a transmission / reception circuit 31, a desuperframe conversion circuit 32, a demultiplexing / deframe conversion circuit 34, a control circuit 35, and a multiplexing / demultiplexing circuit 34.
A framing circuit 36 and a super framing circuit 38 are provided, and further speed conversion circuits 33 and 37 are provided as means for time-compressing a signal to be transmitted.

The operation of the transmission / reception circuit 31, the desuperframe conversion circuit 32, the speed conversion circuit 33, the separation / deframe conversion circuit 34, the multiplexing / frame conversion circuit 36, the speed conversion circuit 37, and the superframe conversion circuit 38 is performed by each of the base stations 4. It is equivalent to the circuit.

The control circuit 35 sets the radio channel used by the transmission / reception circuit 31, and sets the superframe by the signal of the idle time slot extracted by the desuperframe conversion circuit 32 and the control signal separated by the separation / deframe conversion circuit 34. It supplies a signal to be inserted into the idle time slot to the circuit 38, and controls other mobile station 5 inside.

 FIG. 4 shows the flow of control for wireless channel switching.

First, the radio channel F ₂ is designated from the control station to the mobile station and the transfer destination base station. The designation to the mobile station is performed using the control signal from the migration source base station.

The destination base station that received this designation is
Transmits a signal for confirmation at F _2, simultaneously starts the reception of the radio channel F _2. When a confirmation signal from the mobile station is received, a confirmation report is sent to the control station.

The mobile station transmits / receives signals to / from the source base station during the subframes included in the superframe by the radio channel F ₁ . The transmission / reception circuit is switched to the radio channel F ₁ only in the vacant time slot portion included in the superframe, and a signal for confirmation is transmitted to the transfer destination base station, and at the same time, a signal from the transfer destination base station is received. Immediately before the end of the idle time slot, the radio channel of the transmission / reception circuit is switched to F ₁ again to communicate with the migration source base station. At this time, the control signal channel included in the subframe is used to report to the control station whether or not the confirmation signal has been received.

When the confirmation signal cannot be received from at least one of the mobile station and the base station, the control station again designates the same channel as the previously used radio channel for the mobile station and the transfer destination base station.

FIG. 5 shows an example of the structure of a super frame. In this embodiment, a digital signal is framed, some of the frames are collectively time-compressed as one unit, and an empty time slot is added to this to form a superframe. Each frame is called a subframe to distinguish it from a superframe. FIG. 5 shows an example in which a superframe is composed of four subframes and one free time slot.

FIG. 6 shows a time chart of transmission / reception signals of a transfer source base station, a transfer destination base station and a mobile station. In this figure, free time slots are indicated by AF and ag. The same code indicates that transmission / reception is being performed between them.

As shown in FIG. 6, when the wireless base station is designated, the transfer destination base station starts to monitor the channel at the same time as transmitting a signal on that channel. Therefore, the timing of the idle time slot included in the superframe from the mobile station is not missed. Therefore, if there is no error in the wireless channel designation from the control station or in the wireless section, the mobile station and the transfer destination base station can receive the confirmation signal. If the confirmation signal can be received by the mobile station and the transfer destination station, it can be confirmed not only that the wireless channel has been specified without error but also that the mobile station can transmit using the wireless channel.

By this method, the specified wireless channel can be confirmed without disconnecting the wireless line in communication. Further, even if the wireless channel is designated incorrectly, the wireless channel is not completely switched yet, so that the wireless channel designation signal can be easily retransmitted.

FIG. 7 shows a time chart of transmission / reception signals of each station when measuring the quality of a designated wireless channel.

In the switching control described above, it is confirmed whether or not the designated wireless channel can be used, but the quality of that wireless channel is not measured. This quality can also be measured using free time slots.

That is, the mobile station that has received the confirmation signal from the transfer destination base station using the idle time slot and the transfer destination base station that has received the confirmation signal from the mobile station measure the quality of the signal. , The measurement result is added to the confirmation report and notified to the control station. At this time, if either one of the mobile station and the transfer destination base station cannot satisfy the certain quality, a new radio channel is allocated from the control station. At this time, a new radio channel is newly assigned to the mobile station and the transfer destination base station, and the quality is confirmed again by the designation.

With this control method, it is possible to perform a new quality measurement before switching the wireless channel, and after switching the wireless channel, the wireless channel is switched again because the transmission quality of the wireless channel is poor. The load can be eliminated. Also. It is possible to prevent quality deterioration due to communication interruption during loop check signal transmission, which has occurred in the conventional car telephone system.

FIG. 8 shows a time chart of transmission / reception signals of each station when synchronization adjustment is performed at the time of wireless channel switching.

By using the idle time slot, it is possible to prevent signal loss and momentary interruption at the time of wireless channel switching.

To switch the wireless channel so that there is no signal loss or interruption, adjust the delay that occurs in the wired transmission line between the base stations of both the source and the destination, and signal transmission timing at both base stations. Need to match.

To do this, the mobile station makes the uplink synchronization of the radio section dependent on the downlink synchronization, and the transfer destination base station monitors the mobile station in communication and determines the position of the idle time slot of the superframe to be transmitted. A method of adjusting the timing by detecting may be considered.

At this time, the radio channel F ₁ used between the source base station and the mobile station is assigned the one with less interference in the zone. However, due to the influence of interference, it is difficult for the transfer destination base station to receive the radio channel F ₁ . Therefore, it is not practical to monitor the radio channel F ₁ by the transfer destination base station to detect the position of the idle time slot.

However, the newly assigned radio channel F ₂ is considered to be less affected by interference at the transfer destination base station. Therefore, when the mobile station receives the designation of the radio channel F ₂ for switching the radio channel, it uses the idle time slot of the superframe to transmit a signal on the radio channel F ₂ . In the transfer destination base station, when the radio channel F ₂ is assigned, it is switched to the radio channel F ₂ of the transmission / reception circuit to receive the signal from the mobile station. As a result, the transfer destination base station can receive the signal only when the mobile station switches the radio channel in the idle time slot of the superframe. If the signal is transmitted in accordance with this timing, the transmission timing of the transfer destination base station can be matched with the transmission timing of the transfer source base station, and it is possible to prevent the loss and instantaneous interruption of the signal.

Although the car telephone system has been described as an example in the above embodiment,
The present invention can be similarly implemented in other mobile communication systems. Further, the present invention can be similarly implemented by a signal system other than the super frame.

〔The invention's effect〕

As described above, the mobile communication system of the present invention, without disconnecting the line between the mobile station in communication and the base station,
It is possible to confirm the quality of a wireless channel that is not currently used for communication, confirm a new wireless channel when switching the wireless channel, and adjust the cycle. Therefore, there is an effect that the control load can be reduced and line disconnection and other communication quality deterioration during communication can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram of a car telephone system according to an embodiment of the present invention. FIG. 2 is a block diagram showing an example of a base station. is there. FIG. 3 is a block diagram showing an example of a mobile station. FIG. 4 is a diagram showing a flow of control of wireless channel switching. FIG. 5 is a diagram showing a configuration example of a super frame. FIG. 6 is a time chart of transmission / reception signals of a transfer source base station, a transfer destination base station, and a mobile station. FIG. 7 is a time chart of transmission / reception signals of each station when measuring the quality of a designated wireless channel. FIG. 8 is a time chart of transmission / reception signals of each station when synchronization adjustment is performed at the time of wireless channel switching. FIG. 9 is a diagram showing a conventional control procedure for wireless channel switching. FIG. 10 is a diagram showing the relationship between the transmission timing of two base stations and the reception timing of a mobile station. FIG. 11 is a diagram showing the relationship between the transmission timing of two base stations and the reception timing of a mobile station. 1 ... Fixed telephone network, 2 ... Exchange station, 3 ... Control station, 4 ...
... base station, 5 ... mobile station, 21, 36 ... multiplex / frame conversion circuit, 22, 26, 33, 37 ... speed conversion circuit, 23, 38 ... superframe conversion circuit, 24, 31 ... transmission / reception Circuit, 25, 32
…… Desuperframe circuit, 27, 34 …… Separation / deframe circuit, 28,35 …… Control circuit.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-63-48925 (JP, A) JP-A-64-55924 (JP, A) JP-A-64-12628 (JP, A)

Claims (1)

(57) [Claims] 1. A plurality of base stations, and a mobile station wirelessly connected to any of the plurality of base stations, wherein each of the plurality of base stations wirelessly communicates with a mobile station communicating with itself. In the mobile communication system, the mobile communication system includes means for switching the channel and designating to transmit / receive a signal to / from another base station, wherein the mobile station includes means for switching the radio channel according to the designation of the designating means. Each of the plurality of base stations and the mobile station includes means for time-compressing a signal to be transmitted so that an idle time slot occurs in a part of a radio channel allocated for communication, and the switching means is the above-mentioned designation. Before switching to the wireless channel designated by the means, the signal is transmitted / received by the designated wireless channel at the timing of the idle time slot. A mobile communication system characterized by including means for confirming whether or not the wireless channel can be used.