JP2766894B2 - Inter-station synchronization method in mobile communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a digital mobile communication system having a small zone configuration in which communication is performed with a mobile station in a zone of each base station via a wireless channel, and a transmission timing between base stations. The present invention relates to an inter-station synchronization method for synchronizing stations.

[Conventional technology]

In a digital mobile communication system having a small zone represented by a mobile telephone system, a plurality of base stations and an exchange are connected by a communication line, each base station forms a wireless zone, and mobile stations (automobiles) in the zone are formed. ) And a radio channel, and the same control signal is transmitted at the same frequency from a plurality of base stations because a multi-station simultaneous transmission technique is used for transmission of the control signal.

In the small zone digital mobile communication system, it is necessary to switch the channel between the wireless zones as the mobile station moves. In this case, it takes time to set a new channel and the like, so that an instantaneous interruption occurs. In order to reduce the time of the instantaneous interruption or to perform the above-described multi-station simultaneous transmission, it is necessary to synchronize the transmission timing between the base stations.

Therefore, conventionally, a method has been developed in which a dedicated receiver for receiving a signal transmitted from an adjacent base station is provided in the base station, and synchronization between the base stations is established based on the reception timing. That is, in the conventional inter-station synchronization method, the delay time of each communication line from the exchange to many base stations is set to be the same so that the transmission timing can be synchronized for many base stations under one exchange. This is a method of matching, and for this purpose, a method of matching the transmission timing of an adjacent base station with one base station as a reference is used.

[Problems to be solved by the invention]

In this conventional method, a subordinate relationship is set in advance at a number of base stations, a phase difference between the exchange and the base station is measured based on signal transmission in a radio section, and the subordinate station adjusts the phase difference with respect to the master station. The phase difference measurement in the wireless section plays the most important role. Therefore, this conventional method is susceptible to radio conditions such as the propagation path conditions between base stations, the position of base station antennas, and the like at the time of system startup or system expansion, and the installation work is complicated. There were drawbacks.

Further, the system is extremely poor in applicability to a system in which a minimum zone is set to increase the subscriber capacity and a system with a low antenna height, and the system is affected by surrounding buildings even after the system is introduced. Also, when a large area is covered by a very large number of base stations, it is necessary to sequentially adjust the phase synchronization from the master station to the slave station and then to the slave station, and synchronization is established in all service areas. There was a drawback that it took time to complete.

Further, when phase synchronization is performed across an upper station to which the base station belongs (for example, an exchange) or across exchanges, the transfer timing from the upper station and the phase synchronization at the base station between extremely distant base stations. However, there is a disadvantage that the delay amount at the base station increases when any of the timings determined by the above becomes large.

The present invention has been made in view of the above points, and in a mobile communication system having a small zone configuration having a plurality of exchanges and a number of base stations under the exchanges, a large number of services within a wide service area covered by the plurality of exchanges are provided. It is an object of the present invention to provide an inter-station synchronization method in a mobile communication system capable of synchronizing transmission timing in a base station and easily establishing synchronization at the time of system startup and enabling fast synchronization.

[Means for solving the problem]

The inter-station synchronization method in the mobile communication system according to the present invention includes:
A small zone configuration in which a number of base stations are connected to each of a plurality of exchanges via a communication line, each of the plurality of base stations forms a wireless zone, and communicates with a mobile station in the zone via a wireless channel. In this mobile communication system, first, timing information is transferred between exchanges to synchronize the timing phases between the exchanges, and the timing information is transferred to a base station under the exchange.

The base station generates a base station reference timing with this timing information as an initial value, performs transmission frame timing at the base station reference timing, and transmits a transmission signal transmitted by an adjacent base station or a mobile station communicating with the adjacent base station. Synchronize the base station reference timing phase with the adjacent base station based on the timing information obtained by interception.

At this time, when the delay amount of the communication line of the base station exceeds a predetermined value, the timing control amount of the upper exchange is calculated based on the delay amount, and the offset amount is given to the timing phase at the exchange. Control.

[Action]

In the present invention, synchronization is performed by transferring timing information between exchanges, the base station generates a base station reference timing using the timing information from the exchange as an initial value, and establishes base station synchronization by receiving a radio signal. When the amount of delay at the base station becomes large, inter-station synchronization is established by controlling the timing of the exchange.

Therefore, in comparison with the conventional inter-station synchronization method in which only inter-base synchronization is performed by receiving a radio signal, in the present invention, synchronization can be quickly established between a large number of base stations in a wide area, and at the time of system startup or system startup. During expansion or the like, it is possible to be less affected by wireless conditions such as the state of a propagation path between base stations and the position of a base station antenna.

〔Example〕

FIG. 1 shows a configuration diagram of an embodiment of the present invention. In the figure,
101a and 101b are exchange stations, 102a and 103a are base stations, 113 is a mobile station, 114 is a control station, and these constitute a small zone mobile communication system.

Here, the above-mentioned mobile communication system is represented by a car telephone system, and its general system configuration is as shown in FIG. In the figure, 101a, 101b and 101c are exchanges connected to each other by wired communication circuits 115 and 116, the exchange 101a is connected to base stations 102a, 102b and 102c, and the exchange 101b is replaced with base stations 103a and 103c.
Switching stations 101c are separately connected to base stations 104a, 104b, and 104c via wired communication lines, respectively, to b and 103c.

Each of the base stations 102a to 102c, 103a to 103c, 104a to 104c has a plurality of transceivers, performs wireless communication with mobile stations in a predetermined zone, and performs the communication with the switching station 101a, 101b or 101c. Is connected to the communication network 118 via.

In FIG. 3, wireless communication is possible between the base station 102c and the mobile stations 105 and 106, and similarly, the mobile stations 107 and 108 are connected to the base station 103a.
The mobile stations 109 to 111 are located in the zone of the base station 103e, and the mobile station 112 is located in the zone of the base station 104b.

In the mobile telephone system having such a configuration, in the present embodiment, first, synchronization is performed by exchanging timing information between the exchanges 101a to 101c, and the transmission time of the downlink signal for each subordinate base station is synchronized. Therefore, each of the exchanges 101a to 101c
Are the subordinate base stations 102a to 102c, 103a to 103c, 104a to
Send a signal to 104c.

Therefore, each communication line length between the exchange 101a and the base stations 102a to 102c, each communication line length between the exchange 101b and the base stations 103a to 103c, and each communication line length between the exchange 101c and the base stations 104a to 104c. , The signals from the base station should be synchronized, but usually the lengths of the communication lines are not always the same. Therefore, the base stations 102a to 102c, 103a to 103c, 104a to 104c
Synchronizes base stations with each other based on timing information from the upper exchanges 101a to 101b and 101c and a signal obtained by receiving a radio channel signal from an adjacent base station or mobile station.

At this time, if the difference between the timing information from the exchange and the transmission timing is equal to or greater than a specified value, the upper exchange is notified of the fact, and the exchange adjusts the transmission timing to the base station.

Next, the configuration and operation of this embodiment will be described in more detail with reference to FIGS. 1, the same components as those in FIG. 3 are denoted by the same reference numerals.

In FIG. 1, the exchanges 101a and 101b have a relation that the exchange 101a is a master station and the exchange 101b is a slave station, and the exchange 101b sends out a signal at the same timing as the exchange 101a.

The exchange 101a includes a reference timing generation circuit 120a, a timing transfer circuit 121a, a timing addition circuit 122a, and a control circuit 123a.
Similarly, the exchange 101b is a reference timing generation circuit.
120b, timing transfer circuit 121b, timing addition circuit 122
b and a control circuit 123b. Reference timing generation circuit 120a
And the cycle of the reference timing signal generated by 120b is set according to the signal length to be transmitted. Specifically, the transmission signal frame length or an integral multiple thereof is preferable.

The timing transmission / reception circuits 121a and 121b transmit / receive the reference timing signal from the other exchange through a dedicated line or a part of a communication line, and adjust the timing with accuracy within a transfer time difference in this line. Here, since the exchange 101a is the master station, the reference timing signal generated by the reference timing generation circuit 120a in the exchange 101a is transmitted through the timing exchange circuit 121a and the timing exchange circuit via a part of the dedicated line or the communication line. Sent to 121b, received here,
The phase difference (timing difference) from the reference timing signal generated by the reference timing signal generation circuit 120b in the switching station 101b as the slave station is detected.

The control circuit 123b calculates a timing control amount that makes the timing difference zero, and controls the output timing of the reference timing generation circuit 120b. At the same time, the reference timing signal is transferred from the timing exchange circuit 121b to the exchange 101a, and is returned by the timing exchange circuit 121a and received again by the timing exchange circuit 121b to calculate the transfer time, and the transfer time from the exchange 101a is calculated. The transfer time is subtracted from the timing reception time. In this way, it is difficult to completely match the timings because there is a difference in the transfer time depending on the line, but it is possible to substantially match the timing phases between the exchanges 101a and 101b.

Thus, even when there are three or more exchanges, the timing phases can be matched between adjacent exchanges in the same manner as described above, so that accumulation of delay to the exchanges serving as slave stations can be prevented, and accuracy can be reduced. Can be improved.

In addition, by applying to a system in which clocks are synchronized between stations and generating a timing by dividing the frequency based on the clock from the digital clock supply source,
In frequency synchronization, only phase synchronization need be performed as long as the high accuracy of the clock synchronization network is guaranteed.Therefore, after performing fast pull-in phase control at system start-up, the control circuit 123b fails the clock supply source. Unless there is
There is almost no need to control.

The above reference timing signal is supplied to the timing adding circuit 122.
a, 122b, after being added to transmission information from the communication network, the base station 10
2a, 103a, etc. are input to subordinate base stations. Here, the first
In the figure, a solid line indicates a transmission path of the transmission information, and a broken line indicates a transmission path of the reference timing information.

The base station is a base station 102a connected to the master switching station 101a.
And so on as masters, and as slave base stations in order from the base station close to the master. In this example, 102a is the master base station and 103a
Are slave base stations.

The base stations 102a and 103a generate base station reference timing by reference timing generation circuits 124 and 125 based on the timing information transferred from the exchanges 101a and 101b via the communication lines shown by broken lines.

Also, the base stations 102a and 103a have internal buffer circuits 126 and 127
, The transmission information input via the communication line is written at the timing WR of the input reference timing information added thereto, and the generated base station reference timing
Read with RR.

Here, the transmission information is obtained by multiplexing an error correction code or a frame synchronization signal in a transmission / reception unit (not shown), and further multiplexing a plurality of lines in the case of time division multiple access (TDMA).
This is a signal converted into a predetermined wireless section signal format, and as shown by the solid line in FIG.
After being temporarily stored in step 7, it is transmitted according to the base station reference timing. Therefore, the amount of delay by the buffer circuits 126 and 127 corresponds to the time difference between the reference timing information from the exchanges 101a and 101b and the base station reference timing information.

The slave base station 103a intercepts a radio signal from the master base station 102a or a radio transmission signal of the mobile station 113 that is performing radio communication with the master base station 102a, and thereby positions the master base station 102a with respect to the base station reference timing. Detect phase difference. Here, the base station 103a detects the phase difference between its reception timing and its own base station reference timing by the phase comparison circuit 128 by intercepting the radio transmission signal of the mobile station 113.

The above-described phase difference detection result is input to the control circuit 129, which controls the phase of the base station reference timing from the reference timing generation circuit 125 to match the base station reference timing of the master base station 102a. In general, the phase comparison is measured a plurality of times over a certain period of time, and the control is performed using the average value to reduce the jitter of the base station reference timing phase.

In addition, by controlling based not only on the phase difference measurement result due to the reception of the radio signal but also on the timing from the exchange (for example, the difference between the timing information from the exchange and the timing delayed by a certain amount is weighted. And the like, to determine the control amount), thereby preventing the abnormal increase in the buffer delay amount at the base station and the accumulation of the buffer delay amount between distant base stations via a plurality of exchanges.

As in the case of the switching center reference timing, the base station reference timing is applied to a system in which the clocks are synchronized between the stations, and the frequency is divided based on the clock from the digital clock supply source. , Only frequency synchronization needs to be performed as long as high accuracy of the clock synchronization network is guaranteed. Initially set the phase based on the timing from the exchange when starting the system, and after controlling the phase based on the phase difference measurement at the base station, unless there is a failure in the clock supply source,
There is almost no need to control.

Next, the base station reference timing will be described in more detail with reference to FIG. Generally, a base station and an exchange are connected by a plurality of lines according to the amount of traffic, and each line is not necessarily the same in length. Occurs. Fig. 2 (A)-
(C) shows three downlink communication lines from the exchange 101b and the base station 10
3a shows the transferred timing. Based on this, the base station reference timing generation circuit 125 sets an initial value of the timing phase in a certain fixed procedure.

For example, the timing may be a certain amount of delay from a specific line, a certain amount of delay from the average timing of a plurality of lines, or a certain amount of delay from the latest timing of all lines. . Further, a timing at which a timing faster than the timing of all lines becomes a fixed ratio may be used.
FIG. 2 (D) shows a case where the timing obtained by delaying the average timing of three lines by a fixed amount is used. After setting the initial value of the timing, the slave base station 103a measures the phase difference from the base station reference timing of the master base station 102a at a certain fixed time, and changes the timing so as to subtract the average value. The base station reference timing shown in (E) is obtained. At this time, the delay amount of each line at the base station is τ ₁ , τ ₂ ,
the τ _3. The base station 103a of each line temporarily stores the signal in the buffer circuit 127 as described above, and transmits the signal with a delay of this time.

The amount of the downlink buffer in the base station 103a, that is, the delay time increases due to the phase control in the base station 103a, and when the delay time exceeds a certain prescribed value, the control circuit 130 in the control station 114 from the base station.
Report to. The control circuit 130 is also configured to receive a report from another base station, and based on a report from a base station connected to the exchange 101b, gives a certain offset to the timing addition at the exchange 101b. To instruct.

For example, when receiving a report from all the base stations that the delay buffer amount exceeds the specified value by 50 msec, the switching center 101b is instructed to have an offset of 50 msec delay from the switching center reference timing. Alternatively, when the exchange 101b reports that the reception of the timing is behind the base station reference timing on many lines, the switching center 101b is instructed to perform an offset so that the exchange base reference timing is advanced.

In accordance with this instruction, the switching center 101b gives an offset to the timing phase added to the communication line for the base station.
Also, by setting the offset amount independently for each line and setting based on the buffer amount of the line at the base station notified via the control circuit for each line, the buffer amount at the base station is minimized. There are ways.

Note that the control circuit 130 is installed in an independent control station and is connected to the base station 103a and the exchange 101b by a control line, but the exchange 101b or one base station connected to the exchange 101b. May be included.

The control circuit 130 also manages the dependency of the base station in addition to the functions described above. That is, determine the subordination of the base station,
Each base station is notified of a base station to be subjected to phase measurement in each base station. Further, when a failure occurs in the base station reference timing relation of some base stations, a notification of a change in the subordination relation is sent. Furthermore, in the above description, a method is used in which the base station independently performs base station reference timing control by measuring the phase difference of the radio section signal of the base station. A method of indicating control stop, an instruction of execution, and further a method of receiving a report of a phase change amount at a certain base station and instructing a base station subordinate to the base station to control only the change amount. By using this, more stable and fast synchronization can be established.

As described above, in the present embodiment, at the time of system introduction, expansion, or start-up after system down, the timing synchronized by the exchange in the wired line is distributed to many base stations. Since the synchronization control between the base stations is started after setting an initial value irrelevant to the condition of the wireless transmission based thereon, there is an advantage that the synchronization can be quickly established over a wide area. In particular, when the requirements for the phase difference are not strict, most base stations satisfy the synchronization conditions at the initial setting stage, and do not require work such as adjustment of a receiving antenna due to wireless transmission conditions. Sufficient phase synchronization can be quickly established over a wide area by intervening and adjusting the radio section.

Further, as a result of the control based on the reception of the radio section signal at the base station, if the buffer amount of the base station increases, the exchange is instructed to change the exchange reference timing. Even if the phase error in the wired line of the exchange is large between the stations, the phase error can be corrected by this change, so that there is an advantage that the amount of buffer delay in the downlink in the base station can be reduced.

Further, in addition to the present embodiment, when information is compressed on the time axis and transmitted in the wireless section, such as when TDMA is adopted as a multi-access scheme in the wireless section, switching of the wireless channel is completed in an idle time. Accordingly, channel switching can be performed without interrupting communication.

〔The invention's effect〕

As described above, according to the present invention, timing synchronization is established between exchanges, so that synchronization can be quickly established between a large number of base stations in a wide area. In such cases, it is difficult to be affected by radio conditions such as the state of the transmission path between base stations and the position of base station antennas, so that installation work and adjustment at the time of introduction can be simplified, thereby increasing the subscriber capacity. It is suitable to be applied to a system with a minimum zone and a system with an antenna height. Further, according to the present invention, between base stations located at extremely distant distances such as different exchanges, a transfer timing from a higher-order base station and a base station reference timing determined by phase synchronization by the base station itself. The delay amount at the base station can be reduced even when the phase difference becomes large, and when the mobile station moves beyond the wireless zone and switches the base station with which to communicate, the communication is not interrupted instantaneously. And the like.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, FIG. 2 is an explanatory diagram of reference timing of a base station, and FIG. 3 is a system configuration diagram of a mobile communication system. 101a, 101b, 101c ... Exchanges, 102a to 102c, 103a to 103c, 10
4a to 104c: Base station, 105 to 113: Mobile station, 120a, 120b,
124, 125 ... reference timing generation circuit, 121a, 121b ... timing transfer circuit, 123a, 123b, 129, 130 ... control circuit, 1
26,127 ... Buffer circuit.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masami Yabuzaki 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Takanori Utano 1-16-1 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (1)

(57) [Claims] A plurality of base stations are connected to each of a plurality of exchanges via a communication line. Each of the plurality of base stations constitutes a wireless zone, and a mobile station and a mobile station within the zone use a wireless channel. In the mobile communication system having a zone configuration for performing communication, the plurality of exchanges synchronize timing timing by transferring timing information to each other, and transfer the timing information to a subordinate base station. A base station reference timing is generated using the timing information transferred from the switching station as an initial value, and a frame timing for transmitting a digital radio signal to the mobile station is performed at the base station reference timing. Synchronizing the base station reference timing phase with the adjacent base station by the timing information obtained by intercepting the transmission signal transmitted by the mobile station communicating with the base station. Calculates a timing control amount of the switching center of the upper on the basis of the delay amount when it exceeds the specified value delay amount in the communication line of the base station is predetermined,
An inter-station synchronization method in a mobile communication system, wherein a report is made to the exchange via a control line, and an offset is given to a timing phase in the exchange.