JP2825698B2 - Mobile switching system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile switching system, and more particularly to frame synchronization of a digital radio signal.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram showing a conventional mobile switching system. In the figure, 1 is an exchange and 1
a is a control device (hereinafter referred to as C) for executing the call processing of the exchange 1.
1b is a time-division switch for executing the exchange process. 2a and 2b are time-division switches 1 of the exchange 1
b, a base station line unit as an interface means, which interfaces with a radio base station described later and controls the interface. Reference numerals 3a and 3b denote radio base stations controlled by the base station line units 2a and 2b to perform radio / wired signal conversion. Reference numerals 4a and 4b are connected to the radio base stations 3a and 3b by radio lines 5a and 5b. Mobile device.

FIG. 8 is a block diagram showing a conventional mobile switching system. The difference from the mobile switching system shown in FIG. 7 is that the base station line units 2c and 2d use digital signals based on digital radio signals. Is 64Kbp
s (PCM) is provided with a coding / decoding module, and the time division switch 1b exchanges PCM signals.

Next, the operation will be described. Mobile unit 4a,
When the radio lines 5a and 5b with the 4b are digitized,
Frame synchronization in the mobile units 4a and 4b becomes a problem. Since the digitized radio lines 5a and 5b have low transmission efficiency, the 64 Kbps PCM signal used in the telephone switching network cannot be passed as it is. Therefore, it is a general method to perform digital signal processing in a certain time unit, compress the digital signal processing, and cut a frame for each unit for transmission. That is, the transmission of the control information voice information is possible only when the frame synchronization is established.

In FIG. 7, when the mobile units 4a and 4b talk, a digital radio signal transmitted from the mobile unit 4a is converted into a wired digital signal by the radio base station 3a, and is converted by the base station line unit 2a to 64 Kbps. Since the speed is converted to 64 kbps at the base station line unit 2 b through the time division switch 1 b, the radio lines 5 a and 5
The transmission speed is converted to the transmission speed b. And the wireless base station 3b
The signal arrives at the mobile unit 4b via the mobile station 4b, and the transmission of voice becomes possible only after frame synchronization is established in the mobile unit 4b. Here, if the mobile station 4a switches the radio line 5a due to handover (moving a zone) or the like, it becomes necessary to re-establish frame synchronization in the mobile station 4b.

As a method for avoiding the frame re-synchronization processing in the mobile units 4a and 4b, a configuration as shown in FIG. 8 may be adopted. This is because the base station line units 2c and 2d are provided with a module (hereinafter referred to as CODEC) for encoding / decoding a digital signal based on a digital radio signal, so that the digitized radio lines 5a and 5b are connected at one end, that is, at the base station. Line units 2c, 2
By terminating at d, in the time division switch 1b, 6
The exchange is performed using a 4 Kbps PCM signal.
In this configuration, the down-link digital radio signals from the base station line units 2c and 2d to the mobile units 4a and 4b are transmitted from the CODEC on the base station line units 2c and 2d, so that the synchronization is kept constant. Is possible. However, the CODEC is changed to the base station line unit 2
Since two passes are made in c and 2d, a new problem that the sound quality is deteriorated occurs.

[0007] References describing the technology related to such a conventional mobile switching system include, for example, JP-A-64-77334 and JP-A-2-219328.
Gazette, JP-A-1-190035, JP-A 2-2
No. 38732.

[0008]

Since the conventional mobile switching system is configured as described above, in the configuration shown in FIG. 7, it is necessary to resynchronize the frames in the mobile units 4a and 4b every time. In the configuration shown in FIG. 8, there is a problem that although the frame synchronization is ensured, the sound quality is degraded.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a mobile switching system which does not need to re-synchronize the frame with a mobile device every time and does not cause deterioration in sound quality. With the goal.

[0010]

According to a first aspect of the present invention, there is provided a mobile switching system which is disposed between a radio base station and an exchange and which interfaces a radio line with a frame synchronization detecting module. ,flame
Writes shift registers for the number of protection stages and line signals
A multi-frame unit for maintaining a constant frame synchronization of a downstream digital radio signal is provided.

In the mobile switching system according to the second aspect of the present invention, only a frame corresponding to a transmission delay amount is provided.
Each frame has a frame synchronization adjustment circuit for transmitting in advance.
Motivation.

Further, the moving object according to the third aspect of the present invention.
The switching system stores the ring buffer in the receiving ring buffer.
Buffer, the transmit ring buffer, and the receive ring buffer.
Buffer placed between the buffer and the transmit ring buffer.
It consists of a frame conversion unit that performs conversion.
You.

[0013]

According to the first aspect of the present invention, the multi-frame unit is disposed between the radio base station and the exchange, and is provided in the interface means for interfacing the radio line, and keeps the frame synchronization of the downstream digital radio signal constant. Thus, it is not necessary to re-synchronize the frame with the mobile device every time the mobile device is changed, and a mobile switching system with less deterioration in sound quality is realized.

Further, the frame synchronization adjusting circuit according to the second aspect of the present invention is arranged in each mobile station, and performs transmission ahead of a frame corresponding to the transmission delay amount to further reduce the delay amount. A mobile switching system that can be compressed to a value or less is realized.

Further, the frame conversion unit according to the third aspect of the present invention converts the digital signal read from the reception ring buffer into a frame and then writes the digital signal into the transmission ring buffer, thereby further reducing the delay amount. Realizing a mobile switching system that can perform

[0016]

[Embodiment 1] An embodiment of the present invention will be described below with reference to the drawings. FIG.
Is a block diagram showing an embodiment of the invention of this. In the figure, 1 is an exchange, 1a is a CC, 1b is a time-division switch, 3a and 3b are radio base stations, 4a and 4b are mobile stations, 5
Reference numerals a and 5b denote wireless lines, which are the same as or corresponding to those in the related art having the same reference numerals in FIGS.

Reference numerals 2e and 2f denote base station line units as interface means corresponding to those indicated by reference numerals 2a and 2b or 2c and 2d in FIGS. 7 and 8. Reference numerals 6a and 6b denote base station line units. 2e, 2f
And a multi-frame unit for keeping the frame synchronization of the downstream digital radio signal constant. Reference numerals 7a and 7b denote switches 6 on the time-division switch 1b of the exchange 1.
This is a speed conversion module that performs different speed conversion between 4 Kbps and the digitized transmission speed of the wireless lines 5a and 5b (usually several Kbps).

[0018] Figure 2 is a block diagram showing an embodiment of the invention of this, the multi-frame unit 6a, illustrates a detailed configuration of 6b. In the figure, reference numeral 8 denotes a frame synchronization detecting module for detecting a frame pattern from a digital signal based on an input digital radio signal and establishing frame synchronization, and 9 denotes the number of frame protection stages when the frame synchronization detecting module 8 pulls in synchronization. This is a shift register that delays a digital radio signal by an amount. Reference numeral 10 denotes a ring buffer in which a digital signal is written and read out at a predetermined timing.
Reference numerals 1a and 11b denote a serial / parallel converter (hereinafter, referred to as S / P) and a parallel / serial converter (hereinafter, referred to as P / S) for writing / reading the ring buffer 10, and 12 denotes a frame cycle detection. A control unit that controls the module 8, the ring buffer 10, and the like.

Next, the operation will be described. In FIG. 1, for example, a signal transmitted from the mobile station 4a is transmitted in the same way as in the conventional case described with reference to FIG. 7 through the radio base station 3a → the base station line unit 2e → the base station line unit 2f via the time division switch 1b. To the input point of the multi-frame unit 6b.

Here, the multi-frame units 6a, 6
Before describing the operation of b, a brief description will be given of digital radio signals of the radio lines 5a and 5b. It has already been described that voice signals are digitized and signal processing is performed in frame units. This frame flows continuously on the wireless lines 5a and 5b. However, the specific pattern added to the head to indicate the normal frame (this is called a normal frame pattern) is limited, and is cyclic. Used repeatedly. For example, when eight frame patterns are used cyclically, F0 → F1 → F2 →...
F7 → F0. Here, one cycle is referred to as one multi-frame. In the radio lines 5a and 5b, the normal code compression rate, the error rate, and the like are considered, and the
Alternatively, various signal processes are performed in units of multiframes, and in some cases, an encryption process or the like is also performed.

Hereinafter, the operation of the multi-frame units 6a and 6b will be described on the premise of these facts. The ring buffer 10 has a size of one multi-frame, and a frame pattern is located at an address corresponding to the head of the frame. Constant control unit 12
Performs constant reading of the ring buffer 10, and if this reading of the ring buffer 10 is performed once, 1
Multi-frame transmission is possible.

As described above, the digital signal based on the digital radio signal reaching the input point of the multi-frame unit 6b is shifted up to the shift register 9 while monitoring the frame pattern by the frame synchronization detecting module 8. Normally, in a system that detects a frame pattern from a digital signal having the above-described frame configuration and performs frame synchronization, frame protection appropriate for the error rate of the line is applied at the time of synchronization or loss of synchronization. That is, after the number of protection stages, synchronization is established. The shift register 9 is provided to prevent the preceding frame from being lost until the synchronization is established at this time, and has a size corresponding to the number of protection frame stages.

When synchronization is established, the control unit 1
Numeral 2 fetches a digital signal via the S / P 11a and sequentially writes it into the ring buffer 10. At this time, since the frame pattern already exists on the ring buffer 10, if it is discarded, even if the received digital radio signal has an error in the frame pattern, it will be updated anew, and the same frame pattern will be updated. It does not pass over the wireless lines 5a and 5b twice. Since the reading is performed constantly, the read signal is sent to the wireless base station 3b and flows on the downstream wireless line 5b. At this time, the frame synchronization is kept constant. .

Embodiment 2 FIG. In the first embodiment, since the ring buffer 10 has a size of one multi-frame, if the transmitters of the mobile units 4a and 4b are free-running, a delay of a maximum of one multi-frame is required. Will happen. The purpose of the second embodiment is to compress the above-mentioned delay amount. By providing a frame adjustment circuit between the transmitter and the receiver of the mobile units 4a and 4b, the frame is shifted from the received frame by the transmission delay. It is transmitted in advance .

FIG. 3 shows the mobile units 4a, 4 in this embodiment.
It is a block diagram which shows the detailed structure of b. In the figure, 13
Is a receiver for receiving digital radio signals from the radio lines 5a and 5b, and 14 is a transmitter for transmitting digital radio signals to the radio lines 5a and 5b. 15 is a receiver 13
A decoder 16 decodes a digital signal from the digital audio signal and converts it into an analog audio signal. Reference numeral 16 denotes an encoder which encodes an analog audio signal to be transmitted and converts it into a digital signal to the transmitter 14. Reference numeral 17 denotes a speaker to which an analog audio signal is output, and reference numeral 18 denotes a microphone to which audio is input. Reference numeral 19 denotes a frame synchronization detection module which detects a frame pattern of the digital radio signal received by the receiver 13 and establishes frame synchronization, and 20 receives a frame number and timing currently received from the frame synchronization detection module 19. , A frame adjustment circuit for sending the timing and the frame number to be transmitted to the encoder 16 located on the transmission side.

Next, the operation will be described. The encoder 16 performs frame processing based on information from the frame adjustment circuit 20 and sends a digital signal obtained by encoding an analog audio signal from the microphone 18 to the transmitter 14. As a result, the upstream digital radio signal is transmitted from the transmitter 14 to the radio line 5a (5b). At this time, the frame adjustment circuit 20 notifies the encoder 16 of a frame number that is ahead of the currently received frame number in order to advance the transmission delay to the multi-frame unit 6a (6b). As a result, it is possible to reduce the amount of delay generated when the signal of the corresponding frame is stored in the ring buffer 10 of the multi-frame unit 6a (6b).

FIG. 4 is a timing chart showing the effect of compressing the delay amount. The timing when the mobile station 4a (4b) is receiving from frame "0" is shown in FIG.
(A). Here, the mobile device 4a (4b)
The mobile station 4a (4b) assumes that the transmission delay from the first frame to the multi-frame unit 6b (6a) is 1-2 frames.
It is assumed that the frame adjustment circuit 20 transmits data four frames ahead. That is, the mobile device 4a (4
In b), as shown in FIG. 4B, the frame “4” is transmitted at the timing of receiving the frame “0”. FIG.
As shown in (C), the signal that arrives at the multi-frame unit 6b (6a) after receiving the transmission delay of 1 to 2 frames is stored in the ring buffer 10, but on the ring buffer 10, the signal reaches 2 to 3 frames. Since the data is stored at the position preceding the frame, the data is transmitted after a few frames. Therefore, the total delay is consequently reduced to the difference between the preceding frame and the transmission delay,
The amount of delay can be reduced to a certain amount or less than when the transmission timing of the mobile device 4a (4b) is free-run.

Embodiment 3 FIG. Further, in the second embodiment, the transmission is performed in such a manner that the transmission delay amount is set as the preceding frame on the mobile device side and the frame number is advanced, but on the mobile device side, the preceding frame and the transmission delay frame are strictly made almost equal. It is difficult to do so, and it is desirable to reduce the functions of the mobile device as much as possible because of the fate of "compact design". In the third embodiment, the amount of delay is reduced to one frame or less by performing frame conversion in a multi-frame unit .

FIG. 5 is a block diagram showing the detailed configuration of the multi-frame units 6a and 6b in the embodiment. The same parts as those in FIG. In the figure, reference numeral 21 denotes a reception ring buffer for temporarily storing digital signals from the S / P 11a, and reference numeral 22 denotes a transmission ring buffer for storing digital signals to be sent to the P / S 11b. Reference numeral 23 denotes a frame conversion unit which is interposed between the reception ring buffer 21 and the transmission ring buffer 22, converts the digital signal read from the reception ring buffer 21 into a frame, and writes the digital signal into the transmission ring buffer 22. In this embodiment, the ring buffer 10 is constituted by the reception ring buffer 21, the transmission ring buffer 22, and the frame conversion unit 23.

Next, the operation will be described. As described above, in the digitized wireless line 5a (5b), signal processing is performed in units of frames, in units of multiframes, or in units of several multiframes. This indicates that each frame is correlated with the frame number with a certain regularity. Simply rewriting only the frame pattern will decode even if the CODEC of the mobile device 4b (4a) receives it. You can't do that.

The digital signal received by the multi-frame unit 6b (6a) is stored in the reception ring buffer 21 after the frame synchronization is established. The control unit 12 knows when to store the data of the frame and the position of the digital signal stored in the reception ring buffer 21. Therefore, the control unit 12 reads out the data from the reception ring buffer 21 to the frame conversion unit 23, and first reads the position of the received frame. Unleash the signal processing that is being performed in the specific pattern assigned to Specifically, an exclusive OR operation is performed on a code string composed of “0 or 1” with a specific pattern having a certain correlation (also a code string of “0” and “1”). Further, this time, after performing signal processing in a specific pattern corresponding to the position of the frame to be transmitted next to the currently transmitted frame, the signal is written to the transmission ring buffer 22. In this way, the received signal is subjected to frame conversion and transmitted in the next frame currently being transmitted.

FIG. 6 is a timing chart for explaining the effect of compressing the delay amount according to this embodiment. FIG. 6A shows the received signal of the multi-frame unit 6a (6b).
Indicates the timing of the transmission signal. As shown, according to this embodiment, the delay amount can be reduced to one frame or less.

[0033]

As described above, according to the first aspect of the present invention, the frame synchronization detecting module and the number of frame protection stages are provided in the interface means for interfacing the radio line between the radio base station and the exchange. Shift register,
And a ring buffer for writing / reading a line signal, and a multi-frame unit for maintaining a constant frame synchronization of the downstream digital radio signal. This eliminates the need for re-establishing frame synchronization, and provides a mobile switching system with less sound quality degradation by using the CODEC of the mobile device end-to-end.

According to the second aspect of the present invention, each mobile station is provided with a frame synchronization adjusting circuit for transmitting a frame ahead of a frame corresponding to a transmission delay amount. Further, there is an effect that the delay amount can be compressed to a certain value or less.

According to the third aspect of the present invention,
Since the ring buffer of the multi-frame unit is formed by the reception ring buffer, the transmission ring buffer, and the frame conversion unit arranged between the reception ring buffer and the transmission ring buffer, the delay amount is 1 frame or less. There is an effect that can be compressed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram showing a detailed configuration of a multi-frame unit in the embodiment.

FIG. 3 is a block diagram illustrating a detailed configuration of a mobile device according to a second embodiment of the present invention.

FIG. 4 is a timing chart for explaining a compression effect of a delay amount in the embodiment.

FIG. 5 is a block diagram illustrating a detailed configuration of a multi-frame unit according to a third embodiment of the present invention.

FIG. 6 is a timing chart for explaining a compression effect of a delay amount in the embodiment.

FIG. 7 is a block diagram showing an example of a conventional mobile switching system.

FIG. 8 is a block diagram showing another example of a conventional mobile switching system.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Switching equipment 2e, 2f Base station line unit (interface means) 3a, 3b Radio base station 4a, 4b Mobile device 5a, 5b Radio line 6a, 6b Multi-frame unit 8 Frame synchronization detection module 9 Shift register 10 Ring buffer 20 Frame adjustment circuit 21 reception ring buffer 22 transmission ring buffer 23 frame conversion unit

Claims (3)

(57) [Claims] 1. A mobile station in which a plurality of radio base stations are accommodated in an exchange via interface means for interfacing a radio line, and wherein a mobile unit communicates with a radio line set up with the radio base station. In the body exchange system, digital data input to the interface
Frame pattern from digital signal based on wireless signal
Synchronization detection to detect frame synchronization and establish frame synchronization
Module and synchronization of the frame synchronization detection module
The same number of frames as the number of frame protection stages at the time of pull-in
A shift register for delaying a digital signal;
Signal is written and read at a predetermined timing.
It consists of a ring buffer issued, the mobile switching system, characterized in that a coercive wife Ruchi frame unit frame synchronization of the digital radio signal down to a constant. 2. A digital signal transmitted by the mobile station.
Transmitted from the received digital signal
A frame tone that is advanced by a frame equivalent to the delay amount
2. The circuit according to claim 1, further comprising a regulating circuit.
Mobile switching system. 3. The multi buffer according to claim 1, wherein the ring buffer is
For storing digital signals input to the
Transmission ring buffer and the multi-frame unit
Transmit ring buffer for storing output digital signal
And the digital data read from the receiving ring buffer.
Frame to the transmit ring buffer and write it to the transmit ring buffer.
And a frame conversion unit
The mobile switching system according to claim 1.