JP2003249925A - Frame synchronizing system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a frame synchronizing system in which synchronism is hard to step out when a receiving level is low and recapture at the time of synchronization errors can be quickly carried out when the receiving level is high in the case of error correction using hard decision information. <P>SOLUTION: This frame synchronizing system for performing frame processing of a received data string counts the number (X) of times when a synchronous pattern is not detected at a position at which a frame is assumed within a prescribed period of time T in each prescribed period of time T, and changes the number (M) of stages of front protection. For example, control is performed to increase the number (M) of front protection stages, for example, when X exceeds M and to reduce the number (M) of the front protection stages when X does not exceed M. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frame synchronization of a digital radio communication system applied to, for example, a self-employed radio used in a public office or a public radio represented by a PDC (Personal Digital Cellular) system. It is related to the method.

[0002]

2. Description of the Related Art A conventional example of a frame synchronization method (Japanese Patent Application Laid-Open No.
No. 1-136158) is shown in FIG. This discloses a demodulation unit 1 and a DSP 2. The DSP 2 comprises a frame synchronization detection / channel codec section 3 and a soft decision data processing section 4B, and the soft decision data processing section 4B has an error correction / detection section 5B and a voice codec processing section 6.

Here, the soft decision is a method in which a received data string is quantized by several bits, the information of the receiving level is further added, and the result is passed to a decoding process to make a decision with a higher probability. On the other hand, the hard decision is a method in which the demodulated received data string is decided and processed by either "1" or "0". The received data sequence including the soft decision information transmitted from the demodulation unit 1 to the DSP 2 is, for example, a modulation method of π / 4 shift QPSK, and is composed of 2-bit likelihood information per symbol and envelope information indicating a reception level. Let's come in.

First, in the frame synchronization detection / channel codec section 3, a bit string (the relationship between the head of a frame and a symbol point is determined by a hard decision in which the received data string is judged to be "1" or "0" and processed. If determined, synchronization detection is performed for each symbol unit. The bit unit match determination may be all bit match or n / m (n ≦ m) bit match. When the frame synchronization can be acquired and the frame synchronization detection / channel codec unit 3 confirms that the channel is the voice communication channel, the soft decision data processing is started by the channel information.

The frame synchronization method disclosed in this conventional example comprises a synchronization acquisition process, a transition process, and a synchronization holding process. In the synchronization acquisition process, the synchronization pattern matching for each bit unit is determined by a predetermined number (M1). For the predetermined number of frames (M2) of the sync pattern coincidence and the frame error of the error correction information at the candidate position of the frame interval in the transition processing, and the frame is assumed in the synchronization holding processing. A predetermined M frame (M: number of forward protection steps) is checked for whether or not a synchronization pattern is detected at the position, and the number of times of detection is N times (N ≦
M) or more is determined to hold synchronization, and N or less is determined to be synchronization loss.

In this synchronization holding process, the number of forward protection steps is increased (N is fixed) by changing the number of forward protection steps according to the reception level of the received data string (N is fixed), for example, when the reception level is low. The delay until the loss of synchronization is delayed (making it difficult to lose synchronization), and when the reception level is high, the number of forward protection steps (M) is reduced to speed up the loss of synchronization (out of synchronization). Make it easier). On the other hand, when the number of steps (M) of front protection is fixed, the synchronization is easily lost when the reception level is low (the synchronization is immediately lost even if the synchronization is obtained), and the synchronization is hard to be lost when the reception level is high. (There is a problem that the synchronization cannot be often lost at the time of erroneous synchronization).

[0007]

In the above-mentioned conventional example,
Since it is necessary to use soft decision information for error correction when changing the number of forward protection steps (M) according to the reception level,
There is a problem that it cannot be applied in the case of error correction using hard decision information.

Therefore, it is an object of the present invention, even in the case of error correction using hard-decision information, when the reception level is low, it is difficult to lose synchronization, and when the reception level is high, reacquisition at the time of erroneous synchronization can be quickly performed. It is to realize a frame synchronization processing method that can be executed.

[0009]

The frame synchronization method of the present invention is a frame synchronization method for performing frame processing of a received data string, and it is assumed that a frame is assumed every predetermined time period T within the predetermined time period T. The number of times (X) that a synchronization pattern is not detected at a certain position is counted, and the number of forward protection steps (M) is changed according to this number. For example, when X exceeds M, the number of front protection stages (M) is increased, and when X does not exceed M, the number of front protection stages (M) is decreased.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a system diagram for explaining an embodiment of the present invention. This shows the demodulation unit 1 and the DSP 2. D
SP2 includes a frame synchronization detection / channel codec section 3 and a hard decision data processing section 4, and the hard decision data processing section 4 includes an error correction / detection section 5A and a speech codec processing section 6
have.

First, in the frame synchronization detection / channel codec unit 3, a bit string (the relationship between the head of a frame and a symbol point is determined by a hard decision in which the received data string is judged to be "1" or "0" and processed. If determined, synchronization detection is performed for each symbol unit. The bit unit match determination may be all bit match or n / m (n ≦ m) bit match.

When frame synchronization can be obtained and it is confirmed by the frame synchronization detection / channel codec section 3 that the channel is a voice communication channel, the hard decision data processing is started by the channel information.

FIG. 2 is a transition diagram showing an embodiment of the frame synchronization system according to the present invention, in which the processing relating to frame synchronization detection is divided into four stages. Forward protection step number change process 1
4 (at the time of loss of synchronization), at every predetermined period T, the number of times (X) that the synchronization pattern is not detected at the expected position of the frame within the predetermined period T is counted, and the forward protection is performed according to this number. Change the number of steps (M).

The synchronization acquisition processing 11 is intended to find the position of the synchronization candidate quickly by a hard decision. When a synchronization candidate is detected, the process moves to the migration process 12. Migration process 12
Then, the voice decoding process is started, and the synchronization pattern matching at the candidate position of the frame interval is confirmed for the predetermined number of frames. For example, if the sync pattern can be detected continuously at the candidate position of the next frame, the process proceeds to the sync holding process 13. On the contrary, if the synchronization pattern cannot be detected at the candidate position for two consecutive frames, the process proceeds to the synchronization acquisition process 11 again and the voice process is stopped. By thus providing the migration processing 12, the validity of the synchronization candidate is verified.

In the forward protection stage number changing process 14 (at the time of holding synchronization acquisition), the number of times (X) that the synchronization pattern is not detected at the expected position of the frame within the predetermined period T is counted every predetermined period T. The number of front protection steps (M) is changed according to this number. In the synchronization holding process 13, forward protection is applied. The value of the number of frames is an example, and may be set in a field test or the like according to the situation.

FIG. 3, FIG. 4 and FIG. 5 are flowcharts showing the frame synchronization method of the present invention. First, the process 14 of changing the number of forward protection steps (at the time of loss of synchronization) is performed. It is determined whether the predetermined period T has been reached (step S14), and if the predetermined period T has been reached, the number of times (X) that the synchronization pattern is not detected at the expected position of the frame within the predetermined period T is counted. Then, it is judged whether or not the number of times (X) exceeds the number of forward protection steps (M) (step S15), and if it exceeds, the value of the number of forward protection steps (M) is set to M3 (M <M.
3) (step S16) to delay the time until the loss of synchronization. If not, M4 (M>
It is reduced to M4) (step S17) to accelerate the time until the loss of synchronization. Then, (X) is reset (step S18) and the process proceeds to step S1. If it is within the predetermined period T, the process directly proceeds to step S1.

Next, a synchronization acquisition process 11 is performed. The history of detected frames is cleared (step S1), and 1 bit is read from the received data string (step S2). This 1-bit reading is repeated until the synchronization pattern is detected (step S3). When the synchronization pattern is detected, the history of detected frames is updated (step S4), and it is determined whether a predetermined number (M1) of detected frames are continuous (step S5). If it is not continuous, the process returns to step 2, and if it is continuous, the process proceeds to step S6.

Next, a shift process 12 is performed. The received data string is read from the frame buffer (step S6). Then, the decoding process is performed while reading bit by bit (steps S7 to S8). When one frame is read (step S9), it is determined whether a sync pattern is detected (step S10). When the sync pattern is detected, the detected frame history is updated (step S12). If a predetermined number (M2) of detection frames are continuous (step S1
3) and proceeds to step S14. If the number of detected frames is not the predetermined number (M2) in step 13, the process returns to step S6.

Next, a process 14 for changing the number of front protection stages (while holding synchronization) is performed. First, it is determined whether or not the predetermined period T has been reached (step S14). If the predetermined period T has been reached, the number of times (X) that the synchronization pattern has not been detected at the expected position of the frame within the predetermined period T is counted. Then, it is judged whether or not the number of times (X) exceeds the number of forward protection steps (M) (step S15), and if it exceeds, the value of the number of forward protection steps (M) is increased to M3 (M <M3) ( Step S
16) Delay the time until the synchronization disappears. If it does not exceed, it is reduced to M4 (M> M4) (step S17), and the time until loss of synchronization is shortened. Then, (X) is reset (step S18) and then step S1.
Proceed to 9. If it is within the predetermined period T, the process directly proceeds to step S19.

Next, the synchronization holding process 13 is performed. Step S
When the received data string is read from the frame buffer at 19 and decoding processing is performed while reading bit by bit (steps S20 to S21), when one frame is read (step S22), it is determined whether a sync pattern is detected (step S23). ). When the synchronization pattern is detected, the detection frame is updated (step S24). After the detection frame is updated, if the number of times the synchronization pattern is detected at the expected position of the frame is N times (N ≦ M) or more, it is determined that the synchronization is held, and if it is N times or less, it is determined that the synchronization is lost. The processing after step S1 is repeated.

FIG. 6 is an explanatory diagram of the synchronization acquisition processing 11.
In this example, M1 = 2. In FIG. 6A, after starting the synchronization acquisition processing (t0), the synchronization pattern is detected (first time) at time (t1) and the synchronization pattern is detected (second time) at time (t2). Since the synchronization pattern has been detected for two consecutive frames, it is determined that synchronization has been acquired and the transition processing 1
It can transition to 2. Further, in FIG. 6B, after the synchronization acquisition process is started (t0), the synchronization pattern is detected (first time) at time (t1), but the synchronization pattern cannot be detected at time (t2). In this case, the synchronization pattern could not be detected for two consecutive frames, so that the transition process 12 cannot be performed (synchronization acquisition failed). The synchronization pattern is detected again at the time (t3) (first time), the synchronization pattern is detected at the time (t4) (second time), and the synchronization pattern can be detected continuously for two frames. You can do it (successful synchronization acquisition).

FIG. 7 is an explanatory diagram of the migration process 12. In this example, M2 = 2. In FIG. 7A, after starting the migration process (t2), one frame is read from here,
The synchronization pattern is detected (first time) at time (t3), then one frame is read again, and the synchronization pattern is detected (second time) at time (t4). Since the synchronization pattern could be detected continuously for two frames, the synchronization holding process 13
You can transition to. In FIG. 7B, after starting the transition process (t2), one frame is read from here and the synchronization pattern is detected (first time) at time (t3),
Since one frame is read, the synchronization pattern cannot be detected at time (t4), and the synchronization pattern cannot be detected for two consecutive frames (although the synchronization has already been acquired),
It is not possible to make a transition to the synchronization holding process 13. The frame is read again, the sync pattern is detected at time (t5) (first time), the frame is read once again, the sync pattern is detected at time (t6) (second time), and the sync pattern is detected. Since two frames can be detected continuously, it is possible to transit to the synchronization holding process 13.

FIG. 8 is an explanatory diagram of the synchronization holding process 13.
In this example, M = 3 and N = 2. In FIG. 8A, after the synchronization holding process is started (t4), one frame is read from here and the synchronization pattern is detected (1) at time (t5).
The second time), read one frame again, detect the sync pattern at time (t6) (second time), then read one frame again, detect the sync pattern at time (t7) (third time). is doing. As a result, the synchronization pattern can be detected at a position where all of the three frames are supposed to be in the three frames (if the two or more frames can be detected, the synchronization is maintained), so that the synchronization is maintained. In FIG. 8B, after the synchronization holding process is started (t4), one frame is read from here, and the synchronization pattern is detected (first time) at time (t5). (T
The sync pattern cannot be detected in 6), the next frame is read again, and the sync pattern cannot be detected at time (t7). In this case, the synchronization pattern could not be detected at the expected position in only one frame of the three frames, so that the synchronization disappeared.

FIG. 9 is an explanatory diagram of a process for changing the number of front protection stages. In this example, M = 6 (initial value), N = 4, M3 = 1
In this example, 0 and M4 = 4. The number of times (X) that the synchronization pattern is not detected at the expected position of the frame within the predetermined period T is once from the time (t10) to the time (t11). As a result, from X <M (= 6), M = M4 = 4
Is changed to. Next, from time (t11) to time (t12)
Once in. As a result, since X <M (= 6), M = M
4 = 4 remains. Next, from time (t12) to time (t
6 times in 13). As a result, from X ≧ M (= 6),
It is changed to M = M3 = 10. Next, once from time (t14) to time (t15). As a result, X <M (=
From 6), M = M4 = 4 is changed. Next time (t1
Twice from 5) to time (t16). As a result, X <
From M (= 6), M = M4 = 4 remains. Next, twice from time (t15) to time (t16). As a result, since X <M (= 6), M = M4 = 4 is still maintained.

[0025]

As described above, according to the present invention, the number of times that the synchronization pattern is not detected at the expected position of the frame within the predetermined period T is counted every predetermined period T, and the number of times is detected according to this number. By changing the number of forward protection stages, it is possible to obtain a frame synchronization method in which synchronization is less likely to be lost when the reception level is low, and reacquisition can be quickly performed in the case of high synchronization when the reception level is high.

[Brief description of drawings]

FIG. 1 is a DSP using a frame synchronization method according to the present invention.
Functional block diagram of.

FIG. 2 is a transition diagram showing an embodiment of a frame synchronization system according to the present invention.

FIG. 3 is a flowchart (part 1) showing a frame synchronization method according to the present invention.

FIG. 4 is a flowchart (part 2) showing a frame synchronization method according to the present invention.

FIG. 5 is a flowchart (part 3) showing a frame synchronization method according to the present invention.

FIG. 6 is an explanatory diagram showing an embodiment of synchronization acquisition processing.

FIG. 7 is an explanatory diagram showing an embodiment of migration processing.

FIG. 8 is an explanatory diagram showing an embodiment of a synchronization holding process.

FIG. 9 is an explanatory diagram showing an embodiment of a process for changing the number of front protection steps.

FIG. 10 is a functional block diagram of a DSP using a conventional frame synchronization method.

[Explanation of symbols]

1: demodulator, 2: DSP (digital signal processor), 3: frame synchronization circuit / channel coding unit, 4A: hard decision data processing unit, 4B: soft decision data processing unit, 5A: error correction / detection unit (hard Decision), 5B: error correction / detection unit (soft decision), 6: voice codec processing unit,
11: synchronization acquisition processing, 12: migration processing, 13: synchronization holding processing, 14: forward protection stage number change processing.

Claims (3)

[Claims] 1. A frame synchronization method for performing frame processing of a received data sequence, wherein the number of times that a synchronization pattern is not detected at an expected position of a frame within the predetermined period T at every predetermined period T ( X) is counted, and the number of forward protection steps (M) is changed according to this number. 2. The frame synchronization method according to claim 1, wherein the number of times (X) that a synchronization pattern is not detected at an expected position of a frame within a predetermined period T is larger than the number of forward protection steps (M). In the frame synchronization method, when the synchronization is lost, the number of forward protection steps (M) is made larger than the previous value to delay the time until the synchronization is lost. 3. The frame synchronization method according to claim 1, wherein the number of times (X) that a synchronization pattern is not detected at an assumed position of a frame within a predetermined period T is less than the number of forward protection steps (M). A frame synchronization method characterized in that when synchronization is maintained, the number of forward protection steps (M) is made smaller than the previous value to accelerate the time until the synchronization disappears.