RU2763030C1 - Method for eliminating synchronization slides in digital data transmission networks using convolutional codes properties - Google Patents

Abstract

FIELD: communications.

SUBSTANCE: invention relates to the field of communications. The effect is achieved due to the fact that, based on the comparison of the number of bits of the received code sequence with the standard number of bits of the data frame, a conclusion is made about the occurrence of a synchronization failure, the place of synchronization slip is determined based on the growth rate of the path metrics when decoding the received code sequence using the Viterbi algorithm, when increasing path metrics, the decoding process stops and returns to the area of ​​the beginning of the growth of the path metrics, depending on the result of comparing the number of received bits with the standard size of the data frame, the required number of data bits is inserted or removed, after which the decoding process of the code sequence starts from the beginning.

EFFECT: detection and elimination of slippage during synchronization.

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Description

The field of technology.

The claimed method relates to the field of communication technology, namely to the synchronization of digital data transmission networks and can be used in data transmission in conditions of synchronization failures causing slippage.

State of the art.

a) Description of analogs.

There is a known method for detecting synchronization slips (US patent No. 4833675), which consists in adding redundancy to the transmitted code sequence.

The disadvantage of this method is the impossibility of detecting the place of synchronization slip and restoring the correct sequence of the bits of the code sequence.

There is a known method for detecting synchronization slip (US patent No. 5068879), which consists in detecting the location of synchronization slip.

The disadvantage of this method is the impossibility of eliminating the slip of the synchronization of the code sequence.

The closest in technical essence to the claimed one is a method for continuously adjusting synchronization in a telecommunication system (US patent No. 5933468), including the steps of: detecting a slippage point based on the shift of the synchronization bit and inserting data bits to restore synchronization.

Method - the prototype determines the location of the synchronization slip based on the location of the synchronization bit offset. The erroneous block is placed in the processor's memory, and the data in this block is replaced by the data calculated based on the most probable forecast of signal changes.

To reconstruct the frame, an arbitrary bit is additionally inserted (deleted) into the erroneous block, which is accompanied by displacement of the existing bits along the chain to the right.

The disadvantages of the prototype are the high probability of failure to perform the synchronization correction procedure. In addition, the dependence of the probability of correct application of the correction procedure on the number of detected sync bit errors and the block in which the first erroneous sync bit was detected. Failure to perform the correction procedure when the first erroneous sync bit is detected in one or more of the last blocks of the frame.

The analysis of the prior art made it possible to establish that analogues characterized by a set of features identical to all features of the claimed technical solution are absent, which indicates the compliance of the claimed method with the "novelty" condition of patentability.

The search results for known solutions in this and related fields of technology in order to identify features that match the distinctive features of the prototype of the features of the claimed object have shown that they do not follow explicitly from the prior art. The prior art also did not reveal the knowledge of the distinctive essential features that determine the same technical result that is achieved in the claimed method, therefore, the claimed invention meets the requirement of patentability "inventive step".

In the claimed invention, a method is proposed that eliminates the identified disadvantages.

Disclosure of the invention (its essence)

a) the technical result to achieve which the invention is aimed

The object of the invention is to develop a method for eliminating synchronization slip in digital data transmission networks using the properties of convolutional codes.

The technical result is achieved by the fact that in the method of eliminating synchronization slippage in digital data transmission networks using the properties of convolutional codes, the synchronization slip region is detected by analyzing the growth of path metrics during decoding by the Viterbi algorithm, synchronization recovery is carried out by inserting or removing data bits to the standard number of bits data frame, correction of erroneously inserted bits is carried out by re-decoding using the Viterbi algorithm.

b) a set of essential features

The proposed method differs from the known ones in that the area of slippage of synchronization is detected by analyzing the growth of path metrics during decoding by the Viterbi algorithm, synchronization is restored by adding or removing data bits to the standard number of bits of the data frame, correction of erroneously inserted bits is carried out by re-decoding by Viterbi algorithm.

c) a causal relationship between features and technical result

In the claimed method, the probability of detecting a synchronization slip region increases, the probability of correct frame recovery increases due to repeated error-correcting decoding.

Brief Description of Drawings

The claimed method is illustrated by drawings, which show:

FIG. 1 shows a block diagram of how to eliminate synchronization slip in digital data transmission networks, where

1 - data bit counter,

2 - control device,

3 - data storage unit,

4 - calculator of branch metrics,

5 - storage device for branch metrics,

6 - calculator of path metrics,

7 - storage device of path metrics,

8 - path selection block;

FIG. 2 shows a block diagram of an algorithm for eliminating synchronization slip in digital data transmission networks, based on comparing the number of received bits with the standard number of bits of a data frame and decoding using the Viterbi algorithm;

FIG. 3 shows the area of synchronization slip and decoding stop.

Implementation of the invention.

The implementation of the claimed method is explained as follows.

In digital data transmission networks, as the phase shift of the transmit and receive signals accumulates, synchronization slips occur. Synchronization slips lead to the removal or addition of extra bits of the transmitted data code sequence. A problem arises in the correctness of data processing.

One of the ways to reduce the influence of code sequence distortions during digital signal transmission is the use of error-correcting coding. Anti-jamming codes allow you to correct a single or group error of changing the bits of the code sequence, but not the error of adding or removing bits of the code sequence.

Convolutional codes are widely used in digital signal transmission. Convolutional codes are capable of correcting a single or group error of changing the bits of a code sequence, and the properties of convolutional codes allow detecting a synchronization slip region, with the subsequent restoration of the number and correct sequence of data bits.

One of the decoding methods for convolutional codes is the Viterbi algorithm. This method searches for the most appropriate list of states that have the highest probability of the occurrence of events.

The Viterbi algorithm is based on the maximum likelihood method. At each decoding cycle, for each branch of the code trellis, a metric is calculated - a number that characterizes the degree of difference of the bits generated by this branch from the received codeword. The error on each branch serves as a metric for the Hamming distance and corresponds to the number of deviating symbols received. The total metric for each of the possible paths is defined as the path metric.

The Viterbi algorithm chooses the path with the smallest total metric and discards those paths that exceed a certain threshold value at a given time.

The growth rate of the path metrics during decoding of the code sequence, received without errors and with a distorted group error of bit change, reaches a certain value (the area of influence of the error), after which the growth of the path metrics value stops. When decoding the code sequence with a distorted error of adding or removing bits of the code sequence, we observe an increase in the path metrics at each subsequent decoding cycle in Fig. 3.

Thus, observing the growth of the path metrics during decoding, it is possible to determine the place of the missing or added bit, stop the decoding process, return to the place where the path metrics start to grow, insert or remove the data bit and resume the decoding process. By inserting or deleting data bits to the standard number of bits in the data frame, synchronization is restored.

In the proposed method, the search for the synchronization slip region is carried out based on the analysis of the growth of path metrics when decoding the code sequence using the Viterbi algorithm, synchronization is restored by inserting or removing data bits to the standard number of bits of the data frame, correcting erroneously inserted bits is carried out by re-decoding using the algorithm Viterbi.

When receiving data, after demodulating the signal, the data bit counter 1 (Fig. 1) calculates the received bits and sends the received value to the control device 2.

In control unit 2, the number of received bits is compared with the standard number of bits of the data frame. According to the comparison results, the control device decides on the decoding method. When the number of received bits coincides with the standard frame size, the code sequence is decoded using the Viterbi algorithm without re-synchronization. If the number of received bits does not coincide with the standard value of the data frame, the synchronization slip region is searched based on the analysis of the growth of path metrics and the code sequence is decoded using the Viterbi algorithm with synchronization recovery (Fig. 2).

After passing the counter of data bits 1 (Fig. 1), the code sequence is sent to the data storage unit 3. The data storage unit 3 transmits the code sequence to the branch metrics calculator 4, which calculates and transmits data on the value of the metrics to the branch metrics memory 5. The memory device branch metrics 5 transfers the value of the metrics to the path metrics calculator 6. The data storage of the path metrics is carried out in the memory of the path metrics 7. The data from the memory of the path metrics is transmitted and analyzed in the path selection unit 8. When the path metrics increase, the path selection unit 8 sends a signal to control unit 2. The control unit 2 stops the decoding process and returns to the synchronization slip region of FIG.

In the area of synchronization slip, depending on the result of comparing the number of received bits with the standard data frame size of FIG. 2, the control device 2 decides to add or remove data bits in the codeword. After the process of recovering the bits of the code sequence, the code sequence is re-decoded.

Industrial applicability.

The claimed technical solution is implemented using a commercially available element base and can be used in communications technology.

Claims (1)

A method for eliminating synchronization slips in digital data transmission networks using the properties of convolutional codes, including detecting the place of symbol slippage, inserting the required number of missing data bits to restore synchronization, characterized in that the incorrectly inserted bits are corrected by re-decoding; in this case, the synchronization slip region is detected by analyzing the growth of path metrics during decoding by the Viterbi algorithm, and synchronization is restored by inserting or deleting data bits to the standard number of bits of the data frame, and the erroneously inserted bits are corrected by re-decoding using the Viterbi algorithm.

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