Method of adaptive frame synchronization code

 

The invention relates to the transmission of discrete information and can be used for frame synchronization in systems robust protection using corrective, in particular concatenated codes. The technical result - increased robustness frame synchronization when operating in non-stationary communication channels with variable parameters and a high level of interference. The technical result is achieved by the fact that the number of matches numbering and timing sequences, which determine the presence of frame synchronization, takes into account the quality of the communication channel. The quality of the communication channel is estimated the total reliability of the received code words with matching numbering and timing sequences. In turn, the reliability of the received code words are determined based on scales, the magnitude of which depends on the ratio of corrected code word errors. 1 Il.

The invention relates to a method of transmitting digital data and can be used for frame synchronization in systems of error-correcting information security, which are corrective, in particular concatenated codes.

Spasenija, the transmitted sequence of words cyclic error-correcting code. Adaptation in the proposed method will be called automatically and purposeful change of code frame synchronization in order to achieve optimal performance under changing conditions of reception of messages. When the coded frame synchronization clock characteristics are passed on words of error-correcting code. For synchronization does not require the transmission of additional special characters, and uses the redundancy of the error correcting code. After establishing synchronization signs synchronization subtracted from the error-correcting code, not reducing correcting ability of the code.

The most effective use of adaptive coded frame synchronization in noise-tolerant cascade codes. In this case, synchronization is provided by repetition of signs synchronization in different words internal code cascade code.

The main task is to increase the noise immunity of the frame synchronization when operating in non-stationary communication channels with variable parameters and a high level of noise.

The known method cyclic synchronize the synchronization sequence, multiplied by the check polynomial error-correcting code as a result providing the synchronization sequence. Upon detection of a certain combination of the selected synchronization sequence shall take the decision on whether frame synchronization [1].

However, this method is insufficient immunity.

Closest to the proposed method is a method (prototype) code frame synchronization, namely, that the accepted input sequence representing the sum modulo two words cyclic, error-correcting code, numbering and timing sequences, multiplied by the check polynomial of the code. Resulting allocate a sum numbering and timing sequences. Next, the sequence is multiplied by the check polynomial numbering sequence, followed by detection of the synchronizing sequence, and then allocate numbering sequence. Next, define the error vector and carry out the correction of errors in the numbering sequence. Then compare numbering and synchronizing sequence with previously adopted and as a result of comparison oprey synchronizing sequences previously received code words, moreover, if the result of comparison of the number of matches with the threshold value will be exceeded by the number of matches some predetermined threshold value, make a decision about the presence of frame synchronization at the current time. Next, subtract numbering and synchronizing sequence of code words and then perform the decoding code words with the detection and correction of errors [2].

The disadvantage of this method is the low immunity due to the fact that in non-stationary channels with a high level of noise will be present a large number of corrupted code words. The reliability of such code words when correcting errors is low. Consideration of these code words in determining whether frame synchronization along with undistorted code words reduces the immunity frame synchronization.

The purpose of the invention to increase the noise immunity of the frame synchronization messages due to the fact that the presence of frame synchronization is determined taking into account the quality of the communication channel.

To achieve the goal proposed method adaptive code frame synchronization, namely, that the accepted input sequence before the th sequences, multiplied by the check polynomial error-correcting code. As a result, there sum numbering and timing sequences. Next, the sequence is multiplied by the check polynomial numbering sequence, followed by detection of the synchronizing sequence, and then allocate numbering sequence. Next, define the error vector and carry out the correction of errors in the numbering sequence. Then compare numbering and synchronizing sequence with previously adopted and as a result of the comparison determines the number of matches numbering and timing sequences with appropriate numbering and synchronizing sequences previously received code words, and, if the result of comparison of the number of matches with a threshold will be exceeded by the number of hits a certain threshold of matches, take the decision on whether frame synchronization in the current time. Next, subtract numbering and synchronizing sequence of code words and then perform the decoding code words with the detection and correction of errors. What's new is that the number of matches numbering and sinhroniziruete to estimate the total reliability of received code words with matching numbering and timing sequences. In turn, preferably the reliability of the received code words to identify the given weights, the magnitude of which depends on the ratio of corrected code word errors.

The implementation of the method of adaptive coded frame synchronization consider the example of synchronization of the cascade code.

On the transmission side form input sequence. For this purpose, the transmitting side of the original message volume₁m-ary (m >1) characters at the beginning encode m-ary error-correcting code, such as m-ary error-correcting code is a reed-Solomon. A reed-Solomon code is the outer code or code first-stage robust cascade code.

In the encoding information is a code word reed-Solomon code (n₁, k₁), the information length is equal to k₁and block - n₁characters.

Further information code binary code, such as binary Bose - Roy-Chaudhury - Hocquenghem (BCH codes) with the check polynomial h₁(x). Code BCH is an internal code or code of the second stage of error-correcting cascade code. Code BCH has parameters: n - block code length, k is the information length of the code.

The source information for each slo is the result of the encoding code BCH receive n₁binary words BCH code (n, k) or a binary sequence with₁.

Then perform addition modulo two characters BCH code with symbols numbering sequence₂. As the numbering sequence select binary code with block length n and information long₂for example code, reed-Muller (RM) 1-th order (sequence maximum period) with the check polynomial h₂(x). Between the numbers of words in concatenated BCH code and an information part numbering sequence (code RM) is one-to-one correspondence. The first word BCH is folded sequence obtained by encoding the binary combination corresponding to binary 1, the code of the Republic of Moldova, the second in the encoding code RM - 2, and so on, Such an addition is performed with all the words BCH code. If the check polynomials summable codes h₁(x) and h₂(x) are coprime and are divisors of binomial xⁿ+1, this will result in n₁words cyclic BCH code with block length n and information - k+k₂. This code will be quite certain guaranteed minimum code distance and possess the particular BCH, will be constant for all words in the sequence of length n bits that violate the cyclical properties of BCH code. Such a sequence may be any sequence that is not a code word BCH code, for example, a sequence of 10000...000.

At the receiving side input sequence, formed as the sum of the three sequences used for adaptive coded frame synchronization.

The drawing shows the sequence of operations that illustrates the processing of the input sequence at the receiving side.

At the receiving side first carry out a reception of the input sequence.

Next, the input sequence is multiplied by the check polynomial error-correcting code h₁(x), and then multiply the sequence on the check polynomial numbering sequence - h₂(x). Thus, compute the syndrome BCH code or a sequence with₁and code of the Republic of Moldova, or a sequence with₂.

When entering the infallible word syndrome code is zero and the result of the calculation of the syndrome is obtained n-k-k₂bit binary combination of the d₀corresponding to the converted synchronization posledovatelnyi input words with errors will be calculated combination of some set { d_i}, i0, corresponding to the sum of the non-zero syndrome code s_iand converted synchronizing sequence₃: d_i=s_id₀. Further, recognizing the combination of the d₀or a combination of the set {d_i} perform the detection of the synchronization sequence. This is possible if the frequency error is within the correcting ability of the code, the synchronization sequence will be applied to a non-zero syndrome whose values for different fixed combinations of errors will be different from each other. Combination syndrome for such errors can be calculated in advance and, for example, be placed in a table.

Then, upon detection of the synchronization sequence in combinations of d₀or in combination from the set {d_i} implement the allocation of the numbering sequence. For undistorted code word numbering sequence is determined after multiplication of the input sequence on the check polynomial of the BCH code h₁(x) and subtracting from the received combination of the converted synchronizing sequence.

In the case of receiving the input code word Correction of the respective bits of the BCH code number is performed by the recognition of digits syndrome, the respective synchronizing sequence, in a combination of the set {d_i} and the definition of the error vector. In this case, correction of errors in the selected numbering sequence can be performed, for example, by using a predetermined fault tables, the output of which are correctable error vectors, and the input is recognized by the combination syndrome.

Next, a comparison is made of the adopted numbering and timing sequences with appropriate numbering and timing sequences for the previously received code words.

A comparison of the selected numbering sequence with the previously adopted numbering sequence is to verify the compliance of the adopted non-natural sequence of these numbers. Also compare the relative position of the synchronizing sequence for the received code words. Synchronizing sequence must defend from each other at a distance, times the number of bits in the code BCH n.

Next, the number of matches numbering and timing sequences based on the quality of the communication channel.

Link quality is determined by the amount of what can be done, for example, on the basis of the following considerations. Authenticity code word is determined by the probability of undetected errors when correcting errors. Increasing the number of bugs that are fixed in the code word, the probability of undetected errors (the probability of a false decode) and decreases the reliability of the received code word. The ratio of undetected errors [3], which determines the share of transformations depending on the number correct in the code word errorsis estimated by the formulawhere k, n and information, and block length of the code, and t is the number of errors corrected in the code word.

Estimated number of binary bits used for error detection f is equal to f = n-k-log₂(C_n⁰+C_n¹+...+C_n^t).

Authenticity code word(t) when correcting t errors will be evaluated relative to the number of bits of the code word used to detect errors and will be written as follows:thus the reliability of the code word, which was not corrected any errors equal to 1.

Next, a comparison is made of the number of matches with proposedvalue exceeds a certain pre-selected threshold_maxi(t)_maxperformed cycle synchronization. This means that the input information is supplied for further processing. Moreover, the location of the synchronizing sequence uniquely identifies the beginning of the words BCH code, and the numbering sequence determines the position of the first word in concatenated BCH code or the beginning of the message.

In the proposed method, the number of code words with matching numbering and synchronizing sequences, in which the decision about the presence of frame synchronization is established depending on the quality of the communication channel. With the high quality of the communication channel number of matches in which the decision about the presence of frame synchronization decreases. This is because in the good channel as the number of undistorted code words increases. The reliability of the decision is undistorted code words above and for reliable synchronization requires the acceptance of a smaller number of code words. With the deterioration of the quality of the communication channel reliability of the received code words is reduced and reliable synchronization of the output words is accepted with errors.

The maximum number of corrected errors in the code word t and the threshold total reliability code words with matching numbering and synchronizing sequences_maxchoose thus to ensure a high probability of frame synchronization, not inferior, at least, the probability of correct reception of the word robust cascade code without regard to frame synchronization. The optimal choice of these parameters provides a significant decrease in the probability of failure to identify frame synchronization compared with the probability of failure to identify frame synchronization, achieved in the prototype.

For example, for cascade code, the inner code is a binary code BCH(31,16) and the outer code is a reed - Solomon code (24,16) over Galois field GF(2⁸), the estimated probability of failure to identify frame synchronization in the channel with independent errors when the error rate of 0.05 is the method used in the prototype, of 0.03. At the same time for a rational choice of the parameters t and_maxthe probability of failure to identify frame synchronization using the proposed method will be about 3.8

Next, perform the decoding code words with the detection and correction of errors.

Note that in this way cycle synchronization is not only error-free code words and the code words with errors. This increases the robustness frame synchronization and allows synchronization with a higher level of interference in the communication channel, where the number of undistorted code words is reduced.

In the present invention in contrast to the known method when comparing clock and numbering sequence number matching numbering and timing sequences, which determine the presence of frame synchronization varies depending on the quality of the communication channel. The quality of the communication channel is estimated the total reliability of the received code words and takes into account the multiplicity corrected in the code word errors. Each codeword is mapped to a weight characterizing the reliability of code words when correcting errors in a code word. Accounting code words with weights that characterize the DOS is

Achievable technical result of the proposed method adaptive code frame synchronization is to increase the noise immunity.

Sources of information: 1. Losev centuries, Brody E. B., Korzhik Century. And. Search and decoding of complex discrete signals / Ed. by C. I. Korzhik. - M.: Radio and communication, 1988, page 136.

2. Beck, C., B. C. N., Judge O. P. Method of synchronization messages. Sat. : Construction and analysis of communication systems. M.: Nauka, 1980, page 84.

3. Elements of theory of discrete information transmission Ed. by L. P. Purtova, M., Link, 1972, page 129.

Claims

Method of adaptive coded frame synchronization, namely, that the accepted input sequence representing the sum modulo two words cyclic error-correcting code, numbering and timing sequences, multiplied by the check polynomial error-correcting code, as a result, allocate a sum numbering and timing sequences, then the sequence is multiplied by the check polynomial numbering sequence, followed by detection of the synchronizing sequence, and then allocate numbering Polke this compare numbering and synchronizing sequence with previously adopted and as a result of the comparison determines the number of matches numbering and timing sequences with appropriate numbering and synchronizing sequences previously received code words, moreover, if the result of comparison of the number of matches with the threshold value will be exceeded by the number of hits a certain threshold, take the decision on whether frame synchronization in the current time and then subtract numbering and synchronizing sequence of code words, wherein the number of matches numbering and timing sequences determined based on the quality of the communication channel, which estimate the total reliability of the received code words with matching numbering and synchronizing sequences, and the reliability of the received code words are determined based on scales, the magnitude of which depends on the ratio of corrected code word errors.