RU2369023C1 - Method of messages acceptance and transmission within communication system - Google Patents

Abstract

FIELD: communication means.

SUBSTANCE: method of transmission and receiption of messages within communication system pertains to communication technique and may be employed for reliable and noise-immune transmission of messages protected with noise-immune code. Technical result is achieved due to the fact, that on the transmitting site outlet sequence presenting bit-by-bit modulo n sum, two noise-immune codes and synchronising sequences are recurrently continued. On receiving site syndrome for the received sequence is calculated, synchronising sequence is detected and cycle synchronisation of the noise-immune code is set. There after bit-by-bit modulo n sum two accepted and synchronising sequences, noise-immune code and its recurrent continuation are separated. There after syndrome and its recurrent continuation preceding sliding window and following it for the rest of code symbols is calculated. When the number of zero syndrome components for the rest of the code symbols and its recurrent continuation exceeding threshold value, information is restored and given to the recipient. If threshold value is not exceeded, sliding window is off set by one symbol and computations are repeated from the beginning.

EFFECT: improved noise-immunity of messages transmitted in the communication system.

2 cl, 1 tbl

Description

The invention relates to the field of communication technology and can be used to send and receive messages protected by an error-correcting code.

One of the main ways to increase the probability of receiving messages in communication channels with errors is error-correcting coding. In the proposed method for transmitting and receiving messages in a communication system, the loop synchronization and decoding of the error-correcting code are performed. When decoding, the method in question allows one to detect and correct errors whose multiplicity exceeds the corrective ability of the code. For this, it is necessary that at least one undistorted section of characters is accepted in the code, the length of which exceeds the information length of the code and a small number of randomly spaced correct characters (1-2 bytes). The most effectively proposed method can be applied in communication channels with grouping of errors.

There is a known method of transmitting and receiving messages in a communication system, according to which the source information is encoded with an error-correcting code on the transmitting side of the communication system, then a synchronization sequence is added to the error-correcting code and the resulting sequence of characters is transmitted to the communication channel, at the receiving side of the communication system, cyclic synchronization is first performed a sequence of symbols received from the communication channel; for this, a synchronizing signal is detected in the received sequence of symbols consistency, then an error-correcting code is allocated, then this error-correcting code is decoded with error detection and correction in the error-correcting code, and then the information restored when decoding the code is given to the recipient (Lagutenko OI Modems. User Manual. Design by A. Lurie. St. Petersburg. Lan. 1997, p. 188).

The disadvantage of this method is the low noise immunity, especially in communication channels with grouping of errors, due to the fact that the number of errors detected and corrected when decoding the code is limited by the correcting ability of the code.

Closest to the proposed method is a method (prototype) for transmitting and receiving messages in a communication system, in accordance with which the source information is encoded with an error-correcting code on the transmitting side, an output sequence is formed, which is a bitwise sum modulo two error-correcting codes and a synchronization sequence. On the receiving side, a syndrome is computed for the received symbol sequence, a synchronization sequence is detected, and a cyclic synchronization of the error-correcting code is established. Then, the bit-wise sum modulo two received and synchronizing sequences is calculated, an error-correcting code is allocated, an error-correcting code is decoded, and the information recovered as a result of decoding the code is provided to the recipient (Bolkhovitin L.M., Zhurkin S.P., Kvashennikov V.V., Sosin P. A. Transmission of formalized messages with a self-synchronizing code with variable parameters (Communication Technology, Ser. TPS, issue 8, 1990, p. 39).

The disadvantage of this method is the low noise immunity, since when decoding detect and correct errors within the limits limited by the correcting ability of the code. The corrective ability of the code is related to the minimum code distance of the code by the formula

where t _o is the number of errors that the code can detect,

t _u - the number of errors that the code can correct,

d _min - the minimum code distance of the code.

For codes used in practice, d _{min is} small (<11), therefore, the corrective ability of the code according to formula (1) will be small (t _u <6, t _o <10).

The purpose of the invention is to increase the noise immunity of receiving information due to the fact that the number of errors in the symbols of the error-correcting code can exceed its corrective ability.

To achieve the goal, a method is proposed that the source information is encoded with an error-correcting code on the transmitting side, and an output sequence is formed, which is a bitwise sum modulo two error-correcting codes and a synchronization sequence. On the receiving side, a syndrome is computed for the received symbol sequence, a synchronization sequence is detected, and a cyclic synchronization of the error-correcting code is established. Then, the bit-wise sum modulo two of the received and synchronizing sequences is calculated, an error-correcting code is allocated, an error-correcting code is decoded, and the information restored as a result of decoding the code is provided to the recipient. What is new is that on the transmitting side of the communication system, the output sequence, which is a bitwise sum modulo two error-correcting codes and a synchronizing sequence, continues recursively. On the receiving side of the communication system, the calculation of the syndrome for the received sequence of characters is performed in a sliding window, the length of which is greater than the length of the information part of the code. When a predetermined combination of the syndrome is detected, the beginning and end of the error-correcting code are determined, the error-correcting code and its recurrent continuation are extracted, and the syndrome is calculated for the remaining symbols of the code and its recurrence continuation preceding the sliding window and following the sliding window. If a previously known combination of the syndrome is not detected, the sliding window is shifted by one character and the calculation is repeated first. With the number of zero components of the syndrome for the remaining characters of the code and its recurrent continuation preceding the sliding window and following the sliding window that exceeds the threshold value, information is restored and given to the recipient. With the number of zero components of the syndrome for the remaining characters of the code and its recurrent continuation not exceeding the threshold value, the sliding window is shifted by one character and the calculation is repeated again. Moreover, the error-correcting cyclic code is used for message transmission, the recurrence relations specified by the test polynomial of the error-correcting cyclic code are used for the recursive continuation of the code, and the test polynomials of the synchronizing sequence are used for the recurrent continuation of the synchronizing sequence.

The table shows the sequence of operations illustrating the process of processing the source information on the transmitting and input information on the receiving side of the communication system.

Table Transmission side Information coding a ₁ a ₂ ... a _k → b ₁ b ₂ ... b _n Addition of code and synchronization sequence b ₁ b ₂ ... b _n ⊕ c ₁ c ₂ ... c _n → d ₁ d ₂ ... d _n Recursive code continuation d ₁ d ₂ ... d _n → d ₁ d ₂ ... dn ₁ Link Overlay errors in the communication channel d ₁ d ₂ ... d _n1 ⊕ e ₁ e ₂ ... e _n1 → f ₁ f ₂ ... f _n1 Receiving side 1. Calculation of the syndrome in a sliding window of length k + r1 f ₁ f ₂ ... f _{k + r1} → S ₁ S ₂ ... S _r1 2. Check for a combination of syndrome If S ₁ S ₂ ... S _r1 = {S _i }, to go to 3, otherwise go to 1 3. Code highlighting f ₁ f ₂ ... f _n1 ⊕ c ₁ c ₂ ... c _n → V ₁ V ₂ ... V _n1 4. Calculation of the syndrome for the remaining characters of the code V ₁ V ₂ ... V _k V _{k + r1 + 1} ... V _n1 → S _{k + r1 + 1} ... S _n1 5. Counting the number of zero components of the syndrome If S _i = 0, then j: = j + 1, i = k + r1 + 1 ... n1 6. Comparison of the number of zero components of the syndrome with a threshold value If j> p1, then go to 7, otherwise go to 1 7. Information recovery and delivery to its recipient g _m g _{m + 1} ... g _{m + k-1}

The proposed method for transmitting and receiving messages in communication systems is implemented as follows.

An error-correcting code is generated on the transmitting side, for example, an error-tolerant systematic binary cyclic code. To do this, first, the initial message of length k of binary symbols, using the test code ratios, is converted into a noise-resistant code of length n of binary symbols.

To describe the encoding procedure, the initial information is presented in the form of an information polynomial a (x), the coefficients of which are binary symbols of the original information sequence.

The verification part r (x) of the error-correcting code is written in polynomial form in the form

where g (x) generating the polynomial of the error-correcting cyclic code,

n is the block length

k is the informational length of the code.

Expression (1) sets the code verification ratios by which the symbols of the error-correcting code are calculated.

The noise-resistant cyclic code b (x) of length n characters in polynomial form, after calculating the verification part, is written as

Next, the noise-resistant cyclic code b (x) is recurrently continued to a length n1> n using the relation

where h _j are the coefficients of the verification polynomial

Then, the symbols of the recursively continued error-correcting cyclic code are added bitwise to the symbols of the recurrently continued synchronization sequence c (x).

As the synchronization sequence c (x), a sequence of suitable length n ₁ with good synchronizing properties is selected, for example, a sequence of maximum length (Reed-Muller code of the first order). Good synchronizing properties mean that the sequence has an autocorrelation function of the type δ - function. The recurrent continuation of the synchronizing sequence is performed using relations similar to relations (3).

The output sequence of the transmitting part of the communication system will be a sequence of binary symbols representing a bitwise sum modulo two of a recurrently continued noise-resistant cyclic code and a recurrently continued synchronization sequence.

Further, the symbols of the output sequence d (x), converted into a signal, enter the communication channel. In the communication channel due to interference, distortion of the transmitted signal is possible. This can lead to the fact that, depending on the magnitude of the level of this interference, the transmitted sequence will be received with errors

On the receiving side of the communication system for the sequence f (x) supplied to the input of the receiving part, the noise-tolerant cyclic code syndrome is calculated. The syndrome is calculated in a sliding reception window, the length of which exceeds the information length of the error-correcting cyclic code. For the components of the syndrome, relations are true, similar to relations (3). Denote f ₀ f ₁ ... f _k-1 f _k ... f _{k + r1-1} - characters of the sequence received in the sliding reception window of length k + r1. The components of the syndrome are calculated by the formula

For the error-free receiving section, e _i = 0 and f _i = b _i + c _i and (6) can be written as

In view of equality (3), from (7) it follows

Therefore, the components of the syndrome depend only on the symbols of the synchronizing sequence. Since the synchronization sequence is a constant sequence for all error-correcting codes, the components of the syndrome for an error-free sequence will belong to some set {s _i } of predefined syndromes. If a previously known combination of the syndrome is not detected, the sliding reception window is shifted by one symbol, that is, they are waiting to receive a new symbol from the channel and the calculations are repeated again. When a predetermined combination of the syndrome {s _i } is detected, depending on this combination, the beginning and end of the error-correcting cyclic code are determined and the error-correcting cyclic code is allocated. To do this, according to a pre-compiled functional dependence (decision function), the combination of the {s _i } syndrome and the position of the beginning and end of the code and its recurrent continuation determine the location of the code in the received sequence. Then add the received sequence with a recurrently continued synchronization sequence

Next, the components of the syndrome are calculated for the remaining characters of the selected code and its recurrent continuation, preceding the sliding window and following the sliding window. For this, considering the first k characters of the sequence received in the sliding window as informational, the expected verification symbols of the error-correcting cyclic code following the sliding window are calculated

where w _i = ν _i for i = 0 ... k-1.

Due to the cyclic nature of the error-correcting code, the code symbols that precede the sliding window will coincide with the recurrent continuation symbols following the sliding window, and it is not necessary to calculate them separately.

Syndrome components compute, as a bit-wise sum, modulo two expected code validation characters and accepted code validation characters

After that, count the number j of the zero components of the syndrome. If the number j of zero components of the syndrome is greater than the threshold value p1 (j> p1), then the information is restored and given to the recipient. The symbols w _i are obtained on the basis of calculations with undistorted symbols of a sliding window, which means that these symbols are undistorted. Therefore, now for information recovery it is enough to select information symbols in the sequence w _i . The location of the information symbols in the sequence w _i is determined by the value of the combination of the syndrome {s _i }.

If the number j of zero components of the syndrome is not greater than the threshold value p1 (j≤p1), then the sliding reception window is shifted by one character and all the above calculations are repeated first.

Thus, to decode the code, it suffices to have an undistorted segment of characters of length k + r1 and a small number j of undistorted characters (usually 1-2 bytes) giving zero syndromes, the number of which exceeds the threshold value p1. For the implementation of the proposed method, the choice of the optimal values of the length of the original undistorted segment of characters k + r1 and the threshold value p1 is of no small importance. The reliability and noise immunity of the method depend on these values. With an increase in r1, the reliability of reception increases, but at the same time, noise immunity decreases, since the length of the necessary undistorted reception window increases. A similar effect on the reliability and noise immunity is exerted by the value of the threshold value p1. Based on the conditions for ensuring the necessary reliability of reception of at least R _{d the} amount of r1 + p1 can be determined from the equality

For P _D = 10 ^-4 from formula (12) we obtain r1 + p1 = 14. If r1 = p1, then the reception condition can be considered as an undistorted reception in a sliding window of length k + r1 = k + 7 and detection of 7 zero components of the syndrome, i.e. almost 1 byte. There may be errors in other places of the error-correcting cyclic code and its recurrent continuation. Their maximum number can reach the value t = n1-k-r1-p1, which significantly exceeds the number of errors that is specified by the minimum code distance of the noise-resistant cyclic code. Moreover, due to the recurrent continuation of the noise-resistant cyclic code, the value of n1 can be increased and the necessary number of errors corrected by the code can be provided, which means the necessary noise immunity.

As an example, consider a communication system in which messages consisting of 8 bytes of information are transmitted. Messages are protected by a noise-frequency cyclic BCH code (64.32) n = 64, k = 32, the generating polynomial of which is a polynomial of degree 32. In the hexadecimal code, this polynomial is represented as g (x) = 104C11DB7H. The minimum code distance of the code is 11, which allows you to correct only 5 random errors. On the transmitting side, the error-correcting cyclic code is recurrently continued to a length n1 = 80. Therefore, for the method under consideration, the number of errors can reach the value t = n1-k-r1-p1 = 80-32-14 = 34. However, with so many errors, for correct reception there should be one undistorted section of characters of length 39 and at least 7 more randomly located undistorted characters.

The proposed method, in contrast to the prototype, provides the detection and correction of a significantly larger number of errors in a cyclic error-correcting code. Most effectively, this method can be used in communication channels with grouping errors. In such channels, undistorted portions of the sequence of characters necessary for implementing the method more often appear.

Achievable technical result of the proposed method for transmitting and receiving messages in communication systems is to increase the noise immunity of the received information.

Claims (2)

1. The method of transmitting and receiving messages in a communication system, which consists in the fact that the source information is encoded with an error-correcting code on the transmitting side, an output sequence is formed, which is a bit-wise sum modulo two error-correcting codes and a synchronization sequence, on the receiving side, the received symbol sequence is calculated syndrome, detect the synchronization sequence, and establish the cyclic synchronization of the error-correcting code, then calculate the bit sum modulo two received and synchronizing sequences, isolate the error-correcting code, decode the error-correcting code and the information restored as a result of decoding the code is provided to the recipient, characterized in that the output sequence formed on the transmitting side of the communication system, which is a bit sum modulo two error-correcting code and the synchronizing sequence, recurrently continue, on the receiving side of the communication system, the calculation of the syndrome for adopted sequentially These characters are executed in a sliding window, the length of which is longer than the length of the information part of the code, when a previously known combination of the syndrome is detected, the beginning and end of the error-correcting code are determined, the error-correcting code and its recurrent continuation are selected, the syndrome is calculated for the remaining symbols of the code and its recurrent continuation preceding the sliding window and following the sliding window, if a previously unknown combination of the syndrome is not detected, the sliding window is shifted by one character and the calculation is repeated first, with the number of zero components of the syndrome for the remaining characters of the code and its recurrent continuation preceding the sliding window and following the sliding window that exceeds the threshold value, information is restored and issued to the recipient, with the number of zero components of the syndrome for the remaining characters of the code and its recurrent continuation not exceeding the threshold the value, the sliding window is shifted by one character and the calculations are repeated first. 2. The method according to claim 1, characterized in that the error-correcting cyclic code is used for message transmission and the recurrence relations specified by the verification polynomial of the error-correcting cyclic code are used for the code continuation, and the verification polynomials of the synchronizing sequence are used for the recursive continuation of the synchronization sequence.