Method for decoding cyclic interference-resistant code

FIELD: communications engineering, possible use in data transmission systems, for remote measurement, remote control, in radio-transmitting equipment of small spacecrafts and for deep space telemetry.

SUBSTANCE: in accordance to the invention, at transmitting side code words are generated by encoding information symbols using cyclic code without usage of synchronizing patterns, parameters of cyclic code are changed depending on level of interference, transferred information is accumulated at receiving side, thus creating a selection, then for phasing by code words limits of code word are determined, supposed length of code word is set, and in set window "sliding" symbol-wise discrete Fourier transformation is performed in Galois field for whole volume of selection being analyzed, while at each step of "sliding" discrete Fourier transformation in Galois field, selection of zero spectral components is performed as well as determining of quantity thereof together with building a function of number of zero spectral components at each step of "sliding" discrete Fourier transformation in Galois field, then decimation of given function is performed with step, equal to supposed length of code word, with building of a function estimate of mathematical expectation of number of zero spectral components, phasing moments reach maximum of mathematical expectation estimation function of number of zero spectral components, with consideration of resulting maximum, code words are selected, and then estimate of mathematical expectation of code word spectrums is performed and parameters of cyclic code are evaluated on basis of resulting code words, and then cyclotomic classes are determined, the generative polynomial of cyclic code is restored and code words are decoded.

EFFECT: increased interference resistance of cyclic code receipt, automatic adaptation of characteristics of transferred signal to interference intensity, increased speed of information transfer and accelerated phasing process during transfer of code words without synchronizing patterns.

4 dwg

 

The proposed method relates to the field of communication technology and can be used in data transmission systems, and in systems of telemetry, remote control, radio transmitting equipment small satellites and telemetry deep space without the use of synchronously and additional control channel.

There is a method of decoding a cyclic error correcting code (Losev CENTURIES, Brody E.B., cookie monster VI Search and decoding of complex discrete signals, Ed. Vigorita. - M.: Radio and communication, 1988, str), wherein at the receiving side calculates the syndrome of the error correcting code. Upon detection of an undistorted error-correcting code that is determined by a zero syndrome, decide on the admission of error-correcting code and then allocate the information part of the error correcting code.

This method has low immunity due to the low probability of correct synchronization and the fact that the decoding of error-correcting code performs only error detection without correction.

There is also known a method of decoding a cyclic error correcting code (Bolkhovitin L.M., Gurkin S. p., Kvashennikov CENTURIES, Sosin P.A. transfer of the formalized messages self-synchronizing code with variable parameters. Technology communications, vol. TPS, VIP, 1990,p.39), where on the transmission side to form the output sequence representing the sum modulo two of cyclic error-correcting code and a synchronization sequence at the receiving side, the sequence is multiplied by the check polynomial error-correcting code and calculate the synchronization sequence. Upon detection of a certain combination of synchronizing sequence take the decision on whether frame synchronization and then allocate the information part of the error correcting code.

However, this method has low immunity due to the fact that decoding of error-correcting code performs only error detection without correction.

There is also known a method of decoding a cyclic error correcting code (Beck, GV, Bogdanovich V.N., Kireev OP Method of synchronization messages. Sat.: Construction and analysis of communication systems. M.: Nauka, 1980, p.84), namely, that on the transmission side to form the output sequence representing the sum modulo two of cyclic error-correcting code and the synchronizing sequence. At the receiving side adopted the first sequence is multiplied by the check polynomial error-correcting code and calculate the clock on sledovatelnot. Next, carry out the detection of a particular combination synchronizing sequence with accounting errors imposed on the accepted sequence in the communication channel. Upon detection of the synchronization sequence shall take the decision on whether frame synchronization and produce error-correcting code. Then determine the combination of errors and perform error correction in the error correcting code.

The disadvantage of this method is also low immunity, because the message is only possible if the code word errors, the multiplicity of which is not above correcting ability of the code.

Known methods of decoding of cyclic codes (RF patents №№2231216 C2, 2109407 C1, 2024053 C1).

Known methods closest to the present invention is a Method of decoding a cyclic error correcting code (patent RF №2231216 C2), which is selected as a prototype. This method provides increased robustness of reception due to the fact that on the transmission side output sequence recurrently continue using test ratio of cyclic error-correcting code on the receiving side additionally carry out decoding of cyclic extensions of the received sequence. While decoding implementation of tlaut in the sliding receive window and outside sliding window, permit the occurrence of any number of errors in the received sequence, including exceeding the correction capability of error-correcting code, but does not lead to the transformation of the code.

However, using this method requires the presence of the synchronization symbols and the parameters of the correction code remain constant regardless of the jamming environment, which reduces the transmission speed and increase the power transmitting apparatus. Reducing energy consumption is an important task when using small satellites and spacecraft deep space.

An object of the invention is to increase the speed of data transfer by simultaneously reducing the energy consumption of radio transmitting equipment in the communication channels with interference.

The problem is solved according to the method of decoding of cyclic error-correcting code, namely, that on the transmission side to form the output sequence representing the sum modulo two of cyclic error-correcting code and a synchronization sequence, recurrently continue using test ratio of cyclic error-correcting code at the receiving side additionally carry out decoding of cyclic extensions of the received sequence, different those who, that on the transmission side to form code words by encoding the information symbols using a cyclic code without using synchronously, change the parameters of the cyclic code depending on the level of interference at the receiving side perform the accumulation of the transferred information, forming thereby a sample, then for phasing the code words define the boundaries of the code word are expected length of the code word and the given window have a "moving" character of the discrete Fourier transform in the Galois field throughout the volume of the analyzed sample, at each step of the "moving" of the discrete Fourier transform in the Galois field perform allocations zero spectral component and the determination of their the number of building function of the number zero spectral component at each step of the "moving" of the discrete Fourier transform in the Galois field, then perform decimate this function increments the expected length of the code words, with the construction of the evaluation function the mathematical expectation of the number zero spectral component, moments phasing reach the maximum evaluation function the mathematical expectation of the number zero spectral component, based on the obtained maximum allocate a code word, then determine the grade for Mathematica is anyone out items spectra of code words and estimate the parameters of the cyclic code according to the received code words, next, define the cyclotomic classes, restore the generating polynomial of the cyclic code and perform the decoding code words.

Consider the implementation of the proposed method of decoding cyclic error-correcting code.

On the transmission side form the output sequence. To do this, the original message volume k symbols of the first code cyclic error-correcting code. A coding information get the word cyclic code C(n,k)=x0x1, ..., xn-1where k is the number of information symbols, n is the length of the codeword of a cyclic code. Since the code is cyclic, there is a recurrence relation, which receive all control characters code xk+i=f(xix1+i, ..., xk-1+i) where i=0...n-k-1. In this case before the data are assessing the jamming environment and accordingly determine the parameters of error-correcting code. Received code words are transmitted in the communication channel.

At the receiving side perform the accumulation of the transferred information, forming thereby a sampling of L. For phasing the code words, i.e. the definition of the boundaries and the length of the code word are expected length of the code word n and the given window have a "moving" character DPPG on which this volume of the analyzed sample:

At each step of the "moving" DPFG perform allocations zero spectral component and determine their numberwhere N0(s) is the value function of the number of zero elements in s-m-step. The graph of a function of N0(s) when "sliding" DPFG for cyclic code (63,57) is depicted in figure 1 (further graphical material is presented for cyclic code (63,57)).

Next, analyze the functions of N0the number of null elements of the spectrum. Set the size of the analyzed window, equal to the expected length of the code word is n or greater. Assess the mathematical expectation of the number of null elements of this function, using the expressionwhere N- the number of analyzed samples (length of the "window" of the alleged code words).

When adequate synchronization functionevaluation of the mathematical expectation of the number zero spectral elements will be presented on figure 2.

In moments the correct phasing will be highs. If the analysis of a function of N0the number of null elements of the spectrum was taken, the window size is equal to the expected length of the code words is, n, then the graph of the functionevaluation of the mathematical expectation of the number zero spectral elements will have one maximum. If the maximum of this function is not observed, it is necessary to change the length of the estimated code word and to carry out the construction of a function of N0and then.

If the analyzed digital stream spoziroval, i.e. starts with a code word, then the graph of the functionwill be presented on figure 2. If the stream is not spoziroval, then the graph of the functionwill be presented on figure 3.

If the analysis of N0the number of null elements of the spectrum was taken as the window size, two or more times the length of the code word is n, then the graph of the functionevaluation of the mathematical expectation of the number zero spectral elements will be correspondingly two or more maxima of the function, and the period of repetition is equal to the length of the code word n.

If thewill have a maximum, greater or equal to the threshold value, deciding that the detected encoded signal is a cyclic code. The threshold value is determined by the length of the analyzed is th at a discrete Fourier transform in the Galois field of the window. Thus, the phasing method of successive shifts, based on the difference of the synchronous state of the receiver from asynchronous, where the synchronous refers to a state in which only accepts code words (excluding the effect of errors in the line).

After the detection of the encoding, and hence, determine the length of the code word and phasing occurs, the task of determining the structure and parameters of the encoder. For this above code words carry DPFG.

Determine the estimate of the mathematical expectationelements of the spectrum of F(x)

The distribution schedule of the evaluation of the expectationelements of the spectrum presented in figure 4.

As can be seen from the graphs, if the signal is accepted without interference estimate the mathematical expectationelements of the spectrum characterizing the generating polynomials of encoders is equal to 0. In the case of interference in the communication channel values of the spectral components, characterizing the roots of the generating polynomial, which must be equal to 0 will be non-0. The analysis showed that the use of statistical estimates of the expectation values of the spectral components allows to provide ve is aatest identification 0,99 error in the communication channel to 10 -3. Then carry out the determination of the cyclotomic classeswith the subsequent recovery of the generating polynomial encoderwhere αiis a primitive element of GF(n)(q) of degree i, where. Set To equal to the Union of cyclotomic classes.

Depending on the settings of the encoder code word will be showing the structure of the encoder cyclotomic class modulo n=pm-1 zero spectral components.

Thus, the proposed method is compared with the prototype not only provides increased robustness of receiving the codeword of a cyclic code, but also allows you to speed up the process of phasing in the transmission of code words without the use of synchronization symbols. Used the sign for phasing of code words is the same for different classes of codes. Due to the fact that there is no need in characters synchronously, you can increase the speed of information transmission. Thus, you can dynamically modify the characteristics and parameters of the encoder of the transmitting apparatus of the ICA and the SPACECRAFT deep space without using a separate control channel by increasing the speed and reducing energy satr the t for the transmission of information.

The method of decoding of cyclic error-correcting code, namely, that on the transmission side to form the output sequence representing the sum modulo two of cyclic error-correcting code and a synchronization sequence, recurrently continue using test ratio of cyclic error-correcting code at the receiving side additionally carry out decoding of cyclic extensions of the received sequence, characterized in that on the transmission side to form code words by encoding the information symbols using a cyclic code without using synchronously, change the parameters of the cyclic code depending on the level of interference at the receiving side perform the accumulation of the transferred information, forming thereby a sample, then for phasing the code words define the boundaries of the code word are expected length of the code word and the given window have a "moving" character of the discrete Fourier transform in the Galois field throughout the volume of the analyzed sample, at each step of the "moving" of the discrete Fourier transform in the Galois field perform allocations zero spectral component and the determination of their quantity, the building features a number of the STV zero spectral component at each step of the "moving" of the discrete Fourier transform in the Galois field, then perform decimate this function increments the expected length of the code words, with the construction of the evaluation function the mathematical expectation of the number zero spectral component, in moments of phasing reach the maximum evaluation function the mathematical expectation of the number zero spectral component, based on the obtained maximum allocate a code word, then determine the estimate of the mathematical expectation of items spectra of code words and estimate the parameters of the cyclic code according to the received code words, then define the cyclotomic classes, restore the generating polynomial of the cyclic code and perform the decoding code words.



 

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FIELD: communications engineering, in particular, engineering of data transfer systems for decoding cyclic interference-resistant codes without preliminary phasing.

SUBSTANCE: during decoding of cyclic interference-resistant code, range of presumed lengths of code combinations [nmin-nmax] is determined, and assumed phase of beginning of code combination f is set, from phase f in received code series several presumed code combinations Si are selected and pairs are formed from selected combinations in accordance to condition Si≠Sk, N of greatest common divisors, represented by polynomials, is calculated, and from calculated polynomials a polynomial of least order is selected, which is considered equal to original polynomial g(x) of cyclic interference-resistant code, if N of greatest common divisors is equal to "1", then length of proposed code combination n is increased by one, phase of proposed beginning of code combination is altered for one, if greatest common divisor, different from "1", is not found for all n∈[nmin-nmax], combinations of errors are determined in code word and selected code combinations are decoded.

EFFECT: development of method for decoding cyclic interference-resistant code under conditions of adaptation of interference-resistant code to quality of information transfer channel.

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