THE ANALYSIS OF NOISE STABILITY OF UNEVEN CODES APPLIED FOR THE INFORMATION TRANSFER VIA THE COMMUNICATION CHANNEL

The article meets the challenge of the synchronization detection in the code sequence of uneven codes, lost in the result of impact of errors in the communication channel when transmitting compressed messages.

For this purpose, basing on statistical properties of the messages and digital communication channel source, the authors got the observation likelihood functions in the presence and in the absence of synchronization. In this situation, the frequencies of occurrence of volume-defined alphabetic letters in the decoded sequence of characters can be used as the observations. As a primary distribution, the authors used a polynomial distribution, which characterizes the frequencies of occurrence of alphabetic letters in the volume-defined selection depending on their probabilities. The peculiarity of this approach for the synchronization detection is the use of polynomial distribution for description of the function of synchronization unavailability likelihood on the basis of the theory of complex hypotheses recognition with a uniform averaging.

In the result of such approach, the authors obtained the likelihood ratio depending on the probabilities of alphabetic letters occurrence using which it is possible to make the conclusion about the presence or absence of synchronization.

The algorithm for synchronization detection in event of non-uniform encoding was developed on the base of the sequential analysis procedure. The value of average Bayes risk presented in the form of probability of synchronization detection error was selected to be an indicator for the algorithm effectiveness evaluation.

The analysis of noise stability of uneven codes shows that the application of modern multimedia technologies in communication networks increases the amount of transmitted information and used alphabet of messages that leads to the loss of synchronization and the effect of error propagation. It causes partial or total loss of data. The developed algorithm will allow recovering of the compressed messages that were distorted during their transmission via communication channel.