A Study On Blind Estimation Of Algebraic Coding Parameters

In a non-cooperative communication system where the parameters used in channelencoder is unknown, an adversary needs to blindly estimate such parameters byintercepted codes, and thus obtains the transmitted information. Aimed at blindlyestimating the parameters which are involved with algebraic coding, the thesis got someachievements as follows:1. An algorithm was proposed to blindly estimate the length, the starting point andthe parity-check matrix of the linear black code. Firstly, the proposed method exploitedthe statistical properties of the dual codes and Walsh-Hadamard transform to determinewhether a code belonged to dual code or not. Meanwhile, from the principle of "3standard deviation", a theoretical threshold to distinguish dual codes was induced. Thenthe code length and starting point were estimated when the normalized dual spacedimension reached the maximum. Finally, the parity-check matrix was recovered by thedual codes. Computer simulation results show that the proposed method can providegood performance even when the bit error rate is0.03.2. An algorithm was proposed to blindly estimate the length, the starting point andthe parity-check matrix of the hamming code. At first, an intercepted matrix was builtby data received, and by exploiting the assumed number of parity-check digits and theassumed starting point of the hamming code. Then, a parity-check matrix was obtainedby the assumed primitive polynomial, and when all the row-vectors of which were dualcodes of the intercepted matrix, the hamming code parameters could be estimated.Moreover, a theoretical analysis of the proposed algorithm was given. Simulation resultsverify the good performances of the proposed method.3. An algorithm was proposed to blindly estimate the length, the starting point andthe generator polynomial of the BCH code. Firstly, the inter-relationship between thehamming code and the BCH code was investigated. Then, by approximating BCH codeas hamming code, the blind parameter estimation algorithm suited for hamming codecould be applied to BCH code, thus the length, the starting point, and the factor of thegenerator polynomial of BCH code could be obtained. Finally, the generator polynomial was recovered by cyclotomic cosets over finite fields. Simulation results verify the goodperformances of the proposed method.