Research On Bit-Interleaved Coded Modulation With Iterative Decoding

This thesis focuses on the study of the soft information processing-based joint demodulationand decoding techniques of Bit-Interleaved Coded Modulation with Iterative Decoding(BICM-ID). The system of BICM-ID combines decoding with modulation and transforms theHamming distance into Euclidean distance with the designing of mapping rules, acquiringimproved performance over the AWGN channel. At the same time, the interleaver of the systemenhances the resistance capability of fading. In the receiver, the technique of iterative softinformation processing-based joint demodulation and decoding debases the bit error rate of thesystem. BICM-ID has already been widely used in wireless communication because of itsexcellent performance.The main research working can be summarized as follows:Firstly, demapping combine with decoding technique of the soft decision feedback isstudied, and the factor which affects the system capability can be analyzed. The soft input softoutput decoding algorithm is improved, and the extrinsic log-likelihood ratios (LLRs) areinferred.Secondly, the technique of demapping combine with decoding with hard-decision isproposed, and the phenomena of bad performance that the error bit spreading is discussed. Forthis question, two modified algorithms are proposed. One is decreasing the decision of decoderand enlarging the search range; the other is combines with soft-decision feedback algorithm, andalleviates the adverse effect of error propagation by “softening” the hard decisions and extendingthe oriental symbol search rang.Thirdly, the Repeat Accumulate code (RA) and its decoding algorithm are introduced. TheBICM-ID system based on RA code is designed. The influence of iterative times to the systemperformance is analysed, and the reasonable iterative times to achieving good performance isdealed.Finally, the carrier synchronization algorithms of BICM-ID which uses are proposed. Thesealgorithms are compared, and a CA carrier synchronization algorithm is brought forward.The contributions of this thesis can be summarized as follows.1．The SISO decoding algorithm of systematic and non-systematic convolution code ismodified, and the extrinsic LLRs are inferred.2. Targeting at the fact that the high BER of hard decision feedback BICM-ID system atlow SNR, this thesis proposed a modified hard decision feedback demapping algorithm. Themodified algorithm enhances the performance of the system with recalculating Euclideandistance and extending the search range.3. Combining the hard decision feedback and the soft hard decision feedback demappingalgorithm, a new modified algorithm is proposed. The new algorithm alleviates the adverseeffect of error propagation by “softening” the hard decisions and extending the oriental symbolsearch rang. 4. Targeting at the fact that the high BER of BICM based on RA code, a new systemwhich is named BICM-ID based on RA is proposed.5. A new CA carrier synchronization algorithm is proposed which based on expectationmaximization theory. The new algorithm extends the parameter estimating range and satisfys theneed of precision, enhancing the system performance at the same time.