Study On Iterative Synchronization Techniques For Nonbinary LDPC Coded Modulation Systems

In order to estimate the frequency offset and the transmission delay precisely under low signal noise ratio(SNR),the channel coding technology was introduced into the receiver synchronization system.Channel coding technology makes the information sequence perform better at error controlling,which will make sure the receiver can work normally under low SNR.By designing sensible receiver synchronization methods,the communication system can estimate the synchronization parameters accurately,which will help the coherent demodulator work smoothly.Using iterative decoding method,low-density parity-check(LDPC)codes can get performance which is very close to the channel capacity.Comparing to the binary LDPC codes,the nonbinary LDPC codes can be more suitable to work together with high-order modulator under the situation of low SNR and short code length.Based on nonbinary LDPC coded and high-order modulation systems,we did some research about symbol timing recovery and carrier synchronization techniques in receiver synchronization systems.For symbol timing recovery technology,We proposed a novel method which joint the iterative decoding technology with symbol timing recovery systems.When facing with dynamically changing delay,the proposed method can work effectively under low SNR.By using different forms of the decoding feedback information,we proposed two kinds of iterative decoding feedback methods.The simulation results show that by using soft decoding feedback information,the proposed method can get quick and precise estimation of the changing delay.Based on the general data frame structure,we presented a novel frequency estimation algorithm,which will separate the whole frequency estimation into two parts and achieve accurate estimates of frequency offset in large scale.Without the assistance of decoding feedback information,two different kinds of methods were put into practice,and the estimation accuracy of the proposed frequency algorithm and the maximum likelihood phase offset estimation algorithm were compared with the Cramer-Rao bound.Based on Turbo synchronization method,the proposed frequency estimation algorithm can achieve better performance by using soft decoding feedback information.At last,we proposed a practical method to optimize the frame structure,and under the new designed structure,the proposed algorithm can achieve even better performance without the assistance of the decoding feedback information,which means lower complexity and performance loss.The simulation results show that the proposed two-step frequency estimation algorithm can performs close to the ideal carrier synchronizator under the optimized frame structure.