Research On The Joint Coding And Modulation Methods Of LDPC And FQPSK

FQPSK(Feher-Patented QPSK) is a nearly constant envelope modulation mode,which has special advantages of high bandwidth efficiency,rolling down fast and soon. But demodulation performance depends heavily on signal-to-noise ratio (SNR),so demodulation performance for the weak signal has a great loss. In order toimprove performance, the channel coding LDPC (Low Density Parity Check Codes)is joined. The extraction for soft information of FQPSK is analyzed, the joint codingand modulation of FQPSK and LDPC is studied and that performance is analyzed inthe paper.First of all, modulation principle of FQPSK is studied, traditionaldemodulation method is simulated, performance is analyzed and the channel noiseinfluence on demodulation is researched. There is some difficult for being extractedsoft information of FQPSK in traditional demodulation method. A maximum aposteriori probability algorithm is introduced in this paper, analyzing maximum aposteriori probability algorithm, the algorithm is introduced into the algorithm ofFQPSK demodulation and analysis of its performance.Secondly, the channel coding LDPC is researched. The coding method ofLDPC, the structure of the check-up matrix and decoding algorithm are studied.After that, simulation experiment is carried out. This paper used the IEEE802.16estandard LDPC codes and based on the balanced incomplete block of codes areagroup LDPC, according to the result of the experiment, the two LDPC codes allhave strong ability of the error correction. In the study of the basic decodingalgorithm, the new decoding algorithm is improved.Finally, the joint coding and modulation methods based on LDPC and FQPSKis researched. When bit error rate of FQPSK is10-6, the signal-to-noise ratio is needabout12dB, In order to solve the shortcomings of high SNR, the simulationexperiment is carried out using the joint modulation and demodulation method.According to the experimental results, when the bit error rate in10-6, thesignal-to-noise ratio is need about5dB. It is visible that joint modulation anddemodulation can improve the performance of the whole system. This paper alsosimulate the coding, modulation, extraction of soft information of the joint modulation and demodulation methods with hardware simulation.From the above, the impact of channel noise on the demodulation performanceof FQPSK is analyzed and it can improve the performance of the system using thejoint modulation and demodulation method.