Fqpsk Modulation Modulation Of The Joint Coding Of Multiple Ldpc Codes

The exploration in deep space is the one of the three most important acitvites in the new century and it shows the standard of the science and the national comprehensive strength of a country. The deep space indicates the place that is hundreds of thousands or millions far away to the earth. It has the characteristic that more distance, lower SNR, longer delay, more complicated circumanstance and the need of more power effiency, so we need more power effiency modulation, better correction codes. In order to reach the need of this situation, we adopt this menthod that combined the FQPSK modulation with the LDPC code to meet the development of the aerospalace and research its performance and its probability in the application.In this paper, firstly, we introduce the present situation of the deep space's techinique of modulation and encode. We illustrate the disadvantage of the past encodes and modulations and the advantage and the developing prospect of LDPC and FQPSK modulation. In the second chapter, we introduce the method that generates the parity check matrix, decoding method and its graph present of LDPC code. We also reveal the difference of LDPC over GF (q) and binary LDPC codes and its differant pratical usage. In the third chapter, we describe the origination of FQPSK and its development, and analyse its PDF and some conventional demodulation methods.In the fourth chapter, we research the MAP demodulation method of the FQPSK modulation; the scheme of FQPSK modulation adopts the structure of convolutional coding and according to the output of the coding to choose waveforms. According to the difference of the waveforms and mapping shcheme, we adopt the approximation matched filter and joint probability analyze, obtained the MAP demodulation of FQPSK. We simulated its performance, this algorithm has 1.5 gain in the perfomence compared with Viterbi algorithm. In the meantime, we can combine the FQPSK modulation and LDPC code, the soft information from MAP demodulation to decode LDPC codes. We also can use repeat code for outer code, itself for inner codes, and this structure can improve the whole system's performance.In the fifth chapter, we simulink the binary LDPC codes with FQPSK modulation, we also simulink the LDPC codes over GF(q) with FQPSK, the result shows the long code has better performance and the LDPC codes over GF(q) with FQPSK modulation has better performance compared with binary LDPC codes, it meets the communication of deep space.