Researches Of High-order Modulations And Efficient Codings For Broadband Satellite Communications

With the demand for multimedia services rapidly, broadband satellite communications has found wide applications in the military and civilian. To further enhance the spectral efficiency of broadband satellite communication system and increase the system capacity, higher order modulation has been used in broadband satellite communications. Moreover, to guarantee the reliability of signal transmission in satellite communications, a strong and efficient error correction channel coding technique is needed. This thesis studies the efficient codings, the high order modulations and the system carrier recovery techniques, and the main contents are as follows:1. The LDPC encoding method in DVB-S2 standard and the QC-LDPC construction methods based on Euclidean Geometry (EG) and Cyclic Permutation Matrix (CPM) are described. The performance of constructed codes have been simulated in AWGN channel with BPSK modulation, results show that: the performance of EG codes is closed to CPM codes'. When the bit error rate is 10^-7, the CPM codes outperform 0.2dB of codes in DVB-S2 standard with the same code length and rate.2. APSK constellation optimization based on Minimum Euclidean Distance and Maximum Mutual Information are Researched and the optimized constellation parameters are obtained. The performance of coded and modulation system is simulated, and the results show that the performances of optimized APSK+LDPC are almost the same as the performances of QAM+LDPC (the difference is less than 0.1dB) in the AWGN channel.3. For broadband satellite communication with LDPC codes and MAPSK modulations, the frequency estimation unit was designed and a iteration phase recovery solution was proposed. The results show that the solution of carrier recovery estimates the frequency offset and traces the carrier phase well, with a phase deviation of PLL around±2 after stabilization. Compared with performance without frequency and phase offset, the performance loss of iterative carrier phase recovery is only 0.1dB, after frequency offset was estimated and corrected.