Adaptive Coding And Modulation Technique Based On LPDC Codes For Ka-band Satellite Communications

With the rapid development of broadband satellite communications, the typical C-band, Ku-band can’t satisfy the growing requirement. Therefore, Ka-band has been widely used for satellite communications due to its wide bandwidth and excellent anti-interference performance. However, Ka-band satellite communications are seriously affected by rain attenuation. In order to guarantee the reliability of signal transmission and improve the link availability in Ka-band satellite communications, it’s necessary to employ adaptive techniques to combat rain attenuation. This thesis studies the adaptive coding and modulation based on Low-density parity-Check (LDPC) codes for Ka-band satellite communications, and the main contents are as follows:1. Using complex-network theory, one kind of Scale-free Quasi-Cyclic LDPC (SF-QC-LDPC) codes with power-law degree distribution is designed. To lower its error floor, the low-degree distribution of SF-QC-LDPC codes has been constrained, which makes SF-QC-LDPC codes have dual-diagonal structure. The simulation results show that the given SF-QC-LDPC codes have good decoding convergence performance and lower error floor.2. Two Ka-band rain-attenuation channel models are established for link budget and the dynamic characteristics of rain-attenuation, respectively. The effect of different parameters on the autocorrelation and power spectral density of rain-attenuation is also analyzed. The first-order and second-order statistical characteristics of the time-series model are obtained and the validity of the rain-attenuation channel models is verified via simulation.3. An adaptive coding and modulation (ACM) transmission mode based on SF-QC-LDPC codes is designed. By combining the ACM mode, SNR estimation and shifted-threshold technique, an ACM transmission scheme for Ka-band satellite communications is proposed. The simulation results verify that the proposed scheme can adaptively compensate Ka-band rain-attenuation. Comparing to the constant coding and modulation (CCM) transmission scheme, the proposed scheme can effectively improve spectral efficiency under the same link availability condition.