Study On Adaptive Coding And Modulation Technology In Satellite Communication

As complement and extension of terrestrial communications, satellite communication has the advantages that it can cover a wide range, unlimited by geographic environment, and unaffected by natural disasters, so it has the irreplaceable position. But because of its open channel environment, satellite communication is affected by many atmospheric factors, and the influence is especially great with the rain attenuation in Ka frequency. So as one of the fading mitigation technologies (FMT), adaptive coding and modulation (ACM) technology is of great use in satellite communication.In this thesis, the influence of rain attenuation as time passes, the SNR estimation technology in satellite communication, and the application of adaptive coding and modulation technology in satellite communication are studied. The main content of this thesis is described as follows:1. The common components of satellite communication system and its physical layer technologies are summarized, and the satellite channel model, SNR estimation technology and adaptive coding and modulation technology are deeply investigated.2. The influence of different weather conditions to satellite channel is analyzed. A static Ka frequency satellite channel model is built, whose envelope and phase follow Gaussian distribution. The simulation result show different SNR-BER curves under different weather condition. The concept of fading slope in rain attenuation is analyzed and explained. Based on the research of fading slope, a short-time rain process is converted to an N-state Markov model, to generate a rain attenuation series in time sequence, which is a dynamic Ka frequency satellite channel model. The simulation results show that this model can appropriately reflect the influence of short-time rain attenuation to Ka frequency satellite channel.3. Several SNR estimation algorithms, which can be used in satellite communication systems, including EVM algorithm, SSME algorithm, M2M4algorithm, SVR algorithm, MMSE algorithm, and ML algorithm are analyzed in this thesis. Under the same conditions, the performances of different SNR estimation algorithms are compared together.4. The principle and key parts of adaptive coding and modulation are analyzed, and the coding and modulation technologies in DVB-S2standard are studied. DVB-S2standard simulation platform is built, which simulates different coding and modulation schedules. Based on the short-time rain attenuation series in time sequence, the adaptive coding and modulation methods in DVB-S2standard are optimized. The simulation results show that the optimization method can effectively reduce the complexity of the original method in DVB-S2standard, without much performance drop. Based on the Markov state theory, a new CMS selection algorithm is designed. The simulation results show that the performance of new algorithm is better than the traditional threshold method.