Study On Adaptive Transmission Techniques For LDPC Coded OFDM Over Ka Channels

Compared to C-band and Ku-band satellite communications, the satellite communications based on Ka-band has the advantages of wide available bandwidth, large communication capacity, strong ability of anti-interference and good privacy. Therefore it has been widely used in commercial and military communications. However, they are vulnerable to the influence of weather attenuation factors and mobile attenuation factors, lowering the communication quality and reliability. Low density parity check codes, a superior channel coding technique with the capability of approaching the Shannon limit, has become the focus of research in recent years. Orthogonal frequency-division multiplexing technology has advantages such as strong resistance to multipath interference and high spectral efficiency. The application of adaptive transmission technology can improve system resource utilization and system throughput. In this thesis, the three kinds of technology above are applied in Ka-band mobile satellite communication channels to improve the overall performance of the system.This thesis first accomplishes the Ka-band mobile satellite channel modeling, and computer simulation and analysis are carried out. Then, the simulation model of adaptive modulation coded OFDM system based on LDPC codes under this channel (AMC-LDPC-OFDM) is built. For the two criteria of minimizing system sending power and maximizing system transmission rate, simple block loading algorithm and improved greedy algorithm are selected respectively.And the system performance of using CCSDS standard LDPC codes and special LDPC codes--Kite codes is studied, obtaining suitable channel coding under different fading conditions.Finally, the performance of adaptive modulation and coding under combination of different bit-rate and modulation method is researched.And the best combination of bit-rate and modulation method in a variety of channel environment for different SNR region is given under the condition that certain target bit error rate is given.