The Design And Amelioration Of Hybrid-ARQ

In wireless communications, data transmission has played and will play more important role due to the rapid traffic increase in multimedia data and other data exchange. Compare with voice signal, data transmission requires the system more reliable. But in fading and shadowing channels, channle states are not stable due to the affection of atmosphere environment, terrain and motion. This brings a series of problems to reliable data transmission. As a combination of Auto-Repeat-reQuest and Forward Error Correction, Hybrid ARQ provides the advantages of both and is suitable to be used in instable channels. Supported by the National Natural Science Foundation of China (No: 60372067) and National High Technology Research and Development Program of China (863 Program No: 2002AA119010), the performance of hybrid RCPC-ARQ and hybrid RCPT-ARQ system are examined and improved this dissertation. Rayleigh fading channel models are firstly studied. Three fading channel models are considered: slow Rayleigh fading channel, fast Rayleigh fading channel and memoryless fading channel. Secondly, two channel coding arithmetics, Convolutional and Turbo coding, and Viterbi decoding arithmetics are discussed. Convolutional code and Turbo code are tested and compared in fading channels. RCPC-ARQ and RCPT-ARQ system are simulated and compared in different channel conditions. After these work, two improved hybrid ARQ schemes are introduced: one is improved long distance transmission hybrid ARQ scheme. It adaptively adjusts the code rates of first transmission according to the number of average retransmissions at given signal-noise-ratios range. Simulation test result shows that the new scheme yields better throughput than the type II hybrid ARQ in long distance fast fading channels; the other is improved unlimited retransmission number hybrid ARQ scheme. It can adjust the proportion of ARQ and FEC in hybrid ARQ. Simulation test result shows that the new scheme yields better throughput than the type II hybrid ARQ in slow fading channels.