| The basic principle of adaptive modulation and coding techniques is to change the mode of modulation and coding accurately accoding to the instantaneous channel condition and current resource situation, in order to be adapted to channel condition within the system restriction, and thus to achieve the maximum data throughput.This thesis inverstigates the adaptive modulation and coding techniques based on the Beyond IMT-2000 system. As to the modulation techniques, the adaptive modulation system with QAM constellation adjustable is explored, and the decision criterion of threshold decision is presented, which is compared to the traditional threshold modulation method and further indicates the adaptive modulation method with QAM constellation adjustable performs much better than the traditional fixed level modulation method with respect to the dynamic range and frequentcy utilization ratio. Furthermore, the symbol rate and adaptive modulation system with controllable modulation level are studied, mainly focused on the selection of modulation parameters and the calculation of CNR (Carrier to Noise Ratio) decision threshold and delay expansion decision threshold. The adaptive modulation system with symbol rate and level adjustable has the adventages of that with QAM constellation adjustable, and furthermore its peroformance improves greatly with respect to the dynamic range and delay immunity. As to the coding techniques, the regular and irregular LDPC codes are discussed, and the principle of shape of tree decoding and probability decoding is presented. The BP (Belief Propagation) decoding algorithm is studied and its modified decoding algorithm in fading channel is proposed. Simulation on performance of the LDPC codes is done as well. All of the above studies will provide some theoretical reference and inspiration to the practical application of adaptive modulation and coding techniques.Although the construction of the whole system is accomplished in this thesis,... |
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