The Research Of Adaptive Bit And Power Allocation Algorithm In Multi-Carrier System

Multi-carrier system is very suitable for future high-rate wireless communication, due to its robust to multi-path interference and high frequency efficiency. The sub-channels in multi-carrier system suffer different wireless fading, so they have different channel capacity. Through the study of efficient allocation strategy, the performance of multi-carrier system can be improved. Therefore adaptive allocation algorithms have been widespread concerned and become one of the focuses in multi-carrier system research. Basing on the in-depth study of adaptive allocation algorithm, the main research work in this thesis includes:In this thesis, some typical adaptive bit and power allocation algorithm are first introduced. At the same time, we improved the Fischer algorithm and proposed Fischer-Evo algorithm. Then, we analyze these algorithms' performance and complexity. Simulation results show that Fischer-Evo algorithm performs better than others both in performance and efficiency, so it is more applicable for practical implementations.In this thesis, a Track-Control algorithm is proposed for constant-rate OFDM systems. This algorithm uses the former allocation information as system resource pre-distribution, and finishes the optimal or hypo-optimal allocation with partial adjusting. Meanwhile, the iteration can be controlled by setting the adjusting threshold and the complexity can be reduced by sacrificing some performance. So it can come to the balance of algorithm's performance and efficiency. Simulation results show that the proposed algorithm has small algorithmic complexity and high efficiency. In this thesis, An Efficient Variability Rate algorithm is proposed for variable-rate OFDM systems. This algorithm can get the theoretic optimal allocation by using Shannon and Lagrange formula to combine system's optimizing object and limitation condition. Finally, with the bit integer conversion process and the partial sub-channel's power and bit adjusting process, the system resource allocation is finished. Simulation results show that the proposed algorithm has excellent performance and fast operation ability.MC-CDMA is an effective combination of OFDM and CDMA technology. To apply adaptive allocation algorithm to MC-CDMA, a high efficiency MC-CDMA adaptive allocation algorithm is proposed in this thesis. We distribute proper bit and power for each spread branch by using adaptive allocation ideas in OFDM for reference. Simulation results show that the proposed algorithm can remarkably reduce transmission power and improve system performance.