Study Of Channel Estimation For OFDM And OFDMA Systems

Channel estimation for OFDM (Orthogonal Frequency Division Multiplexing)and OFDMA (Orthogonal Frequency Division Multiplexing Access)systems is well studied in this paper. First, a brief introduction of the basic principles of OFDM is presented. Second, the characteristics and modeling methods for wireless channels are studied and several channel models which can represent the channel characteristics are simulated. Third, we focus on the channel estimation algorithms for OFDM system. Since related studies show that there are some shortcomings with LS(Least Square) and MMSE(Minimum Mean Square Error) estimators, we propose a new algorithm which deals with the LS estimation results through wavelet shrinkage denoising based on Stein's unbiased risk estimation (SURE) criterion in this paper. This algorithm can effectively remove the influence of noise in the channels and minimize the estimation risk. Consequently, the sensitivity to noise of LS estimation is diminished. Mathematical analysis and simulation results both show that the proposed algorithm has significant advantage over the LS and its modified methods. Fourth, we study the uplink and downlink channel estimation algorithms for OFDMA system based on 802.16. A detailed study of the channel estimation for several pilot schemes which include uplink-PUSC(Partially Used Subchannelization), uplink-OPUSC(Optional Partially Used Subchannelization), downlink-PUSC and downlink-OFUSC (Optional Fully Used Subchannelization) is presented. We find out a proper estimation algorithm for each scheme. The algorithm proposed in this paper is used in the downlink OFUSC pilot scheme, and simulations in the scenario of 802.16 show that the proposed algorithm has considerable advantages over LS method. Finally, the performance of the channel estimation algorithms based on 802.16 is evaluated on the software platform.