Study On Channel Estimation And Equalization Techniques For OFDM Systems

OFDM (orthogonal frequency division modulation) is regarded as one of the most promising techniques for wireless mobile communication. OFDM sysem can effectively eliminate the disturbance of inter-symbol interference caused by multi-path channel by using cyclic prefix, Besides, OFDM can combat the time selective fading with flexibly designed frame structure according to accurate channel estimation. Due to OFDM system adopting FFT technology, it reduces the complexity of the receiver greatly. So the application of OFDM technology in the domain of wireless communications has attracted wide attention.While the OFDM system architecture can eliminate part of the inter-symbol interferences, accurate channel state information is needed for OFDM system to perform channel equalization and compensate the multi-path fading and Doppler frequency shift greatly. Therefore, channel estimation and equalization has an important impact on performance of the OFDM system.This thesis will discuss channel estimation and channel equalization techniques of OFDM system in the wireless broadband mobile communication environment. First of all, it mainly discusses the channel estimation algorithm for OFDM systems based on the comb pilot and block pilot, which includes least square algorithm,minimum mean squared error(MMSE) algorithm, MMSE algorithm decomposed by singular value decomposition algorithm and decision and feedback algorithm. This thesis also discusses the popular channel interpolation algorithms, which includes constant interpolation, linear interpolation, twise interpolation and DFT interpolation algorithm, and the thesis analyzes and compares the strengths and weaknesses of various algorithms. Then this thesis simulates the algorithms of the OFDM channel estimation with MATLAB software and compares the result of simulation.One of biggest superiorities of OFDM is that it can do simple frequency domain equalize. Thank to cyclic prefix, which eliminates inter-symbol interference. The receiving end can be a simple division to achieve channel equalization. This thesis mainly describes OFDM channel equalization algorithms, and which includes zero forcing algorithm equalization and MMSE equalization algorithm, both of them bases on frequency domain, and it also describes time domain equalization algorithm. The thesis also expounds basic principle and key technologies of single-carrier frequency domain equalization and compares single-carrier frequency domain equalization(SC-FDE) system with OFDM system. Then compare with performances of different structure of single carrier frequency domain equalization system and compare with performances of SC-FDE and OFDM systems under the same external conditions, after analyzing advantages and disadvantages of both of them, The thesis finally discusses a plan that combines OFDM system and SC-FDE system which can make system's performance better.