Reseach On OFDM Channel Estimation And Equalization Based On QAM In Time-varying Channels

Orthogonal Frequency Division Multiplexing(OFDM) technology has good resistance capability to multipath fading and high spectral efficiency, so it has been widely used in the field of communication. Channel estimation and equalization is one of the key technologies of OFDM system, and it relates to the entire OFDM system performance. At the same time the main trend of the future development of wireless communication technology is higher user rates and higher user speed. Therefore, this article focuses on channel estimation and equalization algorithms based on QAM in the fast and slow time-varying channels. The main work includes the following three aspects:Firstly, we study channel estimation and equalization algorithms in the slow channels. In slow time-varying channel, we study classical channel estimation algorithms based on pilot. First we introduce the common pilot structure; then depict channel estimation algorithms at the location of the pilot and non-pilot position in detail;Finally, the simulation results, a detailed analysis and performance verification are presented, so we can select the appropriate algorithms according to the project requirements. As for equalization, we describe a single-tap frequency domain equalization algorithm. For strong frequency selective channel, we propose ZF equalization, decision feedback equalization and an improved decision feedback equalization algorithm.Secondly, we study channel estimation and equalization algorithms in the fast time-varying channels. When the Doppler frequency shift of the channel is large, the system arises a serious sub-carrier interference phenomena, algorithms for slow time-varying channel are not appropriate, So for fast time-varying channel, we study corresponding channel estimation algorithms. In order to track fast time-varying channel in real-time better, channel estimation algorithms based on basis expansion model is studied. This algorithm uses weighted sum approach of a limited set of basic functions to fit time-varying channel. This article describes different types of basic functions; according to analyzing varying channel characteristics, clustering comb-like pilot structure is proposed; and as for various types of basic functions and pilot structure,a large number of simulation is done. In response to the phenomenon of ICI and torestore demodulated transmitted data, block decision feedback equalization algorithm based on BEM is proposed in time-varying channels.Finally, taking into account resource usage and system speed, we make hardware designs for some parts of channel interpolation algorithms based on pilot, equalization algorithms and digital sine and cosine signal generator, and implement them on FPGA hardware platform. Through simulation results and consolidated statements, we give performance results and resources usage in order to select appropriate algorithms according to project requirements.