Channel Estimation Technique Based On OFDM Systems

Orthogonal frequency division multiplexing (OFDM) is a promising technique for achieving high bit rates required for a wireless multimedia service. This new technique has gained increased interest for its high bandwidth efficiency and robust performance in multipath dispersive environment.To reduce the effect of intersymbol interference (ISI), which is caused by the dispersive Rayleigh-fading environment, the symbol duration must be much larger than the channel delay spread. In OFDM, the entire channel is divided into many narrow subchannels, which are transmitted parallel, and so increasing the symbol duration and reducing ISI. Therefore, OFDM is an effective technique for mitigating multipath fading and for high bit rate transmission over mobile wireless channels. In addition, when the cyclic prefix (CP) is adopted as guard interval, the orthogonality among subcarriers will be ensured.However, there are still many difficult problems must be solved when it is applied in practical mobile communication systems, one of which is channel estimation and equalization technologies.This paper mainly focuses on the channel estimation algorithms research for OFDM receivers. Firstly, the basic theory of OFDM systems is introduced, including the structure of OFDM signal, the implementation methods in DFT/IDFT, the structure of guard interval and cyclic prefix, and several difficult problems in OFDM systems. Secondly, the channel characteristics are detailed explained, including powerline channel and wireless channel. Thirdly, channel estimation technologies were detailed discussed. The channel estimation techniques based on pilot for OFDM systems through different algorithms and improved algorithms for channel response estimation at frequency domain and time domain are investigated. Furthermore, different interpolation algorithms were also discussed and compared. At last, the implementation scheme on FPGA of channel estimation was designed, which was put forward by considering the performance and complexity of the channel estimation methods and interpolation algorithms.