The Study Of Channel Estimation In OFDM System

OFDM ( Orthogonal Frequency Division Multiplexing ) is a modulation technology ,which is very popular in recent years, with a good application future in the field of high speed wireless communications. It splits a high-rate data stream into a number of lower-rate data streams that are transmitted simultaneously over a number of subcarriers. The benefits of OFDM are resiliency to inter-symbol interference, high spectral efficiency and efficient to reduce multi-path interference.OFDM system uses circle prefix technology, which can avoid inter-symbol interference and protect the quadrature-phasing of a number of subcarriers. Meanwhile IFFT and FFT are also used in the system, which made the modulation and the demodulation simple. However, the channel transfer function varies with times in the mobile communication. In order to improve communication efficiency and quality, it is necessary to make a dynamic estimation of the current transfer function.Based on related references, the history of the OFDM technology is presented in the paper. And the principle and implementation of OFDM is discussed. On the brief analysis of OFDM system, this paper studies channel estimation for OFDM: LS,MMSE,LMMSE,SVD,Transform-domain,PSAM,Decision directed.Their performance are analyzed and compared by simulation. A novel Adaptive Pilot Algorithm is proposed in this paper. The proposed algorithm can remarkably reduce the pilot overhead without performance degradation, compared to conventional schemes. In the end, we can see the performance of MMSE estimator is the best, and the performance of LS estimator is the worst, while for the complexity of the three channel estimator methods, the condition is reverse comparing with the condition of the performance.