Research Of Pilot-based Channel Estimation In OFDM System

Orthogonal frequency division multiplexing (OFDM) technology which has a high spectrum efficiency can be effective against frequency selective fading, can also provide high-speed and high-quality communication services, it received growing attention and has becomed a key technology of fourth-generation mobile communication and hot spots of current international research in the field of wireless communication. However, due to multipath wireless channel delay and Doppler frequency shift, the receiving end features such as OFDM symbol was interfered between subcarriers. In order to accurately demodulate the OFDM signal, channel estimation must be carried out. Therefore, OFDM channel estimation has considerable research value.This paper systematically analyzes the basic characteristics of wireless channel and the basic principles of OFDM, and research the OFDM system based on pilot channel estimation algorithm, which includes the least squares (LS) algorithm and the minimum mean square error (MMSE) algorithm.Because the channel estimation based on LS algorithm neglect the impact of noised,it is difficult to obtain a good estimation performance. To solve this problem, we propose a scale factor based on the least squares (SLS) algorithm. The algorithm introduces a scale factor, which leads to LS algorithm with a smaller channel estimation mean square error (MSE). To further simplify the calculation, the LS-SLS method is proposed. The algorithm uses conventional LS channel estimation algorithm to obtain the trace of OFDM subcarriers expression to the correlation matrix. Simulation results show the effectiveness of proposed algorithm.Due to the drawbacks that MMSE channel estimation algorithm need to use the channel correlation matrix, and that prior information difficult to obtain in the practical application, we propose a simplified minimum mean square error (SMMSE) algorithm. This algorithm uses a simplified matrix to approximate the correlation matrix of OFDM subcarriers. Based on this algorithm, we deduced MMSE algorithm with a reduced complexity. To further reduce complexity, LS-SMMSE algorithm is proposed. The algorithm uses conventional LS channel estimation algorithm to obtain the trace of OFDM subcarriers expression to the correlation matrix. The simulation results show that the performance of proposed algorithm suffers a decline in the estimates, but is still significantly better than the LS algorithm.