Performance Analysis of Periodic Precoding for Channel Estimation in MIMO- OFDM System

Abstract

In modern wireless communication systems, multiple antennas at transmitter and receiver are employed along with OFDM to achieve very high data rate with significant system reliability. To enhance this task of MIMO-OFDM system we explore blind channel estimation. It is a technique in which no information about transmitted data is used for channel estimation, but statistical properties are considered. In contrast to previous methods of estimating channel, a precoder is used in this dissertation which is able to remove problems like channel-order overestimation, bandwidth expansion caused by oversampling at the receiver and limitations of subspace and training methods. Moreover precoders can be used in both time and frequency dispersive channels. A periodic precoder passes a periodic sequence through each subcarrier of OFDM symbol. A different periodic sequence coefficient is given to each subcarrier of the system to make the system time-invariant. A toeplitz channel matrix is taken and super diagonal elements of the expression are taken for calculations and then cyclostationarity of received signal is generated. Because of cyclostationarity induced, the only indentifiabilty condition imposed is channel impulse response is full column rank. Eigen values and Eigen vectors of channel product matrices are calculated and used to estimate channel. The proposed method is able to work in both conditions of more inputs and more outputs. A technique is stated to choose an optimal periodic sequence in such a way so that it reduces noise at the receiver. BER for MQAM signal is also calculated using SNR of the system. It is observed that SNR depends on precoding sequence and estimated channel and so thus BER and variation of BER with channel estimation error is observed.