A simple channel estimation method for MIMO-OFDM in IEEE 802.16a

Both orthogonal frequency division multiplexing (OFDM) and multiinput multioutput (MIMO) are generic techniques that are being actively considered for applications in 4G mobile. In MIMO applications, the channel between each pair of transmitter and receiver needs to be estimated accurately for coherent demodulation and space-time (ST) codes decoding to work optimally. In this work, we propose a simple channel estimation method for a MIMO-OFDM system based on IEEE 802.16a (wireless Metropolitan Area Network (MAN)). The method works by cyclically rotating the same preamble at each transmitter by a different number of samples in such a way that the channel impulse response (CIR) of the channels from each transmitter can be separated in time. Using just simple processing at each receiver, the CIR of the respective channels from each of the transmitter can be separated and their estimates obtained. The estimation method has been tested extensively in simulations of 2×2 MIMO-OFDM system based on IEEE 802.16a standard developed in Matlab/Simulink. The ST code used is Alamouti´s ST Block Code which gives very good performance and is quite simple to implement. Results show that the overall system BER are nearly as good as the upper bound performance that is obtained with perfect channel state information (CSI).