Adaptive V-BLAST Type Channel Equalizer Design for Cognitive MIMO-OFDM Radios

A channel shortening equalizer design for cognitive Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing (MIMO-OFDM) communication systems is considered in this presentation. The proposed receiver consist of two sections : MIMO decision feedback equalizer (MIMO-DFE) and adaptive Viterbi detection. In MIMO-DFE section, a complete modified Gram-Schmidt orthogonalization of multichannel input data is accomplished using sequential processing multichannel Givens lattice stages, so that a Vertical Bell Laboratories Layered Space Time (V-BLAST) type MIMO-DFE is realized at the frontend section of the equalizer. Matrix operations are accordingly avoided, and only scalar operations are used. A highly modular and regular radio receiver architecture, that has a suitable structure for software defined radio implementations, is achieved. In connection with adaptive Viterbi detection section, a systolic array implementation for each channel is performed so that an receiver architecture with high computational concurrency is attained. The total computational complexity is given in terms of equalizer and desired impulse response filter lengths, and the number of data symbols used. The performance of the proposed equalizer under time-invariant and time-variant channel conditions is presented by means of mean squared error (MSE) and probability of error evaluations.