Adaptive equalization of multiple-input multiple-output (MIMO) frequency selective channels

The purpose of this paper is to propose and investigate a new approach to adaptive spatio-temporal equalization for MIMO (multiple-input multiple-output) channels. A system with n transmit and m (n/spl ges/m) receiver antennas is assumed. An adaptive MIMO linear equalizer has been considered. For the considered equalizer a least squares solution is formulated, based on which a recursive solution using Riccati recursions is proposed. The solutions are tested by simulating the MIMO system. It is shown that the adaptive solutions will achieve the same performance as the optimum least squares solutions. The effect of the nondiagonal channel elements (acting as interference) on the system performance is also studied. It has been shown that in order to achieve better performance, the interference from nondiagonal channel elements needs to be minimized. This can be done by using orthogonal transmission. Moreover the proposed solutions do not require channel identification and will also enable equalizer adaptation to channel changes.