Adaptive equalization of multiple-input multiple-output (MIMO)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 (m greater than or equal to n) receiver antennas is assumed. A decision Feedback equalizer is considered. A least squares solutions is first formulated, based on which a recursive solutions using Riccati recursions are proposed. The proposed 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.