Multiaccess Interference Reduction in OSTBC-MIMO Systems by Adaptive Projected Subgradient Method

We introduce adaptive linear filters based on the adaptive projected subgradient method that are suitable for online implementation of multiple access interference (MAI) suppression in OSTBC-MIMO systems. The proposed adaptive filters track the optimal solution of a new cost function that is robust against channel state information (CSI) mismatch. The adaptive update algorithm is based on projections onto closed convex sets that contain the optimal solution with high probability. The main features of the adaptive filters are that no matrix inversion of a sample covariance matrix is required and that a low-complexity recursive implementation is possible. Convergence analysis and simulation results show the effectiveness of the proposed schemes.