Adaptive Uncoupled Termination for Coupled Arrays in MIMO Systems

In this paper, we present an adaptive uncoupled matching network to compensate any performance degradation of compact multiple-input multiple-output (MIMO) systems due to antenna mutual coupling effects and channel variations. This method varies the antenna terminal loads per symbol-block, based on a random search algorithm, to find an optimum termination network that maximizes the performance metric, such as received power and capacity. It uses the received signals (voltages across the resistances of the terminal loads) to estimate or calculate the performance metric, in order to include the total effects in the optimization process. By applying the random search algorithm, our method does not require any knowledge of the array parameters such as impedance matrix, or derivatives of the performance metric(s) unlike other optimization techniques. We demonstrate this scheme by performing simulations to optimize the capacity of a 3 × 3 MIMO considering different propagation scenarios. We observe significant mean capacity improvements (more than 2 b/s/Hz) for all assumed propagation scenarios, when receive array antennas are spaced close as 0.05λ and terminated non-identically.