The Capacity of MIMO Wireless Systems with Mutual Coupling

MIMO wireless systems employing antenna arrays with close inter-element spacings exhibit a high degree of mutual coupling. In this case, the channel transfer matrix is a function of the matching network employed at transmit and receive. Existing capacity expressions are inappropriate, since the maximum mutual information will depend on antenna element loading. This paper develops a new expression for capacity that includes the effect of mutual coupling and antenna matching. Two simple noise models for realistic high-frequency circuits are introduced. Capacity is computed by maximizing the mutual information in these models subject to a new radiated power constraint. Numerical simulations of realistic two-element arrays demonstrate the basic technique.