MIMO wireless systems: Capacity limits for sparse scattering

Abstract — We present a limiting function for the capacity of a sparsely scattered, outdoor MIMO channel. We use a result from random matrices to show that the capacity of the chan-nel will diminish logarithmically with a parame-ter η. The parameter is inversely dependent on the distance between the transmitter array and the receiver array. This loss is in addition to any free-space losses. We show that below a given value of this parameter, the capacity of the chan-nel is significantly reduced and that the benefits of additional receive or transmit elements do not eventuate. Monte Carlo simulations are used to compare the theoretical results with the physical model. I