Capacity of adaptive MIMO systems in a finite scattering channel

We have investigated the capacity of MIMO systems on a channel containing a finite number of multipath scatterers, using a normalisation which allows us meaningfully to enquire whether capacity increases indefinitely with the number of transmit/receive antenna elements. This normalisation ensures that received signal power equals total transmitted power, and does not increase with increasing number of receive antennas. This allows us to separate out effects due to the receive array gain. We show that for the most common case, where the channel is unknown at the transmitter, the capacity does not increase indefinitely, but tends to a limit determined by the number of scatterers. We upper bound this limit, and also describe an estimate which is closer to results obtained by simulation. We also consider an adaptive system, in which the channel is known to the transmitter, and show that here capacity can increase indefinitely with the number of antennas.