Capacity of multiple-antenna Rayleigh channel with a limited transmit diversity

The capacity of a wireless link is studied when multiple transmit and receive antennas are used. Under the assumption of a narrow-band link and a rich scattering environment, the propagation medium is modeled as a Rayleigh flat fading with a good receive diversity. By contrast to the previous works, the assumption of decorrelated transmit antennas is relaxed. This enables a study of some common scenarios where the transmit antennas occupy a limited volume. For an arbitrary correlation between the transmitting antennas, tight capacity bounds are calculated and an optimal signaling scheme is derived.