  The prospect of base station (BS) cooperation leading to joint combining at
widely separated antennas has led to increased interest in macrodiversity
systems, where both sources and receive antennas are geographically
distributed. In this scenario, little is known analytically about channel
capacity since the channel matrices have a very general form where each path
may have a different power. Hence, in this paper we consider the ergodic sum
capacity of a macrodiversity MIMO system with arbitrary numbers of sources and
receive antennas operating over Rayleigh fading channels. For this system, we
compute the exact ergodic capacity for a two-source system and a compact
approximation for the general system, which is shown to be very accurate over a
wide range of cases. Finally, we develop a highly simplified upper-bound which
leads to insights into the relationship between capacity and the channel
powers. Results are verified by Monte Carlo simulations and the impact on
capacity of various channel power profiles is investigated
