Analysis of Constant-Power Waterfilling in MIMO Channels

In MIMO systems, when channel state information is available at the transmitter, power could be allocated adaptively among multiple transmit antennas to achieve large channel capacity. An upper bound on the maximum difference between the achievable capacity of non-optimal power allocation algorithms and that of conventional waterfilling in MIMO systems is derived. Two suboptimal constant-power waterfilling strategies are proposed and analyzed. Compared with the simple constant power allocation, constant-power waterfilling could achieve more channel capacity with reduced complexity.