Waterfilling in MIMO Systems with Power Constraints on Each Transmitter

In this paper we investigate power allocation in MIMO-OFDM systems. We describe the optimal power allocations under two different constraints: a constraint on the total power of all transmitters (TXs) which is applicable in wireless applications, and a constraint on the power of each TX which is more relevant in wireline applications. We describe the optimal TX/RX structure which in combination with the optimal power allocation achieves the MIMO-OFDM channel capacity (under the chosen constraints), with low complexity. Simulations show the benefits of using a total power constraint in place of a per-TX power constraint are largest when the TXs see channels with significantly different attenuations