Matrix-field water-filling architecture for MIMO transceiver designs with mixed power constraints

In this paper, we discuss MIMO transceiver design under a new type of power constraint named mixed power constraints. Mixed power constraint is referred to the power model in which for a given set of antennas, several subsets are constrained by sum power constraints while the other antennas are subject to individual power constraints. It includes sum power constraint and per-antenna power constraints as its special cases and it can strike a balance between complexity and performance. In our work, we try to solve the optimization problem in an analytical way instead of relying on some famous software packages e.g., CVX or SeDuMi. Firstly, the specific formula of the optimal signal covariance matrix has been derived. Based on the structure, a low complexity non-iterative solution is given in our work, which can be interpreted as a matrix version water-filling solution. This solution has a much clear engineering meaning and is suitable for practical implementations even for massive MIMO systems. Finally, simulation results demonstrate the accuracy of our theoretical results.