Efficient Resource Allocation for Power Minimization in MIMO-OFDM Downlink

In a downlink system using multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM), the subcarrier and power allocations can be optimized to minimize the overall transmit power given user target rates. If done efficiently, this resource allocation helps to reduce the interference ingress to neighbouring cells and limits the power consumption at the base station. The optimal solution can be found with a complexity of O(KM) for a system with K users and M subcarriers. This paper proposes an efficient method using a dual decomposition that has a lower complexity of only O(MK). Linear beamforming is assumed at both the transmitter and the receiver ends. Frequency-flat fading may adversely affect OFDM resource allocation if using a dual decomposition based approach. Flat fading management is thus proposed by using a certain dual proportional fairness, that handles all fading scenarios, including flat or partially frequency-selective fading. Simulations show fast convergence of the algorithm, quickly approaching the optimal solution.