Margin adaptive resource allocation in downlink multiuser MIMO-OFDMA system with Multiuser Eigenmode transmission

This paper studies the downlink multiuser Multiple Input Multiple Output-Orthogonal Frequency Division Multiple Access (MIMO-OFDMA) system for margin adaptive Multiuser Eigenmode Transmission (MET) with perfect channel state information at the transmitter. In margin adaptive objective, Base Station (BS) has to satisfy individual Quality of Service (QoS) constraints of the users subject to transmit power minimization. The solution is hard to achieve because multiple streams from different users on the same subcarrier cause inter-stream interference which forces the use of low complexity beamforming techniques and makes it a joint beamforming and resource allocation problem. We propose a sub-optimal two step solution which decouples beamforming from subcarrier and power allocation. First a reduced number of user groups are formed and then the problem is formulated as a convex optimization problem. Finally an efficient algorithm is developed which allocates subcarriers to these user groups. Simulation results reveal comparable performance with the hugely complex optimal solution.