Efficient Heuristic for Resource Allocation in Zero-Forcing OFDMA-SDMA Systems with Minimum Rate Constraints

Multi-antenna OFDMA-SDMA systems provide the required high spectral efficiency and flexibility to support the ever increasing data rates requirements of real-time multimedia applications in future wireless access systems. However, the resource allocation process becomes extremely complex because of the large number of degrees of freedom and the strict timing requirement of real-time traffic. In this paper, we propose heuristics to efficiently solve the zero-forcing OFDMA-SDMA resource allocation problem and provide, when feasible, guaranteed service to users with minimum rate requirements. The heuristics combine both rate-constrained power allocation and subcarrier reassignment algorithms. We compare the heuristics performance against an upper bound and other methods proposed in the literature and find that, although they have a slightly lower sum rate performance, they support a wider range of minimum rates while significantly reducing the computational complexity, making them suitable for usage in real-time systems.