An efficient multiuser scheduling scheme for MIMO-CDMA wireless systems

In multiuser CDMA wireless systems where the base station is equipped with multiple antennas, the base station takes advantage from the spatial and code separability between the served users in order to enhance the performance of the system. However, this enhancement is constrained by the design of an appropriate scheduling scheme which is responsible of choosing the best users to serve. In this paper, we propose efficient scheduling algorithms for the downlink of multiantenna CDMA wireless systems using zero forcing beamforming. Our proposition maximizes the system sum rate and keeps the computational complexity low. We make use of a graph theoretical approach to represent the system as an undirected weighted graph. As a second step, we formulate the scheduling problem as the maximum weight k-colorable subgraph problem. We propose two heuristic solutions to find the users to serve in each time slot in an acceptable polynomial time. Finally we evaluate the efficiency of the proposed schemes by mean of simulations and the results show the near-optimal performance of the proposed schedulers with very low computational complexity compared to the optimal exhaustive search over all the possible users combinaisons.