A Tabu Search Scheduling Algorithm for MIMO CDMA Systems

In multiuser multiple input multiple output (MIMO) systems, it is optimal to serve multiple users at the same time in order to achieve high data rates. However, the use of a transmit beamforming technique requires a well designed user selection scheme to obtain good performances. The optimal scheduling solution can only be obtained through a highly computationally complex exhaustive search. In addition, when employing a multiple access scheme, such as the code division (CDMA), the complexity of an optimal user selection becomes higher even for moderate number of users and antennas. In this context, this paper proposes a heuristic scheduling algorithm based on a tabu search approach for MIMO CDMA systems using ZFBF as a transmit technique. We use a graph theoretical approach to model the system as a weighted undirected graph. The problem of user selection is then formulated as a graph coloring problem. Numerical results show that the proposed algorithm outperforms the greedy scheduling scheme and achieves performances, in terms of system sum rate, very close to those of the highly complex optimal solution.