User Scheduling for Network MIMO Systems with Successive Zero-Forcing Precoding

In this paper we consider simplified greedy user scheduling algorithms for clustered network multiuser multiple-input multiple-output (MIMO) systems with successive zero-forcing (SZF) precoding. The optimal user scheduling involves an exhaustive search, which is very complex. Among various suboptimal but lower complexity algorithms, greedy algorithms with heuristic scheduling metrics have been shown to achieve performance close to the exhaustive search. In this paper, we propose two simplified algorithms: interference-aware greedy user scheduling (IA-GUS) and interference-whitening greedy user scheduling (IW-GUS). IA-GUS schedules the users based on the information on interference power of the selected users in surrounding cooperating clusters, and IW-GUS schedules the users based on the information on whitened channels of all users requesting the service in the cluster. IA-GUS has lower complexity and performs better than IW- GUS. Simplified metrics for proportionally fair (PF) scheduling are also proposed. Performance of the proposed algorithms is analyzed and compared with dirty paper coding (DPC), block diagonalization (BD) and systems without network coordination. Simulation results demonstrate that the proposed algorithms for SZF achieve much higher outage capacity compared to BD with previously proposed algorithms.