Low-complexity scheduling algorithms for successive zero-forcing dirty paper coded systems

Dirty paper coding scheme (DPC) is known to be a capacity achieving transmission technique in downlink multiuser MIMO channels. As a suboptimal solution to DPC, a precoding technique called successive zero-forcing dirty paper coding (SZF-DPC) has been proposed recently. The condition for the existence of the precoding matrices in SZF-DPC restricts the capability of supporting multiple users simultaneously. Thus, a user scheduling algorithm is needed to achieve multiuser diversity in SZF-DPC as the number of users grows. In this paper, we propose three low-complexity suboptimal scheduling algorithms to exploit the multi-user diversity gain for SZF-DPC. The first algorithm greedily maximizes the true sum capacity. The second algorithm is based on eigenvalues that are closely related to the true capacity. The third algorithm relies on the diagonal elements of the effective channel matrix since we realize a strong relationship between the eigenvalues and diagonal entries of a Hermitian matrix. Simulation results of several cases show that the proposed scheduling algorithms can obtain a significant fraction of sum capacity of the optimal solution.