User pairing algorithms for multi-cell and multi-user communications

Coordinated multi-point (CoMP) transmission/reception has been proposed as an approach to improve the cell-edge throughput for a cellular system. In this paper, we consider a cooperative serving strategy between multiple base stations (BSs) with precoding. We attempt to design low-complexity algorithms for finding an appropriate pair of users between two BSs that can be served using the same resource blocks (RBs). We observe that finding users with precoding that maximize the throughput is a combinatorial optimization problem. This problem has been shown to be an NP-hard problem, since for any given users, finding the optimum precoding matrices with maximum throughput is essentially an NP-hard problem. Two low-complexity algorithms are proposed to solve the problem. Algorithm I is based on sum rate (SR) pairing with simplified precoding which requires to compute precoding matrices for all user pairs under evaluation and hence has a large computational complexity. Our major contribution is to propose Algorithm II based on some simplifications of the sum rate and get a cost function which is independent of the precoding matrices. Therefore, Algorithm II does not require to compute the precoding matrix for all user pairs and hence significantly reduce the computational complexity. Simulation results show that Algorithm II achieves almost the same performance as Algorithm I with a much lower complexity.