Clustering method for CoMP with limited backhaul data transfer using convex relaxation

Joint transmission (JT) is an attractive coordinated multipoint (CoMP) downlink transmission technique in multi-cell networks. It offers high system throughput but needs to distribute each user data to multiple base stations (BSs), which can lead to huge backhaul signaling overhead when the number of users is large. In this paper, we address the problem of jointly optimizing the BS assignment for each user data and the BS transmit beamformer design subject to per-BS power constraints and given quality-of-service (QoS) requirements. Our aim is to minimize the backhaul user data transfer from the data center to the BSs for the JT approach. We formulate such a problem into a sparsity-maximization problem. However, this problem is NP-hard. We propose to tackle it by first applying convex relaxation to an equivalent form of the original problem and improving the obtained results by solving a series of convex ℓ₁-norm minimization problems. Compared to full BS cooperation, the proposed method saves about 13%-35% backhaul user data transfer in our simulations for moderate number of users and QoS requirement.