A second-order cone deflation approach to joint multiuser downlink beamforming and admission control

Multiuser downlink beamforming under quality of service (QoS) constraints has attracted considerable interest in recent years, because it is particularly appealing from a network operator's perspective (e.g., UMTS, 802.16e). When there are many co-channel users and/or the service constraints are stringent, the problem becomes infeasible and some form of admission control is necessary. We advocate a cross-layer approach to joint multiuser transmit beamforming and admission control, aiming to maximize the number of users that can be served at their desired QoS. The problem is NP-hard; we propose and motivate a deflation approach based on second-order cone relaxation. For a moderate number of users, we benchmark the proposed algorithm against the optimal enumeration-based solution and a simpler approach, using both simulated and measured channel data. Our results indicate that the proposed algorithm yields consistently close to optimal performance at an affordable complexity cost.