A robust power allocation scheme for multibeam opportunistic strategies

Scheduling in a downlink channel based on partial channel state information at the transmitter (CSIT) is carried out in an opportunistic way, where several orthogonal beams are randomly generated at the base station transmitter to simultaneously deliver several users with their intended data. However, in practical wireless scenarios the CSIT is imperfect due to non-accurate estimation, so that robust schemes are required to meet the system demands. The paper presents a robust approach through a power allocation over the transmitting beams, where a minimum rate per user restriction is required for each scheduled user, standing as a potential quality of service (QoS) indicator for the system behaviour. The proposed scheme is efficiently solved through convex optimization tools and later compared to a full CSIT beamforming scheme under QoS restrictions.