Transmit beamforming for wireless multicasting using channel orthogonalization and local refinement

The problem of transmit beamforming for single-group multicasting is considered, where the objective is to transmit common information to a (large) number of users. The transmitter is assumed to have accurate downlink channel state information (CSI) for all users, and the objective is to design the beamformer weights to minimize the total transmitted power subject to meeting the quality-of-service (QoS) constraints of all users. This is an NP-hard problem that has recently drawn considerable interest (e.g., in the context of UMTS-LTE / E-MBMS). Several channel orthogonalization-based methods are proposed to solve this problem in an approximate way. Our techniques are shown to offer an improved performance-to-complexity tradeoff as compared to the original semidefinite relaxation (SDR) based multicasting technique.