Opportunistic Collaborative Beamforming with Phase-Compensation and Limited Feedback

For relatively distant message transmitting over independent complex Gaussian channels in ad hoc sensor networks, a low-complexity and near-optimum to the theoretical upper bound opportunistic collaborative beamformer with limited feedback is proposed in this paper. When restricting the transmitting power to unit, to maximize the received power at the destination node, not all the relay nodes should participate in the collaborative beamforming. The proposed beamforming scheme is to opportunistically select a subset of relay nodes and the relay nodes may pre-compensate phases according to the phases of the channels between relay nodes and the destination node, so that the received signals can combine in a quasi-coherent way at the destination node. Then the destination node broadcasts a vector to the pool of selected relay nodes to decide how to pre-compensate phases. Three low-complexity algorithms are proposed in this paper. Simulation results confirm the good performance of the algorithms both under perfect and imperfect channel state information (CSI).