Resource allocation for distributed beamforming with multiple relays and individual power constraints

In wireless communications, beamforming can be exploited to reduce the power consumption considerably. If multiple relay terminals are available, distributed beamforming might be an appropriate transmission scheme. However, due to individual power constraints for all of the relays, the classical beamforming solution can no longer be used to allocate transmit power. Within this paper, closed form expressions for the optimal Power Allocation (PA) at source and regenerative relays are provided as well as an iterative algorithm to identify relay nodes that have to transmit at full power. Furthermore, numerical results will be presented for comparison to alternative relaying strategies, such as single Relay Selection (RS) and distributed Space Time Block Code (STBC). The proposed solution outperforms all the alternative approaches in terms of power consumption as well as outage probability.