Energy Efficient Wireless Communication using Distributed Beamforming

Energy Efficient Wireless Communication using Distributed Beamforming by Raghuraman Mudumbai We consider the use of distributed beamforming to improve the energy efficiency and transmission range of wireless networks. Under distributed beamforming, a number of wireless transmitters collaboratively transmit a common message signal in such way that their individual transmissions combine coherently (i.e. in phase) at the intended receiver. In essence, a set of distributed wireless nodes organize themselves as a virtual antenna array. As in beamforming from a conventional antenna array, highly directional transmissions can be achieved using a virtual array, and therefore substantial SNR gains can be realized compared to a network in which each node transmits independently to the receiver. Distributed beamforming arises naturally from information theoretic analyses of multi-user channels and is an essential ingredient of capacity-achieving coding strategies in several cases. However these analyses are based on baseband models of the channel and as such involve some implicit assumptions. The two most important such assumptions are (1) synchronized carrier signals, and (2) known phase relationship between the transmitters. The main contribution of this thesis is a detailed analysis of the feasibility of these assumptions, and a design for a practical wireless system based on distributed beamforming that explicitly addresses these issues. This design is based on a simple iterative procedure for