Impact of carrier frequency offset in cooperative phase shift beamforming

We study the effects of residual carrier frequency offset (CFO) on the performance of cooperative phase shift (PSB) beamforming schemes. Cooperative beamforming may provide the diversity and the power gains of multi-antenna systems and is therefore seen as a promising technology for the next generation wireless communication systems. Considering the distributed nature of cooperative communications, the carrier frequency of each transmitter deviates from the desired one. In this paper, we present the derivations of the signal-to-noise ratio and diversity gains in the cooperative PSB scheme in presence of residual CFOs. It is shown that even with frequency synchronization prior to transmission, residual CFOs may still significantly degrade the performance due to the in-phase misalignment of the incoming streams at the destination. Furthermore, we show that because of the residual CFOs the collaborative beamforming scheme may perform worse than its non-collaborative counter-part. The results and the accuracy are illustrated through simulations.