Performance analysis of the distributed ZF beamformer in the presence of carrier frequency offset

We study the impact of residual carrier frequency offset (CFO) on the performance of the distributed zero-forcing (ZF) beamformer in the interference channel, i.e., where multiple nodes simultaneously transmit the same data towards multiple receivers. Distributed transmissions have been proposed to mitigate the co-channel interference inherent to such scenarios and provide the gains of multi-antenna systems. However, frequency synchronization among the cooperating transmitters is required. Even when the transmitters perform frequency synchronization before transmission, a residual CFO is to be expected that degrades the performance of the system due to the in-phase misalignment of the incoming streams. This paper presents the signal-to-noise ratio analytically and the diversity semi-numerically of the distributed ZF beamformer for the ideal case and in presence of a residual CFO. We illustrate our results and their accuracy through simulations.