Channel calibration for network MIMO systems

Network MIMO (Multiple-Input-Multiple-Output) techniques have great potential to meet the crucial demands for spectral usages and user data rates of the fifth generation (5G) wireless communication systems. In a typical single-cell time division duplex (TDD) system, channel reciprocity is utilized to obtain channel state information at the transmitter (CSIT). The effects induced by the radio frequency (RF) chains between the base station (BS) and user equipment (UE) are compensated through relative calibration. However, residual carrier frequency offsets (CFOs) resulted from the imperfect synchronization among base stations will break the channel reciprocity and introduce inter-cell interferences. In this paper, we propose a channel reciprocity calibration scheme in the presence of residual CFOs. The performance of the proposed scheme with zero-forcing (ZF) precoding is analyzed and the numerical results demonstrate that the interferences can successfully eased in the network MIMO systems.