Projection based feedback compression for FDD massive MIMO systems

In frequency division duplex (FDD) multiple-input multiple-output (MIMO) systems, channel state information (CSI) is conveyed to the transmitters through feedback link. Since the amount of feedback needs to grow linearly with the number of transmit antennas, feedback overhead becomes overwhelming in massive MIMO regime and it has been of great interest to reduce the feedback overhead. In this paper, a feedback protocol using adaptive compression for FDD massive MIMO systems is proposed. Under the assumption of spatially and temporally correlated massive MIMO channel, the proposed scheme compresses CSI by projecting a vector in M (the number of transmit antennas) dimensional space into a lower dimensional subspace. To find an appropriate subspace, long-term statistics of the channel (spatial and temporal correlation), which can be obtained relatively easily, are exploited. Simulation results show that the proposed scheme can reduce the amount of feedback significantly yielding a marginal performance loss.