Analog Precoder Feedback Schemes With Interference Alignment

This paper presents two analog precoder feedback (PFB) schemes namely the simple PFB (SPFB) scheme and the reduced PFB (RPFB) scheme for interference channels. In the first scheme, each destination transmits full precoder, while in the second one, the size of the precoder to be fed back is reduced by removing the redundant rows of the precoder matrix. This reduced feedback is particularly useful in the systems, where the number of transmit antennas are more than the number of receive antennas. These schemes have been analyzed for the cases where time slots in the feedback duration are independent of the number of users and where the time slots scale linearly with the number of users. For both these schemes, the precoder reconstruction methods are investigated using the chordal distance. For interference alignment, the rate loss upper bound analysis shows that the rate loss increases with signal-to-noise-ratio (SNR) at low SNR, while it remains constant in high SNR range. Simulation results verify that the linear sum rate scaling is preserved at high SNRs. The full precoder feedback dominates, when the source cooperation is assumed, while RPFB yields improvements over SPFB scheme, when no source cooperation is assumed and Kd time slots are utilized in either orthogonal or independent transmission case.