Robust Iterative Interference Alignment for Cellular Networks With Limited Feedback

In theory, coordinated multipoint transmission (CoMP) promises vast gains in spectral efficiency. However, industrial field trials show rather disappointing throughput gains, whereby the major limiting factor is proper sharing of channel state information. Many recent papers have considered this so-called limited feedback problem in the context of CoMP, usually taking the following assumptions, namely, infinite SNR regime, no user selection, and ideal link adaptation, rendering the analysis too optimistic. In this paper, we make a step forward toward a more realistic assessment of the limited feedback problem by introducing an improved metric for the performance evaluation, which better captures the throughput degradation. We find the relevant scaling laws (lower and upper bounds) and show that they are different from existing ones. Moreover, we provide a robust iterative interference alignment algorithm and corresponding feedback strategies achieving the obtained scaling laws. The main idea is that, instead of sending the complete channel matrix, each user fixes a receive filter and feeds back a quantized version of the effective channel. Finally, we underline our findings with simulations for the proposed system.