Transformed-channel feedback for the two-user MISO interference channel

Interference mitigation is central in enhancing the total throughput of wireless systems. Effcient mitigation requires, however, accurate channel state information, which puts a heavy load on the wireless control channels. In this paper, we focus on the multiple-input single-output (MISO) interference channel, and propose a novel enhanced CSI feedback scheme that reduces the feedback overhead required for conveying cross-link CSI to the transmitters. For simplicity, we consider a two-user setting, where single user decoding is employed while treating interference as noise. The proposed scheme creates, by projecting the original channels into an appropriately chosen low-dimensional subspace, an effective cross-link channel which can be quantized more accurately for a given number of quantization bits. The idea is to choose the new subspace such that the effective cross-link channel, as well as the direct channel, maintain their array gain. We show via a comprehensive numerical study that the proposed scheme offers a signifcant reduction of CSI feedback overhead. By providing much more accurate CSI at the transmitters, while maintaining high array gains, the scheme allows for enhanced interference mitigation, and increases the total network throughput.