MIMO Relaying Broadcast Channels with Linear Precoding and Quantized Channel State Information Feedback

TL;DR

This paper analyzes a MIMO relaying broadcast channel with linear precoding and quantized CSI feedback, proposing a feedback scaling strategy to limit rate loss as SNR increases, supported by numerical validation.

Contribution

It introduces a feedback quality scaling strategy for two-hop links in MIMO relaying, ensuring bounded rate loss at high SNRs with quantized CSI feedback.

Findings

Feedback bits for relay and user links should scale linearly with relay transmit power.

Feedback from relay to BS needs to grow with BS transmit power.

Proposed strategy effectively maintains rate loss within a desired gap.

Abstract

Multi-antenna relaying has emerged as a promising technology to enhance the system performance in cellular networks. However, when precoding techniques are utilized to obtain multi-antenna gains, the system generally requires channel state information (CSI) at the transmitters. We consider a linear precoding scheme in a MIMO relaying broadcast channel with quantized CSI feedback from both two-hop links. With this scheme, each remote user feeds back its quantized CSI to the relay, and the relay sends back the quantized precoding information to the base station (BS). An upper bound on the rate loss due to quantized channel knowledge is first characterized. Then, in order to maintain the rate loss within a predetermined gap for growing SNRs, a strategy of scaling quantization quality of both two-hop links is proposed. It is revealed that the numbers of feedback bits of both links should scale linearly with the transmit power at the relay, while only the bit number of feedback from the relay to the BS needs to grow with the increasing transmit power at the BS. Numerical results are provided to verify the proposed strategy for feedback quality control.