MIMO Relaying Broadcast Channels with Linear Precoding and Quantized Channel State Information Feedback
Wei Xu, Xiaodai Dong, and Wu-Sheng Lu

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…
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