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

Abstract

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