Partial Channel Quality Information Feedback in Multiuser Relay Networks Over Nakagami- <inline-formula> <tex-math notation="LaTeX">$m$</tex-math></inline-formula> Fading

Abstract

We propose a new partial feedback scheme in multiuser relay networks (MRNs) where a source communicates with $K$ destinations via a relay. We focus on a practical network model where orthogonal frequency division multiple access (OFDMA) is adopted in the downlink and only limited feedback overhead is supported in the uplink. For this model, we consider that the OFDMA spectrum consists of $M_{\mathrm{RB}}$ resource blocks (RBs). In the proposed scheme, the destinations feed back the channel quality information (CQI) for the best $M_{\mathrm{FB}}$ RBs, instead of all $M_{\mathrm{RB}}$ RBs, to the source through the relay, which fulfills the requirement of feedback overhead. Considering the highly versatile Nakagami- $m$ fading, we derive new closed-form expressions for the exact sum rate for ideal CQI feedback and quantized CQI feedback. We also derive the asymptotic sum rate expression for ideal CQI feedback. We have some new findings to understand the impact of network and channel parameters on the sum rate. First, a more scattering fading environment with a lower $m$ decreases the sum rate for a small $K$ , but increases the sum rate for a large $K$ . Second, the sum rate increases as ${M_{\mathrm{FB}}}$ approaches ${M_{\mathrm{RB}}}$ . Third, the sum rate gap between ideal CQI feedback and quantized CQI feedback increases when $M_{\mathrm{FB}}$ or $K$ increases. Fourth, we demonstrate that the proposed partial feedback scheme achieves almost the same sum rate as the full feedback scheme for a large number of destinations.