Comparison of two SNR-based feedback schemes in multiuser dual-hop amplify-and-forward relaying networks

In this letter, we investigate amplify-and-forward relaying where a source is communicating with the best user through an intermediate relay that covers multiple users. To reduce the amount of feedback that is needed to select the best user, we consider two kinds of SNR-threshold based channel quality information (CQI) reporting: end-to-end SNR based reporting (ETE-R) and second-hop quality based reporting (SH-R). We derive the probability density function (pdf) and the cumulative density function (cdf) of the SNR received at the best user in Rayleigh fading channels, and compare the average capacity, the average number of feedback users and the feedback outage probability of the two reporting schemes, respectively. Numerical results show that SH-R can achieve the same capacity as an ideal full feedback system when the number of users is large while it reduces the amount of feedback greatly, but ETE-R provides relatively poor performance.