Outage-Capacity Based Adaptive Relaying in LTE-Advanced Networks
Shenghui Song, Ali F. Almutairi, Khaled B. Letaief · IEEE Transactions on Wireless Communications · 2013
In this paper, we investigate the benefits of relaying by comparing the transmission rates of both direct transmission (DT) and relaying. It is shown that relaying achieves SNR (signal-to-noise power ratio) gain over DT due to less pathloss, but with several relaying penalties, including a lower multiplexing gain (due to half-duplex), a lower transmit power and a higher outage requirement at each hop (due to multi-hop). We determine the conditions over which relaying outperforms DT, where the SNR gain is greater than the loss due to relaying penalties. The result is applied to the LTE-advanced networks (LTE-A) where the relay nodes (RNs) are implemented to relay information between the user equipment (UE) and the evolutional NodeB (eNB). The major difference between LTE-A and a general relay system lies in that the UE-RN hop consists of multiple frequency-division access links, while the RN-eNB hop is a point-to-point link. By investigating the effects of diversity gain on the transmission rate, we propose an outage-capacity based adaptive relaying (OCA-R) scheme to replace the conventional same-carrier relaying (SC-R). It is shown that the transmission rates of both SC-R and OCA-R are one half of the harmonic means between the outage-capacities for two hops, where the advantage of OCA-R over SC-R comes from a higher diversity gain in the RN-eNB link.