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4778 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, VOL. 12, NO. 9, SEPTEMBER 2013 Outage-Capacity Based Adaptive Relaying in LTE-Advanced Networks S. H. Song, Member, IEEE , Ali F. Almutairi, Senior Member, IEEE, and K. B. Letaief, Fellow, IEEE Abstract—In this paper, we investigate the benefits of relaying respectively. According to the 3GPP proposal, there are three by comparing the transmission rates of both direct transmission kinds of RN where the L1 (layer one) RN utilizes amplify-and- (DT) and relaying. It is shown that relaying achieves SNR (signal- forward (AF) scheme, the L2 RN applies decode-and-forward to-noise power ratio) gain over DT due to less pathloss, but with several relaying penalties, including a lower multiplexing gain (DF) operation, and the L3 RN forwards the user traffic in the (due to half-duplex), a lower transmit power and a higher outage IP layer. requirement at each hop (due to multi-hop). We determine the The advantages of relaying have been investigated from conditions over which relaying outperforms DT, where the SNR gain is greater than the loss due to relaying penalties. The result different points of view [16], [17]. In this paper, we shall is applied to the LTE-advanced networks (LTE-A) where the investigate the benefits of relaying by considering the outage relay nodes (RNs) are implemented to relay information between capacity. It is shown that the advantage of relaying comes the user equipment (UE) and the evolutional NodeB (eNB). The from the dividing of a long hop to multiple short hops where major difference between LTE-A and a general relay system lies each hop experiences less pathl