Multi-hop relay architectures for 3GPP LTE-advanced

The next-generation wireless network is envisaged to incorporate multi-hop ad hoc characteristics into cellular network infrastructure. Multi-hop communication is viewed as an annexe to the cellular network infrastructure in order to increase coverage and capacity. Currently, the Third Generation Partnership Project (3GPP) is investigating multi-hop functionality as one technical component for LTE-Advanced. LTE-Advanced is the evolution of Long-Term Evolution (LTE). Even though multi-hop communication research has been ongoing for the past decades, research work on multi-hop cellular network is premature. This paper serves to provide a comprehensive review on state-of-the-art relaying strategies for LTE-Advanced. Two relaying strategies, namely amplify-and-forward and decode-and-forward are discussed. The relaying strategies are qualitatively compared against a set of criteria. The main conclusion drawn from the review is that each relaying strategy has its benefits and limitations. Thus, LTE-Advanced could deploy a mixture of amplify-and-forward and decode-and-forward relays depending on the needs and scenarios. We also discuss a new problem facing conventional channel-dependent scheduling mechanisms in LTE-Advanced with multi-hop links. Consequently, we propose a multi-hop aware channel-dependent scheduling mechanism to ameliorate the problem.