Capacity Evaluation of DF Protocols for OFDMA Infrastructure Relay Links

We consider a downlink OFDMA transmission system in which an infrastructure-based relay node is deployed for extending the coverage of a base station. Focusing on decode-and-forward (DF) operation, we study how different relay functionalities affect the system performance. The functionalities include fixed or adaptive subcarrier pairing, information redistribution, buffering, and adjustment of the time shares allocated for the two hops. In particular, it is of great interest for system design to be able to evaluate the performance gains due to each functionality, because they come at the expense of increased complexity and cost of the relay architecture. The main contribution of the paper is to analyze the performance of the proposed protocols by deriving new closed-form expressions for the average end-to-end capacity. The calculated expressions facilitate the performance comparison between the different functionalities.