Performance optimization of amplify-and-forward relaying schemes for uplink OFDMA communications

Cooperative communication is a promising technique to enhance the system performance by exploiting the spatial diversity provided by the relay use. Incremental relaying techniques are proposed to limit the resources use to only bad channel conditions. In this paper, we deal with AF and IAF performance optimization for uplink Orthogonal Frequency Division Multiple Access (OFDMA) communications, carried on a packet-per-packet basis. For OFDMA cellular system, we define a cost that reliably quantifies the additional multiple-access interference (MAI) inherent to the relaying use. This MAI cost expression depends highly on the adopted frequency reuse pattern. The optimization, in terms of Packet-Error-Rate (PER), is carried out while keeping this MAI cost constant, for regular and fractional frequency reuse patterns. For FFR, different frequency reuse factors are applied to cell-center and cell-edge areas. Simulation results are showing that IAF relaying outperforms the direct transmission scheme by more than 15 dB gain, in terms of the reduction of the MAI. Additionally, IAF seems to be usually more powerful than AF.