Improved OFDMA Uplink Transmission via Cooperation in the Presence of Frequency Offsets

In this paper, we evaluate the performance improvement in an Orthogonal Frequency-Division Multiple Access (OFDMA) uplink achievable with cooperative relaying in the presence of frequency offsets. We consider both the amplify- and-forward (AF) and decode-and-forward (DF) relays. In each transmission, each node plays two roles i.e., the source node and relay, simultaneously, but at different subcarriers. The proposed scheme improves performance without sacrificing the transmission rate and power of the cooperative relays, and the total power used to transmit each symbol, including the power consumed in node the source node and the relays, is kept constant. The outage information rates of the proposed cooperative transmission scheme are derived, and the diversity gain of each forwarding mode in an interference-limited environment is analyzed in this paper. Numerical results illustrate the superior performance of the proposed scheme over the conventional transmission with regard to outage information rate.