Relay Selection Schemes for Precoded Cooperative OFDM and Their Achievable Diversity Orders

We investigate two different relay selection (RS) methods for precoded decode-and-forward (DF) cooperative OFDM systems: one scheme is to select the best relays for individual precoding groups (IPG-RS), and the other is to choose a single relay for the entire precoding groups (EPG-RS). We derive their diversity performances from the pairwise error probability (PEP) analysis, indicating that both schemes can achieve the full frequency and cooperative diversity with a proper choice of precoding size. Numerical results also show that IPG-RS can either reduce the decoding complexity or improve the error performance significantly as compared to existing solutions whereas EPG-RS has some performance loss as a result of less communication overhead.