Selective Relaying in Cooperative OFDM Systems: Two-Hop Random Network

In this paper, we investigate two selective relaying schemes in cooperative OFDM systems. Selective OFDMA relaying, where the relay selection is performed in a per-subcarrier manner, and selective OFDM relaying, where one best relay among the L potential relays is selected to relay the entire OFDM block, are compared in a two-hop random network. The outage performance of equal bit allocation (EBA), where each subchannel has the same number of bits, and bit loading (BL), where bits are adaptively allocated to each subchannel, are analyzed and compared for these two approaches. The outage analysis clearly shows that a significant performance gain can be achieved by selective OFDMA relaying, whether EBA or BL is employed, compared with selective OFDM relaying. The performance gain remains the same for different relay locations. With EBA, the performance gain increases with an increase in L and N, the number of independent subchannels. For BL, the performance gain also increases with an increase in R, the average number of bits per subchannel, in addition to L and N. Centralized and decentralized implementation issues are also considered. For EBA, selective OFDMA relaying scheme is preferred because of its superior performance and simple decentralized implementation. For BL, selective OFDMA relaying scheme is a good choice for centralized systems and selective OFDM relaying is more suitable for decentralized systems at the expense of a loss in performance.