A Dual-Hop Uplink IM-OFDMA System With Amplify-and-Forward Relays

Index Modulation based Orthogonal Frequency Division Multiple Access (IM-OFDMA) is an uplink scheme that allows a set of users to share a chunk of frequency subcarriers by the means of IM. IM-OFDMA has shown a promising performance as compared to its counterparts, which makes it a good candidate for future networks. To this end, this paper aims to investigate the performance of a dual-hop IM-OFDMA with the aid of Amplify-and-Forward (AF) relays. Unlike other links, employing AF relaying poses a challenge in IM-OFDMA because the identities and the number of active users over a subcarrier is unknown at the relays, which makes popular amplifying strategies not applicable. As such, a dual-hop uplink IM-OFDMA system requires a new amplifying strategy that is compatible with the data-driven subcarrier activation followed in IM-OFDMA systems. This paper proposes two different amplifying strategies that do not rely on the channel gains between the users and the AF relays. The performance of both amplifying strategies are analytically quantified in terms of the Average Bit Error Rate (ABER) at the base station and the energy consumption at the relays. Analytical and simulation results demonstrate the improvement in BER and energy saving achieved by the proposed dual-hop AF-based IM-OFDMA.