Index modulation techniques in OFDM relay systems for 5G wireless networks

Index modulation (IM) technique is introduced in orthogonal frequency division multiplexing (OFDM) based systems as an extension of spatial modulation (SM) principle, assuming that information is delivered to the receiver not only through symbols sent by the transmitter, but also through indices of the selected active subcarriers' set. Index modulated OFDM can be very interesting solution for 5G systems, especially in its range-extended deployment, where relaying is applied. In this paper we analyze bit error rate (BER) performance of dual-hop OFDM decode-and-forward (DF) relay system, implementing both IM and SM (OFDM-IM-SM), for different fading statistics on hops, as well as for various system configurations, in terms of the number of active subcarriers. Based on the simulation obtained results, conclusions are derived on the optimal number of active subcarriers for different signal-to-noise ratio (SNR) values. Moreover, the obtained BER results have shown that the SNR boundary, where OFDM-IM-SM relay system outperforms OFDM relay system is shifted toward lower values, in case of line-of-sight communications.