OFDM With Index Modulation Assisted by Multiple Amplify-and-Forward Relays

A multi-relay assisted orthogonal frequency division multiplexing system with index modulation is proposed in this letter, assuming that amplify-and-forward (AF) relaying protocol is adopted at relays. Two commonly used AF protocols are considered: 1) fixed-gain AF and 2) variable-gain AF relaying protocols. To utilize relays in an efficient manner, we also employ two multi-carrier relay selection schemes termed bulk and per-subcarrier relay selection in the proposed system. We analyze the outage performance of the proposed system and derive closed-form expressions of the average outage probabilities (AOPs) for all cases with different AF relaying protocols and multi-carrier relay selection schemes. In addition, we obtain the asymptotic expressions of AOPs in the high signal-to-noise ratio region, by which it is proven that the full diversity gain equaling the number of relays is attainable.