Performance Analysis of Cooperative OFDM-QIM System With Per-Subcarrier Relay Selection

In this article, we propose a cooperative quadrature index modulation (QIM)-based orthogonal frequency-division multiplexing (OFDM) system, named OFDM-QIM, with per-subcarrier relay selection (RS), where the OFDM-QIM mapping is adopted to determine both the active subcarrier subsets and the modulated symbols for higher spectral efficiency, and per-subcarrier RS is employed to choose the decode-and-forward relay with maximum channel gain for each active subcarrier to provide better system reliability. Considering both the perfect and imperfect channel state information (CSI), the closed-form average outage probability (AOP) and the upper bound of average bit error probability (ABEP) of the cooperative OFDM-QIM system with per-subcarrier RS are derived based on the order statistics and the union upper bound method, respectively. Meanwhile, through the asymptotic analysis of the AOP and the ABEP under the perfect CSI, full diversity can be achieved as the relay number. Numerical results verify the correctness of the theoretical derivation. In addition, the proposed cooperative OFDM-QIM system obtains the improved AOP and ABEP performance over the conventional cooperative OFDM with index modulation system and the non-cooperative OFDM-QIM system.