Compressed Sensing Improves the Performance of Subcarrier Index-Modulation-Assisted OFDM

In orthogonal frequency division multiplexing relying on subcarrier index modulation (OFDM-SIM), the information is conveyed by both the indices of the activated subcarriers and the conventional amplitude-phase modulated (APM) symbols. It has been shown that OFDM-SIM is capable of striking a tradeoff between the attainable spectral efficiency (SE) and energy efficiency (EE). In order to further increase the EE of the OFDM-SIM system, while potentially increasing its SE, we propose a compressed sensing (CS)-assisted signaling strategy for the family of OFDM-SIM systems. Correspondingly, we first consider the joint maximum likelihood detection of the CS-assisted index-modulated (CSIM) and of the classic APM symbols, despite its high complexity. Then, we propose a low complexity detection algorithm, which is termed as the iterative residual check (IRC)-based detector. This is based on the greedy pursuit concept of CS, which makes locally optimal choices at each step. Finally, both analytical and simulation results are provided for characterizing the attainable system performance of our proposed OFDM-CSIM system. We demonstrate that in comparison to the conventional OFDM-SIM system, the proposed OFDM-CSIM arrangement is capable of achieving both a higher SE as well as an increased EE. We also show that the diversity gain provided by the OFDM-CSIM system is much higher than that of the OFDM-SIM system. Furthermore, our investigation of the detection performance shows that the proposed IRC detector is capable of providing an attractive detection performance at a low complexity.