Adaptive OFDM-IM for enhancing physical layer security and spectral efficiency of future wireless networks

In this paper, we propose algorithms for enhancing physical layer security and spectral efficiency of Orthogonal Frequency Division Multiplexing (OFDM) with Index Modulation (IM) systems. Particularly, different activation ratios and/or Constellation Modulation orders are selected adaptively for each subblock based on the channel quality of the legitimate receiver. More specifically, three approaches named as (1) OFDM with Adaptive Index Modulation and Fixed Constellation Modulation (OFDM-AIM-FCM), (2) OFDM with Adaptive Index Modulation and Adaptive Constellation Modulation (OFDM-AIM-ACM), and (3) OFDM with Variable Index Modulation and Variable Constellation Modulation (OFDM-VIM-VCM) are proposed for enhancing physical layer security and spectral efficiency. Simulation results are presented to investigate the effectiveness of the proposed algorithms.