Encrypted subblock design aided OFDM with all index modulation

In recent years, orthogonal frequency division multiplexing with index modulation (OFDM-IM) has been proposed due to its extra diversity gain. Specially, OFDM with all index modulation (OFDM-AIM) was proposed, which removed symbol bits and enhanced the diversity order compared to typical OFDM. However, the security issue of OFDM-AIM has not been given full attention. This paper proposes an encrypted subblock design aided OFDM with all index modulation (ESD-OFDMAIM) scheme to enhance physical layer security. Firstly, an encryption process of subblock design was put forward, which creates a random look-up table and thus the mapping rule of ESD-OFDM-AIM between information bits and subblock realisations becomes random and time varying. Moreover, the scrambling and rotation encryption based on chaotic sequences from channel state information is utilised to prevent the eavesdropper from stealing the information via wireless channel. For eavesdroppers, parameters of ESD-OFDM-AIM such as spectral efficiency (SE), constellation points and the length of look-up table are concealed by the encryption. Finally, analyses of attack models and the information entropy of constellations are also provided to measure the security of ESD-OFDM-AIM. Simulation results show that ESD-OFDM-AIM can effectively improve the system security without the affecting bit error rate performance.