Enhanced Spread Spectrum OFDM-IM with Rotated Zadoff-Chu Sequences

This paper proposes an enhanced scheme of spread spectrum-orthogonal frequency division multiplexing with index modulation (ESS-OFDM-IM), which employs the rotated Zadoff-Chu (ZC) sequences to improve the reliability of SS-OFDM-IM. Particularly, unlike the conventional SS-OFDM-IM which exploits traditional ZC codes only, we design novel rotated ZC sequences for the ESS-OFDM-IM, aiming at maximizing the diversity gain of the system. We then propose a new low-complexity maximum likelihood (ML) detector that can achieve optimal performance at a reduced complexity compared to the ML detector. Moreover, the performance analysis is carried out to clearly show that our proposed scheme can provide the maximum diversity order of being the number of sub-carriers, which is twice larger than that of SS-OFDM-IM. Simulation results are presented to validate the superiority of our proposed scheme over not only the SS-OFDM-IM but also various existing IM schemes.