Multiple-Mode Orthogonal Frequency Division Multiplexing With Cascade Index Modulation

Multiple-mode orthogonal frequency division multiplexing with index modulation (MM-OFDM-IM) is a promising multicarrier transmission technique proposed recently, which focus on exploiting the index domain of the multiple distinguishable modes (constellations) and uses full permutations of the indices of multiple symbol modes to transmit information bits implicitly. Compared to conventional OFDM-IM, a factorial increase of the IM patterns in MM-OFDM-IM prohibits its application in realistic communication systems due to exponentially increased modulation and demodulation complexity when the number of symbol modes is large. In this paper, we propose a novel and efficient MM-OFDM with cascade IM (MM-OFDM-CIM) scheme, which first selects partial symbol modes for multiple mode index modulation (MM-IM) of the first subblock in the cluster and then performs MM-IM based on the rest symbol modes for the second subblock. The proposed CIM method divides the IM process into two steps and achieves considerably low computational complexity in detection. Furthermore, physical layer security can be realized by adjusting the size of subblocks within the cluster due to the flexible CIM designs. Computer simulations show that the proposed MM-OFDM-CIM has potential to achieve near the same bit error rate performance with considerably low computational complexity and achieves excellent secure communication performance between the legitimate users.