Index Modulation Technique Based on Variable Sub-carrier Number

OFDM-IM (Orthogonal Frequency Division Multiplexing Index Modulation) can improve the bandwidth utilization of the system by adding additional index information. However, with the increase of modulation order, the bandwidth utilization of OFDM-IM decreases compared to the traditional OFDM system. To solve this problem, we propose an index modulation method with a variable sub-carrier number based on OFDM-SNM (Orthogonal Frequency Division Multiplexing Sub-Carrier Number Modulation). In this method, the first sub-carrier in each sub-block is fixed to transmit information, and the remaining sub-carriers are fully permuted among the available sub-carriers according to different numbers. This method can significantly increase the transmission bits of additional index information and further improve bandwidth utilization. Our analysis shows that the bandwidth utilization of this new method increases compared with OFDM-IM and OFDM-SNM. Simulation results show that the new method also has good bit error rate (BER) performances under different modulation orders and sub-block sizes.