Zero-Padded Tri-Mode Index Modulation Aided OFDM

Orthogonal frequency division multiplexing (OFDM) with index modulation has emerged as a promising complementary technique for next-generation networks due to its high energy efficiency. In this paper, zero-padded tri-mode index modulation aided OFDM (ZTM-OFDM) is proposed, where subcarriers are partitioned into subblocks. Explicitly, only a fraction of subcarriers are utilized for modulation with two distinguishable constellation alphabets in each OFDM subblock, whilst the others remain empty. By such strategy, additional bits can be conveyed by the subcarrier indices corresponding to the two constellation sets (denoted as index pattern). At the receiver, a maximum-likelihood (ML) detector and a two-stage log-likelihood ratio (LLR) detector with reduced complexity are proposed for demodulation. The proposed ZTM-OFDM is capable of enhancing the spectral and energy efficiency compared with other index modulated OFDM schemes. Theoretical analysis based on the minimum Euclidean distance and Monte Carlo simulation results validate that the proposed ZTM-OFDM can attain performance gain over conventional OFDM and other index modulated OFDM schemes.