Orthogonal Delay-Doppler Division Multiplexing Modulation with Hierarchical Mode-Based Index Modulation

TL;DR

This paper introduces a hierarchical mode-based index modulation (HMIM) scheme integrated with orthogonal delay-Doppler division multiplexing (ODDM) to improve spectral efficiency and reduce detection complexity in doubly selective fading channels.

Contribution

The paper proposes HMIM to simplify detection complexity and combines it with ODDM to exploit channel diversity, offering improved BER performance and lower computational complexity.

Findings

HMIM outperforms conventional IM in BER and complexity at same spectral efficiency.

The proposed SIC-MMSE detector enables low-complexity detection for large frame sizes.

ODDM-HMIM achieves full diversity of the delay-Doppler channel.

Abstract

The orthogonal time frequency space with index modulation (OTFS-IM) offers flexible tradeoffs between spectral efficiency (SE) and bit error rate (BER) in doubly selective fading channels. While OTFS-IM schemes demonstrated such potential, a persistent challenge lies in the detection complexity. To address this problem, we propose the hierarchical mode-based index modulation (HMIM). HMIM introduces a novel approach to modulate information bits by IM patterns, significantly simplifying the complexity of maximum a posteriori (MAP) estimation with Gaussian noise. Further, we incorporate HMIM with the recently proposed orthogonal delay-Doppler division multiplexing (ODDM) modulation, namely ODDM-HMIM, to exploit the full diversity of the delay-Doppler (DD) channel. The BER performance of ODDM-HMIM is analyzed considering a maximum likelihood (ML) detector. Our numerical results reveal that, with the same SE, HMIM can outperform conventional IM in terms of both BER and computational complexity. In addition, we propose a successive interference cancellation-based minimum mean square error (SIC-MMSE) detector for ODDM-HMIM, which enables low-complexity detection with large frame sizes.