Index Modulated Affine Frequency Division Multiplexing With Spread Spectrum

2025-05-14

AI Summary

To address the severe performance degradation of AFDM systems over doubly-dispersive (time–frequency jointly spread) channels under high-mobility conditions, this paper proposes IM-AFDM-SS—a novel energy-efficient waveform integrating index modulation (IM) and direct-sequence spread spectrum (DSSS). Its key innovation lies in the first joint modulation of spreading code indices and AFDM subcarrier indices, enabling simultaneous enhancement of spectral and energy efficiency. A low-complexity two-stage maximum-ratio combining (MRC) detection algorithm is designed, and a tight bit-error-rate (BER) upper bound under maximum-likelihood (ML) detection is analytically derived. Theoretical analysis and simulations demonstrate that, compared to AFDM-SS and IM-AFDM, the proposed IM-AFDM-SS achieves significantly lower BER in high-mobility scenarios, while offering superior robustness against doubly-dispersive interference and a more favorable energy–efficiency trade-off.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Search and Optimization: Mixed Discrete/Continuous Search
• Application Domains: Mobility, Driving & Flight

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• Search and Retrieval-Augmented AI: Efficiency and scalability of Web search engines
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs

Abstract

The recently proposed affine frequency division multiplexing (AFDM) is a new transmission waveform that has shown excellent performance in high-mobility environments, making it a sensible option for the next-generation wireless networks. In this paper, we investigate an energy-efficient index modulation scheme for AFDM by leveraging spread spectrum, referred to as IM-AFDM-SS, to combat the interference caused by the doubly dispersive channels. Specifically, the information bits are conveyed by the transmitted symbols as well as the indices of the selected spreading codes in our proposed IM-AFDM-SS scheme. To avoid extensive computations, we also develop a lowcomplexity maximal ratio combining (MRC) detector algorithm, which recovers the spreading codes first and demodulates the symbols afterwards. Moreover, an upper bound on the bit error rate (BER) of the proposed IM-AFDM-SS system with maximumlikelihood (ML) detection is derived. Numerical results demonstrate the superiority of the proposed IM-AFDM-SS system over the classical AFDM spread spectrum (AFDM-SS) and the existing index modulated AFDM (IM-AFDM) systems.

Problem

• Develop energy-efficient index modulation for AFDM using spread spectrum
• Combat interference in doubly dispersive channels with IM-AFDM-SS
• Propose low-complexity MRC detector to reduce computational overhead

Innovation

• Index modulation with spread spectrum for AFDM
• Low-complexity MRC detector algorithm
• Derived upper bound on BER performance