Non-Orthogonal Affine Frequency Division Multiplexing for Spectrally Efficient High-Mobility Communications

2025-08-13

AI Summary

To address the trade-off between spectral efficiency and reliability in high-mobility scenarios, this paper proposes non-orthogonal affine frequency division multiplexing (nAFDM). By introducing a bandwidth compression factor, nAFDM controllably adjusts subcarrier overlap to enhance spectral efficiency while explicitly modeling inter-carrier interference (ICI). A low-complexity signal generation method based on the inverse discrete Fourier transform (IDFT) is designed, ensuring compatibility with existing IFFT-based hardware. Closed-form analytical expressions for ICI in non-orthogonal modulation are derived, enabling a soft iterative detection algorithm that exploits ICI statistics and incorporates a low-complexity interference suppression mechanism. Simulation results demonstrate that nAFDM achieves bit error rate performance comparable to conventional AFDM, yet significantly outperforms OFDM, UFMC, and standard AFDM in spectral efficiency—achieving a superior balance among spectral efficiency, error-rate performance, and computational complexity.

Technology Category

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

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation
• Security and Privacy: Large-scale security measurements

Abstract

This paper proposes a novel non-orthogonal affine frequency division multiplexing {(nAFDM)} waveform for reliable high-mobility communications with enhanced spectral efficiency {(SE)}. The key idea is {to introduce} a bandwidth compression factor into the AFDM {modulator} to enable controllable subcarrier overlapping. We first {detail the proposed nAFDM transceiver} and derive the corresponding input-output {signal} relationship. Then, an efficient {nAFDM} signal generation method based on the inverse discrete Fourier transform (IDFT) is proposed, enabling practical implementation using existing inverse fast Fourier transform (IFFT) modules without additional hardware complexity. Next, to characterize the impact of non-orthogonal modulation, we derive a closed-form expression {of} inter-carrier interference (ICI), showing its dependence on the bandwidth compression factor. To mitigate the resulting interference, we propose a soft iterative detection algorithm and a low-complexity implementation approach that leverages the distribution characteristics of ICI. {Simulation results demonstrate that 1) in terms of bit error rate (BER), the proposed nAFDM can achieve near identical BER compared to conventional AFDM, while outperforms other waveform counterparts; 2) nAFDM is capable of striking higher SE compared to other existing waveforms; and 3) the proposed nAFDM achieves an attractive BER vs. SE trade-off, and the proposed soft ID scheme can attain a trade-off between BER and complexity.}

Problem

• Proposes nAFDM for high-mobility spectral efficiency
• Derives ICI impact from non-orthogonal modulation
• Introduces soft detection to mitigate interference

Innovation

• Non-orthogonal AFDM with bandwidth compression
• IDFT-based efficient signal generation
• Soft iterative interference mitigation algorithm