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

TL;DR

This paper introduces a non-orthogonal AFDM waveform that improves spectral efficiency and BER performance in high-mobility communications by controlling subcarrier overlap and mitigating interference with a novel detection algorithm.

Contribution

It proposes a new non-orthogonal AFDM waveform with bandwidth compression, an IDFT-based signal generation method, and a soft iterative detection algorithm for high-mobility scenarios.

Findings

Achieves near-identical BER to conventional AFDM

Outperforms other waveforms in spectral efficiency

Provides a BER vs. SE trade-off with low complexity

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 iterative detection (ID) scheme can attain a trade-off between BER and complexity.