A Message Passing Detection based Affine Frequency Division Multiplexing Communication System

TL;DR

The paper tackles reliability in high-mobility wireless channels where OTFS suffers from pilot and multiplexing overhead. It proposes Affine Frequency Division Multiplexing (AFDM), built on the discrete affine Fourier transform (DAFT), to achieve full diversity by adapting to the channel's delay-Doppler profile. A low-complexity message passing (MP) detector exploiting channel sparsity is developed to jointly cancel interference and detect symbols, with a sparse factor-graph formulation and Gaussian-interference approximation. Simulation results show AFDM with MP closely matches OTFS performance and outperforms MMSE/MRC, with improved accuracy and convergence as the symbol count N increases, indicating strong potential for high-mobility applications.

Abstract

The next generation of wireless communication technology is anticipated to address the communication reliability challenges encountered in high-speed mobile communication scenarios. An Orthogonal Time Frequency Space (OTFS) system has been introduced as a solution that effectively mitigates these issues. However, OTFS is associated with relatively high pilot overhead and multiuser multiplexing overhead. In response to these concerns within the OTFS framework, a novel modulation technology known as Affine Frequency Division Multiplexing (AFDM) which is based on the discrete affine Fourier transform has emerged. AFDM effectively resolves the challenges by achieving full diversity through parameter adjustments aligned with the channel's delay-Doppler profile. Consequently, AFDM is capable of achieving performance levels comparable to OTFS. As the research on AFDM detection is currently limited, we present a low-complexity yet efficient message passing (MP) algorithm. This algorithm handles joint interference cancellation and detection while capitalizing on the inherent sparsity of the channel. Based on simulation results, the MP detection algorithm outperforms Minimum Mean Square Error (MMSE) and Maximal Ratio Combining (MRC) detection techniques.

Figures (7)

• Figure 1: Block diagram of the AFDM system
• Figure 2: Structure of $\mathbf{H}_i$ for integer Doppler shifts.
• Figure 3: Factor graph of AFDM system.
• Figure 4: The variation of BER and average number of iterations with $\Delta$.
• Figure 5: The BER performance of 4-QAM AFDM with $N=64$ and 4-QAM OTFS with $N_{\rm{OTFS}}=8$, $M_{\rm{OTFS}}=16$ using MP detection in 4-path LTV channels and 5-path LTV channels with $l_{\max}=\alpha_{\max}=3$.