Affine frequency division multiplexing (AFDM) is an emerging multicarrier waveform that offers a potential solution for achieving reliable communication for time-varying channels. This paper proposes two maximum likelihood (ML) estimators of symbol time offset and carrier frequency offset for AFDM systems. The joint ML estimator evaluates the arrival time and frequency offset by comparing the correlations of samples. Moreover, we propose the stepwise ML estimator to reduce the complexity. The proposed estimators exploit the redundant information contained within the chirp-periodic prefix inherent in AFDM symbols, thus dispensing with any additional pilots. To further mitigate the intercarrier interference resulting from the residual frequency offset, we design a mirror-mappingbased scheme for AFDM systems. Numerical results verify the effectiveness of the proposed time and frequency offset estimation criteria and the mirror-mapping-based modulation for AFDM systems.

翻译：仿射频分复用（AFDM）是一种新兴的多载波波形，为时变信道下的可靠通信提供了潜在解决方案。本文针对AFDM系统提出了两种符号定时偏移与载波频率偏移的最大似然（ML）估计器。联合ML估计器通过比较样本相关性来评估到达时间与频率偏移。进一步地，我们提出了逐步ML估计器以降低复杂度。所提估计器利用AFDM符号中固有的啁啾周期前缀所含冗余信息，因此无需额外导频。为减缓残余频偏引起的载波间干扰，我们设计了一种基于镜像映射的AFDM系统方案。数值结果验证了所提时频偏估计准则及基于镜像映射的调制方案在AFDM系统中的有效性。