This paper proposes a Time-Frequency Space Transformation (TFST) to derive non-orthogonal bases for modulation techniques over the delay-doppler plane. A family of Overloaded Delay-Doppler Modulation (ODDM) techniques is proposed based on the TFST, which enhances flexibility and efficiency by expressing modulated signals as a linear combination of basis signals. A Non-Orthogonal Time-Frequency Space (NOTFS) digital modulation is derived for the proposed ODDM techniques, and simulations show that they offer high-mobility communication systems with improved spectral efficiency and low latency, particularly in challenging scenarios such as high overloading factors and Additive White Gaussian Noise (AWGN) channels. A modified sphere decoding algorithm is also presented to efficiently decode the received signal. The proposed modulation and decoding techniques contribute to the advancement of non-orthogonal approaches in the next-generation of mobile communication systems, delivering superior spectral efficiency and low latency, and offering a promising solution towards the development of efficient high-mobility communication systems.

翻译：本文提出了一种时频空间变换（TFST），用于在时延-多普勒平面上推导非正交基进行调制。基于TFST，提出了一系列过载时延-多普勒调制（ODDM）技术，通过将调制信号表示为基信号的线性组合，增强了灵活性与效率。针对所提出的ODDM技术，推导出非正交时频空间（NOTFS）数字调制方案。仿真结果表明，该方案能够为高移动性通信系统提供更高的频谱效率和更低的延迟，尤其是在高过载因子及加性高斯白噪声（AWGN）信道等具有挑战性的场景下。此外，本文还提出了一种改进的球面解码算法，以高效解码接收信号。所提出的调制与解码技术推动了非正交方法在下一代移动通信系统中的应用，实现了优越的频谱效率与低延迟，为开发高效的高移动性通信系统提供了一种有前景的解决方案。