This paper investigates a unified pilot signal design in an orthogonal frequency division modulation (OFDM)-based integrated sensing and communications (ISAC) system. The novel designed two-dimensional (2D) pilot signal is generated on the delay-Doppler (DD) plane for sensing, while its time-frequency (TF) plane transformation acts as the demodulation reference signal (DMRS) for the OFDM data. The well-designed pilot signal preserves orthogonality with the data in terms of resource occupancy in the TF plane and quasi-orthogonality in terms of codeword in the DD plane. Leveraging these nice properties, we are allowed to implement sensing detection in the DD plane using a simple 2D correlation, taking advantage of the favorable auto-correlation properties of the 2D pilot. In the communication part, the transformed pilot in the TF plane serves as a known DMRS for channel estimation and equalization. The 2D pilot design demonstrates good scalability and can adapt to different delay and Doppler resolution requirements without violating the OFDM data detection and can overcome the fractional Doppler with limited sensing resources. Experimental results show the effective sensing performance of the proposed pilot, with only a small fraction of power shared from the OFDM data,while maintaining satisfactory symbol detection performance in communication.

翻译：本文研究基于正交频分调制(OFDM)的集成感知与通信(ISAC)系统中的统一导频信号设计。所设计的新型二维(2D)导频信号在时延-多普勒(DD)平面上生成以用于感知，而其时频(TF)平面变换则作为OFDM数据的解调参考信号(DMRS)。精心设计的导频信号在TF平面的资源占用方面与数据保持正交性，并在DD平面的码字方面保持准正交性。利用这些优良特性，我们可以借助该二维导频良好的自相关特性，在DD平面上通过简单的二维相关运算实现感知检测。在通信部分，TF平面上的变换后导频作为已知的DMRS用于信道估计与均衡。该二维导频设计展现出良好的可扩展性，能够适应不同的时延与多普勒分辨率要求，且不违反OFDM数据检测，并能在感知资源有限的情况下克服分数多普勒问题。实验结果表明，所提导频仅需从OFDM数据中分配一小部分功率，即可实现有效的感知性能，同时在通信中保持令人满意的符号检测性能。