Foundations of Delay Doppler Communications and Sensing

Integrated sensing and communications (ISAC) is listed as one of the six primary usage scenarios in the forthcoming 6th Generation (6G) network. However, the current wireless infrastructures are far away from meeting the 6G key performance indicators (KPIs) of both sensing and communications. 6G requires a 1.5 to 3 times growth in spectral efficiency compared to 5G, and significant improvements in sensing ability. These stringent requirements cannot be met by the current physical-layer waveform. FUNDOCS advocates a novel “propagation-centric” approach to design waveforms for communications and sensing, embracing instead of combating the wireless channel dynamics by exploiting the most fundamental elements of wireless channels, i.e., delay and Doppler. This leads to the adoption of delay-Doppler (DD) waveforms that are invariant to channel distortions from delay and Doppler but are sensitive to time and frequency shifts. Thus, DD waveforms are naturally suitable for both communications and sensing. Furthermore, DD waveforms show strong compatibility with multiple-input multiple-output (MIMO) transmissions and non-orthogonal signaling, which are key technologies to enhance communication efficiency. However, the current state-of-the-art is far from practical implementation due to the lack of knowledge in DD signal processing, channel exploitation, bandwidth-efficient transmissions, and theoretical performance analysis. This project is developed to establish both theoretical and algorithmic foundations for DD communications and sensing. To ensure the project completion, the PI will investigate these foundational problems via a two-step methodology, which prioritizes the DD channel exploitation for theoretical understanding and considers practical constraints for algorithmic implementation. Our overarching goal is to develop a next-generation physical-layer waveform that not only meets 6G KPIs but also advances beyond sensing to environmental imaging.