Bi-Static ISAC With Asynchronous Transceivers: Mechanism, Solution, and Field Test

Foreseen as a killer application in next-generation wireless networks, integrated sensing and communication (ISAC) has gained tremendous developments in recent years, and will contribute to realize Internet of Everything (IoE). Particularly, by enabling separable sensing transceivers, bi-static sensing is free from self-interference and able to leverage ubiquitous network devices, and thus has become an indispensable scenario of ISAC. However, bi-static sensing suffers from transceiver asynchronization, which induces timing offset (TO), timing drift (TD) and carrier frequency offset (CFO). In this paper, we first give the theoretical analyses on how TO, TD and CFO impact the sensing signal, under the practical configuration following the new radio (NR) protocol. Based on this, we systematically reveal the mechanism of TD and the correspondingly resulted delay-Doppler spectrum dispersion. Specifically, the delay spectrum shifts and the phase drifts induced by TD are analyzed, which are the two main factors eventually leading to the delay-Doppler spectrum dispersion and consequent severe errors in signal detection and parameter estimation. Based on the revealed mechanisms, we develop an asynchronous delay-Doppler (ADD) algorithm for bi-static sensing, including delay spectrum alignment and phase compensation, respectively to suppress the delay spectrum shifts and phase drifts. Thanks to the revealed mechanism, the ADD algorithm does not rely on specific prerequisites. Simulation results have confirmed the revealed mechanisms and verified the effectiveness of the ADD algorithm. Particularly, field tests are conducted on an ISAC prototype, and achieve a centimeter-level positioning accuracy, which further confirms the revealed mechanisms and validates the ADD algorithm.