Integrated Sensing and Communications in Terahertz Systems: A Theoretical Perspective

The unprecedented increase in wireless data traffic has motivated the development of terahertz communications (THzCom) over the years. Since THzCom would suffer from performance degradation and even link outage in mobile scenarios, the integrated sensing and communications (ISAC) are promised to settle the mobility challenges by extracting information from wireless channels. The emerging technique so-called THz-ISAC (T-ISAC) is in the initial stage of theoretical evaluation, yet the existing ISAC theory performs unsatisfactorily without considering THz natures. To this ends, the performance of sensing and communication (S&C) functionalities in T-ISAC systems is researched in this work. Firstly, T-ISAC performance frameworks containing metrics and models are summarized. Combining ISAC theory with THz natures, three aspects of S&C metric correlation in coexistence, coordination and cooperation are orderly elaborated. And the limits of performance in resource-sharing, waveform-integrating and functionality-beneficial gains in T-ISAC systems are accordingly discussed. The challenges and roads ahead of T-ISAC theory efforts are hence concluded into issues on performance models, analysis approaches and metric optimizations.