Communication-Oriented Integrated Sensing and Communication (CO-ISAC) System Design for 6G

After the academic researches in recent years, integrated sensing and communication (ISAC) is now under study for the standardization in the 3rd Generation Partnership Project (3GPP) towards the fifth generation (5G)-Advanced (5G-A) and sixth generation (6G) wireless communication systems. In this paper, to promote the possibility of successful ISAC commercialization, we focus on communication-oriented ISAC system design. We firstly introduce the standardization progress of ISAC in 3GPP, and propose the concept of communication-oriented ISAC (CO-ISAC), and discuss the technologies under CO-ISAC framework including sensing modes, sensing waveform, multiple-input-multiple-output (MIMO) scheme, multiplexing methods for sensing and communication, and reference signal (RS). Then, taking RS design as one example, we propose a common RS for sensing and communication. Pseudo-random (PN) and Zadoff-Chu (ZC) sequences in communication systems are enhanced for sensing performance improvement. For PN, Binary Phase Shift Keying with π/2 rotation (π/2-BPSK) modulation is recommended via proving the low sidelobe in aperiodic ambiguity function (AF). For ZC, the closed-form expressions of aperiodic AF and peak-to-sidelobe ratio (PSLR) are derived, based on which the root index of ZC with low PSLR is designed. Evaluation results validate the gain of proposed PN and ZC sequences on sensing performance. Finally, our views on 6G Day-1 ISAC system design are provided, especially proposing that sensing technologies should be carefully designed by taking communication performance into consideration. Our research work shows the great potential of ISAC technologies to create new values even in CO-ISAC systems. In the future, more efforts on the researches, standardization and trials from academia and industry are needed to push ISAC into reality for 5G-A and 6G.