Low-Overhead Sensing RS Design for Integrated Sensing and Communication (ISAC)

Integrated sensing and communication (ISAC) is one of the most important research topics towards 5th generation (5G)-Advanced and 6th generation (6G) mobile communications. Diverse use cases could be supported from the analysis of measurement results obtained by sensing. Reference signal (RS) is necessary for the measurements, which should be designed to provide good sensing performance at low overhead. Positioning RS (PRS) defined for user equipment (UE) positioning in 5G new radio (NR) is a good starting point for sensing, whose performance on estimation accuracy and maximum unambiguous performance are validated to be good. However, the overhead of NR PRS is too high, limiting its usage for sensing. In this paper, inspired by the multiple pulse repetition frequency (PRF) method in radar systems, we propose a new sensing RS pattern composed by multiple comb RSs with co-prime comb sizes. On the one hand, the comb RS pattern has good backward compatibility with communication systems. On the other hand, the co-prime comb sizes can effectively eliminate the distance ambiguity caused by the comb RS pattern. The evaluation results show that proposed sensing RS pattern could achieve same maximum unambiguous distance with NR PRS but reduce the overhead from 7.14% to 2.21%.