FlexCP: Standard-Compatible Flexible Sensing
Songqian Li, Shuqiang Xia, Yihua Ma, Zhongbin Wang, Dawei Chen · 2024
More and more attention is being drawn into standardization for integrating sensing and communications (ISAC) in 5G-A/6G. The functionalities of the future radio interface are extending from communications to sensing in the upcoming standardization. Given the compatibility issues, cyclic prefix orthogonal frequency division multiplex (CP-OFDM) waveform is one of the primary candidates in the 5G-A/6G standardization. However, one of the critical problems with CP-OFDM sensing is the fixed sensing coverage brought by limited CP options in current standardization. When the delay of the target echoes exceeds the length of CP, the resulting received signal will suffer from inter-symbol-interference (ISI) and inter-carrier-interference (ICI), which degrades the sensing performance. A standard-compatible CP extension paradigm is in demand. In this paper, FlexCP is proposed to enable flexible sensing coverage without introducing new frame structure into NR. With tone reservation in previous OFDM symbol, FlexCP extends the CP duration of the sensing OFDM symbol with preservation of communications resources in the extender symbol. Compared with standard CP options, FlexCP offers target sensing with larger detection range. Moreover, FlexCP can help subspace algorithms such as MUSIC achieving better performance for long-range targets. Simulation results depict enhancements in both detection range and multi-target resolvable range. Moreover, the power of the new designed symbol could be reduced as the original symbol as 1/3 of the reserved tone are used, leaving 2/3 of the subcarriers saved for communications purpose.