ISI-Resistant Reference Signal Design and Processing for OFDM Integrated Communications and Long-Range Radar Sensing

The cyclic prefix orthogonal-frequency-division-multiplexing (CP-OFDM) waveform is considered an important candidate for integrated sensing and communications (ISAC) in B5G/6G networks. However, due to the limited CP duration, especially for mmWave communications, the radar sensing can only achieve a short sensing range without inter-symbol-interference (ISI). To resolve this problem, a novel reference signal (RS) design and corresponding signal processing scheme are developed for OFDM long-range radar sensing. More specifically, the zero-power RS (ZP-RS) and non-zero-power RS (NZP-RS) are alternately deployed at subcarriers. The time samples in the second-half symbol-duration are first extracted, and then a simple fast-Fourier-transform (FFT) or that with additional pre-phase-rotation is conducted for subsequent radar sensing processing to achieve a long ISI-free sensing range. The performance gain over conventional design is first derived by mathematical analysis and further validated by simulation results.