Coordinated and Distributed ISAC: Multi-Static Target Localization Using PRACH

In terms of mobility considerations of next generation wireless networks, localization of moving entities to realize the benefits of Integrated Sensing and Communication (ISAC) based systems becomes a critical issue. To that end, this paper proposes and lays down two new ISAC methods to localize moving targets by utilizing Physical Random Access Channel (PRACH) preambles generated from Zadoff–Chu (ZC) sequences through sensing signals across synchronized base stations (gNBs). The first method utilizes Time Difference of Arrival (TDoA) method, while the second method relies on the back projection on a multistatic setting. The first approach estimates the target position by employing TDoA values derived from ZC sequence-based correlation peaks. On the other hand, the back projection method for a multistatic setup, aligns the phase of channel responses from multiple gNBs on a spatial grid and fuses them to generate a reflectivity map, with the strongest peaks indicating the target location. The simulation results indicate that targets are localized with an error of approximately 40 m and 65 m at the 95% confidence level using the TDoA and the back projection algorithms along the signal to noise ratio (SNR) of -20 dB, respectively. Notably, these results are achieved using the existing 3GPP waveform configuration, including the limited PRACH channel bandwidth and through the cooperation of neighboring gNBs. For a better performance, the 3GPP standard body can make PRACH bandwidth and power flexible parameters, allowing larger bandwidths to be allocated for ISAC applications and/ or allowing inter gNB communication.