An Enhanced Preamble of PRACH Frame for Low-Altitude Long-Distance Integrated Sensing and Communication System

In this paper, we propose an enhanced preamble scheme for the physical random access channel (PRACH) applied to low-altitude integrated sensing and communication (ISAC) systems, aiming to expand the sensing capability of traditional mobile networks with PRACH frames based on ZC sequences. To enable the network to possess target sensing capability before successful terminal access, we transform PRACH from a mere initial access channel into an ISAC system capable of supporting high-speed terminal access and user equipment sensing by introducing a time-frequency orthogonal block structure and orthogonal cover codes (OCCs). Specifically, we first derive the Cramér-Rao lower bound (CRLB) for estimating the distance and velocity of user equipment using OCC-ZC sequences, and establish the evaluation metric for communications named detection probabilities. Then, the ISAC problem is formulated as a multi-objective optimization function. Since the multi-objective optimization problem is non-convex, we propose the NSAG-II algorithm to solve it, simultaneously improving the estimation accuracy of distance and velocity in the sensing aspect and the detection probability in the communication aspect.