SaRA: Sensing-Aware Random Access for Integrated Satellite-Terrestrial Networks

Integrated satellite-terrestrial networks are crucial for critical communications, yet the initial access for user equipment (UE) is hampered by signal blockage and dynamic loads, challenging traditional random access (RA) mechanisms in achieving low latency and high success rates. To address this, we propose a Sensing-aware Random Access (SaRA) mechanism. SaRA introduces a lightweight sensing micro-slot before the standard RACH procedure, leveraging the sensing signal to jointly determine an optimal access decision threshold and a candidate beam set. This proactively filters users with poor channel conditions and narrows the beam search space. We formulate the resource allocation as a constrained optimization problem and propose a practical, low-complexity algorithm. Extensive simulations validate that SaRA provides substantial gains in access latency and system access capacity under high-load conditions compared with the standard 3GPP FR2 RACH baseline, while maintaining competitive first-attempt success probability with minimal additional overhead.