ProSafe: Wi-Fi beaconing for Proximity-based Safety in coastal environments

Abstract:
We present ProSafe, a Wi-Fi–based safety system that enhances situational awareness in coastal waters by enabling vessels to detect swimmers, snorkelers, and small craft through proximity beaconing. ProSafe employs lightweight, GPSequipped smart buoys that periodically broadcast Wi-Fi frames, while vessel-mounted units passively listen and trigger local alerts when a buoy is within range. To balance timely discovery with limited channel capacity, we introduce ADAB (Adaptive Density- Aware Beaconing), a density-based adaptation that adjusts the beacon interval as a function of the locally observed number of neighbors. ADAB operates entirely at the MAC layer, requires no infrastructure, and remains simple enough for commodity hardware. To calibrate the simulator, we first ran a sea trial with two Raspberry Π buoys using a static beaconing rate, measuring over-surface communication performance (reliable reception up to 70m and sporadic up to 120 m). We then performed simulations that incrementally increased the number of nodes and evaluated Broadcast Packet Delivery Ratio (BPDR) against a static baseline. Results show that, as node density grows, ADAB sustains a higher B-PDR compared to fixed-interval beaconing, enabling scalable, low-latency safety awareness in infrastructure-free coastal scenarios.