The emergence of water-proof mobile and wearable devices (e.g., Garmin Descent and Apple Watch Ultra) designed for underwater activities like professional scuba diving, opens up opportunities for underwater networking and localization capabilities on these devices. Here, we present the first underwater acoustic positioning system for smart devices. Unlike conventional systems that use floating buoys as anchors at known locations, we design a system where a dive leader can compute the relative positions of all other divers, without any external infrastructure. Our intuition is that in a well-connected network of devices, if we compute the pairwise distances, we can determine the shape of the network topology. By incorporating orientation information about a single diver who is in the visual range of the leader device, we can then estimate the positions of all the remaining divers, even if they are not within sight. We address various practical problems including detecting erroneous distance estimates, addressing rotational and flipping ambiguities as well as designing a distributed timestamp protocol that scales linearly with the number of devices. Our evaluations show that our distributed system running on underwater deployments of 4-5 commodity smart devices can perform pairwise ranging and localization with median errors of 0.5-0.9 m and 0.9-1.6 m

翻译：防水移动与可穿戴设备（如Garmin Descent和Apple Watch Ultra）专为专业潜水等水下活动设计，其出现为这些设备的水下组网与定位能力开辟了机遇。本文提出首个适用于智能设备的水下声学定位系统。传统系统利用已知位置的浮标作为锚点，我们则设计了一种无需外部基础设施的系统：潜水领队可计算所有其他潜水员的相对位置。我们的核心理念是：在高度互联的设备网络中，若计算成对距离，即可确定网络拓扑形状。通过整合位于领队设备视线范围内的单个潜水员的方位信息，即可估算其余所有潜水员的位置——即使他们不在视线范围内。我们解决了多种实际问题，包括检测错误距离估计、解决旋转与翻转歧义，以及设计一种随设备数量线性扩展的分布式时间戳协议。评估表明，在4-5台商用智能设备组成的水下部署系统中，该分布式系统可实现成对测距与定位，中位误差分别为0.5-0.9米和0.9-1.6米。