LASIGE, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal.
Sensors (Basel). 2020 Jul 20;20(14):4034. doi: 10.3390/s20144034.
Global climate change originates frequent floods that may cause severe damage, justifying the need for real-time remote monitoring and alerting systems. Several works deal with LoRa (Long Range) communications over land and in the presence of obstacles, but little is known about LoRa communication reliability over water, as it may happen in real flooding scenarios. One aspect that is known to influence the communication quality is the height at which nodes are placed. However, its impact in water environments is unknown. This is an important aspect that may influence the location of sensor nodes and the network topology. To fill this gap, we conducted several experiments using a real LoRa deployment to evaluate several features related to data communication. We considered two deployment scenarios corresponding to countryside and estuary environments. The nodes were placed at low heights, communicating, respectively, over the ground and over the water. Measurements for packet loss, received signal strength indicator (RSSI), signal-to-noise ratio (SNR) and round-trip time (RTT) were collected during a period of several weeks. Results for both scenarios are presented and compared in this paper. One important conclusion is that the communication distance and reliability are significantly affected by tides when the communication is done over the water and nodes are placed at low heights. Based on the RTT measurements and on the characteristics of the hardware, we also derive a battery lifetime estimation model that may be helpful for the definition of an adequate maintenance plan.
全球气候变化引发的频繁洪水可能会造成严重破坏，这证明了需要实时远程监测和警报系统。有几项工作涉及到陆地和有障碍物存在情况下的 LoRa（远距离）通信，但对于 LoRa 通信在水中的可靠性知之甚少，因为这种情况可能会在实际洪水场景中发生。已知会影响通信质量的一个方面是节点的放置高度。然而，其在水环境中的影响尚不清楚。这是一个重要的方面，可能会影响传感器节点的位置和网络拓扑结构。为了填补这一空白，我们使用真实的 LoRa 部署进行了多次实验，以评估与数据通信相关的几个特性。我们考虑了对应于农村和河口环境的两种部署场景。节点放置在较低的高度，分别在地面和水面上进行通信。在几周的时间内收集了数据包丢失、接收信号强度指示 (RSSI)、信噪比 (SNR) 和往返时间 (RTT) 的测量值。本文介绍并比较了这两种场景的结果。一个重要的结论是，当通信在水面上进行且节点放置在较低的高度时，潮汐会显著影响通信距离和可靠性。基于 RTT 测量值和硬件特性，我们还推导出了一个电池寿命估计模型，这对于制定适当的维护计划可能很有帮助。
