LongShoT: Long-range Synchronization of Time
LongShoT: Long-range Synchronization of Time
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LongShoT：远程时间同步
DOI：
10.1145/3302506.3310408
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Iannucci, Bob
中科院分区：
文献类型：
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作者：
Ramirez, Ceferino Gabriel;Sergeyev, Anton;Dyussenova, Assya;Iannucci, Bob
低功耗广域网，如LoRaWAN，在无线传感和驱动领域迅速普及。虽然LoRaWAN在应用和性能方面进行了大量研究，但在这种网络中很少有时间概念的特征。许多应用程序将需要具有不同精度级别的同步本地时钟，以保持网络中的一致性和协调性。然而，传统的时间同步协议不适合LoRaWAN的时延固有、低占空比、网络模型和广域部署拓扑。同时，对于低功耗应用来说，依靠GPS来计时是不可行的。在本文中，我们提出了一种基于LoRaWAN的时间同步方案LongShoT，它能够通过单个网络请求将设备时钟同步到10μ sofa以内的参考时钟。这是通过利用LoRaWAN网络的确定性属性以及数据包的硬件和mac级时间戳来实现的。LongShoT在消费者现成的硬件上实现，并使用GPS 1PPS作为参考在物理分布式设备上进行评估。结果表明，在距离网关4km的范围内，LongShoT实现了小于2μ的平均同步误差，并将振荡器漂移补偿到小于0.1ppm。
Low-Power Wide Area Networks, such as LoRaWAN, are rapidly gaining popularity in the field of wireless sensing and actuation. While LoRaWAN is heavily studied in applications and performance, the concept of time has rarely been characterized in such networks. Many applications will require synchronized local clocks with varying levels of precision in order to maintain consistency and coordination in the network. Traditional time synchronization protocols however do not fit LoRaWAN's delay-inherent, low duty cycle, network model and wide-area deployment topology. Meanwhile, relying on GPS for time is not an option for low-power applications.In this paper, we present LongShoT, a time synchronization scheme built on LoRaWAN capable of synchronizing device clocks to within 10μsof a reference clock with a single network request. This is achieved by utilizing the deterministic properties of LoRaWAN networks along with hardware- and MAC-level timestamping of packets. LongShoT was implemented on consumer off-the-shelf hardware and evaluated over physically distributed devices using GPS 1PPS as a reference. Our results show that LongShoT achieves an average synchronization error of less than 2μsand compensates oscillator drift to less than 0.1ppmwith devices distributed within 4kmof a gateway.