Castillo-Secilla José María, Palomares José Manuel, León Fernando, Olivares Joaquín
Department of Computer Technology, University of Alicante, Carretera San Vicente del Raspeig, S/N, 03690 Alicante, Spain.
Department of Computer Architecture, Electronics and Electronic Technology, Universidad de Córdoba, Campus de Rabanales, 14001 Córdoba, Spain.
Sensors (Basel). 2017 Apr 20;17(4):909. doi: 10.3390/s17040909.
Wireless sensor networks are used to sample the environment in a distributed way. Therefore, it is mandatory for all of the measurements to be tightly synchronized in order to guarantee that every sensor is sampling the environment at the exact same instant of time. The synchronization drift gets bigger in environments suffering from temperature variations. Thus, this work is focused on improving time synchronization under deployments with temperature variations. The working hypothesis demonstrated in this work is that the clock skew of two nodes (the ratio of the real frequencies of the oscillators) is composed of a multiplicative combination of two main components: the clock skew due to the variations between the cut of the crystal of each oscillator and the clock skew due to the different temperatures affecting the nodes. By applying a nonlinear filtering, the homomorphic filtering, both components are separated in an effective way. A correction factor based on temperature, which can be applied to any synchronization protocol, is proposed. For testing it, an improvement of the FTSP synchronization protocol has been developed and physically tested under temperature variation scenarios using TelosB motes flashed with the IEEE 802.15.4 implementation supplied by TinyOS.
无线传感器网络用于以分布式方式对环境进行采样。因此，为了确保每个传感器在完全相同的时刻对环境进行采样，所有测量必须进行紧密同步。在温度变化的环境中，同步漂移会变得更大。因此，这项工作专注于在存在温度变化的部署环境下改进时间同步。这项工作中所展示的工作假设是，两个节点的时钟偏差（振荡器实际频率的比率）由两个主要成分的乘法组合构成：由于每个振荡器晶体切割差异导致的时钟偏差以及由于影响节点的不同温度导致的时钟偏差。通过应用非线性滤波，即同态滤波，这两个成分能够以有效的方式分离。提出了一种基于温度的校正因子，该因子可应用于任何同步协议。为了对其进行测试，已开发出FTSP同步协议的改进版本，并在温度变化场景下使用搭载了由TinyOS提供的IEEE 802.15.4实现的TelosB节点进行了物理测试。
