Abstract
This work analyzes several drift compensation mechanisms in wireless sensor networks (WSN). Temperature is an environmental factor that greatly affects oscillators shipped in every WSN mote. This behavior creates the need of improving drift compensation mechanisms in synchronization protocols. Using the Flooding Time Synchronization Protocol (FTSP), this work demonstrates that crystal oscillators are affected by temperature variations. Thus, the influence of temperature provokes a low performance of FTSP in changing conditions of temperature. This article proposes an innovative correction factor that minimizes the impact of temperature in the clock skew. By means of this factor, two new mechanisms are proposed in this paper: the Adjusted Temperature (AT) and the Advanced Adjusted Temperature (A2T). These mechanisms have been combined with FTSP to produce AT-FTSP and A2T-FTSP Both have been tested in a network of TelosB motes running TinyOS. Results show that both AT-FTSP and A2T-FTSP improve the average synchronization errors compared to FTSP and other temperature-compensated protocols (Environment-Aware Clock Skew Estimation and Synchronization for WSN (EACS) and Temperature Compensated Time Synchronization (TCTS)).
Highlights
Time synchronization is critical in most networks, especially in wireless sensor networks (WSN) [1]
As Figure 6 shows, the use of temperature-based synchronization protocols improves the average synchronization error compared to Flooding Time Synchronization Protocol (FTSP) under the same conditions
The TCTS and EACS algorithms were chosen, because (i) these synchronization protocols take into account temperature variations, (ii) are based on obtaining the clock skew of the nodes to improve the synchronization process and (iii) are designed to be used in WSNs
Summary
Time synchronization is critical in most networks, especially in WSNs [1]. Clock accuracy in these types of networks is difficult to achieve, due to energy and processing constraints in the motes.Synchronization protocols [2,3] allow the application of several different policies, such as sensor data fusion, coordinated actuation between nodes and power-efficiency.The work of Vig [4] demonstrates that the “characteristics of crystal units are determined primarily by the angles of cut of the crystal plates with respect to the crystallographic axes of quartz” and “a temperature variation can cause a frequency change due to the energy dissipation in the active area of the resonator”. Time synchronization is critical in most networks, especially in WSNs [1]. Clock accuracy in these types of networks is difficult to achieve, due to energy and processing constraints in the motes. Sugihara et al [5] demonstrate how the temperature variations affect the TelosB oscillator (CMR200T). Using a set of motes with the above mentioned oscillator, this work demonstrates that the synchronization error of FTSP increases, due to temperature variations. A more accurate clock skew is obtained when temperature variations are included in synchronization protocols
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