Temperature Compensated Time Synchronization

Abstract

Time synchronization in embedded sensor networks is an important service for correlating data between nodes and communication scheduling. While many different approaches to the problem are possible, one major effect of clock frequency difference between nodes, environmental temperature changes, has often been left out of the solution. The common assumption that the temperature is static over a certain period of time is often used as an excuse to assume constant frequency errors in a clock. This assumption forces synchronization protocols to resynchronize too often. While there exists hardware solutions to this problem, their prohibitive high cost and power consumption make them unsuitable for some applications, such as wireless sensor networks. Temperature compensated time synchronization (TCTS) exploits the on-board temperature sensor existing in many sensor network platforms. It uses this temperature sensor to autonomously calibrate the local oscillator and removes effects of environmental temperature changes. This allows a time synchronization protocol to increase its resynchronization period, without loosing synchronization accuracy, and thus saves energy and communication overhead. In addition, TCTS provides a stable clock source when radio communication is impaired. We present the theory behind TCTS, and provide initial results of a simulated comparison of TCTS and the flooding time synchronization protocol.