Transmission power control for wireless sensor networks in railway applications

Wireless Sensor Networks are becoming increasingly utilised in the railway industry to facilitate the physical and environmental monitoring of railway assets; in order to optimise operational, maintenance and refurbishment activities. With significant energy constraints imposed on the networked devices, there is a growing need to optimise wireless communications through energy-efficient algorithms and protocols. This paper presents the challenges and opportunities of using a variable transmission power control mechanism in railway environments, under the typical constraints of wireless sensor networks. Extensive empirical results presented in this paper show that radio communication link quality in railway environments is significantly influenced by spatial and temporal factors, and that every link is influenced to a different degree. This phenomena highlights that current wireless sensor network standards, that use a fixed transmission power, do not represent the dynamics of communication quality and thus, result in communications that has poor energy efficiency or reliability. Through profiling the power consumption of the radio hardware under different test conditions, this paper determines that previous theories about the limited impact of transmission power control do not hold, thus concluding that there are significant opportunities for a variable transmission power control mechanism in railway wireless sensor networks.