Characterization of long term channel variations in industrial wireless sensor networks

Wireless sensor networks (WSNs) are being increasingly used for monitoring and control in modern process industries, which until a few years ago were almost exclusively done by cables. In order to successfully integrate WSNs in process industries, proper understanding of the radio channel characteristics is necessary. Predominantly, in control applications, the sensors are static, and variations in the channel are caused by the objects in the region, which move to different locations every now and then. Hence, over a period of several hours, the radio channel will have completely different properties, which will have a significant impact on network performance. In this paper, we conduct and analyze channel measurements in a fully functional factory over a much longer time horizon of 20 hours, which, to the best of our knowledge, have not been undertaken before. A key observation from our analysis is that the radio channel, over a longer time scale, shows a more complicated behavior than over a relatively shorter time period. We also show that if the long-term channel variations are not effectively characterized, then we run the risk of transmitting at a rate, as low as, 94% less than what the channel could actually support.