Wireless sensor node modelling for energy efficiency analysis in data-intensive periodic monitoring

Data-intensive wireless sensor applications, such as remote visual inspection using high-resolution video sensors, require a special design approach in order to save energy and prolong lifetime of a battery-powered wireless sensor node. This study is motivated by searching for the most efficient communication protocol for high-resolution image transmission in environmental monitoring sensor networks, where data should be transmitted periodically, but relatively rarely (usually once or twice per day). Some previous publications propose ZigBee or Wi-Fi as suitable candidates for data-intensive wireless transmission, but the literature lacks a systematic study that would provide a guidance for designing such systems. We construct a measurement-based model of a wireless sensor node with emphasis on the communication unit. We measured the energy consumption of commercially available wireless ZigBee and Wi-Fi modules, as well as the influence of the interface bandwidth limitation that reduces their energy efficiency. The model includes real-world communication channel properties that at high bit-rates reduce the communication range and increase the energy consumption due to a higher susceptibility to noise.Our results show that in scenarios when the node sends up to 64kB of data per session once per day, the estimated lifetime of a ZigBee node is up to 10% longer than of a Wi-Fi node. However, when the amount of data per session increases, the Wi-Fi wins due to its higher energy efficiency during data transfer. When the data amount reaches 10MB, the lifetime of a Wi-Fi node using UDP protocol is 5 times longer than that of a ZigBee node. On the other hand, the Wi-Fi node lifetime decreases with increasing number of sessions per day, because the connection establishment with the access point is very energy consuming. As a result, when 5 sessions per day are required the ZigBee node can offer 40% longer lifetime than the Wi-Fi node when 10kB of data is transmitted per session.