Abstract: It is an important technique to achieve agricultural informationization, automatization and intelligentize that wireless sensor networks is used in agriculture as a monitoring network. Farmland wireless sensor network has the characteristics of ultra largcscale, ultra low-cost and complex topological changing which brings the network protocol rigorous requirements. In this paper, a communication energy model for large-scale fields' sensor network was proposed based on Heinzclman's energy model, which takes the interaction with disposal space distance, transmission semi-diameter, packet size as well as the impact of components into account. Furthermore, a math method to calculate best transmission semi-diameter was presented while the disposal space distance was given. And then, the important factors of the disposal space distance and network scale in the model effect query energy consumption were attained by fitting the simulation results.

Key words: Wireless sensor networks, Energy model, Transmission semi-diameter