# Multiparametric Monitoring in Equatorial Tomato Greenhouses (II): Energy Consumption Dynamics
## 1 Introduction  
The tomato, technically known as _Solanum lycopersicun_, is one of the most significant products contributing to the economy of the Ecuadorian agricultural sector [1]. For this reason, tomatoes are usually grown under greenhouses to increase their production. This structured environment facilitates the implementation of internal and external climate monitoring systems. On the other hand, wireless sensor networks (WSNs) are currently the telecommunication systems with the highest penetration in the use of the population for specialized applications such as precision agriculture. WSNs are implemented with autonomous sensor nodes that collect data packages and transmit them to a coordinator at the expense of an external energy source, such as batteries [2; 3; 4]. Therefore, the energy consumption of the nodes is an especially relevant parameter for the operation quality of these networks.  
At present, the energy consumption characterization of WSNs nodes in terms of telecommunication infrastructure is a topic of interest, because it affects about 1% of the world's electricity consumption, and it has been exponentially increasing [5; 6]. The scientific and technical literature includes works focused to the analysis of energy consumption in relation to the operation mode [7] and the performance of the operating system [8] in the communication radios. In addition, energy-saving techniques using hardware [9; 10; 11; 12] and software [13] have been considered, and most of these studies are applied to WSNs with ZigBee technology and star topology. To our best knowledge, few works involve an extensive knowledge of the detailed statistical description of consumption dynamics and its ergodic properties, as well as a rigorous analysis of the estimation of stationarity. In addition, the contributions with respect to comparisons of the energy consumption behavior of WSNs for different wireless technologies, network topologies, and transmission rates are scarce.  
Based on this background, the present study aims to provide a detailed analysis of the dynamics of the energy consumption in three types of WSNs, namely, ZigBee with star topology, ZigBee with mesh topology (so-called here DigiMesh), and WiFi with access point topology for tomato greenhouse monitoring in Ecuador. We want to provide an accurate statistical characterization of the behavior of WSNs, relating energy consumption, transmission rate, and network topology to provide researchers with the selection criteria of the appropriate network design in terms of energy savings, and oriented to monitoring the climate of greenhouses. For this purpose, the the electrical current time series recorded at each node were studied using stochastic-process analysis methods, including amplitude probability functions and temporal autocorrelation estimation. We also used bootstrap resampling techniques to provide with non-parametric statistical description of confidence intervals (CIs) when convenient, as well as the so-called M-mode plots to represent and compare the statistical properties of the several realizations. The two companion papers are devoted to the analysis of the WSN topologies and their configuration and to the study of the dynamics of the environmental measurements, both of them in Ecuadorian tomato greenhouse monitoring [14; 15]. The first one has the detailed description of the complete system and network setup, and the second one has a short summary of the proposed system for tomato greenhouse monitoring.  
This paper is organized as follows. Section 2 reviews some documents related with the energy consumption dynamics in WSNs. Section 3 describes the statistical analysis tools that are used to study the dynamics of the energy consumption variables. Section 4 presents the detailed results when analyzing each WSN at different speeds. Finally, Section 5 gives the discussion and conclusions.