Energy Consumption Analysis and Lightweight Encryption Evaluation in a CoAP-Based Smart Irrigation System for Kiwifruit Orchards in Gilan ProvinceAli

Background and objectives: Gilan Province, recognized as one of the main hubs of kiwifruit production in Iran, faces several challenges such as high energy consumption, inefficient water resource management, and a lack of technological infrastructure in traditional irrigation systems. Comparative studies indicate that the energy efficiency of kiwifruit orchards in Gilan is considerably lower than in Mazandaran Province and even Shanxi Province in China. In this study, an IoT-based smart irrigation system was designed and simulated for kiwifruit orchards in Talesh County, Gilan Province. The main objective was to enhance decision-making in irrigation scheduling and to investigate the effect of energy consumption in two scenarios: with and without lightweight encryption. Furthermore, the study aimed to analyze the specific energy consumption under both smart and conventional irrigation conditions.
Materials and methods: A pressure-based drip irrigation system was designed and simulated using the CoAP (Constrained Application Protocol) on the Contiki 2.7 platform, an open-source and lightweight operating system specifically developed for resource-constrained IoT and wireless sensor network (WSN) devices. These devices typically have limitations in energy, memory, and computational capability.The default recursive CoAP algorithm was utilized to manage communication processes, and the energy consumption of sensor nodes was measured in two scenarios (encrypted and non-encrypted). The main goal was to evaluate the feasibility of adding lightweight encryption without causing a significant increase in energy usage. The results of this study can be used to develop low-power, secure, and climate-adaptive agricultural systems suitable for northern Iran, particularly Gilan Province.Initially, a wireless sensor network consisting of several sensing nodes was designed to collect parameters such as soil moisture, temperature, and light intensity. These nodes communicated via CoAP in a mesh topology, transmitting the collected data to a smart gateway and then to a central server. The accuracy of data transmission was verified during the initial deployment to ensure stable connectivity between the sensors and the server.The CoAP protocol, designed specifically for constrained devices, enables efficient communication by reducing packet size at the UDP layer. Each CoAP message contains a 32-bit header with fields such as Version (V) and Token Length (TKL) that help minimize communication overhead.For the smart irrigation simulation, a 12-year-old kiwifruit orchard with 16 trees in two rows, located at E 48°91′291″ and N 38°09′039″, was modeled. The system included eight soil-moisture sensors (spaced 5 × 5 m at a depth of 30 cm), one water-level sensor for monitoring the well, and one router node (acting as a gateway between the sensors and the central server). Each sensor node was placed 5 m apart from its neighbor to ensure realistic interactions between nodes and the router.

For CoAP implementation, instead of using Cupper (a command-line tool for testing CoAP messages in IoT systems), the node-coap library—developed in the Node.js environment—was employed as the client agent. Node-coap is one of the widely used tools in IoT projects for managing CoAP communications efficiently.To improve the simulation accuracy, real-time meteorological data were fetched using the OpenWeather API. The irrigation process was fully automated and event-driven: first, the water-level node verified the availability of water in the source. If sufficient water was present, soil-moisture data from all sensors were collected. When the average soil moisture dropped below a predefined threshold, a command was issued to open the irrigation valve. After irrigation, soil moisture was re-measured, and when the average exceeded the threshold, the irrigation system was automatically stopped.
Results: : Based on the simulation output, the average power consumption of the sensor nodes during each 10-minute irrigation event was 4.859709 mW in the non-encrypted mode and 4.863555 mW in the encrypted mode. Considering an annual yield of 35,000 kg per hectare and 221 irrigation cycles per year, the specific energy consumption in both modes was approximately 2.976 MJ kg⁻¹.Analysis of energy distribution among the sensor states revealed that the receive (RX) state accounted for the largest portion of total energy consumption, followed by the transmit (TX) state. Adding encryption caused only a minor increase in processor and transmission energy consumption, while the RX energy remained almost unchanged. This demonstrates that the lightweight encryption algorithm introduced negligible energy overhead and can therefore be used safely in constrained sensor networks.
Conclusion: The results demonstrated that the incorporation of lightweight encryption mechanisms into CoAP-based smart irrigation systems does not lead to any statistically or practically significant increase in overall energy consumption. The marginal increase observed is not substantial enough to influence the general system performance, operational continuity, or long-term functional stability of the deployed network infrastructure. Specifically, the measured difference in power consumption between the encrypted and non-encrypted operational modes was found to be less than one percent, which clearly falls within an acceptable and tolerable range for resource-constrained sensor nodes typically utilized in agricultural wireless sensor networks.This minimal variation indicates that the computational overhead introduced by the encryption process is highly limited and efficiently managed within the processing capabilities of the sensor hardware. Furthermore, the additional operations required for encryption and secure data handling exert only a negligible influence on the duty cycles of the sensing nodes. In practical terms, this means that the frequency of activation, transmission intervals, and reception durations remain largely unaffected by the integration of the security layer.Therefore, it can be conclusively inferred that the deployment of lightweight cryptographic techniques in agricultural wireless sensor networks not only enhances communication security, strengthens data confidentiality, and preserves data integrity, but also maintains energy efficiency without imposing any meaningful degradation in system performance. Moreover, the operational sustainability, reliability, and stability of the smart irrigation framework remain fully preserved under encrypted communication conditions.

Keywords: Precision Agriculture, CoAP, Energy Consumption, Kiwifruit Orchard, Smart Irrigation