# Energy-Efficient Wireless Sensor Networks for Precision Agriculture: A Review
## 5 Challenges and Limitations  
The development of WSNs prompted new research trends in the agricultural domain. Micro electromechanical system (MEMS) technologies allow for the manufacture of cheap and small sensors. The pervasive nature of the process, together with tiny, self-regulating sensor nodes, cost-effective equipment, and scalability, indicate that WSNs can be used for agriculture automation [5]. However, regarding the distribution of WSNs to observe different agricultural climates, a number of open challenges and limitations remain. Several of these challenges and limitations in existing agricultural applications based on WSNs are listed below together with suggestions on how to address them. 1. _Power consumption and battery life_: A WSN consists of three main components: sensors, microcontrollers, and RF transceivers. Given that the battery of a sensor node provides limited energy, ensuring that the components of the sensor node consume minimum power is crucial. In particular, reducing the power consumption of the RF transceiver, which consumes more power than the other components in a sensor node, would alleviate this problem [67; 127]. Moreover, this issue can be addressed in two steps. The first is to propose an intelligent energy-efficient algorithm. The second step can be performed by utilizing available energy-harvesting techniques, such as solar cells, vibration, and WPT. 2. _Communication range_: WSNs suffer from the effect of harsh ecological conditions because of the wide range of open agricultural surroundings [5]. The WSN protocol contains mechanisms to resist the effect of data transmission failures in the network, which increase due to ecological effects. In agricultural applications, most wireless sensor technologies support a relatively short communication range. Therefore, many sensor and router nodes need to be diffused in a WSN. In the point-to-point Zigbee network, the communication distance can reach 100 m in outdoor environments. The ZigBee communication range can be extended by adopting multi-tire, ad-hoc, decentralized, and mesh network topologies. Drones or UAV also can be used as a mobile router node to extend the communication range within a farm field. A drone could pass the collected data from the sensor nodes to the master node through multi-hop. However, using drones entails other challenges and limitations. 3. _Propagation losses_: In agricultural applications, WSNs must be able to work in diverse surroundings, such as ground, bare land, orchards, greenhouses, farms, and complex topography; they must also be able to operate in all climate conditions. All these conditions influence the performance of radio propagation. Whether the topography is simple or complicated, the communication possibility between the points in a WSN still suffers from serious challenges. The signal transmitted from the sensor nodes in agricultural applications need to pass through a heavy crop canopy to arrive to at the receiver nodes, which cannot ensure a sufficient clearance area and will cause signal propagation absorption, reflection, attenuation, and scattering. In this case, the link quality is degraded, especially when the signal spreads through dense crops. Therefore, when deploying WSNs, communication link quality and temporal and spatial variables must be guaranteed. The communication performance of WSNs is related to the working surroundings. Therefore, due to the limited resources and power budget of WSNs, an accurate wireless channel path loss model must be adopted to reflect the propagation features. This model is expected to demonstrate correct optimization and network evaluation performance throughout the deployment design process to develop the energy efficiency of the nodes [15], improve the target detection and localization applications [16], decrease the number of retransmission, and ensure Quality of Service (QoS) of the network [175]. 4.