# Energy-Efficient Wireless Sensor Networks for Precision Agriculture: A Review
## 5 Challenges and Limitations
_Routing_: Different problems can emerge due to packet collision and limited bandwidth, which are introduced by channel propagation, and so on. Therefore, when a WSN is deployed in a wide area in farm fields, multi-hop is required. [PERSON] et al. [3] developed an independent mobile robot platform based on a mobility task for surveillance to overcome channel interference. * _Localization and tracking_: Tracking and localization of a herd of cattle are considered smart farm applications based on WSNs. For example, a WSN can be employed to track and localize of dairy cows to enable herd management. ZigBee wireless protocol is used to monitor animal locations and behaviors, such as walking and standing, lying down, and grazing [16; 18]. In this context, several considerations, such as radio interference, animal situation, and mobility, changes in WSN topology, penetration depth of the signal through the animal body, height of the collar, and access point antennas, need to be taken into account [176]. These considerations pose challenges in the localization and tracking of the animals. * _Reliability_: Agricultural monitoring systems based on different environmental sensors can also be used to monitor pollution aside from climate conditions. Important information on climate conditions is reported to related agencies and farmers from a remote location for advance investigations. Dangerous information needs to be dealt with immediately in an emergency, which means that data transmission in WSNs should demonstrate high reliability [3]. * _Scalability_: In agricultural applications, the construction of WSN-based fault-tolerant and robust hierarchical architectures requires large-scale deployment relative to single-level network architectures. A hierarchical architecture can be scaled up for developing applications by duplicating to several fields. In this context, to increase the number of WSNs over a vast area, multiple wireless router nodes are placed in an agricultural field to guarantee sustained operation. * _Cost_: The total hardware and software costs of sensor nodes are important. The design of sensor nodes for any agricultural application level must involve a low cost while demonstrating a robust performance; moreover, the design needs to be available for use by poor country markets [5]. This challenge can be overcome by reducing software and hardware costs further. * _Real time_: Most crops are vulnerable to climate conditions, such as humidity, intensity of illumination, and temperature. This vulnerability is a burden to farmers who monitor changes in climate conditions hourly and/or daily because doing so is labor-intensive. Moreover, in greenhouses, a fire can occur and lead to severe agricultural disasters. This evidence suggests that the monitoring of the ecological conditions of agricultural WSNs needs to be in real time. Real-time monitoring will enhance yield production and plant growth and avoid dangerous disasters in farms [3]. * _Storage and recording of data_: Large amounts of data are recorded from agriculture observing systems because several WSNs in agricultural applications contain several sensors for crop growth analysis and harvesting estimation. This condition requires the base station to monitor changes in farm fields by analyzing patterns. The base station must thus be supported by a high storage capacity. * _Security_: Security and protection are important issues in agricultural products. Protection from insects or attacks of rodents in grain stores or fields is essential. Such a challenge must be considered to maintain the security level of agriculture. Protection and security can be achieved based on real-time analysis and processing of agricultural information without human intrusion [159]. * _Delay tolerance_: Critical delay poses a challenge to agricultural applications.