# Energy-Efficient Wireless Sensor Networks for Precision Agriculture: A Review
## 2 Wireless Communication Technologies for Agriculture
### Performance Comparison of Wireless Communication Protocols  
Table 1 compares the aforementioned wireless communication protocols or technologies relative to different parameters, including power consumption, communication range, data rate, cost, system  
complexity, and other parameters. The challenges in agricultural applications may be developed from the selection of the deployment range. For instance, the transmitted signal by the sensor node is attenuated when the agriculture field is separated by obstacles. Power consumption is considered as another limitation in the WSN design in agricultural applications [5]. The ZigBee wireless protocol was designed to run with a suitable communication range and low power consumption. LoRa and SigFox are considered to work with low power consumption and long radio range. Accordingly, the power consumption and communication distance of the above technologies have been assessed as follows. Zigbee and Bluetooth low energy (BLE) are designed for battery-powered devices. These technologies conserve power through low duty cycling and enter sleep mode to extend the battery lifetime. Classic BT, WiFi, GPRS, LoRa, and SigFox have a higher power consumption than ZigBee. Although ZigBee has a shorter communication range than LoRa, SigFox, and GPRS, this range may be extended with a router node to overcome the node deployment limitations in agricultural applications. BLE outperforms ZigBee in terms of power consumption, but this wireless protocol is limited in agricultural applications because of its short communication distance of 10 m, as reported in [48]. ZigBee also has a higher network elasticity than BT, thereby permitting various topologies. Given the large number of nodes (more than 65,000) in the ZigBee network, the ZigBee technology can be used to cover a wide agricultural. Accordingly, the ZigBee wireless protocol has been adopted in many agriculture studies [5; 49; 50; 51; 52; 53]. One of these studies [5] prefers to utilize ZigBee in farming domains and agricultural applications owing to its energy-efficient, reliable, and low-cost wireless protocol. The LoRa wireless protocol covers a large communication area with low power consumption. Therefore, it can be suitably deployed in vast agricultural fields. The network size of the LoRa protocol is limited by its duty cycle, where a 1% duty cycle can lead to a maximum communication time of 36 s per hour for each end device [54]. In addition, LoRa gateways have a limited message capacity of less than 100 messages per minute because of the unplanned deployment of LoRa gateways in urban areas, thereby interfering with low power wireless area networks, such as SigFox. Therefore, increasing the number of gateways can challenge the infrastructure of the LoRa network [54]. Moreover, the LoRa technology is complex and has sizable hardware implementations [55]. SigFox has an extremely low data rate (100 bps) and slow transmission time (10 s for 10 bytes) compared with ZigBee and LoRa [56]. SigFox supports star topology supervised by a centralized sever that manages connectivity between devices and the base stations, whereas the LoRa supports wide area network based on star-to-star topology creating a bridge of LoRa gateways. Given that data rate and transmission time are both critical issue in any communication system, SigFox cannot be widely used for agricultural applications. Moreover, this technology does not support the collision avoidance scheme, thereby affecting the network because several M2M devices may be operated in the same area. Moreover, SigFox has a limited reliability because of its one-way communication (without an acknowledgment signal) and low received power. However, both the LoRa and SigFox infrastructures are still in progress. [PERSON] et al. further discuss the limitations of these protocols [56].