## 1 Introduction  
Wireless sensor network (WSNs) are one of the sensor and communication technologies that are rapidly expanding and gaining popularity among users and researchers. Since they are regarded as an essential basic component of the Internet of Things (IoT) [1, 2], WSNs with the IoT can be used in many smart scenarios and applications. WSNs refer to a group of sensor nodes, and they are linked by wireless connections. Generally, the sensor node is composed of four major units: the processing unit, the sensing unit, the communication unit, and the power supply unit. The sensor node, which serves as the source node, collects interesting data from the environment, such as temperature, vibration, water level, images, and so on. Such sensing data are then sent to a sink node, which is the monitoring or control center. Due to the short-range communication characteristic, the radio range of a single node cannot fully cover the test area. Therefore, multi-hop communications are then applied, where each node forwards data to the destination via other relay nodes in the network. In order to achieve successful data delivery in multi-hop networks, appropriate sensor node deployment and efficient wireless communication are required. Since the use of multi-hop WSNs is increasing significantly, they are applied for a variety of purposes, including environmental monitoring, disaster management, military operations,flora and fauna [3], transportation, healthcare, home automation, industrial applications, smart cities, protection and surveillance, object tracking, farming and agriculture, etc. For environmental monitoring applications, many communication technologies, such as the global positioning system (GPS), 4/5G, unmanned aerial vehicles (UAVs), Lora, narrow band (NB)-IoT, and ZigBee, have been applied. Each technology has its advantages and shortcomings. For this work, ZigBee technology is used for this application. The ZigBee IEEE 802.15.4 standard was developed to satisfy the requirements for simple, low-power, and low-cost wireless communications. It operates in the 2.4 GHz ISM band, making the technology simple to use and accessible worldwide. Because the IEEE 802.15.4 protocol focuses on low-power-consumption, low-cost, and low-data-rate wireless networking, it is suited for WSNs. The involvement of low-power wireless communications is an appropriate choice in WSNs aimed at long-term monitoring. Because this work focuses on the actual testing of a multi-hop wireless network in outdoor situations, a review of related works to this issue is discussed here. A summary is also provided in Table 1. [PERSON] et al. [4] demonstrated the development of a multi-hop network for agricultural field surveillance. Twenty-four TeloSB motes with CC2420 transceivers, the IEEE 802.15.4 standard, were implemented, and soil temperature, soil moisture, atmospheric temperature, and relative humidity were included. The authors evaluated RSSI levels, the number of packets sent, packet losses, battery voltage, and residual capacity. The authors found that the wireless connections in the agricultural areas were quite stable, where the system could collect sensor data while saving energy consumption.