# Multi-Hop Routing Protocols for Oil Pipeline Leak Detection Systems
## 1 Introduction
### Wireless Communication for Linear-Based Topology Applications  
In this subsection, we present Linear Wireless Sensor Networks (LSNs) and their application. The linear topologies assume fixed infrastructures, which means the gateways and sensors have fixed arrangements. Problems could include network coverage, lifetime, and routing, but mobility may not be an issue. In the pipeline network, the nodes are arranged along a straight line [5] LSNs have many applications, such as pipeline leak detection [4], road monitoring [6], and tunnel monitoring [7]. In [6], the road monitoring system is used for post-disaster road monitoring and demonstrates high reliability. For monitoring, the authors considered seismic motion sensors, sound sensors, and images. Furthermore, [7] proposed a tunnel monitoring system using a cluster-based routing (PUAR) for providing a low-energy monitoring system. WSN technologies enable network communication and allow devices to share and transport data inside the network [4]. Related standards specify the formats for sharing data, routing, etc. Based on the radio spectrum usage, WSN networks may use either licensed or unlicensed bands which correspond to specific standards [8]. The licensed technology operates on dedicated lower frequency bands, covers a wide area, and consumes high power. The cellular networks are examples of the most popular licensed technology. In comparison, unlicensed technologies use a shared frequency band that is available for various systems and usage scenarios. Such technologies also use higher frequency bands and require less power than a licensed spectrum. Some of the technologies used in unlicensed spectrums are Wi-Fi, Bluetooth, Zigbee, and LoRa [8]. As discussed previously, pipelines run through Saudi Arabia from the east to the west. In populated places, the cellular network can be used, whereas unlicensed wireless communication technologies can be used in unpopulated areas. In our research, we focus on unlicensed wireless communication technologies. In the following, a brief description of these technologies is given. * RFID and NFC  
The Radio Frequency Identifications (RFID) network consists of two types of device readers and tags. The reading device (reader) knows the tags' locations and tracks the tags during the communication. The radiofrequency transponder (RF tag) is embedded inside objects such as animals or goods. The passive tags cover ranges up to 1 m, whereas the active tags extend to 200 m [9]. The network consumes low power and transmits a small block of data [9]. Near Field Communication (NFC) is short-range communication and secure [10]. NFC is similar to the RFID network; however, there are some differences. RFID range is up to 200 m whereas NFC is 1 m. The spectrum bands used in RFID are unlicensed. On the other hand, NFC uses both licensed and unlicensed bands [10]. * Bluetooth  
Bluetooth transmits data over a shortrange with low power and works on a 2.4 frequency band. It is the IEEE 802.15.1 standard. The range of communication is between 10 m and 100 m. The data rate is 24 Mbps [11]. Bluetooth Low Energy (BLE) is the fourth version of Bluetooth designed for short-range, low-power applications. It is significant in the IoT domain for many reasons, such as low power, low cost, and low latency. BLE uses the same Bluetooth topology but adds a separate channel between the master and each device [11]. BLE enhanced power consumption and star topology are supported by a massive number of devices [12]. Bluetooth and BLE are used in wireless control systems and communication between mobile devices [12]. Some examples of this application are the communication between the phone and wireless headset and controlling car systems. * Zigbee  
Zigbee is widely used on the Internet of Things (IoT) because of its low power, low data rate, and large range. These characteristics are very useful in many applications. Additionally, it is designed for a personal, low-power network. The topology can be a star, mesh, or tree.