Governments in the world are faced with the task of ensuring safety of their citizens. Consequently, they have prioritized border security to control entry and exit of terrorist, illegal migrants, drug lords and drug dealers. Several mechanisms have been put forward to aid in ensuring birder security. Such include construction of physical fences, physical patrol on the border and many other techniques. Despite the use of such techniques, they have numerous shortcomings, hence not effective in controlling the border. To complement the shortfall, technology is being harnessed to ensure the border is secured top prevent entry and exit of the illegal migrants, terrorist and the drug lords. In this regard, wireless sensing technology has been embraced. The use of wireless sensor networks creates virtual fence that extends the working capability of border patrol. This technology relies on sensor nodes to collect data to a central processing area where it is analysed. This paper focuses on the working mechanisms of sensor nodes, there benefits and their shortcomings.
The traditional border control techniques are inefficient in detecting intruders. The use of surveillance technologies not only makes border control and patrol efficient but it also ensures high accuracy and minimizing of human support. There are multiple surveillance technologies used to monitor the border. In spite of this, the technologies are used together to complement each other. The most important surveillance technology used in monitoring and controlling the border is the use of wireless sensor networks.
By definition, a wireless sensor network is a network made of various sensor devices interconnected in an ad-hoc mode with an aim of sensing physical phenomena like temperature, movement etc (Karl & Willig, 2007). Basically, a wireless sensor network’s functions is to facilitate information exchange between the sensor nodes and an application platform (Alkhathami & Alazzawi, 2015). The information exchange takes places wirelessly. A wireless sensor network is made up of various components. Such components include a gateway, relay nodes, leaf nodes sensor/actuator nodes. This paper will explore the sensor/actuator node component (Alkhathami & Alazzawi, 2015).
Types of Sensor Nodes
A sensor node can be defined as a component in a network of sensors that that collects data about the surrounding environment and then sends the data for processing via a network. There are various types of sensor nodes (Iyengar & Brooks, 2012). The categories of the sensor nodes are based on there working mechanism (Raghavendra, Sivalingam, & Znati, 2006). The various kinds of sensor nodes commonly used in intrusion detection are: infrared (Thermal) sensor nodes, accelerometer (seismic) sensor nodes and ultrasound sensor nodes (Elkateeb, Alkhathami, & Alazzawi, 2015). Below is a description of each type of sensor and its working mechanisms.
Infrared (thermal) Senor Nodes
An infrared sensor, common referred to as Passive Infrared sensor, detects motion by measuring the light radiating from object that are within the vicinity of the field of view. The functions of this type of sensors does not need generation or radiation of energy, hence referred to as passive sensor (Emary & Ramakrishnan, 2013). The working mechanisms of such sensors to detect movement is such that it “learns” the ambient temperature of the environment and then, when there is movement, detects the temperature change due the objects presence. The use of such sensors has benefits of lower installations costs, and furthermore, it is not affected by change in illumination (Sun, Wang, & Vuran, 2011). The main disadvantage of such sensors while in use in border control systems is it’s because it can be triggered by such things as moving animals hence giving false information. Furthermore, the such a sensor has inability to detect stationery people/objects (Edgar & Callaway, 2003).
Ultrasound Sensor Nodes
This is an active sensor node. It works by emitting ultrasonic sound energy into an area under surveillance. The sensor detects motion by reacting to the change in the pattern of the reflected energy (Emary & Ramakrishnan, 2013). The working principle of this device is based on the on frequency shift technique in the reflected energy to detect motion. The ultrasonic device is equipped with mechanism that transmit ultrasonic sound. The emitted ultrasonic sound uses air as its transmission medium and travels in a wave like manner. The transmitted wave is reflected and the device is able to “hear” the characteristics of the transmitted energy (Raghavendra, Sivalingam, & Znati, 2006).
Accelerometer (Seismic) Sensor Nodes
This are sensor nodes that produce a signal basing on the vibration, acceleration and shock of a body. Basically, accelerometers are used in border control system to determine the position of a body, its speed, its orientation and shock (Emary & Ramakrishnan, 2013).
Sensor node architecture
As earlier connoted, a sensor note is mandated to collect data and send it via a network for processing. Consequently, a sensor node has various components. These components include sensors, memory, processors, GPS, radio transceiver, and a power source the immediate previous section has described some of the sensors (Dargie & Poellabauer, 2010). The processing units of a sensor node is mandated to process and disseminate data (Sharma, Kumar, & Kishore, 2013). The various components of a sensor node are as illustrated in the figure below;
Deployment of Sensor Nodes
In the deployment of the sensor nodes, it is important to consider network topology. Topologies are vital since they aid in minimizing constraints, such as latency, limited energy and computational resources. There are various topologies used in deploy net of sensor nodes within a wireless sensor network. Such topologies include Star topology, mesh topology, and tree topology. However, each of the mentioned topologies have benefits and shortcomings.
The selection of a given topology is dependent on various factor such as self-organization and scalability, energy efficiency, and reliability. Thus, to utilize the benefits of the various network topologies, a hybrid network topology is usually preferred in deploying sensor nodes.
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