**1. Introduction**

A wireless sensor network (WSN) is a network that entails distributed tiny sensor nodes which might be supposed to screen bodily or environmental conditions and communicate with every different and alternate facts and information. Due to their small size, sensor nodes have limited computational power and energy resources. Additionally, the environment wherein they are placed varies dramatically over time. It is essentially critical to analyse sensor data as soon as it is collected. Sensor node data that has not been processed for a long duration is assumed as incomplete and inaccurate. Since WSNs are usually dynamic in nature, their topologies will frequently change. As a result of the connection loss, the network needs to add a new node. The future scope of WSN technology is bright across a wide range of application areas. In this Chapter; we list a few of the most useful ones and also how the different machine learning (ML) techniques are used in deploying the various sensor networks. However there are various other issues when it comes to these networks. The ML algorithms have been proven excellent in resolving issues particularly functional or operational issues, for example: clustering, processing of query, aggregation of data, localization, etc. While some algorithms focus on non-functional and non-operational issues like

quality and efficiency of sensors, quality-of-service (QoS), security and integrity of data, etc. There are also several practical explanations that maximise resource utilisation and extend the life of the network. This chapter is prearranged as follows: Section 1 covers all the basics of WSNs along with applications issues and need of ML techniques. Section 2 presents taxonomy of machine learning algorithms and their details. Finally Section 3 concludes the chapter.

#### **1.1 Overview**

A sensor is a very small gadget that is used to capture data about a physical process or phenomenon and convert it into electrical signals that can be processed, monitored, and analysed further to get the purposeful information. Any type of information from the real environment, including temperature, pressure, light, sound, motion, position, flow, humidity, and radiation, could be referred to as a physical process.

In order to record, observe, and respond to an event or a phenomenon, a structure made up of sensors, processing units, and communication components are known as a sensor network. The controlling or observing body may be a consumer application, a government agency, a civil organisation, a military force, or an industrial entity, and the event may be connected to anything, including the physical world, an industrial environment, a biological system, or an IT (information technology) framework. Such sensor networks can be used for data collecting, surveillance, monitoring, medical telemetry, and remote sensing, etc. Sensors with a controller (base station), and a communication system make up a typical sensor network [1]. **Figure 1** illustrates what is known as a Wireless Sensor Network (WSN) when the connectivity in a sensor network is established utilising a wireless protocol.

#### **1.2 Elements of WSN**

There are two basic elements of WSN:

a. **Sensor node**: A Wireless Sensor Network (WSN) [2] consists of sensor nodes that are deployed in close proximity and frequently on massive scales, and it supports sensing, statistical processing, embedded computing and connectivity. WSNs are innately aid constraints and are chargeable for self-organising the

suitable community infrastructure frequently with multi-hop communication with them. It consists of four basic components:


The sensor node collects the analogue statistics from the consumer, and analogueto-digital convertor (ADC) converts the records into the digital shape. The processing unit is the primary unit, it consists of a storage unit and a microcontroller/microprocessor, which primarily do the information processing and manipulation. It also consists of various other features like network analysis, data correlation and fusion of data from another sensor with its own. The communication system consists of any kind of system that is typically a short-range radio for data transmission and reception (**Figure 2**) [1].

a. **Network architecture**: When a massive number of sensor nodes are deployed in a large region to cooperatively screen the physical surroundings, the network of these sensor nodes is equally important. A sensor node in a WSN no longer only communicates with other sensor nodes, however, also with a Base Station (BS) using wireless communication. The base station sends instructions to the sensor nodes, and the sensor nodes perform the task by collaborating with each other. After gathering all the necessary information, the sensor nodes send the

**Figure 2.** *Structure of a sensor node.*

**Figure 3.** *Subcategories of Military applications of WSN.*

data back to the base station. After receiving the records from the sensor nodes, a base station performs processing of records and sends the updated data to the person using internet.
