Wireless Sensor Network

What is it? 

A wireless sensor network, or WSN, is a group of transducers, i.e., electronic devices that convert energy from one form to another. These transducers have communications infrastructure that allows them to track and record conditions at various locations. 

The conditions monitored by wireless sensors include the following: 

• temperature 
• humidity 
• pressure 
• wind direction 
• wind speed 
• illumination intensity 
• vibration intensity 
• sound intensity 
• power-line voltage 
• chemical concentrations 
• pollutant levels 
• vital body functions 

Types 

• Terrestrial WSNs (used on land to monitor an area’s environmental conditions) 
• Underground WSNs (focusing on utilization of sensors below the ground surface) 
• Underwater WSNs (designed to operate within the limits of aquatic ecosystems) 
• Multimedia WSNs (capable of tracking and monitoring events in multimedia form) 
• Mobile WSNs (comprised of mobile sensor nodes connected wirelessly) 

Classification 

• Stationary (with static sensor nodes) and mobile WSNs 
• Deterministic WSNs (with calculable and fixable sensor node location) 
• Nondeterministic WSNs (with undeterminable node arrangement) 
• Single-base-station and multi-base-station WSNs 
• Static-base-station and mobile-base-station WSNs 
• Single-hop WSNs (where nodes link directly to the base station) 
• Multi-hop WSNs (where intermediary nodes are involved) 
• Self-reconfigurable WSNs (where sensors collaboratively organize the network) 
• Non-self-reconfigurable WSNs (where network arrangement is up to the control unit) 
• Homogeneous WSNs (where all nodes maintain the same energy utilization) 
• Heterogeneous WSNs (where some nodes have higher energy necessities) 

How does it work? 

The structure of a wireless sensor network includes portable detection stations referred to as sensor nodes. Each sensor node is outfitted with a transducer, microcomputer, transceiver, and power source. 

The transducer produces electrical signals grounded on sensed physical phenomena. The purpose of the microcomputer is to process and store the sensor output. It gets this data from the transceiver, which receives commands from the central computer. A battery serves as the power source for each sensor node. 

Where is it used? 

The following are some applications of wireless sensor networks: 

• forest fire detection 
• animal tracking 
• flood forecasting 
• weather prediction 
• seismic event projection 
• military applications 
• patient monitoring 
• dynamic routing management 
• monitoring of parking lots 
• traffic surveillance 
• rapid emergency response 
• supervision of industrial processes 
• automated building climate control 
• ecosystem and habitat observation 

Challenges 

Routing 

The first difficulty associated with WSN routing is the complexity in the assignment of a universal identifiers system for sensor nodes with high quantity. For that reason, wireless sensor nodes cannot use protocols based on classical IP. 

The next question is the need to transmit data from various sources to the base station. Third, the data being generated is marked by redundancy because several sensing nodes may create similar data. It necessitates redundancy management through routing protocols, bandwidth, and energy. 

Wireless nodes are also limited in bandwidth, transmission energy relations, storage, capacity, and energy.  

Design 

Here are major design-related challenges to be considered by the network engineer: energy efficiency, sensor location, complexity, data transmission as well as its models, scalability, strength, delay, low latency, coverage problems, and transmission media. 

Fault performance 

When power loss causes an interruption in the functioning of sensor nodes, physical damage is likely to happen. Therefore, it is necessary to facilitate fault tolerance, i.e., help the sensor network withstand failures of sensor nodes and operate further. 

Scalability 

Nodes used in the detecting area may reach hundreds and even thousands in number. Consequently, routing schemes should possess enough scalability to respond to events effectively.  

Production cost 

The price of each sensor’s node should be kept low. As a sensor network comprises a number of nodes, the price of every single one heavily affects overall network cost. 

Topology issues 

WSN topology faces challenges such as sensor holes (amounts of area that are not covered by any living sensor), geographic routing (when the destination of a message is specified in terms of coordinates, not the network address), and coverage topology. 

Limitations 

Considering the restrictions of wireless sensor networks, they have little storage capacity (a few hundred kilobytes), modest processing power of 8MHz, short communication range together with much power consumed, minimum energy required and thus constrained protocols, batteries with finite lifetime, and not much energy provided by passive devices.