Components of a Sensor Node
A wireless sensor network is made up of sensor nodes. Sensor nodes comprise four basic components which are the power unit, the sensing unit, the processing unit, and the transceiver unit.
The sensing unit is made up of data converters and sensors, once an analogue variable; like sound, is sensed, analogue to digital converters (aka ADCs) convert the signal to digital format before it is passed into the processing unit. The processing unit is usually a microcontroller which computes the data fed into it and passes the processed data to a transceiver.
The processing unit also manages the radio network protocols of the system. As for the power unit, it is made up of batteries that delivers power for the sensor node to operate. Additional components of a sensor node include USB connectors, embedded antennas, and oscillators.
An illustration featuring a typical connection of wireless sensor network nodes and hardware. Image Credit: The University of Rhode Island.
Network Topologies of Wireless Sensor Networks
The network topologies of wireless sensor networks describe the way sensor nodes are connected to how they communicate with one another. We breakdown the various types of network topologies in the following sections.
Star Network Topology
A star network topology consists of sensor nodes that send and receive data from a common base station. The sensor nodes do not communicate with one another. In this network topology, latency in communication is reduced between the sensor nodes and the base stations.
Also, power consumption is minimal. It is important that the base station is in close proximity to the sensor nodes for communication to be within radio transmission range.
Mesh Network Topology
Unlike the star network topology, mesh network topology allows sensor nodes within the radio transmission range to communicate with one another. The power consumption in this network topology is high. There can also be a high latency in communication between sensor nodes and base stations.
An advantage of using mesh network topology is that, if a sensor node wants to send a message to another node out of communication range, an intermediate remote node can be utilised to forward the message to the desired node.
Hybrid Network Topology
This network topology comprises the configuration of the star topology and the mesh topology in a single wireless sensor network. The hybrid topology provides faster communication between sensor nodes and base stations. The power consumed can be minimized by preventing low power sensor nodes from sending messages.
A close-up view on FireFly sensor nodes for utility monitoring and voice communication applications. Image Credit: Carnegie Mellon University.
Design Challenges in Wireless Sensor Networks
Engineers face a lot of challenges when designing and deploying wireless sensor networks. Sensor nodes failure can occur when they are deployed in dangerous environments or when they are physically damaged. This problem can lead to the loss of message transmission between remote sensor nodes and base stations.
Battery sizing to power up the sensor networks is another challenge faced by engineers. The size of the nodes and other operational processes in the network determine the size of the battery to be used in the design. Engineers must carefully choose the perfect battery size that will make the system operate for the application it is used for.
The earlier-discussed network topologies affect the way the entire network operates. They determine the energy consumption of the network, computation power, communication capabilities, and so on. Engineers must choose the right network topology to design an efficient wireless sensor network.
Power Consumption and Hardware Communication
Some wireless sensor networks applications involve the use of additional hardware in the design to improve functionality. This can lead to the high cost of deploying the design, and in some cases, the low power requirement for a power-efficient design will not be met when the additional hardware consumes lots of power.
In addition, communication between nodes can be achieved by using ISM bands, optical, and infrared medium, depending on the intended application. Choosing the wrong message transmission media for communication can make the whole network malfunction.
Other challenges faced by engineers when deploying wireless sensor networks include quality of service, scalability, and security issues.
Applications of Wireless Sensor Networks
Wireless sensor network has a wide range of monitoring and sensing applications in different sectors. It is used in the military for surveillance. In medicals, deploying sensor help doctors track and monitor patients remotely. In the agriculture industry, an autonomous irrigation system using moisture and humidity sensors can be developed on farms.
A wireless sensor network is also used to develop systems that can determine the weather conditions of the environment. In this system, analysis can be made to predict future weather conditions.