What Are Wireless Sensors And Why Are They Useful?

The Internet of Things (IoT) is transforming our
world in tremendous ways.

By enabling everyday objects to communicate
wirelessly, we can automate data exchange and create new efficiencies that
positively impact lives and organizations.

Underlying the IoT is wireless sensor technology,
which allows us to collect information about surrounding environments over
extended periods with little manual effort. Wireless sensors can be configured
to measure a variety of variables, from air temperature to vibration. Overall,
there are many different types of wireless sensors available in the
marketplace.

Many wireless networks contain hundreds,
sometimes thousands, of wireless sensors. Already, these devices are used
across a wide range of sectors, including retail, agriculture, urban planning,
security, and supply chain management.

In this article, we dive deeper into how wireless
sensors work and explain why they are so important for the IoT revolution.

Wireless sensors gather data about local
conditions and share findings with other powerful components or platforms for
further processing. Sensors are typically distributed across large geographic
areas and programmed to communicate with central hubs, gateways, and servers.

One major advantage of wireless sensors is that
they require a low level of maintenance and small amount of power to function.
Sensors can support IoT applications for years before needing a battery change
or charge.

When it comes to building wireless networks, one
of the biggest questions developers face is how to arrange wireless sensors in
the field. Sensors, or “nodes,” must be distributed in such a way that supports
the overarching objective of the network developer.

The two most common arrangements for wireless
sensors are the star and mesh topologies.

The “mesh” topology describes networks in which
sensors connect to as many other nearby nodes as possible. As a result, data
can “hop” from one node to the next without having to follow certain routes or
sensor hierarchies. As a result, connectivity issues are less harmful to
network performance as data can take multiple paths to reach processing
components. Mesh topologies are also easy to expand as new sensors need only to
connect to existing nodes.

On the downside, mesh topologies are costly and
can be difficult to maintain. There are so many connections to create and
manage, which becomes more challenging as networks grow.

The “star” topology describes networks in which
every sensor connects directly to a central gateway or hub. These hubs take
sensor information and transmit it to other applications for processing. In
these arrangements, nodes do not communicate directly with each other.

Compared to mesh networks, star-shaped networks
are more cost-effective as fewer connections are required. However, it is
harder to expand networks as any new sensors must connect central hubs, which
have capacity limitations.

There are several wireless standards available
that can support sensor networks.

Until recently, cellular technology was the most
commonly used option for wide-area network (WAN) connectivity. However,
cellular technology is expensive and consumes significant energy, which is not
well suited for long-range, low-power devices, like wireless sensors.

Outside of cellular technology, WiFi, Bluetooth
Low Energy (BLE), and Zigbee, can also support wireless sensor networks. These
standards also fall under the “traditional wireless solution” category but have
unique advantages and disadvantages.

However, WiFi signals have difficulty penetrating
walls, which is a disadvantage for long-range applications. Additionally, WiFi
networks are managed by local routers that may not always have direct user
interfaces for updating sensor keys.

BLE is a low-power protocol that is distinct from
traditional Bluetooth technology. BLE uses the 2.4GHz frequency band to
transmit small amounts of information. The wireless standard is less costly to
use than WiFi; however, the same problems exist when it comes to sending data
through walls or over long distances. In addition, BLE is susceptible to signal
interference as many other devices and standards use the 2.4GHz frequency band.

Zigbee is a wireless standard that relies on mesh
networking to support large numbers of nodes (>65k) within a single network.
Zigbee is best for wireless sensor networks that do not require much bandwidth.

One disadvantage of Zigbee is that some sensors
must always be on in order to share information for processing. As a result,
Zigbee consumes more total energy than today’s leading standards.

Although traditional wireless standards are
effective, a new class has emerged that is much more effective for wireless
sensor networks. Low-power wide-area networks (LPWANs) are growing as the go-to
technology for long-range data transmission. LPWANs can support billions of
sensors and will be used heavily for IoT applications.

LPWANs offer several advantages over traditional
standards. First, they consume less power from devices because they transmit
information at a much lower bit rate. Sensors can survive several years on
LPWANs on a single battery charge. LPWANs can also support sensors over vast
geographic areas as data can be transmitted over long distances.

There are several downsides to using LPWANs.
LPWANs are not well suited for applications involving large data packets.
Sensor networks that need to transfer more data should use higher capacity
cellular or short-range, WiFi, BLE, and Zigbee networks. Additionally, LPWANs
use unlicensed radio frequencies, which can be harder to manage from an
interference standpoint.

Also Read: What is 4G & How did We Get There?

The three primary LPWANs for wireless sensors are
LoRa, SigFox, and NB-IoT.

LoRa (“long range”) is a widely accepted standard
that uses a chirp spread spectrum modulation scheme to transmit data over very
long distances. LoRa is the foundation for LoRaWAN, a publicly available layer
specification that connects wireless sensors through gateways or LoRaWAN
network providers. LoRaWAN has a higher bandwidth than Sigfox and can transmit
data packets more effectively through noisier environments.

With LoRaWAN, data is sent over encrypted
messages between gateways and network servers. Servers authenticate and decrypt
data that is ultimately sent to end applications. Users can send messages
directly to wireless sensors through LoRaWAN to reconfigure devices.

LoRaWAN sensors are classified into three groups
based on the ability of the sensor to send and receive messages. Class A
devices remain in sleep mode until they have something to transmit. These
sensors can send uplink messages at any time, which makes them especially
useful in wireless sensor and actuator networks (WSAN).

Class B sensors have scheduled windows for
devices to receive downlink messages from servers. Class C devices maintain an
open receive window for messages unless they need to transmit information.
Consequently, C sensors enable low-latency communication but consume more energy
than the other classes of sensors.

With all of these LoRaWAN sensor types, network
developers must have proper gateway hardware to receive data and pass
information along to servers.

SigFox connects wireless sensors directly to base
stations using ultra narrowband transmissions. The standard has coverage in
more than 55 countries and can support more than 100 channels per sub-band in
the U.S. at 600 bps. However, data packets are limited to 12 bytes, and the
standard does not allow message acks. SigFox users pay per device and by the
number of uplink and downlink messages sent per day.

NB-IoT uses existing cell tower infrastructure to
provide expansive coverage for low-power devices. The standard uses guard bands
for narrow channels to avoid interference and can penetrate indoor environments
well. In 2018, T-Mobile added NB-IoT coverage through its 4G network.

There are several critical characteristics of
well-designed wireless sensor networks.

First, nodes should be easy to locate within a
network. Sensor maintenance, such as replacing batteries and updating
components, is much easier when developers know where to find all of their devices.

Second, sensor networks should be able to
withstand node failures without widespread disruption. Topology plays a big
role in how networks handle connectivity issues. Those deploying wireless
sensor networks must choose topologies that can withstand component failures.

Third, networks should be easy to scale.
Developers must be able to grow their wireless sensor networks efficiently
without having to invest significant capital to expand.

Finally, it is important to consider power
consumption when designing a network. The wireless sensors used should align
with the data demands of the IoT application. Otherwise, network managers risk
spending significant time and capital on ongoing maintenance and replacement.

The security sector has embraced wireless sensor
technology in many ways. With wireless sensors, organizations can monitor their
premises, identify suspicious activity, and track valuable assets. Banks can
turn wireless push buttons into panic buttons for employees and retailers can
install wireless window sensors on every building access point. Homeowners can
also use wireless air sensors to detect harmful gases in the air, such as
carbon monoxide.

On the utilities management front, wireless
sensors help automate communication between critical systems and mitigate
future problems. For example, water leak sensors can be mounted on walls to
detect plumbing failures or pipes that may burst in the winter. Wireless rope
sensors are being used in server rooms and data centers to detect the presence
of water near computer hardware.

Wireless sensors are also supporting disaster
management efforts. In Texas, wireless sensors are being installed on bridges
that can detect water levels above a certain threshold, thus indicating potential
flash flooding in the area. Wireless vibration sensors are being in industrial
plants with large machinery to predict equipment failures before they occur.

In healthcare, wireless sensors are helping care
teams monitor patients in real time. Wireless push buttons are serving as PERS
devices in senior care facilities. Humidity sensors are helping hospital
facility managers maintain healthy environmental conditions for patients.

Retailers and grocery stores are using wireless
sensors on the floor to help employees create positive experiences for
customers. Wireless push sensors are being installed in restrooms so that
shoppers can indicate when cleaning is needed. Wireless air temperature devices
are helping superstores monitor refrigerators and non-cold merchandise
simultaneously.

These are just a few examples of how wireless
sensor networks are creating new efficiencies and impacting lives in positive
ways. As the IoT space continues to grow, expect to see more innovative sensor
applications that transform modern industries forever.