Wireless Sensor Network

What Are Wireless Sensor Networks?

Wireless Sensor Networks (WSNs) are adaptable monitoring networks that track, log, and relay multipoint digital data readings to other devices. WSNs vastly improve the quality, depth, and scope of local data capture, often eliminating the need for extensive data wiring and routine manual checks at dangerous, distant, or inaccessible points. It is therefore used to monitor systems and physical or environmental conditions.

How Does a Wireless Sensor Network Work?

A WSN consists of electronic, digital sensors known as nodes. Once installed, a linked grid of nodes will capture and transmit time-stamped readings or imagery to nearby, forwarding routers. A gateway (or base) computer equipped with special software receives, interprets, curates, and displays the incoming data stream.

What Data Types Can WSNs Capture and Collect?

Wireless Sensor Network nodes are versatile. Changeable, customisable sensors mean that each box exactly matches what it needs to measure. Nodes can collect and relay detailed information on temperature, motion, humidity, proximity objects, collisions, speed, vibration, electromagnetic waves – and more.

How Do WSNs Help Us Work?

Thanks to a high spatial resolution, a well-configured WSN allows technicians to access extensive data logs of detailed area snapshots at will. Rather than relying on inferior, limited-scope field sampling at set times, professionals can analyse recent and historic ground conditions across the entire area at any node point and time they so choose.

Wireless Sensor Network Applications

Wireless Sensor Networks help us monitor forestry, farming, sea works, shops, weather stations, power plants, factories, parks, road networks, walkways, and ‘smart’ buildings. Sophisticated, small-scale WSNs ensure that robotic assembly lines, automated picking and packing, ‘smart’ vehicles (e.g. auto-driving cars), and medical and surgical devices complete their tasks flawlessly with down-to-the-millimetre precision. The most common are:

• Internet of things (IoT)
• Industrial automation
• Automated and smart homes
• Traffic and industrial monitoring
• Medical device monitoring
• Robotic control

Can WSNs Run Automated Systems?

Yes. Constant human oversight isn’t crucial with truly sophisticated artificial intelligence (AI) management in place. Clever, reactive computer software can use incoming WSN data to actively manage smart automation grids, IoT setups, autocalibration software, stock management systems, security backstops, and emergency alarms.

Can WSNs Act as Digital CCTV?

Multimedia WSNs can. In a multimedia setup, a fast-rendering, fast-writing gateway stores vast amounts of searchable, high-definition video for operators to review in real-time. Wireless microphones, cameras, and proximity sensors provide users with ‘eyes on’ feedback. Data rapidly relays to the monitors via a high-speed, high-capacity routing protocols (e.g. Wi-Fi).

What Do Wireless Sensor Networks Consist Of?

A standard Wireless Sensor Network (WSN) uses four distinct device groups, all working in sync. A gateway (base) device is always the network’s heart.

• Wireless Sensor Nodes
• Wireless Actuator Nodes
• Routers
• Gateways

Wireless Sensor Nodes

Tiny sensor nodes (wireless sensors) form the network’s backbone. They’re microcomputers, made of four components – sensors, a processor, a transceiver, and a power supply.

How Do Wireless Sensor Nodes Work?

The sensors (e.g. microphones, accelerometers, pressure-sensitive plates) collect raw data. Collected data is passed through an analogue-to-digital converter (if necessary) and forwarded via a circuit bus to a low-power central processing unit (CPU).

The CPU chip then parses the data stream, using a fixed program to turn it into transmissible code. Any irrelevant or corrupt data deletes. The ‘packet’ is then timestamped and stored in a small block of short-term (flash) memory within the CPU for later collection. When requested by radio ping or timer, any held data transmits back while the node’s local memory ‘flashes’ itself empty. The collection cycle then restarts.

How Are Sensor Nodes Powered?

Even with controlled transmission bursts and timed shutdowns, it takes far more power than an off-the-shelf replaceable battery can provide to run a radio antenna for months on end.

Wireless nodes need reliable, dedicated energy sources. Some nodes rely solely on wired-in power and backup capacitors. More remote and inaccessible nodes will use ‘scavenger’ generators to collect green, renewable electricity for a high-volume, lithium-ion rechargeable battery. Windmills, solar panels, and turbines are commonplace ‘scavenger’ solutions.

Wireless Actuator Nodes

Actuator nodes are much the same as any other – with one big difference. These nodes will only switch on when a fifth sensor component, the actuator, is triggered.

What Activates Actuator Nodes?

Actuators are as versatile as the sensors they use. Pressure, proximity, time, or physical forces (e.g. heat, rain, wind) can all act as the trigger. A dedicated circuit switch allows the nodes to capture and transmit data only when actuation occurs. Alternatively, a set outbound gateway command can act as a radio switch.

Do Actuator Nodes Have Any Special Uses?

Ideal for use as condition alarms, actuating nodes are essential for earthquake, flooding, fire, collapse, and landslide detection WSNs. As strictly time-limited nodes, they’re also handy as a cheap, effective power-saving solution for low priority, isolated, and distant spots.

Routers

Routers (or router nodes) are computer-controlled transceivers that redirect inward and outward-bound Wireless Sensor Network (WSN) radio traffic. They don’t collect data of their own. Instead, they receive incoming data from nearby nodes and transfer it back to a gateway.

Routers can also re-route incoming traffic from other routers and gateways. Using a subnet of routers instead of high-power radio signals helps to preserve node power, speeds up the WSN’s traffic, frees bandwidth, and extends the network’s working range.

Gateways

A gateway (or base unit) is any ‘parent’ machine that collects, stores, and forwards finished data from its ‘child’ nodes and routers. As the core of the WSN, the gateway will often come with vast amounts of storage space for archiving.

In more complex Wireless Sensor Networks, the gateway will also control select functions (e.g. power regulation, data ‘calls’, node recalibration) via radio reception. Gateways can also ‘talk’ to other computers to create readouts and linked network clusters.

Can WSNs Gateways Forward Data to the Internet?

If the gateway is TCP/IP enabled and a user grants permission? Yes. WSN data forwarding underpins the tech behind public web readouts (e.g. weather, traffic reports), IoT (Internet of Things) grids, and remote login control hubs. However, many sensitive Wireless Sensor Networks are run firmly offline (or ‘air-gapped’) for greater security and privacy. An alternative solution is to use a secondary network to create a filtered ‘DMZ‘ bridge between requests, data aggregation, and sensitive WSNs.

Wireless Sensor Network Communication Architecture

Wireless Sensor Network engineers have many specialist WSN radio protocols to pick from to link together nodes and gateways. However, modern sensor network design increasingly uses standardised, adapted, and commonly recognised specs to improve compatibility and ease of use while optimising transmission bandwidth. Here are three of the most popular.

Wi-Fi

With a range of up to two miles and fast packet switching as standard, the 802.11 family of short-range, high-bandwidth protocols aren’t just excellent for routing household web browsing. Wi-Fi router nodes can easily transmit high-capacity data feeds (e.g. audio, video) between distant nodes and gateways in near real-time. Due to Wi-Fi’s adaptability and seemingly unstoppable growth in popularity, these WSNs also carry the double-edge of superb public protocol compatibility.

Bluetooth

Bluetooth is a short-range, high-bandwidth protocol that creates fast, stable two-way bridges between radio devices within thirty feet of each other. Miniaturised and ‘Pico’ WSN layouts (e.g. ‘smart’ home layouts, industrial sensor arrays) often substitute Bluetooth into a wireless sensor network as an easy way to bypass any time, money, and compatibility issues. It’s also useful as part of a hybrid solution in private WSNs. Actuating Bluetooth transceivers can help bridge the smaller gaps to longer-range nodes and in-person ‘data harvesters’ (e.g. mobile vans, buoys, router backpacks).

ZigBee

ZigBee is the low fuss, low energy, and low maintenance wireless protocol. First released in 2004, ZigBee boasts an operating range of up to 100 meters, hardware-powered 128-bit encryption, backwards compatibility, unique 2.4 GHz frequencies, and a minimal per-node power footprint. While it’s not instantly compatible with much off-the-shelf wireless tech, ZigBee’s relative obscurity makes it far trickier for unauthorised users to hack.

Wireless Sensor Network Designs

Not all monitored spaces are the same. Here’s how engineers adapt their WSN layouts to different environments.

Terrestrial Wireless Sensor Networks

Terrestrial WSNs track land conditions in the open air. They’re usually positioned in a 2D or 3D grid in urban, suburban, rural, and wild spaces, ensuring blanket coverage. For specific outdoor area tracking in awkwardly shaped polygons (e.g. cliffs, islands), star-cluster annexes of ‘optimised’ nodes replace squares. Nodes above ground can also be solar or wind-powered, optimising and sustaining the WSN with clean energy.

Underground Wireless Sensor Networks

Seismometer, tunnel observation, and flood warning nodes need to stay permanently underground to work. Unfortunately, heavy walls, rock, and packed dirt weaken radio signals. Underground WSNs will use additional ‘sink’ nodes positioned directly above buried sensor nodes to boost muffled data transmissions to a readable quality. For sensors installed in surface-accessible subway lines, holes, and tunnels, linear, ‘lifeline’ router nodes can bounce signals back continuously. Replaceable batteries and buried power lines keep underground nodes running for as long as possible.

Underwater Wireless Sensor Networks

Seas, lakes, and rivers all pose serious challenges to nodes. Water is difficult to transmit radio signals through, currents move free-floating devices around, and flooding can easily damage sensitive electronics. When planning near-shore networks, engineers will use buoy, anchor, or harness lines to create tethered nets of nodes. All waterborne nodes are sealed tight with plastic cladding to prevent corrosion, degradation, and electrical shorts. Deep-sea installations will use buoyed or side-mounted sensors, which can then be periodically ‘harvested’ by a mobile data boat or submarine. Expendable, high-capacity batteries are often picked to power water nodes due to their relatively short working lives.

Classification of Wireless Sensor Networks

Not all WSNs are created equal. What features does your WSN have? Ask yourself the questions below to find out.

Static or Mobile

Are your nodes docile or on the move? If you’re using roaming tracker, floating, transportable, or re-positionable nodes, you’re running a mobile WSN. If the sensor points fix firmly in place and stay there? Static WSN.

Deterministic or Non-Deterministic

A deterministic network is a WSN plan assuming a reasonable certainty that the sensor nodes will be where they started. Their geographical positions are determined and are realistically unchangeable. In a non-deterministic network, node movement may regularly happen due to unavoidable forces such as storms, waves, currents, or erosion. Non-deterministic sensor grid software warns operators of a position change, weak link, or missing sensor.

Single Base Station or Multi Base Station

A single base station network layout uses one gateway to collect and log data. In a multi-base station, a network of two or more gateways and network readers will parse, collate, and forward data back and forth to each other.

Static Base Station or Mobile Base Station

If your sole gateway machine or reader stays in place? You’re running a static base station wireless network. If you can physically move the gateway around to ‘harvest’ data? You own a mobile base station and run a mobile wireless sensor network. Some networks will use a hybrid of these two approaches to reach different sensor nodes.

Single-Hop or Multi-Hop

Can every network node reach the base station (gateway) via radio transmission without using a router? If so, you’re running a Single-Hop WSN. If any of the nodes need one or more router relay boosts? Multi.

Self-Reconfigurable or Non-Self-Configurable

Can your network nodes manage their routing, programs, and focus independently? Is the gateway or base machine used only to collect data. Your network can self reconfigure. If nodes and routing rely on radio instructions from another central computer, dedicated node, or the gateway itself? Your WSN is non-self reconfigurable.

Homogeneous or Heterogeneous

In a homogeneous network, all the sensor nodes are clones. Homogeneous designs use identical sensors and hardware to spot data discrepancies, repeating set measurements across multiple points. Heterogeneous WSN designs vary their sensor node hardware to match local demands, allowing for select, distinct measurements to be collected and processed differently at some nodes.

Disadvantages of Wireless Sensor Networks

• Wireless sensor signals are sometimes vulnerable to intercepts, snooping, and data spoofing by hackers.
• WSNs tend to be centralised and may suffer lengthy outages or shutdowns if a critical link is damaged, glitches, or runs out of power.
• They’re vulnerable to acute electromagnetic interference and ground ‘blocks’ (e.g. industrial machinery, thunderstorms, mountains).
• Low bandwidth and slow response times also bottleneck some older, cheaper, and poorly designed WSNs.

Advantages of Wireless Sensor Networks

• Wireless Sensor Networks don’t need dedicated data cables installed to work well.
• An antenna on each node transmits the collected data via a specialised comms protocol (e.g. ZigBee).
• Using radio transmission improves the working range, affordability, and network lifetime of the Wireless Sensor Network.
• All WSN nodes can be accessed via a central monitoring system.
• It is scalable and flexible and can therefore accommodate new nodes or devices at any time.

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