How to select a wireless sensor network

David Laurence of Adaptive Wireless Solutions reviews the issues and challenges presented by wireless technology and offers a guide you through the supply maze

Great Missenden, UK -- Interest in wireless sensor networks (WSN) continues to grow at a rapid pace and with good reason as these systems promise to deliver previously difficult or unmeasurable data to allow organisations to reduce costs, increase product quality and improve operations.

Studies show that up to 90% of actionable process and environmental data remains uncollected. Automatic data monitoring is generally not built into the systems that must be evaluated, so companies are forced to look elsewhere for solutions.

Unfortunately, wired monitoring systems are often expensive and unrealistic in challenging physical environments, and manual monitoring has proven simply to be cost-prohibitive. Many traditional wireless solutions, meanwhile, fall in to the category of point-to-point or point-to-multipoint. The reliability of these networks is set by the quality of the RF link between the central access point and each endpoint.

In industrial settings, it can be hard to find a location for an access point that provides dependable communications with each endpoint. Moving an access point to improve communications with one endpoint will often degrade communications with other endpoints.

Wireless mesh sensors networks communicate with each other through routers and a gateway to form a mesh network. Router devices relay signals for each other, so if a given sensor is out of range of the gateway, other members of the network carry data.

Since interference patterns can change, the network will automatically adapt to keep all members communicating. This self-healing capability keeps data flowing with up to 100% reliability. However, the reliability of all systems in the market is not the same.

Perhaps the single most important benefit — and the reason for its rapid adoption in industrial settings — is its ability to perform well in challenging locations or large physical spaces, where running wires is impractical or impossible. That means a business can finally collect the vital information it needs to operate at peak efficiency, which can yield very powerful results for a company.

Must-Have Characteristics

The excitement and innovation surrounding wireless sensor networks is good news for end users, because the growing demand makes vendors work harder to develop effective products. Careful examination and evaluation of all the options will ensure that you end up with a solution that is right for your company’s unique requirements.

In general, there are certain characteristics that should be non-negotiable. These include:

Reliable Network Performance

A frequency hopping, spread spectrum, mesh network is critically important because it delivers the very highest level of data transmission reliability. Frequency hopping, spread spectrum eliminates the effects of interference by “spreading” the transmission over a range of frequencies and randomly “hopping” from one frequency to another. If a transmission is blocked on one channel it moves to a clear channel and retries.

Flexible Mesh Network Topology

In a mesh network, data “hops” throughout the network until it reaches the final destination. Placement of mesh nodes is highly flexible and allows for increased range, and the option to achieve implementation success in very challenging physical layouts, for example by routing around radio obstacles, that would be impossible with traditional types of wireless sensing. No other network topology can provide this level of flexibility.

Self-Healing, Self-Managing Functionality

Systems that are simple to install, configure and maintain can ensure rapid ROI.

A self-configuring, self-healing network offers tremendous advantages, particularly in companies with changing requirements, the need to relocate sensors at will or that have an environment with moveable production equipment. In the event a node becomes overloaded or unavailable, a mesh network will automatically reroute the traffic to its destination without outside intervention. The goal should be to spend more time collecting information, not setting up and managing the network.

Multiple Application Support

Many monitoring products are single application systems that specialise in one particular measurement, such as food storage temperature or humidity monitoring. The reality is that most companies have multiple monitoring requirements.

Investing in multiple systems can be costly and make it difficult to get a comprehensive “dashboard view” of the operation. A flexible wireless mesh sensor network supports multiple applications on the same infrastructure and provides more valuable, comprehensive results.

Scalable Architecture

Scaled architecture enables a small network to expand without changes to the underlying infrastructure. Given the incredibly wide range of data that can be collected, this is a smart investment in anticipation of future requirements.

A scalable architecture that allows additional sensors to be added easily, without significant advance planning or technical reconfiguration, is most valuable and should be able to increase in scale to thousands of points as the technology develops. Today, networks of hundreds of monitored points are becoming common.

Third-Party Connectivity

No business operates its monitoring in isolation, and an effective wireless sensor network solution must offer extensive facilities for connecting to external systems and third-party software packages already in use.

Using industry standard protocols such as Modbus and OPC and WEB 2.0 connectivity through XML, SOAP, and ODBC ensures seamless and flexible connectivity with all SCADA systems and business applications. Ethernet in both wired and wireless forms is becoming the transport medium of choice

End-to-End Solution

Collecting the data solves only part of the problem; making sense of it is where the real payoff happens. Ideally, data should flow through the network gateway into a console that can display real-time information, historical data and facilitate certain administrative tasks.

Where businesses do not have monitoring, software vendors should make available the software needed to provide alerting and alarming and meet industry requirements for compliance and validation, whether inside the firewall or accessible from a browser over the Internet.

Having seen how the technology behind WSNs can be used to help solve many of the challenges facing potential industrial users there then comes the question of how to choose a supplier who will help you to achieve the potential identified. Issues to consider include :

Solutions supplier

There is no more overused word than “solution” but in the wireless sensor network market it can be crucial to know that you are working with a supplier who is providing an end to end package – measurement /data transmission/ data processing rather than someone who is limited to offering elements of the solution which then require the user to act as their own systems integrator.

Business case focus

It is inevitable in the early days of new technologies that there is a high degree of focus on the underlying technology itself but at the end of the day what the user wants is a solution to a business problem. A supplier who can talk in those terms and focus on the benefits of the solution and not solely on the detailed technical background can be a powerful ally.

Selling the concept to others in the proponents business whose primary focus is more likely to be costs and benefits will meet with limited success if the supplier can only talk about how novel the technology might be.

Third party relationships

With a technology which has applications in a wide range of industrial sectors no one supplier is likely to have the knowledge and experience of all possible applications therefore it is important to seek out a supplier who partners with others to provide in depth sector knowledge in terms of measurement priorities and data manipulation and presentation expertise.

Training and support

One constraint with any new technology is the perceived effort on the part of the user needed to get up to speed with the terminology and concepts surrounding the subject, seeing the bigger picture and avoiding backing a technology that in the end might lead up a blind alley. Some users will prefer to wait for standards to be fully established which whilst sometimes sensible can also mean missing out on valuable benefits now. Ideally you want a supplier who can advise on those standards issues and also sees the wider context of alternative wireless (or wired) approaches and isn’t determined to force a solution on the user at all costs only to see the project fail down the line.

One important way to gain confidence in a potential supplier is to ask for reference site details, for instance on the suppliers web site, showing how problems were solved.

As the market for wireless sensor networks develops so does the need for standards to be established and it is worth checking whether your supplier is involved in activities to help that standardisation process by getting involved in sector based working parties and presenting at seminars and conferences in order to educate the potential market. Supplier web sites featuring case studies, application notes and white papers can also be a good indicator of the suppliers commitment to the market place.