Wireless sensor networks come of age

The adoption of wireless sensor networks, or mesh networks, has struggled over the years to live up to its hype in commercialized applications and deployments. However, says Martin Hanssmann, with the recent advent of new commercially viable standards, this technology is now proving itself.

The earliest 802.15.4 based standard for Wireless Sensor Networking (WSN) to be introduced to the market was ZigBee with the stated goal of becoming a common standard for industrial, commercial, residential and other applications. WirelessHART, released late in 2007, is a standard specifically targeted at the very well-established wired HART market to provide a secondary wireless data link to its very popular industrial communications bus. Within the context of process monitoring, this standard should find a successful niche for wireless sensor networks requiring 30-50 devices with sampling periods of greater than one second.

Following closely on the heels of WirelessHART is the ISA100.11a standard. In its first instantiation, ISA100.11a is also intended to address process monitoring applications including those with a broader perspective than WirelessHART, particularly in its gateway and network manager integration within industrial automation schemes. Yet another player in the market is Z-Wave with a primary focus on residential markets.

Why so many ‘standards’?
A simple heuristic equation formulated by Millennial Net postulates that an overall mesh network performance, Q, can be seen as a sum of Reliability R + Low Power with Low Latency P + Range L+ Scalability C + Data Rate D + Network Topology T + Security S.

Essentially, this equation states that the overall network performance Q can be considered a constant for all 802.15.4 based solutions and that maximizing parameters such as Data Rate D and Network Topology T can come only at the expense of other parameters such as Reliability R or Scalability C.

The characteristics of the different markets being served by each of the standards drive those parameters most essential to meet their intended applications. WirelessHART, for example, has taken a TDMA approach that maximizes reliability and security but sacrifices data rate, latency and scalability. Zigbee, in its earlier releases, took a CSMA approach with a fairly uniform focus on all of the variables, demonstrating a potential fit for almost any application but was insufficiently optimized to address any specific market need. The new Zigbee Pro standard, although still early in its deployment, much like Z-wave, appears to be optimized more for the home area AMI market.

These approaches currently leave two significant holes in the coverage of WSN standards: the first is a need to address the discrete automation segment (where extremely low latencies of sub-10 milliseconds are required); the second is a need to address the complex commercial buildings market. Organizations such as ISA SP100 (which has formed a Factory Automation Study Group) and the Profibus User Organization (PNO) are now focusing their attentions on the former.

Bi-directional and low latency key drivers
The complex buildings segment includes larger buildings of more than 50,000 square feet and comprise of over 50 percent of total square footage in the US today. The use of a wireless sensor network in such buildings is an extremely appealing alternative for secondary monitoring and control, including demand and response; however, the solution must robustly address the simultaneous need for 150+ sensors and 10+ hops with reliability, range, bi-directional communication and sub-second latency. This need is currently being met with proprietary protocols such as Millennial Net’s MeshScape, now in its fifth generation. With over 50,000 nodes deployed, Millennial Net’s MeshScape protocol is based on a proven Time Adaptive CSMA approach specifically optimized to meet this complex buildings market needs.

An increased understanding of the specific characteristics that each of the WSN standards bring to their market segments leads to successful deployments. With positive user experience, wireless sensor networks are coming of age. However, despite the new standards there continue to be market characteristics not being fully met by standards and to avoid disappointing results, it is increasingly important that the user diligently analyze their needs before choosing a solution.

Martin Hanssmann is President and CEO of Millennial Net, a provider of commercial and industrial wireless sensor network solutions. He has over 25 years of automation experience. Previously, Hanssmann served in a variety of management roles for Brooks Automation and Schlumberger.