Key selection criteria for a WSN technology are cost of ownership and flexibility. Wireless technologies reduce installation costs dramatically compared to wired solutions, but battery changes needed for lifetime goals increase total ownership costs. Protocols must be designed to scale both in density and total number of sensors, to tolerate interference, and survive the loss of individual devices.
WSNs must be designed to work reliably in environments with wide temperature variations, and with link-layer packet delivery ratios (PDR) down to about 50%. For industrial applications, the reliability target is typically to receive at least 99.9% of the generated data, as missing data can trigger expensive alarm conditions. The system must support some minimum number of sensor data packets per second with bounded latency – “stale” packets are typically discarded and count against reliability.
Linear’s Dust Networks SmartMesh™ product line contains both WirelessHART and 6LoWPAN-compliant IPv6 product offerings that leverage 802.15.4 to provide the most reliable, lowest power, secure WSN solutions on the market. Dust Eterna™ motes (LTC5800 family) are single chip devices that couple a Cortex-M3 microprocessor, memory, and peripherals to the lowest power 802.15.4 radio available today. Designers embed a mote in their sensor package, and can rely on the network to form, optimize, and carry their sensor data to their application.
Dust’s managers allow for graceful scaling from tens to thousands of devices, providing data and configuration interfaces for the network. Both product families build highly reliable, multi-hop mesh networks capable of per-node configurable data rates. Some examples of applications using Dust motes and managers include:
Parking – Streetline3 is a smart parking provider that monitors real-time parking space availability with vehicle detectors underneath the spaces and aggregates information into a citywide database. Low-power wireless technology is critical for this application because it is intractable to wire sensors to each space, and path diversity is essential as different vehicle positions change the path quality between device pairs.
Energy Monitoring– Vigilent4 provides intelligent energy management systems for data centers, where air conditioning is often run continuously at full power, wasting energy. Vigilent deploys dense, secure wireless devices that do not interfere with regular data center operation, and has routinely deployed multiple overlapping networks to achieve the required number of sensors.
Multichannel time-synchronized mesh networks based on 802.15.4 radios address many of the challenges involved in building flexible, reliable, low-power wireless sensor networks.
About the authors:
Lance Doherty, and Thomas Watteyne are systems engineers in the Dust Networks Group, Linear Technoogy Corp. Jonathan Simon is Systems Engineering Director, Dust Networks Product Group, Linear Technology Corporation.
2. L. Doherty, W. Lindsay, J. Simon, K. Pister, “Channel-Specific Wireless Sensor Network Path Analysis,” Proc. ICCCN ’07, Honolulu, HI, 2007.