FEATURE SENSING TECHNOLOGY TAKING TO THE ROAD IN A SMART WAY
network nodes run for years on two AA batteries, even routing ones. The intelligent Network Manager automatically assigns RF channels to time slots, enabling channel-hopping on every transmitter-receiver pair for frequency diversity. Furthermore, every device has one or more redundant paths to overcome communications interruptions due to interference, physical obstruction or multipath fading. If a packet transmission fails on one
Figure 1 Figure 2
Linear Technology’s Dust Networks wireless mesh network solution enables Streetline Networks to gather the real-time status of metered parking spots, and uses that data to reduce traffic congestion. Ross Yu, Marketing Manager at Dust Networks Product Group, Linear Technology Corporation explains ...
I
t’s estimated that 30 percent of urban traffic is caused bymotorists looking
for parking. In a study thatmeasured traffic in one small district of Los Angeles, researchers found that drivers drovemore than 950,000miles, produced 730 tons of carbon dioxide and used 47,000 gallons of petrol searching for parking. The frustrations of wasted time, traffic
congestion, road rage and pollution are all aggravated by the difficulty and randomness of finding an empty parking spot. Municipal parking enforcement, too, is an inefficient, labour-draining activity where finding offenders is like looking for the proverbial needle in the haystack. The solution is, of course, to collect data from individual parking spaces in real time, but this is not a simple task. Wiring each parking space for power and communications is out of the question, and so is any requirement for frequent battery changes. Therefore, the solution needs to be wireless and needs to be able to run on batteries for years at a time. Also, the city street is not kind to wireless radio transmissions. Automobiles, vans, trucks and buses present continuous and dynamic barriers which deflect, reflect and attenuate radio signals. The solution, then, must be highly resilient and reliable. Lastly, the solution must be easy to deploy, easy to scale up, and simple to configure, not requiring specialised technicians.
22 MAY 2014 | ELECTRONICS
path, the next retransmission may attempt on a different path and different RF channel. This combination of path and frequency diversity is critical for reliable communications, particularly with sensing nodes placed on the ground. To ensure sustained operation, a
SmartMesh network periodically performs automatic site surveys, gathering performance statistics from each node in the network. The Network Manager uses this information to constantly optimise the pathways in the network. As the RF environment changes, the mesh pathways will automatically adjust to fix communications problems before they occur. The network is self-forming, which
Figure 3
produces nodes to deploy, and does not require specialised technicians. All network configuration and management can be handled remotely using the Network Manager. Streetline’s Smart Parking Solution integrates Dust Networks SmartMesh products into their surface- mounted and embedded sensors which contain an array of sensing components and logic to manage the collection of data at the individual parking spaces. The advanced RF resiliency allows
Streetline Networks selected Dust
Networks SmartMesh wireless mesh network for its >99.999% data reliability, long battery life, and ease of use. Their communications system is comprised of Dust Networks’ wireless nodes and network managers, which communicate using a Time Synchronised Channel Hopping (TSCH) link layer, a technique pioneered by the company. In a TSCH network, all nodes in the
network are synchronised to within a few microseconds. Network communication is organised into time slots, which enables SmartMesh devices to sleep at ultralow power in-between scheduled communications. Wireless nodes are only active in time slots where they are scheduled to transmit or receive, typically resulting in a duty cycle of <1%. With such a low duty cycle, SmartMesh
Figure 1:
Ground-based sensors must work reliably and have multiyear battery life
Figure 2:
SmartMesh Wireless Networks - are
comprised of wireless nodes and a network manager, delivering >99.999% data reliability and multiyear battery life
Figure 3:
If communication fails on the 'green' arrow, node D may retry on the 'purple' arrow using another channel
reliable transmition of street-level data in real time to a web-based suite of parking management applications. These applications can show motorists where to find vacant parking spots, text them when their parking-meter time is running out, and even direct parking enforcement directly to occupied expired meters. A growing number of cities have installed Streetline Networks Systems. Together, these two companies are helping reduce traffic congestion, making cities cleaner and citizens happier, and making valuable municipal resources more efficient.
Linear Technology Corporation
www.linear.com +1 (408) 432-1900
Enter 228 / ELECTRONICS
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