Each hardware platform has different strengths and weaknesses. The Crossbow system can be customized easily but has a maximum data transfer speed of 35 kilobits per second, limiting the network to text messaging. The Gumstix system is less flexible but can transfer data at 54 megabits per second, allowing users to talk and send other data over the network. Both types of node measure approximately five by ten centimeters and cost between $200 and $300.
Moayeri’s team tested the Crossbow network in an 11-story building on the NIST campus in Gaithersburg, MD, deploying 11 nodes in the stairwell. The Gumstix network was tested throughout another NIST building that goes 40 feet belowground and features winding corridors as well as a number of metal doors. A total of eight nodes were used to cover about 300 meters.
Moayeri says that the maximum transmission power for the Gumstix node was about 100 milliwatts while the Crossbow’s MICA2 Mote was approximately three milliwatts. Since a typical police or firefighter radio transmits at one to five watts, far fewer nodes would be needed in a real-world scenario. However, it’s not clear how much it will cost to make rugged and fireproof nodes.
A potential downside of the NIST prototype is that it does not include the ability to track location, unless it is in a building that already has passive RFID chips installed.
Moayeri and his colleague Michael Souryal presented details of the two prototype networks at the third annual Precision Indoor Personnel Location and Tracking for Emergency Responders technology workshop held at Worcester Polytechnic Institute in early August.
Their presentation caught the interest of one workshop attendee–Alan Kaplan, chief technology officer at Drakontas, a company based in Glenside, PA, that makes communications software for public safety and security operations. His firm’s software currently requires users to check connections between nodes as they are deployed. “What I thought was cool is that the technology seemed to help users as they built out this network, telling where they should actually place these nodes,” says Kaplan. “Potentially, this is something that anyone who does public safety or security would want.”