ER-LINK Expedites Medical Response

Crash your car in Tucson, Ariz., and the ambulance will arrive quickly enough to drive you across town to the hospital. The paramedics know what they're doing, but how much better off would you be if a trained trauma specialist could make a diagnosis and recommend treatment right on the scene?

Residents of the 228 square-mile city may soon find out, as city officials and private vendors join forces to roll out a wireless mesh network that will deliver real-time video from ambulances to hospitals in more than 90 percent of the city's populated areas.

Medical experts say the system, known as Emergency Room Link (ER-LINK), could very well save lives, while municipal planners hope the network could keep residents safer in the wake of roadside emergencies.


Instant Expertise
At the University of Arizona Health Sciences Center, Dr. Rifat Latifi, associate director of Telesurgery and International Affairs, talks about the "golden hour." That's the magic window in which trauma care must begin in order to succeed. He says the idea is misleading, since in trauma care an hour is sometimes far too long to wait for care.

"You can't tell me it is OK to let someone bleed for 59 minutes," he said.

Now, with a live video link between ambulances and the trauma center at the emergency room of the Health Sciences Center, patients will have trauma experts present anytime, if and when it's necessary, Latifi said.

"There are no more excuses if someone dies just because there was no trauma surgeon or emergency specialist available," he said. "There is no longer any excuse for that."

Tucson launched the project with the support of a $16 million federal grant, intended to fund development of a mobile communication system to transmit video, voice and data via a Wi-Fi 2.4 GHz transmission signal from moving vehicles to a fixed location.

The initial rollout will connect 14 ambulances to the trauma room.

Wireless Facilities Inc. (WFI) is designing and implementing ER-LINK. By the time the network goes live in late 2006, WFI will have implemented a metro-scale Wi-Fi mesh network architecture by Tropos Networks based in Sunnyvale, Calif., and a patient telemetry system from General Devices located in New Jersey.

The network will build upon an existing fiber-optic network that connects nearly all the city's lampposts and traffic lights for the purpose of traffic control. Engineers will attach 250 radios to this grid to carry Wi-Fi signals from emergency vehicles to fixed destinations, explained Al Brown, vice president of business development at WFI.

"As long as I have a mounting asset such as a streetlight or a traffic signal, I can communicate radio to radio as the network is built out," said Brown, who estimates the system will need to connect to the city's fiber-optic network for every eight to 10 radios to sustain adequate bandwidth. The streetlights and signals will also power the radios, which draw less juice than a 65-watt light bulb.

Even with the possibility of live video, a single emergency vehicle won't need more than 1 MB of bandwidth, and the system is being designed to accommodate 30 MB of throughput.

The nature of the mesh architecture should make bandwidth availability a nonissue, Brown said, because even though bandwidth drops off with multiple hops, the mesh algorithm is optimized to keep the number of connections to a minimum.

"If I have two gateway nodes within three hops of a radio, it will always determine the path of least resistance," he said.

Traditional wireless communication systems use cellular-phone-style radio links, which rely on a point-to-point or point-to-multi-point transmission. Wireless mesh networks, on the other hand, exist as multihop systems in which devices help each other transmit packets of data throughout the network.