In the days immediately following September 11 a pair of articles, one in EE Times and the other in The Washington Post, about emergency cell phone location technology caught my attention. Both articles focused on renewed lobbying efforts on Capitol Hill aimed at forcing cellular providers to meet the FCC’s deadline for implementing Phase II of the Enhanced 911 standard. (At press time, most cellular carriers have requested waivers for the October 1 deadline.)
- In order for a GPS receiver in a handset to determine the owner’s location to within the required 50 m (67% of 911 callers) or 150 m (95%), a clear view of several satellites is required. It can be difficult to get an adequate view of sky in a downtown section of a city (a big part of what those percentage of caller requirements are all about) even on a normal day. Imagine trying to acquire a signal from even one GPS satellite while you’re buried in a pile of rubble that’s ten stories deep and mostly underground (or in a subway system, a traffic tunnel, or many other likely emergency sites, for that matter).
- Even if your handset could somehow manage to acquire a sufficient number of satellites, it’s questionable whether the mandated accuracy range would have been adequate in this disaster. With literally millions of tons of debris to move, even 50 m accuracy is nowhere near precise enough to point rescuers in the proper direction to dig. The larger 150 m radius could put you anywhere within the base of one tower. And how deeply should they look? (Start digging with heavy equipment or hands?)
- Perhaps, in this disaster, network-based triangulation would have been more useful to rescuers. At least it wouldn’t have required victims to have recently upgraded their phones or have a clear view of the sky. Yet the lower required accuracy for this technology (100 m for 67% of 911 callers, 300 m for 95%) would have made the data that much less useful to the rescuers.
In either case, both technologies would require that the victim’s phone be also: still in her possession after the collapse; still in a working condition; and partly or fully charged. In addition, the victim turning on her phone would have to be lucky enough to be greeted by something other than a lack of signal (several base stations were destroyed right in the vicinity of the World Trade Center) or network-busy (cellular and land-based telephone traffic surged even on networks clear across the country).