Archive for November, 2001


Friday, November 23rd, 2001 Michael Barr

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.)

The contradiction underlying the timing of these new lobbying efforts is that the technology, as proposed, would have helped very few, if any, of the thousands of victims of the terrorist attacks. Ignoring that most of those in the twin towers probably didn’t live past the crushing collapses, consider these more technological issues.
Handset-based locators:
  • 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?)
Network-based locators:

  • 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).

Rather than pointing to the need to implement the current generation of E-911 technology more quickly, this tragedy only points to the complete inadequacy of the current requirements for certain kinds of disasters. The current E-911 technology may, in fact, be useful in some sorts of emergencies. But we can’t stop there. In addition to implementing the current technology, other technologies and approaches need to be considered as well. For example, handheld devices that pinpoint the location and distance of handset signals should be available en masse within hours of such disasters.  
Surely someone in our industry is in a position to help solve this problem before the next disaster strikes.