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Can Mobile Phone Networks Be Improved to Better Cope with Emergencies?

8/29/2011 10:09:42 AM

Anyone in the eastern portion of the U.S. last week who was forced to evacuate an office, home or school following Tuesday's magnitude 5.8 earthquake soon noticed that cell phone service was spotty or, in many cases, nonexistent. For New Yorkers herded outside of their skyscrapers and into the streets, it was a communication blackout reminiscent of (although of course not the same as) the 9/11 terrorist attacks. In both situations, mobile phone users were unable to connect to the cell network to communicate with loved ones.

Whereas the 9/11 cell phone outage was the result of many factors—including the downing of cell phone towers—this week's problems (though brief) were caused purely by volume. Countless cell phone users were fighting for limited access, leaving most without service. With Hurricane Irene bearing down on the East Coast, one is left to question the reliability of mobile phones in the face of serious emergencies.

Scientific American spoke with Andrea Goldsmith, a Stanford University electrical engineering professor and researcher at the school's Wireless Systems Lab, about why mobile phone users are often unable to connect during emergencies, as well as options for improving cell network performance when it matters most.

[An edited transcript of the interview follows.]

What is happening when, during an emergency, you try to use your mobile phone and can't get a signal?

There's a finite capacity that the cell phone system can support at any given base station. Say it's 10 users or 100 users talking on their phones. When the 101st user calls in, there's no channel available for that user to occupy. That's a little bit of a simplistic description, but that's effectively what happens. When there's an event like an earthquake that causes people to want to make more phone calls or want to access the Internet more, the systems just become overloaded.

How have cell-phone services changed since 9/11?

Cell phones are coming up now on their fourth generation of technology, so we've had two evolutions of cell phone technology since 2001. Most of the work in between evolutions has been aimed at getting higher data rates because people now also use their phones for accessing the Internet and for exchanging videos and pictures. There have been improvements in capacity, but not enough to keep up with just a tsunami of traffic across the wireless networks.

With the introduction of smartphones, many mobile phone users have the ability to connect over the cell network or via Wi-Fi. Shouldn't this provide additional capacity during emergencies that wasn't there years ago?

Cell networks and Wi-Fi both have limitations. Cell phone networks have a lot less bandwidth than Wi-Fi, but at least the cell phone service providers own the part of the spectrum over which their customers communicate. This enables the cell providers to guarantee a certain quality of service. Still, it's not easy for them to add capacity because there isn't a lot of spectrum available for them to purchase.

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