By using the host of position-relating sensors in modern smartphones, scientists at MIT think they could make the phones and network perform better so your calls don't drop when you're on the move.
When you're strolling or rolling through a crowded city chatting on your cellphone, there are a number of things that can get in the way of your call working properly. A primary culprit is handoff between different cell towers. As you transition between two towers' radio coverage zones, your handset, the towers, and the network infrastructure have to do an intricate dance of passing your data between one tower and the next without interrupting your signal. Which is hard. And sometimes this is why the signal goes kaput.
Researchers in the Computer Science and Artificial Intelligence Laboratory at MIT have been testing their protocols using Wi-Fi equipment on the campus-wide network, and boosted throughput (the time that devices could successfully send and receive data while moving around) by about 50%.
In a normal system, when your cellphone realizes its signal from the tower is getting weak, and another is getting stronger, it alerts the "new" tower of its presence, disconnects from the old one, and instantly sends the next crop of digital data onto the next tower--with the aim of ensuring your voice is seamlessly transmitted over the network. It goes wrong, particularly if the handset has an issue alerting and connecting to the next tower, and by the time it succeeds, you've moved on to an area with a stronger signal from a different tower. The call is dropped.
MIT's protocol uses the phone's GPS and accelerometers to infer a user's trajectory, and thus can let the network prepare itself for an incoming cell phone, and the phone itself make better decisions about when to switch towers. In tests, MITs devices switched transmitters 40% less often then usual. Plus, phones also adjust bit rate on the fly, and that's another calculation that goes wrong when phones are moving--usually. Using MIT's trajectory-sensitive code, phones make better bit-rate calculations and thus have improved throughput.
Image via Flickr user randal-scwartz.