A team at Microsoft Research has created a hardware localization technology that enables you to play a multi-player sword fighting game using only smartphones. To play SwordFight, two players aim their phones at each other and move aiming for each other's handset, and try to jab at the other person’s handset. If a player hits within six inches of their opponent's handset, the opponent loses a point. It's all measured via the phone's accelerometer and digital compass, and the addition of the new little chirp allows the phones to know how close they got to each other. Microsoft Research team have developed this system called FAR. It's a system where one smartphone can locate another smartphone and measure its distance via chirps.One phone sends out a chirp, and a second phone determines the distance and the position of the first phone by measuring the time it takes for the chirp to travel to its speaker.
The team at the Mobile & Sensing Systems Research Group at Microsoft Research Asia acknowledge that distance measuring with sound isn't new, but what their team did was to create faster and more accurate algorithms on top of core processing. Team member David Chu explained the dramatic differences between traditional measuring and the FAR system in an interview with Wired: "If you think about the fact that you could only take one measurement per second, you could have an error of 4 meters. We've been able to improve that, so that we can go 12 samples per second and theoretically up to 22 samples per second," Chu said. "On average, based on our testing, we can actually achieve within 2-centimeter accuracy."