mobile phones to be used on aircraft, pending approval by the FCC and the FAA. This method is similar to that used in most cars on the German ICE train. The aircraft would carry a device known as a picocell. A picocell acts as a miniature base station (like a cellphone tower) communicating with cellphones within the aircraft and relaying the signals to either satellites or a terrestrial-based system. The picocell will be designed and maintained for full compatibility with the aircraft avionics. Communication between the picocell and the rest of the telephone network will be on separate frequencies that do not interfere with either the cellular system or the aircraft's avionics, similarly to the on–board proprietary phone systems already aboard many commercial aircraft. Since the picocell's antennas within the aircraft would be very close to the passengers and inside the aircraft's metal shell both the picocell's and the cell phones' output power could be reduced to very low levels, which would reduce the risk of interference. Such systems have been tested on a few flights within the United States under a waiver from the FCC. ARINC and Telenor have formed a joint venture company to offer such a service aboard commercial aircraft. The cell phone calls are routed via satellite to the ground network and an on-board EMI screening system prevents the cell phones from attempting to contact ground-based networks. These systems are comparatively easy to implement for customers in most of the world where GSM phones operating on one of just two bands are the norm. The multitude of incompatible mobile phone systems in the United States and some other countries makes the situation more difficult—it is not clear if the onboard repeaters will be compatible with all of the different cell-phone protocols (TDMA, GSM, CDMA, iDen) and their respective providers. Technical discussion The U.S. Federal Communications Commission (FCC) currently prohibits the use of mobile phones aboard any aircraft in flight. The reason given is that cell phone systems depend on frequency reuse, which allows for a dramatic increase in the number of customers that can be served within a geographic area on a limited amount of radio spectrum, and operating a phone at an altitude may violate the fundamental assumptions that allow channel reuse to work. See also Air-ground radiotelephone service Airplane mode References Notes Further reading Study: Up To 15 Phones Are Left On During Every