DOT considers shutting down GPS backup system

The Transportation Department kicked off a public comment period that could determine the fate of a Global Positioning System backup system viewed by industry officials as essential for communications network timing signals and electronic navigation.DOT said in a Federal Register notice published Jan. 8 that it wants comments on whether to shut down the ground-based long-range radio navigation (Loran) system operated by the Coast Guard or to develop a fully deployed enhanced Loran (eLoran) system that could serve as a GPS backup. Comments are due Feb. 7.DOT said it is also working with the Homeland Security Department, which includes the Coast Guard, to determine whether investments made so far now merit consideration of eLoran as a complementary electronic system to GPS. The Coast Guard has spent $160 million on Loran modernization since 1997.Chuck Norman, chief design engineer for network strategy at Sprint Nextel, said timing signals are crucial to the operation of complex wired and wireless networks. He said carriers worldwide use GPS for network timing signals, but they need a backup in case of a GPS outage or if GPS signals are jammed.Norman said the Alliance for Telecommunications Industry Solutions (ATIS), whose membership includes all the telecom carriers in the country and equipment vendors, views eLoran as the “only viable alternative to GPS for providing [Coordinated Universal Time] of day and frequency accuracy that is suitable for a telecom primary reference source.” This endorsement of eLoran is contained in an ATIS paper he authored and submitted to the National Institute of Standards and Technology.Sprint uses Loran and atomic clocks as backup to GPS in case of an outage, but Norman said atomic clocks provide only a frequency reference and not a time of day reference. Without accurate timing, network performance could degrade anywhere from eight hours to three days, Norman said. Consequently, someone may be able to place a call using a cell phone while stationary, only to have it dropped when mobile because handoff from one cell site to another relies on accurate timing.Loran stations house two low-frequency transmitters. Receivers determine their location based on the time difference between the signals received from the two transmitters. The U.S. Loran system covers all coastal waters in the continental 48 states and parts of Alaska.ELoran stations broadcast an additional data channel with as many as 16 messages including but not limited to station identification, absolute time, and early and differential correction messages, which improve accuracy, according to a Coast Guard fact sheet.ELoran uses high-powered transmitters and low-frequency signals less susceptible to jamming than low-powered high-frequency GPS signals, the Coast Guard fact sheet states.Randy Kenagy, senior director of advanced technology at the Aircraft Owners and Pilots Association said he viewed DOT’s move to seek public comment on Loran as a positive sign that the department has listened to AOPA’s requests to give careful consideration to the future of Loran.Kenagy said AOPA has more than 400,000 members who need an electronic navigation backup to GPS in case that system fails or is jammed.DOT has recognized GPS’ vulnerability to jamming and attack since September 2001, when the Volpe National Transportation Systems Center research arm assessed the GPS vulnerabilities and urged development of a backup system.The Volpe report states that as GPS penetrates into the civil infrastructure, “it becomes a tempting target that could be exploited by individuals, groups or countries hostile to the United States.”President Bush called for development and maintenance of GPS backup systems in a December 2004 policy statement on space-based positioning, timing and navigation systems, but the policy did not specify the backup system.Aviation Management Associates, a consulting firm, examined GPS backup systems for the Federal Aviation Administration in a white paper last summer and concluded that eLoran is the least expensive national technology that can provide a full backup for GPS and urged policy-makers to “continue Loran, complete modernization and get standards in place for eLoran.”Trinity House, a U.K. organization that provides marine aides to navigation in England, Wales, the Channel Islands and Gibraltar, recently issued a request for proposals for an eLoran system that would complement and back up Global Navigation Satellite Systems such as GPS and Galileo, the European Union-backed GNSS.