Re-evaluating the U.S. GPS System
The U.S. is in the midst of a major re-evaluation of its GPS policy. And it could enhance international acceptance of GPS by mitigating many contentious issues, such as continuous availability and liability concerns, thereby promoting greater global use of GPS. Radionavigation systems previously scheduled for termination, such as Loran, will continue operations for at least another decade. It also appears now that Loran’s capabilities are much better than previously appreciated. New all-in-view Loran receivers typically track 20-30 transmitters in North America and provide performance enhancements analogous to those derived from the change from sequencing to all-in-view GPS receivers. The limitation of the Loran system stems from the performance of the transmitters, which require tighter synchronization to monitoring and control electronics. New developments such as Eurofix, which could distribute differential GPS (DGPS) corrections over the entire United States and substantial oceanic areas in an extremely cost-effective manner, also significantly enhance Loran system capabilities.
Loran/GPS can offer performance neither system can provide alone. For example, all-in-view Loran receivers would allow UTC-synchronized Loran transmitters to be used as GPS pseudolites, improving GPS availability by at least two orders of magnitude. Eurofix could provide Wide Area Augmentation System (WAAS)-like capabilities at minimal cost and better, much more expansive DGPS coverage than even a fully deployed marine radio beacon DGPS system. This combined system would provide true radionavigation redundancy and safety for all users.