Beacon-Loran integrated navigation concept (BLINC): An integrated Medium Frequency ranging system
Date of Original Version
The enhanced Loran (or eLoran) system with ASF corrections can provide sub-20 meter accuracy for Harbor Entrance and Approach. However, in some areas of the country the system accuracy is limited by the Horizontal Dilution of Precision (HDOP) due to the location of the towers. This cannot be improved upon without adding additional Loran towers or increasing the signal power. The maritime DGPS system and nationwide DGPS systems provide differential corrections to GPS using Medium Frequency (MF) towers. These medium power MF signals could also be used as ranging signals. However, by combining ranging signals from beacon sites with Loran signals we could improve upon position accuracy, reliability, and integrity compared to eLoran alone. In order for the beacon signals to be usable for ranging in conjunction with the Loran signals some minor modifications would need to be made to the beacons: • Add a Loran-steered Quartz or Rubidium clock to each beacon site to provide a common frequency reference that is locked to Loran time. This would enable the use of a mix of beacon and Loran signals without having to determine the clock offset between the systems. • Synchronize the beacon transmission bit streams so that a receiver knows which bits correspond to even seconds of time (similar to GPS). This would eliminate the uncertainty in the time of transmission. A receiver at 300KHz can determine the time of reception very accurately by matched-filtering on the RF. Time of transmission is determined by knowing which bit it is (decoding the navigation message) giving an accurate TOA. With transmission times synchronized with Loran time these TOAs could then be used with Loran TOAs in an integrated solution. The frequencies are close enough that the same antenna could be used for both signals. In fact we have successfully used existing Loran H-field antennas to receive beacon signals on previous projects. The integrated system would just require front-end filtering that is broad enough to handle both frequencies, then high speed sampling and processing in software. This paper describes the system concept and initial proofof-concept including analysis of the system.
20th International Technical Meeting of the Satellite Division of The Institute of Navigation 2007 ION GNSS 2007
Johnson, Gregory W., Christian Oates, Mark Wiggins, Peter F. Swaszek, and Richard Hartnett. "Beacon-Loran integrated navigation concept (BLINC): An integrated Medium Frequency ranging system." 20th International Technical Meeting of the Satellite Division of The Institute of Navigation 2007 ION GNSS 2007 4, (2007): 1101-1110. https://digitalcommons.uri.edu/ele_facpubs/1062