Software for the Integration of e-Loran and GPS
 Maine Aerospace Consulting, under contract with CrossRate Technology, LLC in Portland, Maine, is developing the algorithms and associated software required to integrate GPS data with Loran and/or Enhanced Loran (eLoran) pseudo-ranges to produce an optimal positioning solution. Note: The eLoran system is a vastly improved version of the current Loran-C, incorporating state-of-the-art timing, receiver and transmission technologies.
The overall goal of the CrossRate receiver is to provide a comprehensive positioning solution possessing accuracy capabilities at or near that of GPS with the robustness characteristic of Loran. Since Loran is a low frequency, high-power signal, it is significantly more dependable in urban areas, forested areas, inside buildings and other environments in which GPS is normally blocked. Additionally, unlike GPS, Loran is extremely difficult to jam.
The algorithm being designed includes a multi-state discrete Kalman Estimator for incorporation of GPS position and velocity observations (when available) with nominal range estimates generated by a LORAN receiver. The goal of the software is to accommodate all scenarios involving temporary or long term loss (all or partial) of either GPS or Loran signals, and continue producing optimal positioning information regardless. While GPS is present, the algorithm will exploit the accuracy of the GPS position fixes to extract insight into the integrity of the Loran measurements. During GPS outages, the algorithm will utilize this previously learned information to greatly improve the Loran signal by incorporating clock and pseudo-range scale factor correction estimates.
Also, since the accessibility of Loran towers providing valid pseudo-range measurements will, in general, vary as the CrossRate receiver moves, the Loran/GPS (LG) integrator must be capable of accurately integrating measurements from virtually any tower at any time. This capability will require the management of a large state-space internal to the LG integrator, accommodating states associated with up to 10 Loran towers at a given time.
Photo Credit: http://www.loran.org/library/LoranAvionicsMag1.pdf
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