Aiding GPS with Calibrated Loran-C

Abstract

GPS is currently being installed; when it is operational, five satellites will be in view virtually 100 percent of the time. However, the full constellation will not be in place for several years, and even then satellite failures may introduce coverage holes. Additionally, even with the full constellation, a GPS receiver will not always be able to monitor signal integrity unless some external aid is used. Loran‐C can be used effectively to aid GPS. A hybrid receiver can combine Loran lines of position with GPS lines of position to provide a system with great integrity, reliability, and time availability. Indeed, Loran is independent of GPS and can be used to detect GPS system or receiver failures. However, the hybrid receivers must include sophisticated Loran propagation models, which account for both the spatial and temporal anomalies of the propagation paths. Fortunately, GPS can be used to efficiently gather the data for these models. Additionally, GPS observations could be used to calibrate (or tune) these models in real time. This paper reviews the theory of Loran propagation and gives a basic Loran pseudorange model. It also presents some basic approaches for combining Loran and GPS pseudoranges in a position‐fixing receiver. Finally, it estimates the accuracy of the hybrid system.

A Novel Signal Design and Performance Analysis in NavCom Based on LEO Constellation

“…Other signals have less influence on it. 4), and CE-OFDM-PM (8). Obviously, the SSC of our proposed scheme and the above-listed modulation is significantly smaller than that of other spread spectrum signals.…”

“…Obviously, the SSC of our proposed scheme and the above-listed modulation is significantly smaller than that of other spread spectrum signals. Except for CE-OFDM-PM (4) and CE-OFDM-PM (8), which shows that our proposed scheme can easily be compatible with service signals of the same frequency band, while their own compatibility is also remarkable. • Anti-multipath Figure 14 shows the multipath error envelope of different spread spectrum-modulated signals under the condition of multipath delay within 500 m. It can be clearly seen from the envelope line that the solution proposed in this paper (marked by the grey dashed line) is a multipath error and is significantly smaller than that of several other types of spread spectrum-modulated signals, which means that the proposed scheme has a better anti-multipath performance when there are short-distance multipath delays.…”

“…The concept of Aided GPS (A-GPS) was first proposed in the U.S. and originated from the application of inertial navigation and the Loran-C system in the maritime industry [7,8]. However, the Boeing company led the combined Iridium with the GPS (iGPS) program and building of an LEO/MEO satellite hybrid system that combined communication satellite assets, including Iridium, to provide users with enhanced services and innovations regarding the integrity of iGPS [9].…”

“…Anti-multipath Figure 14 shows the multipath error envelope of different spread spectrum-modulated signals under the condition of multipath delay within 500 m. It can be clearly seen from the envelope line that the solution proposed in this paper (marked by the grey dashed line) is a multipath error and is significantly smaller than that of several other types of spread spectrum-modulated signals, which means that the proposed scheme has a better anti-multipath performance when there are short-distance multipath delays. 4), BOCs (5, 2), BOCs (5, 2.5), SRC (0.2, 1), MSK (10), CE-OFDM-PM (1), CE-OFDM-PM (4), and CE-OFDM-PM (8). From the perspective of the row or column, except for CE-OFDM-PM (4) and CE-OFDM-PM (8), regardless of whether our proposed signal is a jammer or desired signal, its interference with other signals or the influence of other jammers is very small.…”

The Accuracy and Coverage of Loran-C and of the Decca Navigator System — and the Fallacy of Fixed Errors

“…Recent developments in Loran-C practice have resulted in very low residual effects due to land paths. Enge and McCullough 9 have shown that imperfectly-mapped conductivity variations and modelling errors result in small systematic discrepancies in the ASF values calculated. These discrepancies can generally be substantially eliminated, and certainly reduced to the order of the minimum random errors of the system, by adjusting the results of the conductivity model to give an optimum fit with a sparse set of survey measurements.…”