Benjamin Peterson

Loran data modulation: extensions and examples

Loran has provided navigation service since 1958. Though not originally designed with data broadcast capabilities, Lorans versatility has enabled data to be broadcast with great benefits. Research in the last two decades has resulted in a tremendous increase in the data capacity of Loran thereby increasing its utility. Currently, a modernized Loran is being evaluated for its capability to backup GPS and data modulation is an integral part of this Loran design. This paper details some recent Loran modulation designs and ideas.

Loran Data Modulation: A Primer [AESS Tutorial IV]

Loran has provided navigation service since 1958. Though not originally designed with data broadcast capabilities, Lorans versatility has enabled data to be broadcast with great benefits. Research in the last two decades has resulted in a tremendous increase in the data capacity of Loran thereby increasing its utility. Currently, a modernized Loran is being evaluated for its capability to backup GPS and data modulation is an integral part of this Loran design. An overview and analysis of Loran modulation techniques is provided.

Improving Loran Coverage with Low Power Transmitters

Enhanced Loran (eLoran) is currently being implemented to provide back up to global navigation satellite systems (GNSS) in many critical and essential applications. In order to accomplish this, eLoran needs to provide a high level of availability throughout its desired coverage area. While the current Loran system is generally capable of accomplishing this, worldwide, there remain a number of known areas where improved coverage is desirable or necessary. One example is in the middle of the continental United States where the transmitter density is not adequate for providing the desired availability for applications such as aviation in some parts. This paper examines the use of lower power, existing assets such as differential GPS (DGPS) and Ground Wave Emergency Network (GWEN) stations to enhance coverage and fill these gaps. Two areas covered by the paper are the feasibility and performance benefits of using the antennas at these sites. Using DGPS, GWEN or other existing low frequency (LF) broadcast towers requires the consideration of several factors. The first is the ability of the transmitting equipment to efficiently broadcast on these antennas, which are significantly shorter than those at a Loran station. Recent tests at the US Coast Guard Loran Support Unit (LSU) demonstrated the performance of a more efficient transmitter. This technology allows for the effective use of smaller antennas at lower power levels. Second is the ability to broadcast a navigation signal that is compatible with the Loran system and the potential DPGS broadcast (when using a DGPS antenna). The paper examines some possibilities for navigation signals. The goal is to develop a suitable low power signal that enhances navigation and is feasible for the transmission system. The second part of the paper examines the benefits of using these stations. The benefits depend on the location of the stations and the ability seamlessly to integrate them within the existing Loran infrastructure. Analysis of these factors is presented and the coverage benefits are examined.

Design and performance of an integrated DGPS/LORAN receiver

Design and implementation of a real-time integrated DGPS/LORAN receiver is described. Previous work by the authors articulated the advantages of integrating these two systems and proposed a tightly coupled Kalman filter architecture; this work examines the essential system interfaces in more detail. Features of these interfaces include a highly stable common frequency reference, hardware measurement of the time offset between GPS and LORAN sampling strobes, data structures incorporating range residuals, and algorithms to align data relative to different assumed positions. Finally, the expected performance of this receiver is briefly described in a variety of operational scenarios. One such operational scenario for integrated DGPS/LORAN is the harbor entrance and approach (HEA) phase of maritime navigation. A critical issue in this scenario is the spatial decorrelation of the LORAN additional secondary factors (ASFs). Most data thus far has focused on the temporal stability of LORAN data and indicates that in evolutions of less than two hours, LORAN may be sufficient to meet the harbor entrance accuracy requirement of 8 to 20 meters. Some preliminary data collected in Connecticuts Thames River are presented and indicates that spatial ASF variations may cause errors much larger than the accuracy requirement. This in turn indicates that precise mapping of these variations using some combination of theoretical calculations and measurements will be necessary in order for integrated DGPS/LORAN to be used in HEA operations.

Hyperbolic navigation system

A navigation system that produces hyperbolic lines or surfaces of position by measuring the differen…

Integrated CIS VLF/Omega receiver design

The design of an integrated Russian-VLF/Omega receiver implemented on a TMS320C30-microprocessor-based SPECTRUM plug-in board installed in a PC-compatible portable computer is presented. The system also requires an external antenna, pre-amp, and frequency reference. The SPECTRUM board digitizes the RF signal to 16 b and then digitally mixes with the sines and cosines of the three Russian frequencies plus 10.2, 11-1/3, and 13.6 kHz. The mixer outputs are low-pass filtered, and the comb filters are implemented for the respective epochs. The computer accesses and processes the comb filter outputs, calculating and logging signal phase and amplitude. The design allows for easy future expansion to include unique and VLF communication frequencies.<<ETX>>