Practical Method for Upgrading Existing GNSS User Equipment with Tightly Integrated Nav-Com Capability

Abstract

A practical method for adding significant new high-performance, tightly integrated Nav-Com capability to any Global Navigation Satellite System (GNSS) user equipment, such as GPS receivers, requires no hardware modifications to the existing user equipment. In one example, the iGPS concept is applied to a Defense Advanced GPS Receiver (DAGR) and combines Low Earth Orbiting (LEO) satellites, such as Iridium, with GPS or other GNSS systems to significantly improve the accuracy, integrity, and availability of Position, Navigation, and Timing (PNT)—in some cases by three orders of magnitude, to enable high precision GNSS carrier phase observable to be more readily exploited to improve PNT availability—even under interference conditions or occluded environments, and to enable new communication enhancements made available by the synthesis of precisely coupled navigation and communication modes. To achieve time synchronization stability to the required sub-20 ps level between the existing DAGR and a plug-in iGPS enhancement module, a special-purpose wideband reference signal is generated by the iGPS module and coupled to the DAGR via the existing antenna port, so that no hardware modification of the DAGR is required.

Description

[0001]This invention is made with Government support under Navy Contract N00173-08-C-2074 awarded by the Naval Research Laboratory. The Government has certain rights in the invention.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]This invention relates to a method of upgrading existing Global Navigation Satellite System (GNSS) user equipment, such as a GPS receiver, in order to add high-performance, tightly integrated navigation and communication (Nav-Com) capability without the need to modify the existing equipment. The invention also relates to an apparatus, which may take the form of a plug-in enhancement module, for adding iGPS to existing GNSS user equipment.[0004]In a preferred embodiment of the invention, the upgrade is to a particular tightly integrated Nav-Com system known as iGPS, which utilizes the carrier phase of signals received from Low Earth Orbiting (LEO) satellites, such as Iridium to provide a special-purpose wideband reference signal. In this emb...

AI Technical Summary

Benefits of technology

[0026]The invention thus provides a method of upgrading and tightly integrating GPS user equipment with other GNSS systems to enhance navigation performance without the need for hardware modifications to the original GPS equipment, and user hardware for implementing the method. The method provides a practical, cost-effective means for bounding adverse differential phase bias drift among critical r.f. components of tightly integrated Nav-Com user equipment. In the preferred embodiment, the performance upgrades enable tightly integrated global Nav-Com capability, and are compatible with iGPS and any other GNSS system.

[0030]According to still further aspects of the preferred embodiments of the invention, the first GNSS user hardware includes Iridium receive capability and the second GNSS user device is a Global Positioning System (GPS) receiver, with the Iridium and GPS signals preferably being input through a common antenna. In this embodiment, the first oscillator provides a common precision oscillator carrier phase reference for both the GPS and Iridium r.f. timing and ranging measurements. In addition, the first GNSS user hardware further includes Iridium transmit capability, while either the first or second GNSS user receiver may include Y-code, M-code, C / A code, Galileo, GLONASS, and / or COMPASS capability. A reference station may be used to calibrate the code and carrier phase of satellites within view and telemeter the calibration data to a communications satellite whose broadcast output is coupled into the first GNSS user hardware and whose calibration data is employed to improve the position, velocity, and time solution.

[0032]In addition, the first GNSS user hardware may include a transmitter component that uses its improved position, velocity, and time estimate to improve a time and frequency synchronization of its transmissions, with the transmissions being coupled to a regional communications network, satellite network, or global network of low earth orbiting satellites.

Problems solved by technology

Instead, signal squaring techniques are employed, which have the unfortunate effect of squaring both the signal and the noise.

Without a suitable infrastructure, the process can become cumbersome.

For example, with only a one-way data link, users and devices may not be able to authenticate with the key management authority.

However, a significant obstacle to implementing iGPS is the cost and effort to outfit user equipment such as the Defense Advanced GPS Receiver (DAGR), which remains user equipment of choice with the military.

Prior art has so far presented two unpalatable approaches: (i) modify the existing user equipment hardware to accept a new precision iGPS interface capable of tight integration and (ii) completely replace the existing user equipment with new tightly integrated iGPS user equipment designed from scratch.

The first approach has caused significant concern because of the economic and technical risk associated with introducing a precision iGPS interface with tight integration.

In particular, since the DAGR does not provide for an external oscillator input, one would have to be added.

There is also a related logistical and configuration control issue that having multiple versions of DAGR hardware would become cumbersome to manage for the users and leadership because, when hardware modifications are made, many of the overall specifications will need to change and be managed.

In addition, there is also technical risk associated with the hardware modifications.

While the navigation processing algorithms can tolerate a slow drift of carrier phase bias between the two components, if thermal or mechanical disturbances are excessive, the system will be incapable of providing useful performance.

The DAGR layout compounds the technical risk because the Iridium and GPS components are by necessity in different boxes which will be subject to different thermal and mechanical stress.

The second approach also encounters resistance.

Given that the U.S. has already made a significant investment in GPS equipment, it is difficult to justify displacing existing inventory.

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