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Here is some valuable information and resources for your Ashtech GPS/GNSS products. Select your product to download Technical Papers in Adobe Acrobat (.pdf file) format.

Technical Papers

• Recommendations on Differential GNSS
• GPS and GPS+GLONASS RTK
• Positioning United States Aids-to-Navigation Around The World
• Airborne Testing of GPS+GLONASS Positioning Sensor Against A Proven Flight Test Truth Source
• GPS+GLONASS Technology and the GG-Surveyor
• GPS+GLONASS Technology and the GG24 Receiver
• Surveying with GPS+Glonass
• GG-RTK White Paper
• USDA Forest Service Reliance Under-Canopy Performance Evaluation
• Reliance Systems Accuracy Analysis
• Instant RTK cm with Low Cost GPS+GLONASS C/A Receivers
• General Purpose Kinematic/Static GPS/GLONASS Postprocessing Engine
• RTK-Based Vehicle Tracking and Unmanned Operation for Agriculture
• Advantages of GPS+GLONASS� in Open Pit Mining
• The Pulling of Delay Lock Loop under Strong Multipath
• Performance Analysis of GPS Positioning Using WAAS and EGNOS
• G12-HDMA: Low Cost, High Performance GPS Space Receiver
• Enhanced Strobe Correlator Multipath Rejection for Code & Carrier
• Ashtech Instant-RTK�: A Revolutionary Solution for Surveying Professionals
• Survey Quality Real-Time GPS: Solving the Time to Fix vs. Reliability Paradox
• The DG-16 Receiver

1. Recommendations on Differential GNSS
The use of differential navigation techniques combined with GLONASS and GPS, collectively referred to as Global Navigation Satellite Service (GNSS), presents maritime authorities with an opportunity to provide highly precise navigation service for harbor entrance and approach areas with a reduced dependence on any one system. The use of 48 satellites (24 GPS and 24 GLONASS) also provides improved availability in situations of partial satellite signal blockage due to terrain, structures, and large vessels. Receiver autonomous integrity monitoring techniques also become highly reliable with this increased number of signals for comparison.

Differential techniques for GPS are well understood and have been standardized across the industry. The Radio Technical Commission for Maritime Services (RTCM) Special Committee 104 has developed a proposed format for messages containing differential GLONASS information. In addition to the data formats to transmit GLONASS corrections a differential GNSS service must resolve the technical issues in combining the separate systems. When GLONASS and GPS measurements are to be combined there are two technical issues that must be resolved. First, the difference in the WGS 84 and PE 90 datum must be adjusted, and second, how to handle the difference between GPS time and GLONASS time. This paper presents the results of this USCG R&D study to determine the best method of integration and recommendations on implementing DGNSS service.

2. GPS and GPS+GLONASS RTK
This paper presents not only two new RTK products, but also a major breakthrough in global positioning technology, taking RTK where it has never gone before. The first new product is the Z-Sensor, a single board implementation of Ashtech's reknowned Z12 receiver. The second product is the GG-RTK receiver, the world's first GPS+GLONASS RTK product.

RTK has represented the peak of GPS performance for several years, but there have been severe limitations - with fewer than 5 GPS satellites in view, RTK does not work at all, or works so slowly as to be almost no better than DGPS in many applications. Now, by combining GPS and GLONASS in an RTK product, you can use RTK in places such as open pit mines, urban canyon, river valleys, etc., where GPS-only RTK simply will not work.

3. Positioning United States Aids-to-Navigation Around The World
The U.S. Coast Guard (USCG) maintains many aids to navigation far from the U.S. mainland, Alaska and Hawaii that are outside of USCG differential GPS (DGPS) coverage. Historically, these aids have been positioned with horizontal sextant angles. The USCG has completely transitioned to the use of DGPS for setting aids-to-navigation where available. This has produced significant efficiency and performance gains. There is a desire to realize equivalent gains in all areas of USCG aids-to-navigation (AtoN) operations. Options for achieving this goal are the military GPS precise positioning service (PPS), contracting for DGPS service via satellite, and most recently, the utilization of combined GPS+GLONASS receivers, known in the industry as GNSS receivers. The USCG accuracy requirement is 10 meters 95% confidence level with recording of integrity measures for positioning. If a GNSS receiver meets this requirement, it would have advantages of no recurring cost (satellite DGPS) and no security requirements (GPS-PPS).

The USCG R&D Center conducted laboratory evaluations to determine if positioning requirements could be met by GNSS receivers. Procedures and methods to ensure that the required accuracy is being met are detailed. The results of this effort and the development of a buoy positioning software tool are presented.

4. Airborne Testing of GPS+GLONASS Positioning Sensor Against A Proven Flight Test Truth Source
As the Russian Global Navigation Satellite System (GLONASS) matures, the potential benefits to airborne navigation and positioning operations have become increasingly obvious. With the continuing degradation of the GPS signals by the US Department of Defense policy of Selective Availability (SA), the accuracy of the GLONASS signal is being leveraged by many organizations in the aviation industry. Designers of Flight Management Systems (FMS), GNSS Landing Systems (GLS) as well as manufacturers of other types of avionics and a myriad of Airborne Mapping firms have already laid plans to take advantage of the capabilities of positioning sensors which combine GPS and GLONASS. The focus of this test was to determine the true airborne accuracy of combined GPS and GLONASS technology. Dual-frequency GPS best lends itself to this testing due to several inherent logistical limitations of Laser Tracking. The GPS+GLONASS technology was flown against an FAA endorsed dual-frequency GPS receiver. The dual-frequency GPS data served as the truth source data; the GPS+GLONASS data was measured against the truth source data.

5. GPS+GLONASS Technology and the GG-Surveyor
From its inauguration in 1993 as a fully operational satellite-based navigation and positioning system, the Global Positioning System (GPS) set a new standard in the means by which to obtain precise measurements. However, like most young technologies, GPS is not yet perfect, and certain limitations exist which preclude its reaching full potential. Many impediments can be significantly reduced, fortunately, with the addition of more satellites.

Halfway around the globe, the Russian Space Forces' satellite-based GLONASS system provides precise navigation and position data to users in a fashion similar to GPS. We developed GPS+GLONASS technology to combine GPS and GLONASS into a powerful 48-satellite constellation. GLONASS augments GPS with additional signals, subsequently improving overall performance. The impact of GPS+GLONASS technology on the future of global positioning is significant with respect to improved satellite availability, system integrity and accuracy for users worldwide.

6. GPS+GLONASS Technology and the GG24 Receiver
This is the original white paper released with the GG24 GPS+GLONASS was introduced in 1996. This paper provides and overview of both GPS and GLONASS, and then examines the advantages of their combined use in satellite availability, position integrity and accuracy.

7. Surveying with GPS+Glonass
There has been a considerable amount of discussion regarding the feasibility of combining GPS and the GLObal NAvigation Satellite System (GLONASS) to provide enhanced performance for surveying applications. This has been primarily due to the technical challenges of optimally combining data from the two dissimilar satellite systems.

"Surveying with GPS+GLONASS" uses real-world field results based on data collected using commercially available equipment to demonstrate that single-frequency GPS+GLONASS surveying rivals the performance of more expensive dual-frequency GPS systems in many operational environments.

8. Surveying with GPS+Glonass
The GG-Surveyor is also now the world's first GPS+GLONASS RTK receiver. GG-RTK technology provides near dual-frequency RTK performance over short baselines, with better availability than GPS alone.

9. USDA Forest Service Reliance Under-Canopy Performance Evaluation
On May 29 and 30, 1997, Ashtech (formerly Magellan Navigation) and USDA Forest Service personnel conducted accuracy and performance tests with the Ashtech Reliance GPS Field Asset Management system on a field test course established by the USDA Forest Service. The test course is located in the Mt. Hood National Forest, Clackamas Ranger District, and was specifically designed to test the capabilities of GPS field data collection systems. The course is built in forest conditions typical of the Pacific Northwest environment. The image at left depicts a typical area of tree canopy and stand density, located at Pt. 7 along the course. The Ashtech Reliance system shown below uses an Ashtech Super C/A single-frequency (L1) 12-channel receiver system, which has been optimized for general GIS data collection, including accurate, efficient operation under tree canopy, as well as 10 cm capability in open areas (no overhead canopy).

10. Reliance Systems Accuracy Analysis
The Ashtech Reliance family of Field Asset Management and GIS data collection tools has redefined the market for GPS/GIS systems. Both the Reliance Submeter System and the Reliance Decimeter System utilize on-the-fly processing software to produce reliable field results at previously unavailable accuracy levels. Working with an easy-to-learn, simple-to-use Windows suite in the office, and straightforward menu-driven software in the field, Reliance systems are designed for use by all levels of field personnel and GIS operators. Reliance systems work with Ashtech's Super C/A advanced 12-channel receiver to continuously track all GPS satellites in view for an unprecedented degree of precision. This accurate, reliable and automatic positioning means that field workers stay focused on collecting feature information. Reliance units have been tested and proven superior on various accuracy and performance evaluation courses around the world. The Windows software guides users through import/export of corrected and edited data files, with direct translation to all popular GIS software systems.

11. Instant RTK cm with Low Cost GPS+GLONASS C/A Receivers
This paper describes a new algorithm developed for a real time kinematic (RTK) engine to process GPS+GLONASS C/A code and carrier phase differential data. The goal of the development was to implement the algorithm in low cost receivers which are capable of tracking the signals of both constellations. The test results, also presented, show that combined RTK processing insures very fast (often instant) on-the-fly (OTF) ambiguity resolution (AR) and centimeter kinematic accuracy for short baselines under an open sky. The data was collected using Ashtech GG24 boards with the RTK option installed. This option does not require any extra processor. The complete firmware, including the RTK engine, runs on a single digital signal processor (DSP).

12. General Purpose Kinematic/Static GPS/GLONASS Postprocessing Engine
The paper deals with the problem of precise carrier phase differential static and kinematic positioning based on the GPS and GLONASS measurements collected from the GG24 single frequency, combined GPS and GLONASS receiver, the Z12 dual frequency GPS receiver, and a prototype of a dual frequency combined receiver as well.

A unified approach for solving positioning problems in both static and kinematic settings is presented. Both of these problems are handled by the same numerical scheme and the same software. The general purpose postprocessing engine has been developed on the base of this idea. So, it is sufficient to have at hand only one engine to cover various processing tasks: static, kinematic, pseudo-kinematic, and mixed static-kinematic. The paper is organized the following way. The numerical method is discussed at first. Then the implementation is briefly described, then there are included numerical results for static, kinematic, and mixed measurements. Mathematical details are given in an Appendix.

13. RTK-Based Vehicle Tracking and Unmanned Operation for Agriculture
The paper presents the key technologies in the field of autonomous land navigation along with a plan for using these technologies to develop a complete navigation system for agriculture. These technologies leverage recent advancement in commercial off-the-shelf technology for satellite positioning equipment and are the result of two years of systems development for the military target community. This will enable the proposed system for agriculture to not only be developed in a timely manner, but will result in a simple to use, cost effective system. The key technologies that can be used in a system for agriculture will be discussed in detail. They include high-performance, full-feature, vehicle-independent, autonomous vehicle navigation using a single GPS+GLONASS receiver; coordinated, configurable multi-vehicle navigation with a leader-follower mode of operation; automatic path (and detour) generation capability and graphical user interface that enables simple and effective user control.

14. Advantages of GPS+GLONASS� in Open Pit Mining
This paper discusses the use of GPS in open pit mining. A solution to the restricted GPS visibility problem is presented by augmenting GPS with GLONASS. The paper presents results obtained using GPS+GLONASS receivers. Comparison of GPS-only and GPS+GLONASS sensors is made. Finally, examples of data from actual operating mines are presented.

15. The Pulling of Delay Lock Loop under Strong Multipath
Analysis of GPS receivers operating in urban areas shows that severe multipath effects may result in sufficient delaying of transient processes in a Delay Lock Loop (DLL). The paper demonstrates several methods to reduce the time of transient processes. It is shown, in particular, that traditional methods including either switching of DLL bandwidth or correlator width during the pulling process can reduce transient time only by 1.5-2.5 times while the algorithm consisting in simultaneous varying of both loop bandwidth and correlator width gives sufficiently more promising gain up to 5-10 times.

16. Performance Analysis of GPS Positioning Using WAAS and EGNOS
With the growing demand for accurate and reliable worldwide differential GPS positioning, there has been a significant move towards the use of real-time GPS augmentation systems with wide area differential positioning capabilities. The US Wide Area Augmentation System (WAAS) and the European Geostationary Navigation Overlay system (EGNOS) are good examples of such a move.

17. G12-HDMA: Low Cost, High Performance GPS Space Receiver
The Ashtech G12-HDMA� is a 12-channel GPS receiver developed for HighDynamics and Missile Applications. It has successfully flown on severalNavy sea-launched test missiles, as well as on sounding rockets launched byNASA at its Wallops Island facility. The G12-HDMA is currently beingintegrated into the X-34 experimental reusable launch vehicle beingdeveloped by Orbital Sciences. Recent firmware modifications have alsoenabled the G12-HDMA to be used by low Earth orbiting spacecraft fornavigation, timing, and precise orbit determination. In this paper, theperformance of the G12-HDMA in a variety of missile, rocket, and spacecraftnavigation tests are described. The test results include acquisition,tracking, and navigation performance.

18. Enhanced Strobe Correlator Multipath Rejection for Code & Carrier
"This paper presents the latest advances in Multipath RejectionTechnology, the Enhanced Strobe Correlator�. We will present indetail practical results in a real controlled environment."

19. Ashtech Instant-RTK�: A Revolutionary Solution for Surveying Professionals
"This paper presents test results demonstrating the performance of the Ashtech Instant-RTK technology as featured in the Z-Xtreme� GPS receiver under different operating conditions and over various baseline lengths. Static and kinematic positioning accuracy of 0.005m+1ppm horizontal and 0.010+1ppm vertical, and 0.010+1ppm horizontal and 0.020+2ppm vertical (standard error), respectively, is demonstrated."

20. Survey Quality Real-Time GPS: Solving the Time to Fix Reliability Paradox
Advanced, adaptive stochastic modeling in addition to careful statistical modeling as implemented in the Ashtech Instant-RTK� technology and featured in the new Z-Xtreme� GPS receiver demonstrates unprecedented success in solving the ambiguity resolution speed vs. reliability paradox.

In this paper, after highlighting the algorithm used in Ashtech Instant-RTK to solve this paradox, test results will be presented to further prove its performance.

21. The DG16 GPS Receiver
The new DG16 evolved from the G12 receiver. The new DG16 receiver is designed to track SBAS satellites (WAAS/EGNOS/MSAS), as well as 300 KHz beacon signals, and to utilize the differential correction data from these systems to provide precise DGPS positioning for navigation and other applications.