GPS MODERNIZATION

Dip-Ing -William Barragán Zaque
Msc. Photogrammetry and Geoinformatics

University of applied sciences Stuttgart
Department of surveying and geoinformática
wbarragan@gmail.com

Abd-el-Hamed Nabial Ibrahim

Msc. Photogrammetry and Geoinformatics

University of applied sciences Stuttgart
Department of surveying and geoinformática
Nabila_gis@yahoo.com

THE GPS MODERNIZATION PROGRAM: IMPACT IN CIVIL USERS

1. GPS Modernization

United States government wants GPS to be the best Global Navigation Satellite System (GNSS) in the world. The system is more than 25 years old and upgrades are needed. As old satellites are taken out of operation, there is an opportunity to replace them with upgraded satellites.

GPS is being modernized in order to further improve positioning, navigation and timing capabilities for both civil and military users. The modernization initiative will result in substantial improvements in GPS positioning accuracy. Removal of Selective Availability (SA) in May 2000 was the first step in the GPS Modernization initiative.

This immediately increased the accuracy of stand‑alone GPS receivers from 30‑100 meters to about 10 meters. SA removal has also benefited fleet management – making tracking the locations of taxis, buses, tractor trailers and boxcars more efficient, especially in crowded parking lots and railway yards. Removal of SA has increased the safety of GPS for non-precision runway approaches and generally improved pilot situational awareness. Recreational benefits include the ability to more precisely locate favorite fishing holes, boating obstacles, and game left for future retrieval. According to the U.S. government’s 2001 Federal Radionavigation Systems report, “SPS (now) provides a global average predictable positioning accuracy of 13 meters (95 percent) horizontally and 22 meters (95 percent) vertically.”

2. New Signals

In the future, when combined with the current civil signal at 1575.42 MHz, the new signals will significantly improve the robustness and reliability of GPS for civil users. Estimated accuracy is one meter or better in real‑time. This new capability will spur new applications for GPS, further expanding the rapidly growing market for GPS equipment and services worldwide.

The second civil signal (called L2C) will be located at 1227.60 MHz along with the current military signal, and will be available for general use in non‑safety‑critical applications. L2C will include a more sophisticated code and is expected to become the most popular GPS signal used in the future. The new signals will not reach initial operational capability (IOC) until 18 satellites are in orbit (probably 2008).

A third civil signal will meet the needs of critical safety‑of‑life applications such as civil aviation. The third civil signal will be located at 1176.45 MHz, within a portion of the spectrum that is allocated internationally for aeronautical radio navigation services. It will provide a higher power level than other carriers and will use a larger bandwidth, enabling longer codes. As a result, acquiring and tracking weak signals will be much easier. It will be implemented beginning with a satellite scheduled for launch in 2005. IOC should occur for the new civil signal at L5 by 2012.

3. GPS Block III

GPS Block III will be a totally new system, not another variation of GPS II. The idea is to put some of the functionality now provided from the ground into the space segment – advantages are enhanced security, ability to incorporate data from other monitoring stations, and performance improvements brought about by making the constellation self-synchronizing. The overall goal is to provide flexibility and robustness to meet evolving military and civil requirements for the next 30 years.

4. Other Improvements

Several improvements to the operational control segment will improve the capability to monitor all signals broadcast from the constellation, make the control network more robust, improve the positioning accuracy of both the civil and military services, and add new functions that are necessary to control the modernized satellites.

A new military signal (M code) will be added on the L1 and L2 frequencies for the Department of Defense (DoD). In addition, a military spot beam will be added to new satellites. The military spot beam is intended to overcome jamming by increasing the power over a limited area. Satellites with all the enhancements will cost over $80 million each.

The current GPS modernization effort should carry the constellation through approximately the year 2010. A new generation of satellites and ground control facilities will be developed for use beyond 2010 through approximately 2030.

5. Other Global Navigation Satellite Systems (GNSS)

GLONASS is a Russian satellite navigation system which now consists of 10 healthy satellites. Some GPS receiver manufacturers have incorporated the capability to receive both GPS and GLONASS signals; this increases the availability of satellites and the integrity of the combined system.

Galileo is Europe's contribution to the next generation Global Navigation Satellite System (GNSS). Unlike GPS, which is funded by the public sector and operated by the U.S. Air Force, Galileo will be a civil‑controlled system that draws on both public and private sectors for funding. The service will be free at the point of use, but a range of chargeable services with additional features will also be offered. These additional features would include improved reception, accuracy and availability.

6. The Future of GPS

Look for autonomous GPS accuracy at the centimeter level within 10 years. GPS equipment capabilities are continually improving, and GPS receivers are being integrated into many other kinds of equipment (ex: cell phones, PDAs)

Receiver sizes and prices continue to decrease Budget problems seem to be an ever-present reality. For now, the U.S. and other countries are cooperating on development and operation of global navigation satellite systems (GNSSs) this cooperation has many benefits for users, including increased accuracy when using receivers that can process signals from more than one system.