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GPS means more than location

Posted: 16 Dec 2004 ?? ?Print Version ?Bookmark and Share

Keywords:gps? military? satellite? space? d-gps?

The global-positioning system (GPS) has become a Swiss-army knife of space-based navigational services, used for everything from pinpointing location for emergency response to synchronizing 3G cellular base stations.

The wealth of civilian and military applications already found for the 29-satellite constellation of navigational units will be enriched even further when satellites with a new suite of signals are launched beginning in 2005, improving the system's accuracy. And when enhancements now slated for 2012 are made, the system, which is managed out of Schriever Air Force Base near Colorado Springs, Colorado, promises to increase in accuracy from the current 10m down to 30-50cm.

The current global market of applications and services, in excess of $3 billion, could grow to $10 billion by 2010, according to Frost & Sullivan.

The mainstream location-based services of GPS have become all but mundane. More than 5 million GPS consumer recreational units were shipped in 2003, according to ABI Research, up from 3.2 million units in 2002. New applications that are making everyday use of GPS signals range from the OnStar automobile service to Microsoft Corp.'s Streets and Trips 2005. The latter includes a GPS receiver for laptops, using a USB port to link Microsoft's previous mapping application to a position finder.

Industry applications range even wider, from geodetic surveys to the accurate base station synchronization described by Symmetricom Inc. in this In Focus section. Some uses span military and civilian applications, such as GPS transceivers used in tracking other satellites in space, as raised by Peregrine Semiconductor Corp.

The accuracy of a sub-$100 consumer receiver increased from 100m to about 10m. At that time, civilian corporations that were gaining better industrial accuracy through differential comparison of GPS signals from the ground found they could achieve sub-10m position accuracy far more cheaply than before.

Upgrades to GPS came in three waves. Just recently, with the launch of GPS-IIR-13, there was an all-time high of 30 GPS satellites in space, consisting of 24 active birds and six on-orbit spares. They reside in six orbital planes. Receivers obtain coordinates in three dimensions plus time stamps by "trilaterating," or triangulating, distances from at least four GPS satellites, which actively broadcast signals in orbit.

Major upgrade

Beginning March, the Lockheed Martin Corp. GPS IIR-M, for "modernized," will add a new military code to the GPS transmissions, while the Boeing GPS-IIF will begin launches in 2006, with additional signals in both military and commercial frequencies. The most significant evolution in GPS architecture will come with GPS III (not to be confused with a consumer receiver of the same name), which will add major security, accuracy and availability features when the first satellite is launched in 2012.

The current generation of IIA/IIR satellites uses two microwave frequencies, the civil L1 and military L2. Since May 2000, civilian users have had access to the L2 frequency, albeit without knowing the L2 pseudorandom codes, and the military has always used both frequencies. When IIR-M launches next March, a second civil signal will be added in the L2 band, while two new military codes will be added to L1 and L2. The IIF satellite will add a third civil signal on a band called L5, since bands L3 and L4 will be reserved for military uses outside traditional navigational duties.

The addition of the new bands will make dual-band navigation on civil frequencies more robust and less costly, since current use of L1 and L2 for commercial applications involves costly DSP resources to calculate L2 signals when pseudorandom noise codes are not known. The users of differential GPS (D-GPS) rely on a stationary reference receiver and a roving receiver to make ground-based corrections on satellite triangulation. Before the May 2000 unblocking of L2, D-GPS was the only means of commercial resolution of location in areas under 10m.

When IIR-M and IIF satellite frequencies are added, D-GPS will offer a position accuracy of 30-50cm.

New services

Such accuracy will be of most interest to demanding commercial users in aviation, farming, public services, geodetic surveys and small-scale mapping. But it will also enable a variety of new services, including location-based advertising to augment existing 2.5/3G services, and even sophisticated personal surveillance tools.

The availability of such precise locators may have social implications as well. In early September, a southern California man earned the dubious distinction of being the first person to be arrested for "stalking" using GPS, a capability that will be enhanced significantly with the more accurate civil frequencies on the horizon.

The military implications for the evolution of GPS, meanwhile, are inescapable. The Pentagon made clear during the early days of the Iraq war that it sees GPS as a war-fighting weapon system, to be used to guide everything from ships and jet fighters to individual precision-guided munitions like the Joint Direct Attack Munition.

The speed with which airborne raids took out a rudimentary Iraqi anti-GPS jammer, and the degree to which the Pentagon touted such jamming as an offensive action, show both how seriously space warfare advocates consider measure/countermeasure battles using GPS, and also how utterly U.S. forces dominate air and space. Indeed, GPS III plans often are referred to as "NavWar" within the Air Force Space Command.

The U.S. Defense Department is looking to GPS III as an enabler for maintaining navigational dominance over emerging systems like the European Space Agency's Galileo network, while still keeping the GPS as open as possible.

In some senses, however, GPS migration to II and III resembles the migration to new generations of the Milstar VHF/EHF communications satellite: There is a lot of talk about maneuverability and survivability, but not a lot of detail in the plans, even for those with the proper security clearance.

GPS III is a going concern, in that competing teams led by Lockheed Martin and Boeing have submitted data for Phase A of the design effort, leading to a system requirement review slated for next spring, and a decision on system go-ahead in November 2005. Assuming a positive review is issued next November, the U.S. Air Force will request proposals for Phase B in early 2006.

Networked warrior

But GPS III barely survived some tough budget juggling between the Afghanistan and Iraq wars, as Congress tried to balance demands between future weapon systems and current troop deployments. Air Force Undersecretary of Space Peter Teets originally agreed with Congress that no funding would be allocated to GPS III in fiscal 2004, because the Air Force was more interested in gaining initial funding for two new programs promoted by the National Reconnaissance Office: Space-Based Radar and Transformational Communications Satellite (TSAT).

Then along came the war in Iraq: GPS capabilities were cited constantly as the way to provide the backbone for the "networked warrior," and to enable precision bombing over Baghdad and Tikrit. During the fiscal 2005 budget process, the Air Force received its full request of $40.5 million for GPS III. By contrast, Space-Based Radar and TSAT have been put on hold by a skeptical Congress, worried that the two new programs are so revolutionary, they will fall victim to the same massive cost overruns that plagued the Space-Based Infrared System, known as SBIRS-High.

If the past is any guide, the capabilities provided to the military in initial launches will be translated to broad and unanticipated civilian applications 10 to 20 years later.

But the Pentagon's wish list for GPS III is still far from formulated. Even if the first GPS III satellite meets its 2012 target, the gap between the first GPS I launch in 1978 and the early civilian applications around 1990 would suggest that the radical upgrade in civilian position-location service resulting from GPS III might not show up until 2025.

- Loring Wirbel

EE Times




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