GPS tracker Modernization and Global Navigation Satellite System
The most important hardware in a GPS surveying operation are the receivers. Their characteristics and capabilities influence the techniques available to the user throughout the work, from the initial planning to processing. There are literally hundreds of different GPS receivers on the market. Only a portion of that number is appropriate for GPS surveying and they share some fundamental elements. They are generally capable of accuracies from submeter to subcentimeter. They are capable of differential GPS (DPGS), real-time GPS, static GPS, and other hybrid techniques. They usually are accompanied by postprocessing software and network adjustment software. And many are equipped with capacity for extra batteries, external data collectors, external antennas, and tripod mounting hardware. These features, and others, distinguish GPS receivers used in the various aspects of surveying from handheld GPS units designed primarily for recreational use.
A GPS receiver, like any electronic tracker, must collect and then convert signals from GPS satellites into measurements. It is not easy. The GPS signal has low power to start with. An orbiting GPS satellite broadcasts this weak signal across a cone of approximately 28ยบ of arc. From the satellite’s point of view, about 11,000 miles up, that cone covers the whole planet. It is instructive to contrast this arrangement with a typical communication satellite that not only has much more power, but a very directional signal as well. Its signals are usually collected by a large dish antenna, but the typical GPS receiver has a very small, relatively nondirectional antenna. Fortunately, antennas used for GPS receivers do not even have to be pointed directly at the signal source.
Stated another way, a GPS satellite spreads a low power signal over a large area rather than directing a high power signal at a very specific area. In fact, the GPS signal would be completely obscured by the huge variety of electromagnetic noise that surrounds us if it were not a spread spectrum coded signal. The GPS signal intentionally occupies a broader frequency bandwidth than it must to carry its information. This characteristic is used to prevent jamming, mitigate multipath, and allow unambiguous satellite tracking.
The configuration of the GPS Space Segment is well-known. A minimum of 24 GPS satellites ensure 24-hour worldwide coverage. But today there are more than that minimum on orbit. There are a few spares on hand in space. The redundancy is prudent. GPS, put in place with amazing speed considering the technological hurdles, is now critical to all sorts of positioning, navigation, and timing around the world. It is that very criticality that requires the GPS modernization. The oldest satellites in the current constellation were launched in 1989. Imagine using a personal computer of that vintage today. It is not surprising that there are plans in place to alter the system substantially. What might be unexpected is many of those plans will be implemented entirely outside of the GPS system itself.
In fact, the goal of a single GPS tracking device that can track all the old and new satellite signals with a significant performance improvement looks possible. But after all, the main attraction of interoperability between these systems is the greatly increased number of satellites and signals, better satellite availability, better dilution of precision, immediate ambiguity resolution on long baselines with three-frequency data, better accuracy in urban settings, and fewer multipath worries. Those are some of the things we look forward to. It is beginning to look like at least some of those things are achievable.
More GPS Tracking Solution at http://www.jimilab.com/ .
A GPS receiver, like any electronic tracker, must collect and then convert signals from GPS satellites into measurements. It is not easy. The GPS signal has low power to start with. An orbiting GPS satellite broadcasts this weak signal across a cone of approximately 28ยบ of arc. From the satellite’s point of view, about 11,000 miles up, that cone covers the whole planet. It is instructive to contrast this arrangement with a typical communication satellite that not only has much more power, but a very directional signal as well. Its signals are usually collected by a large dish antenna, but the typical GPS receiver has a very small, relatively nondirectional antenna. Fortunately, antennas used for GPS receivers do not even have to be pointed directly at the signal source.
Stated another way, a GPS satellite spreads a low power signal over a large area rather than directing a high power signal at a very specific area. In fact, the GPS signal would be completely obscured by the huge variety of electromagnetic noise that surrounds us if it were not a spread spectrum coded signal. The GPS signal intentionally occupies a broader frequency bandwidth than it must to carry its information. This characteristic is used to prevent jamming, mitigate multipath, and allow unambiguous satellite tracking.
The configuration of the GPS Space Segment is well-known. A minimum of 24 GPS satellites ensure 24-hour worldwide coverage. But today there are more than that minimum on orbit. There are a few spares on hand in space. The redundancy is prudent. GPS, put in place with amazing speed considering the technological hurdles, is now critical to all sorts of positioning, navigation, and timing around the world. It is that very criticality that requires the GPS modernization. The oldest satellites in the current constellation were launched in 1989. Imagine using a personal computer of that vintage today. It is not surprising that there are plans in place to alter the system substantially. What might be unexpected is many of those plans will be implemented entirely outside of the GPS system itself.
In fact, the goal of a single GPS tracking device that can track all the old and new satellite signals with a significant performance improvement looks possible. But after all, the main attraction of interoperability between these systems is the greatly increased number of satellites and signals, better satellite availability, better dilution of precision, immediate ambiguity resolution on long baselines with three-frequency data, better accuracy in urban settings, and fewer multipath worries. Those are some of the things we look forward to. It is beginning to look like at least some of those things are achievable.
More GPS Tracking Solution at http://www.jimilab.com/ .
Comments
Post a Comment