One of the most pressing issues facing the GPS system today is the deterioration of the GPS constellation of satellites. This has been significant cause for alarm, as some reports place satellite breakdown as early as 2012. New satellites need to be launched, and GPS modernization promises to update the system to keep it from falling apart.
This isn’t just a question of deterioration, however. The technology that GPS depends on has advanced greatly, particularly with regards to providing higher powered signals. The current satellites, the Block I and II, are obsolete, and modernization will upgrade them to provide state-of-the-art technology.
GPS use has also exploded, now infiltrating almost every part of our daily lives, from navigation on the streets, to companies tracking their inventory to logistical use in wars abroad to faster responses to car accidents. There is simply more demand for a better GPS, and the government hopes to answer that call.
Competition with other GNSS systems is also an important aspect. GPS has been competing with the more restrictive Russian GLONASS system for decades now, and has largely won out in the commercial market. However, two new GNSS systems are currently being developed as well, the EU’s Galileo system, and China’s COMPASS. How the GPS system will fare against these, even with current modernization, is anyone’s guess.
GPS III sees the addition of four new signals, three new civilian signals and a military signal. One of the civilian signals and one of the military signals will be used to provide redundancy, making the signal difficult to interfere with either through intentional or accidental jamming of the signal.
Another handy little benefit: by using two different signals, you can directly measure any delay error that happens in the ionosphere as the signal makes its way towards Earth, and thus remove it from the calculations the receiver makes during triangulation. This will subtly, but significantly increase the accuracy of GPS receivers. Receivers that are capable of receiving two signals are known as dual frequency receivers.
The new redundant civilian signal is known as L2, compared to the original L1. The new military signal is known as M-code.
Another of the civilian signals will be used exclusively for aviation safety services, particularly the commercial aviation that occurs on a mass scale in today's globalized world. Radar technology is slowly being replaced by GPS technology in commercial aviation to provide more accurate and more reliable positioning, and these benefits may be guaranteed through use of a dedicated signal. This signal is appropriately referred to as safety of life, the formal name being L5.
The fourth, and final civilian signal is designed to allow for interoperability between GPS and other GNSS systems such as GLONASS, COMPASS and Galileo, as all of these systems plan on broadcasting this signal in addition to their own. This will allow for previously unknown coverage, a truly global network, with all of the GNSS constellations capable of working as one. It will operate on the same frequency as the original civilian signal, L1.
All of these signals will also be higher powered than previously, meaning that the signal will be significantly stronger when it arrives at the Earth’s surface. GPS signals are, as you might imagine, quite weak after they have traveled thousands of miles to the Earth’s surface. Even a small amount of signal degradation, such as the signal multipath that happens when the signal reflects off of surfaces such as within an urban canyon, or attenuation as the signal passes through solid surfaces like a roof as it goes indoors, can mean little or no reception. Background interference is also a concern in an increasingly radio-noisy world.
With this more powerful signal, less of the signal is likely to degrade, resulting in more satellites in a faster acquisition time with greater accuracy.
One new addition to GPS technology: spot beam antennas. These antennas will essentially transmit a high powered GPS signal to a small area on the Earth, one that is a few hundred kilometers in diameter. This is a directional antenna, in that it can move to point at different parts of the Earth and thus provide greater accuracy where needed.
This will only be available for military use, however, in places with current US military conflict.
It’s important to get a sense of how long this has been in the making. The GPS system was rendered complete in its current state in 1995. Already by then, technology had already moved forward, and greater coverage was desired. In 1998 the White House initiated the GPS modernization effort, which was authorized by Congress in 2000. This included an end to selective availability, which was artificial degradation of the civilian signal so that it would not be as accurate as the military one.
The contract for the modernization effort wasn’t awarded until just a few days ago as of the writing of this article, in February of 2010 to Raytheon. The target date for completion is 2013, with incentives offered for completion as early as 2011. So, while we’ve been waiting a long time for this, we should be seeing the effects of this program soon!
For a good in-depth piece on some of the changes proposed by GPS modernization, check out this piece from 2002 from Crosslink.
For information from the government regarding these plans, check out the Space Commerce website’s overview of GPS modernization.
For the latest news on GPS modernization, check out the GPS modernization section of GPS World.