This letter appeared in the July, August and September 2008 JAVAD GNSS ads in The American Surveyor:
The Future Is Not What It Used To Be
A few decades ago, companies like AT&T, Ford, IBM, General Electric, Standard Oil, Pan American, J.P. Morgan, and others were making five, ten, even twenty-year plans. The future was predictable. But now companies adjust their plans several times a year and still get shocking surprises. The future is not what it used to be. In many respects, it is no longer predictable.
To transmit signals, GPS uses CDMA (Code Division Multiple Access) and GLONASS uses FDMA (Frequency Division Multiple Access). Simply put, all GPS satellites use the same frequency while broadcasting different codes, while GLONASS satellites use the same code but on different frequencies. In previous pages we explained how we had to work harder to make GLONASS as good as GPS for precision applications. Why such a drastic difference between GPS and GLONASS? The answer is that the difference was not drastic until surveyors showed up! When GPS and GLONASS were on the drawing boards, no one had a clue that these systems could be used for millimeter-level accuracy and that the precise community would be potential users. With GPS we just got lucky. With GLONASS we have had to work harder to achieve comparable accuracies.
Don’t feel bad. More than 90% of today’s users were not part of the intended user-crowd. Even then the future for the satellite usage was not predictable. Cell phones did not exist and car navigation was not on the horizon. Well after the initial GPS satellites were launched, scientists at JPL thought of using the GPS carrier phase for accurate measurements. Before then, accuracy of ten meters was the best that could be hoped for and even that was reserved for military applications. In 1983, at an Institute of Navigation conference, I presented a paper along with a homemade video clip showing that GPS could be used for street navigation. A senior vice president of Rockwell borrowed the clip to show to the U.S. Congress and in return I got a tour of the fabulous Rockwell rocket facilities.
In early proposals, thought was given to applying a user-fee to each piece of GPS equipment. Later, it was decided that the cost of collecting user fees would be more than the actual money collected. Even today I am eager to see the calculations for this conclusion! With hindsight, we see today that the number of users are in the hundreds of millions and the companies from which to collect the user-fees number less than 100.
Don’t worry, it is too late to change the user-fee policy, and with GPS being free Galileo will not be able to charge either!
In such a volatile and unpredictable world we should salute all those who gave the FREE gift of GPS to the world, which after 30 years, is still a marvel. Equally, we should be thankful to the creators of GLONASS, and we should encourage the Galileo authorities to follow the same well-proven and beneficial path.
There are many rumors regarding the "relationship" between GPS and GLONASS. One says that the Russians "copied" the U.S. GPS and Space Shuttle programs. We all know that in the 1950s the Russians jumped ahead of U.S. in space by launching "Sputnik", the first satellite. When following the location of Sputnik from known locations, U.S. scientists quickly realized that satellites could be used in the reverse role: if the orbit of the satellite was known the location of the user could be determined. Another rumor says Russian scientists were well aware of the use of satellites for navigation but could not get funding from their military because, according to Russian intelligence, there was not such a program in the US military at that time! Whether these rumors are true or not, the fact is that today the cooperation of bright minds is helping users all around the world.
Back to the CDMA vs. FDMA discussion. The Russians are seriously considering employing CDMA techniques for future generations of GLONASS satellites. I have been privileged to participate in some of the discussions between Russian and U.S. scientists to make both systems more interoperable. Many people on both sides of the globe are working hard to make this happen. I do not wish to give false hope; if such a switch happens, the operational GLONASS CDMA satellites will not appear any time soon. And meanwhile, we have found a perfect solution for handling GLONASS biases while keeping the clear advantage of more satellites in the sky.
Until the next issue