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Military Tech: GPS and Networking
king of birds writes "The New York Times has an interesting article on the present military use of GPS. While some units have rather modern system that can graphically display locations of other troops, others rely on 10-year-old 5 channel receivers. Kind of odd when I can 12 channels on my civilian model (with admittedly lower spatial accuracy)." aaronvegh writes "From the Canadian Press, a story about how a US infantry division uses a system of transponders and servers to track friendly and enemy units, from the headquarters to inside individual tanks. Talk about total information awareness! No friendlies were harmed in the making of this story."
WW II: 21,000 (16%)
Vietnam war: 8,000 (14%)
Gulf War: 35 (23%)
Afghanistan (2002): 4 (13%)
The difference today is instant communications. And the small number of total casualties allows the media to focus on each death.
Many military radios can do frequency hopping - changing frequencies many times a second. So unless you have a similar device AND you know the algorithm, AND you know the starting frequency, AND you know when the radios were turned on...
Come on, I know someone works in a Comm MOS and can 'splain it better ;-)
A pilot, in those days, was the only unfettered and entirely independent human being that lived in the earth.-Mark Twain
Many military radios can do frequency hopping - changing frequencies many times a second. So unless you have a similar device AND you know the algorithm, AND you know the starting frequency, AND you know when the radios were turned on...
I use to work on military communications. The version I worked on switched frequencies about 10,000 times a second. That was ten years ago. Not only is this harder to track, but even more importantly it's harder to jam. Keys were changed daily.
From the article:
The new system will also track all 12 G.P.S. satellites in each hemisphere at once. The old units can only track five satellites at once, and signals from four satellites are required to establish a three-dimensional position. In addition, current G.P.S. receivers are somewhat vulnerable to enemy equipment that beams false G.P.S. signals to indicate the wrong location, a technique known as spoofing.
Here's the thing: the article is correct about the PLGR needing four locked satellites to establish a three-dimensional position. However, a PLGR can also establish a two-dimensional position with two locked signals and one intermittent one. The important part here is that the PLGR's most common use (determining position for individual soldiers and vehicles) doesn't need a 3D position. Your position (including elevation) can be plotted on any map using only two coordinates. 3D positions are only important for aircraft, air defense, and artillery. And for the most part, those guys aren't using PLGRs. Oh, and PLGRs can track up to 10 satellites.
This corrective post brought to you by a US Army Cavalry Scout. (None of this information, by the way, is classified or restricted. The reporter just didn't check sources very well.)
Arr! The laws of physics be a harsh mistress!
Slow? resource intensive?
GPS uses triangulation, essentially, although it's a lot easier since it sends out a timestamp. To triangulate a unit, you would have to have 3 stations be time-synchronized and all would have to know they heard the same signal -- which is undoubtedly coded making it EASIER to know it was the same.
In other words, tank A sends out an encrypted digital message of "here is my location". If 3 stations hear the signal and timestamp it to the nanosecond, they can them compare the signal--without knowing what it actually broadcast--and tell it was the same broadcast. Using the time data and and the exact location of each station, it's a simple matter to plot the location of the transmission. The farther apart the 3 stations, the better the accuracy. More stations would lead to more accuracy, plus you'd couldn't shut it down by bombing a single tower as long as 3 remained.
This would essentially be a reverse-gps. It's only resource-intensive and slow if you have a single unit driving around with a directional antenna, like the FCC did to locate pirate stations. If you can synchronize the clocks and timestamp signals accurately, it's almost trivial to pinpoint the location.