GPS Ideas

I was reading some stuff today about GPS and had a few ideas. I'm curious as to if anyone things they have any practicality. I am by no means an expert on GPS and basically this is my first time even reading about some of the specs and stuff. I did take several courses in physics several years ago by I have forgotten most, if not all of what I have learned. These are just ideas and I am not saying they will work or even make sense... just trying to get some feed back. (note, everyone is non-relativistic for simplicity)

I was thinking that one could attach to each satellites two frequencies to transmit on. This might help in solving the problem of the speed of light changing due to the different mediums that it transmits through.

The data that the satellite transmits would include the distance from itself to all other satellites and to a reference on the ground.

The idea for the different frequencies is to somehow build up a differential method of dealing with the change in the speed of light as it passes from the transmitter to the receiver. I'm not sure if it will work but I was thinking that, say, if satellite A transmits the signal on frequency X and frequency Y that one might be able to remove the changes in the speed of light through the different mediums because it will effect both signals the same amount. Not sure if this would lead to something worthwhile though. Basically it would seem that one could compute the dispersion due to the medium between the transmiter and receiver to "repair" the distance computed. Maybe there are other ways to do this too by using only one signal and by using some modulation method.

By including the distances(and maybe positions too) from all the satellites from each other, which are able to computed in a vacuum(I think, not sure if it will go through the ionosphere but maybe the method above could work too). This might not be practical as the satellites would have to send signals to each other too and some power would be wasted.

It would seem that by knowing the complete geometry of all the satellites one could use that information to compute a more accurate location of the GPS receiver. Basically all the information to find the location on earth would be sent by just one signal. Since the receiver would be getting atleast three signals(or six) and a series of data that should be identical except for the computed distances to the reciever from each of the 3 satellites, it could compute errors in the distances and possibly use statistics to increase the accuracy of the data. One could also calcuate angles for whatever reason too. By having ground facillaties included, which would essentially be "fixed" satellites, would could tie everything together. i.e., angles could be computed from a reference point, say the north and south poles. One could possibly, say, know how far they are from the polar axis and such... which at this point I think at this point one has to reply on "maps" to figure things like that out.

Not sure if that makes sense or would work but just an idea.

Thanks, Jon

Reply to
Abstract Dissonance
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GPS works fine just the way it is. A $100 receiver will get you 5m general accuracy, a more expensive survey or military model will get you down to the cm range. In the US you guys have WAAS which gets you even better accuracy.

I'd suggest taking up Geocaching, the fresh air might do you some good! :->

Dave :)

Reply to
David L. Jones

In the GPS Specs I just read it said that the best is ~20meters, with waas its like 5 and with differential GPS its about 1-3 meters.

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While I'm sure thats a tremendous amount of resolution for such long distances surely any improvement would be a good thing? (not that I am saying I can improve it but mainly I was just wondering about the feesibility of my ideas).

Also I'm sure that if one wants to increase the accuracy then it requires more expensive equipment and perhaps larger equipment?

Reply to
Abstract Dissonance

That's what the specs say for instantaneous accuracy. But in practice you can easily get

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Yes, if you spend (a lot) more money on a receiver and you get cm accuracy. The capability is already there in the current system. Larger?, maybe a bit, but my GPSr that fits on my wrist and gets 5m is good enough for most normal purposes.

Dave :)

Reply to
David L. Jones

Yes but GPS wasn't created just for you? ;)

Surely you can think of several applications where higher resolution GPS would allow for much more scientific endevours? Its not that I'm claiming I have a method to make GPS better but I was just wondering about its theoretical implications. I'm sure there are a lot of scientists that would love < 1mm accuracy with gps to measure geological movements and such. Also it could be useful for engineering work such as digging tunnels(but I doubt it would be that usefull as surely there are already much better methods for this). Could be used for autopilot systems(again, maybe not that great but who knows... it could reduce components used since one could potentially calculate acceleration from it(but I dont' know how accurate it would be).

Reply to
Abstract Dissonance

Like I said, it's already available. Commercial Survey GPSs can go down to a few centimeters. You can't expect much better than that due to the physical size and position of the receiving antenna!

They already use GPS for digging tunnels and other construction stuff, plus autopilot systems. GPS receivers can already calculate acceleration and a whole host of other parameters. I saw a doco the other day on the new 800m high tower being built in Dubai. They have to use GPS surveying to ensure that the tower is being built precisely vertically!

Dave :)

Reply to
David L. Jones

Un bel giorno Abstract Dissonance digitò:

They already do that, there is the commercial L1 band (around 1500 MHz) and the military L2 band (around 1200 MHz). And even if you don't know the P-code sent through the L2 band, you can still feed some correlator with this signal to get useful informations about ionospheric delay propagation and increase accuracy by 30-50%; a lot of high-end commercial GPS do that.

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Reply to
dalai lamah

They do? That's interesting, looks like all the precision navigation and

3-D accelerometer people are out of business then.

Really?! That's one helluva geodesic survey there!

Reply to
Fred Bloggs

It's already done. GPS has two frequencies L1 and L2. The L2 signal is AFAIK only available for military users. The new Galileo system shoud have 4 or 5 frequencies.

Reply to
Dan Oprisan

My wrist GPS can show me my speed, average speed, elevation, rate of climb, distance travelled, time to reach wapoints or backtrack and a whole host of other stuff. Doesn't do acceleration, but it would be a simple firmware mod if they so desired.

They ain't mucking around with this thing!

Dave :)

Reply to
David L. Jones

Yeah, in another reply the guy said they already do what I said. So I suppose they use that to get down to a few cm's or so.

I was under the impression that GPS couldn't be more accurate than a few meters when I wrote this. I didn't know it could go down to centimeters. Would be cool if one could get it down to millimeters... ofcourse some would say this is overkill but I'm sure there would be uses for it.

Thanks, Jon

Reply to
Abstract Dissonance

Yes, but the point was to use the two frequencies to measure the dispersion to remove the problem with the speed of light changing. which, from what I read was the most significant problem with accuracy.

Although what I mentioned was pretty much exactly what they do anyways from what I have been told on another newsgroup.

Jon

Reply to
Abstract Dissonance

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When the first portable civilian GPS systems came out, I was told that they would not operate it they determined that they were moving at over 60 mph in order to prevent them being used for blind aircraft landings. I bel;ieved this because of the bad vertical accuracy, especially before SA was turned off.

Reply to
Richard Henry

It's probably not so much "the speed of light changing" as refraction in the atmosphere that affects the reception.

But, as have been said, they seem to be doing a pretty good job at compensating for that right now.

Got $100M for research? ;-)

Cheers! Rich

Reply to
Rich Grise

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Reply to
Wes Stewart

That is exactly what happens. The system already corrects wholesale for atmospheric delays (using ground segment measurements) and a dual-frequency receiver can work out most of the remaining error from the relative propagation delay between the two frequencies.

Regards,

Iwo

Reply to
Iwo Mergler

The 'speed of light' (strictly, the phase velocity) changing in different media is what causes refraction in the first place.

Tim

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Reply to
Tim Auton

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