Land-Based Positioning

> Would it not be inherently easier to create a positioning system from terestrially based towers?

You mean like............Bilby towers?;-)

Seriously, considering transmitting range, line of sight, etc., etc., how many towers would we need to cover the entire USA?

Most of the US already has cell phone coverage, but it's not the same, especially if you are looking for survey-grade accuracy.

Not to knock you, but I've done a fair share of surveying for communication towers. Have you ever looked at one (especially really tall ones) in the wind? I've seen them sway 10 feet or so. I think that RTK from wifi and cell towers is a mixture of really poor ideas. They all have merit, but I don't think it would work.

However, I bet Loyal can kick in here and tell us more about it.

From what I understand there's a company called lightsquared that is trying to build a bunch of towers that broadcast a powerful signal.

🙂

Structures can be built to not sway.

I would think the bigger hurdle is the fact that each satellite has a cesium clock, but couldn't be addressed by other means?

Towers typically aren't.

i had issues with the early topcon hyper lite plus systems once. I had to call tech support and they guided me through using their tower but it was really crappy solutions. I too, do not think that the towers are the way to go..... unless.... you could put sensors at the tips of the towers and at the base that could account for the sway. then re-calc the cntr position and project that the same way the carrier sig holds the UTC time and SAT positions. then you might have an RTK chance..... just a thought.... oh, and with every sway in the horizontal, you will have a change in vertical, which would have to be determined point along the arch where you placed your transmitter, add-to-which, will be constantly changing..... hummmmm.... IDK.... we might be better off. good question though.

Loran. spent much time in a Bellanca Viking with a turbo for high altitude flying. It was Loran that guided us around the sky. Did not use it on the fishing boat I rode from Seattle to Alaska and back in 65. It was chart, compass and a depth finder for guidance.
jud

Adam, Welcome to the board. There are quite a few lightsquared discussions down the list.

Couldn't the compromise for the Lightsquared situation be some kind of 4g RTN? Could someone smarter than me explain why the GPS receiver would have to be on "top" of the tower and subject to sway?

I saw that there were other threads about lightsquared. Lightsquared is an asides to my original subject of land-based positioning.

GPS was conceived and implemented for global recon/spying and guidance.

Lightsquared will only disrupt GPS in the continental United States.

What is the cost of the typical satellite launch? astronomical in comparison to building a ground base RTN positioning tower. And they can be built to not sway. Think power transmission lines (it is supposed to take gale-force winds to move these). Still a heck of a deal when weighed against building/launching satellites.

The idea of WiFi positioning was kicked around a few years ago. It basically used datum-referenced routers over a small area, such as, a football stadium. I use this comparison because I remember reading an article about how they could but a receiver inside the football to mark yardage, first downs, etc.

Not only are they cheaper to build, but wouldn't the ambiguities be easier to mathematically model out as well? No ephemerides to deal with, no atmosphere to model out (except near ground-level, and we are possibly talking relatively short distances).
There is also the concept of stronger signals. Isn't a GPS satellite's signal weakness due to the inherent constraints of solar power?

Just as a disclaimer, I don't intend to portray myself as an authority on any of these matters. My questions are not rhetorical.

My hypothetical eliminates "GPS" receivers entirely. The tower becomes the satellite.

Good idea in fact I have put up hundreds of towers for positioning systems i.e. autotape, syledis, and others mosty in the 460mhz range. The problem will not be a lat/long solution but it is going to be very diffucult at best to get any type of elevation solution.

We already have a system that works. Why would we need more towers?

Personally I don't like looking at towers every five miles that I travel down the road. I can only see a SV when there is no light pollution in the night sky and I look very carefully to spot one.

We need more towers like we need more traffic.

Jim

Accurate Land-Based Positioning ?

Requires universally accurate clocks as a starter. Without GPS it is a dead issue.

After that the position depends on the reliability of each tower position. It should be expected that towers may move up to 10 times the GPS wavelength. Well, there goes integer fixing out the window.

What was the question again?

Paul in PA