Non GPS based Positioning System

[Tuner]

Being somone who strives for effeciency and multipupose design. I thought Hmm if most of these aircraft require radio telemetry why can we not use the radio telemetry for positioning especialy on landings near the base station.

This could add to redundency and rubustness of the system.

Possible with having 3 anntennas one at each wingtip and one at the tail and analyse the time arrival difference though I think it would be very small this could allow you to triangulate the radio source in 3 dimentions in theory right?

Any way just wanted to see if anyone has worked with systems like this.
I know they use a similar type system for Auto Racing like NASCAR for tracking the cars position.

[XJet]

Many years ago, before GPS was a reality, I designed and built a system for aerial spraying that used three ground-based transmitters to provide signals that were received by an onboard system which then calculated the desired flight path and outputted the result on a bar of LEDs.

When the pilot was flying the correct path a single green LED would remain lit, and as he deviated left or right, LEDs to the left or right of that center-light would be illumnated to indicate the error direction and magnitude.

The system worked very well but was eventually made redundant by (D)GPS.

So the answer is "yes" you could produce a ground-based reference system but it would involve more than just using the telemetry transmitter as a reference and is probably beyond the scope of all but the keenest DIY experimenter.

[Tuner]

I have just heard of this being done with bluetooth a long time ago and figured if it can be done modifying the bluetooth protocol then maybe????

And like you siad you used 3 ground based antennas probably spaced rather fare apart.

Im not letting go of this quite yet but thanks I already felt it was out of my scope but I know some teletnted EE's so I was hoping to find some info on some designs.

I have considered using a cellphone for telemetry despite its long latencies one could posibly use the built in Positioning system based off the cell towers. This would be very doable though I am sure I am missing something like it has a very low refresh rate or awful accuracy????

Thanks!

[kodel]

cell phone based positioning is cerainly possible. With a PDA (Windows Mobile) based GSM phone, you can extract BSSID, signal strength and phase shift of the signal. With that (and a database of all the antenna locations, which is not freely available but "hackable" by spidering the website that has the building permits for the antenna towers online in pdf format, at least in belgium) you can calculate your position.
But it has nowhere near the accuracy of GPS, so for airborne use it makes no sense. When you're inside buildings cellphone based positioning is more usefull. In Europe, mobile operators offer this as a service (to application builders). After the user gives his permission to your application, the application can retrieve the position of the user. However, cost is quite high per position request (0,1 - 0,5 euro). But it saves you the hassle of setting up a location system yourselves.

greets,

Koen

[Iraqigeek]

Though this isn't my exact field of expertise, but I had the luck of being involved in such a positioning system back in university as it was a graduation project of a friend in the EE dept.

Basically, each pair of antennae triangulates the signal and gives you an angle whose reference is a line perpendicular to the line connecting the pair of antennae. With a third antenna, you will get two angles, which in turn triangulates the distance as well as direction of the transmitter. To get altitude, you will need a fourth a fourth antenna that is considerably higher or lower than the triplet providing the XY position. The accuracy of such an arrangement is highly dependant on the distance between the antennae. In my friend's project (which was for the military at the time) the three antennae were 100 meters apart each and, if I recall correctly, gave an error of about 50 meters at 10km distance.

As for using a mobile phone, if we are talking about GSM, I wouldnt rely on it for any positioning calculation that is used for navigational purposes. While it is possible to have rather good position calculation from your mobile operator, the object has to be moving in order for BTSs at the towers to be able to get a good triangulation. In any case, the handset alone can only give you a very lousy positioning that depends on the BTS ssids it is detecting, and then match those ssids to a database containing the locations of those BTSs. However, the operator can get a rather accurate triangulation of your position by calculating the phase shift of your phone's signal since all the operators BTSs MUST be time synchronous. Doing this on the phone is not possible since the phone can be locked on a single channel only at any time.

Now, if you are in a building, things can get really messy, especially if we are talking about big buildings since most of those will usually have one or more repeaters mounted on their roofs with antennae spread isnide the building to improve signal reception. IF the building has more than one repeater, or if the repeater has more than one internal antenna (which is the norm), the operator can get an approximate position based which antenna is picking you best. I seriously doubt that it is possible to triangulate someone's position inside a large building in the precense of a repeater as very impractical to triangulate a phon'es position based on the signals sensed on the internal antennae since the repeater will have to have knowledge about so many parameters such as the exact lengths of the cables connecting each antenna to the repeater, the exact location of each antenna, and many other factors.

I am not familiar with CDMA networks, so I cant say whether they do a better or worse job at calculating position from the phone itself.