[time-nuts] Need advice for multilateration setup

Robert Watzlavick rocket at watzlavick.com
Fri Apr 3 23:51:34 EDT 2015

To head off a bunch of replies - I think I stumbled upon what is being 
suggested.  To extract the pseudorange, you have to figure out the 
offset of the locally generated PN code against the one that is 
received. In this reverse GPS case, I assume each ground station would 
have to start their local PN codes at the same time?  Then you would be 
able to get the pseudoranges at each ground station and use those values 
for the multilateration equations.  You still would have an uncertainty 
of one clock cycle since the phases of the local clocks at the stations 
wouldn't be aligned but several folks have suggested ways around that.


On 04/03/2015 10:12 PM, Robert Watzlavick wrote:
> I have an amateur radio license (mostly CW/HF and some VHF/UHF 
> experience) and I've written some driver software for an IQ 
> demodulation board but I have to admit, I would have no idea how to 
> begin setting up that system as initially described by Attila and 
> expanded by you and others.  I have a rudimentary understanding of the 
> modulation schemes involved but I don't fully understand how the 
> various codes mentioned fit in. I've poked around a bit at some 
> articles on PN codes and I can see how data would be transmitted but I 
> think I'm missing something key that allows you to extract positions, 
> velocities, etc. out of the various links.  I think I have some more 
> reading to do :)
> Thanks,
> -Bob
> On 04/03/2015 06:08 AM, Magnus Danielson wrote:
>> I think this is a good idea, and it is relatively straight-forward to 
>> do.
>> You can observe both code and carrier phase this way, given that the 
>> transmitting radio is coherent with the code generation clock. 
>> Doppler also pops out of the tracking station.
>> A good coding-gain reduces the need for a strong transmitter.
>> The issue might be the allowed width of the signal being transmitted, 
>> forcing the chipping rate down.
>> Cheers,
>> Magnus

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