21 Sep
2016
21 Sep
'16
4:48 p.m.
Hi. On the front page of the wiki (http://op25.osmocom.org/trac/wiki) I
see the following bullet point:
"Locate and track the locations of P25 mobile stations."
What exactly is meant by this? How could such a thing be accomplished?
--
Alex
22 Sep
22 Sep
1:30 a.m.
Hi Alex,
Some of those ideas/tasks date back to 2008 when the project was its'
initial embryonic stages. The idea back then was to find a way to track a
P25 station geographically - for example, using multiple time and frequency
sync'd USRP's (with GPSDO for location and time sync) to do time difference
of arrival type location determination, or even a Roanoke Doppler style of
receiver.
Since then, Motorola TRBO and DMR has become very popular, and with it,
services such as LRRP are transmitting data over some of these networks. I
know that some of the Motorola APX and TRBO series radios can be set up to
transmit their GPS locations in the clear, which could be easily read over
the air. This has been done in other projects with TRBO, but not with P25
to my knowledge.
These are just a few ideas I threw around, Balint (with some assistance
from me) implemented a great SDR Doppler RDF. It wasn't tuned for P25 but
it did work well on whatever it was tuned to.. Balint since went to
California and worked on another setup using a USRP and an algorithm called
MUSIC that worked very well...
In short, there are many ways of determining the direction an RF signal is
coming from, and then using this to triangulate a position..
Cheers,
Matt
On 22 September 2016 at 02:48, Alex alex323(a)gmail.com [op25-dev] <
op25-dev(a)yahoogroups.com> wrote:
Hi. On the front page of the wiki (http://op25.osmocom.org/trac/wiki) I
see the following bullet point:
"Locate and track the locations of P25 mobile stations."
What exactly is meant by this? How could such a thing be accomplished?
--
Alex
1:52 a.m.
On Thu, 22 Sep 2016 11:30:52 +1000
"Matt Ames matt.ames7bc(a)gmail.com [op25-dev]"
<op25-dev(a)yahoogroups.com> wrote:
Hi Alex,
Some of those ideas/tasks date back to 2008 when the project was its'
initial embryonic stages. The idea back then was to find a way to
track a P25 station geographically - for example, using multiple time
and frequency sync'd USRP's (with GPSDO for location and time sync)
to do time difference of arrival type location determination, or even
a Roanoke Doppler style of receiver.
Since then, Motorola TRBO and DMR has become very popular, and with
it, services such as LRRP are transmitting data over some of these
networks. I know that some of the Motorola APX and TRBO series radios
can be set up to transmit their GPS locations in the clear, which
could be easily read over the air. This has been done in other
projects with TRBO, but not with P25 to my knowledge.
These are just a few ideas I threw around, Balint (with some
assistance from me) implemented a great SDR Doppler RDF. It wasn't
tuned for P25 but it did work well on whatever it was tuned to..
Balint since went to California and worked on another setup using a
USRP and an algorithm called MUSIC that worked very well...
In short, there are many ways of determining the direction an RF
signal is coming from, and then using this to triangulate a position..
Cheers,
Matt
Hi Matt,
Thank you for that detailed explanation. I am a DSP neophyte, but I am
absolutely interested in helping out in any way I can with this. In
fact, I just ordered a B200 with GPSDO from Ettus and will be
experimenting with it when it arrives.
I have read up on cyclostationary signals and am currently trying to
implement SPECCOA to determine a TDOA for multilateration.
Unfortunately, I am having difficulty understanding some of the math.
Are you familiar with SPECCOA, or do you know anyone I could talk to
off-list who can answer some questions I have?
--
Alex
3197
days inactive
3198
days old
2 comments
2 participants
participants (2)
-
Alex alex323＠gmail.com [op25-dev] -
Matt Ames matt.ames7bc＠gmail.com [op25-dev]