Forum: GNU Radio Tetra receiver

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7210062a1bf6b5d008a6537ab410095c?d=identicon&s=25 Grzegorz Suder (Guest)
on 2009-01-19 10:57
(Received via mailing list)
Hello,
I've looked through Wiki and discussion archives but I haven't found
answer
for my question. Is there any working code for Gnu Radio that is able to
receive Tetra subscriber (not base station) signal and convert it into
bitstream? I believe that demodulation is already done (DQPSK as I know)
but
there is still timing and slot separation issue. Seems that there were
attempts to introduce support for inband signaling for Gnu Radio but
last
information I've found are from 2007.
Regards,
745d8202ef5a58c1058d0e5395a78f9c?d=identicon&s=25 Eric Blossom (Guest)
on 2009-01-21 20:17
(Received via mailing list)
On Mon, Jan 19, 2009 at 10:56:13AM +0100, Grzegorz Suder wrote:
> Hello,
> I've looked through Wiki and discussion archives but I haven't found answer
> for my question. Is there any working code for Gnu Radio that is able to
> receive Tetra subscriber (not base station) signal and convert it into
> bitstream? I believe that demodulation is already done (DQPSK as I know) but
> there is still timing and slot separation issue. Seems that there were
> attempts to introduce support for inband signaling for Gnu Radio but last
> information I've found are from 2007.
> Regards,

I don't know of anybody who's done this, but it should be possible.
(There's not much (any?) Tetra in the US, so those of us in the US
haven't spent any time on it.)  If you're doing receive only, you
don't need the inband features.  Just grab all of the signal and sort
out the framing structure on the host.

Eric
7210062a1bf6b5d008a6537ab410095c?d=identicon&s=25 Grzegorz Suder (Guest)
on 2009-01-21 21:20
(Received via mailing list)
Actualy what I am worrying about are discontinuous TDMA signals (for
example: receiving specific time slot). I guess that capturing such TDMA
signal (Tetra is just an example due to 4 time slots) where only one
slot is
transmitting may require synchronization to external time source.
79723aa1b24981dcec2dbf7fd59403c1?d=identicon&s=25 Brian Padalino (Guest)
on 2009-01-21 21:27
(Received via mailing list)
On Wed, Jan 21, 2009 at 3:17 PM, Grzegorz Suder
<suder.grzegorz@gmail.com> wrote:
> Actualy what I am worrying about are discontinuous TDMA signals (for
> example: receiving specific time slot). I guess that capturing such TDMA
> signal (Tetra is just an example due to 4 time slots) where only one slot is
> transmitting may require synchronization to external time source.

If you're only doing reception, then there is no real need for time
synchronization at the hardware level.

You can detect the signal on your host computer and the timebase is
irrelevant.

Only if you are transmitting do you really have the hard timeslot that
you have to follow - or else you step on each others toes.

Brian
31f5273cd19f7bf24a99e5596c2c321d?d=identicon&s=25 Tommi Rouvali (Guest)
on 2009-01-22 07:03
(Received via mailing list)
Hello,

I have been thinking about this. I have access to two TETRA terminals.
The down side is I am beginner in Gnu Radio and DSP in general.

Is the π/4 DQPSK modulation really supported by Gnu radio? Any examples
about this?
7210062a1bf6b5d008a6537ab410095c?d=identicon&s=25 Grzegorz Suder (Guest)
on 2009-01-22 10:00
(Received via mailing list)
dqpsk.py module depends on mpsk_receiver_cc. In file
$GNURADIO/gnuradio-core/src/lib/general/gr_mpsk_receiver_cc.h there is
information:

 * This block takes care of receiving M-PSK modulated signals through
phase,
frequency, and symbol
 * synchronization. It performs carrier frequency and phase locking as
well
as symbol timing recovery.
 * It works with (D)BPSK, (D)QPSK, and (D)8PSK as tested currently. It
should also work for OQPSK and
 * PI/4 DQPSK.
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