Re: [Discuss-gnuradio] TETRA phase adjustment bits

[Tom Rondeau]

On Sun, Jan 2, 2011 at 3:02 PM, Harald Welte <address@hidden> wrote:
> Hi!
>
> I know this is slightly off-topic, as it is not really related to gnuradio
> (despite the USRP and gnuradio being used in my current experiments regarding
> TETRA):


I think this list is a fine place to ask these kinds of questions.


> Does anyone know how the phase alignment bits in TETRA exactly work?
>
> I'm reading ETSI EN 300 392-2 V3.2.1 and can find the definition at
> Section 9.4.4.3.6.
>
> So the phase adjustment bits need to be set to the negated sum of the
> phase shift of two other bits in the burst.
>
> Let's assume I'm using hc1, hc2 and thus look at the symbols 8 (bit 15+16) and
> 108 (bit 215+216).
>
> If all of those four bits are 1 (like in the case of the synchronization
> continuous down-link burst), there is a total phase shift of -6pi/4 (two times
> -3pi/4).
>
> But how do you correct such a phase shift in only a single adjustment symbol?
> Using the two bits in the adjustment symbol, I can only apply +1pi/4, -1pi/4,
> +3pi/4 or -3pi/4 ?!?
>
> Any help is appreciated.
>
> Regards,
>        Harald

Harald,
Have you looked at this paper?
http://wsl.stanford.edu/~ee359/doppler2.pdf

It provides a very nice description of pi/4 DQPSK and a receiver
architecture for it. It might provide the answers you're looking for.

Tom