Re: [Discuss-gnuradio] Polyphase clock sync ccf symbols needed ?

[Sam mite]

> Hi list,
>
> I want to calculate the number of symbols taken by my Polyphase clock sync
> ccf block after which it locks. Although I am getting 0 BER (except at
> start) but I want to know after how many symbols loop get lock. And then by
> varying different parameters I want to observe the lock time/symbols needed.
> From which plot I can get this information and how? . Current parameters set
> are:
>
> Sample/symbpol= 4
> Loop BW= pi/100
> damp factor= 0.707
> filter size = 32
> output sps = 1
> max rate dev = 1.5
> initial_phase=16
>
> Phase plot is showing some sinusoidal output. Attached are the two phase
> plots. phase2.jpg is zoomed in version of phase1.jpg.
>
> Thanks ahead of time.
>
>
> --
> Best Regards,
>
> Sam

Sam,

Yes, the phase output port of the sync block is the one you want to
look at. The phase rounded to the nearest integer (unless it's the
floor) is the number of the filterbank being used at that time, which
represents the phase offset of the signal.

Are you tracking a real signal being received or a simulated signal?
You're going to see some movement, plus or minus, around the closest
phase, though. If its a real signal being received, there's going to
be some small jitter in the timing between the two radios that the
algorithm is trying to track. Also noise will affect if somewhat as it
tries to keep a lock. The fact that it looks like it's actually
oscillating is interesting. Have you tried to reduce the loop
bandwidth to see how that affects things?

Tom

Thanks Tom,

Currently, I am tracking a simulated signal (although I am getting zero BER through USRPs as well). There is currently no additive noise. Reducing loop bandwidth by a factor of 4 gives nice plots, as tracking become good by reducing noise bandwidth. But, steady state value of 24 reaches after approximately 9000samlples. That means my loop is taking 9000/4 symbols to get lock? And after that it 'll produce desired output.  Am i doing something wrong? Something I am missing?

Attached are the snapshots of new phase plots.

--

Best Regards,

Sam

phase.png
Description: PNG image

phase_zoomed.png
Description: PNG image