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Re: [Discuss-gnuradio] Question about carrier syncronization fordemodula

From: Matt Ettus
Subject: Re: [Discuss-gnuradio] Question about carrier syncronization fordemodulating QPSK/BPSK signal.
Date: Thu, 01 Jun 2006 23:14:41 -0700
User-agent: Mozilla Thunderbird 1.0.8-1.1.fc4 (X11/20060501)

Eric Blossom wrote:

On Thu, Jun 01, 2006 at 08:54:28AM -0400, Tom Rondeau wrote:
Set the
alpha value somewhere around 0.005 - 0.05 to get started (and play with it
from there). The beta value should be about an order of magnitude smaller
(it's been set to 0.25*alpha^2; I'm not sure where that comes from, though).
The next two arguments are the max and min frequency deviation in terms of
scaled frequency, so 0.05 and -0.05 work well. The final value of the
reference phase can just be set to 0. This block's been around for a bit of
time and used in BPSK.

beta = alpha^2/4 gives a critically damped loop.

From here, you'll need to worry about symbol synchronization. We build a
complex modified Mueller and Muller clock recovery circuit for this called
gr_clock_recovery_mm_cc (this file existed already, but we modified it
some). Set mu=0.05, omega is approximately the samples per baud,
gain_mu=0.05, gain_omega=0.25*mu^2, and omega_rel_limit=0.5. These values
will get you started.
Same way of setting beta here.


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