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Re: [Discuss-gnuradio] gr.clock_recovery_mm_ff() help

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] gr.clock_recovery_mm_ff() help
Date: Sun, 25 Mar 2007 07:34:39 -0700
User-agent: Mutt/1.5.9i

On Fri, Mar 23, 2007 at 11:40:39PM -0700, George Barrinuevo wrote:
> Hello,
> I am trying to use the gr.clock_recovery_mm_cc (float
> omega, float gain_omega, float mu, float gain_mu). 
> What do I set for the omega, gain_omega, mu, and
> gain_mu?  There is also a version of this function
> with 5 parameters.

For a shoot-from-the-hip introduction, take a look at some of the
places in the Python code where these blocks are instantiated.

Without a good understanding of the algorithm, trying to explain these
is tough.  I suggest starting with these books and papers:

 * \brief Mueller and Müller (M&M) based clock recovery block with complex 
input, complex output.
 * \ingroup block
 * This implements the Mueller and Müller (M&M) discrete-time error-tracking 
 * See "Digital Communication Receivers: Synchronization, Channel
 * Estimation and Signal Processing" by Heinrich Meyr, Marc Moeneclaey, & 
Stefan Fechtel.
 * ISBN 0-471-50275-8.

  Modified Mueller and Muller clock recovery circuit
     G. R. Danesfahani, T.G. Jeans, "Optimisation of modified Mueller and 
     algorithm,"  Electronics Letters, Vol. 31, no. 13,  22 June 1995, pp. 1032 
- 1033.

> Also, what should be the number of samples per bit
> going into this gr.clock_recovery_mm_ff() or how much
> oversampling per bit should be used as the input?

About 2 samples per symbol should be fine.

Also, because of the constraints given by the filters implemented
within gri_mmse_fir_interpolator_cc, the input signal must contain no
significant energy above Fs/4, where Fs is the sampling rate.  Note
that this restriction is twice as tight as the Nyquist criterion.


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