Clock Recovery MM

GNU Radio
1

Hi all,

looking at the clock recovery MM code, I wonder if
d_omega_relative_limit is a relative or absolute deviation from d_omega.

Here it looks like absolute
https://github.com/gnuradio/gnuradio/blob/next/gr-digital/lib/clock_recovery_mm_ff_impl.cc#L107

Here it is relative
https://github.com/gnuradio/gnuradio/blob/next/gr-digital/lib/clock_recovery_mm_ff_impl.h#L57

(even though this code has no impact since d_{min,max}_omega is not
used.)

I dont have access to the book linked in the docs atm.

Best,
Bastian

2

On Mon, Sep 8, 2014 at 5:49 PM, Bastian B. [email protected]
wrote:

https://github.com/gnuradio/gnuradio/blob/next/gr-digital/lib/clock_recovery_mm_ff_impl.h#L57

(even though this code has no impact since d_{min,max}_omega is not used.)

I don’t have access to the book linked in the docs atm.

Best,
Bastian

It is supposed to be relative. I’d have to verify the math on that line
107
in the .cc file, but it’s supposed to adjust the center position of the
current omega estimate and then apply the clipping. Then it adds the mid
point back to get it back to where it’s centered. Try walking through
that
line one more time to verify that it’s doing that properly. But yes,
it’s
supposed to be relative to the original setting of omega.

Tom

3

On 09 Sep 2014, at 15:42, Tom R. [email protected] wrote:

So this line asserts that the current (absolute) deviation (d_mega -
d_omega_mid) is smaller than the maximum allowed absolute deviation
(d_omega_mid * d_omega_relative_limit). AFAIS, the second argument is
missing * d_omega_mid.

I will create a patch, then you can check if I got you right.

Bastian