Re: [Discuss-gnuradio] Phase locked loop

[Marcus Müller]

Hi Daniele,

> Also, I don't see why you cannot combine other blocks to realize
> your own PLL implementation.  Where did you read that you "can’t use
> companion to add and drop the current available blocks to construct a
> phase locked loop"?
Wai Yee has a point here -- you can't have a circle in your (sample
stream) flow graph -- GNU Radio doesn't allow that for reasons of
causality.

You can have a "loose" loop with feedback done with message ports, but
that's not the same as a control loop (since there's no defined delay
between the sample for which a error was estimated and the sample where
the error correction is applied when using the asynchronous messages).

Thus, you can't drag'n'drop together a "proper" control loop from
discrete things like adders and integrators  that you could design and
analyze theoretically.

In effect, GNU Radio's control loops are monolithic blocks -- that's
somewhat sad from a modularity perspective, but then again, there's the
control loop base class that allows you to implement arbitrary control
loops rather easily, so Wai Yee, I recommend looking at the
documentation [1], the referenced paper and the source code[2] of the
existing costas loop.

Best regards,
Marcus Müller

PS:
> I am using *USRP N210* for the hardware and I have installed *Gnuradio 
> Companion* in *Ubuntu 12.04 LTS* (running in VMplayer).
as a side note, I don't recommend running your digital signal processing
for a high-rate capable device inside a VM, unless you know what you're
doing -- the additional overhead in network packet handling might prove
to be a problem. At lower rates, it should work fine.
Also, why are you using a three years old Ubuntu? There's a new LTS
release, almost a year old now, 14.04; I recommend using a modern platform.

[1]
http://gnuradio.org/doc/doxygen/classgr_1_1digital_1_1costas__loop__cc.html
[2]
https://github.com/gnuradio/gnuradio/blob/master/gr-digital/lib/costas_loop_cc_impl.cc

On 03/17/2015 09:12 AM, Daniele Nicolodi wrote:
> On 17/03/15 02:05, yee_yy1992 wrote:
>> Hi, Currently I am doing my Final Year Project to develop a phase
>> measurement using Phase Locked Loop theory. I am using *USRP N210* for
>> the hardware and I have installed *Gnuradio Companion* in *Ubuntu 12.04
>> LTS* (running in VMplayer). I have studied online that I can’t use
>> companion to add and drop the current available blocks to construct a
>> phase locked loop.
> Hello,
>
> what to you mean by that last sentence? GNURadio comes with PLL blocks
> in a few different fashions that can be used from the companion just
> fine.  Also, I don't see why you cannot combine other blocks to realize
> your own PLL implementation.  Where did you read that you "can’t use
> companion to add and drop the current available blocks to construct a
> phase locked loop"?
>
> Cheers,
> Daniele
>
>
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