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Re: [Discuss-gnuradio] Rectangular Pulse Shape w/ PFB Clock Sync

From: Andy Walls
Subject: Re: [Discuss-gnuradio] Rectangular Pulse Shape w/ PFB Clock Sync
Date: Wed, 28 Sep 2016 09:15:39 -0400

>                              From: 
> John Malsbury
>                           Subject: 
> [Discuss-gnuradio] Rectangular
> Pulse Shape w/ PFB Clock Sync
>                              Date: 
> Wed, 28 Sep 2016 00:07:46 -0700
> ______________________________________________________________________
> I'm struggling with something pretty basic.  I am trying to achieve
> near theoretical performance detection of a rectangular (no RRC) QPSK
> signal at 2 or 4 sps.  I have an existing  solution that uses a
> discrete FIR filter followed by a Gardner timing recovery loop.  The
> taps of the FIR filter are a box car function.  It works quite well
> and implementation loss is negligible.
> However, I'd like to achieve the same thing using the stock PFB clock
> sync.

It won't work.  The PFB clock recovery uses a derivative filter based on
the matched pulse filter, and relies on a peaked match pulse filter
shape. (Which has a derivative filter tap value of ideally 0 at the
center of the matched pulse filter taps.)

The derivative filter of a matched pulse filter for square pulses
doesn't have the properties the PFB clock sync block needs.


>   For the life of me I can't figure out the proper specification of
> nfilts, and taps.
> Given a signal with rectangular pulse shape at 'sps', can someone
> spell out the taps and nfilt i need to enter into PFB clock sync for a
> properly matched filter bank?
> -John
> ______________________________________________________________________

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