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

From: Neil Schafer
Subject: Re: [Discuss-gnuradio] Rectangular Pulse Shape w/ PFB Clock Sync
Date: Wed, 28 Sep 2016 09:41:39 -0400

I haven’t tried it myself, but wouldn’t using a raised cosine or Gaussian filter for your taps still provide some pulse shaping for the PFB clock sync to track? You’re essentially leap-frogging the RRC matched filters at transmitter and receiver, and placing the entire burden at the receiver, but at the decision point of the clock synch the end result should be the same.




From: Discuss-gnuradio [mailto:address@hidden On Behalf Of Garver, Paul W
Sent: Wednesday, September 28, 2016 7:49 AM
To: John Malsbury <address@hidden>
Cc: address@hidden
Subject: Re: [Discuss-gnuradio] Rectangular Pulse Shape w/ PFB Clock Sync


I have tried to use PFB clock sync without success on rectangular pulses as well. Presumably you've seen the documentation [1] on nfilts and taps. I tried making the filter a rectangular pulse with x sps upsampled by nfilts. One theory I have is that the polyphase clock sync may not work with rectangular pulses. If you read the paper, the derivative of the pulse is required. Perhaps that's a problem since for typical RRC pulses the derivative is well defined but for a rectangular pulse the derivative is 0. 




Paul Garver


On Sep 28, 2016, at 3:09 AM, John Malsbury <address@hidden> wrote:

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.  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?



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