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

Neil,

Yes. It does lock and track with those taps.  But with about 0.2-0.3 dB of added implementation loss. 

-John

On Thu, Sep 29, 2016 at 7:46 AM, Usman Haider <usmanhaider89@gmail.com> wrote:

Hi Neil,

Can you please share some more details on how the end result could be same?

Regards,

Usman

On Wed, Sep 28, 2016 at 6:41 PM, Neil Schafer <neil.schafer@nrl.navy.mil> wrote:

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.

 

Neil

 

From: Discuss-gnuradio [mailto:discuss-gnuradio-bounces+neil.schafer=nrl.navy.mil@gnu.org] On Behalf Of Garver, Paul W
Sent: Wednesday, September 28, 2016 7:49 AM
To: John Malsbury <jmalsbury.personal@gmail.com>
Cc: discuss-gnuradio@gnu.org
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. 

 

[1] http://gnuradio.org/doc/doxygen/page_pfb.html

 

 

Paul Garver

 

On Sep 28, 2016, at 3:09 AM, John Malsbury <jmalsbury.personal@gmail.com> 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?

 

-John

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