Re: [Discuss-gnuradio] Polyphase clock synchronization issue

[Tom Rondeau]

On Tue, May 13, 2014 at 11:11 AM, Irfan Ullah <address@hidden> wrote:

Hi all,

I have a problem here with polyphase clock synchronization block when i set the output samples per symbol to one the constellation have much more ISI and noise and when output sps value is 2 the constellation have no noise and no ISI.I am using the firdes.root_raised_cosine filter design in polyphase clock synchronization block with the follwoing parameters

 
Polyphase clock synchronization block parameters

filter size =32

firdes.root_raised_cosine(nfilts,1.0,1.0/(nfilts*sps), rolloff, int(11*sps*nfilts))  with  sps=2  nfilts=32  rolloff=0.7

My flow graph picture is attached with this mail.

please tell me if there is any problem in my parameters (I m using QPSK using the chunks to symbol block with const.points() function for mod  and constellation decoder block with const.base() function in the constellation object parameter for demod)

If there are any errors in my flowgraph parameters please guaid me.

Regards,

Irfan Ullah

You have the output SPS set to 2. Set that to 1. Basically, at 1 sps out, you'll get the sampled symbol that you then pass to the Costas loop for phase and fine frequency recovery. If you output at 2 sps like you have now, then there's nothing that takes that down to the single bit or symbol sample that you want. The 2 sps output is specifically designed to go into an equalizer as the next stage, which will take 2 sps in and produce the 1 symbol out after equalization.

Tom