On Tue, May 13, 2014 at 11:11 AM, Irfan Ullah <irfanlums...@gmail.com>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
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