Hello,
My goal is symbol timing using the Polyphase Clock Sync block. I generated a QPSK waveform which I input to the Channel Model block with epsilon set to 1.0005 (small signal timing offset) and pass the signal to the
Polyphase Clock Sync. The Polyphase filter is designed to run with 32 arms and receive the tap coeff's from the RRC Filter Taps. The parameters for RRC Filter Taps block are are set with defined variables as follows:
Gain =1
Sample_rate (Hz): sample_rate
Symbol_rate (Hz): sample_rate/sps (where sps is samples/symbol and
defined)
Excess_BW: excess_bw
Num Taps: 32*(sps*6*2) (designing for overlap of +/-6 symbols with "sps" samples/symbol)
1) When I run the GRC and look at the constellation plot at the output of the Polyphase Clock Sync, all I see is a dot at the origin of the I/Q plot.
2) So I tried changing the number of taps to see if things change and only when I try the number of taps equal to 32*11 do I get something that makes some sense. I get data over the 4 quadrants between +/-.04 +/-0.4j, spread out. Of course, it keeps smearing into one.
Will appreciate any suggestions on how to use the Polyphase Clock Sync block in conjunction with the RRC Filter Taps for symbol timing.
Thank you!
Regards,
George