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Hi Damindra,
that's hard to say without knowing your flow graph in detail;
generally, you seem to have two competing control loops in there;
that might be fine, but I'm not sure the costas loop is able to
sync succesfully on 8PSK.
Greetings,
Marcus
On 14.08.2016 20:26, Damindra Bandara
wrote:
Hi,
I am trying to send 8PSK modulated signal using Ettus
USRP. I designed the application using GNURadio PSK
Mod/Demod blocks. The two blocks worked perfectly for BPSK
and QPSK modulations. However for 8PSK modulation did not
work as expected. The receiver received packets only once
in a while and the throughput was less than 1%. Then I
decomposed the blocks inside the PSK demod block and I
observed that the constellations after the Costas loop
looks very strange. A figure is attached herewith. With
some readings and playing with the GNURadio channel models
I realized this is because I am not using the equalizers
properly. Currently I am using "CMA equilizer" with the
following settings: Num of taps=15, modulus=1, Gain=10m,
sps=2.
1-Will this problem resolve if I choose the correct
equalizer and its settings (or is this some other problem
that I do not understand?)? 2-How can I decide which
equalizer to use?
My current flowgraph is,
USRP_source --> Polyphase Clock Sync--> CMA equalizer
--> Costas loop --> Packet decoder --> File sink
I appreciate if anyone could help me to resolve this issue
and get the 8PSK modulation working.
Thank you very much,
Damindra
Damindra Savithri Bandara,
Ph.D.
in Information Technology (Candidate)
George Mason University,
Fairfax,
Virginia
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