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[Discuss-gnuradio] Problems in Costas loop for QPSK
From: |
Minsuk Kang |
Subject: |
[Discuss-gnuradio] Problems in Costas loop for QPSK |
Date: |
Tue, 22 Mar 2011 00:23:30 +0900 |
Dear all,
I use mpsk_receiver_cc() to synchronze DQPSK symbols at a receiver.
Since I get too many packet losses when running the benchmark(in the digital folder) with DQPSK, I have closely looked at the codes.
I finally found that the output of costas_loop is not well synchronized from time to time. If I use higher rate like 500k, it happens more often.
Here's the constellation of the output of the Costas loop (
http://bit.ly/ij4ytv) when it is not well synchronized. Sometimes the constellation becomes worse than this.
I used the default parameters of dqpsk.py except fmin and fmax.
(When I set fmin/fmax=-0.1/0.1 instead of -0.25/0.25, I get better constellation.)
Is there anyone who has encountered the same problem?
Or, is there any other code that I can use to synchronize QPSK symbols at the receiver?
PS. I'am using USRP1 / gnuradio 3.3.0 / Ubuntu 10.04
Thanks in advance.
--
Minsuk Kang
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