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[Discuss-gnuradio] QAM receiving

From: Mason
Subject: [Discuss-gnuradio] QAM receiving
Date: Thu, 26 Jun 2008 00:44:20 -0500
User-agent: Thunderbird (X11/20080505)

Hello list,
I've been working on a basic implementation of QAM using a slightly modified version of the MPSK receiver. I'll be the first to admit I'm not a great programmer in either C++ or python yet. I've gotten it to work on a lossless channel but it seems to be hitting a stumbling block over the air or even on the channel simulator -- it looks like the AGC loop isn't keeping the amplitude steady, which is making it even harder for the receiver to make a good constellation, but other failures are possible too. Heck, sometimes it doesn't even see packets. In addition, most of the constants were chosen pretty much through guesswork and trial and error.
That said, anything jump out as particularly wrong or improvable?
The patch is located here:

It also includes a change or two to benchmark_loopback.py at the top of the patch: channel modeling is now a command-line, rather than source-level, option (-c), and the verbose option will also tell you what was received as what. (This should probably go to stderr? It's slightly less output-intensive than --log, at least.)


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