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Re: [Discuss-gnuradio] OFDM implementation

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] OFDM implementation
Date: Thu, 14 Jun 2007 10:12:55 -0400
User-agent: Thunderbird (Windows/20070326)

Martin Dvh wrote:
Tom Rondeau wrote:
Just the status report from the work done the past couple of weeks on
OFDM. With Matt Ettus, Bob McGwier, and Eric Blossom, we successfully
transmitted and received OFDM over the air with BPSK, QPSK, and 16QAM.
I have merged the code into the trunk so others can use it, though I
currently restricted the subcarrier modulations to use only BPSK or QPSK
(M-QAM will be coming soon I hope).

Is the not-completed QAM code in one of the developer branches (which one)
Maybe I can do some work at it as soon as I get to work on OFDM.
(I am now working on optimizing the wfm_rcv_pll code, my goal is a factor 4 

It's actually in the trunk, it's just hidden from the benchmark code. For the modulator, we have built a few different versions called "gr_ofdm_bpsk_mapper" and "gr_ofdm_qpsk_mapper." There is also "gr_ofdm_qam_mapper" that's kind of in shambles to force QAM16. I'd much rather get rid of these and make one "gr_ofdm_mapper" or "gr_ofdm_vector_mapper" function that receives a vector of constellation points as an argument. Then we can just use qam.py and psk.py to generate the constellation in Python and pass it to the mapper function that simply takes log2(len(constellation)) number of bits in at a time and maps them to constellation points. The only real trick is to handle residual bits on byte boundary (8PSK, 8QAM, etc.). We'll then have to have a corresponding demapper on the receiver.

Just a heads-up, I'm moving to Ireland over the next week and leaving my computer behind, so I'll be pretty much unavailable for about a week and a half to two weeks as I settle in over there (and get my new computer). The work on this is pretty trivial, but I won't be able to touch it for a while, so if you feel like working on it, great!


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