Re: OFDM Updates

Hello Tom,

Based on your information below I know the problem will be receiver.
However, if I want to solve the receiver’s problem. Where is the
starting point you suggestion? From the gnu-radio core part?

Chin-Ya

From: Tom R.
Subject: [Discuss-gnuradio] OFDM Updates
Date: Thu, 07 Feb 2008 14:09:58 +0000
User-agent: Thunderbird 2.0.0.9 (Windows/20071031)
For anyone working with the OFDM code, my latest check-in to the trunk
fixes some of the main issues of transmitting over the air. Using
benchmark_ofdm_rx and benchmark_ofdm_tx on different machines, I am now
able to successfully capture most packets with any modulation at the
appropriate signal level.

I say most packets because there is still an issue involved in the
receiver where the regenerator signal pops up before the peak detector
signal resets it and causes a problem in the packet sampler. To see what
I mean, run
“benchmark_ofdm.py --log”

And look at the output of the regen and peak detector blocks:
gr_plot_char.py ofdm_sync_pn-regen_b.dat ofdm_sync_pn-peaks_b.dat

This will plot a series of 0’s with a few 1’s, where the peaks occur.
The peak detector sends it out once, and then the regenerator takes
over. For every packet, there is one output of the peak detector. If you
look, sometimes the peak detector will hit just after a regenerated
signal. By this point, it’s too late and the ofdm_sampler has already
triggered off of the regen signal and ignores the peak.

It’s a bit of a hassle, but I’ll look into it soon. Any help is
appreciated, though :slight_smile:

Tom

CHIN-YA HUANG wrote:

Hello Tom,

Based on your information below I know the problem will be receiver. However, if I want to solve the receiver’s problem. Where is the starting point you suggestion? From the gnu-radio core part?

Chin-Ya

This problem will be fixed once I get time to merge my current branch,
which will be in a few days, hopefully.

Tom

Hi Tom,

Would you mind release your modified code for me as reference first?
Thanks

Chin-Ya
----- Original Message -----
From: Tom R. [email protected]
Date: Wednesday, March 26, 2008 9:50 am
Subject: Re: [Discuss-gnuradio] OFDM Updates
To: CHIN-YA HUANG [email protected]
Cc: [email protected]

Thanks Bob.
However, what I concern is Tom mentioned that the released code has some
error in the receiver, doesn’t it? We did experiment, and really see
some problems in receiver. That’s why I sent e-mail to see if I can get
more information about the problem since I have no idea how to modify
it.

Chin-Ya
----- Original Message -----
From: Bob McGwier [email protected]
Date: Monday, March 31, 2008 11:54 pm
Subject: Re: [Discuss-gnuradio] OFDM Updates
To: CHIN-YA HUANG [email protected]
Cc: [email protected]

Hey Tom,

I find your new version about OFDM part : Changeset 8144.
Does it the part you mean last time you want to the merge?
Anyway, I will try this first. Thanks Bob for giving me the link.

Chin-Ya
----- Original Message -----
From: Bob McGwier [email protected]
Date: Monday, March 31, 2008 10:54 am
Subject: Re: [Discuss-gnuradio] OFDM Updates
To: CHIN-YA HUANG [email protected]
Cc: [email protected]

I wonder if you are told several more times that it is already released
in an svn branch if you will finally look to see how to get it?

http://gnuradio.org/trac/browser/gnuradio/branches/developers/trondeau/ofdm

That took me less than 2 minutes to find. It will take you less than
two minutes to figure out how to do an svn download on that source.

What doesn’t work is up to you to fix. That is the nature of GPL
projects such as this one.

Have fun.

Bob

CHIN-YA HUANG wrote:

Cc: [email protected]

It’s a bit of a hassle, but I’ll look into it soon. Any help is
Discuss-gnuradio mailing list
[email protected]
http://lists.gnu.org/mailman/listinfo/discuss-gnuradio


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