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Re: [Discuss-gnuradio] OFDM Benchmark Tx Issue?

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] OFDM Benchmark Tx Issue?
Date: Tue, 21 Feb 2012 10:05:14 -0500

On Tue, Feb 21, 2012 at 10:00 AM, Michael Dickens <address@hidden> wrote:
On Feb 21, 2012, at 9:44 AM, Tom Rondeau wrote:
> It's because with the larger bandwidth, the subcarriers, too, have a larger bandwidth. The coarse frequency correction is only set to look at so large an offset based on a number of subcarriers (+/-5 or 10), so now with the same frequency offset, 5 (or 10) carriers is a larger frequency span to check.

Ah; yes.  That makes sense.  My mind is thrashing with multi-thread dilemmas, not signal processing, right now.

>> 1 MHz off at 5 GHz is 200 ppm (yes?).  IIRC a reasonable spec on these boards is 5-10 ppm.   So, > 10x off the spec?  I doubt it.  My guess is it's something in GNU Radio that wasn't fixed when the benchmarks were transitioned from gr-usrp* to UHD.
> I think this is a known problem with the XCVR that has been fixed. Make sure you have the most up-to-date master branch of both the UHD and GNU Radio.

They were both the most recent as of yesterday.  I'll update right now & see if that helps, but I'm doubtful since none of the commits since yesterday seem to impact the behavior of the XCVR.  I'll also remove any cruft in /usr/local before re-installing.  More later. - MLD

No, this would have been fixed weeks/months ago, so updating today won't help.

Are you seeing the 1 MHz offset when you use the uhd_siggen.py? Or is it just with the OFDM transmitter?


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