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Re: [Discuss-gnuradio] OFDM with noise - lost packets

From: Martin Braun
Subject: Re: [Discuss-gnuradio] OFDM with noise - lost packets
Date: Mon, 21 Dec 2015 10:30:24 -0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.4.0

I need to check the loopback flowgraph you mentioned, but the header
detection should work down to very low Eb/N0 values.

However, you mention a noise amplitude of 1.5. IIRC, that would yield an
SNR below 0 dB, not 13 dB as you mention.


On 19.12.2015 17:41, Mateusz wrote:
> Hello, I have been evaluating the OFDM examples (at the beginning of my
> Bachelor Thesis)
> In ofdm_rx I have added noise source and file sinks to plot BER(SNR) in
> matlab. I added a Tag Debug on the output.
> The result is disappointing, I observe plenty of lost packets already at
> the SNR of about 13dB and below (noise amplitude about 1.5 in an
> unmodified ofdm_rx).
> So are those examples useful, with such a performance, to utilize with
> USRP and antennas?
> Which part of a synchronization process fails, that causes missing
> indexes of data packets (observed in a Tag Debug) in a noisy channel)?
> I think it's at the loop of 'header recognition', so it's the 'coarse
> frequency offset' that is too big for 'channel estimator'.
> I mainly want to know if it's only possible to use ofdm_rx with a low
> noise, with SNR over about 13 dB.
> Mateusz Loch
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