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Re: [Discuss-gnuradio] BER & constellation plot for OFDM transmit/receiv
From: |
Martin Braun |
Subject: |
Re: [Discuss-gnuradio] BER & constellation plot for OFDM transmit/receive |
Date: |
Mon, 18 Apr 2016 10:26:50 -0700 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 |
Are you comparing the correct packets? E.g., if packets get lost, do you
take that into account?
M
On 04/16/2016 02:38 PM, Jingyi Sun wrote:
> Hi everyone,
>
> We are working on an experiment for a conference paper deadline in two
> weeks, and need to transmit and receive OFDM packets and want to study
> the constellation diagram and BER.
>
> I put together a flow graph consisting of an *OFDM transmitter block*
> and an *unpacked OFDM receiver* based on the online example rx_ofdm.grc.
> Here's how I'm trying to measure constellation diagram and BER:
>
> * I inserted a QT constellation sink right before the constellation
> decoder on the payload IQ stream, but it does not seem to output
> anything meaningful. The plot just shows single, clean points, which
> I am pretty sure does not correspond to real data. I suspect that
> the plots are not triggering properly, but am not sure.
>
> * For BER, we tried several different configurations, and they mostly
> give BER = 0.5 (i.e. random). Our leading theory is that we're not
> comparing the data at the correct points in the flow graph. Any
> suggestions as to what the BER inputs should be would be helpful.
>
> We've been running some diagnostics that seem to eliminate our
> communication channel as the problem:
>
> * We are transmitting the data over-the-air at 915 MHz using
> two omnidirectional antennas, placed roughly 1 meter apart. The
> output spectra at the transmitter output and receiver input are
> attached - all signals are comfortably above the noise floor.
> * From the tag debug output, we see that the OFDM packet headers are
> being received. For example, we can see when the packets are
> received, the packet numbers, as well as the channel estimation tap
> values. We take this to mean that we are receiving data
> successfully, and that our difficulties regarding BER and
> constellation diagram are something we're executing incorrectly in
> the software.
>
>
> The relevant annotated GRC block diagrams are attached.
>
> Thanks so much,
> Jenny
>
>
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>
- [Discuss-gnuradio] BER & constellation plot for OFDM transmit/receive, Jingyi Sun, 2016/04/16
- Re: [Discuss-gnuradio] BER & constellation plot for OFDM transmit/receive,
Martin Braun <=
- Re: [Discuss-gnuradio] BER & constellation plot for OFDM transmit/receive, Jingyi Sun, 2016/04/18
- Re: [Discuss-gnuradio] BER & constellation plot for OFDM transmit/receive, Jingyi Sun, 2016/04/21
- Re: [Discuss-gnuradio] BER & constellation plot for OFDM transmit/receive, Martin Braun, 2016/04/21
- Re: [Discuss-gnuradio] BER & constellation plot for OFDM transmit/receive, Jingyi Sun, 2016/04/21
- Re: [Discuss-gnuradio] BER & constellation plot for OFDM transmit/receive, Jingyi Sun, 2016/04/22
- Re: [Discuss-gnuradio] BER & constellation plot for OFDM transmit/receive, Martin Braun, 2016/04/22