We are not compensating for any lost packets, although we would be aware of them thanks to the packet number. Could you tell us if there’s a block to do this, or would we need a custom block?
Also, could you tell us why the constellation diagram is not displaying properly? Thanks, Jenny On Mon, Apr 18, 2016 at 1:26 PM, Martin Braun <martin.br...@ettus.com> wrote: > 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 > > > > > > _______________________________________________ > > Discuss-gnuradio mailing list > > Discuss-gnuradio@gnu.org > > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >
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