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
