What do you mean by "hard-decision" equalizer, and "drop them down"?
Thanks so much!! On Thu, Apr 21, 2016 at 2:01 PM, Martin Braun <martin.br...@ettus.com> wrote: > That's because the equalizer used is a hard-decision equalizer. You can > write your own equalizers and drop them down for better results; that's > something I've been meaning to do for a while, but haven't found the > time yet. > > Cheers, > M > > On 04/20/2016 09:56 PM, Jingyi Sun wrote: > > Hope pictures below give more context. Has anyone seen this happen > before? > > > > To reword the part of our question about constellation plots a little, > > does anyone know when the constellation block would output just four > > single points? > > > > The problem we’re currently facing is that the constellation plot does > > not even really show up -/there’s not even a giant blob to indicate > > noise/. Instead, we get only 4 points, one in each of the four locations > > you’d expect for a QPSK signal - but only those 4 points./It almost > > feels like the constellation plot stops triggering after these first > > four points/, and that’s why we don’t receive anymore data. *We’re using > > a free trigger on the positive slope, centered at 0, *which I feel > > should trigger at least something even if it’s just noise. We have also > > tried other trigger methods, which output either 4 points, 5 points (1 > > additional point in the center), or just 1 center point. > > > > > > > > > > > > > > On Mon, Apr 18, 2016 at 5:01 PM, Jingyi Sun <sunjing...@gmail.com > > <mailto:sunjing...@gmail.com>> wrote: > > > > 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 <mailto: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 <mailto:Discuss-gnuradio@gnu.org> > > > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > > > > > > _______________________________________________ > > Discuss-gnuradio mailing list > > Discuss-gnuradio@gnu.org <mailto: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 > > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >
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