No it wouldn't work. You have to synchronize before you start de-spreading.
Rich On Fri, Feb 5, 2016 at 3:07 PM, Henry Barton <kw...@outlook.com> wrote: > The last thing I wonder is, can a receiver just pick up a DSSS signal and > start applying the despreading code? I watched a YouTube video about this > and the example involved multiplying the spreading code by the voltages of > the composite waveform and averaging them. My system takes 16 chips to > express 1 bit. Let’s say my demodulator starts on the 10th chip and goes on > for 16 chips, getting 6 chips from this cycle and 10 from the next. If it > keeps on like this, it will never fall into sync, and without being in sync > it can’t get any real bits to help itself align. > > Sent from Windows Mail > > *From:* Richard Bell <richard.be...@gmail.com> > *Sent:* Friday, February 5, 2016 5:59 PM > *To:* Henry Barton <kw...@outlook.com>, discuss-gnuradio@gnu.org > > It will depend on how the rest of the radio is built up. I'm not familiar > with VP9, but can I assume it's a spec on bits in a higher layer then Layer > 1? Another words, you are assuming you have bits to correlate with, as > opposed to wave shapes? > > You're getting into the difficulties of radio design now. You need to > fully understand the needs of your system to make decisions like this. You > don't have bits until you've synchronized and demodulated your signal. If > you require some sort of FEC, it will need block alignment before you can > decode it, so the correlator will need to be in the waveshape domain. You > can still use the known VP9 headers to correlate to in this cas > , but you wouldn't correlate to the bit version, you would correlate to > the modulated version of those headers. > > P.S. Please reply to the mailing list, so others can see and reply if need > be. > > Rich > > > > On Fri, Feb 5, 2016 at 2:53 PM, Henry Barton <kw...@outlook.com> wrote: > >> I'm hoping to transmit a VP9 transport stream, so perhaps the predictable >> headers will be enough? >> >> Sent from Windows Mail >> >> *From:* Richard Bell <richard.be...@gmail.com> >> *Sent:* Friday, February 5, 2016 5:51 PM >> *To:* Henry Barton <kw...@outlook.com>, discuss-gnuradio@gnu.org >> >> So long as you know what you're looking for in any given scenario, you >> can use that to correlate to. It can be data or a preamble. If your >> receiver knows the data will always be a certain way ahead of time though, >> it's hard to call that data. Semantics at that point. >> >> Rich >> >> On Fri, Feb 5, 2016 at 2:44 PM, Henry Barton <kw...@outlook.com> wrote: >> >>> That sounds great, Richard. But I wonder, what if the useful payload >>> contains that sequence by chance? >>> >>> Sent from Windows Mail >>> >>> *From:* Richard Bell <richard.be...@gmail.com> >>> *Sent:* Friday, February 5, 2016 5:27 PM >>> *To:* Henry Barton <kw...@outlook.com> >>> *Cc:* discuss-gnuradio@gnu.org >>> >>> Typically a correlator is used to look for a known sequence of bits, >>> so the radio can align the rest of the processing from the end of this >>> known sequence. This is referred to as frame synchronization. You could use >>> the correlation estimation block to implement something like this. It would >>> place a tag on the stream when it finds your known sequence and you would >>> then know how everything is aligned from then on. >>> >>> Rich >>> >>> On Fri, Feb 5, 2016 at 1:04 PM, Henry Barton <kw...@outlook.com> wrote: >>> >>>> Hi all. I've successfully written a DSSS modulator and demodulator in >>>> Windows with a chip rate of 16x. It writes samples to a file that the >>>> demodulator can read and despread. Before I try any practical >>>> implementations, I need to know how a DSSS stream would be >>>> synchronized. Assuming the transmitter and receiver were perfectly clocked >>>> in unison, what stops the receiver from tuning in in the middle of a >>>> byte, thus getting a nibble from the current byte and a nibble from the >>>> next? >>>> >>>> _______________________________________________ >>>> 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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