On Wed, Jul 23, 2014 at 9:45 PM, Tom Rondeau <t...@trondeau.com> wrote:
> On Wed, Jul 23, 2014 at 8:42 AM, Activecat <active...@gmail.com> wrote: > >> Dear Sir, >> >> I am learning to use the built-in "QAM Mod" and "QAM Demod" blocks. >> Refer below flowgraph. >> >> The problem is, at the output of the "QAM Demod" block, I can't get what >> I fed into the "QAM Mod" block. >> What is missing ..? >> > > All modulators take in packed bits and all demodulators output unpacked > bits. First, remember that there are filters involved, so there's going to > be a delay. You'd need to synchronize the output of the demodulator to some > known word to understand which output bit is the correct start of the data > stream. Easier would be to unpack the source data. Out of the 'head' block, > make another connection to a 'unpack_k_bits' block with an unpacking value > of 8. Use this to compare to the demodulated bits. > > Also, the vector source should generate values from 0 to 255 to create the > packed bits needed as input to the modulator. Otherwise, you'll just be > heavily biasing the constellation to just a few points. You can stick a > constellation display block on the output of the modulator to see. > > Tom > Thank you very much.
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