On Mon, Nov 10, 2014 at 1:31 PM, Richard Bell <[email protected]> wrote:
> Hi Tom, > > I read that page before making my post, and that's what lead me to > conclude the symbol map wasn't working as intended. I ran a test by > changing the symbol map array [0, 1, 3, 2] vs [1, 0, 3, 2] and noticed the > output didn't change. Only changing the constellation point order made a > change in the output. [1+1j, -1+1j, -1-1j, -1+1j] vs [-1+1j, 1+1j, -1-1j, > -1+1j] > > This lead me to conclude the symbol table wasn't controlling anything, it > was the index of the constellation point array that was mapping symbols. > Correct me if you experience different. > > Rich > Yes, I've used the symbol map a lot to change behavior. A simple way to explore this is to create a test application with a vector_source -> constellation modulator -> throttle -> qtgui constellation sink. The vector_source can be set to just repeat the same symbol over and over again 0 -> 0x00, 1 -> 0x55, 2 -> 0xAA, and 3 -> 0xFF. That way, you'll only output one constellation point (assuming QPSK here). Then change your symbol map table to see how it affects where the constellation point goes. Tom > On Nov 10, 2014, at 10:04 AM, Tom Rondeau <[email protected]> wrote: > > On Tue, Nov 4, 2014 at 9:11 PM, Richard Bell <[email protected]> > wrote: > >> The symbol map feature of the constellation object doesn't seem to do >> anything. In fact, you can leave it blank. The index of the constellation >> points is used to map the complex points to bits. The documentation leads >> one to believe otherwise. Working as intended? >> >> v/r, >> Rich >> > > > The symbol map is a list that maps to the constellation points. So > constellation_points[i] holds the symbol defined in symbol_map[i]. An easy > test to see this working is to take the default Constellation Object in > GRC, which is defined for QPSK, and change the map to [0,1,3,3] and notice > that the symbol 2 (10b) is missing in the output constellation. Without a > symbol map defined, it defaults to it being [0, ..., i-1]. The alternative > is to crash or catch that the vector is empty and exit on an error. > > There is the Digital Modulation page in the manual that describes these > things. If you have suggestions for how to improve them, please send them > along: > > http://gnuradio.org/doc/doxygen/page_digital.html > > Tom > >
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