Il 06/04/13 15:33, Tom Rondeau ha scritto:
On Fri, Apr 5, 2013 at 1:41 PM, Arturo Rinaldi <[email protected]> wrote:
Hi folks, i have bumped into an error while updating my thesis research to
the latest version of gnuradio.
It is a simple tool to estimate the BER of the digital modulation. I had to
change some lines of code due to the
fact that now the block constellation_decoder_cb accepts as input a
"constellation object" and not a complex
point tuple (i.e. [1+1j,1-1j,-1-1j,-1+1j] and so on) so i modified my code
in the following way (only the
deconding part). By asking to the gnuradio mailing list i got the following
advice :
rot = (3.0/2.0)*sqrt((8.0/5.0)*bit_energy)
rotated_const = map(lambda pt: pt * rot,
qam.make_nondifferential_constellation(16,gray_coded=True)
constell = digital.constellation_calcdist(rotated_const,[],1,1).base() #
(1) to get the base points and constellation object
self.slicer = digital.constellation_decoder_cb(constell)
# if self._gray_code:
# self.symbol_mapper = gr.map_bb(qam.gray_to_binary[arity])
# else:
# self.symbol_mapper = gr.map_bb(qam.ungray_to_binary[arity])
# unpack the k bit vector into a stream of bits
self.unpack = gr.unpack_k_bits_bb(self.bits_per_symbol()) # (2)
self.connect(self,self.slicer, self.unpack,self)
which works fine for M-PSK modulation but since QAM is a mix of both phase
and amplitude modulation i can't
recover the exact position of the constellation points. I think the error
stays in a wrong calculation of the
euclidean distance. Any suggestions ? i really need help or otherwise the
functionality of my tool will be
dramatically reduced ! ! !
Thanks in advance,
Arturo
P.S. : The modulator block is shaped in the "old way", by just only passing
as parameter the constellation
points to the block
self.chunks2symbols = gr.chunks_to_symbols_bc(rotated_const)
I also use (2) because of my way to compare original bit by decoded bit and
then calculating the BER. However
the main issue is the wrong decoding of the constellation points by (1)
Arturo,
Take a look at the constellation_decoder. This uses the constellation
objects and handles the symbol slicing for you. The slicers are
defined in constellation.{cc,h}, and if you come up with a
smarter/cheaper way of slicing, you can add it here. I think this
might help simplify things for you.
Tom
I still can't figure out which is the correct slicer to use. I can't use
*digital.constellation_calcdist* because it works only constellations
with a small number of points (and for M-PSK is fine). I usually build
the qam-16 constellation with the old source code of gnuradio (the 3.3.0
one, I really prefer it......) and when using
*digital.**constellation_rect**().points()* as slicer i get different
different points decoded instead of the ones i originally sent, this is
the code :
/arity = 16//
//
//rot = (3.0/2.0)*sqrt((8.0/5.0)*1.0)// # base point distance. See
"Simon Haykin - Communication Sytems"
//
//side = int(sqrt(arity))//
//width = 2.0/(side-1)//
//#//
//#//
//#//
//rotated_const = map(lambda pt: pt * rot, qam.constellation[arity])//
# from 3.3.0 qam.py source
//#//
//decoded_points =
digital.constellation_rect(rotated_const,[],4,side,side,width,width).points()//
//#//
//print "ORIGINAL POINTS\n"//
//print rotated_const//
//print " "//
//print "DECODED POINTS\n"//
//print decoded_points/
returning :
/ORIGINAL POINTS//
//
//[(-0.6324555320336758-0.6324555320336758j),
(-0.6324555320336758-1.8973665961010275j),
(-1.8973665961010275-0.6324555320336758j),
(-1.8973665961010275-1.8973665961010275j),
(-0.6324555320336758+0.6324555320336758j),
(-0.6324555320336758+1.8973665961010275j),
(-1.8973665961010275+0.6324555320336758j),
(-1.8973665961010275+1.8973665961010275j),
(0.6324555320336758-0.6324555320336758j),
(0.6324555320336758-1.8973665961010275j),
(1.8973665961010275-0.6324555320336758j),
(1.8973665961010275-1.8973665961010275j),
(0.6324555320336758+0.6324555320336758j),
(0.6324555320336758+1.8973665961010275j),
(1.8973665961010275+0.6324555320336758j),
(1.8973665961010275+1.8973665961010275j)]//
////
//DECODED POINTS//
//
//((-0.33385056257247925-0.33385056257247925j),
(-0.33385056257247925-1.0015517473220825j),
(-1.0015517473220825-0.33385056257247925j),
(-1.0015517473220825-1.0015517473220825j),
(-0.33385056257247925+0.33385056257247925j),
(-0.33385056257247925+1.0015517473220825j),
(-1.0015517473220825+0.33385056257247925j),
(-1.0015517473220825+1.0015517473220825j),
(0.33385056257247925-0.33385056257247925j),
(0.33385056257247925-1.0015517473220825j),
(1.0015517473220825-0.33385056257247925j),
(1.0015517473220825-1.0015517473220825j),
(0.33385056257247925+0.33385056257247925j),
(0.33385056257247925+1.0015517473220825j),
(1.0015517473220825+0.33385056257247925j),
(1.0015517473220825+1.0015517473220825j))/
This issue, generally speaking, also breaks the compatibility with my
ASK-based modulation code. I really put an effort writing these source
codes on my own and now all my work is almost wasted.....:(.
A perfect solution would be to build a pure
*/digital_constellation_sptr/* object and pass it to the decoder but
when i try to do it with
/digital.digital_constellation(rotated_const, [], 1, 1)/
but i obviously get an *abstract class* error. Do you mind to insert the
old *constellation_decoder_cb* module as a deprecated one in the next
release ? It would really solve my problems and my thesis research would
be working again as it should !
I hope you can help me out......thx in advance
Kind Regards,
Arturo
P.S. : Would it be possible to get the source code of the old
/constellation_decoder_cb/ from the 3.3.0 tarball and build as a new
block with gr-how-to-make-block by modyfing the *.i, *.cc and *.h files ?
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