Need help for digital.constellation_decoder_cb in release 3.5.0

GNU Radio
#1

I noticed dramatic changes in the 3.5.0 release in the generation of the
constellation points of digital modulations. So, if the easy part is to
again modify the source code to match my needs, i need some help in
using the new block :

/digital.constellation_decoder_cb(arg1)/

instead of
/
gr.constellation_decoder(arg1,arg2)/

I usually used the last one where /arg1/ is a list containing the
complex values of a generic digital modulation and /arg2/ is the symbol
mapping (Gray Coding for instance). Which blocks do i need to put
together to get the same result ?

Regards, Arturo

#2

On Thu, Dec 8, 2011 at 5:33 PM, Arturo R. [email protected]
wrote:

https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

Simplest solution is probably:

constell = digital.digital_constellation(list_of_complex_points, [], 1,
1)
decoder = digital.constellation_decoder_cb(constell)

To get the symbol mapping you want, just choose the appropriate order
of the complex points in the list.

The 2nd, 3rd and 4th arguments to the constellation constructor while
not relevant to this example are:

  • a mapping to be applied before differential encoding.
  • the rotational-symmetry of the constellation
  • the dimensionality of the constellation (i.e. number of complex
    points that together map to one symbol)

Functions to simplify the creation of commonly used constellations can
be found in digital.bpsk, digital.qpsk, digital.psk, and digital.qam.

Ben

#3

Nella citazione in data ven 09 dic 2011 05:55:57 CET, Ben R. ha
scritto:

gr.constellation_decoder(arg1,arg2)
[email protected]

Ben

i made some progress in simplyfing the creation of the constellations
but i still need help in the decoding part.

I’m trying to calculate the modulation BER by using this flow graph :

http://imageshack.us/photo/my-images/819/bersimgrchomeartynetscr.png/

i removed all the unnecessary parameters to my study (excess bw ,
differential coding etc.) because i need only gray coding. and the
decoding part is this one

http://pastebin.com/wADRx7Hj

could you please help me ? the grc blocks are made by invoking only the
psk_new.py source

http://pastebin.com/kawSfuPg

modified by me. please help me. thx in advance

Regards, Arturo.

#4

On Thu, Mar 8, 2012 at 8:19 PM, Arturo R. [email protected]
wrote:

same
Simplest solution is probably:

  • the rotational-symmetry of the constellation
    still need help in the decoding part.

could you please help me ? the grc blocks are made by invoking only the
psk_new.py source

http://pastebin.com/kawSfuPg

modified by me. please help me. thx in advance

Regards, Arturo.

I’d be happy to help but I’m not quite sure what exactly your
problem/question is.

Maybe you could post the python generated by grc, along with the issue
you’re having?

#5

Nella citazione in data Fri Mar 9 19:50:05 2012, Ben R. ha
scritto:

the new block :
Coding for instance). Which blocks do i need to put together to get the

  • a mapping to be applied before differential encoding.
    i made some progress in simplyfing the creation of the constellations but i
    http://pastebin.com/wADRx7Hj
    I’d be happy to help but I’m not quite sure what exactly your
    problem/question is.

Maybe you could post the python generated by grc, along with the issue
you’re having?

here it is

http://pastebin.com/hQsPXbjJ

my goal is to perform a baseband simulation for a simple BER estimation
(modulator-channel-demodulator). when i posted the issue some time ago
i used the block

decoder =
gr.constellation_decoder_cb($constellation_points,$symbol_value)

i.e. for a qpsk modulation ----->
constellation_points=[1+1j,-1+1j,-1-1j,1-1j] , symbol_value=[0,1,2,3]

after that i “un-grayed” the symbols by connecting the map block

gr.map_bb([0,1,3,2])

Since i’m usign the 3.5.2 tarball, the new block

digital_swig.constellation_decoder_cb($constellation)

(and not digital.constellation_decoder_cb) that you suggested me takes
as argument a “constellation” object and not a “constellation_bpsk”,
“constellation_qpsk” object and so on. So i think i’m unable to assign
the right symbols to the decoded constellation and perform a correct
BER estimation. I tried to use also with the object

digital.constellation($constellation_points)

as you suggested to build my own constellation but the log file says
that it is an “abstract class” so it can’t be used. I hope I explained
myself well this time. Please help me because i need to update my work
to the 3.5.x gnuradio version.

PS : I also thought that I could take the old block
gr.constellation_decoder_cb from the 3.4.2 tarball (.h , .i and .cc
files) and build it with gr-how-to-make-a-block-3.5.2…would it be
possible ?

Best Regards, Arturo

#6

Nella citazione in data Sun Mar 11 02:30:43 2012, Arturo R. ha
scritto:

of the
gr.constellation_decoder(arg1,arg2)
Regards, Arturo
[], 1, 1)
points that together map to one symbol)

problem/question is.
estimation (modulator-channel-demodulator). when i posted the issue
gr.map_bb([0,1,3,2])
digital.constellation($constellation_points)

Best Regards, Arturo

i forgot to mention that i deleted any block for RRC filtering and
recovery. my goal is a simple baseband simulation. I attach again my
new version (v2) of the source file “generic_mod_demod” and the grc
image of the flow graph :

http://imageshack.us/photo/my-images/838/bersimulationgrchomeart.png/

http://pastebin.com/i3nxY6u0

Regards, Arturo

#7

On Sun, Mar 11, 2012 at 4:25 PM, Arturo R. [email protected]
wrote:

On Thu, Dec 8, 2011 at 5:33 PM, Arturo R.[email protected]

Coding for instance). Which blocks do i need to put together to get

The 2nd, 3rd and 4th arguments to the constellation constructor while

differential coding etc.) because i need only gray coding. and the
modified by me. please help me. thx in advance

i.e. for a qpsk modulation ----->
argument a “constellation” object and not a “constellation_bpsk”,

http://imageshack.us/photo/my-images/838/bersimulationgrchomeart.png/

http://pastebin.com/i3nxY6u0

Regards, Arturo

Hi Arturo,

To generate a generic constellation use:

constellation = digital.constellation_calcdist(complex_points, [], 1,
1).base()

In my earlier email I forgot about the ‘_calcdist’ and the ‘.base()’.
Hopefully the above will work better for you.
I’m also including an simple example that works for me, in case that
doesn’t fix your problem.

Cheers,
Ben

import random

from gnuradio import gr, digital

def get_BER(constellation, noise_level, data_length=1000):
data = tuple(
[random.randint(0,1) for i in range(0, data_length)])
tb = gr.top_block()
src = gr.vector_source_b(data)
pack = gr.unpacked_to_packed_bb(1, gr.GR_MSB_FIRST)
bytes2chunks =
gr.packed_to_unpacked_bb(constellation.bits_per_symbol(),
gr.GR_MSB_FIRST)
chunks2symbols = gr.chunks_to_symbols_bc(constellation.points())
noise = gr.noise_source_c(gr.GR_GAUSSIAN, noise_level)
adder = gr.add_cc()
decoder = digital.constellation_decoder_cb(constellation)
unpack = gr.unpack_k_bits_bb(constellation.bits_per_symbol())
snk = gr.vector_sink_b()
tb.connect(src, pack, bytes2chunks, chunks2symbols)
tb.connect(noise, (adder, 0))
tb.connect(chunks2symbols, (adder, 1))
tb.connect(adder, decoder, unpack, snk)
tb.run()
errors = 0
for i, j in zip(data, snk.data()):
if i != j:
errors += 1
return 1.0*errors/data_length

if name == “main”:
points = [1+3j, 4, 5, 6-8j]
constellation = digital.constellation_calcdist(points, [], 1,
1).base()
BER = get_BER(constellation, 1)
print(“BER = {0}”.format(BER))

#8

Nella citazione in data Mon Mar 12 03:36:20 2012, Ben R. ha
scritto:

the new block :
(Gray
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

Ben
i removed all the unnecessary parameters to my study (excess bw ,

(and not digital.constellation_decoder_cb) that you suggested me takes as
gnuradio version.
of the source file “generic_mod_demod” and the grc image of the flow graph :

import random
gr.GR_MSB_FIRST)
tb.run()
print(“BER = {0}”.format(BER))

ok perfect, it worked. I’m using your code to fix my project and it is
working very well. I’ll need only few tweaks in the deconding part of
the digital modulations.

thank you very much again Ben :wink: