Re: [Discuss-gnuradio] need help for digital.constellation_decoder_cb in release 3.5.0

[Ben Reynwar]

On Sun, Mar 11, 2012 at 4:25 PM, Arturo Rinaldi <address@hidden> wrote:
> Nella citazione in data Sun Mar 11 02:30:43 2012, Arturo Rinaldi ha scritto:
>
>> Nella citazione in data Fri Mar 9 19:50:05 2012, Ben Reynwar ha scritto:
>>>
>>> On Thu, Mar 8, 2012 at 8:19 PM, Arturo Rinaldi<address@hidden>
>>> wrote:
>>>>
>>>> Nella citazione in data ven 09 dic 2011 05:55:57 CET, Ben Reynwar ha
>>>> scritto:
>>>>
>>>>> On Thu, Dec 8, 2011 at 5:33 PM, Arturo Rinaldi<address@hidden>
>>>>> wrote:
>>>>>>
>>>>>>
>>>>>> 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
>>>>>>
>>>>>> _______________________________________________
>>>>>> Discuss-gnuradio mailing list
>>>>>> address@hidden
>>>>>> 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
>>>>>
>>>>
>>>> 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.
>>>
>>>
>>> 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
>
>
> 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

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))