Re: [Discuss-gnuradio] Question on DQPSK Modulation - issue with output

[Ben Reynwar]

On Sun, Jun 3, 2012 at 4:31 PM, Ben Reynwar <address@hidden> wrote:
> Hi Vahid,
>
> First I'd try using a much longer string of bits and see if that help.
>
> Second I'd find an example in gnuradio
> (gr-digital/python/qa_constellation.py should have a working dqpsk
> test) and then work from there.
>
> Thirdly if you want pi/4-dqpsk you won't be able to use the standard
> dqpsk_mod and dqpsk_demod, but will need to define a two-dimensional
> constellation and use the generic_mod and generic_demod blocks.  The
> two-dimensional constellation would be defined something like:
>
> normal_qpsk_points = [blah, blah, blah, blah]
> rotated_qpsk_points = [blah, blah, blah, blah]
> two_d_points = []
> for p in normal_qpsk_points:
>    for q in rotated_qpsk_points:
>        two_d_points += [p, q]
> pi4dqpsk_constellation = digital.constellation_calcdist(two_d_points, [], 4, 
> 2)

Just checked the code and it looks like multi-dimensional
constellations aren't supported yet by generic_mod and generic_demod.
Another way might be to edit digital.constellation_receiver_cb so that
it shifts the phase back and forth by pi/4.

>
> Cheers,
> Ben
>
> On Sat, Jun 2, 2012 at 4:20 PM, Vahid Behzadan <address@hidden> wrote:
>>
>> Dear all,
>>
>> I am currently trying to implement a pi/4 dqpsk modulator and demodulator. I
>> have tried two approaches, one uses the CQPSK.py (included in osmocom's
>> TETRA project) and the other uses digital.qpsk.dqpsk_mod. Both of these
>> approaches have failed to return the same string of bits after the process
>> of modulations->demodulation. The input comes from a .dat file and is a
>> string of bits (tried different sizes, from 2 bits to 32 bits), then the
>> output of modulation is written to a sink.dat as gr_complex. This file is
>> then fed to a demodulator which saves the output to a final.dat. I have
>> attached important bits of the code which uses qpsk.dqpsk_mod/demod. I would
>> greatly appreciate any advice.
>> Also, could anyone please confirm that what I can achieve a --PI/4--DQPSK
>> using the dqpsk_mod?
>>
>> Best Regards,
>>
>> Vahid
>> ---------------------------
>> Modulator:
>>
>> .
>> .
>> .
>>        sample_rate = options.sample_rate
>>        symbol_rate = 18000
>>        sps = 2
>>
>>    IN = gr.file_source(gr.sizeof_gr_complex, options.input_file, repeat =
>> False)
>>    #IN = (1,0,0,0,1,1,0,0)
>>    src = gr.vector_source_b (IN)
>>    MOD = digital.qpsk.dqpsk_mod( samples_per_symbol = sps,
>>                                 excess_bw=0.35,
>>                log=options.log, gray_coded=True,
>>
>>                                 verbose=options.verbose)
>>
>>    self.connect(src,MOD)
>>        OUT = gr.file_sink(gr.sizeof_gr_complex, options.output_file)
>>
>>    self.sink1 = gr.vector_sink_f()
>>    self.sink2 = gr.vector_sink_f()
>>
>>    real = gr.complex_to_real()
>>    imag = gr.complex_to_imag()
>>    self.connect(MOD,real)
>>    self.connect(MOD,imag)
>>
>>    self.connect(real,self.sink1)
>>    self.connect(imag,self.sink2)
>>    self.connect(MOD,OUT)
>>    def print_data(self):
>>    print "data in sink1 is: ",self.sink1.data()
>>    print "data in sink2 is: ",self.sink2.data()
>> .
>> .
>> .
>> ---------
>> Demodulator:
>>
>>
>> sample_rate = options.sample_rate
>>        symbol_rate = 18000
>>        sps = 2
>>       # output rate will be 36,000
>>        ntaps = 11 * sps
>>        new_sample_rate = symbol_rate * sps
>>
>>        channel_taps = gr.firdes.low_pass(1.0, sample_rate,
>> options.low_pass, options.low_pass * 0.1, gr.firdes.WIN_HANN)
>>
>>        FILTER = gr.freq_xlating_fir_filter_ccf(1, channel_taps,
>> options.calibration, sample_rate)
>>    IN = gr.file_source(gr.sizeof_gr_complex, options.input_file)
>>    #IN = (1,1,0,1,1,1,0,0)
>>    #src = gr.vector_source_b (IN)
>>    DEMOD = digital.qpsk.dqpsk_demod( samples_per_symbol = sps,
>>                                 excess_bw=0.35, gray_coded=True,
>>                log=options.log,
>>
>>                                 verbose=options.verbose)
>>
>>
>>    OUT = gr.file_sink(gr.sizeof_char, options.output_file)
>>
>>    self.sink1 = gr.vector_sink_b()
>>
>>        r = float(sample_rate) / float(new_sample_rate)
>>
>>        INTERPOLATOR = gr.fractional_interpolator_cc(0, r)
>>
>>        self.connect(IN, FILTER, INTERPOLATOR, DEMOD, OUT)
>>    self.connect(DEMOD,self.sink1)
>>    def print_data(self):
>>    print "data in sink1 is: ",self.sink1.data()
>>
>>
>> --
>> View this message in context: 
>> http://old.nabble.com/Question-on-DQPSK-Modulation---issue-with-output-tp33950307p33950307.html
>> Sent from the GnuRadio mailing list archive at Nabble.com.
>>
>>
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