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

[Ben Reynwar]

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)

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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