[Discuss-gnuradio] BPSK modulation

[Jose luis jose louis]

Hello im i student of engineering telecommunication  and im try to build a 
bpsk modulation, doing the modulation and saving  in a audio.dat (computer 
to computer without usrp), thus the demodulation that obtain have a  lot of 
noise, very very bad S/N,
the code .....

//////////////Modulator 
Bpsk///////////////////////////////////////////////////////////////////
class bpsk_mod(gr.hier_block):
   def __init__(self, fg, spb, excess_bw, gray_code=True, verbose=True, 
debug=False):
       """
       self.fg = fg
       #self.spb = spb
       self.spb= 48e3
       self.excess_bw = excess_bw #factor roll-off

       if not isinstance(spb, int) or spb < 2:
           raise TypeError, ("sbp must be an integer >= 2, is %d" % spb)

       arity = pow(2,self.bits_per_baud())

       # turn bytes into k-bit vectors
       self.bytes2chunks = \
         gr.packed_to_unpacked_bb(self.bits_per_baud(), gr.GR_MSB_FIRST)

       self.chunks2symbols = 
gr.chunks_to_symbols_bc(psk.constellation[arity])

       ntaps = 4 #
       # pulse shaping filter
        self.rrc_taps = gr.firdes.root_raised_cosine(
                2,              # gain  (spb since we're interpolating by spb)
       self.spb,            # sampling rate
                8,              # symbol rate
                self.excess_bw, # (roll-off factor)
               ntaps)

        self.rrc_filter = gr.interp_fir_filter_ccf(2, self.rrc_taps)

        # Connect and Initialize base class

       self.fg.connect(self.bytes2chunks,self.chunks2symbols, 
self.rrc_filter)
        gr.hier_block.__init__(self, self.fg, self.bytes2chunks, 
self.rrc_filter)


//////////////////Demodulator_bpsk//////////////////////////////////////////////////////////////////////////////////////////////

class bpsk_demod__coherent_detection_of_psk(gr.hier_block):
   def __init__(self, fg, spb=2, excess_bw=0.2, costas_alpha=0.005, 
gain_mu=0.05, mu=0.5,
                gray_code=True, verbose=True, debug=False):


       self.fg = fg
       self.spb = spb
       self.excess_bw = excess_bw
       self.costas_alpha = costas_alpha
       self.gain_mu = gain_mu

       if spb < 2:
           raise TypeError, "sbp must be >= 2"

       arity = pow(2,self.bits_per_baud())
#\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ºº
       # Automatic gain control

       self.preamp = gr.multiply_const_cc(1e-4)
       #self.fg.connect(self.preamp, gr.file_sink(gr.sizeof_gr_complex, 
"preamp.dat"))
       self.agc = gr.agc_cc(1e-3, 1,1.0)

#\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ºº
       # Costas loop (carrier tracking)
       costas_order = 2
       self.costas_alpha *=  15  # 2nd order loop needs more gain
       beta = .25 * costas_alpha * costas_alpha

#\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ºº
       self.costas_loop = gr.costas_loop_cc(self.costas_alpha, beta, 0.05, 
-0.05, costas_order)

#\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ºº
       self.fg.connect(self.costas_loop, gr.file_sink(gr.sizeof_gr_complex, 
"costas.dat"))

       # RRC data filter
       ntaps = 11*(2)
       self.rrc_taps = gr.firdes.root_raised_cosine(
           1,                # gain
           48000,                # sampling rate
           1,                # symbol rate
           self.excess_bw,     # excess bandwidth (roll-off factor)
           ntaps)

       self.rrc_filter=gr.fir_filter_ccf(5, self.rrc_taps)
       self.fg.connect(self.rrc_filter,gr.file_sink(gr.sizeof_gr_complex, 
"rrc.dat"))
       
#\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

       
#\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
       # symbol clock recovery
       omega = spb #=2
       gain_omega = 0.25 * gain_mu * gain_mu #gain_mu =0.05
       omega_rel_limit = 1
       mu = 0.05
       self.gain_mu = 1
       self.clock_recovery=gr.clock_recovery_mm_cc(omega, gain_omega, mu, 
self.gain_mu, omega_rel_limit)

       # find closest constellation point
       #rot = .707 + .707j
       rot = 1
       rotated_const = map(lambda pt: pt * rot, psk.constellation[arity])

       self.slicer = gr.constellation_decoder_cb(rotated_const, 
range(arity))
       self.gray_decoder = gr.map_bb(psk.gray_to_binary[arity])

       
self.unpack=gr.unpacked_to_packed_bb(self.bits_per_baud(),gr.GR_LSB_FIRST)

       # Connect and Initialize base class
       self.fg.connect(self.costas_loop, self.rrc_filter, \
                       self.clock_recovery, self.slicer, self.gray_decoder, 
self.unpack)
       gr.hier_block.__init__(self, self.fg, self.costas_loop, self.unpack)

If my audio.dat sample is 48k in modulation:
The RRC sample rate = 48k ? and simbol rate is the bits of sound card output 
(16 bits)??
and wha is the size on ntaps ??
and the RRC in the demodulator  is the same params than in the modulator?

the code it is  rigth?? tanks

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