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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