Hi,
I'm new to gnu radio. To get familiar with this project, I'm trying to
simulate a dbpsk link.
My flow graph look like this :
stream of bits => Modulation => frequency up translation => Noisy channel
=> frequency down translation => Demodulation
But, there is something going wrong!! If the input stream looks like this
: 0 0 1 1 0 0 1 1 0 0 1 1..... the output will be ( after Costa's loop and
MM are stabilized ) : 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1......
I looked for an undesired decimation, but didn't find any. Do you Have
any idea of what is going wrong?
Axel
My code :
class my_top_block(gr.top_block):
def __init__(self):
gr.top_block.__init__(self)
fg = gr.flow_graph()
sps = 8
symbol_rate = 1625000.0 / 6.0
sample_rate = sps * symbol_rate
p_size = 1024
lo_freq = 7.5e5
lp_cutoff = 2.5e5
lp_tw = 5e5
noise_mag = 0.0
#Source
self.src_data = (big stream of : 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1
1)
self.src0 = gr.vector_source_b (self.src_data)
######
###Modulation####
self.objMod = dbpsk.dbpsk_mod(sps,0.35,False,False,False)
#################
### Canal########
# Mix to IF
self.lo = gr.sig_source_c(sample_rate, gr.GR_SIN_WAVE,
lo_freq,1.0, 0)
self.mixer = gr.multiply_cc()
self.connect(self.lo, (self.mixer, 1))
# Simulate noise in the channel
self.noise = gr.noise_source_c(gr.GR_GAUSSIAN, noise_mag)
self.air_noise = gr.add_cc()
self.connect(self.noise, (self.air_noise, 1))
# Mix to baseband
self.chan_taps = gr.firdes.low_pass(1.0, sample_rate,
lp_cutoff, lp_tw,
gr.firdes.WIN_HAMMING)
self.chan_filter = gr.freq_xlating_fir_filter_ccc(1,
self.chan_taps,-lo_freq, sample_rate)
###################
### Demodulation######
self.objDeMod=dbpsk.dbpsk_demod(sps,0.35)
######################
######Connection des blocs#####
self.connect(self.src0,self.objMod, self.mixer, self.air_noise,
self.chan_filter, self.objDeMod)
#####################
################# Observation entree/sortie########
self.sink1 = gr.vector_sink_b()
self.connect(self.objDeMod,self.sink1)
self.sink2 = gr.vector_sink_b()
self.connect(self.src0,self.sink2)
def print_data(self):
print "demod: ",self.sink1.data()
print len(self.sink1.data())
print "check: ",self.sink2.data()
print len(self.sink2.data())
################################################
if __name__ == '__main__':
try:
tb=my_top_block()
tb.run()
tb.print_data()
except KeyboardInterrupt:
pass
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