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#!/usr/bin/env python
# _*_ coding: utf8 _*_
# Andreas Müller, 2008
# andrmuel@ee.ethz.ch
#
# this code may be freely used under GNU GPL conditions
"""
Simulate channel with sampling frequency offset
"""
import math, random, pylab
import dab_tb, ber
NUM_BYTES = 1000000
MODES=[1,2,3,4]
MODES=[1]
SAMPLE_RATE_ERROR = pylab.linspace(0.99, 1.01, 50)
PLOT_FORMAT=['-','-x','--x','-.x',':x']
# initialise test flowgraph
tb = dab_tb.dab_ofdm_testbench(autocorrect_sample_rate=True, ber_sink=True)
tb.gen_random_bytes(NUM_BYTES)
# prepeare plot
pylab.xlabel("Sampling frequency offset (ratio)")
pylab.ylabel("BER")
# open logfile
logfile = open("sampling_frequency_offset_ber_log.txt",'w')
logfile.write("number of bytes: " + str(NUM_BYTES) + "\nRange of sampling rate ratios: " + str(SAMPLE_RATE_ERROR) + "\n\n")
for mode in MODES:
print "Mode: "+str(mode)+"\n-------\n"
tb.setup_flowgraph(mode, ber_skipbytes=5*tb.dp.bytes_per_frame)
ber_values = []
bytes_received = []
# estimate signal energy for this mode (disturbed by FFT ...)
tb.set_signal_energy(1)
tb.set_noise_energy(0)
tb.run()
tb.demod.stop()
tb.set_power_correction(tb.probe_signal.level())
print "estimated energy: " + str(tb.probe_signal.level()) + "\n"
for ratio in SAMPLE_RATE_ERROR:
print "Mode: "+str(mode)+" Ratio: "+str(ratio)
# reset and run the test
tb.rewind_sources()
tb.clear_sinks()
tb.clear_state()
tb.set_sampling_frequency_offset(1/ratio)
tb.set_signal_energy(math.pow(10,1.5))
tb.set_noise_energy(1)
tb.run()
tb.demod.stop()
print "signal power: " + str(tb.probe_signal.level())
print "total power: " + str(tb.probe_total.level())
# get the result
bytes_received.append(tb.sink.bytecount())
print "bytes sent: " + str(NUM_BYTES)
print "bytes received: " + str(tb.sink.bytecount())
ber_values.append(tb.sink.ber())
print "BER: " + str(ber_values[-1])
print
# write log
logfile.write("Mode: " + str(mode)+"\n" +
"=======\n\n" +
"Actual to real sampling frequency ratio: BER (number of bytes received)\n" +
"-----------------------------------\n")
for i in range(0,len(SAMPLE_RATE_ERROR)):
logfile.write(str(SAMPLE_RATE_ERROR[i])+": "+str(ber_values[i])+" (" + str(bytes_received[i]) + ")\n")
logfile.write("\n\n")
# plot it:
if sum([abs(x) for x in ber_values])==0:
print "all BER values are 0 - not plotting"
else:
pylab.semilogy(SAMPLE_RATE_ERROR, ber_values, PLOT_FORMAT[mode], label="Mode "+str(mode))
# pylab.plot(SAMPLE_RATE_ERROR, ber_values, PLOT_FORMAT[mode], label="Mode "+str(mode))
logfile.close()
# pylab.axis([SAMPLE_RATE_ERROR[0],SAMPLE_RATE_ERROR[-1],0,0.52])
pylab.legend()
pylab.show()
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