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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 noise channel to evaluate BER vs SNR
"""
import math, random, pylab
import dab_tb, ber
NUM_BYTES = 1000000
MODES=[1,2,3,4]
SNR_DB = range(-5,21)
PLOT_FORMAT=['-','-x','--x','-.x',':x']
# initialise test flowgraph
tb = dab_tb.dab_ofdm_testbench()
tb.gen_random_bytes(NUM_BYTES)
# prepeare plot
#pylab.title("BER in noisy channel") # add caption in LaTeX -> looks better
pylab.xlabel("SNR [dB]")
pylab.ylabel("BER")
# open logfile
logfile = open("snr_ber_log.txt",'w')
logfile.write("number of bytes: " + str(NUM_BYTES) + "\nSNR range: " + str(SNR_DB) + "\n\n")
for mode in MODES:
print "\nMode: "+str(mode)+"\n-------\n"
tb.setup_flowgraph(mode)
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.set_power_correction(tb.probe_signal.level())
print "estimated energy: " + str(tb.probe_signal.level()) + "\n"
for snr_db in SNR_DB:
print "\nMode: "+str(mode)+" SNR: "+str(snr_db)
# reset and run the test
tb.rewind_sources()
tb.clear_sinks()
tb.clear_state()
tb.set_signal_energy(math.pow(10,snr_db/10.))
tb.set_noise_energy(1)
tb.run()
print "signal power: " + str(tb.probe_signal.level())
print "total power: " + str(tb.probe_total.level())
# get the result
result = tb.sink.data()
expected_result = tb.random_bytes[tb.dp.bytes_per_frame:]
bytes_received.append(len(result))
print "bytes sent: " + str(NUM_BYTES)
print "bytes received: " + str(len(result))
# calculate bit error rate
ber_values.append(ber.find_ber(expected_result,result))
print "BER: " + str(ber_values[-1])
print "Phase - sqrt(var): " + str(math.sqrt(tb.demod.probe_phase_var.level()))
# write log
logfile.write("Mode: " + str(mode)+"\n" +
"=======\n\n" +
"SNR: BER (number of bytes received)\n" +
"-----------------------------------\n")
for i in range(0,len(SNR_DB)):
logfile.write(str(SNR_DB[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(SNR_DB, ber_values, PLOT_FORMAT[mode], label="Mode "+str(mode))
# pylab.plot(SNR_DB, ber_values, PLOT_FORMAT[mode], label="Mode "+str(mode))
logfile.close()
# pylab.axis([SNR_DB[0],SNR_DB[-1],0,0.52])
pylab.legend()
pylab.show()
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