def receive_prefix(symbols):
S = common.take(symbols, len(train.prefix))[:, config.carrier_index]
sliced = np.round(S)
if pylab:
pylab.figure()
show.constellation(S, sliced, 'Prefix')
bits = np.array(np.abs(sliced), dtype=int)
if any(bits != train.prefix):
raise ValueError('Incorrect prefix')
log.info('Prefix OK')
nonzeros = np.array(train.prefix, dtype=bool)
pilot_tone = S[nonzeros]
phase = np.unwrap(np.angle(pilot_tone)) / (2 * np.pi)
indices = np.arange(len(phase))
a, b = sigproc.linear_regression(indices, phase)
freq_err = a / (config.Tsym * config.Fc)
last_phase = a * indices[-1] + b
log.debug('Current phase on carrier: %.3f', last_phase)
expected_phase, = set(np.angle(sliced[nonzeros]) / (2 * np.pi))
log.debug('Excepted phase on carrier: %.3f', expected_phase)
sampling_err = (last_phase - expected_phase) * config.Nsym
log.info('Frequency error: %.2f ppm', freq_err * 1e6)
log.info('Sampling error: %.2f samples', sampling_err)
return freq_err, sampling_err
def train_receiver(symbols, freqs):
filters = {}
scaling_factor = len(freqs) # to avoid saturation
training = np.array(train.equalizer)
if pylab:
pylab.figure()
symbols = common.take(symbols, len(training) * len(freqs))
for i, freq in enumerate(freqs):
size = len(training)
offset = i * size
S = symbols[offset:offset+size, i]
filt = sigproc.train(S, training * scaling_factor)
filters[freq] = filt
Y = list(filt(S))
y = np.array(Y) / scaling_factor
if pylab:
pylab.subplot(HEIGHT, WIDTH, i+1)
show.constellation(y, modem.qam.symbols,
'Train: $F_c = {}Hz$'.format(freq))
pylab.plot(S.real, S.imag, '.-')
train_result = np.round(y)
if not all(train_result == training):
raise ValueError('#{} training failed on {} Hz'.format(i, freq))
noise = y - training
Pnoise = sigproc.power(noise)
log.info('%10.1f kHz: Noise sigma=%.4f, SNR=%.1f dB',
freq/1e3, Pnoise**0.5, 10*np.log10(1/Pnoise))
return filters
def main(args):
log.info('Running MODEM @ {:.1f} kbps'.format(modem.modem_bps / 1e3))
fd = sys.stdin
signal = stream.iread(fd)
skipped = common.take(signal, args.skip)
log.debug('Skipping first %.3f seconds', len(skipped) / float(modem.baud))
stream.check = common.check_saturation
size = 0
signal, amplitude = detect(signal, config.Fc)
bits = receive(signal, modem.freqs, gain=1.0/amplitude)
try:
for chunk in decode(bits):
sys.stdout.write(chunk)
size = size + len(chunk)
except Exception:
log.exception('Decoding failed')
duration = time.time() - stats['rx_start']
audio_time = stats['rx_bits'] / float(modem.modem_bps)
log.debug('Demodulated %.3f kB @ %.3f seconds (%.1f%% realtime)',
stats['rx_bits'] / 8e3, duration, 100 * duration / audio_time)
log.info('Received %.3f kB @ %.3f seconds = %.3f kB/s',
size * 1e-3, duration, size * 1e-3 / duration)
if pylab:
pylab.figure()
symbol_list = np.array(stats['symbol_list'])
for i, freq in enumerate(modem.freqs):
pylab.subplot(HEIGHT, WIDTH, i+1)
show.constellation(symbol_list[i], modem.qam.symbols,
'$F_c = {} Hz$'.format(freq))
