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recv: fix detection logic a bit

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Roman Zeyde
2014-11-14 16:49:41 +02:00
parent b23a38295b
commit ea5e577953
2 changed files with 22 additions and 23 deletions
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2
amodem-cli
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@@ -98,7 +98,7 @@ def main():
receiver.add_argument( receiver.add_argument(
'-w', '--wave', default=False, action='store_true') '-w', '--wave', default=False, action='store_true')
receiver.add_argument( receiver.add_argument(
'--skip', type=int, default=128, '--skip', type=int, default=320,
help='skip initial N samples, due to spurious spikes') help='skip initial N samples, due to spurious spikes')
receiver.add_argument( receiver.add_argument(
'--plot', action='store_true', default=False, '--plot', action='store_true', default=False,

43
amodem/recv.py
View File

@@ -15,13 +15,14 @@ from . import common
from . import framing from . import framing
from . import equalizer from . import equalizer
class Detector(object): class Detector(object):
COHERENCE_THRESHOLD = 0.99 COHERENCE_THRESHOLD = 0.9
CARRIER_DURATION = sum(train.prefix) CARRIER_DURATION = sum(train.prefix)
CARRIER_THRESHOLD = int(0.99 * CARRIER_DURATION) CARRIER_THRESHOLD = int(0.9 * CARRIER_DURATION)
SEARCH_WINDOW = 10 # symbols SEARCH_WINDOW = int(0.1 * CARRIER_DURATION)
def __init__(self, config): def __init__(self, config):
self.freq = config.Fc self.freq = config.Fc
@@ -43,39 +44,37 @@ class Detector(object):
counter = 0 counter = 0
if counter == self.CARRIER_THRESHOLD: if counter == self.CARRIER_THRESHOLD:
length = (self.CARRIER_THRESHOLD - 1) * self.Nsym
begin = offset - length
amplitude = self.report_carrier(bufs, begin=begin)
break break
else: else:
raise ValueError('No carrier detected') raise ValueError('No carrier detected')
length = (self.CARRIER_THRESHOLD - 1) * self.Nsym
begin = offset - length
x = np.concatenate(tuple(bufs)[-self.CARRIER_THRESHOLD:-1])
Hc = dsp.exp_iwt(-self.omega, len(x))
Zc = np.dot(Hc, x) / (0.5*len(x))
amplitude = abs(Zc)
start_time = begin * self.Tsym / self.Nsym
log.info('Carrier detected at ~%.1f ms @ %.1f kHz:'
' coherence=%.3f%%, amplitude=%.3f',
start_time * 1e3, self.freq / 1e3,
np.abs(dsp.coherence(x, self.omega)) * 100, amplitude)
log.debug('Buffered %d ms of audio', len(bufs)) log.debug('Buffered %d ms of audio', len(bufs))
bufs = list(bufs)[-self.CARRIER_THRESHOLD-self.SEARCH_WINDOW:] bufs = list(bufs)[-self.CARRIER_THRESHOLD-self.SEARCH_WINDOW:]
trailing = list(itertools.islice(samples, self.SEARCH_WINDOW*self.Nsym)) n = self.SEARCH_WINDOW + self.CARRIER_DURATION - self.CARRIER_THRESHOLD
trailing = list(itertools.islice(samples, n * self.Nsym))
bufs.append(np.array(trailing)) bufs.append(np.array(trailing))
buf = np.concatenate(bufs) buf = np.concatenate(bufs)
offset = self.find_start(buf, self.CARRIER_DURATION*self.Nsym) offset = self.find_start(buf, self.CARRIER_DURATION*self.Nsym)
log.debug('Carrier starts at %.3f ms', start_time += (offset / self.Nsym - self.SEARCH_WINDOW) * self.Tsym
offset * self.Tsym * 1e3 / self.Nsym) log.debug('Carrier starts at %.3f ms', start_time * 1e3)
return itertools.chain(buf[offset:], samples), amplitude return itertools.chain(buf[offset:], samples), amplitude
def report_carrier(self, bufs, begin):
x = np.concatenate(tuple(bufs)[-self.CARRIER_THRESHOLD:-1])
Hc = dsp.exp_iwt(-self.omega, len(x))
Zc = np.dot(Hc, x) / (0.5*len(x))
amp = abs(Zc)
log.info('Carrier detected at ~%.1f ms @ %.1f kHz:'
' coherence=%.3f%%, amplitude=%.3f',
begin * self.Tsym * 1e3 / self.Nsym, self.freq / 1e3,
np.abs(dsp.coherence(x, self.omega)) * 100, amp)
return amp
def find_start(self, buf, length): def find_start(self, buf, length):
N = len(buf) N = len(buf)
carrier = dsp.exp_iwt(self.omega, N) carrier = dsp.exp_iwt(self.omega, N)