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https://github.com/romanz/amodem.git
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split carrier detection into detect.py
This commit is contained in:
Roman Zeyde
83
amodem/detect.py
Normal file
83
amodem/detect.py
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@@ -0,0 +1,83 @@
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import numpy as np
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import logging
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import itertools
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import collections
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log = logging.getLogger(__name__)
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from . import dsp
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from . import train
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from . import common
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class Detector(object):
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COHERENCE_THRESHOLD = 0.9
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CARRIER_DURATION = sum(train.prefix)
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CARRIER_THRESHOLD = int(0.9 * CARRIER_DURATION)
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SEARCH_WINDOW = int(0.1 * CARRIER_DURATION)
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TIMEOUT = 10.0 # [seconds]
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def __init__(self, config):
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self.freq = config.Fc
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self.omega = 2 * np.pi * self.freq / config.Fs
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self.Nsym = config.Nsym
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self.Tsym = config.Tsym
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self.maxlen = config.baud # 1 second of symbols
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self.max_offset = self.TIMEOUT * config.Fs
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def run(self, samples):
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counter = 0
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bufs = collections.deque([], maxlen=self.maxlen)
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for offset, buf in common.iterate(samples, self.Nsym, enumerate=True):
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if offset > self.max_offset:
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raise ValueError('Timeout waiting for carrier')
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bufs.append(buf)
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coeff = dsp.coherence(buf, self.omega)
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if abs(coeff) > self.COHERENCE_THRESHOLD:
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counter += 1
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else:
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counter = 0
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if counter == self.CARRIER_THRESHOLD:
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break
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else:
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raise ValueError('No carrier detected')
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length = (self.CARRIER_THRESHOLD - 1) * self.Nsym
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begin = offset - length
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x = np.concatenate(tuple(bufs)[-self.CARRIER_THRESHOLD:-1])
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Hc = dsp.exp_iwt(-self.omega, len(x))
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Zc = np.dot(Hc, x) / (0.5*len(x))
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amplitude = abs(Zc)
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start_time = begin * self.Tsym / self.Nsym
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log.info('Carrier detected at ~%.1f ms @ %.1f kHz:'
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' coherence=%.3f%%, amplitude=%.3f',
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start_time * 1e3, self.freq / 1e3,
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np.abs(dsp.coherence(x, self.omega)) * 100, amplitude)
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log.debug('Buffered %d ms of audio', len(bufs))
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bufs = list(bufs)[-self.CARRIER_THRESHOLD-self.SEARCH_WINDOW:]
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n = self.SEARCH_WINDOW + self.CARRIER_DURATION - self.CARRIER_THRESHOLD
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trailing = list(itertools.islice(samples, n * self.Nsym))
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bufs.append(np.array(trailing))
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buf = np.concatenate(bufs)
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offset = self.find_start(buf, self.CARRIER_DURATION*self.Nsym)
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start_time += (offset / self.Nsym - self.SEARCH_WINDOW) * self.Tsym
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log.debug('Carrier starts at %.3f ms', start_time * 1e3)
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return itertools.chain(buf[offset:], samples), amplitude
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def find_start(self, buf, length):
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N = len(buf)
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carrier = dsp.exp_iwt(self.omega, N)
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z = np.cumsum(buf * carrier)
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z = np.concatenate([[0], z])
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correlations = np.abs(z[length:] - z[:-length])
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return np.argmax(correlations)
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@@ -2,7 +2,6 @@ import numpy as np
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import logging
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import itertools
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import functools
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import collections
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import time
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log = logging.getLogger(__name__)
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@@ -14,79 +13,7 @@ from . import train
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from . import common
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from . import framing
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from . import equalizer
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class Detector(object):
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COHERENCE_THRESHOLD = 0.9
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CARRIER_DURATION = sum(train.prefix)
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CARRIER_THRESHOLD = int(0.9 * CARRIER_DURATION)
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SEARCH_WINDOW = int(0.1 * CARRIER_DURATION)
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TIMEOUT = 10.0 # [seconds]
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def __init__(self, config):
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self.freq = config.Fc
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self.omega = 2 * np.pi * self.freq / config.Fs
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self.Nsym = config.Nsym
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self.Tsym = config.Tsym
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self.maxlen = config.baud # 1 second of symbols
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self.max_offset = self.TIMEOUT * config.Fs
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def run(self, samples):
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counter = 0
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bufs = collections.deque([], maxlen=self.maxlen)
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for offset, buf in common.iterate(samples, self.Nsym, enumerate=True):
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if offset > self.max_offset:
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raise ValueError('Timeout waiting for carrier')
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bufs.append(buf)
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coeff = dsp.coherence(buf, self.omega)
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if abs(coeff) > self.COHERENCE_THRESHOLD:
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counter += 1
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else:
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counter = 0
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if counter == self.CARRIER_THRESHOLD:
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break
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else:
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raise ValueError('No carrier detected')
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length = (self.CARRIER_THRESHOLD - 1) * self.Nsym
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begin = offset - length
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x = np.concatenate(tuple(bufs)[-self.CARRIER_THRESHOLD:-1])
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Hc = dsp.exp_iwt(-self.omega, len(x))
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Zc = np.dot(Hc, x) / (0.5*len(x))
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amplitude = abs(Zc)
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start_time = begin * self.Tsym / self.Nsym
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log.info('Carrier detected at ~%.1f ms @ %.1f kHz:'
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' coherence=%.3f%%, amplitude=%.3f',
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start_time * 1e3, self.freq / 1e3,
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np.abs(dsp.coherence(x, self.omega)) * 100, amplitude)
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log.debug('Buffered %d ms of audio', len(bufs))
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bufs = list(bufs)[-self.CARRIER_THRESHOLD-self.SEARCH_WINDOW:]
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n = self.SEARCH_WINDOW + self.CARRIER_DURATION - self.CARRIER_THRESHOLD
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trailing = list(itertools.islice(samples, n * self.Nsym))
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bufs.append(np.array(trailing))
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buf = np.concatenate(bufs)
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offset = self.find_start(buf, self.CARRIER_DURATION*self.Nsym)
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start_time += (offset / self.Nsym - self.SEARCH_WINDOW) * self.Tsym
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log.debug('Carrier starts at %.3f ms', start_time * 1e3)
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return itertools.chain(buf[offset:], samples), amplitude
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def find_start(self, buf, length):
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N = len(buf)
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carrier = dsp.exp_iwt(self.omega, N)
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z = np.cumsum(buf * carrier)
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z = np.concatenate([[0], z])
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correlations = np.abs(z[length:] - z[:-length])
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return np.argmax(correlations)
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from . import detect
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class Receiver(object):
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@@ -292,7 +219,7 @@ def main(args):
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reader.check = common.check_saturation
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detector = Detector(config=config)
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detector = detect.Detector(config=config)
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receiver = Receiver(config=config, plt=args.plot)
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success = False
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try:
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@@ -3,6 +3,7 @@ import pytest
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from amodem import dsp
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from amodem import recv
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from amodem import detect
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from amodem import train
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from amodem import sampling
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from amodem import config
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@@ -14,7 +15,7 @@ def test_detect():
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t = np.arange(P * config.Nsym) * config.Ts
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x = np.cos(2 * np.pi * config.Fc * t)
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detector = recv.Detector(config)
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detector = detect.Detector(config)
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samples, amp = detector.run(x)
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assert abs(1 - amp) < 1e-12
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@@ -46,7 +47,7 @@ def test_prefix():
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def test_find_start():
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sym = np.cos(2 * np.pi * config.Fc * np.arange(config.Nsym) * config.Ts)
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detector = recv.Detector(config)
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detector = detect.Detector(config)
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length = 200
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prefix = postfix = np.tile(0 * sym, 50)
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