How to use the amodem.equalizer.prefix function in amodem

import logging

import numpy as np

from . import dsp
from . import equalizer
from . import common

log = logging.getLogger(__name__)


class Detector:

    COHERENCE_THRESHOLD = 0.9

    CARRIER_DURATION = sum(equalizer.prefix)
    CARRIER_THRESHOLD = int(0.9 * CARRIER_DURATION)
    SEARCH_WINDOW = int(0.1 * CARRIER_DURATION)
    START_PATTERN_LENGTH = SEARCH_WINDOW // 4

    def __init__(self, config, pylab):
        self.freq = config.Fc
        self.omega = 2 * np.pi * self.freq / config.Fs
        self.Nsym = config.Nsym
        self.Tsym = config.Tsym
        self.maxlen = config.baud  # 1 second of symbols
        self.max_offset = config.timeout * config.Fs
        self.plt = pylab

    def _wait(self, samples):
        counter = 0
        bufs = collections.deque([], maxlen=self.maxlen)

def test_detect():
    P = sum(equalizer.prefix)
    t = np.arange(P * config.Nsym) * config.Ts
    x = np.cos(2 * np.pi * config.Fc * t)

    detector = detect.Detector(config, pylab=common.Dummy())
    samples, amp, freq_err = detector.run(x)
    assert abs(1 - amp) < 1e-12
    assert abs(freq_err) < 1e-12

    x = np.cos(2 * np.pi * (2*config.Fc) * t)
    with pytest.raises(ValueError):
        detector.run(x)

    with pytest.raises(ValueError):
        detector.max_offset = 0
        detector.run(x)

def test_prefix():
    omega = 2 * np.pi * config.Fc / config.Fs
    symbol = np.cos(omega * np.arange(config.Nsym))
    signal = np.concatenate([c * symbol for c in equalizer.prefix])

    def symbols_stream(signal):
        sampler = sampling.Sampler(signal)
        return dsp.Demux(sampler=sampler, omegas=[omega], Nsym=config.Nsym)
    r = recv.Receiver(config, pylab=common.Dummy())
    r._prefix(symbols_stream(signal))

    with pytest.raises(ValueError):
        silence = 0 * signal
        r._prefix(symbols_stream(silence))

def _prefix(self, symbols, gain=1.0):
        S = common.take(symbols, len(equalizer.prefix))
        S = S[:, self.carrier_index] * gain
        sliced = np.round(np.abs(S))
        self.plt.figure()
        self.plt.subplot(1, 2, 1)
        self._constellation(S, sliced, 'Prefix')

        bits = np.array(sliced, dtype=int)
        self.plt.subplot(1, 2, 2)
        self.plt.plot(np.abs(S))
        self.plt.plot(equalizer.prefix)
        errors = (bits != equalizer.prefix)
        if any(errors):
            msg = 'Incorrect prefix: {0} errors'.format(sum(errors))
            raise ValueError(msg)
        log.debug('Prefix OK')

def _prefix(self, symbols, gain=1.0):
        S = common.take(symbols, len(equalizer.prefix))
        S = S[:, self.carrier_index] * gain
        sliced = np.round(np.abs(S))
        self.plt.figure()
        self.plt.subplot(1, 2, 1)
        self._constellation(S, sliced, 'Prefix')

        bits = np.array(sliced, dtype=int)
        self.plt.subplot(1, 2, 2)
        self.plt.plot(np.abs(S))
        self.plt.plot(equalizer.prefix)
        errors = (bits != equalizer.prefix)
        if any(errors):
            msg = 'Incorrect prefix: {0} errors'.format(sum(errors))
            raise ValueError(msg)
        log.debug('Prefix OK')

def start(self):
        for value in equalizer.prefix:
            self.write(self.pilot * value)

        symbols = self.equalizer.train_symbols(equalizer.equalizer_length)
        signal = self.equalizer.modulator(symbols)
        self.write(self.silence)
        self.write(signal)
        self.write(self.silence)

def _prefix(self, symbols, gain=1.0):
        S = common.take(symbols, len(equalizer.prefix))
        S = S[:, self.carrier_index] * gain
        sliced = np.round(np.abs(S))
        self.plt.figure()
        self.plt.subplot(1, 2, 1)
        self._constellation(S, sliced, 'Prefix')

        bits = np.array(sliced, dtype=int)
        self.plt.subplot(1, 2, 2)
        self.plt.plot(np.abs(S))
        self.plt.plot(equalizer.prefix)
        errors = (bits != equalizer.prefix)
        if any(errors):
            msg = 'Incorrect prefix: {0} errors'.format(sum(errors))
            raise ValueError(msg)
        log.debug('Prefix OK')