radiosonde_auto_rx/auto_rx/autorx/fsk_demod.py

#!/usr/bin/env python
#
#   radiosonde_auto_rx - fsk_demod modem statistics parser
#
#   Copyright (C) 2019  Mark Jessop <vk5qi@rfhead.net>
#   Released under GNU GPL v3 or later
#
import json
import logging
import time
import numpy as np


class FSKDemodStats(object):
    """
    Process modem statistics produced by fsk_demod and provide access to
    filtered or instantaneous modem data.

    This class expects the JSON output from fsk_demod to be arriving in *realtime*.
    The test script below will emulate relatime input based on a file.
    """


    FSK_STATS_FIELDS = ['EbNodB', 'ppm', 'f1_est', 'f2_est', 'samp_fft']


    def __init__(self,
        averaging_time = 5.0,
        peak_hold = False,
        decoder_id = ""
        ):
        """

        Required Fields:
            averaging_time (float): Use the last X seconds of data in calculations.
            peak_hold (bool): If true, use a peak-hold SNR metric instead of a mean.
            decoder_id (str): A unique ID for this object (suggest use of the SDR device ID)
            
        """

        self.averaging_time = float(averaging_time)
        self.peak_hold = peak_hold
        self.decoder_id = str(decoder_id)

        # Input data stores.
        self.in_times = np.array([])
        self.in_snr = np.array([])
        self.in_ppm = np.array([])


        # Output State variables.
        self.snr = -999.0
        self.fest = [0.0,0.0]
        self.fft = []
        self.ppm = 0.0



    def update(self, data):
        """
        Update the statistics parser with a new set of output from fsk_demod.
        This can accept either a string (which will be parsed as JSON), or a dict.

        Required Fields:
            data (str, dict): One set of statistics from fsk_demod.
        """

        # Check input type
        if type(data) == bytes:
            data = data.decode('ascii')

        if type(data) == str:
            # Attempt to parse string.
            try:
                _data = json.loads(data)
            except Exception as e:
                self.log_error("FSK Demod Stats - %s" % str(e))
                return
        elif type(data) == dict:
            _data = data
        
        else:
            return

        # Check for required fields in incoming dictionary.
        for _field in self.FSK_STATS_FIELDS:
            if _field not in _data:
                self.log_error("Missing Field %s" % _field)
                return

        # Now we can process the data.
        _time = time.time()
        self.fft = _data['samp_fft']
        self.fest[0] = _data['f1_est']
        self.fest[1] = _data['f2_est']

        # Time-series data
        self.in_times = np.append(self.in_times, _time)
        self.in_snr = np.append(self.in_snr, _data['EbNodB'])
        self.in_ppm = np.append(self.in_ppm, _data['ppm'])


        # Calculate SNR / PPM
        _time_range = self.in_times>(_time-self.averaging_time)
        # Clip arrays to just the values we want
        self.in_ppm = self.in_ppm[_time_range]
        self.in_snr = self.in_snr[_time_range]
        self.in_times = self.in_times[_time_range]

        # Always just take a mean of the PPM values.
        self.ppm = np.mean(self.in_ppm)

        if self.peak_hold:
            self.snr = np.max(self.in_snr)
        else:
            self.snr = np.mean(self.in_snr)


    def log_debug(self, line):
        """ Helper function to log a debug message with a descriptive heading. 
        Args:
            line (str): Message to be logged.
        """
        logging.debug("FSK Demod Stats #%s - %s" % (str(self.decoder_id), line))


    def log_info(self, line):
        """ Helper function to log an informational message with a descriptive heading. 
        Args:
            line (str): Message to be logged.
        """
        logging.info("FSK Demod Stats #%s - %s" % (str(self.decoder_id), line))


    def log_error(self, line):
        """ Helper function to log an error message with a descriptive heading. 
        Args:
            line (str): Message to be logged.
        """
        logging.error("FSK Demod Stats #%s - %s" % (str(self.decoder_id), line))



if __name__ == "__main__":
    import sys
    _filename = sys.argv[1]

    _f = open(_filename,'r')

    stats = FSKDemodStats(averaging_time=2.0, peak_hold=True)

    rate = 10.0
    updaterate = 10
    count = 0

    for _line in _f:
        try:
            _line = json.loads(_line)
        except:
            continue
            
        stats.update(_line)

        time.sleep(1/rate)

        if count%updaterate == 0:
            print("%d - SNR: %.1f dB, FEst: %s, ppm: %.1f" % (count, stats.snr, stats.fest, stats.ppm))

        count += 1