Added SNR Test utility.

auto_rx/auto_rx.py

@@ -577,6 +577,7 @@ def decode_rs41(frequency, ppm=0, gain=-1, bias=False, rx_queue=None, timeout=12
     else:
         gain_param = ''
 
+    # rtl_fm -p 0 -g -1 -M fm -F9 -s 15k -f 405500000 | sox -t raw -r 15k -e s -b 16 -c 1 - -r 48000 -b 8 -t wav - lowpass 2600 2>/dev/null | ./rs41ecc
     # Note: Have removed a 'highpass 20' filter from the sox line, will need to re-evaluate if adding that is useful in the future.
     decode_cmd = "rtl_fm %s-p %d %s-M fm -F9 -s 15k -f %d 2>/dev/null |" % (bias_option, int(ppm), gain_param, frequency)
     decode_cmd += "sox -t raw -r 15k -e s -b 16 -c 1 - -r 48000 -b 8 -t wav - lowpass 2600 2>/dev/null |"

auto_rx/utils/snr_test.py

@@ -0,0 +1,108 @@
+#!/usr/bin/env python
+#
+# Demodulator Performance Testing
+# Really simple testing of how the demodulators cope with added white noise.
+#
+# Copy in the relevant demod binaries to this directory.
+# Run with: python snr_test.py -f test_file.bin -d RS92
+#
+# The input test file should be the FM demodulated signal, with the sox post-processing.
+# For example:
+#     RS92: rtl_fm -p 0 -M fm -F9 -s 12k -f 400500000 | sox -t raw -r 12k -e s -b 16 -c 1 - -r 48000 -b 8 -t wav - highpass 20 lowpass 2500 2>/dev/null > test_file.bin
+#     RS41: rtl_fm -p 0 -M fm -F9 -s 15k -f 405500000 | sox -t raw -r 15k -e s -b 16 -c 1 - -r 48000 -b 8 -t wav - lowpass 2600 2>/dev/null > test_file.bin
+#
+# I'm unsure how comparable the RS92 and RS41 results are. Take the results with a healthy lump of salt.
+# At the very least, this should be useful to compare performance of different demod revisions.
+#
+
+import sys
+import os
+import numpy as np
+import argparse
+import subprocess
+
+# Demodulator calls. Replace as appropriate.
+RS92_DEMOD = "./rs92ecc --crc --ecc --vel"
+RS41_DEMOD = "./rs41ecc --crc --ecc --ptu"
+
+# Noise level range (gaussian distribution, standard deviation referred to full scale), in dB.
+# Both demods seem to fall over by -15 dB of added noise.
+NOISE_LEVELS = np.arange(-30.0, -15, 1.0)
+
+TEMP_FILENAME = 'temp.bin'
+
+def read_file(filename):
+	''' Read in file and convert to floating point '''
+	data = np.fromfile(filename,dtype='u1')
+	header = data[:44] # This is a bit of a hack. The RS demods want a wave header, so we store this for later writeout.
+	data = (data[44:].astype('float') - 128.0) / 128.0
+
+	return (data,header)
+
+
+def write_file(filename, data, header):
+	'''  Convert an array of floats to uint8 and write to a file '''
+
+	data = (data*128.0)+128.0
+	data = data.astype('u1')
+	f = open(filename,'wb')
+	f.write(header.tobytes())
+	f.write(data.tobytes())
+	f.close()
+
+def add_noise(data, noise_level):
+	''' Add white noise to a file '''
+	noise_level_linear = 10**(noise_level/20.0)
+	noise = np.random.normal(scale=noise_level_linear, size=data.shape)
+
+	return data + noise
+
+def run_demod(filename, demod='RS92'):
+	if demod == 'RS92':
+		demod_bin = RS92_DEMOD
+	else:
+		demod_bin = RS41_DEMOD
+
+	demod_command = "cat %s | %s" % (filename, demod_bin)
+
+	# Run demod.
+	with open(os.devnull, 'w') as devnull:
+		output = subprocess.check_output(demod_command, shell=True, stderr=devnull)
+
+
+	if demod == 'RS92':
+		# RS92 demod just gives us one line per frame.
+		return len(output.split('\n'))
+	else:
+		# RS41 demod gives us a lot more...
+		frames = 0
+		for _line in output.split('\n'):
+			if _line != '':
+				if _line[0] == '[':
+					frames += 1
+		return frames
+
+
+if __name__ == '__main__':
+	# Command line arguments. 
+	parser = argparse.ArgumentParser()
+	parser.add_argument("-f", "--filename", type=str, help="Input file. Assumed to be unsigned 8-bit, 48 kHz file.")
+	parser.add_argument("-d", "--demod", type=str, help="Demodulator to test, either RS92 or RS41.")
+	args = parser.parse_args()
+
+	print("Reading: %s" % args.filename)
+	# Read in input file.
+	(data,header) = read_file(args.filename)
+	print("Samples: %d" % len(data))
+
+	for noise_lvl in NOISE_LEVELS:
+		temp_data = add_noise(data, noise_lvl)
+		write_file(TEMP_FILENAME, temp_data, header)
+
+		frame_count = run_demod(TEMP_FILENAME, args.demod)
+		print("%f dB: Frames Recovered: %d" % (noise_lvl,frame_count))
+
+
+
+
+