Add IQ parsing example.

parse-and-plot-iq.py

+#!/usr/bin/env python3
+"""Parse and plot baseband IQ samples captured via a patched version of srsLTE. """
+
+import argparse
+import struct
+
+import matplotlib.pyplot as plt
+import numpy as np
+
+
+parser = argparse.ArgumentParser()
+parser.add_argument('iqfile', help='IQ file to be parsed/plotted.')
+parser.add_argument('--fs', help='Sample rate.', type=float, default=7.68e6)
+args = parser.parse_args()
+
+IQ_FILE = args.iqfile
+FS = args.fs
+IQ_PER_REC = int(FS / 1000)
+STRUCT_REP = '8B 3d {}f'.format(IQ_PER_REC * 2)
+
+TS_INDEX      = 8
+TX_RATE_INDEX = 9
+TX_GAIN_INDEX = 10
+IQ_INDEX      = 11
+
+
+def parse_iq_recs(iq_recs):
+    num_iq_recs = len(iq_recs)
+    ts = np.zeros((num_iq_recs * IQ_PER_REC))
+    tx_rates = np.zeros((num_iq_recs * IQ_PER_REC))
+    tx_gains = np.zeros((num_iq_recs * IQ_PER_REC))
+    samples = np.zeros((num_iq_recs * IQ_PER_REC), dtype=np.complex)
+
+    for i, iq_rec in enumerate(iq_recs):
+        cur_ts = iq_rec[TS_INDEX]
+        rec_inds = np.arange(IQ_PER_REC * i, IQ_PER_REC * (i + 1))
+        ts[rec_inds] = 1.0 / FS * np.arange(IQ_PER_REC) + cur_ts
+
+        # These don't seem to change, but they may in other cricumstances
+        tx_rates[rec_inds] = iq_rec[TX_RATE_INDEX]
+        tx_gains[rec_inds] = iq_rec[TX_GAIN_INDEX]
+
+        # data is packed as IQIQIQ... where I and Q are float
+        samples[rec_inds] = \
+            np.array(iq_rec[IQ_INDEX::2]) + 1j * np.array(iq_rec[IQ_INDEX + 1::2])
+
+    return ts, tx_rates, tx_gains, samples
+
+
+with open(IQ_FILE, 'rb') as fd:
+    barray = fd.read()
+
+iq_struct = struct.Struct(STRUCT_REP)
+iq_recs = [iq_struct.unpack(barray[iq_struct.size * i:iq_struct.size * (i + 1)])
+           for i in range(len(barray) // iq_struct.size)]
+ts, tx_rates, tx_gains, samples = parse_iq_recs(iq_recs)
+ts_shifted = ts - ts[0]
+
+plt.figure()
+ax1 = plt.subplot(2, 1, 1)
+plt.title('In Phase')
+plt.plot(ts_shifted, samples.real)
+ax2 = plt.subplot(2, 1, 2, sharex=ax1, sharey=ax1)
+plt.plot(ts_shifted, samples.imag)
+# plt.plot(ts_shifted - 800e-6 - 1 / FS, samples.imag)
+plt.title('Quadrature')
+plt.xlabel('time (s)')
+plt.show()