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#!/usr/bin/env python
#
# Correlate with the phase reference symbol
#
# Licence: see LICENCE file
import numpy as np
import matplotlib.pyplot as pp
import sys
if len(sys.argv) != 3:
print("Usage")
print(" script [fc64|u8] <filename>")
print(" fc64: file is 32-bit float I + 32-bit float Q")
print(" u8: file is 8-bit unsigned I + 8-bit unsigned Q")
sys.exit(1)
print("Reading file")
file_in = sys.argv[2]
if sys.argv[1] == "u8":
channel_out1 = np.fromfile(file_in, np.uint8)
print("Convert u8 IQ to fc64 IQ")
channel_out2 = channel_out1.reshape(2, int(len(channel_out1)/2))
channel_out3 = channel_out2[0,...] + 1j * channel_out2[1,...]
channel_out = channel_out3.astype(np.complex64) / 256.0 - (0.5+0.5j)
elif sys.argv[1] == "fc64":
channel_out = np.fromfile(file_in, np.complex64)
print(" File contains {} samples ({}ms)".format(
len(channel_out), len(channel_out) / 2048000.0))
# T = 1/2048000 s
# NULL symbol is 2656 T (about 1.3ms) long.
T_NULL = 2656
# Full transmission frame in TM1 is 96ms = 196608 T.
T_TF = 196608
print("Reading phase reference")
phase_ref = np.fromfile("phasereference.2048000.fc64.iq", np.complex64)
def calc_cir(channel, start_ix):
"""Calculate correlation with phase reference"""
channel_out
# As we do not want to correlate of the whole recording that might be
# containing several transmission frames, we first look for the null symbol in the
# first 96ms
print("Searching for NULL symbol")
# Calculate power on blocks of length 2656 over the first 96ms. To gain speed,
# we move the blocks by N samples.
N = 20
channel_out_power = np.array([np.abs(channel[start_ix+t:start_ix+t+T_NULL]).sum() for t in range(0, T_TF-T_NULL, N)])
# Look where the power is smallest, this gives the index where the NULL starts.
# Because if the subsampling, we need to multiply the index.
t_null = N * channel_out_power.argmin()
print(" NULL symbol starts at ix={}".format(t_null))
# The synchronisation channel occupies 5208 T and contains NULL symbol and
# phase reference symbol. The phase reference symbol is 5208 - 2656 = 2552 T
# long.
if len(phase_ref) != 2552:
print("Warning: phase ref len is {} != 2552".format(len(phase_ref)))
# We want to correlate our known phase reference symbol against the received
# signal, and give us some more margin about the exact position of the NULL
# symbol.
print("Correlating")
# We start a bit earlier than the end of the null symbol
corr_start_ix = t_null + T_NULL - 50
# In TM1, the longest spacing between carrier components one can allow is
# around 504 T (246us, or74km at speed of light). This gives us a limit
# on the number of correlations it makes sense to do.
max_component_delay = 500 # T
cir = np.array([np.abs(np.corrcoef(channel[start_ix + corr_start_ix + i:start_ix + corr_start_ix + phase_ref.size + i], phase_ref)[0,1]) for i in range(max_component_delay)])
return cir
num_correlations = int(len(channel_out) / T_TF)
print("Doing {} correlations".format(num_correlations))
cirs = np.array([
calc_cir(channel_out, i * T_TF)
for i in range(num_correlations) ])
print("Plotting")
pp.subplot(211)
pp.plot(cirs.sum(axis=0))
pp.subplot(212)
pp.imshow(cirs)
print("Done")
pp.show()
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