diff options
| -rwxr-xr-x | correlate_with_ref.py | 78 |
1 files changed, 44 insertions, 34 deletions
diff --git a/correlate_with_ref.py b/correlate_with_ref.py index de68c9d..193fa8c 100755 --- a/correlate_with_ref.py +++ b/correlate_with_ref.py @@ -40,58 +40,68 @@ T_TF = 196608 print("Reading phase reference") phase_ref = np.fromfile("phasereference.2048000.fc64.iq", np.complex64) -# 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 +def calc_cir(channel, start_ix): + """Calculate correlation with phase reference""" -print("Searching for NULL symbol") + channel_out -# Calculate power on blocks of length 2656 over the first 96ms. To gain speed, -# we move the blocks by 10 samples. -channel_out_power = np.array([np.abs(channel_out[t:t+T_NULL]).sum() for t in range(0, T_TF-T_NULL, 10)]) + # 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") -# Look where the power is smallest, this gives the index where the NULL starts. -# Because if the subsampling, we need to multiply the index. + # 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)]) -t_null = 10 * channel_out_power.argmin() + # 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)) + 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. + # 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))) -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 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 -# 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 -# 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. + 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 -max_component_delay = 1000 # T +num_correlations = int(len(channel_out) / T_TF) +print("Doing {} correlations".format(num_correlations)) -cir = np.array([np.abs(np.corrcoef(channel_out[corr_start_ix + i:corr_start_ix + phase_ref.size + i], phase_ref)[0,1]) for i in range(max_component_delay)]) +cirs = np.array([ + calc_cir(channel_out, i * T_TF) + for i in range(num_correlations) ]) -print("Done") +print("Plotting") -fig = pp.figure() -ax = fig.add_subplot(111) -hi = ax.plot(channel_out_power) +pp.subplot(211) +pp.plot(cirs.sum(axis=0)) +pp.subplot(212) +pp.imshow(cirs) -fig = pp.figure() -ax = fig.add_subplot(111) -hi = ax.plot(cir) +print("Done") pp.show() + |