mirror
/
dji_droneid
kopia lustrzana https://github.com/proto17/dji_droneid
1
0
Forkuj 0
Kod Zgłoszenia Projekty Wydania Wiki Aktywność

Now looking at the second symbol for coarse freq offset

gr-droneid-3.8
David Protzman 2022-04-19 18:12:57 -04:00
rodzic 6aafc41f8f
commit 48d08f5dff
1 zmienionych plików z 10 dodań i 3 usunięć
Pokaż statystyki Ściągnij plik aktualizacji Ściągnij plik porównania Expand all files Collapse all files

13
matlab/updated_scripts/process_file.m
Wyświetl plik

@ -53,6 +53,13 @@ data_carrier_indices = get_data_carrier_indices(file_sample_rate);
% Initial value for the second LFSR in the scrambler
scrambler_x2_init = fliplr([0 0 1, 0 0 1 0, 0 0 1 1, 0 1 0 0, 0 1 0 1, 0 1 1 0, 0 1 1 1, 1 0 0 0]);
% This determines which OFDM symbol's cyclic prefix is used to determine the coarse frequency offset. Some drones use 9
% OFDM symbols, and some use 8. It seems that those drones that use 8 OFDM symbols have a short cyclic prefix in the
% first symbol. Skipping the first symbol for those drones that have 9 OFDM symbols results in the new "first" symbol
% having a short cyclic prefix as well. So, since the burst extractor always assumes that there are 9 symbols, the
% first symbol is skipped for the purposes of coarse CFO
coarse_cfo_symbol_sample_offset = fft_size + long_cp_len + 1;
%% Burst Processing
for burst_idx=1:size(bursts, 1)
% Get the next burst
@ -66,10 +73,10 @@ for burst_idx=1:size(bursts, 1)
offset = filter_tap_count * 1.5;
burst = burst(offset-1:end);
%% Coarse frequency offset adjustment using the first OFDM symbol
%% Coarse frequency offset adjustment using one of the OFDM symbols (see coarse_cfo_symbol_sample_offset definition)
% Get the cyclic prefix, and then the copy of the cyclic prefix that exists at the end of the OFDM symbol
cp = burst(1:long_cp_len);
copy = burst(fft_size + 1:fft_size + 1 + long_cp_len - 1);
cp = burst(coarse_cfo_symbol_sample_offset:coarse_cfo_symbol_sample_offset + long_cp_len - 1);
copy = burst(coarse_cfo_symbol_sample_offset + fft_size + 1:coarse_cfo_symbol_sample_offset + fft_size + 1 + long_cp_len - 1);
% Calculate the frequency offset by taking the dot product of the two copies of the cyclic prefix and dividing out
% the number of samples in between each cyclic prefix sample (the FFT size)