kopia lustrzana https://github.com/proto17/dji_droneid
Now looking at the second symbol for coarse freq offset
rodzic
6aafc41f8f
commit
48d08f5dff
|
@ -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)
|
||||
|
|
Ładowanie…
Reference in New Issue