dji_droneid/matlab/updated_scripts/transmit/create_burst.m

function [samples] = create_burst(sample_rate, frame_configuration, add_turbo_path, temp_path, show_debug_plots)
    frame_bytes = create_frame_bytes(frame_configuration{:});
    
    %% Turbo encoding and rate matching
    if (~ isfile(add_turbo_path))
        error("Could not find Turbo encoder application at '%s'.  Check that the program has been compiled",...
            add_turbo_path);
    end
    
    % Where to store the files used to talk to the add_turbo binary
    frame_bin_file = fullfile(temp_path, 'frame.bin');              % Will write payload bytes here
    turbo_encoded_file = fullfile(temp_path, 'frame.bin.encoded');  % The add_turbo binary will create this
    
    % Write out the payload to Turbo encode and rate match
    file_handle = fopen(frame_bin_file, "w");
    assert(file_handle ~= -1, 'Could not open output temp file "%s"', frame_bin_file);

    try
        fwrite(file_handle, frame_bytes, 'uint8');
    catch
        error('Could not write to temp file "%s"', frame_bin_file);
    end

    fclose(file_handle);
    
    % Call the Turbo encoder
    [retcode, out] = system(sprintf("%s '%s' '%s'", add_turbo_path, frame_bin_file, turbo_encoded_file));
    if (retcode ~= 0)
        warning("Failed to run the Turbo encoder.  Details: %s", out);
    end
    
    % Remove the Turbo encoder input temp file
    delete(frame_bin_file);
    
    % Verify that it created the expected output file
    if (~ isfile(turbo_encoded_file))
        error("Turbo encoder did not produce an output file");
    end
    
    % Read in all bytes from the encoded output file
    file_handle = fopen(turbo_encoded_file, "r");
    assert(file_handle ~= -1, 'Could not open Turbo encoder output file "%s"', turbo_encoded_file);
    encoded_bits = uint8(fread(file_handle, inf, 'uint8'));
    fclose(file_handle);

    % Remove the Turbo encoder output temp file
    delete(turbo_encoded_file);
    
    % Make sure that there are exactly the right number of bytes in the file created by the Turbo encoder
    required_bytes = 7200;
    if (length(encoded_bits) ~= required_bytes)
        error("Expected %d bytes, but got %d", required_bytes, length(encoded_bits))
    end
    
    %% Scrambler Application
    
    % Convert to a matrix of 8 rows so that each symbol has it's own row
    encoded_bits = reshape(encoded_bits, [], 6).';
    
    % 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]);
    
    % Create scrambler for all data bits and reshape so that each OFDM symbol has a row
    scrambler = uint8(reshape(generate_scrambler_seq(7200, scrambler_x2_init), [], 6).');
    
    encoded_bits = [scrambler(1,:); encoded_bits];
    
    % Apply the scrambler to each OFDM symbol's data bits
    for idx=1:6
        encoded_bits(idx+1,:) = bitxor(encoded_bits(idx+1,:), scrambler(idx,:));
    end
    
    %% OFDM Symbol Creation Setup
    
    % Get some required params
    fft_size = get_fft_size(sample_rate);
    [long_cp_len, short_cp_len] = get_cyclic_prefix_lengths(sample_rate);
    
    % Define the size of each symbols cyclic prefix
    cyclic_prefix_schedule = [
        long_cp_len, ...
        short_cp_len, ...
        short_cp_len, ...
        short_cp_len, ...
        short_cp_len, ...
        short_cp_len, ...
        short_cp_len, ...
        short_cp_len, ...
        long_cp_len ...
    ];
    
    % Number of data carriers per OFDM symbol
    data_carrier_count = 600;
    
    %% Bits to Symbol Mapping
    
    % Create the QPSK samples for each OFDM symbol
    symbol_data = zeros(9, data_carrier_count);
    
    encoded_bits_ptr = 1;
    for symbol_idx=1:9
        % There's no work to be done for symbols 4 and 6 as they are ZC sequences
        if (symbol_idx == 4)
        elseif (symbol_idx == 6)
        else
            % Convert from bits to QPSK constellation
            symbol_data(symbol_idx,:) = to_qpsk(encoded_bits(encoded_bits_ptr,:));
            encoded_bits_ptr = encoded_bits_ptr + 1;
        end
    
        if (show_debug_plots)
            figure(1);
            subplot(3, 3, symbol_idx);
            plot(symbol_data(symbol_idx,:), 'o');
        end
    end
    
    %% Frequency Domain Symbol Creation
    % Create the frequency domain representation of each OFDM symbol
    freq_domain_symbols = zeros(9, fft_size);
    
    % Get the carriers that will contain the QPSK samples
    data_carrier_indices = get_data_carrier_indices(sample_rate);
    
    for symbol_idx=1:9
        % Copy the freq domain samples to the buffer
        freq_domain_symbols(symbol_idx,data_carrier_indices) = symbol_data(symbol_idx,:);
    
        if (show_debug_plots)
            figure(2);
            subplot(3, 3, symbol_idx);
            plot(abs(freq_domain_symbols(symbol_idx,:)).^2);
        
            figure(3);
            subplot(3, 3, symbol_idx);
            plot(freq_domain_symbols(symbol_idx,:), 'o');
        end
    end
    
    %% Time Domain Symbol Creation
    % Create the time domain representation of each OFDM symbol (no cyclic prefix at this point)
    time_domain_symbols = zeros(9, fft_size);
    
    for symbol_idx=1:9
        % Move to the time domain
        samples = ifft(fftshift(freq_domain_symbols(symbol_idx,:)));

        % Normalize the output of the FFT
        samples = samples / fft_size;
        
        time_domain_symbols(symbol_idx,:) = samples;

        if (show_debug_plots)
            figure(4);
            subplot(3, 3, symbol_idx);
            plot(10 * log10(abs(time_domain_symbols(symbol_idx,:)).^2))
        end
    end
    
    % Replace the contents of symbols 4 and 6 with the correct ZC sequence
    time_domain_symbols(4,:) = create_zc(fft_size, 4) / fft_size;
    time_domain_symbols(6,:) = create_zc(fft_size, 6) / fft_size;
    
    %% Add Cyclic Prefix

    samples = zeros(1, sum(cyclic_prefix_schedule) + (fft_size * length(cyclic_prefix_schedule)));
    samples_ptr = 1;
    for symbol_idx=1:9
        cp_len = cyclic_prefix_schedule(symbol_idx);
        symbol = time_domain_symbols(symbol_idx,:);
        cp = symbol(end-cp_len+1:end);
        symbol_with_prefix = [cp, symbol];
        samples(samples_ptr:samples_ptr + length(symbol_with_prefix) - 1) = symbol_with_prefix;
        samples_ptr = samples_ptr + length(symbol_with_prefix);
    end
    
    if (show_debug_plots)
        figure(7);
        plot(10 * log10(abs(time_domain).^2));
        
        filter_out = filter(conj(create_zc(fft_size, 4)), 1, samples);
        figure(8);
        plot(abs(filter_out).^2);
    end
end