ASCII Framing Script - Used by the Transmitter for Frame Generation

The code in this script performs the operations required to convert the ASCII message into individual frames with an appended frame number. The parameters set in the ASCII Transfer Binary Source block mask are retrieved and used to: limit the number of ASCII characters, append appropriate frame numbers to the ASCII message, insert the required number of padding bits to each frame and finally construct the full frame with preamble header.

Contents

Clear workspace structure

clear('src');                                                              % remove the 'src' (Source) structure if it already exists

Obtain Parameters Set in the Simulink Block Mask

src.msg_tx = get_param(gcbh,'msg_tx');                                     % obtain the ASCII message
src.ascii_len = str2num( get_param(gcbh,'ascii_len') );                    % obtain the length for each ASCII bit representation and convert char type to num
src.fs = str2num( get_param(gcbh,'fs') );                                  % obtain the sampling rate and convert char type to num

Initialise Variables

src.preamble = [1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,0,0,0,0,0,1,1,1,1,1,1,0,0,0,1,1,1,0,0,0,1,1,1]; % set the preamble in unipolar form — used at the beginning of each frame
src.preamble_len = length(src.preamble);                                   % find length of the preamble
src.preamble_pad_len = rem(src.preamble_len,2);                            % determine if preamble requires padding
src.preamble_pad = zeros(1,src.preamble_pad_len);                          % create padding to make preamble an even length (if required)

src.frame_pad_len = 2;                                                     % set the padding to be appended to the end of the frame
src.frame_pad = zeros(1,src.frame_pad_len);                                % initialise padding variable to length set by pad_len

Append Frame Number To ASCII Message

src.input_len = length(src.msg_tx);                                        % find length of ASCII message
if src.input_len > 50                                                      % if message length > 50
    src.msg_tx = src.msg_tx(1:50);                                         % limit the message length
end

src.count_lim = 100;                                                       % set max number for counter appended to frames
src.counter = (1:src.count_lim);                                           % create counter
src.ascii_msg = zeros(100,1);                                              % initialise variable for storing full ASCII message
clear('msg_output');
% generate frames of bits after appending counter number
for c = 1:1:src.count_lim
    src.full_msg = [src.msg_tx,' ',num2str(src.counter(c),'%03d')];        % append space character and counter number
    msg_output(c,:) = src.full_msg;                                        % store the generated frames for observation
    src.ascii_msg = de2bi(int8(src.full_msg),src.ascii_len,'left-msb');    % convert message string to matrix of ASCII bit representations

    src.len = size(src.ascii_msg);                                         % obtain both dimensions of ASCII matrix
    src.msg_len = src.len(:,1);                                            % obtain the number of ASCII characters
    src.data_len = src.len(:,1)*src.len(:,2);                              % multiply dimensions to get the vector length of the data

    src.temp_msg = reshape(double(src.ascii_msg).',src.data_len,1)';       % reshape ASCII matrix into a single vector
    src.master_msg(c,:) = src.temp_msg;                                    % fill storage variable with bit sequences for each frame
end
clear('c');

Construct the Full Frame — With Any Additional Padding

src.hasField = isfield(src , 'master_frame');                              % check if master_frame already exists
if src.hasField
    src = rmfield(src , 'master_frame');                                   % remove master_frame from structure if it does exist
end

% append the message bits to the preamble
for c = 1:1:src.count_lim
    src.temp_frame = [src.preamble,src.preamble_pad,src.master_msg(c,:),src.frame_pad]';   % construct each new frame with the preamble and insert padding
    src.master_frame(:,c) = src.temp_frame;                                % store the frames for transmission
end
src.master_frame_len = length(src.temp_frame);                             % determine length of master frame

run_time = (length(src.temp_frame)*(src.count_lim+1))/src.fs;              % create time variable for running model

% create time variable
src.hasField = isfield(src , 'master_time');                               % check if master_time exists
if src.hasField
    src = rmfield(src , 'master_time');                                    % remove master_time from structure if it does exist
end
src.master_time = (0:1/src.fs:(length(src.master_frame)-1)/src.fs)';       % create time variable for the master frame

Clear Workspace Variables

clear('src.i','src.ascii_msg','src.data_len','c');                         % clear particular variables from structure

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Published with MATLAB® R2014b