despread.m

此代码仿真了一个语音输入输出系统

% DESPREAD  De-pread's the received voice signal.
%   Because the Walsh Code is a piece of the whole system,
%   the Walsh and extended Walsh data will not be created
%   again (locally).  They will come from what was
%   already created and left in the workspace by SPREAD.  It
%   should be noted that real-world systems are usally
%   designed in a way such that all parties generate their
%   codes locally.

%   Completeed: July 24, 2005

%   Terrence Irving
%   2005 NSF REU in SDR
%   Stevens Institute of Technology
%   Hoboken, NJ USA



% This will use much of the same ideas and code from spread.m,
% as the Walsh Code system is considered to be a mutual component of
% the entire spread spectrum system.

% Globalize object handles that this component must access.
global file help new speakers_pb spkrs_image adc_pb bpsk_pb dac_pb
global debpsk_pb despread_pb speakers_pb spread_pb srrc_1_pb srrc_2_pb
global done_text_fontsize despread_done_dims dac_pb

% Globalize the appropriate data created by this component.
global voice_data_received 

% Change previous button's color (MATLAB 7 precaution).
set(dac_pb, 'backgroundcolor', 'white');
set(dac_pb, 'foregroundcolor', 'black');

% De-spread the receieved data (receiver, of course, knows the Walsh Code
% that was used for this transmission).
voice_data_extended_received = voice_data_spread_received.*walsh_extended;

% Allocate voice data array.
voice_data_received = ones(voice_data_extended_length/walsh_factor, 1);

disp('De-spreading signal');
% De-extend the extended received voice data by taking only every
% walsh_factorth piece of extended data to compose the voice data.
index = 1; % index into voice_data_received (manually incremented)
for i = [walsh_factor: walsh_factor: voice_data_extended_length] % take the 4th, 8th, etc, because data is repeated walsh_factor times in extended array
    voice_data_received(index, 1) = voice_data_extended_received(i, 1);
    index = index + 1; % increment index
end
disp('Original voice data recovered');

% One-second long input signal was sampled at 8 kHz, meaning 8000 samples
% were taken.
total_input_samples = 8000;

disp('Clipping signal amplitude');
% If values of the received signal are greater than 1, clip them.
for i = 1: total_input_samples
    if voice_data_received(i, 1) > 1
        voice_data_received(i, 1) = 1;
    end
end

% Run a separate loop to clip values less than -1.
for i = 1: total_input_samples
    if voice_data_received(i, 1) < -1
        voice_data_received(i, 1) = -1;
    end
end
disp('Signal amplitude clipped');
disp('Received signal de-spread');
disp(' '); % blank line
disp('3SA simulation complete');

% Change button color and update text when component is finished.
set(despread_pb, 'backgroundcolor', 'white');
set(despread_pb, 'foregroundcolor', 'black');
despread_done = uicontrol(sssa_base,...
    'style', 'text',...
    'fontsize', done_text_fontsize,...
    'foregroundcolor', 'white',...
    'backgroundcolor', [.5 0 0],... % matches background image color
    'horizontalalignment', 'center',...
    'string', 'DONE',...
    'position', despread_done_dims);

% Enable the main window menu items when component is finished running.
set(file, 'enable', 'on');
set(help, 'enable', 'on');

% Enable all pushbuttons except for the microphone when the simulation is 
% finished running (forces user to do "File: New") and change status text.
% Also change component pushbuttons' color to white (MATLAB 7 precaution).
set(file, 'enable', 'on');
set(new, 'enable', 'on');
set(help, 'enable', 'on');
set(speakers_pb, 'cdata', spkrs_image);
set(adc_pb, 'enable', 'on');
set(adc_pb, 'backgroundcolor', 'white');
set(adc_pb, 'foregroundcolor', 'black');
set(bpsk_pb, 'enable', 'on');
set(bpsk_pb, 'backgroundcolor', 'white');
set(bpsk_pb, 'foregroundcolor', 'black');
set(dac_pb, 'enable', 'on');
set(dac_pb, 'backgroundcolor', 'white');
set(dac_pb, 'foregroundcolor', 'black');
set(debpsk_pb, 'enable', 'on');
set(debpsk_pb, 'backgroundcolor', 'white');
set(debpsk_pb, 'foregroundcolor', 'black');
set(despread_pb, 'enable', 'on');
set(despread_pb, 'backgroundcolor', 'white');
set(despread_pb, 'foregroundcolor', 'black');
set(speakers_pb, 'enable', 'on');
set(spread_pb, 'enable', 'on');
set(spread_pb, 'backgroundcolor', 'white');
set(spread_pb, 'foregroundcolor', 'black');
set(srrc_1_pb, 'enable', 'on');
set(srrc_1_pb, 'backgroundcolor', 'white');
set(srrc_1_pb, 'foregroundcolor', 'black');
set(srrc_2_pb, 'enable', 'on');
set(srrc_2_pb, 'backgroundcolor', 'white');
set(srrc_2_pb, 'foregroundcolor', 'black');
set(status_txt, 'string', 'Simulation Complete');

% Free memory.
clear i index voice_data_extended_length voice_data_extended_received;

% Return control to spread.
return;