FSKDecoder

function [x, amntSigns] = FSKdecoder(signal, fstart, fend, Tsymbol, fs)

% FSK Decoder made by group 8

% fstart    % transmission band frequency start
% fend      % transmission band frequency end
% Tsymbol   % symbol duration in seconds
% fs        % sampling frequency


amntSigns = length(signal) / (Tsymbol*fs);                      % Finding symbol amount
farray = round(linspace(fstart, fend, 256));                    % 256 frequencies spread out in band

freq = 1:amntSigns;                                             % Preallocating space

for i = 1:amntSigns                                             % Find frequencies for each symbol in the signal
    decodeSignal = signal((i-1)*Tsymbol*fs+1:i*Tsymbol*fs);     % Dividing the signal - isolating each symbol
    [~,maximum] = max(abs(fft(decodeSignal)));                  % Find the maximum of fft to find the frequency
    freq(i) = maximum / Tsymbol;                                % Converting to actual frequency
end

xDec = 1:amntSigns;                                             % Preallocating space

for i = 1:amntSigns                                             % Find decimal value for ASCII character
    done = 0;                                                   % Register to check if frequency was found
    for n = 1:256                                               % Checking all frequencies in farray and compare to calculated freq
        if (farray(n) >= freq(i)) && (done == 0)                % Finding the interval of frequencies & check if it's done already
            xDec(i) = n-1;                                      % Assigning the decimal value (-1 because it's bigger than to find interval)
            done = 1;                                           % Setting done - so we don't overwrite decimal value
        end
    end
end

x = char(xDec);                                                 % Output signal - converted to char