function y = demodulation(x,b,e,h)

% function y = demodulation(x,b,e,h)
% find the smybol in the defined modulation scheme map which has the minimum distance to the received symbol, 
%   output the binary code corresponding to the index

% x is input symbols, in the form of row vector
% y is demodulated output, in the form of row vector
% b is the subcarrier bit allocation, b(i) is the number of bits allocated to ith subcarrier 
% e is the subcarrier energy allocation, same size as b
% h is the channel value in frequency for all subcarriers. X_estimate = X / H

% ------- demodulation.m -----------------------------------
% Black team
% April-11-05
% ----------------------------------------------------------

% load the modulation sheme
load bpsk.mat;
load qpsk.mat;
load 16qam.mat;
load 64qam.mat;
load 256qam.mat;

y=[];

for i = 1:length(b)
    switch b(i)
        case{1}
            [value index] = min( abs( p2 - x(i)/sqrt(e(i))/h(i) ) ); 
            y = [y d2(index,:)];      
        case{2}
           [value index] = min( abs( p4 - x(i)/sqrt(e(i))/h(i) ) ); 
           y = [y d4(index,:)];     
        case{4}
           [value index] = min( abs( p16 - x(i)/sqrt(e(i))/h(i) ) ); 
            y = [y d16(index,:)];     
        case{6}
            [value index] = min( abs( p64 - x(i)/sqrt(e(i))/h(i) ) ); 
            y = [y d64(index,:)];     
        case{8}
            [value index] = min( abs( p256 - x(i)/sqrt(e(i))/h(i) ) ); 
            y = [y d256(index,:)];     
        otherwise
            index = 0;
    end
end