function [a]=Q(rx_symbol,modulation)
%***********************************************************************
% This file carries out 'slicing' operation to the nearest constellation
%***********************************************************************

if ~isempty(findstr(modulation, 'BPSK'))
%BPSK
a = real(rx_symbol); 
elseif ~isempty(findstr(modulation, 'QPSK'))
% QPSK
soft_bits = zeros(2*size(rx_symbol,1),size(rx_symbol,2));

bit0 = real(rx_symbol); 
bit1 = imag(rx_symbol);

soft_bits(1:2:size(soft_bits, 1),:) = bit0;
soft_bits(2:2:size(soft_bits, 1),:) = bit1;

a=bit0+j*bit1;

elseif ~isempty(findstr(modulation, '16QAM'))
%16QAM
soft_bits = zeros(4*size(rx_symbol,1), size(rx_symbol,2));  % Each symbol consists of 4 bits

bit0 = real(rx_symbol);
bit2 = imag(rx_symbol);

bit1 = 2/sqrt(10)-(abs(real(rx_symbol)));
bit3 = 2/sqrt(10)-(abs(imag(rx_symbol)));

soft_bits(1:4:size(soft_bits,1),:) = bit0;
soft_bits(2:4:size(soft_bits,1),:) = bit1;
soft_bits(3:4:size(soft_bits,1),:) = bit2;
soft_bits(4:4:size(soft_bits,1),:) = bit3;


a=bit0+j*bit2;

elseif ~isempty(findstr(modulation, '64QAM'))
%64QAM
soft_bits = zeros(6*size(rx_symbol,1), size(rx_symbol,2));  % Each symbol consists of 6 bits
bit0 = real(rx_symbol);
bit3 = imag(rx_symbol);

bit1 = 4/sqrt(42)-abs(real(rx_symbol));
bit4 = 4/sqrt(42)-abs(imag(rx_symbol));


for m=1:size(rx_symbol,2)
   for k=1:size(rx_symbol,1)
      if abs(4/sqrt(42)-abs(real(rx_symbol(k,m)))) <= 2/sqrt(42)  % bit is one
         bit2(k,m) = 2/sqrt(42) - abs(4/sqrt(42)-abs(real(rx_symbol(k,m))));
      elseif abs(real(rx_symbol(k,m))) <= 2/sqrt(42) % bit is zero, close to real axis
         bit2(k,m) = -2/sqrt(42) + abs(real(rx_symbol(k,m)));
      else
         bit2(k,m) = 6/sqrt(42)-abs(real(rx_symbol(k,m))); % bit is zero 
      end;
      
      if abs(4/sqrt(42)-abs(imag(rx_symbol(k,m)))) <= 2/sqrt(42)  % bit is one
         bit5(k,m) = 2/sqrt(42) - abs(4/sqrt(42)-abs(imag(rx_symbol(k,m))));
      elseif abs(imag(rx_symbol(k,m))) <= 2/sqrt(42) % bit is zero, close to real axis
         bit5(k,m) = -2/sqrt(42) + abs(imag(rx_symbol(k,m)));
      else
         bit5(k,m) = 6/sqrt(42)-abs(imag(rx_symbol(k,m)));
      end;
   end;
end;

soft_bits(1:6:size(soft_bits,1),:) = bit0;
soft_bits(2:6:size(soft_bits,1),:) = bit1;
soft_bits(3:6:size(soft_bits,1),:) = bit2;
soft_bits(4:6:size(soft_bits,1),:) = bit3;
soft_bits(5:6:size(soft_bits,1),:) = bit4;
soft_bits(6:6:size(soft_bits,1),:) = bit5;


a=bit0+j*bit3;

end