16-QAM , how to modify this code for 16-QAM, I have BPSK and QPSK Modulation,

%16-QAM , how to modify this code for 16-QAM, I have BPSK and QPSK Modulation, % Please Help me in this issue what to write in the place of Question Marks. % email: [e-mail]

function [bit_sequence] = symbol2bit(symbol_sequence); % Calculates bit_sequence from the symbol_sequence depending % on the modulation type

global signal;

switch signal.modulation_type

 case 'BPSK'
  bit_sequence = symbol_sequence;

 case 'QPSK'
   bit_sequence = [real(symbol_sequence), imag(symbol_sequence)];

 case '16-QAM'

??????????????????????

function [symbol_sequence] = bit2symbol(bit_sequence) % Calculates symbol_sequence from the bit_sequence depending on % the modulation type

global signal;

switch signal.modulation_type

 case 'BPSK'
  symbol_sequence = bit_sequence;  

 case 'QPSK'
  symbol_sequence = bit_sequence(1:signal.nr_of_symbols) + j*...
   bit_sequence(signal.nr_of_symbols + 1 : signal.nr_of_bits);

    case '16-QAM'

????????????????????????????

function y = ber2snr(x); % Calculates the SNR of the channel % % The SNR of the channel can be estimated/calculated when the % BER of the channel is known.

global signal;

switch signal.modulation_type

 case 'QPSK'
  y = qinv(x) .^ 2;

 case 'BPSK'
  y = qinv(x) .^ 2 / 2;

 case '16-QAM'

???????????????????

 otherwise
  error(['Modulation-type unknown: ', signal.modulation_type])
end

function [y] = ber(snr, modulation_type, fading_type); % Calculates the BER(SNR) depending on the modulation-type and % the fading-type

switch fading_type

 case 'Rayleigh'
  switch modulation_type

      case 'BPSK'
    y = (1 - sqrt(snr ./ (1  + snr))) / 2; 
      case 'QPSK'
    y = (1 - sqrt(snr ./ (1 / 2 + snr))) / 2;

     case '16-QAM'
    ???????????????????????

   otherwise
    error(['Modulation-type unknown: ', modulation_type])
  end

 case 'no'
  switch modulation_type

   case 'BPSK'
    y = q(sqrt(2 * snr));

   case 'QPSK'
    y = q(sqrt(snr));

    case '16-QAM'
    ????????????????

   otherwise
    error(['Modulation-type unknown: ', modulation_type])
  end

 otherwise
  error(['Fading-type unknown: ', fading_type])
end

function y = snr2ber(x) % Calculates the BER of the channel

global signal;

switch signal.modulation_type

 case 'QPSK'
  y = q(sqrt(x));  

 case 'BPSK'
  y = q(sqrt(2 * x)); 

case '16-QAM'
??????????????????

 otherwise
  error(['Modulation-type unknown: ', signal.modulation_type])
end