% QAM.m compares OFDM (multicarrier) to multi-level QAM (single carrier)
% when they transmit the same # of bits in a given time period

read		% read data for QAM - does not affect OFDM
data_in_pol = bin2pol(data_in);		% Converts binary data to polar data

% check to see if num_carriers is a power of 2
is_pow_2 = num_carriers;
temp_do_QAM = 0;
if is_pow_2 ~= 2
	while temp_do_QAM == 0
		temp_do_QAM = rem(is_pow_2,2);
		is_pow_2 = is_pow_2/2;
		if is_pow_2 == 2
			temp_do_QAM = -99;		% it is a power of 2 -> can do QAM
		end
	end
else
	temp_do_QAM = -99;	% 2 is a power of 2
end
if temp_do_QAM ~= -99
	do_QAM = 0;	% don't do it if it's not possible
	disp(' '),disp('ERROR: Cannot run QAM because num_carriers is not valid.')
	disp('       Please see "setup.m" for details.')
end


if do_QAM == 1
	tic	% Start stopwatch to calculate how long QAM simulation takes
	
	disp(' '), disp('------------------------------------------------------------')
	disp('QAM simulation'), disp('Transmitting')
	
	% Pad with zeros so data can be divided evenly
	data_length = length(data_in_pol);
	r = rem(data_length,num_carriers);
	if r ~= 0
		for i = 1:num_carriers-r
			data_in_pol(data_length+i) = 0;	%pad input with zeros to complete last data set
		end							%speed improve possible
	end
	data_length = length(data_in_pol);		%update after padding
	
	num_OFDM_symbols = ceil(data_length / (2*num_carriers));
	% num QAM symbols that represent equal amount of data to one OFDM symbol
	num_QAM_symbols = num_carriers / 2;
	% num samples per QAM symbol
	num_symbol_samples = fft_size / num_QAM_symbols;
	
	% convert polar data [-1, 1] to 4 level data [-3, -1, 1, 3]
	data_in_4 = zeros(1,data_length/2);
	for i = 1:2:data_length
		data_in_4(i - (i-1)/2) = data_in_pol(i)*2 + data_in_pol(i+1);
	end
	
	% define sample points between 0 and 2*pi
	ts = linspace(0, 2*pi*QAM_periods, num_symbol_samples+1);
	
	% Generate 16-QAM data
	% total length of 16-QAM transmission
	tx_length = num_OFDM_symbols * num_QAM_symbols * num_symbol_samples;
	QAM_tx_data = zeros(1,tx_length);
	for i = 1:2:data_length/2
		for k = 1:num_symbol_samples
			QAM_tx_data(k+((i-1)/2)*num_symbol_samples) = data_in_4(i)*cos(ts(k)) + data_in_4(i+1)*sin(ts(k));
		end
	end
	
	% Do channel simulation on QAM data
	xmit = QAM_tx_data;		% ch uses 'xmit' data and returns 'recv'
	ch
	QAM_rx_data = recv;		% save QAM data after channel
	clear recv				% remove 'recv' so it won't interfere with OFDM
	clear xmit				% remove 'xmit' so it won't interfere with OFDM
	
	disp('Receiving')			% Recover Binary data (Decode QAM)
	cos_temp = zeros(1,num_symbol_samples);		%
	sin_temp = cos_temp;					%
	xxx = zeros(1,data_length/4);				% Initialize to zeros for speed
	yyy = xxx;								%
	QAM_data_out_4 = zeros(1,data_length/2);		%
	
	for i = 1:2:data_length/2	% "cheating"
		for k = 1:num_symbol_samples
			% multiply by carriers to produce high frequency term and original data
			cos_temp(k) = QAM_rx_data(k+((i-1)/2)*num_symbol_samples) * cos(ts(k));
			sin_temp(k) = QAM_rx_data(k+((i-1)/2)*num_symbol_samples) * sin(ts(k));
		end
		% LPF and decide - we will do very simple LPF by averaging
		xxx(1+(i-1)/2) = mean(cos_temp);
		yyy(1+(i-1)/2) = mean(sin_temp);
		% Reconstruct data in serial form
		QAM_data_out_4(i) = xxx(1+(i-1)/2);
		QAM_data_out_4(i+1) = yyy(1+(i-1)/2);
	end
	
	% Make decision between [-3, -1, 1, 3]
	for i = 1:data_length/2
		if QAM_data_out_4(i) >= 1, QAM_data_out_4(i) = 3;
		elseif QAM_data_out_4(i) >= 0, QAM_data_out_4(i) = 1;
		elseif QAM_data_out_4(i) >= -1, QAM_data_out_4(i) = -1;
		else QAM_data_out_4(i) = -3;
		end
	end
	
	% Convert 4 level data [-3, -1, 1, 3] back to polar data [-1, 1]
	QAM_data_out_pol = zeros(1,data_length);	% "cheating"
	for i = 1:2:data_length
		switch QAM_data_out_4(1 + (i-1)/2)
			case -3
				QAM_data_out_pol(i) = -1;
				QAM_data_out_pol(i+1) = -1;
			case -1
				QAM_data_out_pol(i) = -1;
				QAM_data_out_pol(i+1) = 1;
			case 1
				QAM_data_out_pol(i) = 1;
				QAM_data_out_pol(i+1) = -1;
			case 3
				QAM_data_out_pol(i) = 1;
				QAM_data_out_pol(i+1) = 1;
			otherwise
				disp('Error detected in switch statment - This should not be happening.');
		end
	end
	QAM_data_out = pol2bin(QAM_data_out_pol);	% convert back to binary
	
	% Stop stopwatch to calculate how long QAM simulation takes
	QAM_simulation_time = toc;
	if QAM_simulation_time > 60
		disp(strcat('Time for QAM simulation=', num2str(QAM_simulation_time/60), ' minutes.'));
	else
		disp(strcat('Time for QAM simulation=', num2str(QAM_simulation_time), ' seconds.'));
	end
end