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% OFDM 2 transmitter/receiver transmission % Name: Benjamin Pham % Student ID: 25957066 % % Task: to simulate a transmission of data using OFDM technique % blocks to so simulate, modulation block, IFFT, P/S, % FFT, demodulate, recover signal. then add (2) Noise,(3) Multipath Channel clc;clear all;close all; warning off %% Set Parameters % amount of data to be transmitted % 64kb is 2^16 % ^20 is a megabit n = 16; bits = 2^n; p = log2(bits); % Modulation type (4QAM or 16QAM) 4QAM = 1; 16QAM = 2; mod_type = '4QAM'; mod_types = {'4QAM','16QAM'}; mod_value = find (ismember (mod_types, mod_type)); % Eb/No assume 4G network, SNR = Eb/No * Rb/B % rb is bit rate = 100Mbps , B = 20MHz % Rb = 100*10^6; % B = 20*10^6; % fft/ifft size n_fft = 64; %pilot length n_p = 4; % cyclic prefix size n_cp = 16; % snr snr = [0:1:35]; % attenuation for a = 1:1 % change 64 to 1, to produce just a single complex number, equalising works attenuation(a) = rand() + i*rand(); end % eb_no = snr.*(B/Rb); for mod_value = [1:2] % bits per symbol if mod_value == 1 symbols = 2; else symbols = 4; end %% TRANSMITTER %% Generate data to be sent % 64kb of data t_data = round(rand(bits,1)); % generate data t_data = dec2bin(t_data); % changes vector to char type %% symbol mapping % 4QAM, 16QAM reshape_data = reshape(t_data,length(t_data)/symbols, symbols ); % reshape into pairings of 2 bits per symbol decimal_data = bin2dec(reshape_data); % must be a char vector if mod_value == 1 mod_data = qammod(decimal_data,4,'unitaveragepower',true); else mod_data = qammod(decimal_data,16,'unitaveragepower',true); end %figure() %scatterplot(mod_data) %% reshaping X = mod_data; X_blocks = reshape(X,n_fft,length(X)/n_fft); % reshape into 64 block subcarriers %% insert pilot symbols % pilot symbol is inserted on each subcarrier (block type) pilots = ones(1,1); if mod_value == 1 mod_pilots = qammod(pilots,4,'unitaveragepower',true); else mod_pilots = qammod(pilots,16,'unitaveragepower',true); end [c,d] = size(X_blocks); X_block = zeros(c,d+1); for i2 = 1:n_fft X_block(i2,:) = [mod_pilots, X_blocks(i2,:)]; end % mod_pilots(1,2) X_block(i2,(length(X_block)/4+1):length(X_block)/2) ... % mod_pilots(1,3) X_block(i2,(length(X_block)/2+1):3*(length(X_block)/4)) mod_pilots(1,4) X_block(i2,(3*(length(X_block)/4)+1):end)]; %% IFFT % Moves the data from the time domain to the frequency domain x = ifft(X_block); % Inverse fast fourier transform %% add CP x_cp = [x(:,(end - n_cp + 1) :end),x]; % add CP to end of data %% Parallel data to Serial stream x_s = x_cp(:); %% CHANNEL %% Multipath Channel % delays and attentuation that affects the signal channel = attenuation; H_x = conv(x_s,channel,'same'); %H_x = x_s; %% AWGN Noise for i = 1:length(snr) H_noise = awgn(H_x,snr(i),'measured'); %% RECEIVER %% Serial to Parallel y_p = reshape(H_noise, n_fft, length(H_noise + n_cp - 1)/n_fft); % remove cp x_p_cp = y_p(:,(n_cp + 1):end); %% FFT % converts signal from time domain to frequency domain Y_blocks = fft(x_p_cp); Y = reshape(Y_blocks, (length(X)+n_fft*length(pilots)),1); %% Channel Estimation % because we send pilot symbols, we can estimate the channel. symbols that % are known beforehand. So its the received signal divided by the pilot % symbol. Y_hat = zeros(c,d+1); for i2 = 1:n_fft H_hat(i2) = Y_blocks(i2,1)./X_block(i2,1); % estimating channel using pilot symbols Y_hat(i2,:) = H_hat(i2) .* X_block(i2,:); end % % mean squared error % for m = 1:length(H_hat) % se(m) = (abs(Y(m) - Y_hat(m)))^2; % mse(m) = sum(se)/length(se); % end % mmse(mod_value,i) = min(mse); %% equalisation H_hat_e = mean(H_hat); Y_blocks2 = Y_blocks/H_hat_e; % cancelling out the channel effects with the estimated channel % remove pilot Y_blocks = Y_blocks(:,2:end); Y_blocks2 = Y_blocks2(:,2:end); %% Demodulate if mod_value == 1 y = qamdemod(Y_blocks,4,'unitaveragepower',true); else y = qamdemod(Y_blocks,16,'unitaveragepower',true); end received_sym = dec2bin(y); received_sig = reshape(received_sym, length(t_data), 1); errors(mod_value,i) = 0; for k = [1:length(received_sig)] if received_sig(k) ~= t_data(k) errors(mod_value,i) = errors(mod_value,i) + 1; end end ber(mod_value,i) = errors(mod_value,i)/length(t_data); %% Demodulate equalistation part if mod_value == 1 y2 = qamdemod(Y_blocks2,4,'unitaveragepower',true); else y2 = qamdemod(Y_blocks2,16,'unitaveragepower',true); end received_sym2 = dec2bin(y2); received_sig2 = reshape(received_sym2, length(t_data), 1); errors2(mod_value,i) = 0; for m = [1:length(received_sig2)] if received_sig2(m) ~= t_data(m) errors2(mod_value,i) = errors2(mod_value,i) + 1; end end ber2(mod_value,i) = errors2(mod_value,i)/length(t_data); end % graph ber of recovered signals %figure() semilogy(snr,ber(mod_value,:),'x-',snr,ber2(mod_value,:),'o-'); title('BER vs SNR'); legend('4QAM','4QAMeq','16QAM','16QAMeq'); xlabel('SNR'); ylabel('BER'); grid on; hold on end