OFDM_ofdm_用MATLAB生成OFDM信号_

clear all; close all; carrier_count=200;%子载波数 symbols_per_carrier=12;%每子载波含符号数 bits_per_symbol=4;%每符号含比特数,16QAM调制 IFFT_bin_length=512;%FFT点数 PrefixRatio=1/4;%保护间隔与OFDM数据的比例 1/6~1/4 GI=PrefixRatio*IFFT_bin_length ;%每一个OFDM符号添加的循环前缀长度为1/4*IFFT_bin_length 即保护间隔长度为128 beta=1/32;%窗函数滚降系数 GIP=beta*(IFFT_bin_length+GI);%循环后缀的长度20 SNR=15; %信噪比dB %================================================== %================信号产生=================================== baseband_out_length = carrier_count * symbols_per_carrier * bits_per_symbol;%所输入的比特数目 carriers = (1:carrier_count) + (floor(IFFT_bin_length/4) - floor(carrier_count/2));%共轭对称子载波映射 复数数据对应的IFFT点坐标 conjugate_carriers = IFFT_bin_length - carriers + 2;%共轭对称子载波映射 共轭复数对应的IFFT点坐标 baseband_out=round(rand(1,baseband_out_length));%输出待调制的二进制比特流 %==============16QAM调制==================================== complex_carrier_matrix=qam16(baseband_out);%列向量 complex_carrier_matrix=reshape(complex_carrier_matrix',carrier_count,symbols_per_carrier)';%symbols_per_carrier*carrier_count 矩阵 figure(1); plot(complex_carrier_matrix,'*r');%16QAM调制后星座图 title('16QAM调制后星座图') axis([-4, 4, -4, 4]); grid on %=================IFFT=========================== IFFT_modulation=zeros(symbols_per_carrier,IFFT_bin_length);%添0组成IFFT_bin_length IFFT 运算 IFFT_modulation(:,carriers ) = complex_carrier_matrix ;%未添加导频信号 ，子载波映射在此处 IFFT_modulation(:,conjugate_carriers ) = conj(complex_carrier_matrix);%共轭复数映射 %================================================================= signal_after_IFFT=ifft(IFFT_modulation,IFFT_bin_length,2);%OFDM调制 即IFFT变换 time_wave_matrix =signal_after_IFFT;%时域波形矩阵，行为每载波所含符号数，列ITTF点数，N个子载波映射在其内，每一行即为一个OFDM符号 %=========================================================== %=====================添加循环前缀与后缀==================================== XX=zeros(symbols_per_carrier,IFFT_bin_length+GI+GIP); for k=1:symbols_per_carrier; for i=1:IFFT_bin_length; XX(k,i+GI)=signal_after_IFFT(k,i); end for i=1:GI; XX(k,i)=signal_after_IFFT(k,i+IFFT_bin_length-GI);%添加循环前缀 end for j=1:GIP; XX(k,IFFT_bin_length+GI+j)=signal_after_IFFT(k,j);%添加循环后缀 end end time_wave_matrix_cp=XX;%添加了循环前缀与后缀的时域信号矩阵,此时一个OFDM符号长度为IFFT_bin_length+GI+GIP=660 %==============OFDM符号加窗========================================== windowed_time_wave_matrix_cp=zeros(1,IFFT_bin_length+GI+GIP); for i = 1:symbols_per_carrier windowed_time_wave_matrix_cp(i,:) = real(time_wave_matrix_cp(i,:)).*rcoswindow(beta,IFFT_bin_length+GI)';%加窗 升余弦窗 end %========================生成发送信号，并串变换================================================== windowed_Tx_data=zeros(1,symbols_per_carrier*(IFFT_bin_length+GI)+GIP); windowed_Tx_data(1:IFFT_bin_length+GI+GIP)=windowed_time_wave_matrix_cp(1,:); for i = 1:symbols_per_carrier-1 ; windowed_Tx_data((IFFT_bin_length+GI)*i+1:(IFFT_bin_length+GI)*(i+1)+GIP)=windowed_time_wave_matrix_cp(i+1,:);%并串转换，循环后缀与循环前缀相叠加 end %======================================================= Tx_data=reshape(windowed_time_wave_matrix_cp',(symbols_per_carrier)*(IFFT_bin_length+GI+GIP),1)';%加窗后 循环前缀与后缀不叠加 的串行信号 %================================================================= temp_time1 = (symbols_per_carrier)*(IFFT_bin_length+GI+GIP);%加窗后 循环前缀与后缀不叠加 发送总位数 figure (2) subplot(2,1,1); plot(0:temp_time1-1,Tx_data );%循环前缀与后缀不叠加 发送的信号波形 grid on ylabel('Amplitude (volts)') xlabel('Time (samples)') title('循环前后缀不叠加的OFDM Time Signal') temp_time2 =symbols_per_carrier*(IFFT_bin_length+GI)+GIP; subplot(2,1,2); plot(0:temp_time2-1,windowed_Tx_data);%循环后缀与循环前缀相叠加 发送信号波形 grid on ylabel('Amplitude (volts)') xlabel('Time (samples)') title('循环前后缀叠加的OFDM Time Signal') %===============加窗的发送信号频谱================================= symbols_per_average = ceil(symbols_per_carrier/5);%符号数的1/5，10行 avg_temp_time = (IFFT_bin_length+GI+GIP)*symbols_per_average;%点数，10行数据，10个符号 averages = floor(temp_time1/avg_temp_time); average_fft(1:avg_temp_time) = 0;%分成5段 for a = 0:(averages-1) subset_ofdm = Tx_data(((a*avg_temp_time)+1):((a+1)*avg_temp_time));%利用循环前缀后缀未叠加的串行加窗信号计算频谱 subset_ofdm_f = abs(fft(subset_ofdm));%分段求频谱 average_fft = average_fft + (subset_ofdm_f/averages);%总共的数据分为5段，分段进行FFT，平均相加 end average_fft_log = 20*log10(average_fft); figure (3) subplot(2,1,2) plot((0:(avg_temp_time-1))/avg_temp_time, average_fft_log)%归一化 0/avg_temp_time : (avg_temp_time-1)/avg_temp_time hold on plot(0:1/IFFT_bin_length:1, -35, 'rd') grid on axis([0 0.5 -40 max(average_fft_log)]) ylabel('Magnitude (dB)') xlabel('Normalized Frequency (0.5 = fs/2)') title('加窗的发送信号频谱') %====================添加噪声================================= Tx_signal_power = var(windowed_Tx_data);%发送信号功率 linear_SNR=10^(SNR/10);%线性信噪比 noise_sigma=Tx_signal_power/linear_SNR; noise_scale_factor = sqrt(noise_sigma);%标准差sigma noise=randn(1,((symbols_per_carrier)*(IFFT_bin_length+GI))+GIP)*noise_scale_factor;%产生正态分布噪声序列 Rx_data=windowed_Tx_data +noise;%接收到的信号加噪声 %=====================接收信号 串/并变换 去除前缀与后缀========================================== Rx_data_matrix=zeros(symbols_per_carrier,IFFT_bin_length+GI+GIP); for i=1:symbols_per_carrier; Rx_data_matrix(i,:)=Rx_data(1,(i-1)*(IFFT_bin_length+GI)+1:i*(IFFT_bin_length+GI)+GIP);%串并变换 end Rx_data_complex_matrix=Rx_data_matrix(:,GI+1:IFFT_bin_length+GI);%去除循环前缀与循环后缀，得到有用信号矩阵 %============================================================== % OFDM解码 16QAM解码 %=================FFT变换================================= Y1=fft(Rx_data_complex_matrix,IFFT_bin_length,2);%OFDM解码 即FFT变换 Rx_carriers=Y1(:,carriers);%除去IFFT/FFT变换添加的0，选出映射的子载波 Rx_phase =angle(Rx_carriers);%接收信号的相位 Rx_mag = abs(Rx_carriers);%接收信号的幅度 figure(4); polar(Rx_phase, Rx_mag,'bd');%极坐标坐标下画出接收信号的星座图 title('极坐标下的接收信号的星座图') %====================================================================== [M, N]=pol2cart(Rx_phase, Rx_mag); Rx_complex_carrier_matrix = complex(M, N); figure(5); plot(Rx_complex_carrier_matrix,'*r');%XY坐标接收信号的星座图 title('XY坐标接收信号的星座图') axis([-4, 4, -4, 4]); grid on %====================16qam解调======================================= Rx_serial_complex_symbols=reshape(Rx_complex_carrier_matrix',size(Rx_complex_carrier_matrix, 1)*size(Rx_complex_carrier_matrix,2),1)' ; Rx_decoded_binary_symbols=demoduqam16(Rx_serial_complex_symbols); %============================================================ baseband_in = Rx_decoded_binary_symbols; figure(6); subplot(2,1,1); stem(baseband_out(1:100)); title('输出待调制的二进制比特流') subplot(2,1,2); stem(baseband_in(1:100)); title('接收解调后的二进制比特流') %================误码率计算========================================== bit_errors=find(baseband_in ~=baseband_out); bit_error_count = size(bit_errors, 2) ber=bit_error_count/baseband_out_length