OFDM仿真程序

clc
clear allIFFT_bin_length=128; %IFFT点数128个
carrier_count=50;  %子信道（子载波）数目
bits_per_symbol=2; %4进制符号
symbols_per_carrier=200;%每个子信道或者说子载波有200个符号
SNR=0:1:40;
for num=1:41baseband_out_length=carrier_count*symbols_per_carrier*bits_per_symbol; %总bit数
%下面是载波位置，为了满足得到的是实数信号，载波的位置要满足共轭对称
carriers=(1:carrier_count)+(floor(IFFT_bin_length/4)-floor(carrier_count/2)); %floor函数是朝负无穷大四舍五入
conjugate_carriers=IFFT_bin_length-carriers+2;%baseband_out=round(rand(1,baseband_out_length));%20000个0-1信源符号,round函数为四舍五入为最近的小数
baseband_out=randi(2,1,baseband_out_length)-1;   %返回一个介于1和2之间的1*20000的数组
%将一行20000的数据交叉转换为2行10000的数据
convert_matrix=reshape(baseband_out,bits_per_symbol,length(baseband_out)/bits_per_symbol);
%不如写个函数将值映射成0-3，如00-0，01-1，10-2，11-3
for k=1:(length(baseband_out)/bits_per_symbol)modulo_baseband(k)=0;for i=1:bits_per_symbolmodulo_baseband(k)=modulo_baseband(k)+convert_matrix(i,k)*2^(bits_per_symbol-i);end
end%串并转换
%将本次的模4的串行数据流转换为并行数据流，其中，每行整体是一个OFDM符号，每一个OFDM符号由所有载波在该采样点叠加产生，每列代表一个子载波
carrier_matrix=reshape(modulo_baseband,symbols_per_carrier,carrier_count);%采用了差分相移键控调制
carrier_matrix=[zeros(1,carrier_count);carrier_matrix];%补了一行全0，作为编码的参考起点
for i=2:(symbols_per_carrier+1)carrier_matrix(i,:)=rem(carrier_matrix(i,:)+carrier_matrix(i-1,:),2^bits_per_symbol); %rem函数是除后的余数
end%将差分编码转换为相位变化
carrier_matrix=carrier_matrix*((2*pi)/(2^bits_per_symbol));%将相位转换为一个复数
%这句代码保证幅值都是1
[X,Y]=pol2cart(carrier_matrix,ones(size(carrier_matrix,1),size(carrier_matrix,2)));
%构造映射，将相位的值转换为极坐标上的一个复数点0-1，pi/2-j.pi--1,3pi/2--j
complex_carrier_matrix=complex(X,Y);%将每个子载波分配到之前定义好的IFFT输入端，根据IFFT的对称性，这样可以得到实值序列
IFFT_modulation=zeros(symbols_per_carrier+1,IFFT_bin_length);
IFFT_modulation(:,carriers)=complex_carrier_matrix;
IFFT_modulation(:,conjugate_carriers)=conj(complex_carrier_matrix);%画出未经过IFFT的离散幅度谱,总共有50+50个输入端有数据，所以频谱图显示为两个矩形形状
% figure(1)
% stem(0:IFFT_bin_length-1,abs(IFFT_modulation(2,1:IFFT_bin_length)),'b*-')
% grid on;axis([0,IFFT_bin_length -0.5 1.5]);xlabel('IFFT BIN');ylabel('Magnitude');
% title('OFDM Carrier Frequency Magnitude');
%画出未经过IFFT的离散相位谱
% figure(2)
%所有128个点的相位图
% plot(0:IFFT_bin_length-1,(180/pi)*angle(IFFT_modulation(2,1:IFFT_bin_length)),'go');
% hold on;
%带数据的100个点的相位图
% stem(carriers-1,(180/pi)*angle(IFFT_modulation(2,carriers)),'b*-');
% stem(conjugate_carriers-1,(180/pi)*angle(IFFT_modulation(2,conjugate_carriers)),'b*-');
% axis([0 IFFT_bin_length -200 200]);grid on;ylabel('Phase');xlabel('IFFT Bin');
% title('OFDM Carrier Phase');%IFFT变换
time_wave_matrix=ifft(IFFT_modulation,[],2);%对列进行离散傅里叶反变换
%time_wave_matrix=time_wave_matrix;%作图
figure(3)
plot(0:IFFT_bin_length-1,time_wave_matrix(2,:));
grid on;
ylabel('幅度');xlabel('时间');
title('一个OFDM符号时域信号波形图');%colors=['r' 'g' 'b' 'k']
%for f=1:4%temp_bins(1:IFFT_bin_length)=0+0j;%temp_bins(carriers(f))=IFFT_modulation(2,carriers(f));%temp_bins(conjugate_carriers(f))=IFFT_modulation(2,conjugate_carriers(f));%temp_time=ifft(temp_bins');%figure(4)%plot(0:IFFT_bin_length-1,temp_time,colors(f));%hold on;
%end
%grid on;ylabel('幅度');xlabel('时间');title('分离出的时域波形');% 添加一个窗函数，就是滤波器，减弱信号的不连续点
% 每一个时间波形表示所有载波的一个符号周期
% 因为时域矩阵中所有虚部都等于0，所以利用Hamming窗时，只保留实部用于加窗
for i=1:symbols_per_carrier+1windowed_time_wave_matrix(i,:)=real(time_wave_matrix(i,:)).*hamming(IFFT_bin_length)';
%     windowed_time_wave_matrix(i,:)=real(time_wave_matrix(i,:));
end%将调制波形序列化(并串转换）
ofdm_modulation=reshape(time_wave_matrix,1,IFFT_bin_length*(symbols_per_carrier+1));%作图
% temp_time=IFFT_bin_length*(symbols_per_carrier+1);
% figure(5)
% plot(0:temp_time-1,ofdm_modulation);
% grid on;
% ylabel('幅度');xlabel('时间（采样）');title('OFDM时间信号');%频谱图
% symbols_per_average=ceil(symbols_per_carrier/5);
% avg_temp_time=IFFT_bin_length*symbols_per_average;
% averages=floor(temp_time/avg_temp_time);
% average_fft(1:avg_temp_time)=0;
% for a=0:(averages-1)
%     subset_ofdm=ofdm_modulation(((a*avg_temp_time)+1:((a+1)*avg_temp_time)));
%     subset_ofdm_f=abs(fft(subset_ofdm));
%     average_fft=average_fft+(subset_ofdm_f/averages);
% end
% average_fft_log=20*log10(average_fft);
% figure(6)
% plot((0:(avg_temp_time-1))/avg_temp_time,average_fft_log);
% hold on;
% plot(0:1/IFFT_bin_length:1,-35,'rd');grid on;
% axis([0 0.5 -40 max(average_fft_log)]);ylabel('幅度(dB)');xlabel('标准化频率(0.5=fs/2)');
% title('OFDM 信号频谱');
Tx_data=ofdm_modulation;%上变频，不一定用得到%经过信道
Rx_data=awgn(Tx_data,SNR(num));
% Rx_data=Tx_data;%%%%%%%%%%%%%%%%%%接收端%%%%%%%%%%%%%%%%%%%%%%%%%串并转换
Rx_data_matrix=reshape(Rx_data,symbols_per_carrier+1,IFFT_bin_length);%FFT变换
Rx_spectrum=fft(Rx_data_matrix,[],2);%经过FFT的频域相应图
figure(7)
stem(0:IFFT_bin_length-1,abs(Rx_spectrum(1:IFFT_bin_length,2)),'b*-');
grid on;axis([0 IFFT_bin_length -0.5 1.5]);ylabel('幅度');xlabel('FFT Bin');
title('OFDM 接收频谱，幅度');
% figure(8)
% plot(0:IFFT_bin_length-1,(180/pi)*angle(Rx_spectrum(1:IFFT_bin_length)),'go');
% hold on;
% stem(carriers-1,(180/pi)*angle(Rx_spectrum(carriers,2)),'b*-');
% stem(conjugate_carriers-1,(180/pi)*angle(Rx_spectrum(conjugate_carriers,2)),'b*-');
% axis([0 IFFT_bin_length -200 200]);
% grid on;ylabel('相位谱');xlabel('FFT Bin');
% title('OFDM 接受信号相位谱');%将128中真正含有数据的50个载波提取出来
Rx_carriers=Rx_spectrum(:,carriers);%画出每一个接收符号
% figure(9)
% Rx_phase_P=angle(Rx_carriers);
% Rx_mag_P=abs(Rx_carriers);
% polar(Rx_phase_P,Rx_mag_P,'rd');%对每个FFT点，解映射出对应的相位值
Rx_phase=angle(Rx_carriers)*(180/pi);
phase_negative=find(Rx_phase<0);
Rx_phase(phase_negative)=rem(Rx_phase(phase_negative)+360,360);%将负的相位对应为0-2pi内的值%从差分相移编码中，提取相位差值，这里利用diff()函数
Rx_decoded_phase=diff(Rx_phase);
phase_negative=find(Rx_decoded_phase<0);
Rx_decoded_phase(phase_negative)=rem(Rx_decoded_phase(phase_negative)+360,360);%解映射，将不同的相位转换为0-3的信源符号，0的相位范围为-45，45，1的相位范围为45-135，依此类推
base_phase=360/2^bits_per_symbol;
delta_phase=base_phase/2;
Rx_decoded_symbols=zeros(size(Rx_decoded_phase,1),size(Rx_decoded_phase,2));for i=1:(2^bits_per_symbol-1)center_phase=base_phase*i;plus_delta=center_phase+delta_phase;minus_delta=center_phase-delta_phase;decoded=find((Rx_decoded_phase<=plus_delta)&(Rx_decoded_phase>minus_delta));Rx_decoded_symbols(decoded)=i;
end
%Rx_decoded_symbols=Rx_decoded_symbols';
%并串转换
Rx_serial_symbols=reshape(Rx_decoded_symbols,1,size(Rx_decoded_symbols,1)*size(Rx_decoded_symbols,2));%将4进制的符号解码为二进制符号
for i=bits_per_symbol:-1:1if i~=1Rx_binary_matrix(i,:)=rem(Rx_serial_symbols,2);Rx_serial_symbols=floor(Rx_serial_symbols/2);elseRx_binary_matrix(i,:)=Rx_serial_symbols;end
end
baseband_in=reshape(Rx_binary_matrix,1,size(Rx_binary_matrix,1)*size(Rx_binary_matrix,2));%求误码率
bit_errors=find(baseband_in~=baseband_out);
bit_error_count(num)=size(bit_errors,2);
BER(num)=bit_error_count(num)/baseband_out_length;
end
figure(10)
semilogy(SNR,BER,'-ob','MarkerFaceColor','b','MarkerSize',5,'LineWidth',2);hold on;grid on;
title('DPSK-OFDM信噪比与误码率曲线');xlabel('SNR(dB)');ylabel('BER');
plot([0 35],[3.8e-3,3.8e-3],'r','LineWidth',1);hold on;
legend('DPSK-OFDM','FEC(3.8x10^-^3)');