基于matlab实现OFDM的编码

figure(2);
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
%==========分配载波到指定的IFFT位置==========================
clc;
clear all;
close all;
fprintf('OFDM系统仿真\n');
carrier_count=input('输入系统仿真的子载波数: \n');%子载波数128,64,32,16
symbols_per_carrier=30;%每子载波含符号数
bits_per_symbol=4;%每符号含比特数,16QAM调制
end
figure(7);
plot(0:IFFT_bin_length-1+GI+GIP,windowed_time_wave_matrix_cp(2,:));
axis([0, 700, -0.2, 0.2]);
grid on;
ylabel('振幅');
xlabel('时间');
title('加窗之后OFDM信号的波形');
%==============16QAM调制====================================
complex_carrier_matrix=qam16(baseband_out);%列向量
complex_carrier_matrix=reshape(complex_carrier_matrix',carrier_count,symbols_per_carrier)';%串并转换，转换为symbols_per_carrier*carrier_count矩阵
IFFT_bin_length=1024;%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256
beta=1/32;%窗函数滚降系数
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
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,:);%循环后缀与循环前缀相叠加
title('OFDM载波相位谱')
%========通过IFFT将频域转化为时域，得到时域信号===============
signal_after_IFFT=ifft(IFFT_modulation,IFFT_bin_length,2);%OFDM调制即IFFT 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，子载波映射在其内，每一行即为一个OFDM符号
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
grid on
ylabel('振幅'); xlabel('时间');
title('循环前后缀叠加的OFDM信号')
%=================未加窗发送信号频谱=========================
symbols_per_average = ceil(symbols_per_carrier/5);
%==============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
GIP=beta*(IFFT_bin_length+GI);%循环后缀的长度40
SNR=10; %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
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
axis([0, 8000, -0.4, 0.4]);
end
average_fft_log = 20*log10(average_fft);
figure (9)
subplot(2,1,1);
plot((0:(avg_temp_time-1))/avg_temp_time, average_fft_log)
hold on
plot(0:1/IFFT_bin_length:1, -35, 'rd')
subset_ofdm= Tx_data_withoutwindow (((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);
avg_temp_time = (IFFT_bin_length+GI+GIP)*symbols_per_average;
averages = floor(temp_time1/avg_temp_time);
average_fft(1:avg_temp_time) = 0;
for a = 0:(averages-1)
figure(6);
plot(0:length(time_wave_matrix_cp)-1,time_wave_matrix_cp(2,:));
axis([0, 700, -0.2, 0.2]);
grid on;
ylabel('振幅');
xlabel('时间');
title('加入循环前缀后缀的OFDM波形');
IFFT_modulation=zeros(symbols_per_carrier,IFFT_bin_length);%添0组成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
end
%=======================并串转换=========================
Tx_data_withoutwindow=reshape(time_wave_matrix_cp',(symbols_per_carrier)*(IFFT_bin_length+GI+GIP),1)'; %不加窗，循环前缀与后缀不叠加的串行信号
figure(5);
plot(0:IFFT_bin_length-1,time_wave_matrix(2,:));
axis([0, 700, -0.2, 0.2]);