VSB调制仿真及其抗噪声性能分析

function modulation_performance_comparing %不同调制方法的调制性能比较，调制方法有 %AM—标准幅度调制，包络检波解调；相干解调类似于DSB，这里不考虑 %DSB—双边带调制 %SSB—单边带调制 %VSB—残留边带调制 %% %%%%%%%%%%%%%%%%%%%%%%%%%%%%信号源 %%%%%基波信号 f0 = 1;%基波信号频率，单位：Hz T0 = 5;%信号时域截断长度——>为了减小截断效应对频谱的影响，最少截断长度为多少？ dt = 0.003;%时域采样间隔 Fs = 1/dt;%时域采样频率，即频域延拓周期，单位：Hz t = 0:dt:T0;%时间序列，单位：s m_t = cos(2*pi*f0*t);%基波信号采样序列 df = 0.003;%频域采样间隔 [M_f,m_t,df1,f]=T2F(m_t,dt,df,Fs);%基波信号频谱 %%%%%载波信号 A = 2;%载波信号幅度 fc = 10;%载波信号频率，单位：Hz m2_t = A*cos(2*pi*fc*t);%载波信号采样序列 [M2_f,m2_t,df1,f]=T2F(m2_t,dt,df,Fs);%载波信号频谱 %% %%%%%%%%%%%%%%%%%%%%%%%%%%%%信号调制 %%%%%AM信号调制 S_AM_t = (m_t(1:length(t))+A/2).*m2_t(1:length(t));%AM已调信号 [S_AM_f,S_AM_t,df1,f]=T2F(S_AM_t,dt,df,Fs);%AM已调信号频谱 %%%%%DSB信号调制 S_DSB_t = m_t(1:length(t)).*m2_t(1:length(t));%DSB已调信号 [S_DSB_f,S_DSB_t,df1,f]=T2F(S_DSB_t,dt,df,Fs);%DSB已调信号频谱 %%%%%SSB信号调制 S_SSB_t = m_t(1:length(t)).*m2_t(1:length(t))... -imag(hilbert(m_t(1:length(t)))).*imag(hilbert(m2_t(1:length(t))));%SSB已调信号 [S_SSB_f,S_SSB_t,df1,f]=T2F(S_SSB_t,dt,df,Fs);%SSB已调信号频谱 %%%%%VSB信号调制 fa = 0.15*fc;%VSB调制滤波器特定频率参数 [H_VSB_f ,f]=vsb_lpf(length(S_DSB_t),fc,fa,df1,Fs,1);%VSB调制滤波器频率响应函数 S_VSB_f = H_VSB_f.*S_DSB_f;%VSB已调信号频谱 [S_VSB_t] = F2T(S_VSB_f,Fs);%VSB已调信号波形 %% %%%%%%%%%%%%%%%%%%%%%%%%%%%%加入信道 signal_AM_power = power_x(S_AM_t(1:length(t)));%AM信号功率 signal_DSB_power = power_x(S_DSB_t(1:length(t)));%DSB信号功率 signal_SSB_power = power_x(S_SSB_t(1:length(t)));%SSB信号功率 signal_VSB_power = power_x(S_VSB_t(1:length(t)));%VSB信号功率 %功率归一化 S_AM_t = S_AM_t(1:length(t))/signal_AM_power; [S_AM_f,S_AM_t,df1,f]=T2F(S_AM_t,dt,df,Fs); S_DSB_t = S_DSB_t(1:length(t))/signal_DSB_power; [S_DSB_f,S_DSB_t,df1,f]=T2F(S_DSB_t,dt,df,Fs); S_SSB_t = S_SSB_t(1:length(t))/signal_SSB_power; [S_SSB_f,S_SSB_t,df1,f]=T2F(S_SSB_t,dt,df,Fs); S_VSB_t = S_VSB_t(1:length(t))/signal_VSB_power; [S_VSB_f,S_VSB_t,df1,f]=T2F(S_VSB_t,dt,df,Fs); %%%%% % M = 100; s = randn(1,length(t))+i*randn(1,length(t));%单位噪声序列 % s = sum(s)/M; N = 100; SNR_AM_inp = zeros(1,N); SNR_AM_out = zeros(1,N); SNR_DSB_inp = zeros(1,N); SNR_DSB_out = zeros(1,N); SNR_SSB_inp = zeros(1,N); SNR_SSB_out = zeros(1,N); SNR_VSB_inp = zeros(1,N); SNR_VSB_out = zeros(1,N); for snr_lin = 1:N B = 2.4;%带通滤波器带宽 %%%%%噪声功率 noise_AM_power = (signal_AM_power*Fs)/(snr_lin*B); noise_DSB_power = (signal_DSB_power*Fs)/(snr_lin*B); noise_VSB_power = (signal_VSB_power*Fs)/(snr_lin*B); B = 1.2; noise_SSB_power = (signal_SSB_power*Fs)/(snr_lin*B); %%%%%产生噪声 noise_AM_t = sqrt(noise_AM_power)*s; noise_DSB_t = sqrt(noise_DSB_power)*s; noise_VSB_t = sqrt(noise_VSB_power)*s; noise_SSB_t = sqrt(noise_SSB_power)*s; %%%%%噪声频谱 [noise_AM_f,noise_AM_t,df1,f] = T2F(noise_AM_t,dt,df,Fs); [noise_DSB_f,noise_DSB_t,df1,f] = T2F(noise_DSB_t,dt,df,Fs); [noise_SSB_f,noise_SSB_t,df1,f] = T2F(noise_SSB_t,dt,df,Fs); [noise_VSB_f,noise_VSB_t,df1,f] = T2F(noise_VSB_t,dt,df,Fs); %%%%%%%%%AM B = 2.4; f_start = fc-B/2;%起始频率 f_cutoff = fc+B/2;%截至频率 [H_BPF_f,f] = bp_f(length(S_AM_t),f_start,f_cutoff,df1,Fs,1); [H_LPF_f,f] = lp_f(length(S_AM_t),B/2,df1,Fs,1);%理想低通滤波器频谱 %%%%%输入信噪比 noise_1_AM_f = H_BPF_f.*noise_AM_f;%经过带通滤波 [noise_1_AM_t] = F2T(noise_1_AM_f,Fs); noise_AM_inp_power = power_x(abs(noise_1_AM_t(1:length(t))));%带通输出噪声功率 signal_AM_inp_power = power_x(S_AM_t(1:length(t))); %%%%%输出信噪比 S_1_AM_t = S_AM_t(1:length(t))+noise_1_AM_t(1:length(t));%实际输入信号 S_2_AM_t = abs(S_1_AM_t)-mean(abs(S_1_AM_t));%包络输出信号同时隔直 [S_2_AM_f,S_2_AM_t,df1,f] = T2F(S_2_AM_t,dt,df,Fs); S_AM_out_f = H_LPF_f.*S_2_AM_f;%低通滤波输出 S_AM_out_f = fftshift(abs(S_AM_out_f)); signal_AM_out_power = sum(S_AM_out_f(find(f>0.8 & f<1.2))); noise_AM_out_power = sum(S_AM_out_f)-signal_AM_out_power; %%%%% SNR_AM_inp(snr_lin) = signal_AM_inp_power/noise_AM_inp_power; SNR_AM_out(snr_lin) = signal_AM_out_power/noise_AM_out_power; %%%%%%%%%DSB [noise_DSB_inp_power,noise_DSB_out_power] = coherent_demodulation_power_transf... (t,noise_DSB_f,m2_t,df,dt,H_BPF_f,H_LPF_f,Fs); [signal_DSB_inp_power,signal_DSB_out_power] = coherent_demodulation_power_transf... (t,S_DSB_f,m2_t,df,dt,H_BPF_f,H_LPF_f,Fs); SNR_DSB_inp(snr_lin) = signal_DSB_inp_power/noise_DSB_inp_power; SNR_DSB_out(snr_lin) = signal_DSB_out_power/noise_DSB_out_power; %%%%%%%%%VSB [noise_VSB_inp_power,noise_VSB_out_power] = coherent_demodulation_power_transf... (t,noise_VSB_f,m2_t,df,dt,H_BPF_f,H_LPF_f,Fs); [signal_VSB_inp_power,signal_VSB_out_power] = coherent_demodulation_power_transf... (t,S_VSB_f,m2_t,df,dt,H_BPF_f,H_LPF_f,Fs); SNR_VSB_inp(snr_lin) = signal_VSB_inp_power/noise_VSB_inp_power; SNR_VSB_out(snr_lin) = signal_VSB_out_power/noise_VSB_out_power; %%%%%%%%%SSB B = 1.2; f_start = fc;%起始频率 f_cutoff = fc+B;%截至频率 [H_BPF_f,f]=bp_f(length(S_DSB_t),f_start,f_cutoff,df1,Fs,1); [H_LPF_f,f] = lp_f(length(S_DSB_t),B,df1,Fs,1);%理想低通滤波器频谱 [noise_SSB_inp_power,noise_SSB_out_power] = coherent_demodulation_power_transf... (t,noise_SSB_f,m2_t,df,dt,H_BPF_f,H_LPF_f,Fs); [signal_SSB_inp_power,signal_SSB_out_power] = coherent_demodulation_power_transf... (t,S_SSB_f,m2_t,df,dt,H_BPF_f,H_LPF_f,Fs); SNR_SSB_inp(snr_lin) = signal_SSB_inp_power/noise_SSB_inp_power; SNR_SSB_out(snr_lin) = signal_SSB_out_power/noise_SSB_out_power; end plot(10*log10(SNR_DSB_inp),10*log10(SNR_DSB_out),'r') hold on plot(10*log10(SNR_VSB_inp),10*log10(SNR_VSB_out),'b') hold on plot(10*log10(SNR_SSB_inp),10*log10(SNR_SSB_out),'g') hold on plot(10*log10(SNR_AM_inp),10*log10(SNR_AM_out),'k') xlabel('输入信噪比/dB') ylabel('输出信噪比/dB') title('不同调制方法的抗噪性能比较')