二进制FSK调制及包络检波解调过程仿真实现

clear all; Ts = 1; %码元周期 N_sample = 1000; %每个码元抽样点数 fs=N_sample; %抽样频率 fs_c1 = 5; %载波1频率 fs_c2 = 15; %载波2频率 dt = Ts/N_sample; %抽样的时间间隔 N = 200; %码元数 t = 0:dt:(N*N_sample-1)*dt; df = fs/length(t); f = -fs/2:df:fs/2-df; %定义频率矢量（频谱图的横坐标） % 基本码元 g(t) = 1 gt0 = zeros(1,N_sample); gt1 = ones(1,N_sample); %单极性不归零 %生成随机码元 random_code = randi([0,1],1,N); %单极性波形的最后结果 yt1 = zeros(1,N*N_sample-1); %单极性不归零NRZ波形 for i = 1:N if random_code(i) == 1 %得到波形图 yt1((i-1)*N_sample+1:i*N_sample) = gt1; %单极性不归零NRZ波形 else yt1((i-1)*N_sample+1:i*N_sample) = gt0; end end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% figure(1) subplot(211) plot(t,yt1); axis([0 8 -0.1 1.1]); title('单极性不归零二进制基带信号'); xlabel('时间t/s'); grid; subplot(212) carrier1 = cos(2*pi*fs_c1*t); carrier2 = cos(2*pi*fs_c2*t); for i=1:length(t) if yt1(i) == 0 yt1_mod(i) = carrier1(i); else yt1_mod(i) = carrier2(i); end end plot(t,yt1_mod); axis([0 8 -1.1 1.1]); title('2FSK调制信号'); xlabel('时间t/s'); grid; %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %频谱图 figure(2) subplot(211) fmt=fft(yt1); % 对时域信号进行FFT变换，计算其频谱 fmt=fftshift(fmt); fmt=abs(fmt); fmt_dB=fmt.^2/Ts; maxF=max(fmt_dB); fmt_dB=fmt_dB/maxF; fmt_dB= 10*log10(fmt_dB +eps); plot(f,fmt_dB);grid on; axis([-5 5 -150 0]); xlabel('频率(Hz)');ylabel('功率谱幅度值(dB)'); title('单极性不归零二进制基带信号功率谱密度(db)'); subplot(212) fmt=fft(yt1_mod); % 对时域信号进行FFT变换，计算其频谱 fmt=fftshift(fmt); fmt=abs(fmt); fmt_dB=fmt.^2/Ts; maxF=max(fmt_dB); fmt_dB=fmt_dB/maxF; fmt_dB= 10*log10(fmt_dB +eps); plot(f,fmt_dB);grid on; axis([-25 25 -150 0]); xlabel('频率(Hz)');ylabel('功率谱幅度值(dB)'); title('2FSK调制信号功率谱密度(db)'); %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %叠加噪声 figure(3) subplot(211) plot(t,yt1_mod); axis([0 8 -1.1 1.1]); title('2FSK调制信号'); xlabel('时间t/s'); grid; subplot(212) yt1_mod_awgn = awgn(yt1_mod,10,'measured'); plot(t,yt1_mod_awgn); axis([0 8 -2 2]); title('接收端叠加噪声后的FSK调制信号波形图'); xlabel('时间t/s'); grid; %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %低通滤波,以5hz为中心 figure(4) subplot(211) % 进行低通滤波 fpass = 0; fstop = 7; [f1,fmt1] = IdealFilter(length(t),fs,fpass,fstop,fft(yt1_mod_awgn)); % 进行理想带通滤波 spf_t1 = ifft(fmt1); plot(t,spf_t1);grid on; axis([0 8 -1.1 1.1]); xlabel('时间(s)');ylabel('电压值(V)'); title('FSK调制信号理想低通滤波后信号波形图mt1'); subplot(212) spf1=fft(spf_t1); % 对时域信号进行FFT变换，计算其频谱 spf1=fftshift(spf1); plot(f,abs(spf1));grid on; axis([-30 30 -1000 40000]); xlabel('频率(Hz)');ylabel('频谱幅度值'); title('FSK调制信号理想低通滤波结果f1'); %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %带通滤波,以10hz为中心 figure(5) subplot(211) % 进行低通滤波 fpass = 12; fstop = 17; [f2,fmt2] = IdealFilter(length(t),fs,fpass,fstop,fft(yt1_mod_awgn)); % 进行理想带通滤波 spf_t2 = ifft(fmt2); plot(t,spf_t2);grid on; axis([0 8 -1.1 1.1]); xlabel('时间(s)');ylabel('电压值(V)'); title('FSK调制信号理想低通滤波后信号波形图mt2'); subplot(212) spf2=fft(spf_t2); % 对时域信号进行FFT变换，计算其频谱 spf2=fftshift(spf2); plot(f,abs(spf2));grid on; axis([-30 30 -1000 40000]); xlabel('频率(Hz)');ylabel('频谱幅度值'); title('FSK调制信号理想低通滤波结果f2'); %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %全波整流以5HZ载波进行 figure(6) subplot(211) spf_t1 = abs(spf_t1); plot(t,spf_t1); axis([0 8 -0.2 1.2]); title('m1(t)全波整流信号波形图'); xlabel('时间t/s'); grid; subplot(212) spf1=fft(spf_t1); % 对时域信号进行FFT变换，计算其频谱 spf1=fftshift(spf1); plot(f,abs(spf1));grid on; axis([-30 30 -100 61000]); xlabel('频率(Hz)');ylabel('频谱幅度值'); title('m1(t)全波整流信号幅频特性'); %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %包络检波，以频率为5hz的载波 figure(7) subplot(211) % 进行低通滤波 fpass = 0; fstop = 5; [f1,spf1] = IdealFilter(length(t),fs,fpass,fstop,fft(spf_t1)); % 此处的频谱不能用fftshift后的！！！！！ spf_t1 = ifft(spf1); plot(t,spf_t1);grid on; axis([0 8 -0.1 0.9]); xlabel('时间(s)');ylabel('电压值(V)'); title('m1(t)包络检波信号波形图'); subplot(212) spf=fft(spf_t1); % 对时域信号进行FFT变换，计算其频谱 spf1=fftshift(spf); plot(f,abs(spf1));grid on; axis([-15 15 -1 61000]); xlabel('频率(Hz)');ylabel('频谱幅度值'); title('m1(t)包络检波信号的幅频特性'); %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %全波整流以10HZ载波进行 figure(8) subplot(211) spf_t2 = abs(spf_t2); plot(t,spf_t2); axis([0 8 -0.2 1.2]); title('m2(t)全波整流信号波形图'); xlabel('时间t/s'); grid; subplot(212) spf2=fft(spf_t2); % 对时域信号进行FFT变换，计算其频谱 spf2=fftshift(spf2); plot(f,abs(spf2));grid on; axis([-40 40 -1000 61000]); xlabel('频率(Hz)');ylabel('频谱幅度值'); title('m2(t)全波整流信号幅频特性'); %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %包络检波，以频率为10hz的载波 figure(9) subplot(211) % 进行低通滤波 fpass = 0; fstop = 5; [f1,spf2] = IdealFilter(length(t),fs,fpass,fstop,fft(spf_t2)); % 此处的频谱不能用fftshift后的！！！！！ spf_t2 = ifft(spf2); plot(t,spf_t2);grid on; axis([0 8 -0.1 0.8]); xlabel('时间(s)');ylabel('电压值(V)'); title('m2(t)包络检波信号波形图'); subplot(212) spf=fft(spf_t2); % 对时域信号进行FFT变换，计算其频谱 spf2=fftshift(spf); plot(f,abs(spf2));grid on; axis([-15 15 -1 61000]); xlabel('频率(Hz)');ylabel('频谱幅度值'); title('m2(t)包络检波信号的幅频特性'); %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %恢复基带信号 r=zeros(1,N_sample*N); for i = 1:N-1 if spf_t1((i-0.5)*N_sample) < spf_t2((i-0.5)*N_sample) %得到波形图 r((i-0.5)*N_sample+1:(i+0.5)*N_sample) = gt1; %单极性不归零NRZ波形 else r((i-0.5)*N_sample+1:(i+0.5)*N_sample) = gt0; end end figure(10) subplot(211) plot(t,yt1); axis([0 12 -0.1 1.1]); title('发送端的被调制信号波形图'); xlabel('时间t/s'); grid; subplot(212) plot(t,r); axis([0 12 -0.1 1.1]); title('接收采样判决后恢复的被调制信号波形图'); xlabel('时间t/s'); grid;