通信系统仿真课后答案.docVIP

第章-1 答： 输入：syms t w Xf=fourier(5*cos(6*pi*t)+3*sin(8*pi*t)) 输出：Xf=pi*(5*dirac(w+6*pi)+3*i*dirac(w+8*pi)-3*i*dirac(w-8*pi)+5*dirac(w-6*pi)) matlab程序： t=0:0.02:8; L=length(t); xt=5*cos(6*pi*t)+3*sin(8*pi*t); f1=fft(xt); fs=10;Ts=1/fs; t1=8:-0.02:0; f=1./t1; Pt=zeros(1,L); for i=1:8:L Pt(i)=1; end Xst=xt.*Pt; f2=fft(Xst); f3=fs*f1; f4=ifft(f3); subplot(2,2,1) plot(f,f1) axis([0 10 -1000 3000]) xlabel(f);ylabel(x(f)); subplot(2,2,2) plot(f,f2) axis([0 10 -200 400]) xlabel(f);ylabel(Xs(f)); subplot(2,2,3) plot(f,f3) axis([0 10 -2000 4000]) xlabel(f);ylabel(Xr(f)); subplot(2,2,4) plot(t,f4) xlabel(t);ylabel(Xr(t)); axis([0 6 -50 50]) 3-2 答：matlab程序： t=0:0.02:8; L=length(t); xt=5*cos(6*pi*t)+3*sin(8*pi*t); f1=fft(xt); fs=7;Ts=1/fs; t1=8:-0.02:0; f=1./t1; Pt=zeros(1,L); for i=1:8:L Pt(i)=1; end Xst=xt.*Pt; f2=fft(Xst); f3=fs*f1; f4=ifft(f3); subplot(2,2,1) plot(f,f1) axis([0 10 -1000 3000]) xlabel(f);ylabel(x(f)); subplot(2,2,2) plot(f,f2) axis([0 10 -200 400]) xlabel(f);ylabel(Xs(f)); subplot(2,2,3) plot(f,f3) axis([0 10 -2000 4000]) xlabel(f);ylabel(Xr(f)); subplot(2,2,4) plot(t,f4) xlabel(t);ylabel(Xr(t)); axis([0 6 -50 50]) 3.5 信号， （a）信号的动态范围为。 （b）信号的波峰因素为。其中，S为信号的功率，所以。 （c）信噪比，以dB为单位， 当比特时，计算得 3.11 k = 50; % samples per lobe nsamp = 50000; % total frequency samples snrdb = zeros(1,17); % initialize memory x = 4:20; % vector for plotting for m = 4:20 signal = 0; noise = 0; % initialize sum values f_fold = k*m/2; % folding frequency for j = 1:f_fold term = (sin(pi*j/k/2)/(pi*j/k/2))^4; signal = signal+term; end for j = (f_fold+1):nsamp term = (sin(pi*j/k/2)/(pi*j/k/2))^4; noise = noise+term; end snrdb(m-3) = 10*log10(signal/noise); end plot(x,snrdb) % plot results xlabel(Samples per symbol) ylabel(Signal-to-aliasing noise ratio) 三角脉冲波形的信号混叠信噪比 矩形脉冲波形的信号混叠信噪比 3-11 答：matlab程序： k=50; nsamp=50000; snrdb=zeros(1,17)