1、时域上看,单极性不归零码,无电压用来表示0,而恒定的正电压用来表示1。从功率谱密度函数来看,单极性不归零函数根据表达式可知,其功率谱函数值在0点含有冲击。三 单极性归零(NZ)波形时域及功率谱密度如图所示:时域上分析,单极性归零码,当发码时,发出正电流,但持续时间短于一个码元的时间宽度,即发出一个窄脉冲;当发码时,仍然不发送电流;从功率谱密度函数来看,单极性归零函数根据表达式可知,其功率谱函数值在f=m*fs点含有冲击。四 理想低通系统的时域图形及功率谱密度如图所示:从时域分析,抽样函数在抽样判决时有较大的不确定性,可以看出其不利于准确的进行抽样判决。从功率谱密度来看,用抽样函数带宽比矩形波的
2、带宽窄,频带利用率有所提高。%clear all;close all;Ts=1;N_sample = 15; %dt = Ts/N_sample; %N = 100; %t = 0:dt:(N*N_sample-1)*dt;T = N*N_sample*dt;gt1 = ones(1,N_sample); %NRZgt2 = ones(1,N_sample/2); %RZgt2 = gt2 zeros(1,N_sample/2);mt3 = sinc(t-5)/Ts);gt3 = mt3(1:10*N_sample);d = ( sign( randn(1,N) ) +1 )/2;data =
3、 sigexpand(d,N_sample); %N_sample-1st1 = conv(data,gt1);st2 = conv(data,gt2);d = 2*d-1; %data= sigexpand(d,N_sample);st3 = conv(data,gt3);f,st1f = T2F(t,st1(1:length(t);f,st2f = T2F(t,st2(1:f,st3f = T2F(t,st3(1:figure(1)subplot(321)plot(t,st1(1:length(t) );gridaxis(0 100 -1.5 1.5);ylabel(NRZ);subplot(322);plot(f,10*log10(abs(st1f).2/T) );axis(-10 10 -40 10);NRZ(dB/Hz)subplot(323)plot(t,st2(1:RZsubplot(324)plot(f,10*log10(abs(st2f).2/T);RZsubplot(325)plot(t-5,st3(1:axis(0 100 -2 2);sincxlabel(t/Tssubplot(326)plot(f,10*log10(abs(st3f).2/T);saf*Ts