1、SSR中頻COSTA新解調(diào)原理及MATLAB（碼1.解調(diào)算法模型SSRASK單調(diào)采用改進(jìn)的costas環(huán)解調(diào)方式，原理框圖如下圖1所示Opt iana II；.帶速游波m（1 ： s isi：i( j ihp ;1度相位求的CORDIC幅度相位.圖1SSRASKS調(diào)原理框圖AD采樣后的中頻信號(hào)進(jìn)入FPG秋部后，可選擇性引入帶通FIR濾波器，對(duì)帶外噪聲信號(hào)進(jìn)行衰減，以提高中頻信號(hào)的信噪比。不過(guò)需注意的是，F(xiàn)IR濾波器的群延時(shí)會(huì)增加解調(diào)系統(tǒng)處理時(shí)間，在機(jī)載應(yīng)答機(jī)對(duì)處理時(shí)間要求苛刻的環(huán)境下，是否引入帶通FIR濾波器需充分評(píng)估。vl二m(1)sin(w/)*sin(wif+(p)=sin(p+sin(

2、2wf+ip)v2=m(/)sin(wf)*cos(wt+=2ffl(f)cosp+cos(2w/+*3hm(l)sin中v4-lffl(0cospamp=sqrt(y3*v3+v4*v4)*4phase-atan(v3/v4)2.MATLAB源碼%SS種頻ASK解調(diào)程序，對(duì)于DPSKS調(diào)原理類(lèi)似closeall;clearall;f0=70000000;%原始中頻信號(hào)頻率fs=85000000;%SamplingFrequencyfl=15000000;%中頻采樣后中頻信號(hào)主頻點(diǎn)%!擬兩個(gè)SSF答信號(hào)SSR0=zeros(1,430);SSR0(1:9)=1;%F1SSR0(30:38)=1

3、;%C1SSR0(59:67)=1;%A1SSR0(88:96)=1;%C2SSR0(117:125)=1;%A2SSR0(146:154)=1;%C4SSR0(175:183)=1;%A4SSR0(204:212)=0;%XSSR0(233:241)=0;%B1SSR0(262:270)=1;%D1SSR0(291:299)=0;%B2SSR0(320:328)=1;%D2SSR0(349:357)=1;%B4SSR0(378:386)=0;%D4SSR0(407:415)=1;%F2SSR=rectpulse(SSR0,4);ssr_length=length(SSR);t=0:1/fs:

4、(ssr_length-1)/fs;sin_IF=sin(2*pi*f0*t)+1;IF_signal=zeros(1,ssr_length);%給中頻信號(hào)插入一定噪聲SNR=30;sin_IF=awgn(sin_IF,SNR);%給向量上插入一定信噪比%生成中頻采樣后的信號(hào)fori=1:ssr_lengthIF_signal(i)=10000*sin_IF(i)*SSR(i);end%顯示原始信號(hào)頻譜fs_xianshi=fs;dlengh=length(IF_signal);dlenghlog=nextpow2(dlengh)-1;%nextpow2returnsthesmallestpo

5、weroftwogreaterthanorequaltolength(A).datalengh=2Adlenghlog;m_dpsk=20*log10(abs(fft(IF_signal,datalengh);x_f=0:(fs_xianshi/datalengh):fs_xianshi/2;m2=m_dpsk(1:length(x_f);figure(1);plot(x_f,m2,-.);legend(采樣后的中頻信號(hào)頻譜);xlabel(頻率(Hz);ylabel(幅度(dB);gridon;= 20;%OrderFc1 = 10;%FirstCutoffFrequency(單位MH)ZF

6、c2=20;%SecondCutoffFrequency(單位MHZ)flag=scale;%SamplingFlagFs=85;%濾波器采樣頻率(單位MHZ)%Createthewindowvectorforthedesignalgorithm.win=hamming(N+1);%CalculatethecoefficientsusingtheFIR1function.b=fir1(N,Fc1Fc2/(Fs/2),bandpass,win,flag);(N-%對(duì)采樣后的IF信號(hào)先進(jìn)行一次帶通濾波,提高信噪比(濾波引入延時(shí)：1)/(2*Fs),對(duì)于上述濾波器，延時(shí)為111.7ns)%對(duì)于對(duì)解調(diào)

7、延時(shí)要求比較高的場(chǎng)合，要設(shè)置恰當(dāng)?shù)臑V波器階數(shù)，不能茫然追求帶外衰減，提高濾波器階數(shù)，造成較大的群延時(shí)IF_signal_f=filter2(b,IF_signal);%IF_signal_f=IF_signal;%-對(duì)中頻信號(hào)進(jìn)行正交混頻操作sin_VCO=sin(2*pi*f1*t-pi/4);cos_VCO=cos(2*pi*f1*t-pi/4);I_signal=zeros(1,ssr_length);Q_signal=zeros(1,ssr_length);fori=1:ssr_lengthI_signal(i)=IF_signal_f(i)*sin_VCO(i);Q_signal(i

8、)=IF_signal_f(i)*cos_VCO(i);end%-對(duì)混頻后的正交信號(hào)進(jìn)行濾波Fs=85;%SamplingFrequencyN=30;%OrderFc=10;%CutoffFrequencyflag=scale;%SamplingFlag%Createthewindowvectorforthedesignalgorithm.win=hamming(N+1);%CalculatethecoefficientsusingtheFIR1function.b=fir1(N,Fc/(Fs/2),low,win,flag);%普通低通FIR濾波操作，濾除混頻引入的高頻成分。濾波引入延時(shí)：(

9、N-1)/2*Fs),對(duì)于上述濾波器，延時(shí)為1776ns)%對(duì)于對(duì)解調(diào)延時(shí)要求比較高的場(chǎng)合，要設(shè)置恰當(dāng)?shù)臑V波器階數(shù)，不能茫然追求帶外衰減，提高濾波器階數(shù)，造成較大的群延時(shí)I_fir_result=filter2(b,I_signal);Q_fir_result=filter2(b,Q_signal);%顯示普通濾波后信號(hào)頻譜fs_xianshi=fs;dlengh=length(I_fir_result);dlenghlog=nextpow2(dlengh)-1;%nextpow2returnsthesmallestpoweroftwogreaterthanorequaltolength(A)

10、.datalengh=2Adlenghlog;m_dpsk=20*log10(abs(fft(I_fir_result,datalengh);x_f=0:(fs_xianshi/datalengh):fs_xianshi/2;m2=m_dpsk(1:length(x_f);figure(2);plot(x_f,m2,-.);legend(普通FIR濾波后信號(hào)頻譜)；xlabel(頻率(Hz);ylabel(幅度(dB);gridon;%科斯塔斯環(huán)解調(diào)結(jié)果demodulate_amp=sqrt(I_fir_result.*I_fir_result+Q_fir_result.*Q_fir_resu

11、lt)*4;%解調(diào)幅度解調(diào)相位為 IF方式求解相位，因此demodulate_phase=atan(I_fir_result./Q_fir_result);%信號(hào)載波相對(duì)混頻I路信號(hào)相位關(guān)系，由于采用arctangent存在1、3象限；2、4象限的相位模糊%繪制解調(diào)前后信號(hào)波形對(duì)比圖figure(6);subplot(3,1,1);plot(IF_signal(1:ssr_length),-g,linewidth,2);legend(原始碼元);axis(0length(IF_signal)025000);xlabel(采樣點(diǎn));ylabel(幅度);gridon;holdall;subplot(3,1,2);plot(demodulate_amp(1:ssr_length),-b,linewidth,1);legend(解調(diào)幅度);axis(0length(demodulate_amp)02500