MSK调制解调器及同步性能的仿真分析(3)

for SNR = 0:8 signal_mod1 = 0.01 * awgn(signal_mod,SNR); N=300;

% 滤波器的阶数为(N+1)?? ??? F=[0,fc-1000,fc+1000,Fs/2]*2/Fs; A=[1,1,0,0]; lpf=firls(N,F,A); [amp_lpf,w]=freqz(lpf);

I_dem=signal_mod1.*cos(2*pi*fc*t)*2 .* cos(pi*t*Rb/2); I_dem=conv(I_dem,lpf);

I_dem=I_dem(N/2+1:N/2+length(I_temp));

Q_dem=signal_mod1.*sin(2*pi*fc*t)*2 .* sin(pi*t*Rb/2); Q_dem=conv(Q_dem,lpf);

Q_dem=-Q_dem(N/2+1:N/2+length(I_temp)); I_dem_out=zeros(1,length(I_dem)/multi); % 抽取 ???

Q_dem_out=zeros(1,length(Q_dem)/multi); for i=1:length(I_dem_out)

I_dem_out(i)=I_dem(multi*(i-1)+1); Q_dem_out(i)=Q_dem(multi*(i-1)+1); end;

%解调，判决

demod_data = zeros(1,data_len); for i = 1:data_len

I_dem1(i) = I_dem_out(i*sample_number)>0; Q_dem1(i) = Q_dem_out(i*sample_number)>0; end

for i = 1:2:data_len m1(i) = Q_dem1(i); end

for i = 2:2:data_len m1(i) = I_dem1(i); end

m1 = 2*m1-1; %差分解码

demod_data = zeros(1,data_len); demod_data(1) = 1 * m1(1); for i = 2:data_len

demod_data(i) = m1(i-1) * m1(i);