dsss.rar_psk解调_扩频解调_扩频调制解调_调制 扩频_调制解调 matlab

function [bit_errs_ss,i_out,q_out]=despread(tiq,sumiq,cs_t,sn_t,seq1,seq2,data,N,fcarr) %Bob Gess, June 2008, for EE473 %Portions copied and modified from QPSK_TX_IQ_RX by JC and posted on %Mathworks Dec 2005 %This module multplies the carrier frequency by the prn sequence and then %demodulates the incoming signal by the composite signal (prn and carrier) %The data is also filtered to produce the I-channel, Q-channel. %The program aso displays the number of bit errors and the bit error rate %in the command window at the end of the simulation. %fcarr=20e3; % Carrier frequency(Hz) %N=1e3; % Number of data bits(bit rate) fs=8*10e3; % Sampling frequency Fn=fs/2; % Nyquist frequency Ts=1/fs; % Sampling time = 1/fs T=1/N; % Bit time randn('state',0); % Keeps PRBS from changing on reruns td=[0:Ts:(N*T)-Ts]';% Time vector(data)(transpose) %prn and carrier si=cs_t.*seq1; sq=sn_t.*seq2; %demodulate and despread ibit=sumiq.*si; qbit=sumiq.*sq; combined=ibit+qbit; %simple low pass filter rc1=1/N; %time constant ht1=(1/rc1).*exp(-tiq/rc1);%impulse response flt_ibit=filter(ibit,1,ht1)/fs; f5=length(flt_ibit) %Verifies progress of program %filter for q channel rc=1/N; %time constant ht=(1/rc).*exp(-tiq/rc);%impulse response flt_qbit=filter(qbit,1,ht)/fs; f6=length(flt_qbit) %Verifies progress of program bit1=sign(flt_ibit);%+/-1 bit2=sign(flt_qbit);%+/-1 %Second filtering stage (optional, but does give slight improvement) bit3=filter(bit1,1,ht1)/fs; f7=length(bit3) %Verifies progress of program bit4=filter(bit2,1,ht)/fs; f8=length(bit4) %Verifies progress of program bit5=sign(bit3);%+/-1 bit6=sign(bit4);%+/-1 shaped_ibit=bit5 >0;%0 and 1 shaped_qbit=bit6 >0;%0 and 1 i_out=[shaped_ibit]';%transpose q_out=[shaped_qbit]';%transpose %compare received data to transmitted data by sampling at end of time %cycle for data bit. This compensates for delay created by filtering (plus %more accurately simulates how processor would capture the data). x=1; for i=(fs/N-2):(fs/N):39998 serial(x)=(i_out(i)+i_out(i+1)+i_out(i+2))/3; x=x+1; serial(x)=(q_out(i)+q_out(i+1)+q_out(i+2))/3; x=x+1; end data_1=data >0; serial_1=serial >.5; bit_errs_ss=xor(data_1,serial_1); ss_bit_errors=sum(bit_errs_ss) ss_ber=ss_bit_errors/N %======================================================================== %Take FFT of modulated spread carrier %======================================================================== y=sumiq; NFFY=2.^(ceil(log(length(y))/log(2))); FFTY=fft(y,NFFY);%pad with zeros NumUniquePts=ceil((NFFY+1)/2); FFTY=FFTY(1:NumUniquePts); MY=abs(FFTY); MY=MY*2; MY(1)=MY(1)/2; MY(length(MY))=MY(length(MY))/2; MY=MY/length(y); f1=(0:NumUniquePts-1)*2*Fn/NFFY; %======================================================================== %Take FFT of despread combined signal (for demo purposes) %======================================================================== y=combined; NFFY=2.^(ceil(log(length(y))/log(2))); FFTY=fft(y,NFFY);%pad with zeros NumUniquePts=ceil((NFFY+1)/2); FFTY=FFTY(1:NumUniquePts); DY=abs(FFTY); DY=DY*2; DY(1)=DY(1)/2; DY(length(DY))=DY(length(DY))/2; DY=DY/length(y); f1=(0:NumUniquePts-1)*2*Fn/NFFY; %===================================================================== %Plots %====================================================================== figure(8) subplot(4,1,1) plot(tiq,ibit) axis([0 20/N -2 2]); grid on xlabel(' Time') ylabel('Amplitude') title('I channel Output Waveform') subplot(4,1,2) plot(tiq,qbit) axis([0 20/N -2 2]); grid on xlabel(' Time') ylabel('Amplitude') title('Q channel Output Waveform') subplot(4,1,3) plot(tiq,si) axis([0 5/N -2 2]); grid on xlabel(' Time') ylabel('Amplitude') title('i demod sig Waveform') subplot(4,1,4) plot(tiq,sq) axis([0 5/N -2 2]); grid on xlabel(' Time') ylabel('Amplitude') title('q demod sig Waveform') figure(9) subplot(2,1,1) plot(tiq,i_out) axis([0 20/N -2 2]); grid on xlabel(' Time') ylabel('Amplitude') title('SS I Channel Data') subplot(2,1,2) plot(tiq,q_out) axis([0 20/N -2 2]); grid on xlabel(' Time') ylabel('Amplitude') title('SS Q Channel Data') figure(12) subplot(2,1,1); plot(f1,MY);xlabel('');ylabel('AMPLITUDE'); axis([0 40000 0 1]);%zoom in/out title('Frequency domain received'); grid on subplot(2,1,2); plot(f1,20*log10(abs(MY).^2));xlabel('FREQUENCY(Hz)');ylabel('DB'); axis([0 40000 -80 0]);%zoom in/out grid on title('Received QPSK spread signal') figure(12) subplot(2,1,1); plot(f1,MY);xlabel('');ylabel('AMPLITUDE'); axis([0 40000 0 1]);%zoom in/out title('Frequency domain received'); grid on subplot(2,1,2); plot(f1,20*log10(abs(MY).^2));xlabel('FREQUENCY(Hz)');ylabel('DB'); axis([0 40000 -80 0]);%zoom in/out grid on title('Received QPSK spread signal') figure(14) subplot(2,1,1); plot(f1,DY);xlabel('');ylabel('AMPLITUDE'); axis([0 4*N 0 1]);%zoom in/out title('Frequency domain despread combined signal'); grid on subplot(2,1,2); plot(f1,20*log10(abs(DY).^2));xlabel('FREQUENCY(Hz)');ylabel('DB'); axis([0 4*N -80 0]);%zoom in/out grid on title('Received despread combined signal') end