【導讀】較高的頻譜利用率、較強的抗干擾性、在電路上實現(xiàn)也較為簡單。調制技術是通信領。QPSK調制是一種具有較高頻帶利用率和良好的抗噪聲性能的調制方式，在數(shù)字移動通信中已經得到了廣泛的應用。本次設計在理解QPSK調制解調原理的基。已調信號的波形，解調后的信號波形，眼圖和誤碼率。在仿真的基礎上分析比較了各。術也越來越重要。進入20世紀以來，隨著晶體管、集成電路的出現(xiàn)與普及、無線通信。特別是在20世紀后半葉，隨著人造地球衛(wèi)星的發(fā)射，大規(guī)模集成

　　

【正文】 )。%225 degrees end if (imp==0)amp。amp。(p==1) d(n)=exp(j*7*pi/4)。%315 degrees end end qpsk=d。 SNR=0:30。%change SNR values BER1=[]。 SNR1=[]。 SER=[]。 SER1=[]。 sigma1=[]。 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %Rayleigh multipath/AWGN(Additive White Gaussian Noise) %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% for SNR=0:length(SNR)。%loop over SNRchange SNR values (0,5,10 etc dB) sigma = sqrt(^(SNR/))。 sigma=sigma/2。%Required a division by 2 to get close to exact solutions(Notes)WHY? %Is dividing by two(2) legitimate? %sigma1=[sigma1 sigma]。 %add Rayleigh multipath(no LOS) to signal(qpsk) x=randn(1,nr_symbols)。 y=randn(1,nr_symbols)。 ray=sqrt(*(x.^2+y.^2))。%variance= theoritical PDF closely 20 mpqpsk=qpsk.*ray。 %add noise to QPSK Gray coded signals with multipath mpsnqpsk=(real(mpqpsk)+sigma.*randn(size(mpqpsk))) +i.*(imag(mpqpsk)+sigma.*randn(size(mpqpsk)))。 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %Receiver %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% r=mpsnqpsk。%received signal plus noise and multipath %DetectorWhen Gray coding is configured as shown, the detection process %bees fairly simple as shown. A system without Gray coding requires a much %more plex algorithim detection method bhat=[real(r)0。imag(r)0]。%detector bhat=bhat(:)39。 bhat1=bhat。%039。s and 139。s ne=sum(b~=bhat1)。%number of errors BER=ne/nr_data_bits。 SER=ne/nr_symbols。%consider this to be Ps=log2(4)*Pb=2*Pb SER1=[SER1 SER]。 BER1=[BER1 BER]。 SNR1=[SNR1 SNR]。 end %Notes: Theoritical QPSK EXACT SOLUTION for several SNR=Eb/No points on BER/SER plot %Assuming Gray coding and AWGN %Pb=Q(sqrt(2SNRbit)) %Ps=2Q(sqrt(2SNRbit))[(sqrt(2SNRbit))] %SNR=7dB %SNRbit=10^(7/10)= get ratio %Pb=Q(sqrt(2*SNRbit))=Q(sqrt())= (bit error rate) %where Q=.5*erfc(sqrt()/) %Ps=2*^2=2*()()^2= (symbol error rate) %SNR=9dB %SNRbit=10^(9/10)= get ratio %Pb=Q(sqrt(2*SNRbit))=Q(sqrt())= (bit error rate) 21 %Ps=2*^2=2*()()^2= (symbol error rate) %0,1,2,3,4,5,6,8,10,11,12 You can do the rest of these with a loop and hold %or hand plot on Simulation of BER/SER for QPSK with Gray coding %(Rayleigh multipath and AWGN) graph 2 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %Plots %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% figure(1)。 plot(d,39。o39。)。%plot constellation without noise axis([2 2 2 2])。 grid on。 xlabel(39。real39。)。 ylabel(39。imag39。)。 title(39。QPSK constellation39。)。 figure(2)。 semilogy(SNR1,BER1,39。*39。,SNR1,SER1,39。o39。)。 grid on。 xlabel(39。SNR=Eb/No(dB)39。)。 ylabel(39。BER/SER39。)。 title(39。Simulation of BER/SER for QPSK with Gray coding( Rayleigh multipath and AWGN)39。)。 legend(39。BERsimulated39。,39。SERsimulated39。)。 figure(3) plot(real(qpsk))。 grid on。 axis([1 200 2 2])。 title(39。QPSK symbols39。)。 xlabel(39。symbols39。)。ylabel(39。Amplitude39。)。 figure(4) plot(20*log10(abs(ray)))。 grid on。 axis([1 200 30 10])。 title(39。Rayleigh Fading Envelope(variance=)39。)。 xlabel(39。symbols39。)。ylabel(39。Amplitude/RMS(dB)39。)。 22 %References %This website shows Matlab code for various fading channels that may be helpful % or %search the web for Mobile Radio Channels Modeling in MatlabNikolay KOSTOV. If %you go through and understand this paper, I39。m sure it will be helpful. I even learned %how to use inf. %PROAKIS, Digital Communications 4th ed. (chapter 14) Fading Multiphase Signals