正交相移键控（Quadrature Phase Shift Keying，QPSK）是一种数字调制方式。它分为绝对相移和相对相移两种。由于绝对相移方式存在相位模糊问题，所以在实际中主要采用相对移相方式DQPSK。
QPSK是一种四进制相位调制，具有良好的抗噪特性和频带利用率，广泛应用 于卫星链路、数字集群等通信业务。
程序主入口：
clear; SNR = 0:1:10; % Range of SNR values, in dB. for n = 1:length(SNR) pbawgn(n) = QPSK_AWGN_Simu(SNR(n)); pbrayleigh(n) = QPSK_Rayleigh_Simu(SNR(n)); pbricean(n) = QPSK_Ricean_Simu(SNR(n)); end % Compute theoretical performance results, for comparison. BERtheoryAWGN = berawgn(SNR,'psk',4,'nondiff'); BERtheoryRayleigh = berfading(SNR,'psk',4,1); BERtheoryRice = berfading(SNR,'PSK',4,1,4); % Plot BER results. semilogy(SNR,BERtheoryAWGN,'k-',SNR,pbawgn,'k*',SNR,BERtheoryRayleigh,'b-',SNR,pbrayleigh,'b*',SNR,BERtheoryRice,'m-',SNR,pbricean,'m*'); legend('Theoretical AWGNBER','Simulated AWGNBER','Theoretical rayleighBER','Simulated rayleighBER','Theoretical riceanBER','Simulated riceanBER'); xlabel('SNR (dB)'); ylabel('BER'); title('BER of awgn,rayleigh,ricean');
