MATLAB实现QPSK调制与解调仿真

%QPSK Transmitter and I-Q Correlation Receiver
%JC 12/23/05-revised 2/14/06
%Run from editor debug(F5)
%m-file for simulating a QPSK transmitter and receiver by modulating with a pseudo
%random bit stream. A serial to parallel conversion of the pseudo random
%bit stream is performed with mapping of two bits per symbol(phase). A cosine and
%sine carrier is configured and the I and Q symbols modulate these
%carriers via mixers. The I and Q carriers are combined and time and frequency domain
%plots are provided showing key waveforms at various positions in the QPSK
%transmitter and correlation receiver. A parallel to serial conversion is used on the
%output of the receiver. The simulation uses a serial "passband" approach.
%In  other words a carrier is used. Notes are provided at the end of the m-file.
%===================================================================
clear;
fcarr=5e3;         % Carrier frequency(Hz)
N=8;         % Number of data bits(bit rate)
fs=20*1e3;     % 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)
%===================================================================
% The Transmitter.
%===================================================================
data=sign(randn(N,1))';%transpose
data1=ones(T/Ts,1)*data;
data2=data1(:);

%display input data bits in command window

data_2=data2';%transpose
data_2=data_2 >0;
Transmitted_data_bits=data_2(1:(fs)/N:end)

%Serial to parallel (alternating)
tiq = [0:Ts*2:(N*T)-Ts]';% Time vector for I and Q symbols(transpose)

bs1=data(1:2:length(data));%odd
symbols=ones(T/Ts,1)*bs1;
Isymbols=symbols(:);%I_waveform

bs2=data(2:2:length(data));%even
symbols1=ones(T/Ts,1)*bs2;
Qsymbols=symbols1(:);%Q_waveform

%generate carrier waves
%cosine and sine wave
%2 pi fc t is written as below
twopi_fc_t=(1:fs/2)*2*pi*fcarr/fs; 
a=1;
%phi=45*(pi/180)
phi=0;%phase error
cs_t = a * cos(twopi_fc_t + phi);
sn_t = a * sin(twopi_fc_t + phi);

cs_t=cs_t';%transpose
sn_t=sn_t';%transpose
si=cs_t.*Isymbols;%multiply I bitstream with cosine
sq=sn_t.*Qsymbols;%multiply Q bitstream with sine
sumiq=si+sq;%transmitter output