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numbits 
bits=rand(1,numbits)>0.5; 
nb=length(bits);%number of bits 
ns=ceil(nb/2);%number of symbols 
 
b0=zeros(1,ns*2);%zero padding 
b0(1:nb)=bits; 
 
j=sqrt(-1); 
for s=1:ns 
     ba=b0(((s-1)*2)+1);%分别取数据流第1个 
     bb=b0(((s-1)*2)+2);%分别取数据流第2个 
     k=bb+ba*2; 
     p=((pi/4)*(2*k-1))-pi ;%相位 
      
     Sc(s)=cos(p);%同相成分 
     Ss(s)=sin(p);%正交相成分 
     S(s)=Sc(s)+j*Ss(s);%合成 
end 
fp=1e9;%central frequency 
fc=50e9;%sampling frequency 
T0=242.4e-9;%information lenght 
TP=60.6e-9;%cyclic prefix 
TG=70.1e-9;%total guard time 
A=1;%amplitude of the rectangular impulse 
%response 
N=128; %number of carriers of the OFDM system 
%------------ 
% Step One OFDM modulator 
%------------ 
tc=T0/N;%chip time 
ntcp=floor(TP/tc);%number of tones of the cyclis prefix 
n=(-ntcp+1:1:N);%tone counter 
NT=length(n);%total number of tones per symbor 
nb=ceil(length(S)/N);%number of OFDM blocks to be transmitted 
S0=zeros(1,nb*N);%zero padding 
S0(1:length(S))=S; 
dt=1/fc;%sampling period 
if ntcp>0 % coming into the data area 
    tc=(T0+TP)/NT;%tone duration  
                  %NT=length(n);%total number of tones per symbor 
                  %n=(-ntcp+1:1:N);%tone counter 
end 
tonesamples=floor(tc/dt);%samples per tone 
toneres=floor((TG-TP)/dt);%samples for the residual part 
symsamp=(tonesamples*NT)+toneres; 
%number of samples representing one OFDM symbol 
totsamp=symsamp*nb; 
%number of samples representing the transmitted signal  
X=[zeros(1,totsamp)']; 
for b=1:nb 
    c=S0((1+(b-1)*N):(N+(b-1)*N));%blick extraction 
    %Serial to paralllel conversion and zero padding 
    A=length(c); 
    a1=floor(A/2); 
    a2=A-a1; 
    FS=2*A; 
    Czp=zeros(FS,1); 
    Czp(1:a1)=[c(1:a1).']; 
    Czp(FS-a2+1:FS)=[c(A-a2+1:A).']; 
    C=ifft(Czp);%ifft of the zero-padded input 
    if ntcp>0%insertion of the cyclic prefix 
        C1=zeros(length(C)+2*ntcp,1); 
        C1(1:(2*ntcp))=C(2*N+1-(2*ntcp):2*N); 
        C1(2*ntcp+1:length(C1))=C; 
    else 
        C1=C; 
    end 
    % 
    zp=floor(tonesamples/2); 
    C2=[C1.';zeros((zp-1),length(C1))]; 
    C3=C2(:); 
    g=ones(1,zp); 
    C4=conv(g,C3); 
    C4=C4(1:(zp*NT*2)); 
    ics=1+(b-1)*symsamp+toneres; 
    X(ics:ics+length(C4)-1)=C4; 
end%for b=1:nb 
    XM=X';%Parallel to Serial conversion 
        XM=XM(1:totsamp); 
I=real(XM); 
Q=imag(XM); 
%carrier modulation 
time=linspace(0,totsamp*dt,length(I)); 
SI=I.*(cos((2*pi*fp).*time)); 
SQ=Q.*(sin((2*pi*fp).*time)); 
stx=SI-SQ;