cdmasim.m

CDMA的Matlab例程

%主程序
%File:  cdmasim.m
function [BER,ErrorRun]=cdmasim(N,SF,EbNo,...
    NumInterferers,MPathDelay,Kfactor_dB)
rand('state',sum(100*clock));randn('state',sum(100*clock));
NIterate=1e3;          %default block size
NumberOfIterations=ceil(N/NIterate);
ErrorState=0;ErrorRun=[];RunCount=1;%itialize
Kfactor=10^(Kfactor_dB/10);%linear units
EbNolinear=10^(EbNo/10);%linear units
MPathComponents=length(MPathDelay);
%
%Determine amplitude in multipath components and store as
%vector. Determine the total power in all the scattered components.
%Determine LOS component.
%
MPathAmp(2:MPathComponents)=rand(MPathComponents-1,1);
ScatPower=MPathAmp*MPathAmp.';
MPathAmp(1)=sqrt(ScatPower*Kfactor);%LOS component
%
%Determine which component has the largest energy (amplitude).
%Normalize vector so that strongest component has unit amplitude.
%
[fee MaxComponent]=max(MPathAmp);MPathAmp=MPathAmp/fee;
%
%Design IIR filter for fading signal.
%
FilterOrder=4;Ripple=0.5;BW=0.01;%filter parameters
[b,a]=cheby1(FilterOrder,Ripple,BW);%4th order filter
%
%Error checking.
%
if NumInterferers>(SF-1)
    error(['NumInterferers must not exceed',int2str(SF-1),'.'])
end
if length(MPathDelay)~=length(MPathAmp)
    error('MPathDelay and MPathAmp must have the same length.')
end
if min(MPathDelay)<0
    error('MPathDelay must not have negative components.')
end
fee=diff(MPathDelay);
if min(fee)<=0
    error('MPathDelay must be monotonically increasing.')
end
clear fee
%
%End Error Checking
%
%Generate spreading sequences. The spreading sequences for 
%the interferers are shifted versions of the desired sequence
%with a shift offset.
%
DesiredSequence=MSequence(SF+1);%desired signal
offset=fix(length(DesiredSequence)/(NumInterferers+1));
M=length(DesiredSequence);
for k=1:NumInterferers
    InterfererSequence(k,:)=[DesiredSequence(M-(k-1)*offset:M)...
        DesiredSequence(1:M-1-(k-1)*offset)];
end
%
%The simulation loop begins here.
%
zf=zeros(FilterOrder,MPathComponents);
for cnt=1:NumberOfIterations
    %
    %Generate and spread symbols for dsired and interfering users.
    %
    DesiredSymbols=sign(rand(1,NIterate)-0.5);
    InterferingSymbols=sign(rand(NumInterferers,NIterate)-0.5);
    DesiredChips=reshape(DesiredSequence.'*DesiredSymbols,1,...
        M*NIterate);
    for k=1:NumInterferers
        InterferingChips(k,:)=reshape(InterfererSequence(k,:).'*...
            InterferingSymbols(k,:),1,M*NIterate);
    end
    %
    %Generate noise.
    %
    NoiseAmplitude=sqrt(SF/(2*EbNolinear));
    MaxDelay=max(MPathDelay);
    DesiredNoise=NoiseAmplitude*randn(1,M*NIterate+MaxDelay);
    %
    %Apply multipath.
    %
    MPathLinAmp=MPathAmp;
    MPathComponents=length(MPathDelay);
    DesiredMPathSignal=zeros(1,M*NIterate+MaxDelay);
 if NumInterferers>0,
     InterferingMPathSignal=...
         zeros(NumInterferers,M*NIterate+MaxDelay);
     for k=1:MPathComponents
         index=1+MPathDelay(k):NIterate*M+MPathDelay(k);
         InterferingMPathSignal(:,index)=...
             InterferingMPathSignal(:,index)+...
             MPathLinAmp(k)*InterferingChips;
     end
 end
 for k=1:MPathComponents
     if k==1,fading=ones(1,M*NIterate);
     else
         fading=randn(size(DesiredSymbols))+...
             j*randn(size(DesiredSymbols));
         [fading zf(:,k)]=filter(b,a,fading,zf(:,k));
         fading=interp(fading,SF);
         fading=abs(fading/sqrt(mean(fading.*conj(fading))));
     end
     if k==MaxComponent
         fadesign=sign(fading);
     end
     faa(k,:)=MPathLinAmp(k)*fading;
     index=1+MPathDelay(k):NIterate*M+MPathDelay(k);
     DesiredMPathSignal(index)=...
         DesiredMPathSignal(index)+...
         (MPathLinAmp(k)*fading).*DesiredChips;
 end
 %
 %Add intererence and noise
 %
 if NumInterferers>0
     IncomingSignal=DesiredMPathSignal+...
         sum(InterferingMPathSignal,1)+DesiredNoise;
 else
     IncomingSignal=DesiredMPathSignal+DesiredNoise;
 end
 %
 %Receive and detect incoming signal.
 %
 index=1+MPathDelay(MaxComponent):M*NIterate+...
     MPathDelay(MaxComponent);
 IncomingChips=reshape(fadesign.*...
     IncomingSignal(index),M,NIterate);
 DespreadSymbols=DesiredSequence*IncomingChips;
 DetectedSymbols=sign(DespreadSymbols);
 %
 %Compute Bit Error Rate
 %
 ErrorVector=0.5*abs(DetectedSymbols-DesiredSymbols);
 ErrorsIterate(cnt)=sum(ErrorVector);
 BERIterate(cnt)=ErrorsIterate(cnt)/NIterate;
 for k=1:NIterate
     if (ErrorVector(k)==0)&(ErrorState==0)
         RunCount=RunCount+1;
     elseif (ErrorVector(k)==0)&(ErrorState==1)
         ErrorRun=[ErrorRun RunCount];
         RunCount=1;ErrorState=0;
     elseif (ErrorVector(k)==1)&(ErrorState==0)
         ErrorRun=[ErrorRun RunCount];
         RunCount=1;ErrorState=1;
     elseif (ErrorVector(k)==1)&(ErrorState==1) 
         RunCount=RunCount+1;
     else
         s1=sprintf('ErrorVector(%d)=%d,ErrorState=%d! Unexpected Condition!');
         error(s1);
     end
 end
end
Errors=sum(ErrorsIterate);BER=mean(BERIterate);
ErrorRun=[ErrorRun RunCount];
%End of funcion file.