phase_shift.m

相移方法降低OFDM旁瓣

function returna = phase_shift(q1,q2);
%UNTITLED1 Summary of this function goes here
%  Detailed explanation goes here
%----------------DVB-T 2K Transmission----------------
% clear all;
% close all;

%-------------------DVB-T Parameters------------------
% Tu=224e-6;              %useful OFDM symbol period
% T=Tu/256;               %baseband elementary period
T=(1/4.125)*1e-6;
G=1/8;                  %choice of 1/4, 1/8, 1/16, and 1/32
% delta=G*Tu;             %guard band duration
% Ts=delta+Tu;            %total OFDM symbol period
M=128;                  %number of subcarriers
FS=128;                  %IFFT/FFT length
Ts=T/M;
% q=5;                    %carrier period to elementary period ratio
% fc=q*1/T;               %carrier frequency
% Rs=4*fc;                %simulation period
Ns=20;
N1=20;
M1=12;
K=1;
P=4;
% SNR=10;
t=0:T/M:((M-1)/M)*T;
L=2.^10;
Q1=q1;
Q2=q2;

% tt=0:T/2:Tu;

%--------------------Data Generator-------------------
sigSource=-1+2*round(rand(1,M*Ns*2));
sigBit=reshape(sigSource,M,Ns*2);
for i=1:Ns
    tempI(:,i)=sigBit(:,2*i-1);
    tempQ(:,i)=sigBit(:,2*i);
end
tempA=tempI+tempQ.*j;
tempX=[tempA(1:N1,:);zeros(M1,Ns);tempA((N1+M1+1):M,:)];
for k=1:K
    pk=[zeros(N1-Q1,1);(floor(P*rand(1,Q1)))';zeros(M1,1);(floor(P*rand(1,Q2)))';zeros(M-N1-M1-Q2,1)];
    p1k=(exp(j*2*pi/P)).^pk;
    for  i=1:Ns
        tempX1(:,i)=tempX(:,i).*p1k;      
    end
    tempY=ifft(tempX1);
    % tempY=[tempY1;zeros((1024-M),Ns)];
    % tempB=[tempY(FS-G*FS+1:FS,:);tempY];
    y=reshape(tempY,1,M*Ns);
    pwk(:,k)=pwelch(y,[],[],L,M/T);
end
% pwk1=mean(pwk(:,1));k1=1;
% for k=1:K
%     if (mean(pwk(:,k))<pwk1);
%         pwk1=mean(pwk(:,k));
%         k1=k;
%     end
% end
% pw=pwk(:,k1);
for k=1:K
    av=0;                   %基准线
   for i=1:floor(L*N1/M);
       av=pwk(i,k)+av;
   end
   for i=ceil(L*(N1+M1)/M):L;
       av=pwk(i,k)+av;
   end
   av=10*log10(av/(floor(L*N1/M)+L-ceil(L*(N1+M1)/M)+1));
 
   pwk2(:,k)=10*log10(abs(pwk(:,k)))-av;
end
% pwk1=mean(pwk2(160:250,1));k1=1;
% for k=1:K
%     if (mean(pwk2(160:250,k))<pwk1);
%         pwk1=mean(pwk2(160:250,k));
%         k1=k;
%     end
% end

for k=1:K;   %K=1
    v=0;
  for  i=2:L-1;
     if (pwk2(i,k)>=pwk2(i-1,k))&(pwk2(i,k)>=pwk2(i+1,k))&(pwk2(i,k)<-8); %计算旁瓣
       v=v+1;a(v)=pwk2(i,k);
     end
  end
end

a1=a(round(v/2));
a2=count(tempX);
returna=abs(a2)-abs(a1);

% My_OFDM1(tempX);
% 
%  k=0:L-1;w=(2*pi/L)*k;
%  figure(1)
%  subplot(1,2,2)
%  plot(w/(2*pi*Ts),pw);
%  title('with phase shift');
%  grid on;
%  ylabel('Power Spectrum (dBr)');
%  xlabel('Frequency(Hz)');
%  axis([0,6e8,-25,5]);
%  hold on;