hi all , Recently , I have generated a OFDM signal , but meanwhile I have noticed that my Analytical & Computer Simulation of my SER are totally difference, Moreover , the Numbers of Errors in my signal also quite large, therefore i am wondering whether there are some Errors in my signal detection or the progress of generate OFDM signal. Actually I should generate channel estimation of OFDM signal , but i have stuck at this part quite long time , therefore i am really need help from all of you with my sincere. Thank you. Eric ********************************************************************************************* %generate 64 QAM signal aqam=[-7 -5 -3 -1 1 3 5 7]; A=repmat(aqam,8,1); B=flipud(A'); konst_qam=A+j*B; konst_qam=konst_qam(:); qam=konst_qam(randint(1024,1,64)+1); %Random Generate 1024 symbol of 64 QAM signal F=ifft(eye(1024)); %Convert the signal from Frequency domain to Time domain Fs=F*qam; %Fs1=repmat(Fs,1,100); C=zeros(1024,1); R=zeros(1,1024); for(i=1:6) h(1,i)=rand+j*rand; end R(1,1:6)=h; C(1:6,1)=h'; H=toeplitz(C,R); x=H*Fs; %generate Noise n=randn(size(x))+j*randn(size(x)); %randn generates Gaussian distributed noise SNR=20; %SNR-ratio p=std(x)/(std(n)*10^(SNR/20)); %add noise to signal x1=x+n*p; %Receiver F1=fft(eye(1024)); %Convert the Signal back from Time Domain to Frequency Domain. y1=F1*x1; D=F1*H*F; %Equalization s_final1=(inv(D))*y1; %Symbol Detection s_f1=repmat(s_final1,1,64).'; konst_block=repmat(konst_qam,1,1024); distance1=abs(s_f1-konst_block); [z1,ind_2]=min(distance1); qam_det1=konst_qam(ind_2); %Theoretical SER d=2; sigma=std(real(n*p)); Q=0.5*erfc(d/(sqrt(2)*2*sigma)); sep_theo1=3.5*Q-3.0625*Q^2; %Simulated SER error=sum(qam~=qam_det1); sep=error/1024;

# Trouble in generate SER in OFDM

Started by ●February 26, 2007

Posted by ●February 26, 2007

On Feb 26, 9:42 am, "ericknightX" <wil...@gmail.com> wrote:> hi all , > > Recently , I have generated a OFDM signal , but meanwhile I have noticed > that my Analytical & Computer Simulation of my SER are totally difference, > Moreover , the Numbers of Errors in my signal also quite large, therefore i > am wondering whether there are some Errors in my signal detection or the > progress of generate OFDM signal. Actually I should generate channel > estimation of OFDM signal , but i have stuck at this part quite long time > , therefore i am really need help from all of you with my sincere. > > Thank you. > > Eric >Eric, Your code is quite confusing to follow. I'm not entirely certain what the F=ifft(eye(.....))) is all about? When you say that you have generated an OFDM signal have you actually veriifed the performance with the theoretical AWGN, without sticking it through a channel? Have a look at this link for a freq flat fading to get some ideas and then come back with questions. http://groups.google.com/group/comp.dsp/browse_frm/thread/febe0248d368fbe8/0f61c99347e8de3a?lnk=gst&q=Maybe+a+short+example+will+help%3F+&rnum=1#0f61c99347e8de3a col

Posted by ●February 27, 2007

Thanks col , I have checked your code , & i think i have get some idea. I am wondering that maybe i have the same problem with Shahin. Actually i have skipped the step in insert cyclic prefix & remove cyclic prefix in my code , since i assume the process is ideal. Therefore there is no IBI. Meanwhile , there is only the AWGN might affect my SER , but i really no idea , why the theoretical SER & simulate SER is totally difference , & the number of error is too large. the F=ifft(eye(.....))) & direct ifft the transmitted signal actually is the same , since i am try to do in block transmission & equalization. And I am referring this Journal http://www.ece.iastate.edu/~zhengdao/group/publications/papers/wagi00m.pdf Regards Eric