IFFT circular shifting problem

Hi all,This is Yugandhar. I am working on communication system design. In this process I am using IFFT at the receiving end. I am sending one EM signal into the medium; it will reflect from the medium of discontinuity. But I am unable to get the time difference between the incident to reflected signals as expected. I have used the circular shift, but I am confusing how many samples I have to shift. It is like trail and error for me. Is there any rule to shift. How to resolve these issues. Can anyone help me. I am attaching the code. if true % codeclc; clear all; close all; Co=3e8; fc = 10e9; % center frequency f1 = 4e9; % start freq f2 = 16e9; % stop freq f0 = f2; % fmax srate = 7; % sampling rate, fs=srate*f0 fs = srate*f0; % sampling frequency N = 1024; %Number of points in the DFT d1=700*1e-3; df = fs/N; % sampling in freq (delta_f) dt = 1/fs; % sampling interval in seconds Tv = (0:N-1)*dt; % time vector (window span:[0,N*dt]sec) % dt=1e-12; % fs=1/dt; % N = round(Tr/dt); % Tv=(0:N-1)*dt; % df = fs/N; % Variables used for window creation n1 = round(f1/df); n2 = round(f2/df); n3 = round(fs/2/df); fvec = linspace(0,fs,N); er2=4.5; e0=10; % Intrinsic impedances of the mediums eta1= 120*pi; eta2= eta1/sqrt(er2); % Reflection and transmission coefficients calculation tau12= (2*eta2)/(eta2+eta1); gamma0=(eta2-eta1)/(eta2+eta1); % Window creation to apply in the lower side of the DGFspectrum M = (n2-n1)+1; Wf0= [zeros(1,n1-1),window(@chebwin,M)',zeros(1,N-n2)]; %Window creation to apply in the higher side of the DGFspectrum Wfh= [zeros(1,N-n2),window(@chebwin,M)',zeros(1,n1-1)]; n=0; for freq=fvec omega = 2*pi*freq; % angular frequency beta= omega/Co; % phase constant of the second medium n=n+1; % gamma(1,n)= (gamma0)*exp(-1i*2*beta*d1); Ei(1,n)=e0*exp(-1i*beta*d1); Er(1,n)=gamma0.*(e0*exp(1i*beta*d1)); end Xf2(1,:)= Ei(1,:)+Er(1,:); % XWf = filterd output from window applied at LSB Spectrum XWf0(1,:) = Wf0.*Xf2(1,:); % XWfh = filterd output from window applied at HSB Spectrum XWfh(1,:) = Wfh.*Xf2(1,:);

% XWF = Filtered output of the DGF Spectrum XWF0(1,:) =(XWfh(1,:)+XWf0(1,:)); %time domain signal obtained at the receiver end xwt1(1,:) = ifft(XWF0(1,:),N); % xwt1 = circshift(real(xwt1),[1,-floor(N/2)])

figure, plot(Tv,real(xwt1(1,:))); grid on; end