git-svn-id: http://svn.eurecom.fr/openair4G/trunk@6270 818b1a75-f10b-46b9-bf7c-635c3b92a50f

targets/PROJECTS/CORRIDOR/init_dpss.m

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+function p_dpss = init_dpss(p,tau_max)
+
+%% init DPSS
+% channel parameters
+theta_max = tau_max * p.frame_length*100 / p.useful_carriers; % TS = 1/(p.frame_length*100)
+N_sub = floor(theta_max*p.useful_carriers)+1; % number of approximate subspace dimensions
+%N_sub = 1;
+
+% DPSS generation
+nDmax=min(ceil(N_sub*1.25),p.useful_carriers);
+[Udps,Sdps]=dpss(p.useful_carriers,theta_max*p.useful_carriers/2,nDmax);
+
+% the fftshift is needed dependig in which format the frequency response is used 
+%V=fftshift(diag(exp(-2*pi*1i*theta_max/2*(0:(p.nN-1))))*Udps);
+p_dpss.V=diag(exp(-2*pi*1i*theta_max/2*(0:( p.useful_carriers-1))))*Udps;
+
+% compute the optimal subspace dimension based on the expected SNR
+p_dpss.SNR=0:30;
+for SNR=p_dpss.SNR
+    % calculate optimum subspace dimension as bias variance tradeoff for a
+    % given noise variance (assuming pilot symbols with energy one)
+    sigma2 = 10.^(-SNR/10);
+    [~,p_dpss.Dopt(SNR+1)]=findminimumd(sigma2, p.useful_carriers,nDmax,1/theta_max*Sdps);
+end
+
+% % precompute the filters for DPSS estimation for the required number of
+% % basis function
+% Dvec = min(Dopt):max(Dopt);
+% for ind=1:length(Dvec)
+%     Dind = Dvec(ind);
+%     
+%     for itx=1:p.nant_tx
+%         % f_start and t_start indicate the start of the pilots in time
+%         % and frequency according to the specifications (see .doc file).
+%         % t_start has to be >=2, since the first symbol is the PSS.
+%         f_start = mod(itx-1,2)*2+1;
+%         t_start = floor((itx-1)/2)+1;
+%         
+%         % filter for DPSS channel estimation
+%         M = conj(diag(squeeze(transmit_f(itx,t_start,f_start:4:end))) * V(f_start:4:end,1:Dind));
+%         Mpinv = (M'*M)\M.';
+%         % to compute the basis coefficients do
+%         % psi = Mpinv*(symb0(2:6:end));
+%         
+%     end
+%     
+% end