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function [LLR_SD,M,H_back,rx_layer_x_equalized] = LTE_detect_IA(MCS_and_scheduling,rx_user_symbols,H_est_user,LTE_params,BS_nAtPort,receiver,receiver_k,sigma_n2)
% Interference Alignment detection.
% Authors: Joerg Reitterer, jreitter@nt.tuwien.ac.at, Stefan Schwarz,
% sschwarz@nt.tuwien.ac.at
% (c) 2010 by INTHFT
% www.nt.tuwien.ac.at
nLayers = MCS_and_scheduling.nLayers;
rx_user_symbols_suppressed_interference = zeros(length(rx_user_symbols),nLayers);
rx_layer_x_equalized = zeros(length(rx_user_symbols),nLayers);
M = zeros(1,size(MCS_and_scheduling.CQI_params,2));
for i = 1:size(MCS_and_scheduling.CQI_params,2)
M(i) = MCS_and_scheduling.CQI_params(i).modulation_order;
end
switch nLayers % when layer number is unequal to codeword number we need to do something
case 2
if(MCS_and_scheduling.nCodewords == 1) % 1 codewords, 2 layers
M = [M,M];
end
case 3 % 2 codewords, 3 layers
M = [M(1),M(2),M(2)];
case 4 % 2 codewords, 4 layers
M = [M(1),M(1),M(2),M(2)];
end
bittable = false(sum(M(1:nLayers)),2^max(M));
symbol_alphabet = zeros(nLayers,2^max(M));
for i = 1:nLayers
bittable(sum(M(1:i-1))+(1:M(i)),1:2^M(i))=LTE_params.bittable{M(i)}; % Bitmapping table
symbol_alphabet(i,1:2^M(i))=LTE_params.SymbolAlphabet{M(i)}.'; % Symbol alphabet
end
LLR_SD = zeros(sum(M),length(rx_user_symbols)); % Log likelihood Ratios of the Spere decoder
l = 1:length(rx_user_symbols);
p = mod(l-1,nLayers)+1; % needed for the choice of the precoding matrix (see 3GPP TS 36.213 section 7.1.3)
k = mod(floor((l-1)/nLayers),4)+1;
if (BS_nAtPort == 2)
period = 2;
else
period = lcm(seqperiod(k),seqperiod(p));
end
H_back = zeros(l(end),size(H_est_user,2),nLayers);
for ctr = 1:l(end)
V = MCS_and_scheduling.V;
U = MCS_and_scheduling.U;
if LTE_params.IA_time_granularity == 14
time_index = 1;
elseif LTE_params.IA_time_granularity == 7
time_index = LTE_params.IA_time_granularity*(MCS_and_scheduling.slot_indices(ctr)-1)+1;
else
time_index = 1; % at the moment only slot and subframe time granularity is implemented
end
H_complete = U{MCS_and_scheduling.freq_indices(ctr),time_index}'*squeeze(H_est_user(ctr,:,:))*V{MCS_and_scheduling.freq_indices(ctr),time_index};
rx_user_symbols_suppressed_interference(ctr,:) = (U{MCS_and_scheduling.freq_indices(ctr),time_index}'*rx_user_symbols(ctr,:).');
switch receiver
case 'SSD'
rx_layer_x = pinv(H_complete)*rx_user_symbols_suppressed_interference(ctr,:).';
[Q,R] = qr(H_complete); % for SS Decoder
siz = size(R,2);
if (siz < size(R,1)) % chop off unnecessary data
R = R(1:siz,:);
Q = Q(:,1:siz);
end
LLR_SD(:,ctr) = LTE_softsphere(rx_layer_x,rx_user_symbols_suppressed_interference(ctr,:),Q,R,symbol_alphabet,bittable,nLayers,M);
case 'SSDKB'
rx_layer_x = pinv(H_complete)*rx_user_symbols_suppressed_interference(ctr,:).';
[Q,R] = qr(H_complete); % for SS Decoder
siz = size(R,2);
if (siz < size(R,1)) % chop off unnecessary data
R = R(1:siz,:);
Q = Q(:,1:siz);
end
LLR_SD(:,ctr) = LTE_softsphere_kbest(rx_layer_x,rx_user_symbols_suppressed_interference(ctr,:),Q,R,symbol_alphabet,bittable,nLayers,M,receiver_k);
case 'ZF'
inv_temp = pinv(H_complete);
rx_layer_x = inv_temp*rx_user_symbols_suppressed_interference(ctr,:).';
rx_layer_x_equalized(ctr,:) = rx_layer_x;
Hg = inv_temp*H_complete;
noise_enhancement_tmp = sum(abs(inv_temp).^2,2);
noise_enhancement = [];
for ii = 1:length(M)
noise_enhancement = [noise_enhancement;repmat(noise_enhancement_tmp(ii),M(ii),1)];
end
LLR_SD(:,ctr) = LTE_demapper(rx_layer_x,symbol_alphabet,bittable,nLayers,M,Hg,noise_enhancement);
case 'MMSE'
temp = H_complete'*H_complete;
inv_temp = (temp+sigma_n2*eye(size(temp)))^-1*H_complete';
rx_layer_x = inv_temp*rx_user_symbols_suppressed_interference(ctr,:).'; % MMSE receiver
rx_layer_x_equalized(ctr,:) = rx_layer_x;
Hg = inv_temp*H_complete;
noise_enhancement_tmp = sum(abs(inv_temp).^2,2);
noise_enhancement = [];
for ii = 1:length(M)
noise_enhancement = [noise_enhancement;repmat(noise_enhancement_tmp(ii),M(ii),1)];
end
LLR_SD(:,ctr) = LTE_demapper(rx_layer_x,symbol_alphabet,bittable,nLayers,M,Hg,noise_enhancement);
case 'MMSE_SIC' % just a hard decision SIC
% choose better stream to decode first
[C,first] = max(sum(abs(H_complete).^2,1));
if first == 1
second = 2;
bittab1 = bittable(1:M(first),:);
bittab2 = bittable(M(first)+1:M(first)+M(second),:);
else
second = 1;
bittab1 = bittable(M(second)+1:M(second)+M(first),:);
bittab2 = bittable(1:M(second),:);
end
temp = H_complete'*H_complete;
inv_temp = (temp+sigma_n2*eye(size(temp)))^-1*H_complete';
rx_layer_x = inv_temp*rx_user_symbols_suppressed_interference(ctr,:).'; % calculate MMSE solution
Hg = inv_temp(first,:)*H_complete(:,first);
noise_enhancement_tmp = sum(abs(inv_temp(first,:)).^2,2);
noise_enhancement = repmat(noise_enhancement_tmp,M(first),size(rx_layer_x,2));
LLR_temp1 = LTE_demapper(rx_layer_x(first,:),symbol_alphabet(first,:),bittab1,1,M(first),Hg,noise_enhancement);
% hard decision
symbols1 = symbol_alphabet(1,2.^(0:1:M(first)-1)*(1+sign(LLR_temp1))/2+1);
% second stream
rx_user_symbols_suppressed_interference(ctr,:) = rx_user_symbols_suppressed_interference(ctr,:)-(H_complete(:,first)*symbols1).';
inv_temp = pinv(H_complete(:,second));
rx2 = inv_temp*rx_user_symbols_suppressed_interference(ctr,:).';
Hg = inv_temp*H_complete(:,second);
noise_enhancement_tmp = sum(abs(inv_temp).^2,2);
noise_enhancement = repmat(noise_enhancement_tmp,M(second),length(rx2));
LLR_temp2 = LTE_demapper(rx2,symbol_alphabet(second,:),bittab2,1,M(second),Hg,noise_enhancement);
if first == 1
LLR_SD(:,ctr) = [LLR_temp1;LLR_temp2];
else
LLR_SD(:,ctr) = [LLR_temp2;LLR_temp1];
end
end
end