functionZFBF.m

function wZFBF = functionZFBF(H,D)
%Calculates the zero-forcing beamforming (ZFBF) vectors for a
%scenario where all or a subset of antennas transmit to each user.
%
%This is version 1.0.
%
%INPUT:
%H  = Kr x Kt*Nt matrix with row index for users and column index
%     transmit antennas
%D  = Kt*Nt x Kt*Nt x Kr diagonal matrix. Element (j,j,k) is one if j:th
%     transmit antenna can transmit to user k and zero otherwise
%
%OUTPUT:
%wZFBF = Kt*Nt x Kr matrix with normalized ZFBF




%Number of users
Kr = size(H,1);

%Total number of antennas
N = size(H,2);

%If D matrix is not provided, all antennas can transmit to everyone
if nargin<2
    D = repmat( eye(N), [1 1 Kr]);
end

%Pre-allocation of MRT beamforming
wZFBF = zeros(size(H'));

%Computation of ZFBF, based on Definition 3.4
for k = 1:Kr
    effectivechannel = (H*D(:,:,k))'; %Effective channels
    channelinversion = effectivechannel/(effectivechannel'*effectivechannel); %Compute zero-forcing based on channel inversion
    wZFBF(:,k) = channelinversion(:,k)/norm(channelinversion(:,k));  %Normalization of zero-forcing direction
end