% Zero Force Decode
function X_receive = ZF_decode(H11, H12, H21, H22, X_odd, X_even, Ncarr)

% prepare for normalization                        h = h11*conj(h12)+h21*conj(h22)
H = H11.*conj(H12) + H21.*conj(H22);

% linear combining
X_est1 = (conj(H12).*X_odd.' + H21.*X_even')./H;   % conj(h12)*R1 + h21*conj(R2) = (h11*conj(h12)+h21*conj(h22))*X1
X_est2 = (conj(H22).*X_odd.' - H11.*X_even')./H;   % conj(h22)*R1 - h11*conj(R2) = (h11*conj(h12)+h21*conj(h22))*X2

% equlization in frequence domain
X_receive(1:2:Ncarr) = X_est1;                     % the received symbols
X_receive(2:2:Ncarr) = X_est2;