otfs_mimo_1.m

clear;
M = 4;
N = 4;
W = exp(1j * 2 * pi * (0:(M*N-1))' * (0:(M*N-1)) / N / M) / sqrt(N * M);

Nt = 3;
Nr = 2;

## In the slide 39 of this:
## https://ecse.monash.edu/staff/eviterbo/OTFS-VTC18/Tutorial_ICC2019___OTFS_modulation.pdf
## Assume that s is MNN_t cross 1

## H = [. -> each entry becomes Nr x Nt matrix]
## -> H size is MNN_r x MNN_t

L = 1;
H_1 = [1 2 3;-3 4 2];
P = zeros(M*N);
P(1,end) = 1;
P(2:(M*N),1:(M*N-1)) = eye(15);
D = diag(exp(1j * 2 * pi * 1 * (0:(M*N-1))/(M*N)));
## We will construct P_mimo which is a MNNr x MNNr matrix
P_mimo = kron(P, eye(Nr));
H_1_mimo = kron(eye(M*N), H_1);
D_mimo = kron(D, eye(Nt));
## Sanity check:
disp(max(max(abs(H_1_mimo - kron(W', eye(Nr)) * H_1_mimo * kron(W, eye(Nt))))));
H_1_rect_eff = kron(W, eye(Nr)) * P_mimo * kron(W', eye(Nr)) * H_1_mimo * kron(W, eye(Nt)) * D_mimo * kron(W', eye(Nt));