I have a question about using MIMO with DS-CDMA. suppose we are using
4 TX antennas, and
4 RX antennas, then the Reyleigh channel generated randomly of MIMO system will be of dimension
H = [4x4], assuming also the transmitted signal using QAM modulation is
x done as below:
x = [0.7 + 0.7i; 0.7 - 0.7i; -0.7 + 0.7i; -0.7 -0.7i];
So the received signal
r is supposed to be
r = H*x , which is of dimension of [4x1].
Now, suppose we are spreading that signal with PN/walsh code of dimension [4x1], by using the function of
"kron" in MATLAB, so the dimension of the new transmitted signal will be [16x1], equivalent that
x_1 = kron(x,c); where
c is the code used to spread the signal before transmission.
My question is, how can we transmit that signal after spreading it
x_1 over the noted channel
H of dimension H with dimension