# MIMO System Model in Matlab

I have this lame doubt which has ended up confusing me which is probably trivial. I am modelling a MU-MIMO system with a Rayleigh fading channel. I have created a wanted signal as an OFDM signal, and generated a 3D Rayleigh Channel matrix over all sub carriers. I want to now multiply the transmit vector(OFDM signal) to the 3D channel matrix. Should i convert both the channel matrix and wanted signal in frequency domain and add noise

$y(f) = H(f)x(f)+n(f)$, and then convert it back to time domain $\textrm{ifft}(y(f))$ and provide an estimate using MRC, ZF or MMSE methods.

$\hat{y}(t) = H(t)’ y(t)$

Or is it just a direct multiplication of

$y(t)=H(t)x(t)+n(t)$

as i understand from most of the literature (y = H x+n)is the usual system model in time domain. If so why isn't it convolved when its combined in time domain, similar to any communication system, where the input vector is convolved with the channel matrix to obtain the output vector in time.

The noise still affects the estimated signal, of course; if the received vector is $r$, a naive ZF receiver would calculate
Since the noise $Hn$ is correlated, this receiver has terrible performance.