I am trying to simulate an MC-CDMA system. I have NXK matrix $S$ which consists of subcarriers ($s_n,_k$ represents subcarrier $n$ of user $k$) and KX1 vector $X$ consists of user symbols. So my received signal is $Y=SX+N$. To include the channel response I am confused in flat fading and frequency selective fading.
$\:$ For flat fading i.e., coherence bandwidth $>$ signal bandwidth, and I have a 3 tap channel impulse response in time domain. So in frequency domain I have NX1 vector $h_k$ for user $k$.
Now to include the channel fading for user $k$,
- Should I do
S(:,k) .* H(:,k) %% H is channel matrix
i.e., each subcarrier is multiplied by a different channel coefficient while coeffecients have nearly same magnitude, or S(:,k)*h(k)
i.e., multiplying whole sequence by a single coefficient. and what thath(k)
value should be ?
- Should I do
For frequency selective fading does only the values of channel coefficient will change or I will have multiple taps for each subcarrier and will need to convolve in frequency domain?