Multi-user Uplink Channel

We first consider 2-user model. The baseband discrete-time model for the uplink AWGN channel with two users is
$$
y[m]=x_1 [m] + x_2 [m] + w[m]
$$
where $w[m] \sim \mathcal{C N}\left(0,N_0\right)$ is i.i.d. complex Gaussian noise. User $k$ $\left(k=1,2\right)$ has an average power constraint of $P_k$.

In the multiuser case, the concept of *Channel Capacity* is extended to *Capacity Region*: this is the set of all pairs $\left(R_1, R_2\right)$ such that simultaneously user 1 and 2 can reliably communicate at rate $R_1$ and $R_2$, respectively.

In the following two slides, principles of Orthogonal Multiple Access (OMA) and Non-Orthogonal Multiple Access(NOMA) will be discussed.