  In this paper, we focus on the throughput of random access with power-domain
non-orthogonal multiple access (NOMA) and derive bounds on the throughput. In
particular, we demonstrate that the expression for the throughput derived in
[1] is an upper-bound and derive a new lower-bound as a closed-form expression.
This expression allows to find the traffic intensity that maximizes the
lower-bound, which is shown to be the square root of the number of power levels
in NOMA. Furthermore, with this expression, for a large number of power levels,
we obtain the asymptotic maximum throughput that is increased at a rate of the
square root of the number of power levels.
