Non-orthogonal multiple access (NOMA) has been
investigated to support massive connectivity for Internet-of-
things (IoT) networks. However, since most IoT devices suffer
from limited power and decoding capabilities, it is not desirable
to pair a large number of devices simultaneously, which en-
courages two-user NOMA grouping. Additionally, most existing
techniques have not considered the diversity in the target QoS
of IoT devices, which may lead to spectrum inefficiency. Few
investigations have partially considered that issue by using an
order-based power allocation (OPA) approach, where the power
is allocated according to the order to the user’s target throughput
within a priority-based NOMA (PNOMA) group. However, this
does not fully capture the effects of diversity in the values of
the users’ target throughputs. In this work, we handle both
problems by considering a throughput-based power allocation
(TPA) approach, that captures the QoS diversity, within a three-
users PNOMA group as a compromise between spectral efficiency
and complexity. Specifically, we investigate the performance
of a time-division PNOMA (TD-PNOMA) scheme, where the
transmission time is divided into two-time slots with two-users
per PNOMA group. The performance of such TD-PNOMA is
compared with a fully PNOMA (F-PNOMA) scheme, where
the three users share the whole transmission time, in terms
of the ergodic capacity under imperfect successive interference
cancellation (SIC). The results reveal the superiority of TPA
compared with OPA approach in both schemes, besides that the
throughput of both schemes can outperform each other under
imperfect SIC based on the transmit signal-to-noise ratio and
the deployment scenarios.