  In this paper, we develop a resource allocation technique for a hybrid time
division multiple access (TDMA) - non-orthogonal multiple access (NOMA) system
with opportunistic time assignment. In particular, the available transmission
time is divided into several time-slots, through which multiple users are
served by exploiting power-domain NOMA. To fully exploit underlying benefits of
this hybrid TDMA-NOMA system, we utilize the available resources efficiently by
jointly allocating transmit power and time-slots to several groups of users in
the system. Furthermore, these resources are allocated to maximize minimum rate
of the users in the system. However, this max-min resource allocation problem
is non-convex due to coupled design parameters of time and power allocations.
Hence, we exploit a novel second-order cone formulation to overcome this
non-convexity issue and develop an iterative algorithm to realize a solution to
the original max-min problem. Simulation results show that this joint resource
allocation technique has a considerable performance enhancement in terms of
both minimum achieved rate and overall system throughput compared to that of
the conventional resource allocation technique where equal time-slots are
assigned to the groups of users.
