NOMA and Coded Multicasting in Cache-Aided Wireless Networks

Coded multicasting is considered to be an effective
approach to simultaneously serve multiple users in the same
frequency/time/code resource, which is made possible by exploiting
the information available in users’ caches. Recently,
non-orthogonal multiple access (NOMA) has emerged as an
alternative transmission technique for cache-aided network. In
cache-aided NOMA system, cache-enabled interference cancellation
(CIC) is employed to cancel the interference using the
information in the cache, and thus enhance the user transmission
rate, particularly for the weak users. Despite the enhanced
spectral efficiency offered by both techniques, complexity issue
arises from handling large number of users. Therefore, user
pairing/clustering should be employed to limit the number of
users served in the same time-frequency resource. However,
the key question is which delivery technique performs better
under different pairing scenarios. In this paper, the performance
of NOMA and coded multicasting for two-user pairing are
investigated in terms of probability of sum rate comparison and
outage probability. In order to exploit the benefits of NOMA and
coded multicasting, we also propose a hybrid delivery scheme,
which select either NOMA or coded multicasting depending on
the channel conditions of the paired users in each resource
block (RB). A joint mode selection, power allocation and user
pairing scheme is developed to enhance the performance of the
hybrid scheme. Both analytical and simulation results demonstrate
that NOMA outperforms coded multicasting when pairing
users whose channel gains are highly distinctive, while coded
multicasting is preferred when the paired users have similar
channel gains. In addition, the hybrid scheme is demonstrated to
offer enhanced sum rate performance in comparison to NOMA
and coded multicasting.