Non‑orthogonal Multiple Access: An Enabler for Massive Connectivity

Abstract

Two of the most challenging goals for the fifth generation
(5G) and beyond communication systems are massive connectivity
and higher capacity. The use of traditional orthogonal multiple access
techniques limits the number of users that can be served using available
resources due to orthogonality constraint. Moreover, the available
resources may not be utilized effectively by alloted users thereby resulting
in inefficiency and user unfairness. This imposes a severe drawback
in cases where the number of users to be served are high, like in the
Internet of Things or ultra-dense 5G networks. Hence, introducing nonorthogonality to multiple access scheme is advocated as a superior
methodology to serve multiple users simultaneously, thereby achieving
multi-fold enhancement in connectivity. In scenarios with massive number
of users, non-orthogonal multiple access scheme (NOMA) increases
the number of active connections by superimposing signals of multiple
users on the same resource block, thereby also utilizing the available
resources efficiently. This article presents an overview of the integration
of NOMA with several other leading technologies for 5G and beyond networks to enhance the connectivity.