  The key idea of non-orthogonal multiple access (NOMA) is to serve multiple
users simultaneously at the same time and frequency, which can result in
excessive multiple-access interference. As a crucial component of NOMA systems,
successive interference cancelation (SIC) is key to combating this
multiple-access interference, and is focused on in this letter, where an
overview of SIC decoding order selection schemes is provided. In particular,
selecting the SIC decoding order based on the users' channel state information
(CSI) and the users' quality of service (QoS), respectively, is discussed. The
limitations of these two approaches are illustrated, and then a recently
proposed scheme, termed hybrid SIC, which dynamically adapts the SIC decoding
order is presented and shown to achieve a surprising performance improvement
that cannot be realized by the conventional SIC decoding order selection
schemes individually.
