  In this letter, the performance of non-orthogonal multiple access (NOMA) is
investigated in a cellular downlink scenario with randomly deployed users. The
developed analytical results show that NOMA can achieve superior performance in
terms of ergodic sum rates; however, the outage performance of NOMA depends
critically on the choices of the users' targeted data rates and allocated
power. In particular, a wrong choice of the targeted data rates and allocated
power can lead to a situation in which the user's outage probability is always
one, i.e. the user's targeted quality of service will never be met.
