On the Performance of Non-Orthogonal Multiple Access in 5G Systems with   Randomly Deployed Users
  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. 
Zhiguo Ding and Zheng Yang and Pingzhi Fan and H. Vincent Poor
cs.IT math.IT