Non-orthogonal multiple access (NOMA) that exploits the differences of transmission powers of users or power domain NOMA is an attractive technology to meet the increasing demands of 5G network users. In this paper, a multiuser diversity gain analysis for power domain NOMA is introduced to compare the reliability of various power transmission methods in case of uplink communications. Accordingly, a power transmission scheme that ensures a certain quality of user experience (QoE) for all users is compared with the power back-off transmission scheme inherited from LTE. The results show that the QoE based power transmission can exploit the diversity gain and has much lower symbol error rate than the power back-off method for both ideal successive interference cancellation (SIC) and practical imperfect SIC at the receiver.