This work presents a performance analysis for downlink non-orthogonal multiple accesses (DL-NOMA) systems where the channel gains follow the - fading distribution. Specifically, closed-form expressions are derived for DL-NOMA in terms of the outage probability (OP), bit error rate (BER), and ergodic capacity (EC). The OP analysis considers two main scenarios, the first is when the individual user's rate is required to satisfy a certain quality of service (QoS), while the second is when the individual user's NOMA rate is less than that of the conventional orthogonal multiple access (OMA) rate. Moreover, the derived BER performance is generalized for the case of -ary quadrature amplitude modulation (MQAM). The results demonstrate the interplay between the system performance, the power allocation coefficients, target data rates, and the channel fading parameters. Moreover, the OP results reveal that NOMA users with OMA data rate experience higher outage compared to NOMA with fixed target data rate. The accuracy of the derived expressions is validated using extensive Monte Carlo simulation.