This chapter develops a precoding and power allocation strategy to further enhance the system performance in terms of sum rate. Two NOMA relay schemes are presented and evaluated, namely NOMA cooperative scheme and NOMA time division multiple access scheme. In NOMA cooperative scheme, the completion of one round information transmission consists of two time slots. The chapter then analyzes the system performance in terms of outage probability, which represents the probability of an event that the achieved data rate is less than a predefined one. Outage probability is a good metric for QoS in the system design. A closed-form analytical outage probability is derived for different users, based on which a high SNR approximation is presented. The unprecedented growth of mobile devices including smart phones, tablets, laptops, and IoT devices drives the wireless telecommunication industry to a new level.