Abstract—Non-Orthogonal Multiple Access (NOMA) technology is considered a strong candidate for 5G systems. The essence of this technique is to ensure that the near user can detect and subtract the far user's signal to get its signal for the detection. In addition, the system still provides enough signal strength for the far user. The article is interested in a 5G system that combines the primary and secondary networks, using an intermediate relay to support signals for the far secondary user. Several techniques involve inducing the transmit beamforming at the relay to produce the best signal at the far secondary user. Still, at the same time, it can generate the lowest interference to the primary; near secondary users and minimize its noise. These methods have some disadvantages, such as the complex optimal transmit beamforming algorithms or still not guaranteeing the smallest outage probability for the near and far users. The method proposed in this paper focuses on providing a book of beams combined with a hierarchical search algorithm to search for the productive beam faster, without complexity, and at the same time can minimize the outage probability thanks to the beamwidth that can be adjustable.
 

Index Terms—NOMA, beamforming, relay, multiple antenna, outage probability