On the Spectral Efficiency and Security Enhancements of NOMA Assisted Multicast-Unicast Streaming

This paper considers the application of non-orthogonal multiple access (NOMA) to a multi-user network with mixed multicasting and unicasting traffic. The proposed design of beamforming and power allocation ensures that the unicasting performance is improved while maintaining the reception reliability of multicasting. Both analytical and simulation results are provided to demonstrate that the use of the NOMA assisted multicast-unicast scheme yields a significant improvement in spectral efficiency compared to orthogonal multiple access (OMA) schemes which realize multicasting and unicasting services separately. Since unicasting messages are broadcasted to all the users, how the use of NOMA can prevent those multicasting receivers intercepting the unicasting messages is also investigated, where it is shown that the secrecy unicasting rate achieved by NOMA is always larger than or equal to that of OMA. This security gain is mainly due to the fact that the multicasting messages can be used as jamming signals to prevent potential eavesdropping when the multicasting and unicasting messages are superimposed together following the NOMA principle.