Analyzing Hybrid NOMA Schemes Underlining Energy-Spectral Efficiency and SIC Tradeoff

To cope with soaring users demand an appropriate multiple access technique becomes crucial in 5G and beyond wire-less communications. Non-orthogonal multiple access (NOMA) technique is superior to the existing orthogonal multiple access (OMA) technique utilizing the limited resources, though NOMA grants manageable interferences by non-orthogonal resource allocation. Successive Interference Cancellation (SIC) can efficiently mitigate the impact of interference when implemented massively, but it raises computational complexity significantly, hence, reduces energy efficiency. This paper focuses on comparative performance analysis among hybrid NOMA schemes such as MIMO-NOMA, NOMA-GSSK and STBC-CNOMA in terms of bit error probability, energy and spectral efficiency and number of SIC occurrence. The closed form expression to compute channel capacity for STBC-CNOMA scheme has been derived and less complex expression to calculate bit error probability for NOMA-GSSK scheme has been suggested. Numerical analysis and simulation results validate the superiority of the NOMA-GSSK scheme in terms of bit error probability and spectral efficiency than the other two promising schemes. The findings also demonstrate that STBC-CNOMA certainly outweighs the other two schemes considering system complexity and energy efficiency.