Study and improve the performance of multiuser sharing access for 5G networks

Non-orthogonal Multiple Access (NOMA) technologies are considered as one of the proposed solutions to meet the requirements of the fifth generation. It has the ability to improve spectral efficiency through users' sharing of radio resources, and increasing the degree of freedom in the number of non-orthogonal resources. However, these technologies suffer from interference between users' signals due to the absence of orthogonality, which can be reduced by using advanced receivers of high complexity. The Power Domain non-orthogonal multiple access (PD-NOMA) and Multi-User Sharing Access (MUSA) schemes are types of NOMA Technologies. They improve system efficiency by increasing the number of users on the same radio resource and achieving higher flexibility in reuse of system resources. Both schemes can be used in both downlink and uplink systems based on Minimum Mean Square Error - Successive Interference Cancellation (MMSE-SIC) receiver to improve decoding performance. In this study, the performance of the MUSA system has been improved in the uplink by applying the PD-NOMA scheme and the effect on the error probability and minimum rate performance of the system caused by cross-correlation between the complex spreading sequences and the power allocation scheme has been analyzed. Also, the optimal solution for the spreading sequences and the power coefficients allocation that achieve the maximum minimum signal to interference and noise ratio on which the rate and bit error rate performances in the hybrid NOMA scheme depends, has been studied. Two iterative algorithm has been proposed to solve the optimization problem separately. OMA (Orthogonal Multiple Access) scheme has been proposed as a benchmark. The simulation results showed that our proposed scheme outperforms on the OMA benchmark in terms of achievable minimum rate per user and total power consumption. Besides, the bit error rate performance is improved in the proposed scheme compared to the conventional MUSA scheme.