Theoretical Method Study On Novel Non-orthogonal Multiple Access

With the growing demands for wireless services,the sixth generation(6G)mobile com-munication system will face more challenges on massive connectivity,higher transmission data rates,and higher reliability.Conventional orthogonal multiple access(OMA)is insufficient to meet the overwhelming demands.Thus,novel non-orthogonal multiple access technologies are expected to be developed,wherein power domain non-orthogonal multiple access(PD-NOMA)and rate-splitting multiple access(RSMA)are two promising candidates.PD-NOMA allows multiple users to share the same resource block multiplexing in the power domain,and thus,can accommodate more users than conventional orthogonal multiple access systems.NOMA also provides higher spectrum efficiency and lower latency.RSMA can mitigate interference through rate-splitting,and thus,can achieve a higher spectral efficiency,a higher energy effi-ciency,and better robustness.Motivated by the above observation,this dissertation conducts a theoretical method study on novel non-orthogonal multiple access.The main research contents and contributions are summarized as follows:(1)This dissertation investigates the downlink PD-NOMA transmission design for error probability minimization.In this dissertation,imperfect successive interference cancellation(SIC)and practical modulation schemes are taken into account for downlink PD-NOMA de-sign.The exact expressions of the bit error rates(BERs)for arbitrary-order quadrature ampli-tude modulation(QAM)schemes are derived.Based on this,a minimum error probability power allocation can be obtained via the exhaustive search.Furthermore,lower and upper bounds of the BERs are derived and an optimization problem is formulated to minimize the bounds.A closed-form solution is derived,and thus,a low-complexity power allocation method is pro-posed for PD-NOMA.The superiority of the proposed power allocation over OMA and exist-ing PD-NOMA schemes in terms of error performance is theoretically proven.Comprehensive numerical results demonstrate the superiority of the proposed PD-NOMA design.(2)This dissertation investigates the downlink PD-NOMA transmission design for effec-tive throughput maximization.For downlink multi-user multi-channel PD-NOMA systems,im-perfect SIC and QAM modulations are considered.The expression of the effective throughput is derived,which takes into account both the data rate and the error performance.To maximize the effective throughput,a joint resource optimization problem of the power allocation,channel assignment,and modulation selection is formulated.An efficient power allocation solution is proposed by deriving a closed-form power allocation within channels and a waterfilling-form power budget allocation among channels.The channel assignment algorithms based on swap matching policies and a modulation selection method based on machine learning(ML)are de-veloped.A joint resource allocation algorithm is proposed for downlink PD-NOMA.Numeri-cal results show that the proposed PD-NOMA scheme outperforms OMA and other PD-NOMA schemes by 10%-40% in terms of the effective throughput.(3)This dissertation investigates the uplink PD-NOMA transmission design for practical QAM modulations.The expressions of the symbol error rates(SERs)are derived for arbitrary-order QAM modulations considering the constellation rotation caused by the phase difference between the channel coefficients in uplink PD-NOMA systems.On this basis,the expression of the effective throughput is derived and the maximum effective throughput power control scheme can be obtained via the two-dimensional joint search.To decrease the computational complexity,the lower bound of the effective throughput is derived.Then,an optimization prob-lem is formulated to maximize the lower bound and a closed-form solution is developed,which reveals the relationship among the optimal transmission power,the modulation orders,and the channel coefficients.On this basis,a low-complexity power control method for uplink PD-NOMA is proposed.Numerical results show that the proposed power control scheme achieves the near-optimal effective throughput,which outperforms OMA and other uplink PD-NOMA schemes.(4)This dissertation investigates a flexible RSMA scheme for finite blocklength.For downlink multiple-input single-output(MISO)systems,the expression of the effective through-put with finite blocklength is derived to consider both the data rate and the error performance.A effective throughput maximization problem is formulated by jointly optimizing the beamform-ing vectors,transmission data rates,and rate-splitting user selection.For beamforming design,an optimal algorithm based on monotonic optimization and a low-complexity algorithm based on successive convex approximation are developed.Furthermore,a semi-closed-form solution of the optimal data rates and an efficient rate-splitting user selection algorithm based on simu-lated annealing are provided.A joint resource allocation method for RSMA is proposed,which allows the system to flexibly decide whether a user should employ the rate-splitting scheme or not.Numerical results verify the superiority of the proposed flexible RSMA scheme over other multiple access methods in terms of the effective throughput.