Research On Power Allocation Algorithm In Downlink Non-orthogonal Multiple Access Systems

Non-Orthogonal Multiple Access(NOMA)technology,as an alternative new multiple access scheme in 3GPP,has attracted extensive attention in the industry since it was proposed because it can greatly increase the number of the access devices and improve the system spectrum efficiency(SE).Considering the power multiplexing characteristics of NOMA,it is of great significance to study the power control problem of NOMA system for meeting the increasingly diversified communication demands and improving the status quo of scarce spectrum resources.Therefore,for the performance indicators such as system capacity,energy efficiency(EE),SE and physical layer security,this thesis carries out in-depth discussion and analysis on the power optimization design of different downlink NOMA systems.The research will involve single-carrier(SC),multi-carrier(MC)and millimeter-wave(MMWave)communication scenarios.The main work is summarized as follows:1.Aiming at the downlink MC-NOMA transmission scenario,the optimization problem about system capacity is studied.Combining the two-sides matching theory and the water filling algorithm based on the rate increment maximization principle,a joint user-subcarrier matching power allocation scheme is proposed.Simulation shows that the proposed scheme can quickly achieve the stable matching between users and subcarriers and improve the system capacity while ensuring the user's quality of service(Qo S)and keeping the stability of the successive interference cancellation(SIC).2.Based on the SC-NOMA scenario,this thesis considers the joint optimization problem of system EE and SE with multiple users.By defining a new system performance measurement function and combining the linear weighted summation method,the original multi-objective optimization problem is transformed into a univariate optimization problem,and finally a two-layer power allocation algorithm is proposed.The proposed algorithm firstly guarantees the Qo S of all access users by constraining the minimum transmit power of the system.Furthermore,the simulation results show that under the condition of ensuring the optimal overall system performance,the weighting factor can be flexibly adjusted according to real-time communication requirements to achieve a compromise between EE and SE.3.Considering the mm Wave communication with ultra-wide bandwidth to further improve the NOMA system performance,a downlink mm Wave-NOMA transmission scenario is constructed in this thesis.Because the users' channel correlation in the same mm Wave beam are relatively high,it is easy to generate security risks of collective information leakage or eavesdropping.Therefore,this thesis specifically studies the system secrecy energy efficiency(SEE)when there is an eavesdropper.Assuming that multiple users can be served by one beam,an iterative power allocation scheme based on Dinkelbach-like(DL)algorithm and Difference of Concave(DC)programming theory is finally proposed.Simulations show that the proposed scheme can effectively improve the system security performance while ensuring the minimum target rate of legitimate users.In addition,the proposed mm Wave-NOMA system is superior to the traditional mm Wave-OMA system for secrecy sum rate(SSR)and SEE.