On Low Power Consumption For IRS-Aided CoMP-NOMA System

The fifth generation(5G)mobile communication technology has been deployed in the worldwide.According to the developing law of “one generation per decade” for mobile communications,the investigation on the sixth generation(6G)mobile communication has been put on the agenda.Non-orthogonal multiple access(NOMA)has been recogonized as a promising technique for future mobile communication system,which is capable of boosting spectral and power efficiency.Thus,NOMA has sparked a great deal of attention in both academia and industry.The primary feature of NOMA is that multiple users’ signals are linearly superposed with different power levels by using the superposition coding scheme.At the receiver,the successive interference cancelation(SIC)is carried out to separate different user’s signal.Therefore,the signals of diffenent users can be transmited on the same time slot and frequency simultaneously.Besides,intelligent reflecting surface(IRS)has been envisioned to be a cost-effective,energy-efficient,and sustainable technology for 6G.An IRS consists of a vast number of low-cost passive reflecting elements,each of which can independently manipulate the phase shift of the incident signals,thus a favourable wireless transmission channel is created.It is clear that both IRS and NOMA are key techniques for future communication systems.By introducing IRS into NOMA,the channel difference between NOMA users can be reshaped smartly,in which the potential of IRS and NOMA can be released in a further way.This thesis considers IRS-assisted multi-cell NOMA system,and proposes the transmit power minimization schemes for the uplink and the downlink scenarios,respectively.The detailed works are listed as following:Firstly,a power minimization scheme is proposed for IRS-assisted two-cell NOMA uplink system.In the system model,two cell-center users served by their associated base stations(BSs)and one celledge user served by two BSs with coordinated multiple point(CoMP)reception are considered.Specifically,an IRS is deployed at the edge of the cell to enhance the signal quality for the cell-edge user.Aiming at soloving the power control and the phase shift joint optimization problem,the relationship between each user’s transmit power and phase shift is derived.Then,the joint optimization problem with regards to power allocation and phase shift is converted into a pure phase shift determination problem.Based on minorize maximization(MM)technique,an efficient algorithm is proposed to optimize the phase shift.The simulation results show that the transmit power consumption of the proposed scheme is less than those of various benchmarks when each user’s quality of service(QoS)is satisfied.Secondly,a transmission power minimization scheme is proposed for IRS-assisted two-cell NOMA downlink system.Cosidering an IRS-aided two-cell NOMA system,the cell-center user is served by its associated BS,while the cell-edge user is served by the two BSs by using the CoMP technique.A problem of minimizing transmit power is formulated under the condition that the QoS for each user and the constant module constraint of each phase shift are satisfied.In order to solve the formulated transmit power minimization problem,the relationship between the power allocation coefficients at BS and the phase shift matrix of IRS is derived.Therefore,a sequential phase rotation algorithm is used to further solve the phase shift optimization problem.By using the iterative algorithm,the optimal solution of each phase rotation is obtained and then the optimal phase shift matrix is constructed.It is shown by simulations that under the same experimental setups,the performance of the proposed scheme is obviously better than several benchmarking schemes in terms of the total transmit power consumption.