The Technology Of Non-orthogonal Multiple Access In Broadband Wireless Communication Systems

The popularity of the Internet of Thing and cloud-base applications impose higher require-ments for the next generation communication system,especially in terms of spectral efficiency,energy efficiency,delay and so on.In order to meet these requirements,the introduction of more efficient multiple access technology has become an effective method.As one of the can-didates of the multiple access technology,nonorthogonal multiple access(NOMA)is capable of supporting overloaded transmission and improving the spectral efficiency,which has been pro-posed as one of the key technologies in the next generation communication system.Moreover,power domain can be seen as a reused resource,which provides an additional design dimension for NOMA.In the power domain NOMA system,the problem of resource allocation is one of the key problems for the system performance.However,the problem of resource allocation mainly includes power allocation and user grouping,which is a difficult mixed integer problem.Furthermore,since multiple antennas are able to provide the flexibility and degrees of freedom,the integration of multi-antenna transmission and NOMA can further improve the spectral ef-ficiency.The key problem of the multi-antenna NOMA system is the design of beamforming vectors.In addition,how to integrate NOMA and some new communication technologies,e.g.,mobile edge computing(MEC)and intelligent reflecting surface(IRS),to achieve significant performance improvement is also a hot issue to be solved.Based on the above observation and analysis,this article conducts the research titled”The technology of NOMA in broadband wire-less communication systems".The main research contents and contributions are summarized as follows:For the resource allocation problem in NOMA systems,under various performance mea-sures,the optimal power allocation is proposed for all the users through multiple channels in closed form or semi-closed form.The considered performance measures include maximizing fairness,sum rate,and energy efficiency.Different from most of the existing works,the power order constraint in each channel is considered,which determines whether the process of suc-cessive interference cancellation(SIC)is successful.Moreover,by incorporating the matching algorithm with the optimal power allocation,a low-complexity efficient method to jointly op-timize channel assignment and power allocation in NOMA systems is proposed.Simulation results show that the joint resource optimization using our optimal power allocation yields bet-ter performance than the existing schemes.For the problem of beamforming design in multi-antenna NOMA systems,the design of beamforming vectors is based on solving the transmission power minimization problem with QoS constraints.This is the first work that provides the optimal beamforming vectors with quasi-degradation condition,which is proved to achieve the same performance as dirty paper coding(DPC).At the same time,the quasi-degradation condition for multiple users is also pro-posed.For the special case of two users,the optimal beamforming vectors are characterized in closed-form.Simulation results show that the proposed optimal NOMA beamforming outper-forms orthogonal multiple access(OMA)schemes and can even achieve the system capacity region.The proposed solutions dramatically simplify the problem of beamforming design in the downlink MISO NOMA systems and improve the system performance.For reducing the system latency and power consumption in MEC systems,we propose hybrid NOMA MEC frame.The problem of resource allocation is investigated respectively for three schemes(pure NOMA,hybrid NOMA,and OMA).In this system,multiple users are classified into different groups and each group is allocated a dedicated time slot.In each group,a user first offloads parts of its task by sharing a time slot with another user,and then solely offloads the remaining task during a time interval.In order to reduce delay and energy consumption,resources of power,time,and user grouping are jointly optimized.We prove that all the three strategies might possibly happen to the users when taking different values of weight factors,deadlines,and channel gains.In addition,by incorporating the matching algorithm with the optimal power and time allocation,an efficient method to optimize user grouping is proposed.Simulation results demonstrate that the proposed resource allocation method in the hybrid NOMA MEC systems not only yields better performance than the conventional OMA scheme but also achieves quite close performance as global optimal solution.IRS is capable of changing users' channels,which makes NOMA system realize capacity region.Thus,we propose the IRS-assisted multiple-input-single-output(MISO)NOMA frame.In this system,the IRS element matrix and beamforming vectors are jointly optimized to mini-mize the transmission power.In addition,we propose the improved quasi-degradation condition with IRS,which guarantees that NOMA achieves the same performance as DPC.For a compar-ison,the zero-forcing beamforming(ZFBF)is studied as well,where the beamforming vectors and the IRS phase shift matrix are also jointly optimized.Comparing NOMA with ZFBF,it is shown that,with the same IRS phase shift matrix and the improved quasi-degradation con-dition,NOMA always outperforms ZFBF.At the same time,the condition under which ZFBF outperforms NOMA is identified,which motivates the proposed hybrid NOMA transmission.Simulation results show that the proposed IRS-assisted MISO system outperforms the MISO case without IRS,and the hybrid NOMA transmission scheme always achieves better perfor-mance than orthogonal multiple access.