Research On User Cooperation And Power Allocation In Indoor NOMA-VLC Systems

With the growing number of mobile communication devices and the popularity of diversified communication methods in the future,visible light communication(VLC)technology,which has great spectrum potential,can satisfy the demand for higher capacity and ultra-high experience rate,and is an effective supplementary means of wireless communications.However,the performance improvement of VLC is still limited by the narrow modulation bandwidth of LED and its sensitivity to occlusion,etc.To this end,this dissertation considers the introduction of non-orthogonal multiple access(NOMA)technology with higher spectral efficiency and larger system capacity into the indoor VLC system,aiming to improve the spectral efficiency and performance of VLC.This dissertation mainly focuses on the optimization of the total system performance,and analyzes the impact of power allocation among users under limited resources,user grouping and cooperation on system performance in multi-user scenarios.The main innovative contributions of this dissertation are as follows.This paper focuses on the study of indoor VLC systems,commencing with the analysis of VLC channels and the resource allocation strategy design for energy efficiency optimization,then extending the study to the design and resource allocation of hybrid VLC/RF systems,finally investigating the network selection for heterogeneous networks.The main contributions of this thesis are listed as follows:(1)To address the resource allocation among users in indoor NOMA-VLC systems with limited resources,this dissertation proposes an improved power allocation scheme among users within a single subcarrier based on multi-factor constraints(MFC),which aims to maximize the system throughput while ensuring users’ quality of service(QoS)requirements,human eye safety,transmitted power limitations,indoor illumination requirements,and user fairness.Then,the corresponding power allocation mathematical optimization problem is analyzed and modeled,where the original problem is transformed and solved using optimization theory by introducing auxiliary variables and implementing variable transformations to form the MFC-based power allocation optimization algorithm.Simulation results show that the proposed power allocation optimization scheme achieves a performance improvement of more than 40 Mbps in the throughput of the indoor NOMA-VLC system compared to other strategies,regardless of the presence of residual interference at the receiver.(2)To address user grouping,collaboration and resource allocation in a multi-user NOMA-VLC scenario,this dissertation proposes an intelligent user association(IUA)scheme based on channel conditions under the condition that each user’s position is relatively stationary.Then,an improved resource allocation strategy is proposed to maximize the system capacity under the premise of user association(UA)while considering users,QoS requirements,human eye safety,transmitted power limitation,indoor illumination and the inherent characteristics of VLC signals.Next,the corresponding power allocation mathematical optimization problem is analyzed and established,which is transformed and solved by introducing auxiliary variables and optimization theory to form an IUA-based power allocation optimization scheme considering MFC.Simulation results show that the algorithm can help the system achieve a performance improvement of up to 40 Mbps to 100 Mbps in throughput,regardless of whether SIC at the receiver is perfect or not.In addition,it is found that the throughput performance of NOMA-VLC can be further improved by adjusting the user’s field of view(FOV).(3)In order to optimize user grouping and association patterns in multi-user NOMAVLC,this dissertation proposes an adaptive mult-user association(AMUA)strategy based on different decomposition criteria,through which multiple users can be decomposed,reconstructed,associated and multiplexed in different ways to generate as many potential UA schemes as possible.Afterwards,the system capacity of different UA schemes can be obtained through power allocation.Later,according to the actual objectives or requirements,it is possible to select the best one from the generated UA solutions,thus achieving further optimization of the NOMA-VLC system in multiuser scenarios.The simulation results show that several different UA schemes can be obtained by implementing the proposed AMUA strategy regardless of the presence of residual interference at the receiver.Compared with the existing UA scheme,the proposed strategy enables the NOMA-VLC system to achieve a capacity increase of more than 100 Mbps,thus verifying the effectiveness of the proposed algorithm.(4)In order to expand the service range and improving the user service experience in multi-user NOMA-VLC scenarios,this dissertation considers the introduction of radio frequency(RF)links in indoor VLC networks to build a hybrid NOMA-based indoor VLC/RF network model.Subsequently,this dissertation proposes an adaptive virtual user association(AVUA)strategy oriented to users’QoS requirements.By dynamically grouping,reconstructing,associating and multiplexing users,a dynamic adaptive user collaboration mechanism is established with VLC links as the primary and RF links as the secondary.The proposed strategy can improve the throughput of NOMA-VLC systems by more than 100 Mbps in both perfect and imperfect SICs,while guaranteeing the QoS requirements of users,and also improving the user rate performance.(5)In order to fully utilize the resources of the constructed hybrid system and reduce the system energy consumption,this dissertation introduces simultaneous wireless information and power transfer(SWIPT)technology in the constructed indoor NOMAVLC/RF hybrid network,aiming to realize the dual functions of signal transmission and energy harvesting,create a collaborative communication mode for users,provide a variety of information reception methods for edge users and fully utilize the transmitting power,in order to extend the lifetime of the whole network.Based on this,this dissertation designs and proposes three mutually independent user cooperation and downlink transmission mechanisms based on NOMA and SWIPT-NOMA.Subsequently,in order to further enhance the service experience of users,this dissertation proposes a dynamic adaptive user cooperation and downlink network selection strategy oriented to users’ QoS requirements in hybrid networks,aiming to further expand the limited service range of VLC,increase the number of users that can be served by the system,and improve the spectrum efficiency and system capacity.Simulation results show that in both perfect and imperfect SIC scenarios,the proposed scheme can achieve at least two hundred Mbps performance improvement in system throughput while guaranteeing users,QoS requirements and complete coverage of users in the room.In addition,the simulation also shows that even if there is a certain degree of VLC link blockage,the proposed scheme can still effectively meet users,QoS requirements and achieve a maximum performance improvement of more than seven hundred Mbps in system throughput.Based on the above research,the contribution in this thesis might bring some theoretical values to the performance improvement of indoor NOMA-VLC systems and lay a theoretical foundation for higher goals of future wireless communication systems.