Performance Analysis And Resources Optimization For Non-Orthogonal Multiple Access-Enabled Visible Light Communication Systems

Visible light communication(VLC)as a promising candidate technology in sixth generation wireless communication networks can provide high-bandwidth and highcapacity communication services based on the rich and license-free spectrum resources.Moreover,the dense and small VLC cell can be quickly deployed with the aid of the existing extensive light emitting diode(LED)illumination infrastructure.In this context,the non-orthogonal multiple access(NOMA)technology can be effectively introduced into VLC systems to further unlock the advantages of visible light communication in the frequency spectrum and massive connections with the controllable system complexity.However,there are some open but important issues need to be considered.Specifically,it is difficult to analyze the performance of the NOMA-enabled VLC system due to the inter-user interference caused by the superimposed code.Moreover,due to the spectrum openness and the superimposed code based on NOMA that is transmitted into the same time-frequency resource,the information transmission of NOMA-enabled VLC system faces security problem.Furthermore,in the process of introducing wireless energy transfer technology to improve the energy efficiency of VLC,it is also easy to cause information leakage and the trade-off between the secure communication and energy transfer due to the simultaneous consideration of information and energy transmission.In order to tackle the above-mentioned issues,the bit error rate(BER)and security performance analysis and resource optimization for the NOMA-enabled VLC systems are investigated in this thesis.The main contributions of this thesis are summarized as follows.(1)In order to tackle the problem that it is difficult to analyze the BER performance due to inter-user interference in the NOMA-enabled VLC systems,this thesis proposes an effective analysis method based on the analytical framework of bitwise-decision axis.The BER analytical expression of the common modulation schemes that include multiple-phase shift keying,multiple-pulse amplitude modulation,and multiplequadrature amplitude modulation are achieved.Moreover,the analysis method is extended to the case that different users adopted different modulation orders.Furthermore,the power allocation factor of the minimum BER for different modulation methods is also analyzed,which provides meaningful guidance for the considered system to adaptively choose the appropriate modulation method according to the user's communication quality of service requirements.(2)In order to tackle the problem that the severe security information transmission of NOMA-enabled VLC systems,this thesis firstly considers the general system scenario where the location information of both legitimate user and eavesdroppers is randomly distributed.Then,this thesis derives the tight upper and lower bound expressions for the secrecy outage probability and average secrecy capacity of the considered systems with the aid of statistical geometry method.Moreover,the artificial noise-aided beamforming technology is introduced to give full play to the natural advantages of multiple light sources and to improve the security performance of NOMA-enabled VLC systems.Specifically,based on both secure communication and dimming control constraints,the resource allocation strategy to minimize the transmission power is given in the case of that the channel state information(CSI)of both legitimate users and eavesdropper exist estimation error.Furthermore,by investigating the impact of the number of LEDs and their deployment height on the system performance,the optimal number and height configuration of LED to save transmission power under the requirements of secure communication is obtained.(3).In order to tackle problem that the secure information leakage and the energy efficiency caused by the simultaneous information and energy transmission requirements,this thesis firstly adopts a nonlinear model for the analysis of energy harvesting to improve the accuracy of quantified energy transfer process and the effectiveness of optimized solutions.Then,the resource allocation model is investigated in the orthogonal multiple access-enabled visible light communication and energy transfer systems.Specifically,on one hand,the resource allocation model to minimize the transmission power is formulated subject to the constraints of dimming control,minimum secrecy capacity and energy harvesting.On the other hand,the resource allocation model to maximize the minimum secure capacity is formulated subject to the constraints of dimming control and minimum energy harvesting.Based on the semidefinite program and(50)-Procedure,the bi-section search algorithm is given and the optimal resource allocation strategies are obtained in the cases of both perfect and imperfect CSI.Lastly,the resource allocation model to minimize the transmission power is formulated subject to the constraints of dimming control,minimum secure capacity and energy harvesting in the NOMA-enabled visible light communication and energy transfer systems.The successive convex approximation method is introduced and the iterative optimize algorithm is given to tackle the non-convex model.Moreover,the feasible resource allocation strategies are obtained in the cases of both perfect and imperfect CSI.