Research On Channel Capacity And Non-Orthogonal Multiple Access In Visible Communication Networks

At present,with the rise of wireless communication networks and the exponential growth of mobile terminal equipment,wireless spectrum resources have been exhausted,and energy consumption has also increased exponentially.Visible Light Communication(Visible Light Communication,VLC),has attracted widespread attention due to rich spectrum resources and the use of low-power LED lights,which has become the key technology for indoor and outdoor high-speed wireless communications in the future.Meanwhile,it is difficult to support largescale users by using limited radio resources in future wireless network allocation.In order to meet this challenge,Non-Orthogonal Multiple Access(NOMA)came into being.As a promising multiple access scheme,it can achieve high spectrum efficiency and user fairness.However,since the light modulation signal is real and non-negative,the traditional Shannon formula is not applicable in visible light.Up to now,the VLC multiple access channel capacity and the achievable rate of the VLC NOMA network are also unknown.Therefore,this thesis takes visible light communication and non-orthogonal multiple access technology as research objects,and studies key aspects of channel capacity and power allocation.1.For VLC multiple access channels(Multiple Access Channels,MAC),considering the signal peak constraints and optical power constraints,studied the VLC MAC capacity.Specifically,assuming that the signal follows discrete input distribution,the VLC MAC exact channel capacity can be modeled as a hybrid discrete optimization problem.Since the objective function has no closed expression,it is a non-convex problem.We use inexact gradient projection method to solve this problem.Among them,the proposed inner bounds are established by employing the single-user exact channel capacity achieving input distribution for each user.The proposed outer bounds are derived by determining single-user capacities for each user,and calculating a sum capacity upper bound by relaxing the input constraints.Numerical results show that the proposed new bounds are extremely tight,and outperform existing bounds over wide ranges of SNRs.2.For the visible light non-orthogonal multiple access system,the achievable rate and optimal power allocation of static users in the VLC NOMA downlink are studied.Specifically,considering the signal peak constraints,average optical power and electrical power constraints,we first obtain the upper and lower bounds of the achievable rate closed expression for static user in downlink VLC NOMA.Based on the derived lower bound,we minimize transmit power under the minimum rate requirements and individual light emitting diodes(LED)power constraints.To solve this non-convex problem,by exploiting the semi-definite relaxation(SDR)technique,the optimal power allocation scheme can be obtained by solving a convex semi-definite program(SDP).The simulation results show that the proposed upper and lower bounds are tighter than the uniform distribution,and the gap between the upper and lower bounds is also smaller.In addition,the performance of the beamforming scheme proposed in this paper is also better than that of uniform distribution.3.Based on the research of static users in VLC NOMA,the closed-form expression of the achievable rate of mobile users is further derived,and the optimal power allocation scheme is proposed for mobile users.Specifically,Due to users 'movement,the estimated channel state information(CSI)may be inaccurate.We first characterize the CSI uncertainties as ellipsoidal regions,and derive a lower bound of the achievable rate expression for mobile users.Then,the paper studies the transmit power minimization problem while meeting the Quality of Service(QoS)requirements of different users,which is non-convex.By applying S-lemma and SDR,the transmit power minimization problem can be reformulated as a convex SDP.Simulation results are presented to verify the effectiveness and robustness of the proposed power allocation schemes.There are 25 figures,4 tables and 122 references in this thesis.