Research On The High Energy Efficiency Mechanism Of Visible Light Communication Networks

With the development of wireless communications and the rapid popularization of smart devices,wireless spectrum resources are in shortage and energy consumption is increasing.Therefore,under the premise of ensuring both of information transmission speed and quality of service,the problem of enhancing the energy efficiency is urgent to be solved.As a potential key technology for 5G indoor and outdoor green high-speed wireless communications,visible light communication(VLC)can simultaneously support both wireless communications and illumination.However,in the current research of VLC system's energy efficiency,transmission rate models are all built based on the Shannon formula and the power consumption modes are too ideal for VLC systems.Therefore,this thesis analyzes the link power consumption of VLC system in detail.And in combination with the transmission rate expression applicable to VLC systems,the thesis also investigates how to obtain the optimal energy efficiency.The main works are as follows:Firstly,for the single-input-single-output(SISO)VLC system,this thesis systematically analyzes the power consumption along the signal processing path,establishes the relation between the power consumption of the power amplifier(PA)and achievable rate expression of SISO VLC systems and proposes an explicit energy efficiency expression,which is a quasi-concave function with respective to the power consumption of the PA.Moreover,this thesis investigates the energy efficiency maximization problem under the power constraints and the transmission rate requirement.This concave-linear fractional problem is solved by using the Dinkelbach algorithm and obtained the optimal power control of PA.Secondly,for the multi-input-single-output(MISO)VLC system,this thesis extends the introduced power consumption model to the case of multi-LED,and studies the energy efficiency maximization problem subject to each LED's power constraint and rate constraint,which turns out to be a non-convex problem.By using the Dinkelbach algorithm,the energy efficiency maximization problem can be reformulated as a convex problem,and the optimal solution can be efficiently obtained.Numerical results are presented to show the performance of the proposed optimal solutions.It is shown that the power is preferentially allocated to the subchannels with higher channel gain in the MISO VLC system.Meanwhile,SISO can beat MISO in terms of energy efficiency for low rate requirement applications,and MISO outperforms SISO for high rate requirement applications.Thirdly,this thesis studies the energy efficiency maximization problem of NOMA VLC broadcast networks based on the research of SISO and MISO,and proposes an achievable rate expression with closed-form of each user and an energy efficiency expression.Moreover,this thesis investigates the energy efficiency maximization problem under power constraints and each users' transmission rate requirement.Because this problem is NP-hard,an approximate solution is proposed in this thesis.First,the maximum weight matching algorithm is used to solve the user grouping problem.Then the bisection method and the Branch-and-Reduce-and-Bound(BRB)algorithms are used to solve the power allocation problem.At last,under the premise of obtaining the optimal energy efficiency,the optimal user grouping and power allocation are obtained correspondingly.In addition,numerical results show that users with the highest channel gain and users with the lowest channel gain are not always grouped,and the power allocated by the user is inversely proportional to the channel gain.