Research On Channel Capacity And Interference Management Of Visible Light Communication Networks

Visible light communication(VLC)is a promising green technique for 5G indoor and outdoor green high-speed wireless communications,because it has many advantages in spectrum resources,controllable coverage,confidential transmission,and electromagnetic compatibility.However,there are many open problem demanding prompt solution for the basic theory of VLC networks,especially channel capacity and interference management mechanism.Due to nonnegative and limited transmit signal of VLC,the classic conclusions,like the Shannon formula,can not be directly applied to VLC networks.Meanwhile,interference management mechanism,an important method improving network capacity,is also unknown,since the closed-form achievable rate is unknown now.Therefore,this thesis mainly studies the channel capacity of VLC pointto-point channel,broadcast channel and interference channel,and interference management mechanism for VLC broadcast channel and interference channel.The specific research contents are as follows:Firstly,for the single-user point-to-point channel,the thesis derives the upper bound and lower bound–ABG lower Bound–with close-form of channel capacity under the peak optical power constraint,the average optical power constraint,and the average electrical power constraint by the entropy power inequality and other theories,and the continuous input distribution–ABG distribution–corresponding to the ABG lower bound is obtained by the variational method.Besides,it is proved that the continuous uniform distribution and truncated Gaussian distribution are special cases of ABG distribution.Numerical simulations show that ABG lower bound can approach the upper bound.Then,for the broadcast channel,the thesis derives the corresponding achievable rate with close-form and the inner bound–ABG inner bound for VLC broadcast channel–and outer bound of channel capacity,where ABG inner bound can close to the outer bound.Based on these,the optimal beamforming under the constrains of transmission rate and transmit power is researched to reduce the multi-user interference.The main method is to convert this non-convex quadratically constrained quadratic programming problem into a convex semi-definite programming problem by semi-define relaxation,and then to use the interior point method and Gaussian randomization to solve a high quality suboptimal solution.Numerical simulations show that the beamforming scheme can meet the constraints of transmission rate and transmit power.Finally,for the interference channel,the thesis derives the corresponding achievable rate with close-form and the inner bound–ABG inner bound for VLC interference channel–and outer bound of channel capacity,where ABG inner bound can approach the outer bound.In order to reduce inter-cell interference,based on the achievable rate with closed-form,the thesis design two optimal joint beamforming schemes–centralized beamforming and distributed cooperative beamforming–under the constrains of transmission rate and transmit power.For the centralized beamforming scheme,the semidefine relaxation is used to solve this non-convex quadratically constrained quadratic programming problem and there is no loss of optimality.Further,the thesis equivalently converted the centralized beamforming scheme to a distributed cooperative beamforming scheme using the alternating direction method of multiplier method to reduce transmission cost and delay.