Research On User Access And Resource Allocation For Indoor Heterogeneous Visible Light Communication Networks

Visible light communications(VLC)has become a potential high-speed wireless access scheme due to its advantages such as high transmission power,no electromagnetic interference and no need for spectrum authentication.However,in a practical scenario,a single wireless communication system composed of VLC has some potential problems such as small-coverage,difficult to implement uplink transmission,easily affected by occlusion,etc.,so researchers began to try to integrate VLC with other wireless communication technologies flexibly to form a heterogeneous network.Currently,key technologies such as networks integration technology,channel modeling technology,multi-user access technology and resource allocation scheme are required to make breakthroughs in heterogeneous networks based on VLC.Therefore,in order to enhance the throughput of indoor heterogeneous VLC/ radio frequency(RF)networks,this paper studies user access technology and resource allocation scheme of heterogeneous VLC/RF networks.First,to meet the demand of indoor lighting,access points(AP)need to decorate intensively in heterogeneous VLC networks.Aiming at the user access problem where the user is overlapped by multiple VLC AP signals,a user access algorithm with joint considering demands of transmitting and receiving(UAJTR)is proposed in chapter three.In UAJTR algorithm,firstly,the access network is selected for users according to characteristics of different APs' layout and the occlusion of VLC AP.Besides,the access principles for special users under extreme channel conditions are designed accordingly.Then,based on the gravitational theory,the user access process for the remaining unconnected users is abstracted as mutual attraction between users and VLC APs.Considering demands of transmitting and receiving simultaneously,the weights of APs' mass and users' mass are designed,and user access results are determined according to the gravity value between them.Simulation results show that the UAJTR algorithm can improve the throughput and service fairness under different heterogeneous network layouts effectively.Secondly,due to the limited modulation bandwidth of individual light-emitting diode in heterogeneous VLC networks,it is necessary to incise the limited modulation bandwidth of each VLC AP and reuse subchannel resources flexibly to achieve highspeed transmission.To handle the problem of subchannel allocation in heterogeneous VLC networks,a subchannel allocation scheme based on improved genetic algorithm(GA)and interference suppression subchannel allocation(IGA-ISSA)is proposed in chapter four.In IGA-ISSA scheme,the access network is selected for users according to the occlusion of VLC AP.Then,for users using VLC network,IGA-ISSA divides three priority levels for users based on characteristics of user locations,and designs interference suppression subchannel allocation schemes based on conflict graph for users of different priority levels.Besides,chromosomes are constructed based on subchannel allocation results.At the same time,to optimize the search performance of GA,a crossover scheme based on invalid information perturbation is designed.Additionally,for users in RF network,IGA-ISSA algorithm allocates subchannels based on differentiated rate requirements.Simulation results show that IGA-ISSA scheme can effectively improve the throughput and user satisfaction for heterogeneous VLC networks.