Research On Vertical Handover Algorithm In Heterogeneous Visible Light Communication Networks

As an emerging wireless communication technology developed from the white light emitting diode (LED) technology, visible light communication (VLC)combines communication and lighting organically, and makes an area accessible to wireless network as long as lighting facilities are settled there, which raises a kind of convenient and natural way for data transmission. VLC is considered as a promising high speed wireless access technology. However, the line-of-sight(LOS) nature of visible light limits VLC coverage and user mobility. On the contrary, radio frequency (RF) provides much more extensive coverage, though its link bit rate is lower by contrast.In order to enhance each other in certain advantages of VLC and conventional wireless communication technologies, the thesis considers to use different types of media for data transmitting in a network system, and apply a cooperation of VLC and RF. This makes the establishment of system architecture and mechanism in heterogeneous networks critical to the efficient and reliable transmission in heterogeneous visible light communication networks. The mobility management is especially important. The thesis need to design suitable and efficient algorithms for the vertical handover (VHO)between VLC and RF.The main contents of this thesis are listed as follows:Firstly, based on the analysis of channel and noise model for visible light communication, this thesis introduces the architecture of heterogeneous visible light communication networking briefly. Tightly coupling and loosely coupling are proposed here as two heterogeneous integration models. This thesis also analyzes the feature set of multi-mode terminals (MTs) supporting visible light communication.Secondly, under single-hotspot-single-user scenario, a novel vertical handover algorithm utilizing prediction called PVHO is proposed based on two existing algorithms: IVHO and DVHO. This algorithm firstly improves the DVHO method and then takes real-time statistics and calculations from the condition of the visible light networking in order to predict which of the two schemes has a lower transfer delay. Finally, it selects the better one from IVHO and the advanced DVHO in terms of performance before executing the switching. The simulation validates the performance superiority of PVHO under many different circumstances.Thirdly, under multi-hotspot-multi-user scenario, this thesis proposes a VHO algorithm based on decision selection. This approach considers multiple attributes including dynamic network parameters and actual traffic preferences by utilizing analytic hierarchy process (AHP). Additionally, it can compensate for the weakness of classic AHP in comparing the criteria (such as message delay, queue length and bit rate) values of different candidates by applying a two-person cooperative game (CG) model. Finally, the rationality degree (RD)of each decision is calculated by combining the results of AHP and CG, and the decision with the higher RD is selected. Simulation results show that AHP-CG outperforms existing algorithms in the metric about which the current traffic type cares most. That is to say, AHP-CG proves to have better traffic adaptability.Additionally, it can reduce handover overhead greatly compared with always performing VHO.Due to the priorities of PVHO and AHP-CG VHO in different scenarios,both efficient VHO algorithms are promising in guaranteeing the quality of service (QoS) of VLC heterogeneous networks.