Research Of MAC Layer Protocol In Visible Light Communication System

Visible Light Communication(VLC)is becoming one of the research focus in the filed of wireless communication in recent years because it has the advantages of providing illumattion,spectrum license free,environmental protection and high security.In this paper,the media access control(MAC)layer protocol in indoor visible light communication is studied.The main content of this article is as follows:Firstly,an adjustment scheme is proposed for applying the access protocol in the wireless communication scenario to the indoor visible light communication scene in which the uplink adopts a multi-LED overlay scheme and the uplink adopts a traditional wireless or infrared light scheme.Besides,The backoff algorithm in the access scheme is improved.In order to enable the coordinator to master the relative position of the user terminal,a RTS/CTS procedure is added on the basis of the traditional wireless RTS/CTS mode,because the user terminals can not listen to each other in the multi-LED scenario.The mathematical expression of user access collision probability and system normalized throughput is deduced.In addition,an improved scheme to improve the fairness of user access is proposed by combining the merits of slowly reducing the contention window scheme and quickly solving the collision scheme.This improvement is based on the the backoff algorithm in the access scheme.Secondly,an improved adaptive guaranteed slot allocation scheme is proposed.Combining the advantages of the non-uniform guaranteed time slot allocation scheme and the shared guaranteed time slot allocation scheme,an improved adaptive guaranteed slot allocation scheme is proposed.The improved scheme combines the first two schemes,and the users feedback their arrival rate periodicly so that the coordinator can adjust the guaranteed time slot allocation as soon as possible so as to avoid the decrease of the utilization rate of the guaranteed time slot bandwidth due to the rapid decrease of the user arrival rate.Thirdly,The scheme of user access and guaranteed time slot allocation priority in visible light communication is proposed.The basic idea of a user access priority scheme is that a high priority user sets a smaller initial contention window and a smaller maximum backoff order while a lower priority user sets a larger initial contention window and a larger maximum backoff order.Higher-priority users are more likely to have access to the system than low-priority users.In addition,the mathematical expression of user access collision probability and system normalized throughput of priority access is deduced.The basic idea of ensuring the priority of guaranteed time slot allocation is as follows:The number of guaranteed time slots that can be used by each priority user is variable,which is related to the arrival rate of the user applying guaranteed slots;the number of guaranteed slots for high-priority users is larger,and the corresponding blocking rating is low.The number of guaranteed time slots that can be used by low-priority users is smaller,and the corresponding blocking rate is high.Fourthly,the differences of hard handover and soft handover performance in visible light communication are compared and analyzed.Based on the distinction between hard handover and soft handover,the mathematic expressions of the new call blocking rate and switching call drop rate are deduced by using queuing theory.