Research On Handover Problem In LED-based Visible Light Communication

With the development of science,people's living standards and quality continue to improve,for a variety of handheld terminals,including smart phones,tablet PCs,handheld games and other access speed and communication quality requirements are getting higher and higher,which makes people on the indoor wireless The speed requirements are getting higher and higher.These demands have prompted researchers to continue to explore new high-speed wireless access technologies where current RF and infrared communications are not sufficient.At the same time with the new lighting technology-LED(LED-Light-Emitting Diode)the application and popularization,the researchers noticed its characteristics: small,pollution-free,high efficiency,high brightness,low price,making the light-emitting diode As the wireless optical communication access light source get more and more attention and research.At the same time,the modulation bandwidth of the diode is between 10 MHz and 103 MHz,the spectrum of sufficient resources,these spectrum resources do not need to apply for permission,easy to use.In addition,the use of LED as a wireless communication base station,does not cause electromagnetic interference,which makes optical communication than other wireless communication has a better security.In view of these advantages of light-emitting diodes,the researchers selected it as a visible light communication(VLC-Visible Light Communication)network transmitter light source,LED lighting based on the increase in modulation equipment that LED drive circuit,the circuit is simple and easy to improve the existing Of the equipment,making it as a wireless communication access terminal possible.The use of LED as an access point,can effectively cope with the current frequency band congestion,slow transmission of the situation.Visible light communication can meet people at the same time on the lighting,high-speed communications,confidentiality,security,environmental protection and energy conservation and a series of requirements.Future visible traffic may go into the tens of thousands of households,but so many access points will face avery practical problem that is different between the access point switching problem,if such a wireless communication can be done in multiple access points To achieve a seamless connection between,then the visible light communication will have more rapid development,and even can be used as a networking point in the family.In this paper,we mainly carry out the research on the problem of handover between access points.Firstly,some characteristics of the transmitter and receiver of visible light communication are analyzed,and then the main problem of switching is analyzed.Mainly divided into: for indoor application scenarios,proposed based on soft switching,relay switching and hard switching visible light access point switching method.Specifically,the method based on soft handover is to compare the optical power of different access points at each location where the optical signal coverage overlaps,and an access point with better selection signal is accessed,and during the moving process,The face of multiple access points have signal coverage of the situation based on the trend of signal gradient to determine the most suitable access to the access point;based on the relay switching method is also used in the overlapping area of ??the switching method,which Is a two-way communication when there is a switching method.In the communication,the receiver first connects the uplink of the access point of the target,disconnects the original uplink,and then connects the downlink of the target access point,and then disconnects the original downlink;Hard switching method is in the optical signal can not cover the location of the switch,the main method is to disconnect the original access point and then access the new access point,and we put forward at the receiving end Leaving the memory,in advance to load non-instant messaging content,making the normal communication of the user does not have a significant impact.And then analyzed how to switch between indoor and outdoor work,the advantages and disadvantages of various switching methods,and a variety of switching applications.