Generation And Application Of Vortex Electromagnetic Wave In Wireless Communication

With the explosive growth of multimedia services and the vigorous development of mobile Internet applications,the contradiction between capacity demand and spectrum resource shortage has become increasingly prominent.Orbital angular momentum(OAM),as a new transmission dimension,can simultaneously transmit multiple channels of information in the same frequency band,which can effectively solve the problem of shortage of spectrum resources.Under this background,this paper takes vortex electromagnetic waves based on uniform circular arrays as research objects,and mainly studies two key problems in OAM wireless communication systems.The generation and optimization of arbitrary modal vortex electromagnetic waves in time-modulated uniform circular array(TMCA).The problem of the inter-mode interference in multi-mode vortex electromagnetic wave communication system.1.This paper proposes a method based on time-modulated uniform circular array to generate vortex electromagnetic waves of arbitrary modes and perform beam steering(BS).The theory of the generation of OAM beams is derived in theory,that by properly opening the radio frequency(RF)switch and designing the duty of each periodic square wave,TMCA can generate not only integer-order OAM beams but also fractional-order OAM beams.Secondly,it is proved that as long as certain switch opening conditions and duty conditions on different array elements are met,the non-sequential switch of TMCA turning on the RF switch is the same as the sequential switch,and can generate OAM beams.Although non-sequential switch can be used to generate OAM beams,in theory,the sequential switch is optimal in minimizing transmit power consumption.When using TMCA to generate integer-order and fractional-order OAM beams,it is also possible to perform beam steering on the generated OAM beams by controlling the RF switch.Finally,a special case of uniform circular array based on time modulation is proposed,which is a method of generating vortex electromagnetic waves by a single antenna with circular motion.2.This paper studies the equivalent channel model of multi-mode OAM communication based on uniform circular array.When the transmitter and the receiver are aligned,the equivalent channel matrix can be similarly diagonal,which means that there is inter-mode interference between OAM modes at the receiver.When the transmitter is not aligned with the receiver,the performance of the communication system will decrease rapidly due to inter-mode interference between OAM modes.If only increase the number of UCA array antennas,even large-scale antennas,the inter-mode interference will still exist.However,beam steering at the receiver can effectively eliminate inter-mode interference,so that the equivalent channel matrix can be similarly diagonal.When describing the performance of the OAM communication system,we defined the signal-to-interference and noise ratio(SINR)of multi-mode OAM communication to perform an intuitive quantitative analysis of the degree of inter-mode interference between modes.Finally,through the simulation experiment,we obtain that beam steering can eliminate the influence of inter-mode interference and greatly improve multi-mode OAM communication system performance.