Research On Key Theory And Techniques Of Ultraviolet MIMO Communication System

Mobile wireless communication is facing the shortage of spectrum resources,the proliferation of large-scale access nodes,the increasing energy costs,and and the growing demand of high data flow and highquality mobile service business demand.Optical wireless communication(OWC)technology,as an important supplement and future trend of radio frequency(RF)wireless communication,is being focused on and continuously developed.As one of OWC,non-line-of-sight(NLOS)ultraviolet communication(UVC)has unique advantages such as low noise interference,all-weather application in all regions,high regional security,flexible mobility,no need of tracking and aiming.It has a wide range of applications.With the rapid development of semiconductor transceiver devices for solar blind ultraviolet communication,UVC has great potential application and research value in military defense and commercial communication.Although a variety of performance enhancement technologies such as high-order modulation,channel error correction coding and beam shaping have been developed and applied,the transmission rate and communication distance of NLOS UVC system are still low.The channel fading and pulse broadening caused by UV atmospheric scattering restrict the realization of high speed and high reliability communication hardware system.Inspired by the wide application of multiple input multiple output(MIMO)technology in RF wireless communication,multi antenna technology had also been introduced into the field of UVC.However,the current UV multi antenna technology is still in its infancy,and the existing research mainly focuses on SIMO diversity receiving system.Although these systems have the ability of anti-turbulence and anti-noise,they still can not achieve the enhancement effect similar to the RF MIMO configuration.For the following issues:a)The definition of channel spatial correlation in UVC MIMO research is not clear;b)High power requirement for long-distance atmospheric turbulence NLOS UVC channel;c)The bandwidth of NLOS scattering channel is limited and prone intersymbol interference(ISI);d)Point-to-point NLOS UVC system has short communication distance and poor mobility;e)The interference between UVC signals based on intensity modulation direct detection(IM/DD)cannot be distinguished effectively.This paper puts forward some innovative theories of UVC MIMO channel,and discusses and analyses the effect of MIMO schemes under different architectures on the above problems.The main content and results are divided into the following four parts:1.The atmospheric scattering transmission theory of ultraviolet light is analyzed,and the equivalent narrowband channel without ISI is discussed according to the characteristics of key channel parameters such as path loss of pulse response.Secondly,by comparing the characteristics of radio frequency and OWC MIMO,the spatial correlation theory of UVC MIMO channel is redefined and explained,and the mathematical characterization of channel capacity of UVC MIMO is deduced.In addition,two sets of hardware experimental system platforms are given,and outdoor performance tests of UVC NLOS links are carried out.UVC MIMO experiments are further designed to verify the limitations of previous studies on the definition of channel spatial correlation.2.An innovative UV MIMO long-range turbulent scattering channel model with spatial correlation is constructed,and the effects of the key parameters such as the elevation of the transmitter and receiver,the communication distance,and the turbulence intensity on the correlation between channels are studied.We also propose a piecewise correlation channel characterization method to generate a complex correlation channel random matrix.The channel capacity of the UVC MIMO system is further simulated and analyzed.The numerical results show the correlation between the UVC MIMO channels.Changing the elevation of the transceiver can reduce the average correlation of the channel matrix.Although the correlation can not be eliminated to achieve full utilization,it can also make the turbulent scattered UVC gain spatial multiplexing and improve the channel capacity.In addition,this UVC MIMO architecture based on elevation angle separation has the ability to resist atmospheric turbulence and noise interference.3.A high-speed spatial multiplexing(SDM)NLOS UVC framework based on non-coplanar rotation angle is established for the first time.The influence of SDM structure parameters on the inter-channel interference is studied,and the optimal configuration parameters of the transceiver are obtained.Secondly,a Gaussian approximation PMT signal detection model is proposed to simplify the calculation of bit error rate(BER)to meet the requirements of scene analysis for complex inter-channel interference.In addition,the influence of the interference factor on the BER is analyzed,and a low interference scheme is proposed to increase the data rate or decrease the alignment configuration by increasing the power.Finally,this MIMO framework can be extended to other NLOS OWC systems.4.A ring topology for code division multiple access(CDMA)multiuser access to UVC network is presented for the first time,which avoids link interference failure caused by IM/DD mode.Compared with traditional Relay-assisted topology or cellular network topology,the advantages of this ring topology and its basic unit settings are analyzed.In addition,a non-coplanar NLOS SDM UVC architecture is deployed in this network to provide high-speed anti-jamming downlink between access points and users.Finally,network coverage and transmission performance of multi-user systems are evaluated by numerical simulation.