Scattering Interference Model Analysis And Link Enhancement Technologies For Ultraviolet Communications

The ultraviolet communication employs the "solar-blind" waveband as information carries with the advantages of non-line-of-sight ability,low background noises,high local security,and anti-electromagnetic interference.These advantages enable ultraviolet communication as an important supplement for future wireless communications,e.g.,the military security communication and the civil communication in electromagnetic sensitive environment.However,the strong scattering effect of ultraviolet signals in the atmosphere will result in serious interference among non-line-of-sight links,reduce the communication capacity and limit the practical application of ultraviolet communications.First,the strong scattering effect of ultraviolet signals will result in time dispersions of the channel impulse response(CIR),which inevitably causes serious inter-symbol interference(ISI)problem.Second,when using full-duplex ultraviolet communications,the strong scattering effect of ultraviolet signals will lead to serious self-interferences problems between the transmitting and receiving links.Besides,the strong scattering effects will cause serious inter-relay interference problems among multi-hop relay links.Considering the ISI problem,this work studies the scattering interference quantification and achievable rate analysis for single ultraviolet communication link.Then,focusing on the self-interference problem,this paper studies the self-interference quantification and achievable rate analysis for full-duplex ultraviolet communication links.At last,aiming at the inter-relay interference problem,this paper studies joint optimization of power and position for multi-hop relay links.The main research and innovation points of this paper are summarized as follows:1.Scattering Interference Quantification and Achievable Rate Analysis for Single Ultraviolet Communication LinkThe strong scattering effect of ultraviolet signals in the atmosphere will result in time dispersion of the CIR.When the transmission rate is large,the time dispersion of the CIR will inevitably cause serious ISI.Therefore,it is meaningful to precisely quantify the CIR of ultraviolet communications and explore the impact of CIR on the ISI and the ultraviolet communication performance.However,the CIR of the ultraviolet links are closely related to the transceiver geometry.The precise analytical CIR for the ultraviolet channel is absent.To address this problem,this paper analyzes the influence of both coplanar and non-coplanar geometries on CIR for multiple scattering effects and proposes a modified Gamma function(MGF)for precise analytical CIR.Based on the MGF model,this paper quantifies the ISI and derives the probability density of the received photons for the photon-counting receiver.Then,this paper derives the bit-error rate(BER)and the achievable rate of both on-off keying(OOK)modulation and 2-pulse-position modulation(2-PPM).The simulation results showed that the proposed MGF model can achieve higher fitting precision of both CIR and BER compared with the existing Gamma function model.Besides,this paper finds that the achievable rate for the ultraviolet communication can achieve more than ten Mbps under the typical transceiver geometry.2.Self-Interference Quantification and Achievable Rate Analysis for FullDuplex Ultraviolet Communication LinksThe technology of space-division full-duplex communication can improve the spectrum utilization of time-division/wavelength-division duplex communication.However,the strong scattering effect of the ultraviolet signal in the atmosphere results in serious self-interference.To address this problem,this paper first quantifies the self-interference using an analytical CIR function.Then,based on the quantified self-interference,this paper derives the error rate and the corresponding achievable rate for OOK modulation,4-digital-pulseinterval modulation(4-DPIM)and 4-PPM.Besides,this paper proposes a selfinterference cancelling(SIC)method to mitigate the impacts of interferences.Simulation results show that the proposed SIC method can significantly improve the error rate and achievable rate performances.Furthermore,this paper finds that the full-duplex UV communication will gradually lose its advantage over the half-duplex ultraviolet communication as either the communication distance or the elevation angle increases.However,using the proposed SIC method,the full-duplex ultraviolet communication can hold its advantage in a wide range of system geometries.3.Joint Optimization of Power and Position for Multi-Hop Relay LinksMulti-hop full-duplex relay is the key technology to improve the distance of non-line-of-sight ultraviolet communication.However,the relays share the same time-frequency resources to transmit and receive information,which inevitably causes serious inter-relay interference.The relay position and the distance between relays directly determine the path loss of inter-relay interference links.To reduce the inter-relay interference and improve the system performance,this paper studies joint optimization of power and location for multi-hop relays.First,this paper derives the BER and the achievable rate for ultraviolet multi-hop full-duplex relay system.Then,this paper proposes an alternate iterative-Newton method,using joint optimization the relay position and the transmitting power of each relay to achieve minimization system BER.This paper further proposes the space-division technology to mitigate the impact of inter-relay interference.Simulation results show that increasing the number of relays or increasing the transmission power can improve the BER performance and achievable rate of the multi-hop full-duplex relay based ultraviolet communication systems.Besides,this paper finds that the space-division technology can further improve the BER performance,but sacrifices about half of achievable rates.To address the problems of ISI,self-interference and inter-relay interference due to the strong scattering effect of ultraviolet signals in the atmosphere,this paper studies the scattering interference model analysis and link enhancement technologies for ultraviolet communications.The relevant research results can effectively reduce the impact of interference on ultraviolet communication links,improve the system performance of ultraviolet communication links,and promote the practical application for ultraviolet communications.