Free Space Optical （FSO） networks, also known as optical wireless networks, have emerged as viable candidates for broadband wireless communications in the near future. The range of the potential application of FSO n...Free Space Optical （FSO） networks, also known as optical wireless networks, have emerged as viable candidates for broadband wireless communications in the near future. The range of the potential application of FSO networks is extensive, from home to satellite. However, FSO networks have not been popularized because of insufficient availability and reliability. Researchers have focused on the problems in the physical layer in order to exploit the properties of wireless optical channels. However, recent technological developments with successful results make it practical to explore the advantages of the high bandwidth. Some researchers have begun to focus on the problems of network and upper layers in FSO networks. In this survey, we classify prospective global FSO networks into three subnetworks and give an account of them. We also present state-of- the-art research and discuss what kinds of challenges exist.展开更多
We examine theoretically the performance of an Hg0.77Cd0.23Te based p-n photodetector/HFET optical receiver due to its possible application at 10.6 μm free space optical communication system at high bit rate.A rigoro...We examine theoretically the performance of an Hg0.77Cd0.23Te based p-n photodetector/HFET optical receiver due to its possible application at 10.6 μm free space optical communication system at high bit rate.A rigorous noise model of the receiver has been developed for this purpose.We calculate the total noise and sensitivity of the receiver.The front-end of the receiver exhibits a sensitivity of -45 dBm at a bit rate of 1 Gb/s and -30 dBm at a bit rate of 10 Gb/s,and the total mean-square noise curren t〈i2n〉=5×10-15 A2 at a bit rate of 1 Gb/s an d〈i2n〉 =10-12 A2 at a bit rate of 10 Gb/s,and a 3-dB bandwidth of 10 GHz.展开更多
The demand for broadband data services on high-speed trains is rapidly growing as more people commute between their homes and workplaces.However,current radio frequency(RF)technology cannot adequately meet this demand...The demand for broadband data services on high-speed trains is rapidly growing as more people commute between their homes and workplaces.However,current radio frequency(RF)technology cannot adequately meet this demand.In order to address the bandwidth constraint,a technique known as free space optics(FSO)has been proposed.This paper presents a mathematical derivation and formulation of curve track G2T-FSO(Ground-to-train Free Space Optical)model,where the track radius characteristics is 2667 m,divergence angle track is 1.5°for train velocity at V=250 km/h.Multiple transmitter configurations are proposed to maximize coverage range and enhance curve track G2T-FSO link performance under varying weather conditions.The curved track G2T-FSO model was evaluated in terms of received power,signal-to-noise ratio(SNR),bit error rate(BER),and eye diagrams.The results showed maximum coverage lengths of 618,505,365,and 240 m for 4Tx/1Rx,3Tx/1Rx,2Tx/1Rx,and 1Tx/1Rx configurations,respectively.The analyzed results demonstrate that the G2T-FSO link can be effectively implemented under various weather conditions.展开更多
An appropriate coding method that can reduce the error rate of communication system is especially important to the free space optical communication. STBC （space-time block code） is an orthogonal encoding method inte...An appropriate coding method that can reduce the error rate of communication system is especially important to the free space optical communication. STBC （space-time block code） is an orthogonal encoding method integrating space domain and time domain. The technology can combat fading effectively and improve error rate performance. In this paper, first, an STBC fit for optical communication with intensity modulation and direct detection （IM/DD） is proposed by combining the orthogonality of the Alamouti space-time code and the QPPM modulation. Then, the error rate performance of the system is analyzed under four cases： with or without channel fading, with or without background radiation. At last, this scheme is confirmed by Monte Carlo approach. It is shown that this method not only realizes the full speed rate transmission, and can improve the error rate performance of the system effectively, but also overcomes the scintillation effect exerted by atmosphere turbulence. When the symbol error probability （SEP） is 2×10^-3, according to the 1× 1 system, the sending power of the 2×1 system is nearly reduced by 3.5 dBJ, and the 2×2 system is nearly reduced by 9 dBJ.展开更多
Mobile free space optical networks have aroused much attention due to the ability of providing high speed connectivity over long distance using the wireless laser links,while requiring relatively high available bandwi...Mobile free space optical networks have aroused much attention due to the ability of providing high speed connectivity over long distance using the wireless laser links,while requiring relatively high available bandwidth resource and less energy consumption.However,maintaining the network with laserlinks is quite challenging due to a number of issues,such as the link fragility,the difficulty in pointingand tracking of the link,which also raises the great difficulty in the control of the network.In this paper,we present the methodology for the deployment of the mobile freespace optical networks based on our proposed OpenFlow-based control architecture.In addition,a new routing scheme is proposed and demonstrated on the testbed based on this control architecture.Delivery ratio,average delivery delay and time complexity are given to verify the performance of the OpenFlow-based control architecture.展开更多
Dynamic tracking of laser spot is a key process in the establishment of free space optical communication. In this paper, a dynamic tracking system was presented. In this system, a two-dimensional （2D） galvanometer w...Dynamic tracking of laser spot is a key process in the establishment of free space optical communication. In this paper, a dynamic tracking system was presented. In this system, a two-dimensional （2D） galvanometer was used to change the angle of the optical axis of the incident beam at a certain scanning frequency as optical signal jitter simulator, and another galvanometer was used to track the jitter with quadrant detector （QD） and data processing module to acquire the position information of laser spot. Results indicated that the tracking accuracy of this system mainly composed of 2D galvanometer was as high as 27,8 ~rad, and its linear deviation was less than 0.013. The system could still keep the dynamic tracking of the spot stable when the jitter frequency of the optical signal was less than 1000 Hz. Those results suggested that this system could be suitable for the short distance in free space communication due to its simple structure, easy to control and low cost compared with conventional system.展开更多
Free space optical （FSO） communication has been considered as an alternative to radio relay link line-of- sight （LOS） communication systems. The total attenuation is a combination of atmospheric attenuation in the...Free space optical （FSO） communication has been considered as an alternative to radio relay link line-of- sight （LOS） communication systems. The total attenuation is a combination of atmospheric attenuation in the atmosphere and geometric losses. The purpose of this paper is to study the geometric loss versus link range （in kin）, divergence angle, transmitter aperture diameter, and receiver aperture diameter. Total attenuation versus low visibility, average visibility, beam divergence, link range and rainfall rate were presented in this paper. Atmospheric attenuation （in dB） and scattering coefficient （in km-~） for several Yemeni main cities were explored. The study was concentrated on received power versus low and average visibilities and link range. Series of related simulation results were illustrated and discussed in this paper about the climate effects on performance of FSO communication systems in Yemen.展开更多
The light＇s orbital angular momentum （OAM） is a consequence of the spiral flow of the electromagnetic energy. In this paper, an analysis of light beams with OAM used for free space optics （FSO） is conducted. The ...The light＇s orbital angular momentum （OAM） is a consequence of the spiral flow of the electromagnetic energy. In this paper, an analysis of light beams with OAM used for free space optics （FSO） is conducted. The basic description and conception of light＇s OAM are reviewed. Both encoding information into OAM states of single light beam and encoding information into spatial structure of the mixed optical vortex with OAM are discussed, and feasibility to improve the FSO＇s performance of security and obstruction of line of sight is examined.展开更多
There is growing global interest in establishing free-space optical(FSO)communication links,such as groundsatellite links(GSLs)of at least hundreds of kilometers,intersatellite links of thousands of kilometers,and fut...There is growing global interest in establishing free-space optical(FSO)communication links,such as groundsatellite links(GSLs)of at least hundreds of kilometers,intersatellite links of thousands of kilometers,and future deep space links of much greater dimensions.Enabling outdoor wireless FSO communication systems to be utilized during daylight hours can increase their availability in space-air-ground networks;however,this is usually accompanied by incoherent background radiation that impairs the signal-to-noise ratio(SNR)and bit error rate(BER).Therefore,a preliminary review of the background noise is required before constructing ground terminals with a suitable SNR in a harsh environment with high levels of solar noise.Herein,we evaluated the background noise that sunlight provides to ground terminals and quantitatively examined its impact on the SNR,communication performance,and beacon detection accuracy of the developed all-free-space ground terminal.Furthermore,we present the results of a daytime demonstration of a 7-km terrestrial free-space optical communication link by employing our ground terminal that was designed based on these analyses.The results verified that 2.5-Gbps data transmission up to 7 km is feasible,even in expected daytime satellite tracking scenarios with high background noise,by the developed system with spectral and spatial filtering to achieve an acceptable SNR.The background noise results of our research are anticipated to further the research on quantum communication networks,light detection and ranging(LiDAR),and green energy technologies.展开更多
Free-space optical communication and space optical information network offer many more superiorities over optical fiber,RF,or microwaves communication techniques,with higher data transfer rate,smaller platforms to lau...Free-space optical communication and space optical information network offer many more superiorities over optical fiber,RF,or microwaves communication techniques,with higher data transfer rate,smaller platforms to launch and lower costs.A comprehensive overview on the architectures of the space high-speed optical information network was provided.In fundamental system,networking approach and operation mechanisms of the space optical information network were fully emphasized to be discussed a lot.The interactions of light waves and microwave network have been outlined.A blueprint for space optical information network technology is presented to be used in various communication fields in the future.展开更多
When the light beam propagates in the atmosphere, the signal will be absorbed and scattered by the gas molecules and water mist in the atmosphere, which will cause the loss of power rate. The complex atmospheric envir...When the light beam propagates in the atmosphere, the signal will be absorbed and scattered by the gas molecules and water mist in the atmosphere, which will cause the loss of power rate. The complex atmospheric environment will produce a variety of adverse effects on the signal. The interference produced by these effects overlaps with each other, which will seriously affect the strength of the received signal. Therefore, how to effectively suppress the atmospheric turbulence effect in the random atmospheric turbulence channel, ensure the normal transmission of the signal in the atmospheric channel, and reduce the bit error rate of the communication system, is very necessary to improve the communication system. When processing the received signal, it is an important step to detect the transmitted signal by comparing the received signal with the threshold. In this paper, based on the atmospheric turbulence distribution model, the adaptive signal decision threshold is obtained through the estimation of high-order cumulant. Monte Carlo method is used to verify the performance of adaptive threshold detection. The simulation results show that the high-order cumulant estimation of atmospheric turbulence parameters can realize the adaptive change of the decision threshold with the channel condition. It is shown that the adaptive threshold detection can effectively restrain atmospheric turbulence, improve the performance of free space optical and improve the communication quality.展开更多
Intelligent Transport Systems(ITS)are crucial for safety,efficiency,and reduced congestion in transportation.They require efficient,secure,high-speed communication.Radio Frequency(RF)technologies like Fifth Generation...Intelligent Transport Systems(ITS)are crucial for safety,efficiency,and reduced congestion in transportation.They require efficient,secure,high-speed communication.Radio Frequency(RF)technologies like Fifth Generation(5G),Beyond 5G(B5G),and Sixth Generation(6G)are promising,but spectrum scarcity mandates coexistence with Optical Wireless Communication(OWC)networks,which offer high data rates and security,forming a strong foundation for hybrid RF/OWC applications in ITS.In this paper,we delve into the application of Machine Learning(ML)to enhance data communications within OWC systems in ITS.We commence by conducting an in-depth examination of the data communication prerequisites and the associated challenges within the ITS domain.Subsequently,we elucidate the compelling rationale behind the convergence of heterogeneous RF technologies with OWC for data communications in ITS scenarios.Our investigation then pivots towards elucidating the indispensable role played by ML in optimizing data communications via OWC within ITS.To provide a comprehensive perspective,we systematically evaluate and compare a spectrum of ML methodologies employed in OWC ITS data communications.As a culmination of our study,we proffer a set of valuable recommendations and illuminate promising avenues for future research endeavors that warrant further exploration within this critical intersection of ML,OWC,and ITS data communications.展开更多
基金This work is supported in part by the US National Science Foundation under Grants CNS-1320664, and by the Wireless Engineering Research and Education Center （WEREC） at Auburn University, Aubur, AL, USA.
文摘Free Space Optical （FSO） networks, also known as optical wireless networks, have emerged as viable candidates for broadband wireless communications in the near future. The range of the potential application of FSO networks is extensive, from home to satellite. However, FSO networks have not been popularized because of insufficient availability and reliability. Researchers have focused on the problems in the physical layer in order to exploit the properties of wireless optical channels. However, recent technological developments with successful results make it practical to explore the advantages of the high bandwidth. Some researchers have begun to focus on the problems of network and upper layers in FSO networks. In this survey, we classify prospective global FSO networks into three subnetworks and give an account of them. We also present state-of- the-art research and discuss what kinds of challenges exist.
文摘We examine theoretically the performance of an Hg0.77Cd0.23Te based p-n photodetector/HFET optical receiver due to its possible application at 10.6 μm free space optical communication system at high bit rate.A rigorous noise model of the receiver has been developed for this purpose.We calculate the total noise and sensitivity of the receiver.The front-end of the receiver exhibits a sensitivity of -45 dBm at a bit rate of 1 Gb/s and -30 dBm at a bit rate of 10 Gb/s,and the total mean-square noise curren t〈i2n〉=5×10-15 A2 at a bit rate of 1 Gb/s an d〈i2n〉 =10-12 A2 at a bit rate of 10 Gb/s,and a 3-dB bandwidth of 10 GHz.
基金funded by the Deputyship for Research&Innovation,Ministry of Education in Saudi Arabia,grant number S-1443-0223.
文摘The demand for broadband data services on high-speed trains is rapidly growing as more people commute between their homes and workplaces.However,current radio frequency(RF)technology cannot adequately meet this demand.In order to address the bandwidth constraint,a technique known as free space optics(FSO)has been proposed.This paper presents a mathematical derivation and formulation of curve track G2T-FSO(Ground-to-train Free Space Optical)model,where the track radius characteristics is 2667 m,divergence angle track is 1.5°for train velocity at V=250 km/h.Multiple transmitter configurations are proposed to maximize coverage range and enhance curve track G2T-FSO link performance under varying weather conditions.The curved track G2T-FSO model was evaluated in terms of received power,signal-to-noise ratio(SNR),bit error rate(BER),and eye diagrams.The results showed maximum coverage lengths of 618,505,365,and 240 m for 4Tx/1Rx,3Tx/1Rx,2Tx/1Rx,and 1Tx/1Rx configurations,respectively.The analyzed results demonstrate that the G2T-FSO link can be effectively implemented under various weather conditions.
基金Supported by the Defence Major Laboratory Fund (Grant No. 9140C3601010701)the Science Special Fund of the Education Department of Shaanxi Province (Grant No. 07JK332)+2 种基金the Natural Science Fund of Shaanxi Province (Grant No. 2007F12)the Science and Technology Project of the Communications of Guangdong Province (Grant No. 2007-26)and the Fund of Excellent Doctor Degree of Xi’an University of 9 Technology (Grant No. 602-210808)
文摘An appropriate coding method that can reduce the error rate of communication system is especially important to the free space optical communication. STBC （space-time block code） is an orthogonal encoding method integrating space domain and time domain. The technology can combat fading effectively and improve error rate performance. In this paper, first, an STBC fit for optical communication with intensity modulation and direct detection （IM/DD） is proposed by combining the orthogonality of the Alamouti space-time code and the QPPM modulation. Then, the error rate performance of the system is analyzed under four cases： with or without channel fading, with or without background radiation. At last, this scheme is confirmed by Monte Carlo approach. It is shown that this method not only realizes the full speed rate transmission, and can improve the error rate performance of the system effectively, but also overcomes the scintillation effect exerted by atmosphere turbulence. When the symbol error probability （SEP） is 2×10^-3, according to the 1× 1 system, the sending power of the 2×1 system is nearly reduced by 3.5 dBJ, and the 2×2 system is nearly reduced by 9 dBJ.
基金supported in part by 863 program(2012AA011301)973 program (2010CB328204)+3 种基金NSFC project(61271189, 61201154)RFDP Project(20120005120019)the Fundamental Research Funds for the Central Universities(2013RC1201)Fund of State Key Laboratory of Information Photonics and Optical Communications(BUPT)
文摘Mobile free space optical networks have aroused much attention due to the ability of providing high speed connectivity over long distance using the wireless laser links,while requiring relatively high available bandwidth resource and less energy consumption.However,maintaining the network with laserlinks is quite challenging due to a number of issues,such as the link fragility,the difficulty in pointingand tracking of the link,which also raises the great difficulty in the control of the network.In this paper,we present the methodology for the deployment of the mobile freespace optical networks based on our proposed OpenFlow-based control architecture.In addition,a new routing scheme is proposed and demonstrated on the testbed based on this control architecture.Delivery ratio,average delivery delay and time complexity are given to verify the performance of the OpenFlow-based control architecture.
基金This work wassupported by the National Natural Science Foundation of China （Grant Nos. 61475058 and 11104094）, Wuhan Science And Technology Proj ect （No. 2015010101010001 ）, Shenzhen Basic Research Project （No. JCYJ20140419131733980）, and the Open Fund of TheState Key Laboratory of High Performance Complex Manufacturing （No Kfkt2013-07）.
文摘Dynamic tracking of laser spot is a key process in the establishment of free space optical communication. In this paper, a dynamic tracking system was presented. In this system, a two-dimensional （2D） galvanometer was used to change the angle of the optical axis of the incident beam at a certain scanning frequency as optical signal jitter simulator, and another galvanometer was used to track the jitter with quadrant detector （QD） and data processing module to acquire the position information of laser spot. Results indicated that the tracking accuracy of this system mainly composed of 2D galvanometer was as high as 27,8 ~rad, and its linear deviation was less than 0.013. The system could still keep the dynamic tracking of the spot stable when the jitter frequency of the optical signal was less than 1000 Hz. Those results suggested that this system could be suitable for the short distance in free space communication due to its simple structure, easy to control and low cost compared with conventional system.
文摘Free space optical （FSO） communication has been considered as an alternative to radio relay link line-of- sight （LOS） communication systems. The total attenuation is a combination of atmospheric attenuation in the atmosphere and geometric losses. The purpose of this paper is to study the geometric loss versus link range （in kin）, divergence angle, transmitter aperture diameter, and receiver aperture diameter. Total attenuation versus low visibility, average visibility, beam divergence, link range and rainfall rate were presented in this paper. Atmospheric attenuation （in dB） and scattering coefficient （in km-~） for several Yemeni main cities were explored. The study was concentrated on received power versus low and average visibilities and link range. Series of related simulation results were illustrated and discussed in this paper about the climate effects on performance of FSO communication systems in Yemen.
文摘The light＇s orbital angular momentum （OAM） is a consequence of the spiral flow of the electromagnetic energy. In this paper, an analysis of light beams with OAM used for free space optics （FSO） is conducted. The basic description and conception of light＇s OAM are reviewed. Both encoding information into OAM states of single light beam and encoding information into spatial structure of the mixed optical vortex with OAM are discussed, and feasibility to improve the FSO＇s performance of security and obstruction of line of sight is examined.
文摘There is growing global interest in establishing free-space optical(FSO)communication links,such as groundsatellite links(GSLs)of at least hundreds of kilometers,intersatellite links of thousands of kilometers,and future deep space links of much greater dimensions.Enabling outdoor wireless FSO communication systems to be utilized during daylight hours can increase their availability in space-air-ground networks;however,this is usually accompanied by incoherent background radiation that impairs the signal-to-noise ratio(SNR)and bit error rate(BER).Therefore,a preliminary review of the background noise is required before constructing ground terminals with a suitable SNR in a harsh environment with high levels of solar noise.Herein,we evaluated the background noise that sunlight provides to ground terminals and quantitatively examined its impact on the SNR,communication performance,and beacon detection accuracy of the developed all-free-space ground terminal.Furthermore,we present the results of a daytime demonstration of a 7-km terrestrial free-space optical communication link by employing our ground terminal that was designed based on these analyses.The results verified that 2.5-Gbps data transmission up to 7 km is feasible,even in expected daytime satellite tracking scenarios with high background noise,by the developed system with spectral and spatial filtering to achieve an acceptable SNR.The background noise results of our research are anticipated to further the research on quantum communication networks,light detection and ranging(LiDAR),and green energy technologies.
基金supported by Excellent Satellite Optical Communications Team in Harbin Institute of Technology.
文摘Free-space optical communication and space optical information network offer many more superiorities over optical fiber,RF,or microwaves communication techniques,with higher data transfer rate,smaller platforms to launch and lower costs.A comprehensive overview on the architectures of the space high-speed optical information network was provided.In fundamental system,networking approach and operation mechanisms of the space optical information network were fully emphasized to be discussed a lot.The interactions of light waves and microwave network have been outlined.A blueprint for space optical information network technology is presented to be used in various communication fields in the future.
文摘When the light beam propagates in the atmosphere, the signal will be absorbed and scattered by the gas molecules and water mist in the atmosphere, which will cause the loss of power rate. The complex atmospheric environment will produce a variety of adverse effects on the signal. The interference produced by these effects overlaps with each other, which will seriously affect the strength of the received signal. Therefore, how to effectively suppress the atmospheric turbulence effect in the random atmospheric turbulence channel, ensure the normal transmission of the signal in the atmospheric channel, and reduce the bit error rate of the communication system, is very necessary to improve the communication system. When processing the received signal, it is an important step to detect the transmitted signal by comparing the received signal with the threshold. In this paper, based on the atmospheric turbulence distribution model, the adaptive signal decision threshold is obtained through the estimation of high-order cumulant. Monte Carlo method is used to verify the performance of adaptive threshold detection. The simulation results show that the high-order cumulant estimation of atmospheric turbulence parameters can realize the adaptive change of the decision threshold with the channel condition. It is shown that the adaptive threshold detection can effectively restrain atmospheric turbulence, improve the performance of free space optical and improve the communication quality.
文摘Intelligent Transport Systems(ITS)are crucial for safety,efficiency,and reduced congestion in transportation.They require efficient,secure,high-speed communication.Radio Frequency(RF)technologies like Fifth Generation(5G),Beyond 5G(B5G),and Sixth Generation(6G)are promising,but spectrum scarcity mandates coexistence with Optical Wireless Communication(OWC)networks,which offer high data rates and security,forming a strong foundation for hybrid RF/OWC applications in ITS.In this paper,we delve into the application of Machine Learning(ML)to enhance data communications within OWC systems in ITS.We commence by conducting an in-depth examination of the data communication prerequisites and the associated challenges within the ITS domain.Subsequently,we elucidate the compelling rationale behind the convergence of heterogeneous RF technologies with OWC for data communications in ITS scenarios.Our investigation then pivots towards elucidating the indispensable role played by ML in optimizing data communications via OWC within ITS.To provide a comprehensive perspective,we systematically evaluate and compare a spectrum of ML methodologies employed in OWC ITS data communications.As a culmination of our study,we proffer a set of valuable recommendations and illuminate promising avenues for future research endeavors that warrant further exploration within this critical intersection of ML,OWC,and ITS data communications.
