Intersatellite laser crosslinks provide significantly higher data throughput than traditional RF communication systems. They take advantage of lasers' small wavelengths and highly directed beams to transmit data over long distances with minimal losses. A laser crosslink system consists of a transmitter, receiver, acquisition subsystem to initially align the links, and a tracking subsystem to maintain the alignment during data transmission. Optical communications offer wide bandwidths and high data transmission rates well beyond what is possible with RF technologies. Various laser crosslink systems are discussed to understand their subsystems and implementations.
IJCER (www.ijceronline.com) International Journal of computational Engineerin...ijceronline
This document summarizes a research paper on statistical multipath signal detection in CDMA for ad hoc networks. The paper presents simulation results of transmitting a signal through 5 different Rayleigh fading channels and selecting the signal with the highest SNR. The selected signal is then transmitted over an ad hoc network using a shortest path routing algorithm. Key aspects covered include: Rayleigh fading modeling, CDMA, OFDM, theoretical and simulated BER comparisons of BPSK over Rayleigh and AWGN channels, implementation of signal transmission over 5 channels in MATLAB, and use of the highest quality signal for transmission in an ad hoc network.
FUTURE TRENDS IN FIBER OPTICS COMMUNICATIONIJCI JOURNAL
This document discusses future trends in fiber optic communication. It begins with an introduction to fiber optic communication and how advances in technology have increased data transmission capacity through optical fibers. The document then discusses several potential future trends, including all optical communication networks that process data entirely in the optical domain, multi-terabit optical networks enabled by dense wavelength division multiplexing, and intelligent optical transmission networks that can dynamically allocate resources. Overall, the document outlines how fiber optic communication is expected to continue advancing to support higher data rates, more advanced switching techniques, and smarter network architectures.
FSO networks under turbulence - Northumbria University 2013 Research ConferenceJoaquin Perez
FSO networks: understanding route diversity under turbulence phenomena towards reliable FSO mesh networks design.
In last mile extensions of MANs, wireless mesh networks are multi-hop networks being used as backbone networks connecting end-users with the access points connected to the Internet. Wireless mesh networks are an attractive option over optical fibres because of their ease of installation and cost effectiveness of deployment[1]. Moreover, Free Space Optics (FSO) technology is an attractive option for use in mesh networks [2, 3]. However, time-variant influence of the atmosphere in FSO links that introduces one of the main drawbacks [4]. In order to overcome the turbulence induced fading in FSO systems, several techniques have been proposed These include: spatial transmitter/receiver diversity [5] [6]; adaptive beam forming [7]; wavelength diversity [8], multiple-beam communication [9], novel modulation techniques and hybrid RF/optical link scheme. Moreover, topology design and routing are essential tools for FSO mesh networks performance. The turbulence phenomena also influences in the topology and routing design of complex FSO networks, then route diversity techniques will improve the mesh network reliability [14]. For example, route diversity application within mesh optical networks deployed Tokyo provided interesting experiment results in [15]. This presentation will offer an overview of turbulence phenomena on FSO mesh networks from route diversity point of view.
References
[1] I. F. Akyildiz, X. Wang, and W. Wang, "Wireless mesh networks: a survey," Computer Networks, vol. 47, pp. 445-487, 2005.
[2] Z. Hu, P. Verma, and J. J. Sluss, "Improved reliability of free-space optical mesh networks through topology design," J. Opt. Netw., vol. 7, pp. 436-448, 2008.
[3] A. Kashyap, K. Lee, M. Kalantari, S. Khuller, and M. Shayman, "Integrated topology control and routing in wireless optical mesh networks," Computer Networks, vol. 51, pp. 4237-4251, 2007.
[4] Z. Ghassemlooy, W. Popoola, and S. Rajbhandari, Optical Wireless Communications : System and Channel Modelling with MATLAB: CRC Press 2012.
[5] S. M. Navidpour, M. Uysal, and M. Kavehrad, "BER performance of free-space optical transmission with spatial diversity," IEEE Trans. Wireless Commun., vol. 6, pp. 2813-2819, Aug 2007.
[6] H. Moradi, H. H. Refai, and P. G. LoPresti, "Switch-and-stay and switch-and-examine dual diversity for high-speed free-space optics links," IET Optoelectron, vol. 6, pp. 34-42, 2012.
[7] R. K. Tyson, "Bit-error rate for free-space adaptive optics laser communications," J. Opt. Soc. Am. A:, vol. 19, pp. 753-758, Apr 2002.
[8] V. Weerackody and A. R. Hammons, "Wavelength Correlation in Free Space Optical Communication Systems," in Proceedings of IEEE Military Communications Conference 2006, 2006, pp. pp. 1-6.
This document provides an overview of free space optics (FSO) communications. It discusses the history and development of FSO from the late 19th century experiments of Alexander Graham Bell to modern military and satellite applications. The basic components and designs of FSO links are described, including the advantages and disadvantages of directed line-of-sight and diffuse links. Advanced techniques to improve link performance through diversity and adaptive signal processing are also summarized. Key effects on FSO link performance like scattering and limitations are outlined. The document concludes with a discussion of security benefits and references for FSO communications.
This document discusses free-space optical (FSO) links, which transmit optical signals through the atmosphere without fiber. It provides a history of optical communication beginning with Bell's photophone in 1880. The document outlines the basic characteristics and advantages/disadvantages of FSO links. It also presents models to characterize laser beams, power budgets, and link margins for FSO systems. Overall, the document provides an overview of FSO link technology and modeling.
Under Water Optical Wireless CommunicationIRJET Journal
This document discusses underwater wireless optical communication (UWOC). It begins by introducing some key challenges of UWOC, such as attenuation and fading caused by absorption, scattering, and turbulence in water. It then discusses different modulation techniques that have been used for UWOC, including on-off keying (OOK), digital pulse interval modulation (DPIM), and polarization shift keying (Polk). The document proposes a new modulation scheme called polarized DPIM (P-DPIM) that combines PPM and Polk to improve power efficiency and error performance over long distances. It presents the results of a simulation comparing P-DPIM to other modulation schemes at different transmission distances, finding that P-DPIM provides better performance
IJCER (www.ijceronline.com) International Journal of computational Engineerin...ijceronline
This document summarizes a research paper on statistical multipath signal detection in CDMA for ad hoc networks. The paper presents simulation results of transmitting a signal through 5 different Rayleigh fading channels and selecting the signal with the highest SNR. The selected signal is then transmitted over an ad hoc network using a shortest path routing algorithm. Key aspects covered include: Rayleigh fading modeling, CDMA, OFDM, theoretical and simulated BER comparisons of BPSK over Rayleigh and AWGN channels, implementation of signal transmission over 5 channels in MATLAB, and use of the highest quality signal for transmission in an ad hoc network.
FUTURE TRENDS IN FIBER OPTICS COMMUNICATIONIJCI JOURNAL
This document discusses future trends in fiber optic communication. It begins with an introduction to fiber optic communication and how advances in technology have increased data transmission capacity through optical fibers. The document then discusses several potential future trends, including all optical communication networks that process data entirely in the optical domain, multi-terabit optical networks enabled by dense wavelength division multiplexing, and intelligent optical transmission networks that can dynamically allocate resources. Overall, the document outlines how fiber optic communication is expected to continue advancing to support higher data rates, more advanced switching techniques, and smarter network architectures.
FSO networks under turbulence - Northumbria University 2013 Research ConferenceJoaquin Perez
FSO networks: understanding route diversity under turbulence phenomena towards reliable FSO mesh networks design.
In last mile extensions of MANs, wireless mesh networks are multi-hop networks being used as backbone networks connecting end-users with the access points connected to the Internet. Wireless mesh networks are an attractive option over optical fibres because of their ease of installation and cost effectiveness of deployment[1]. Moreover, Free Space Optics (FSO) technology is an attractive option for use in mesh networks [2, 3]. However, time-variant influence of the atmosphere in FSO links that introduces one of the main drawbacks [4]. In order to overcome the turbulence induced fading in FSO systems, several techniques have been proposed These include: spatial transmitter/receiver diversity [5] [6]; adaptive beam forming [7]; wavelength diversity [8], multiple-beam communication [9], novel modulation techniques and hybrid RF/optical link scheme. Moreover, topology design and routing are essential tools for FSO mesh networks performance. The turbulence phenomena also influences in the topology and routing design of complex FSO networks, then route diversity techniques will improve the mesh network reliability [14]. For example, route diversity application within mesh optical networks deployed Tokyo provided interesting experiment results in [15]. This presentation will offer an overview of turbulence phenomena on FSO mesh networks from route diversity point of view.
References
[1] I. F. Akyildiz, X. Wang, and W. Wang, "Wireless mesh networks: a survey," Computer Networks, vol. 47, pp. 445-487, 2005.
[2] Z. Hu, P. Verma, and J. J. Sluss, "Improved reliability of free-space optical mesh networks through topology design," J. Opt. Netw., vol. 7, pp. 436-448, 2008.
[3] A. Kashyap, K. Lee, M. Kalantari, S. Khuller, and M. Shayman, "Integrated topology control and routing in wireless optical mesh networks," Computer Networks, vol. 51, pp. 4237-4251, 2007.
[4] Z. Ghassemlooy, W. Popoola, and S. Rajbhandari, Optical Wireless Communications : System and Channel Modelling with MATLAB: CRC Press 2012.
[5] S. M. Navidpour, M. Uysal, and M. Kavehrad, "BER performance of free-space optical transmission with spatial diversity," IEEE Trans. Wireless Commun., vol. 6, pp. 2813-2819, Aug 2007.
[6] H. Moradi, H. H. Refai, and P. G. LoPresti, "Switch-and-stay and switch-and-examine dual diversity for high-speed free-space optics links," IET Optoelectron, vol. 6, pp. 34-42, 2012.
[7] R. K. Tyson, "Bit-error rate for free-space adaptive optics laser communications," J. Opt. Soc. Am. A:, vol. 19, pp. 753-758, Apr 2002.
[8] V. Weerackody and A. R. Hammons, "Wavelength Correlation in Free Space Optical Communication Systems," in Proceedings of IEEE Military Communications Conference 2006, 2006, pp. pp. 1-6.
This document provides an overview of free space optics (FSO) communications. It discusses the history and development of FSO from the late 19th century experiments of Alexander Graham Bell to modern military and satellite applications. The basic components and designs of FSO links are described, including the advantages and disadvantages of directed line-of-sight and diffuse links. Advanced techniques to improve link performance through diversity and adaptive signal processing are also summarized. Key effects on FSO link performance like scattering and limitations are outlined. The document concludes with a discussion of security benefits and references for FSO communications.
This document discusses free-space optical (FSO) links, which transmit optical signals through the atmosphere without fiber. It provides a history of optical communication beginning with Bell's photophone in 1880. The document outlines the basic characteristics and advantages/disadvantages of FSO links. It also presents models to characterize laser beams, power budgets, and link margins for FSO systems. Overall, the document provides an overview of FSO link technology and modeling.
Under Water Optical Wireless CommunicationIRJET Journal
This document discusses underwater wireless optical communication (UWOC). It begins by introducing some key challenges of UWOC, such as attenuation and fading caused by absorption, scattering, and turbulence in water. It then discusses different modulation techniques that have been used for UWOC, including on-off keying (OOK), digital pulse interval modulation (DPIM), and polarization shift keying (Polk). The document proposes a new modulation scheme called polarized DPIM (P-DPIM) that combines PPM and Polk to improve power efficiency and error performance over long distances. It presents the results of a simulation comparing P-DPIM to other modulation schemes at different transmission distances, finding that P-DPIM provides better performance
Free space optical communication(final)kanusinghal3
This document provides an overview of free space optical communication (FSO). It discusses the motivation for using FSO due to increasing bandwidth needs and spectrum scarcity. FSO uses visible or infrared light to transmit broadband communications in a line-of-sight fashion. The document outlines key challenges of FSO including attenuation from environmental factors like fog and scattering. It also reviews the advantages of low cost and high security as well as disadvantages such as sensitivity to obstructions. The document concludes that FSO is a promising supplemental technology to wireless and fiber for short-range applications.
Transmission media is the physical medium used to transmit data between a sender and receiver. The two main types are guided and unguided media. Guided media uses physical pathways like cables to direct signals over shorter distances at high speeds securely. Common examples are twisted pair, coaxial, and fiber optic cables. Unguided media transmits electromagnetic waves without physical pathways, broadcasting signals through the air over longer distances less securely. Common examples are radio waves, microwaves, and infrared waves used in wireless technologies.
International Journal of Computational Engineering Research(IJCER) ijceronline
International Journal of Computational Engineering Research (IJCER) is dedicated to protecting personal information and will make every reasonable effort to handle collected information appropriately. All information collected, as well as related requests, will be handled as carefully and efficiently as possible in accordance with IJCER standards for integrity and objectivity.
The document describes the design of a free space optical link. It begins with an overview of what free space optical communication is and its advantages over other wired technologies. It then discusses the basic components of an FSO link including the transmitter, receiver, and transceiver implementation. The transmitter section focuses on the laser diode source and driver circuitry. The receiver section covers the photodetector, preamplifier, and decision circuitry. Lastly, it discusses modeling the FSO channel and the factors that can impact signal propagation through the atmosphere.
Free space optics (FSO) uses visible light communication or infrared light to transmit data wirelessly. It works by transmitting a laser beam between an optical transmitter and receiver using lenses or telescopes. FSO can provide high-speed wireless connectivity for applications such as last mile internet access, enterprise connectivity, fiber backup links, and cellular backhaul. It has advantages over radio frequency technologies in that it has unlimited spectrum, high bandwidth, low latency, and security from wireless tapping. However, FSO performance can be impacted by atmospheric conditions like fog, rain and turbulence. The document provides an overview of the history, working mechanism, applications and advantages of FSO technology.
The document summarizes free space optical communication (FSO). It discusses the operation of FSO links, their advantages over fiber and microwave links, and applications. The key points are:
1. An FSO link consists of a transmitter, receiver, and tracking system to direct light beams between nodes. It allows license-free, high-speed connections but is susceptible to weather.
2. Applications include point-to-point links between buildings and potential mesh networks or use on high altitude platforms. Mesh networks provide better coverage but at a higher cost than point-to-point links.
3. Compared to fiber and microwave links, FSO systems have lower costs and power needs but higher data rates and
Descripcion de la tecnologia y sistemas de luz para transmitir señales
Sistemas de transmision por fibra optica, equipos de fibra optica para transmision inalambrica
This document provides an overview of free space optics communication (FSO). It begins with an introduction that defines FSO as using visible or infrared light beams through the atmosphere for optical communications. It then describes how FSO works using low power infrared lasers and photon detectors. The document outlines the basic architecture of FSO systems including transmitters, receivers, and modulation techniques. It discusses applications, advantages such as low cost and flexibility, and disadvantages like interference from weather. In conclusion, the document presents FSO as a wireless optical technology alternative to traditional wired networks.
Free space optics (FSO) uses lasers to transmit data through the air between two points without fiber. FSO can transmit at speeds up to 2.5 Gbps currently and is expected to reach 10 Gbps soon. It uses infrared lasers and photo detectors for full duplex communication. FSO provides a cost-effective solution for the "last mile" problem of connecting buildings to high-speed fiber backbone networks when laying new fiber is not feasible or affordable. Major advantages of FSO include low costs, high security, and no licensing requirements compared to other wireless technologies.
Optical multiplexers allow multiple signals to be transmitted simultaneously over a single optical fiber link. There are different optical multiplexing techniques, including wavelength division multiplexing (WDM) and optical time division multiplexing (OTDM). WDM assigns each signal a unique wavelength, while OTDM separates signals in the time domain. Optical multiplexers and demultiplexers use passive optical filters to combine and separate the wavelength signals. This increases bandwidth utilization and reduces transmission costs.
This document provides an overview of different transmission media used for data communication, including both guided and unguided media. It discusses various types of guided media such as twisted pair cables, coaxial cables, and fiber optic cables. It describes their characteristics, applications, advantages and disadvantages. The document also covers unguided or wireless transmission media such as radio waves, microwaves, and infrared. It explains propagation methods for unguided signals and the role of antennas. Finally, it discusses some issues with signal transmission such as attenuation, distortion and noise.
The document presents information on free space optics communication. It discusses how FSO works by transmitting data as invisible light pulses between a transmitter and receiver. FSO provides benefits like high bandwidth, bit rate, power efficiency, and data security at low cost. However, it faces challenges from environmental factors like absorption, scattering, fog, scintillation, solar interference, dispersion, and building motion that can attenuate the signal. The document lists manufacturers in the FSO field like LightPointe, AirFiber, and Terabeam and the funding they have received.
The document discusses laser communication and provides details about its key aspects. It begins with an introduction to laser communication and describes how it works. It then explains why laser communication is preferable to fiber optics and microwaves in certain situations. The document outlines the main types of lasers used in communication systems and highlights features like bandwidth, power requirements, and security advantages over radio frequency systems. It also examines link parameters, transmitter and receiver design considerations, and reliability factors for laser communication links.
FSO (Free Space Optics) uses visible light or infrared lasers to transmit data through the air, providing broadband communications. It works similar to fiber but without the physical infrastructure, transmitting focused beams of light between optical transceivers. While challenges include atmospheric effects like fog, it has applications for last mile access and enterprise connectivity due to low costs, ease of deployment, and flexibility.
The document discusses optical wireless communication and free space optics. It provides an introduction to free space optics concepts, how free space optic systems work, their applications, advantages, components like transmitters and receivers, and compares LED and laser diode light sources. It also discusses propagation concepts, link budget calculations and considerations for signal propagation and data security in free space optic systems.
This presentation discusses freespace optical communication (FSO), which transmits modulated beams of light through the atmosphere for broadband communications. It provides a brief history of FSO, describes how FSO works by converting network traffic to light pulses, and lists its advantages like low cost, high security, and immunity to electromagnetic interference. The presentation also outlines FSO's applications like metro networks and last mile access, and discusses its disadvantages such as reliance on line of sight and susceptibility to atmospheric conditions.
This document summarizes a technical seminar on free space optics (FSO) presented by Kartik K Benageri at Jain Institute of Technology in Davangere, Karnataka, India. The seminar covered the introduction, key features, working principles, advantages, limitations, and conclusions of FSO technology. FSO uses lasers and photo detectors to transmit data, voice, or video at speeds up to 2.5 Gbps in a line-of-sight fashion without the need for fiber. While offering benefits like flexibility, low cost, and security compared to fiber or microwave, FSO performance can be impacted by environmental factors like fog, rain, scattering, and building sway. The seminar provided information
Free-space optical (FSO) communication uses visible light or infrared light beams to transmit data through the air. It works similarly to fiber optics but transmits the light beam through the air instead of glass fibers. FSO systems can transmit data at rates similar to fiber optics over distances up to a few kilometers. They provide a wireless complement to radio-based communication systems. The main requirements are having an unobstructed line-of-sight between the transmitter and receiver and clear atmospheric conditions.
The Effect of PMD (Polarization Mode Dispersion) the Fibers of New and Old In...inventionjournals
This is a study conducted in a laboratory at the university as a simulation to see the effect of new fiber PMD for different distances. This is done to compare the performance of the digital system with optical fiber WDM. In this simulation are not included remission, chromatic dispersion and nonlinear effects. In this way all of the signal distortions caused only by different combinations of PDM. Polarization effects are very important in communications systems with optical fiber. Optical fiber that is used mainly during the simulation is a standard single mode fiber (SSMF).
The document summarizes recent developments in node clustering for wireless sensor networks. It discusses how clustering helps organize the network topology to balance load and prolong lifetime. Several key challenges in clustering sensor networks are outlined, including the need for distributed clustering algorithms that rely only on local neighborhood information. Clustering approaches are classified based on their objectives and design principles. Key issues that affect practical deployment of clustering techniques are also discussed.
Study on Laser Communication: Features, Application, Advantagesijtsrd
Laser communications offer a viable alternative to RF communications for intersatellite links and other applications where high-performance links are necessary. High data rate, small antenna size, narrow beam divergence, and a narrow field of view are characteristics of laser communication that offer a number of potential advantages for system design. The high data rate and large information throughput available with laser communications are many times greater than in radio frequency (RF) systems. The small antenna size requires only a small increase in the weight and volume of host vehicle. In addition, this feature substantially reduces blockage of fields of view of the most desirable areas on satellites. The smaller antennas, with diameters typically less than 30cm, create less momentum disturbance to any sensitive satellite sensors. The narrow beam divergence of affords interference-free and secure operation. Prof. Atul A. Padghan | Prof. Ankit P. Jaiswal"Study on Laser Communication: Features, Application, Advantages" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-2 | Issue-3 , April 2018, URL: http://www.ijtsrd.com/papers/ijtsrd10798.pdf http://www.ijtsrd.com/engineering/electronics-and-communication-engineering/10798/study-on-laser-communication-features-application-advantages/prof-atul-a-padghan
This document provides an overview of reconfigurable intelligent surfaces (RIS) for wireless communications. It discusses two main implementations of RIS - using reflectarrays or metasurfaces. Reflectarray-based RIS use electronically controlled antenna elements to backscatter and phase-shift incident signals, while metasurface-based RIS can precisely control the amplitude and phase of scattered waves using subwavelength resonant structures. The document also examines how RIS can impact channel modeling and optimize wireless system performance by controlling propagation environments. RIS have the potential to improve capacity and overcome challenges in higher frequency bands by enhancing channel conditions.
Free space optical communication(final)kanusinghal3
This document provides an overview of free space optical communication (FSO). It discusses the motivation for using FSO due to increasing bandwidth needs and spectrum scarcity. FSO uses visible or infrared light to transmit broadband communications in a line-of-sight fashion. The document outlines key challenges of FSO including attenuation from environmental factors like fog and scattering. It also reviews the advantages of low cost and high security as well as disadvantages such as sensitivity to obstructions. The document concludes that FSO is a promising supplemental technology to wireless and fiber for short-range applications.
Transmission media is the physical medium used to transmit data between a sender and receiver. The two main types are guided and unguided media. Guided media uses physical pathways like cables to direct signals over shorter distances at high speeds securely. Common examples are twisted pair, coaxial, and fiber optic cables. Unguided media transmits electromagnetic waves without physical pathways, broadcasting signals through the air over longer distances less securely. Common examples are radio waves, microwaves, and infrared waves used in wireless technologies.
International Journal of Computational Engineering Research(IJCER) ijceronline
International Journal of Computational Engineering Research (IJCER) is dedicated to protecting personal information and will make every reasonable effort to handle collected information appropriately. All information collected, as well as related requests, will be handled as carefully and efficiently as possible in accordance with IJCER standards for integrity and objectivity.
The document describes the design of a free space optical link. It begins with an overview of what free space optical communication is and its advantages over other wired technologies. It then discusses the basic components of an FSO link including the transmitter, receiver, and transceiver implementation. The transmitter section focuses on the laser diode source and driver circuitry. The receiver section covers the photodetector, preamplifier, and decision circuitry. Lastly, it discusses modeling the FSO channel and the factors that can impact signal propagation through the atmosphere.
Free space optics (FSO) uses visible light communication or infrared light to transmit data wirelessly. It works by transmitting a laser beam between an optical transmitter and receiver using lenses or telescopes. FSO can provide high-speed wireless connectivity for applications such as last mile internet access, enterprise connectivity, fiber backup links, and cellular backhaul. It has advantages over radio frequency technologies in that it has unlimited spectrum, high bandwidth, low latency, and security from wireless tapping. However, FSO performance can be impacted by atmospheric conditions like fog, rain and turbulence. The document provides an overview of the history, working mechanism, applications and advantages of FSO technology.
The document summarizes free space optical communication (FSO). It discusses the operation of FSO links, their advantages over fiber and microwave links, and applications. The key points are:
1. An FSO link consists of a transmitter, receiver, and tracking system to direct light beams between nodes. It allows license-free, high-speed connections but is susceptible to weather.
2. Applications include point-to-point links between buildings and potential mesh networks or use on high altitude platforms. Mesh networks provide better coverage but at a higher cost than point-to-point links.
3. Compared to fiber and microwave links, FSO systems have lower costs and power needs but higher data rates and
Descripcion de la tecnologia y sistemas de luz para transmitir señales
Sistemas de transmision por fibra optica, equipos de fibra optica para transmision inalambrica
This document provides an overview of free space optics communication (FSO). It begins with an introduction that defines FSO as using visible or infrared light beams through the atmosphere for optical communications. It then describes how FSO works using low power infrared lasers and photon detectors. The document outlines the basic architecture of FSO systems including transmitters, receivers, and modulation techniques. It discusses applications, advantages such as low cost and flexibility, and disadvantages like interference from weather. In conclusion, the document presents FSO as a wireless optical technology alternative to traditional wired networks.
Free space optics (FSO) uses lasers to transmit data through the air between two points without fiber. FSO can transmit at speeds up to 2.5 Gbps currently and is expected to reach 10 Gbps soon. It uses infrared lasers and photo detectors for full duplex communication. FSO provides a cost-effective solution for the "last mile" problem of connecting buildings to high-speed fiber backbone networks when laying new fiber is not feasible or affordable. Major advantages of FSO include low costs, high security, and no licensing requirements compared to other wireless technologies.
Optical multiplexers allow multiple signals to be transmitted simultaneously over a single optical fiber link. There are different optical multiplexing techniques, including wavelength division multiplexing (WDM) and optical time division multiplexing (OTDM). WDM assigns each signal a unique wavelength, while OTDM separates signals in the time domain. Optical multiplexers and demultiplexers use passive optical filters to combine and separate the wavelength signals. This increases bandwidth utilization and reduces transmission costs.
This document provides an overview of different transmission media used for data communication, including both guided and unguided media. It discusses various types of guided media such as twisted pair cables, coaxial cables, and fiber optic cables. It describes their characteristics, applications, advantages and disadvantages. The document also covers unguided or wireless transmission media such as radio waves, microwaves, and infrared. It explains propagation methods for unguided signals and the role of antennas. Finally, it discusses some issues with signal transmission such as attenuation, distortion and noise.
The document presents information on free space optics communication. It discusses how FSO works by transmitting data as invisible light pulses between a transmitter and receiver. FSO provides benefits like high bandwidth, bit rate, power efficiency, and data security at low cost. However, it faces challenges from environmental factors like absorption, scattering, fog, scintillation, solar interference, dispersion, and building motion that can attenuate the signal. The document lists manufacturers in the FSO field like LightPointe, AirFiber, and Terabeam and the funding they have received.
The document discusses laser communication and provides details about its key aspects. It begins with an introduction to laser communication and describes how it works. It then explains why laser communication is preferable to fiber optics and microwaves in certain situations. The document outlines the main types of lasers used in communication systems and highlights features like bandwidth, power requirements, and security advantages over radio frequency systems. It also examines link parameters, transmitter and receiver design considerations, and reliability factors for laser communication links.
FSO (Free Space Optics) uses visible light or infrared lasers to transmit data through the air, providing broadband communications. It works similar to fiber but without the physical infrastructure, transmitting focused beams of light between optical transceivers. While challenges include atmospheric effects like fog, it has applications for last mile access and enterprise connectivity due to low costs, ease of deployment, and flexibility.
The document discusses optical wireless communication and free space optics. It provides an introduction to free space optics concepts, how free space optic systems work, their applications, advantages, components like transmitters and receivers, and compares LED and laser diode light sources. It also discusses propagation concepts, link budget calculations and considerations for signal propagation and data security in free space optic systems.
This presentation discusses freespace optical communication (FSO), which transmits modulated beams of light through the atmosphere for broadband communications. It provides a brief history of FSO, describes how FSO works by converting network traffic to light pulses, and lists its advantages like low cost, high security, and immunity to electromagnetic interference. The presentation also outlines FSO's applications like metro networks and last mile access, and discusses its disadvantages such as reliance on line of sight and susceptibility to atmospheric conditions.
This document summarizes a technical seminar on free space optics (FSO) presented by Kartik K Benageri at Jain Institute of Technology in Davangere, Karnataka, India. The seminar covered the introduction, key features, working principles, advantages, limitations, and conclusions of FSO technology. FSO uses lasers and photo detectors to transmit data, voice, or video at speeds up to 2.5 Gbps in a line-of-sight fashion without the need for fiber. While offering benefits like flexibility, low cost, and security compared to fiber or microwave, FSO performance can be impacted by environmental factors like fog, rain, scattering, and building sway. The seminar provided information
Free-space optical (FSO) communication uses visible light or infrared light beams to transmit data through the air. It works similarly to fiber optics but transmits the light beam through the air instead of glass fibers. FSO systems can transmit data at rates similar to fiber optics over distances up to a few kilometers. They provide a wireless complement to radio-based communication systems. The main requirements are having an unobstructed line-of-sight between the transmitter and receiver and clear atmospheric conditions.
The Effect of PMD (Polarization Mode Dispersion) the Fibers of New and Old In...inventionjournals
This is a study conducted in a laboratory at the university as a simulation to see the effect of new fiber PMD for different distances. This is done to compare the performance of the digital system with optical fiber WDM. In this simulation are not included remission, chromatic dispersion and nonlinear effects. In this way all of the signal distortions caused only by different combinations of PDM. Polarization effects are very important in communications systems with optical fiber. Optical fiber that is used mainly during the simulation is a standard single mode fiber (SSMF).
The document summarizes recent developments in node clustering for wireless sensor networks. It discusses how clustering helps organize the network topology to balance load and prolong lifetime. Several key challenges in clustering sensor networks are outlined, including the need for distributed clustering algorithms that rely only on local neighborhood information. Clustering approaches are classified based on their objectives and design principles. Key issues that affect practical deployment of clustering techniques are also discussed.
Study on Laser Communication: Features, Application, Advantagesijtsrd
Laser communications offer a viable alternative to RF communications for intersatellite links and other applications where high-performance links are necessary. High data rate, small antenna size, narrow beam divergence, and a narrow field of view are characteristics of laser communication that offer a number of potential advantages for system design. The high data rate and large information throughput available with laser communications are many times greater than in radio frequency (RF) systems. The small antenna size requires only a small increase in the weight and volume of host vehicle. In addition, this feature substantially reduces blockage of fields of view of the most desirable areas on satellites. The smaller antennas, with diameters typically less than 30cm, create less momentum disturbance to any sensitive satellite sensors. The narrow beam divergence of affords interference-free and secure operation. Prof. Atul A. Padghan | Prof. Ankit P. Jaiswal"Study on Laser Communication: Features, Application, Advantages" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-2 | Issue-3 , April 2018, URL: http://www.ijtsrd.com/papers/ijtsrd10798.pdf http://www.ijtsrd.com/engineering/electronics-and-communication-engineering/10798/study-on-laser-communication-features-application-advantages/prof-atul-a-padghan
This document provides an overview of reconfigurable intelligent surfaces (RIS) for wireless communications. It discusses two main implementations of RIS - using reflectarrays or metasurfaces. Reflectarray-based RIS use electronically controlled antenna elements to backscatter and phase-shift incident signals, while metasurface-based RIS can precisely control the amplitude and phase of scattered waves using subwavelength resonant structures. The document also examines how RIS can impact channel modeling and optimize wireless system performance by controlling propagation environments. RIS have the potential to improve capacity and overcome challenges in higher frequency bands by enhancing channel conditions.
This report gives the viewers a broad description about using a light wave generated from a typical LED's or LASER source for an effective communication.
Performance of symmetric and asymmetric links in wireless networks IJECEIAES
Wireless networks are designed to provide the enabling infrastructure for emerging technological advancements. The main characteristics of wireless networks are: Mobility, power constraints, high packet loss, and lower bandwidth. Nodes’ mobility is a crucial consideration for wireless networks, as nodes are moving all the time, and this may result in loss of connectivity in the network. The goal of this work is to explore the effect of replacing the generally held assumption of symmetric radii for wireless networks with asymmetric radii. This replacement may have a direct impact on the connectivity, throughput, and collision avoidance mechanism of mobile networks. The proposed replacement may also impact other mobile protocol’s functionality. In this work, we are mainly concerned with building and maintaining fully connected wireless network with the asymmetric assumption. For this extent, we propose to study the effect of the asymmetric links assumption on the network performance using extensive simulation experiments. Extensive simulation experiments were performed to measure the impact of these parameters. Finally, a resource allocation scheme for wireless networks is proposed for the dual rate scenario. The performance of the proposed framework is evaluated using simulation.
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of system’s components, e.g. modulation, coding, filtering. The objective is to describe the viability of an optical free-space visible light transceiver as a basis for indoor wireless networking and to achieve acceptable bit error rate (BER) performance for indoor use, with a low cost system.
Optical intersatellite communication uses lasers instead of radio waves to transmit data between satellites. It offers several advantages over traditional radio frequency communication methods, including higher bandwidth for faster data transfer, smaller antenna sizes, better security due to tightly focused beams, and reduced interference. Key applications of this technology include earth observation, satellite constellations, deep space exploration, and secure military communication. Overall, optical intersatellite communication has the potential to significantly improve space-based data transmission capabilities.
Visible light communication (VLC) uses LED lights to transmit data by varying the intensity of light in a way imperceptible to the human eye. It provides wireless connectivity without interfering with existing RF systems. VLC offers security since light cannot penetrate walls, allowing each room to function as an independent cell. Potential applications of VLC include wireless connectivity in offices, factories, shopping areas, and warehouses by exploiting existing lighting infrastructure.
Wireless telecommunications involves the transfer of information between two or more points without a physical connection. It uses forms of energy like radio frequencies to transmit information over various distances, from a few meters to thousands of kilometers. While wireless operations allow for long-range communication without wires, the wireless channel is susceptible to factors like interference, path loss, and fading that restrict reliability and throughput. Adaptation techniques and MIMO can help improve performance but spectrum and interference remain limitations of wireless networks.
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9 Aab32 Dd Bdb9 137 E Ca2184 F057753212 154710guestbd2263
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PHYSICAL LAYER SECURITY OF OPTICAL NETWORKS.pdfadeel paracha
Abstract
The physical layer of an optical network may be attacked in numerous ways, such as by jamming, assaults on the physical infrastructure, eavesdropping, and interception. As the requirement for network capacity develops, the physical layer of the optical network must be kept secure. In this overview article, specialists look at security problems in optical networks and discuss a variety of novel approaches to defending optical networks. In the first section of this study, researchers discuss a variety of security issues that might harm the optical layer of an optical network. These weaknesses include jamming, physical infrastructure assaults, eavesdropping, and interception. Enhanced optical network security has gained a lot of interest in the sectors described above. Real-time signal processing is essential in order to apply security measures at the physical layer without slowing down the pace of optical communications. The key advantages of optical processing for optical layer security include rapid reaction, wide-band operation, resilience to electromagnetic fields, compact size, and low latency. In the second part of this research, we look into optical steganography, optical encryption, optical code-division multiple access (CDMA) secrecy, self-healing, survivable optical rings, anti-jamming, and optical CDMA confidentiality.
I. Introduction
Introduction Optical communication systems are employed in many different fields, including business, the military, and personal communication. Optical networks are unusual in that their data speeds are greater than 40 GB/s, and this figure will only increase as time goes on. Physical layer security measures have to function in real time, which is not achievable with standard electronic computing. Side-channel assaults are less likely to emerge in optical communication networks because optical components don’t leave electromagnetic traces. With optical encryption, communications may be encrypted fast and with minimum latency (at speeds not attainable with standard electrical implementations) (at rates not possible with conventional electrical implementations). In addition to data encryption, optical steganography may be used to obscure the flow of data over an open transmission channel.
II. Threats and defenses in optical networks at the optical layer
There are many different forms of optical networks, from local area networks to the backbone networks of the Internet. Each network may tackle a particular threat type in a different manner. Researchers investigate the optical layer to examine whether there are any threats to privacy, availability, authentication, and secrecy (Skorin-Kapov, 2016).
A. Confidentiality
Even though optical networks don’t have an electromagnetic signature, an attacker may nonetheless listen in on them by physically tapping into the optical fiber or by pretending as a lawful subscriber and listening to residual crosstalk from an adjacent channel. It is not hard to tap an
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Smart dust are tiny wireless sensing devices that combine computing, communication, and power capabilities. They are very small, just a few millimeters, and can be suspended in air like dust particles. Smart dust motes have components like an optical transmitter and receiver, signal processing circuitry, and a power source. They communicate using radio frequency, passive laser optics which reflect signals, or active laser beams. Challenges include fitting all components in a small size while providing enough power. Potential applications include environmental monitoring, health monitoring, factory automation, and more. Research aims to make smart dust as small and inexpensive as possible to enable widespread use.
Temple of Asclepius in Thrace. Excavation resultsKrassimira Luka
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1. I. INTRODUCTION
Intersatellite laser crosslinks (ISLs) provide a
Intersatellite Laser Crosslinks method of communication that has significantly
increased the data throughput that can be managed
over typical RF communication systems. The data rate
growth potential is well beyond the few gigabit per
second range of RF technology. The use of lasers in
JOHN E. MULHOLLAND, Senior Member, IEEE transmitting optical data takes advantage of its small
Villanova University wavelength and low beam divergence.
SEAN ANTHONY CADOGAN The ISL is subdivided into five major subsystems.
Martin Marietta Corp.
The transmitter is typically a semiconductor laser, or
laser diode. The receiver has a design very dependent
on the method of communication, and transmitter
construction. The acquisition subsystem is responsible
Intersatellite laser crosslinks (ISL) provide a method
for aligning the transmitter and receiver to prepare
of communication that has significantly increased the data for communication. The tracking subsystem must
throughput that can be managed over typical RF communication maintain the link with the stability necessary to allow
systems, and has significant growth potential. Optical for reliable data transmission. The communication
communications offer very wide bandwidths which can be subsystem is responsible for encoding and decoding
effectively utilized with wavelength division multiplexing the data to be sent between satellites.
techniques. The data rate growth potential is well beyond the few The RF atmospheric coefficient of attenuation is
gigabit per second range of RF technology. The use of lasers in very low, which results in RF signals slowly losing
transmitting optical data takes advantage of its small wavelength strength in the atmosphere and can therefore travel
and low beam divergence to send highly directed signals over long distances, including over the horizon. On the
significant distances with controlled losses in intensity. The contrary, laser signals are highly directional, permit
high directivity of the laser aids in resistance to jamming
large bandwidths, and are attenuated to a significant
extent by the atmosphere. This, in addition to the fact
communications between satellites, or between satellites and
that they are line-of-sight [1], causes some important
ground stations.
design problems that must be addressed.
Various intersatellite laser optical crosslink systems are
Various ISL systems are discussed in order to
discussed including the Massachusetts Institute of Technology’s
display the various subsystems which comprise a laser
Laser Intersatellite Transmission Experiment (LITE), the crosslink, and their implementations. Discussion on
McDonnell Douglas Electronic Systems Company Laser the strengths of laser communications is provided, and
Crosslink System, and The Ball Aerospace Optical Intersatellite related to RF technology.
Link, in order to display the various subsystems and their Background is provided on earlier system
implementations. Link budget calculations are performed on the architectures and methods of laser communication,
most commonly used modulation formats to determine system as well as presently implemented systems. Optical link
parameters necessary to close the crosslink. budget calculations are performed for various methods
Background is provided on primal system architectures and of communications. The author provides some insights
methods of laser communication, as well as presently implemented on where intersatellite laser optical crosslink systems
systems. The authors provide some insights on where ISL systems
have opportunity to increase their data throughput and
reduce acquisition time.
have opportunity to increase their data throughput and reduce
acquisition time.
II. INTERSATELLITE LASER CROSSLINKS
A. Why Satellite?
McDonnell Douglas Electronic Systems Company
Manuscript received June 18, 1994; revised March 27, 1995. (MDC) was chosen by the U.S. government in 1981
IEEE Log No. T-AES/32/3/05872. to bring laser communications into production by
Authors’ addresses: J. E. Mulholland, Dept. of Electrical and
developing a satellite-to-satellite crosslink. The system
Computer Engineering, Villanova University, Villanova, PA was to be installed on an already existing satellite.
19085-1681; S. A. Cadogan, Martin Marietta Corp., Management Therefore to minimize any impact to the satellite, the
and Data Systems, King of Prussia, PA. laser crosslink needed to be a stand-alone, bolt-on
package, which provided terminal control, a despun
0018-9251/96/$10.00 ° 1996 IEEE
c line of sight, and could operate from raw spacecraft
IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. 32, NO. 3 JULY 1996 1011
2. power [2]. The profitability of communications by
satellite becomes evident when reviewing the key
features of the MDC laser crosslink subsystem:
1) reduction of the reliance on foreign ground stations,
2) survivability, 3) jam resistance, 4) low probability of
data intercept, and 5) field of view (FOV) limited only
by gimbal location relative to the sensor.
With one centralized U.S. ground station which
takes inputs from multiple satellites, the dependence
on multiple foreign ground stations is greatly reduced.
This alleviates the time delays and increased factors of
error associated with the distributive nature of multiple
foreign ground stations. Survivability is especially
important in times of natural disaster, war, or other
events which can be detrimental to low altitude
communication devices (i.e., air craft systems) and
ground-station-to-ground-station communications. Jam
resistance and low probability of error, features of the
Fig. 1. Synchronous range crosslink aperture.
MDC laser crosslink system, are results of the narrow
beamwidth used. The high altitude of the satellites
leads to a much more expansive FOV which is only advantage over the best achievable communication
limited by the gimbal location relative to the sensor. in the RF spectrum. The extremely low beam
divergence minimizes signal loss and a narrow receiver
FOV makes it extremely difficult to jam. The short
B. Why Optical?
wavelength of lasers offers the opportunity to modulate
The Optical Communications Group at M.I.T. at very high data rates. Laser communication offers
Lincoln Laboratory has been investigating and 1) low probability of data intercept, 2) jam resistance,
developing the technologies required to make high and 3) high bandwidth capabilities.
to very high data rate optical intersatellite crosslink The highly directional nature of lasercom makes
a reality for over ten years. According to Boroson it difficult to intercept and jam communication. The
[3], optical communications allows the use of high directivity arises from the short wavelengths of
comparatively small antenna (telescope) packages visible and nearly infrared energy. Lasercom sidelobes
because of its very short wavelength. RF technology, are also generally much lower than RF or millimeter
even in the upper EHF region over 60 GHz, requires wave sidelobes, resulting in an inherent resistance
antenna apertures on the order of several feet in to interception or jamming [1]. There are many
diameter to support links with capabilities of more constraints which must be taken into account when
than a few tens of megabits per second. Fig. 1 choosing a laser subsystem. Some of these constraints
compares the package apertures for 40,000 km links are identified in a later section, which discusses the
which quantifies the difference in aperture size for RF transmitter of a laser crosslink system.
versus optical communications at various data rates.
With the utilization of satellites, special attention must III. SYSTEMS APPROACH
be taken to payload constraints on size and weight
added by the communications subsystem. A. General Parameters
Optical communications also offers very
There are many parameters which the system
wide bandwidths, especially when utilizing
designer must consider in the development of an ISL.
wavelength-division multiplexing techniques. RF
For instance, in order to get maximum use of the
technology, on the contrary, does not have data rate
relatively low power of the laser diodes, the designer
growth potential beyond a few gigabits per second,
must pay particular attention to beam pointing
especially in a network where frequency reuse may not
and tracking, wavefront quality, package rigidity,
be possible.
point-ahead accuracy, and maintenance of these
properties through the temperature and vibrational
C. Why Laser? extremes of the lifetime of a satellite. In order to
arrive at a successful lasercom design, all of these
The development of laser communication began constraints must be fulfilled simultaneously in a full
at MDC in the late 1960s under both U.S. Air Force system context. The lasercom should be compact,
and company sponsorship. Laser communication lightweight, and have a relatively simple package
at short wavelengths theoretically holds a great design as a result of the solution with these constraints.
1012 IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. 32, NO. 3 JULY 1996
3. Mass, prime power, and volume estimates
for reliable ISL payloads were performed in a
telecommunications system that provides a full-duplex
interconnection of three wideband transponders
between two spacecraft separated by 60 deg along
the geostationary arc by R. Marshalek of the Ball
Aerospace Systems Group and D. Paul of COMSAT
Laboratories [5]. The following conclusions related to
transmitter laser choice were made.
1) The CO2 system demands excessive laser
redundancy and large payload mass to support a 10-yr
Fig. 2. LITE engineering model block diagram. high reliability (0.9) mission.
2) Redundancy increases payload weight by about
20 to 30 kg int he Nd:YAG, InGaAsP, and GaAlAs
It must be noted that there are many different ways systems.
of configuring an ISL, and along with this, different 3) GaAlAs systems entail lower payload mass
system parameters which must be considered. and prime power, and are recommended for a
In general, the total weight of the transmitter, telecommunications ISL.
receiver, acquisition, tracking and communications
subsystems should be within the range of 200—300 lb.
C. Receiver
It was also noted that state of the art systems transmit
at approximately 300 Mbit/s. Using Fig. 1, for a data Many different types of receivers can be utilized
rate on the order of 100 Mbit/s, a 0.1 W laser requiresin the lasercom system. Some of these receivers
an aperture diameter of about 0.4 ft, and a 1 W laser are introduced in a general nature. In general, the
of only about 0.2 ft. receiver or detector must be able to transform light
into electrical signals. Many, but not all, have some
B. Transmitter amount of built-in gain to better detect the incoming
signal. Depending on the operating wavelength, there
There are many considerations in designing a will be different materials used. The receiver is also
transmitter. The laser used must not only be powerful application dependent. If direct modulation is used as
enough to transmit the necessary beam over a a communications method, a detector and amplifier is
specified distance, but it must pass a screening test needed. If a synchronous detection method (such as
designed to select lasers with acceptable operating RF links) is employed, a local oscillator (laser) must
temperature, narrow linewidths, acceptable optical be used. This is the heterodyne case. The detector
properties, reasonable FM responses, and prospects of choice for Nd:YAG and GaAs wavelengths is the
for long life [4]. A laser must qualify for space avalanche photodiode (APD). An APD can be used
usage in a satellite crosslink system. For example in the tracking and communication phase, which is
gas lasers (i.e., He-Ne) are not practical in space discussed in a later section.
due to their relatively low efficiency and large size. The system impact of resonant laser receivers for
Inability to maintain uniformity of the vapor in the free-space laser communications has been studied,
discharge region has ruled out metal vapors such and the major advantage of the resonant receiver
as Zn, Hg, Sn, and Pb which have displayed laser design approach is that it enables laser communication
transition in the visible spectrum [11]. Therefore a link closure for many applications, by using an
solid state or semiconductor laser is the device of available 14 cm aperture and existing compact diode
choice. Semiconductor lasers, particularly the GaAlAs laser sources (for acquisition and high-data-rate
family, are good candidates for the laser source communication). The problem of having to close the
in a heterodyne system. Semiconductor lasers are communication link with a reasonably sized aperture
compact, have high power conversion efficiency (with has now been circumvented. This alleviates the
prime-to-optical output power conversion efficiency problem that previously existed with the traditional
between 20% and 50%), architectural simplicity, direct-detection approach to laser communications
and utilize single-frequency operation. As a part of with a reliable, high-power high-beam-quality (Strehl
the Laser Intersatellite Transmission Experiment ratio) transmitter that controls system mass and
(LITE) project [3], M.I.T. has built many laboratory beam-pointing requirements [6]. The resonant receiver
communications links based on commercially available design approach also has immunity to large optical
30 mW GaAlAs lasers with wavelengths between 0.83 background interference, while not overloading
and 0.86 ¹m. These lasers were adequate for crosslinks requirements on transmitter frequency, thermal
in the 100 Mbit/s class (see Fig. 2). stability, or receiver frequency tracking that increase
MULHOLLAND & CADOGAN: INTERSATELLITE LASER CROSSLINKS 1013
4. the complexity of the alternative heterodyne-detection
approach. For most parameters, the resonant receiver
requirements lie between those for direct detection
and heterodyne detection. The resonant receiver
approach attacks those key areas that have been major
drivers on system reliability, performance, and cost by
offering a balanced design approach to long-distance
high-data-rate laser communications.
For digital traffic, the full bandwidth, direct,
and heterodyne-detection GaAlAs systems entail
comparable mass, power, and volume. However,
for analog traffic, the GaAlAs heterodyne-detection
system is superior because it uses far less mass
and volume. The major reason that the GaAlAs
heterodyne-detection system is so successful for analog
traffic is that it efficiently accommodates the three
multiplexed communication transponders with a
direct-optical-carrier-frequency modulation technique Fig. 3. Acquisition time.
[7]. The LITE engineering model at M.I.T. utilizes a
semiconductor coherent (heterodyne) detection which
and communications. Initially, there is a large ratio
allows for nearly quantum-limited performance with
between the initial angular uncertainty and the narrow
sensitivity better than that of direct detection at all
beam divergences in the tracking and communication
but the very lowest data rates. Heterodyne detection
links to conserve the limited laser power.
also allows operation with a bright object, such as the
The Laser Crosslink Subsystem (LCS) of
sun, in the FOV; whereas, direct detection systems are
McDonnell Douglas Electronic Systems Company
significantly degraded.
uses the direct pulse detection technique, and
therefore their acquisition algorithm is different
D. Acquisition and Tracking from one using coherent (heterodyne) detection.
Acquisition refers to the process in which the A 100¹ rad acquisition beam is initially scanned
receiving satellite determines where the incoming over the region of uncertainty. The pulse rate of the
beam sent by the transmitting satellite is located. laser is reduced during acquisition to provide higher
Bridging a 42,000 km link with the very narrow peak pulse power required to compensate for the
beamwidth of a laser poses a serious design problem, expanded beam divergence. When each LCS terminal
however, multiple sequential methods of acquisition detects illumination from the opposite terminal, the
are discussed. pointing converges and scan fields are reduced in
One goal for laser communication is the reduction order to increase scan frequency. This continues
in acquisition time and the improvement of acquisition until pointing accuracies are sufficient to support
techniques. The relation between the beamwidth of communications. The scans are then suspended and
the transmitted beam, the receiver’s FOV, and the each LCS transitions to 10¹ rad communications beam
maximum time it takes for acquisition is well displayed pointing and data transmission [2].
in Fig. 3. This figure plots curves of maximum
acquisition time against azimuth uncertainty angle (for E. Tracking and Maintaining Links
constant elevation uncertainty) for a number of beam
size and FOV combinations. The curve on the far left Tracking refers to the process in which the
indicates that the acquisition time may be more than satellites maintain their communication links. In the
five min for a 0.5 deg initiator beam and a one deg LITE system the high bandwidth steering mirror
responder FOV. An examination of the curves towards (HBSM) also correctly points the transmitted beam
the right of Fig. 6 indicates that short search times to the other terminal as it keeps the incoming
can be implemented over much larger volumes of beacon signal centered on the tracking detector.
uncertainty if the FOV of the detector and the beam This allows the compensation of pointing variations
divergence of the initiator are large enough. It should caused by spacecraft motion and vibration. Once
be noted that for wide initiator beam divergences, high the laser transmitter is set up and stabilized, and the
power lasers must be employed in order to close the beam-steering system has completed the bore-sighting
link. procedure (alignment of transmit and receive beams),
For mutual acquisition to occur, each satellite must LITE is ready to acquire and track the incoming signal.
reduce its initial knowledge of the opposing satellite’s Once the signal is acquired the beam is narrowed
location to values compatible with fine tracking which increases its power. When the other terminal
1014 IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. 32, NO. 3 JULY 1996
5. senses this, it sends the signal over to its tracking receive signal in conjunction with envelope detection
receiver, narrows its beacon and points it toward as in RF systems [8]. The key components are transmit
LITE. LITE senses this increased power and increases and local oscillator lasers, optical input couplers, and
the tracking bandwidth to 1 KHz to improve tracking high bandwidth electronics.
performance. After all acquisition is complete, the
communications session can begin [4]. IV. LINK BUDGET
Fine tracking allows the use of narrow
communication beams for high-data-rate transfer A. SNR and Data Errors
between the two satellites, simultaneously maintaining
point-induced burst communication errors at The final performance of the system depends
acceptably low levels. A burst error rate of 10¡5 to on the signal-to-noise ratio (SNR). Noise in an RF
10¡6 is acceptable and is achievable with a 1 ¾ tracking system is usually thermal noise, or device noise. In
accuracy of about one-twentieth of the null-to-null link budget calculations for an RF communication
transmit beamwidth. The spectral content of the link the carrier is an electromagnetic wave. Noise in an
satellite platform disturbance errors determines the optical system consists of thermal, as well as quantum
track detector update rate (bandwidth). noise generated by asynchronous photon plinking in
signals, because for an optical communication system,
the carrier is a photon.
F. Communications
In free-space laser optic communications, the link
There are different methods of modulation of the budget is defined by an allowable bit error rate (BER).
laser beam which can be used to send information The acceptable BER commonly used in analysis
in the beam. In the beginning of lasercom, direct of optical links is 10¡9. From this BER, a SNR is
modulation was the only option available. Information determined. These two factors, in conjunction with
was sent via the duration of pulses of laser power. the range of transmission, are utilized in choosing
Now the lasers can be modulated like RF carriers (i.e., the transmitter and receiver. If the digital traffic
frequency or even phase modulation, see [5]). is received with a 10¡9 BER it corresponds to a
The communications subsystem is composed of SNR of 16.2 dB for quadrature PSK (QPSK) traffic
five major parts in the Ball Aerospace design; the and 17 dB for baseband digital traffic, including a
laser/modulator, detector/local oscillator, LO laser 1.4 dB modem implementation margin in both cases
(heterodyne system), communication electronics, [10]. The analog traffic requires a 17 dB SNR at the
processing electronics, and passive optics. receiver output. For the receiver, when determining
The data format has to be constructed according to the receiver specifications, the modulation format, as
the nature of the data. For pulse-position modulation well as the detection scheme must be considered. The
(PPM), digital modulators are required [7], while necessary SNR must also be taken into account. The
on—off keying (OOK) systems are usually implemented sensitivity of the receiver is measured as number of
using scramblers, or forward error correction coding in detected photons per bit (at peak power) necessary to
order to improve the correlation properties of the data achieve a BER of 10¡9. Once the receiver sensitivity
signal [8]. In order to recover the signal and regenerate is known, the amount of power needed from the
the information sent, PPM maximum likelihood transmitter must be determined. There are various
receivers require a symbol clock recovery circuit. other noise-inducing factors, such as differences in
For OOK systems the amplitudes are regenerated by temperature throughout the atmosphere significant to
threshold decision. The synchronization requires a cause a perceptible change in the index of refraction
phase-locked loop triggered by data transitions [11]. presented to a laser beam as it passes through. This
A quadrant detector composed of four APDs split can result in beam broadening, tearing and steering
at a focal plane by a pyramid, light pipes, or fibers of portions of the beam, causing fades and surges in
may also be used as a communications detector (3 ns the optical beam as a result of variations in power
rise and fall) in addition to a track detector, if the density. The probability of bit error is therefore
quadrant outputs are summed. Duchmann and Planche dramatically increased. Atmospheric turbulence, and
indicate that in their communications system, the pointing inaccuracies are other factors which can
receive function consists of a low noise APD-based introduce bit errors and degrade the performance of
direct detection of the incoming signal followed by a communications link.
a non-return-to-zero (NRZ) regeneration of the
baseband electrical signal [9]. B. Link Budget Calculations
In fiber-based state of the art heterodyne receivers,
continuous phase frequency-shift keying (FSK), The link budget is a numerical calculation that
or differentially encoded phase-shift keying (PSK) proves link closure. It is used to determine whether
modulation is used. The detection principle consists the SNR is high enough for data to be successfully
of the active mixing of a local oscillator signal and the transferred. Link budget calculations determine system
MULHOLLAND & CADOGAN: INTERSATELLITE LASER CROSSLINKS 1015
6. TABLE I
Optical Intersatellite Link System Parameters
performance for communication configurations by
trading off such parameters as aperture, transmitter
power, and data rate. This section shows the design
and definition of the communications link. Optical
power budget calculations are performed in six systems
to determine antenna diameter requirements as a
function of average transmitter power. The systems
are: 1) carbon dioxide laser system with heterodyne
detection, 2) neodymium-doped laser system with
direct detection, as in the LCS laser of McDonnell
Douglas, which utilizes solid state GaAs diodes to
pump a Nd : YAG rod, 3) In GaAsP laser system
with direct detection, 4) GaAlAs laser system with
direct detection, 5) GaAlAsP laser system with
wavelength division multiplexing and direct detection,
and 6) GaAlAs laser system with heterodyne detection.
These systems have been previously introduced in
earlier sections which discuss transmitter and receiver
options.
Typical parameter values are used throughout
this discussion in order to determine the antenna
requirement for each of the six systems as a function
of optical transmitter power. Table I gives the system Fig. 4. Antenna diameter requirements for CO2 system.
parameters used in the link budget calculations
for the different optical intersatellite link systems.
These calculations were performed for each of the The Nd-doped system was evaluated uner mode-locked
modulation formats discussed, and a link margin of conditions. Results for the other systems are similar
5 dB was assumed in all cases. The results for the CO2 to the GaAlAs System. It must also be noted that
and AgAlAs systems are displayed in Figs. 4 and 5. the actual average transmitter power for the analog
1016 IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. 32, NO. 3 JULY 1996
7. TABLE II
Antenna Diameter Requirements for Baseband Digital Transmission (360-Mbit/s Total Throughput With 10-9 BER) Over 42,000 km
Range
Note: *Optical power of each transmitter.
engineer, requires a substantial reduction in average
transmitter power than the nonheterodyne case.
The CO2 heterodyne, GaAlAs WDM, and GaAlAs
heterodyne systems require the smallest antennas for
analog transmission. Since the WDM system is very
reliable and simpler to implement, it is preferred in
short-term applications. With technological advances
in GaAlAs heterodyne systems it will become the
preferred choice for analog transmission of three
separate transponder signals [11].
V. CONCLUSIONS
Different methods of laser beam modulation have
been used over the years to send information. In the
early days of lasercom, direct modulation was used
where the laser was turned on and off just as Morse
code signals were used. The speed of modulation
had to be checked as well. Now the lasers can be
modulated like RF carriers (i.e., frequency or even
phase modulation).
The range in data rate from tens of kilobits to
tens of megabits was previously exclusively covered
Fig. 5. Antenna diameter requirements for GaAlAs system. by Nd : YAG lasers modulated with an M-ary PPM
format. Now, new pulsed diode arrays are capable of
operating with PPM modulation with peak powers
formats is 0.75 times the value read from the graph of tens of watts at megabit data rates. State of the art
[11]. systems now transmit at approximately 300 Mbit/s.
Anticipated transmitter power levels in an ISL It is the authors’ opinion that there are several
were estimated to compare the six systems, and the methods which can be incorporated into the
corresponding antenna diameters were then obtained acquisition and tracking phase, as well as the
for transmission of three baseband digital transponder communications phase to improve system performance.
signals. Table II gives the modulation formats, power Sections VA and VB discuss these proposed system
levels, and calculated diameters of these baseband enhancements.
signals. Table III provides a similar comparison for the
transmission of three QPSK transponder signals. The A. Acquisition and Tracking Enhancements
CO2 and Nd systems require the smallest diameters
for transmission of baseband digital signals but use The narrow beamwidth of the transmitted optical
more complicated modulation techniques and less beam presents design difficulties in the actual
efficient transmitters than systems based on GaAlAs acquisition of the signal. To broaden the beam and
heterodyne detection system, although difficult to send it out from the laser calls for much more power
MULHOLLAND & CADOGAN: INTERSATELLITE LASER CROSSLINKS 1017
8. TABLE III
Antenna Diameter Requirements for Transmission of Three 72 MHz QPSK Transponders Over 42,000 km Range
Note: *Optical power of each transmitter.
**In CW operations.
than the laser may be able to provide if the same terminal. Either multiple processors can be used to
amount of intensity is to be sent over 42,000 km links. process the different incoming beams, which would
The authors propose using the fact that in the far linearly increase payload size and weight, or a single
field (Fraunhouffer) light sent through an aperture processor can take multiple inputs and process them
will be captured in the focal plane, at the receiver as separately, and multiplex the results accordingly.
the Fourier transform of the signal. This cannot only This approach would allow certain options such
be done in time and frequency but also in space and as multiple users transmitting data simultaneously,
spatial frequency. A rectangular slit will result in a utilizing only one transmitting and one receiving
sinx=x, and a sinx=x will result in a square pulse. The satellite without concern for their data becoming
resulting far field pattern should be chosen so that its available to other users (particularly important in
symmetry will facilitate finding the “center” where the personal communications and proprietary or secure
actual beam will be present. It should have an area communications). Due to the short wavelength of
of increased spatial area, or of spatial area significant optical systems, it has been noted that there is a
enough to make it useful to place the initial field high degree of directivity. Careful attention must be
through an aperture. If the signal is broader, it will paid so that once the acquisition signal is received
be easier to find. It has been discussed that a 2-phase and the system switches to communication beams
acquisition phase can be used to save energy while the that the beam divergence is not wide enough to
receiver satellite is trying to locate the transmitting allow interference between the various incoming
satellite. Another suggestion by the author is to use communication signals.
a three-phase approach. Trades should be made to The Optical Communications Technology group
determine if a very large, very powerful pulse or at Lincoln Laboratory believes that the technology
pulse sequence as an initial phase will cut down the is available for deployment of operational laser
receivers initial field of uncertainty or FOV enough to communication systems in the several hundred
significantly decrease acquisition time. megabits per second range, with near term technology
to be able to support multipke gigabits per second
B. Communications Enhancements links in small and reliable packages [3].
It has been noted in certain systems (such as the C. Receiver Enhancements
LITE system), that redundant laser diodes are present
but are used solely as backup when other diodes fail. In recently developed low-effective k silicon APDs
They may also be used to provide the necessary power (k = 0:002 to 0.005, depending on wavelength), a
in the case of weaker lasers. The authors suggest sensitivity of 68 photons per bit at a BER of 10¡9
that data throughput be increased by simultaneous has been measured on a direct-detection receiver
operation of multiple lasers in the transmitter section, developed using a lser diode (¸ = 810 nm) with an
to be received by an array of receivers at the receiving extinction ratio of 0.02 [13].
1018 IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. 32, NO. 3 JULY 1996
9. REFERENCES [9] Feher, K. (1983)
Baseband transmission systems and power efficient
[1] Casey, W. L., Doughty, G. R., Marston, R. K., and Muhonen, J.
modulation techniques for linear and nonlinear satellite
(1990)
channels.
Design considerations for air-to-air laser communications.
Digital Communications: Satellite/Earth Station
In SPIE Proceedings, 1417, Los Angeles, CA, 21-2, 1990.
Engineering.
[2] Deadrick, R. B., and Deckelman, W. F. (1992)
Englewood Cliffs, NJ: Prentice-Hall, 1983.
Laser crosslink subsystem–An overview.
[10] Marshalek, R. G., and Koepf, G. A. (1988)
SPIE, Vol. 1635, Los Angeles, CA, Jan. 23—24, 1992.
Comparison of optical technologies for intersatellite links
[3] Boroson, D. M.
in a global telecommunications network.
An overview of Lincoln Laboratory development of
Optical Engineering, 27, 1 (Aug. 8, 1988).
lasercom technologies for space.
[11] McIntyre, R. J. (1991)
MIT Lincoln Laboratory.
Comments on performance of coherent optical receivers.
[4] Marshalek, R. G., and Paul, D. K. (1990)
Proceedings of the IEEE, 79, 7 (July 1991), 1080—1082.
Mass, prime power, and volume estimates for reliable
[12] Boroson, D. M. (1993)
optical intersatellite link payloads.
LITE engineering model–I: Operation and performance
In SPIE Proceedings, 1218, Los Angeles, CA, Jan. 15—17,
of the communications and bean-control subsystem.
1990.
In SPIE Proceedings, 1866, Los Angeles, CA, Jan. 1993.
[5] Marshalek, R. G., Smith, R. J., and Begley, D. L. (1992)
[13] Hect, E. (1987)
System impact of the resonant laser receiver for free-space
Optics (2nd ed.).
laser communications.
Reading, MA: Addison-Wesley, 1987.
SPIE Proceedings, 1635, Los Angeles, CA, Jan. 23—24,
[14] Pillsbury, A. D., Taylor, J. A. (1990)
1992.
Optomechanical design of a space-based diode laser
[6] Borner, S., and Heicher, J. (1989)
transmitter assembly.
4-PPM modulator/demodulator with fully digital signal
In SPIE Proceedings, 1218, Los Angeles, CA, Jan. 15—17,
regeneration.
1990.
In SPIE Proceedings, 1131 (1989), 195.
[15] Verdeyen, J. T. (1989)
[7] Noldeke, C. (1992)
Laser Electronics (2nd ed.).
Survey of optical communication system technology for
Englewood Cliffs, NJ: Prentice-Hall, 1989.
free-space transmission.
[16] Ross, M. (1975)
In SPIE Proceedings, 1635, Los Angeles, CA, Jan. 23—24,
Direct photodetection space laser communications.
1992.
In Convention Record: Electronics and Aerospace Systems
[8] Duchmann, O., and Planche, G. (1991)
Conb., 1975, 174-I—174-H.
How to meet intersatellite links mission requirements by
[17] Chan, V. W. (1983)
an adequate optical terminal design.
Heterodyne lasercom systems using GaAs lasers for ISL
In SPIE Proceedings, 1417, Los Angeles, CA, Jan. 21—22,
applications.
1991.
In Conference Record: International Conference on
Communications, 1983, E1.5.1—1.5.7.
MULHOLLAND & CADOGAN: INTERSATELLITE LASER CROSSLINKS 1019
10. Sean A. Cadogan was born in Brooklyn, NY in 1968. He received his B.S. in electrical engineering from the
Massachusetts Institute of Technology, Cambridge, in 1990, and an M.S. in electrical engineering from Villanova
University, Villanova, PA, in 1993.
From 1990 to 1992, he worked at General Electric Aerospace as an Edison Engineering Program member
holding positions in the Systems Integration, Systems Analysis, and Verification and Test Engineering groups
in Management and Data Systems. While in the Sensor Systems Engineering groups in Management and Data
Systems. While in the Sensor Systems Engineering group he was the project leader on a study that quantified
the impacts of bit errors on digital processing, and the implementation of the Bose—Chaudhuri—Hocquenghem
(BCH) coding algorithm to detect and correct bit errors. He is presently a Hardware Systems Engineer at Martin
Marietta Aerospace, formerly GE, in Valley Forge, PA and resides in Norristown, PA.
John E. Mulholland (S’57–M’61–SM’87) received the B.E.E. degree from Villanova University, Villanova,
PA, in 1960, the M.S.E.E. degree from Drexel Institute of Technology, Philadelphia, PA, in 1965, and the Ph.D.
degree in electrical engineering from the University of Pennsylvania, Philadelphia, in 1969.
In 1985, he joined the faculty of the Department of Electrical and Computer Engineering at Villanova
University to develop the microwave engineering technology area for both education and research. Before joining
Villanova University, he was employed at the General Electric Space Division as Manager of the Communication
Equipment and Antenna Engineering Laboratories. His assignments have included the development of
microwave filter analytical techniques and the design of waveguide and directional filters and the Ku and X
frequency bands and the development of automated RF measurement techniques for components and systems.
More recently he has led the development of the interface definition of the command and control segment with
the microwave transmission segment of a major military satellite data communications system. Prior to joining
General Electric, he provided consultation in radar clutter, multipath, propagation effects and radiation hazards
at the RCA Missile and Surface Radar Division. He also provided analytical support for the AN SPY-1 radar in
the areas of antenna matching, random materials, monopulse tracking collimation and alignment, and sidelobe
blanking.
Dr. Mulholland is a registered Professional Engineer in Pennsylvania, past Chairman of the Antenna
Propagation/Microwave Theory and Techniques (AP/MTT) Society, Philadelphia Section of IEEE.
1020 IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. 32, NO. 3 JULY 1996