Free space optics (FSO) technology is proving to be an exceptionally beneficial supplement to conventional Fiber Optics and radio frequency (RF) links. FSO and RF links are greatly affected by atmospheric conditions. Hybrid FSO/RF systems have emerged as a promising solution for high data rate wireless communication. FSO technology can be used effectively in multi-user scenarios to support Point-to-Multi-Point (P2MP) networks. In this work we present and analyse a P2MP Hybrid FSO/RF network that uses a number of FSO links for data transmission from the central node to different remote nodes of the network. A common backup RF link is used by the central node to transmit data to any of the remote nodes in case of failure of any FSO links. Each remote node is assigned a transmit buffer at the central node for the downlink transmission. We deploy a non-equal priority protocol and p-persistent strategy for nodes accessing the RF link and consider the back up RF transmission link with lower frame transmission rates as compared to the FSO link. Under different atmospheric conditions, we also study various performance metrics of the network. We study the throughput from the central node to the remote nodes individually as well as the following: the average transmit buffer size, the frame queuing delay in the transmit buffers, the efficiency of the queuing systems and the frame loss probability. / Graduate

Optical wireless communication (OWC) offers many benefits over established radio frequency–based communication links. Particularly in, high-data services, high security, and license-free operation, OWC link are becoming an attractive solution for the next generation of communication systems. In OWC, precise alignment of the incoming beam is necessary to close the communication link. However, precisely aligning the beam between the transceivers is challenging due to the laser beam’s narrowness and external disturbances that can significantly reduce, destroy, or scatter the beam signal. Therefore, designing optimized control strategies can significantly improve the alignment precision, which is the main motivation for this work. This thesis deploys standard and optimal control techniques, with an emphasis on optimized control strategies, to address the alignment problem in underwater optical wireless communication (UOWC) and in laser beam stabilizer systems within a vibrating environment. First, the UOWC system’s alignment problem was investigated in a vibrating scenario. For its effective control, the properties of light propagation were considered by accounting for the dynamical model that describes the propagation characteristics of the signal beam between transceivers. To control the UOWC system, we designed an observer-based optimal controller approach that combined the unconstrained and constrained optimal controllers, namely linear quadratic regulator (LQR) and model predictive control (MPC) with the extended Kalman filter (EKF). The latter enabled estimations of the beam dynamics from the power of the received beam signal. Extensive simulation tests were conducted that demonstrated the efficiency of the MPC algorithm compared to the LQR, fractional order proportional integral derivative (FOPID) and conventional PID controllers in terms of tracking and robustness against the disturbance levels. Second, the alignment problem in the laser beam stabilizer system was considered, whereby the designed control algorithms were tested experimentally in a vibrating disturbance. For this particular system, the LQR and MPC optimal controllers were designed both in simulation and experimental environments. The designed optimal control algorithms were compared to a conventional PID controller and its optimized variants (e.g., fractional and robust), demonstrating the MPC design’s outperformance in terms of tracking error and robustness to different voltage disturbance levels.

The COVID-19 global pandemic forced long lock-downs and physical distancing in different world regions. As a consequence, many jobs, services, and courses switched to online mode. This sudden turn of events created a dramatic increase in internet bandwidth demand, which has reached crisis point—even in developed countries—and widened the gap between those living in cities and far-flung regions. Installing new optical fibers to extend the capacity can be expensive. Radiofrequency (RF) is cur- rently the technology of choice to satisfy the bandwidth demand in under-connected regions, but is bandwidth-limited and strictly regulated. Connecting the unconnected via laser beams propagating in the atmosphere can be an efficient solution to provide fiber-like connectivity, while also being economically profitable. Free-space optics (FSO) is an unlicensed technology that uses infrared links to connect two communi- cating terminals. FSO systems can be running quickly compared to RF ones. FSO is also seen as a potential solution to provide high-speed connectivity between satellites and ground stations, and fly unmanned aerial vehicles (UAVs) and ground terminals. However, FSO is subject to various channel-related challenges, including atmospheric attenuation, turbulence, and pointing errors. In this thesis, we develop an FSO chan- nel simulation tool that considers the various effects that could potentially occur in terrestrial and vertical channels. We extend our study to cover structured light beams, which have been intensively considered in the last decade, as an extra degree of freedom for FSO. Finally, we consider realistic meteorological data from different regions in the Kingdom of Saudi Arabia to identify the best locations to deploy FSO systems.

No description available.

ITC/USA 2008 Conference Proceedings / The Forty-Fourth Annual International Telemetering Conference and Technical Exhibition / October 27-30, 2008 / Town and Country Resort & Convention Center, San Diego, California / We design irregular Low-Density Parity-Check (LDPC) codes for free-space optical (FSO) channels for different transmitter-receiver link distances and analyze the error performance for different atmospheric conditions. The design considers atmospheric absorption, laser beam divergence, and random intensity fluctuations due to atmospheric turbulence. It is found that, for the same transmit power, a system using the designed codes works over much longer link distances than a system that employs regular LDPC codes. Our analysis is particularly useful for portable optical transceivers and mobile links.

Free-space optical (FSO) communication offers significant technical and operational advantages such as higher bandwidth capacity, robustness to electromagnetic interference, a high degree of spatial confinement (bringing virtually unlimited reuse and inherent security), low power requirements, and unregulated spectrum. FSO communication can be deployed as an efficient solution for a wide range of applications such as last-mile access, fiber backup, back-haul for wireless cellular networks, and disaster recovery among others. Although FSO system have many appealing features, they have rather disappointing performance for long links due to the degrading effects of atmospheric turbulence-induced fading. In this dissertation, we investigate different diversity techniques to boost the performance of FSO systems in the presence of the atmospheric turbulence-induced fading. In Chapter 3, we investigate receive diversity in coherent FSO systems considering both turbulence-induced amplitude and phase fluctuations under weak turbulence regime. To mitigate the wavefront phase distortion effect, modal compensation is deployed at the receiver. Under the assumption of Rician channel that models the combined effects of the atmospheric fading and modal compensation, we derive outage probability and diversity- multiplexing tradeoff of such systems. Our results show that, at high signal to noise ratio (SNR) regime, the diversity gain as great as the number of receiving apertures is achieved. Moreover, it is found that the modal compensation provides finite-SNR diversity advantages in coherent receivers. In Chapter 4, we investigate multi-hop transmission (serial relaying) as a form of diversity technique to combat atmospheric fading in coherent FSO systems. Utilizing the same channel model as in Chapter 3 and considering decode-and-forward relaying strategy, we quantify the outage probability and the finite-SNR diversity-multiplexing tradeoff of this relaying scheme. Exploiting the fact that fading variance is distance-dependent in the atmospheric channel, our results demonstrate that the multi-hop transmission takes advantage of the resulting shorter hops and yields significant performance improvements in the presence of fading. In Chapter 5, we study hybrid-ARQ protocols in coherent FSO communications over Gamma-Gamma atmospheric fading channels. We investigate and compare the performance of three hybrid-ARQ protocols in terms of the outage probability and throughput. Furthermore, we characterize the outage performance at high-SNR regime by diversity and coding gains. Our results provide insight into the performance mechanisms of different hybrid-ARQ protocols in coherent FSO systems and demonstrate that hybrid-ARQ significantly improves the outage performance of a coherent FSO system particularly in strong turbulence regime. In Chapter 6, we investigate parallel relaying in an intensity modulation/direct detection (IM/DD) FSO system. Assuming Gamma-Gamma fading model, we analyze both decode-and-forward and amplify-and-forward modes of cooperation. Focusing on high SNR regime, we investigate the outage probability and characterize it by the diversity and coding gains. The diversity-multiplexing tradeoff expression of each cooperation mode is also derived. Our performance analysis reveals that large energy savings can be achieved through the use of parallel relaying in FSO systems.

Terrestrial free-space optical (FSO) communication uses visible or infrared wavelengths to broadcast high speed data wirelessly through the atmospheric channel. The performance of terrestrial FSO channel mainly depends on the local atmospheric conditions. Ad hoc networks offer cost-effective solutions for communications in areas where infrastructure is unavailable, e.g., intelligent transport system, disaster recovery and battlefield scenarios. Traditional ad hoc networks operate in the radio frequency (RF) spectrum, where the available bandwidth faces the challenge of rapidly increasing demands. FSO is an attractive alternative for RF in ad-hoc networks because of its high bandwidth and interference-free operation. This thesis investigates the influencing factors for routing traffic from given s-d pair while satisfying certain Quality of Services in terrestrial FSO ad hoc mesh networks under the effect of stochastic atmospheric turbulence. It starts with a comprehensive review of FSO technology, including the history, application, advantages and limitations. Subsequently the principle of operation, the building blocks and safety of FSO communication systems are discussed. The physics of atmosphere is taken into account to investigate how propagation of optical signals is affected in terrestrial FSO links. A propagation model is developed to grade the performance and reliability of the FSO ad hoc links in the network. Based on that model and the K-th shortest path algorithm, the performance of the path with highest reliability, the path with a second highest possible reliability and an independent path with no common links shared with the former two paths, were compared according to the simulation scenarios in node-dense area and node-sparse area. Matlab simulation shows that the short/long range dependent transmission delay are positively proportional to number of hops of the paths. Lower path reliability only dominate the cause of severe delay when traffic flow approaches near its upper link capacity in node-sparse area. In order to route traffic from given s-d pairs with satisfying certain Quality of Services, the path with highest reliability may not be the best choices since they may hold more hops which will degrade the QoS. Meanwhile, in case of exponential traffic congestion, it is recommended that both traffic demand and traffic flow propagating through the links should be pressed below a value close to the effective capacity, where the nonlinearity of the transmission delay curve starts to obviously aggravate.

Free-space optical (FSO) communication offers significant technical and operational advantages such as higher bandwidth capacity, robustness to electromagnetic interference, a high degree of spatial confinement (bringing virtually unlimited reuse and inherent security), low power requirements, and unregulated spectrum. FSO communication can be deployed as an efficient solution for a wide range of applications such as last-mile access, fiber backup, back-haul for wireless cellular networks, and disaster recovery among others. Although FSO system have many appealing features, they have rather disappointing performance for long links due to the degrading effects of atmospheric turbulence-induced fading. In this dissertation, we investigate different diversity techniques to boost the performance of FSO systems in the presence of the atmospheric turbulence-induced fading. In Chapter 3, we investigate receive diversity in coherent FSO systems considering both turbulence-induced amplitude and phase fluctuations under weak turbulence regime. To mitigate the wavefront phase distortion effect, modal compensation is deployed at the receiver. Under the assumption of Rician channel that models the combined effects of the atmospheric fading and modal compensation, we derive outage probability and diversity- multiplexing tradeoff of such systems. Our results show that, at high signal to noise ratio (SNR) regime, the diversity gain as great as the number of receiving apertures is achieved. Moreover, it is found that the modal compensation provides finite-SNR diversity advantages in coherent receivers. In Chapter 4, we investigate multi-hop transmission (serial relaying) as a form of diversity technique to combat atmospheric fading in coherent FSO systems. Utilizing the same channel model as in Chapter 3 and considering decode-and-forward relaying strategy, we quantify the outage probability and the finite-SNR diversity-multiplexing tradeoff of this relaying scheme. Exploiting the fact that fading variance is distance-dependent in the atmospheric channel, our results demonstrate that the multi-hop transmission takes advantage of the resulting shorter hops and yields significant performance improvements in the presence of fading. In Chapter 5, we study hybrid-ARQ protocols in coherent FSO communications over Gamma-Gamma atmospheric fading channels. We investigate and compare the performance of three hybrid-ARQ protocols in terms of the outage probability and throughput. Furthermore, we characterize the outage performance at high-SNR regime by diversity and coding gains. Our results provide insight into the performance mechanisms of different hybrid-ARQ protocols in coherent FSO systems and demonstrate that hybrid-ARQ significantly improves the outage performance of a coherent FSO system particularly in strong turbulence regime. In Chapter 6, we investigate parallel relaying in an intensity modulation/direct detection (IM/DD) FSO system. Assuming Gamma-Gamma fading model, we analyze both decode-and-forward and amplify-and-forward modes of cooperation. Focusing on high SNR regime, we investigate the outage probability and characterize it by the diversity and coding gains. The diversity-multiplexing tradeoff expression of each cooperation mode is also derived. Our performance analysis reveals that large energy savings can be achieved through the use of parallel relaying in FSO systems.

Os sistemas de comunicação óptica por espaço livre, comumente denominados sistemas FSO (Free Space Optics), servem para estabelecer enlaces de comunicação do tipo wireless, ponto-a-ponto, a uma elevada taxa de dados e com alcances que podem variar de algumas centenas de metros a alguns quilômetros. O interesse pela tecnologia FSO tem sido estimulado pela necessidade de se fornecer soluções complementares às tradicionais (e.g. fibra óptica e RF) visando a atender à crescente demanda por conexões de banda larga. Algumas de suas aplicações mais importantes são a conexão de redes locais de computadores, a conexão de estações rádio base de telefonia móvel às centrais e o acesso de última milha. Embora a tecnologia FSO venha sendo empregada em pequena escala no Brasil, vislumbra-se o potencial de maior aplicação desta tecnologia em um futuro próximo, razão pela qual se propõe este estudo, focado no projeto de sistemas FSO. A principal contribuição deste trabalho é demonstrar uma possível solução para a realização de um enlace óptico operando em espaço livre, destinado a conectar duas redes locais de computadores Ethernet Rápida (100 Mbps). As seguintes atividades foram desenvolvidas: estudo das questões mais relevantes pertinentes ao projeto de sistemas FSO; projeto, construção e caracterização eletro-óptica de circuitos; montagem e demonstração do funcionamento de uma versão de testes do sistema, realizadas em laboratório; estudo de características associadas à transferência de radiação óptica de transmissor para receptor, envolvendo o balanço de potência para estimativa do alcance do enlace, sob condições atmosféricas ideais. Como resultado, obtivemos um sistema de comunicação do tipo full-duplex, operando no comprimento de onda de 850 nm em formato de modulação OOK, a uma taxa de dados efetiva de 125 Mbps. Com base na experiência obtida, melhoras ao sistema são sugeridas no final do trabalho. / Free space optical communication systems (FSO systems) provide wireless, point-to-point communication links at high data rates, at maximum distances ranging from hundreds of meters to several kilometers. The growing interest in FSO technology arises from the necessity of providing complementary and alternative solutions to those already adopted (eg. fiber optics and RF), aiming to satisfy the increasing demand for broadband connections. Some of its most important applications are connecting local area networks (LANs), backhauling wireless networks and providing last mile access. Although today FSO is not widely adopted in Brazil, the technology has the potential for being adopted in a greater scale in the near future, which is the reason we propose a study focused on issues related to the design of FSO systems. This work\'s main contribution is to demonstrate a possible solution for the construction of a FSO system intended to connect two Fast Ethernet LANs (100 Mbps). For this purpose, the following activities were developed: study of the main aspects related to FSO system design; design, construction and electrooptical characterization of circuits; mounting and demonstration, in the lab, of a test version of the system; study of characteristics related to radiation transfer from transmitter to receiver, involving the use of the link power budget for an estimation of the maximum distance achievable under ideal atmospheric conditions. The result is a full-duplex communication system that employs the 850 nm wavelength in OOK modulation format, operating at an effective bit rate of 125 Mbps. Based on the knowledge achieved, improvements to the system are suggested at the end of this work.

Os sistemas de comunicação óptica por espaço livre, comumente denominados sistemas FSO (Free Space Optics), servem para estabelecer enlaces de comunicação do tipo wireless, ponto-a-ponto, a uma elevada taxa de dados e com alcances que podem variar de algumas centenas de metros a alguns quilômetros. O interesse pela tecnologia FSO tem sido estimulado pela necessidade de se fornecer soluções complementares às tradicionais (e.g. fibra óptica e RF) visando a atender à crescente demanda por conexões de banda larga. Algumas de suas aplicações mais importantes são a conexão de redes locais de computadores, a conexão de estações rádio base de telefonia móvel às centrais e o acesso de última milha. Embora a tecnologia FSO venha sendo empregada em pequena escala no Brasil, vislumbra-se o potencial de maior aplicação desta tecnologia em um futuro próximo, razão pela qual se propõe este estudo, focado no projeto de sistemas FSO. A principal contribuição deste trabalho é demonstrar uma possível solução para a realização de um enlace óptico operando em espaço livre, destinado a conectar duas redes locais de computadores Ethernet Rápida (100 Mbps). As seguintes atividades foram desenvolvidas: estudo das questões mais relevantes pertinentes ao projeto de sistemas FSO; projeto, construção e caracterização eletro-óptica de circuitos; montagem e demonstração do funcionamento de uma versão de testes do sistema, realizadas em laboratório; estudo de características associadas à transferência de radiação óptica de transmissor para receptor, envolvendo o balanço de potência para estimativa do alcance do enlace, sob condições atmosféricas ideais. Como resultado, obtivemos um sistema de comunicação do tipo full-duplex, operando no comprimento de onda de 850 nm em formato de modulação OOK, a uma taxa de dados efetiva de 125 Mbps. Com base na experiência obtida, melhoras ao sistema são sugeridas no final do trabalho. / Free space optical communication systems (FSO systems) provide wireless, point-to-point communication links at high data rates, at maximum distances ranging from hundreds of meters to several kilometers. The growing interest in FSO technology arises from the necessity of providing complementary and alternative solutions to those already adopted (eg. fiber optics and RF), aiming to satisfy the increasing demand for broadband connections. Some of its most important applications are connecting local area networks (LANs), backhauling wireless networks and providing last mile access. Although today FSO is not widely adopted in Brazil, the technology has the potential for being adopted in a greater scale in the near future, which is the reason we propose a study focused on issues related to the design of FSO systems. This work\'s main contribution is to demonstrate a possible solution for the construction of a FSO system intended to connect two Fast Ethernet LANs (100 Mbps). For this purpose, the following activities were developed: study of the main aspects related to FSO system design; design, construction and electrooptical characterization of circuits; mounting and demonstration, in the lab, of a test version of the system; study of characteristics related to radiation transfer from transmitter to receiver, involving the use of the link power budget for an estimation of the maximum distance achievable under ideal atmospheric conditions. The result is a full-duplex communication system that employs the 850 nm wavelength in OOK modulation format, operating at an effective bit rate of 125 Mbps. Based on the knowledge achieved, improvements to the system are suggested at the end of this work.