In recent years, free space optical (FSO) communication has gained significant importance owing to its unique features: large bandwidth, license free spectrum, high data rate, easy and quick deployability, less power, and low mass requirements. FSO communication uses optical carrier in the near infrared band to establish either terrestrial links within the Earth’s atmosphere or inter-satellite/deep space links or ground-to-satellite/satellite-to-ground links. It also finds its applications in remote sensing, radio astronomy, military, disaster recovery, last mile access, backhaul for wireless cellular networks, and many more. However, despite of great potential of FSO communication, its performance is limited by the adverse effects (viz., absorption, scattering, and turbulence) of the atmospheric channel. Out of these three effects, the atmospheric turbulence is a major challenge that may lead to serious degradation in the bit error rate performance of the system and make the communication link infeasible. This paper presents a comprehensive survey on various challenges faced by FSO communication system for ground-to-satellite/satellite-to-ground and inter-satellite links. It also provides details of various performance mitigation techniques in order to have high link availability and reliability. The first part of this paper will focus on various types of impairments that pose a serious challenge to the performance of optical communication system for ground-to-satellite/satellite-to-ground and inter-satellite links. The latter part of this paper will provide the reader with an exhaustive review of various techniques both at physical layer as well as at the other layers (link, network, or transport layer) to combat the adverse effects of the atmosphere. It also uniquely presents a recently developed technique using orbital angular momentum for utilizing the high capacity advantage of optical carrier in case of space-based and near-Earth optical communication links. This survey provides the reader with comprehensive details on the use of space-based optical backhaul links in order to provide high capacity and low cost backhaul solutions.

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Optical Communication in Space: Challenges and Mitigation Techniques

In recent years, free space optical communication has gained significant importance owing to its unique features: large bandwidth, license-free spectrum, high data rate, easy and quick deployability, less power and low mass requirements. FSO communication uses the optical carrier in the near infrared band to establish either terrestrial links within the Earth's atmosphere or inter-satellite or deep space links or ground-to-satellite or satellite-to-ground links. However, despite the great potential of FSO communication, its performance is limited by the adverse effects viz., absorption, scattering, and turbulence of the atmospheric channel. This paper presents a comprehensive survey on various challenges faced by FSO communication system for ground-to-satellite or satellite-to-ground and inter-satellite links. It also provides details of various performance mitigation techniques in order to have high link availability and reliability. The first part of the paper will focus on various types of impairments that pose a serious challenge to the performance of optical communication system for ground-to-satellite or satellite-to-ground and inter-satellite links. The latter part of the paper will provide the reader with an exhaustive review of various techniques both at physical layer as well as at the other layers i.e., link, network or transport layer to combat the adverse effects of the atmosphere. It also uniquely presents a recently developed technique using orbital angular momentum for utilizing the high capacity advantage of the optical carrier in case of space-based and near-Earth optical communication links. This survey provides the reader with comprehensive details on the use of space-based optical backhaul links in order to provide high-capacity and low-cost backhaul solutions.

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FSO is a communication system where free space acts as medium between transceivers and they should be in LOS for successful transmission of optical signal. Medium can be air, outer space, or vacuum. This system can be used for communication purpose in hours and in lesser economy. There are many advantages of FSO like high bandwidth and no spectrum license. The transmission in FSO is dependent on the medium because the presence of foreign elements like rain, fog, and haze, physical obstruction, scattering, and atmospheric turbulence are some of these factors. Different studies on weather conditions and techniques employed to mitigate their effect are discussed in this paper.

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Free Space Optics: Current Applications and Future Challenges

In recent years, free space optical (FSO) communication has gained significant importance owing to its unique features: large bandwidth, license free spectrum, high data rate, easy and quick deployability, less power and low mass requirement. FSO communication uses optical carrier in the near infrared (IR) and visible band to establish either terrestrial links within the Earths atmosphere or inter-satellite or deep space links or ground to satellite or satellite to ground links. However, despite of great potential of FSO communication, its performance is limited by the adverse effects (viz., absorption, scattering and turbulence) of the atmospheric channel. Out of these three effects, the atmospheric turbulence is a major challenge that may lead to serious degradation in the bit error rate (BER) performance of the system and make the communication link infeasible. This paper presents a comprehensive survey on various challenges faced by FSO communication system for both terrestrial and space links. It will provide details of various performance mitigation techniques in order to have high link availability and reliability of FSO system. The first part of the paper will focus on various types of impairments that poses a serious challenge to the performance of FSO system for both terrestrial and space links. The latter part of the paper will provide the reader with an exhaustive review of various techniques used in FSO system both at physical layer as well as at the upper layers (transport, network or link layer) to combat the adverse effects of the atmosphere. Further, this survey uniquely offers the current literature on FSO coding and modulation schemes using various channel models and detection techniques. It also presents a recently developed technique in FSO system using orbital angular momentum to combat the effect of atmospheric turbulence.

Free Space Optical Communication: Challenges and Mitigation Techniques

The next generation (NG) optical technologies will unveil certain unique features, namely ultra-high data rate, broadband multiple services, scalable bandwidth, and flexible communications for manifold end-users. Among the optical technologies, free space optical (FSO) technology is a key element to achieve free space data transmission according to the requirements of the future technologies, which is due to its cost effective, easy deployment, high bandwidth enabler, and high secured. In this article, we give the overview of the recent progress on FSO technology and the factors that will lead the technology towards ubiquitous application. As part of the review, we provided fundamental concepts across all types of FSO system, including system architecture comprising of single beam and multiple beams. The review is further expanded into the investigation of rain and haze effects toward FSO signal propagation. The final objective that we cover is the scalability of an FSO network via the implementations of hybrid multi-beam FSO system with wavelength division multiplexing (WDM) technology.

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A Survey of Free Space Optics (FSO) Communication Systems, Links, and Networks

Proposed parameters of specific rain attenuation prediction for Free Space Optics link operating in tropical region

Free Space Optics (FSO) link have capabilities of providing optical communications similar to fiber optics based communications. However, the operational status of an FSO link is highly weather dependent which hampered the FSO link with feasibility issue. Among the major effect on FSO links under local weather condition is due to attenuation of heavy rainfall. Attenuation due to rainfall can restrict the path length of communication systems at frequencies above 10 GHz. The studies on the effect of rain intensity variation have been proposed by many models based on the radio wave propagation at centimeter or millimeter wavelength. Among the models are Lin Model, Moupfouma Model, Assis Model, Dissanayake and Allnutt Model, ITU Model, Abdulrahman Model and Silva Mello Model. The objective of this research to investigate the effect of rain intensity variation on the rain attenuation prediction for FSO links.

Effects of rain intensity variation on rain attenuation prediction for Free Space Optics (FSO) links

Free Space Optics (FSO) as potential high speed connectivity has capability similar to fiber optic in term of speed and bandwidth. The advantages of FSO over fiber are time and cost of deployment. However, since the transmission medium of FSO is atmosphere, atmospheric scattering is the major cause for interruption of FSO link. In temperate region, fog is the main factor that affects the availability of the link. However, in tropical region non-selective scattering is expected to be the major drawback. Non-selective scattering is wavelength independent and exists due to rainfall. In country like Malaysia rain season with heavy rain can reduce the received power of FSO link to below the threshold. In this paper the preliminary analysis is presented for the use in the larger scale to construct the tropical rain attenuation model for FSO. The result from the analysis showing that heavy rain will cause the attenuation of the link however the 99.999% is still achievable for the FSO system under Malaysia weather condition.

A.K. Wajdi

Papers

Proposed parameters of specific rain attenuation prediction for Free Space Optics link operating in tropical region

Effects of rain intensity variation on rain attenuation prediction for Free Space Optics (FSO) links

Preliminary analysis on the effect of rain attenuation on Free Space Optics (FSO) propagation measured in tropical weather condition