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Optical wireless communications (OWC) has witnessed a revival recently among researchers in both academia and industry. The main reason for this resurgence is the exhausted radio-frequency (RF) spectrum, which is getting too crowded to handle the increasingly high demand for data rates. The optical band offers an opportunity to relieve the RF spectrum by accommodating part of the load. Other reasons behind the interest in OWC include relatively simple deployment, unlicensed bandwidth, high data rate, and dense spatial reuse. Practical outdoor applications include free-space optical communication for backhaul links between base-stations, and for ground-to-satellite/satellite-to-ground and inter-satellite communication. Indoor applications include visible-light communication to establish Light-Fidelity (LiFi) access and positioning, and enables combining illumination and communication functionalities using LED fixtures. Several works in the literature studied OWC from theoretical and practical perspectives, and demonstrated the capability of this technology to achieve high data rates.

This Best Readings section presents papers on optical wireless communications that cover several fronts, including information theoretic aspects, communication theoretic aspects, and implementation aspects. While the following list is by no means exhaustive, it highlights papers that could constitute a starting point for researchers interested in this area.

Issued August 2018


Anas Chaaban
School of Engineering
University of British Columbia 
Kelowna, BC, Canada

Zouheir Rezki
Department of Electrical and Computer Engineering
University of Idaho
Moscow, ID, USA

Hany ElGala
Department of Electrical and Computer Engineering
University of Albany - State University of New York
Albany, NY, USA

Mohamed-Slim Alouini
Computer, Electrical, and Mathematical Sciences and Engineering Division 
King Abdullah University of Science and Technology (KAUST)
Thuwal, Saudi Arabia

Editorial Staff

Matthew C. Valenti
Editor-in-Chief, ComSoc Best Readings
West Virginia University
Morgantown, WV, USA


H. Hemmati, Ed., Deep Space Optical Communications, Wiley, 2006.
This book captures a quarter century of research and development in deep space optical communications from the Jet Propulsion Laboratory (JPL). Additionally, it presents findings from other optical communications research groups from around the world for a full perspective. It covers the latest developments in optical communications technology, as well as the state of the art in component and subsystem technologies, fundamental limitations, and approaches to develop and fully exploit new technologies.

S. Arnon, J. Barry, G. Karagiannidis, R. Schober, and M. Uysal, Eds., Advanced Optical Wireless Communication Systems, Cambridge University Press, 2012.
This book is an excellent reference for researchers working on the theory of OWC. It guides readers through key concepts including coding, modulation, equalization, multiple access, and channel capacity. It covers many applications including infrared communication, visible light communication, non-line-of-sight ultraviolet communication, underwater OWC, and hybrid RF/OWC.

Z. Ghassemlooy, W. Popoola, and S. Rajbhandari, Optical Wireless Communications: System and Channel Modelling with MATLAB, CRC Press, 2013. 
This book provides a detailed description of OWC system and channel modeling using MATLAB ®, covering optical sources and detectors, transmitters and receivers, and indoor and outdoor channel models. Additionally, the book introduces fundamental OWC principles at the device and system level, in addition to applications of OWC. The book also includes MATLAB® source code for simulating various aspects of OWC.

M. Uysal and C. Capsoni, S. Ghassemlooy, A. Boucouvalas, and E. Udvary, Eds., Optical Wireless Communications: An Emerging TechnologySpringer International Publishing, 2016.
This book is a valuable guide for theoreticians and practitioners working in the area of OWC. It reviews OWC technologies (visible-light, ultraviolet (UV) and infrared (IR) communications) and applications (indoor, vehicular, terrestrial, underwater, intersatellite, deep space, etc.), and it explains propagation modelling and channel characterization, information-theoretic aspects, physical-layer methodologies, upper-layer protocols, and cross-layer designs.

H. Kaushal, V. K. Jain, and S. Kar, Free Space Optical Communication, Springer India, 2017. 
This book focuses on outdoor free space optical (FSO) communication systems. It explains various aspects of FSO including propagation through atmospheric turbulence, design methodologies and trade-offs, acquisition, tracking and pointing (ATP) techniques, and link-feasibility analysis.

Z. Wang, Q. Wang, W. Huang, and Z. Xu, Visible Light Communications: Modulation and Signal Processing, Wiley-IEEE Press, 2017.
This book focuses on visible light communication (VLC), and constitutes a practical guide for theoreticians and practicioners to designing VLC systems with lighting constraints. It details modern modulation and signal processing techniques for VLC from theoretical and practical viewpoints.

Overviews and Tutorials

M. A. Khalighi and M. Uysal, “Survey on Free Space Optical Communication: A Communication Theory Perspective,” IEEE Communications Surveys & Tutorials, vol. 16, no. 4, pp. 2231-2258, Fourth Quarter 2014.
This paper presents a survey on free-space optical communication systems and covers various topics including channel models, transmitter/receiver structures, information-theoretic limits, and algorithmic-level system design.

D. Karunatilaka, F. Zafar, V. Kalavally, and R. Parthiban, “LED Based Indoor Visible Light Communications: State of the Art,” IEEE Commununication Surveys and Tutorials, vo. 17, no. 3, pp. 1649-1678, Third Quarter 2015.
This paper reviews visible light communication utilizing light-emitting diodes, with an emphasis on combined communication and lighting functionalities. It discusses modulation, dimming, filtering, beamforming, and various other topics, and also highlights future research directions.

Z. Ghassemlooy, S. Arnon, M. Uysal, Z. Xu, and J. Cheng, “Emerging Optical Wireless Communications-Advances and Challenges,” IEEE Journal on Selected Areas in Communications, vol. 33, no. 9, pp. 1738-1749, September 2015.
This paper presents an overview of OWC systems focusing on visible-light communications, free-space optics, transcutaneous OWC, underwater OWC, and optical scattering communications.

P. H. Pathak, X. Fen, P. Hu, and P. Mohapatra, “Visible Light Communication, Networking, and Sensing: A Survey, Potential and Challenges,” IEEE Communication Surveys and Tutorials, vol. 17, no. 4, pp. 2047-2077, Foruth Quarter 2015.
This paper provides a review of existing works on visible light communication and sensing. It covers physical-layer as well as medium-access techniques, in addition to various applications such as sensing, indoor localization, gesture recognition, screen-camera communication, and vehicular networking. It also highlights challenges for future research.

H. Kaushal and G. Kaddoum, “Optical Communication in Space: Challenges and Mitigation Techniques,” IEEE Communications Surveys & Tutorials, vol. 19, no. 1, pp. 57-96, First Quarter 2017.
This paper surveys challenges of OWC for ground-to-satellite, satellite-to-ground, and inter-satellite links, and discusses several physical-, link-, network-, and transport-layer mitigation techniques to overcome these challenges.

Z. Zeng, S. Fu, H. Zhang, Y. Dong, and J. Cheng, “A Survey of Underwater Optical Wireless Communications,” IEEE Communications Surveys & Tutorials, vol. 19, no. 1, pp. 204-238, First Quarter 2017.
This paper provides a comprehensive and exhaustive survey of the state-of-the-art in underwater OWC research, with a focus on channel characterization, modulation, and coding techniques, together with practical implementations.

X. Li, R. Zhang, and L. Hanzo, “Optimization of Visible-Light Optical Wireless Systems: Network-Centric Versus User-Centric Designs,” to appear in IEEE Communications Surveys and Tutorials, 2018.
This paper presents first a survey on the user-centric design and optimization of VLC networks and offers some design guidelines for these networks.

M. Z. Chowhury, M. T. Hossain, A. Islam, and Y. M. Jang, “A Comparative Survey of Optical Wireless Technologies: Architectures and Applications,” IEEE Access, vol. 6, pp. 9819-9840, March 2018. 
This paper presents a survey of different OWC technologies such as VLC, light fidelity (LiFi), optical camera communication (OCC), FSO communication, and light detection and ranging (LiDAR). It highlights the similarities and differences among these different promising optical wireless technologies and contrasts these technologies with corresponding similar existing RF technologies.

Special Issues

Special Issue on Optical Wireless CommunicationsIEEE Journal on Selected Areas on Communications, vol. 27, no. 9, December 2009.

Special Issue on Optical Wireless CommunicationsIEEE Journal on Selected Areas on Communications, vol. 33, no. 9, September 2015.

Special Section on Optical Wireless Technologies for 5G Communications and BeyondIEEE Access, 2017.

Special Issue on Localisation, Communication and Networking with VLCIEEE Journal on Selected Areas on Communications, vol. 36, no. 1, January 2018.

Topic: Performance Analysis

S. M. Navidpour, M. Uysal, and M. Kavehrad, “BER Performance of Free-Space Optical Transmission with Spatial Diversity,” IEEE Transactions on Wireless Communications, vol. 6, no. 8, August 2007.
This paper investigates the bit error rate of free-space optical communications with spatial diversity under log-normal atmospheric turbulence and quantifies the effect of spatial diversity and possible spatial correlations in a log-normal channel.

T. A. Tsiftsis, H. G. Sandalidis, G. K. Karagiannidis, and M. Uysal, “Optical Wireless Links with Spatial Diversity over Strong Atmospheric Turbulence Channels,” IEEE Transactions on Wireless Communications, vol. 8, no. 2, pp. 951-957, February 2009.
This paper investigates the error rate of free-space optical communication systems for K-distributed atmospheric turbulence channels and presents approximated closed-form expressions for the average bit-error rate of single-input multiple-output systems.

E. Bayaki, R. Schober, and R. K. Mallik, “Performance Analysis of MIMO Free-Space Optical Systems in Gamma-Gamma Fading,” IEEE Transactions on Communications, vol. 57, no. 11, pp. 3415-3424, November 2009.
This paper provides a fast and accurate way to evaluate the pairwise error probabilities of single-input single-output and multiple-input multiple-output free-space optical systems in Gamma-Gamma fading channels. It also provide simple closed-form expressions for the diversity gain and the combining gain for repetition coding and equal gain combining or maximal ratio combining.

M. Niu, J. Cheng, and J. F. Holzman, “Error Rate Performance Comparison of Coherent and Subcarrier Intensity Modulated Optical Wireless Communications,” IEEE/OSA Journal of Optical Communications and Networking, vol. 5, no. 6, pp. 554-564, June 2013.
This paper presents a detailed analysis and comparison for coherent and subcarrier-intensity-modulation-based OWC systems in terms of error rate over weak-to-strong Gamma-Gamma distributed turbulence conditions. It also derives error rate expressions for maximum ratio combining, equal gain combining, and selection combining schemes.

I. S. Ansari, F. Yilmaz, and M.-S. Alouini, “Performance Analysis of Free-Space Optical Links over Málaga-(M) Turbulence Channels with Pointing Errors,” IEEE Transactions on Wireless Communications, vol. 15, no. 1, pp. 91-102, August 2016. 
This paper derives closed-form expressions for the outage probability, error rate, and ergodic capacity of OWC using M-ary modulation schemes.

Topic: Performance Limits

S. Aghajanzadeh and M. Uysal, “Diversity-Multiplexing Trade-Off in Coherent Free-Space Optical Systems with Multiple Receivers,” Journal of Optical Communications and Networking, vol. 2, no. 12, pp. 1087-1094, December 2010.
This paper studies the diversity-multiplexing trade-off in coherent OWC with multiple receivers, and considers the performance gains of deploying multiple receive apertures and phase compensation techniques.

Y. Sapenov, A. Chaaban, Z. Rezki, M. Abdallah, K. Qaraqe, and M.-S. Alouini, “Diversity Order Results for MIMO Optical Wireless Communications,” IEEE Wireless Communication Letters, vol. 7, no. 1, February 2018.
This paper characterizes the maximal diversity order of multiple-input multiple-output Gaussian OWC channels, from the outage probability and error probability perspectives.

Topic: Transmission Schemes

J. Pierce, “Optical Channels: Practical Limits with Photon Counting,” IEEE Transactions on Communications, vol. 26, no. 12, pp. 1819-1821, December 1978.
This paper comments on practical limitations of photon counting due to code implementation.

M. Safari and M. Uysal, “Relay-Assisted Free-Space Optical Communication,” IEEE Transactions on Wireless Communications, vol. 7, no. 11, pp. 4445-4448, December 2008.
This paper studies relay-assisted free-space optical communications with amplify-and-forward and decode-and-forward modes as a means to mitigate outage probability due to atmospheric turbulence induced fading.

F. Xu, A. Khalighi, P. Caussé, and S. Bourennane, “Channel Coding and Time-Diversity for Optical Wireless Links,” Optics Express, vol. 17, no. 2, pp. 872-887, January 2009.
This paper studies exploiting temporal diversity via coding and interleaving to combat the effect of atmospheric turbulence in OWC.

J. Armstrong, “OFDM for Optical Communications,” IEEE Journal of Lightwave Technology, vol. 27, no. 3, pp. 189-204, February 2009.
This paper presents aspects of orthogonal frequency division multiplexing (OFDM) that are important in optical communication applications, and outlines new forms of OFDM which have been developed for such applications.

M.-A. Khalighi, N. Schwartz, N. Aitamer, and S. Bourennane, “Fading Reduction by Aperture Averaging and Spatial Diversity in Optical Wireless Systems,” Journal of Optical Communications and Networking, vol. 1, no. 6, pp. 580-593, November 2009.
This paper studies the improvement in error rate and outage capacity due to aperture averaging and diversity combining in OWC.

L. Zeng, D. C. O'Brien, H. L. Minh, G. E. Faulkner, K. Lee, D. Jung, Y.-J. Oh, and E. T. Won, “High Data Rate Multiple Input Multiple Output (MIMO) Optical Wireless Communications Using White LED Lighting,” IEEE Journal on Selected Areas in Communications, vol. 27, no. 9, December 2009.
This paper investigates the use of non-imaging and imaging multiple-input multiple-output techniques in OWC and shows via simulations that they can lead to several hundred Mbit/s, and up to Gbit/s in many circumstances.

Topic: Poisson Channels

J. Pierce, E. Posner, and E. Rodemich, “The Capacity of the Photon Counting Channel,” IEEE Transactions on Information Theory, vol. 27, no. 1, pp. 61-77, January 1981.
This paper characterizes the capacity of OWC with a photon-counting receiver in terms of the average power, Boltzmann constant, and temperature, which are important criteria for space applications.

A. D. Wyner, “Capacity and Error Exponent for the Direct Detection Photon Channel—Part I,” IEEE Transactions on Information Theory, vol. 34, no. 6, pp. 1449–1461, November 1988.
A. D. Wyner, “Capacity and Error Exponent for the Direct Detection Photon Channel—Part II,” IEEE Transactions on Information Theory, vol. 34, no. 6, pp. 1462–1471, November 1988.
Part I of this paper characterizes the capacity of the direct-detection photon channel modelled as a continuous-time Poisson channel with average and peak intensity constraints. It also provides a lower bound on the error exponent. Part II of the paper provides a tight upper bound on the error exponent, thus completing the characterization.

A. Lapidoth and S. Shamai, “The Poisson Multiple-Access Channel,” IEEE Transactions on Information Theory, vol. 44, no. 2, pp. 488-501, March 1998.
This paper characterizes the capacity of the Poisson multiple-access channel under peak and average intensity constraints.

S. M. Haas and J. H. Shapiro “Capacity of Wireless Optical Communications,” IEEE Journal on Selected Areas in Communications, vol. 21, no. 8, October 2003.
This paper studies the ergodic capacity of the multiple-input multiple-output Poisson channel under average and peak intensity constraints, in addition to the outage probability under log-normal fading.

A. Lapidoth and S. M. Moser, “On the Capacity of the Discrete-Time Poisson Channel,” IEEE Transactions on Information Theory, vol. 55, no. 1, pp. 303–322, January 2009. 
The Poisson channel models photon detection in OWC. In this channel, the received signal is Poisson distributed with parameters that depend on the transmit signal and background noise.  This paper derives capacity bounds and the high-SNR asymptotic capacity of the discrete-time Poisson channel, under average and peak optical intensity constraints.

H. Kim, B. Nachman, and A. El Gamal, “Superposition Coding Is Almost Always Optimal for the Poisson Broadcast Channel,” IEEE Transactions on Information Theory, vol. 62, no. 4, pp. 1782-1794, April 2016.
This paper studies the capacity of the Poisson broadcast channel as a model for optical communication channels, under average and peak intensity constraints. It shows that superposition coding achieves the capacity region for most cases.

Topic: Free-Space Optical Intensity Channels

S. Hranilovic and F. R. Kschischang, “Capacity Bounds for Power- and Band-Limited Optical Intensity Channels Corrupted by Gaussian Noise,” IEEE Transactions on Information Theory, vol. 50, no. 5, pp. 784-795, May 2004.
This paper derives bounds on the capacity of the Gaussian OWC channel with power and bandwidth constraints under any time-disjoint signalling scheme. The bounds converge at high SNR.

A. Lapidoth, S. M. Moser, and M. A. Wigger, “On the Capacity of Free-Space Optical Intensity Channels,” IEEE Transactions on Information Theory, vol. 55, no. 10, pp. 4449-4461, October 2009.
The free-space optical intensity channel models OWC with a large number of received photons. This channel is an additive Gaussian noise channel, where noise is either input-independent or input-dependent according to the regime of operation. This paper develops bounds on the capacity of the Gaussian OWC channel with average and peak intensity constraints, and derives asymptotic capacity expressions for high and low SNR regimes.

A. A. Farid and S. Hranilovic, “Channel Capacity and Non-Uniform Signalling for Free-Space Optical Intensity Channels,” IEEE Journal on Selected Areas in Communications, vol. 27, no. 9, pp. 1-12, December 2009.
This paper proposes a non-uniform discrete input distribution and multi-level coding as a means to approach the capacity of the Gaussian OWC channel with average and peak intensity constraints.

A. A. Farid and S. Hranilovic, “Capacity Bounds for Wireless Optical Intensity Channels with Gaussian Noise,” IEEE Transactions on Information Theory, vol. 56, no. 12, pp. 6066-6077, December 2010.
This paper derives capacity bounds for the Gaussian OWC channel with an average intensity constraint, and develops a discrete input distribution that approaches this capacity at high SNR.

S. M. Moser, “Capacity Results of an Optical Intensity Channel with Input-Dependent Gaussian Noise,” IEEE Transactions on Information Theory, vol. 58, no. 1, pp. 207-223, January 2012.
This paper derives capacity bounds and asymptotic capacity expression for Gaussian OWC channels with input-dependent noise.

A. Chaaban, Z. Rezki, and M.-S. Alouini, “On the Capacity of the Intensity-Modulation Direct-Detection Optical Broadcast Channel,” IEEE Transactions on Wireless Communications, vol. 15, no. 5, pp. 3114-3130, May 2016.
This paper derives bounds on the capacity region of the Gaussian OWC broadcast channel with average and peak intensity constraints, in addition to asymptotic characterizations of capacity at high and low SNR.

A. Chaaban, O. M. S. Al-Ebraheemy, T. Y. Al-Naffouri, and M.-S. Alouini, “Capacity Bounds for the Gaussian IM-DD Optical Multiple-Access Channel,” IEEE Transactions on Wireless Communications, vol. 16, no. 5, pp. 3328-3340, May 2017.
This paper studies the capacity region of the Gaussian OWC multiple access channel, and derives asymptotic capacity characterizations.

S. M. Moser, L. Wang, and M. Wigger, Capacity Results on Multiple-Input Single-Output Wireless Optical Channels,” to appear in IEEE Transactions on Information Theory, 2018.
This paper derives the capacity bounds for the MISO Gaussian OWC channel, and determines input distributions that approach capacity at high and low SNR.

A. Chaaban, Z. Rezki, and M.-S. Alouini, “Capacity Bounds and High-SNR Capacity of MIMO Intensity-Modulation Optical Channels,” IEEE Transactions on Wireless Communications, vol. 17, no. 5, pp. 3003-3017, May 2018.
This paper characterizes the high-SNR asymptotic capacity of the multiple-input multiple-output Gaussian OWC channel when the channel matrix has full column rank, and provides capacity bounds for channels with a general channel matrix.

M. Soltani and Z. Rezki, “Optical Wiretap Channel with Input-Dependent Gaussian Noise and Amplitude Constraint,” to appear in IEEE Transactions on Information Theory, 2018. 
This paper studies the secrecy capacity of the Gaussian OWC wiretap channel with input-dependent noise, and shows that the optimal input distribution is discrete with a finite support.

Topic: Visible-Light Communications Systems

H. Elgala, R. Mesleh, and H. Haas, “Indoor Optical Wireless Communication: Potential and State-of-the-Art,” IEEE Communications Magazine, vol. 49, no. 9, pp. 56-62, September 2011.
This article discusses challenges, applications and prospects of OWC with a focus on indoor deployment scenarios. Issues include duplex transmission, multiple access, medium access control protocols, and link capacity improvements.

A. H. Azhar, T. Tran, and D. O’Brien, “A Gigabit/s Indoor Wireless Transmission Using MIMO-OFDM Visible-Light Communications,” IEEE Photonics Technology Letters, vol. 25, no. 2, pp. 171-174, January 2013.
This paper presents an experimental demonstration of indoor visible-light communication transmission at 1 Gb/s. The system consists of a four-channel multiple-input multiple-output link that uses white light emitting diode sources and a nine-channel imaging diversity receiver.

D. Tsonev, et al., "A 3-Gb/s Single-LED OFDM-Based Wireless VLC Link Using a Gallium Nitride μLED," IEEE Photonics Technology Letters, vol. 26, no.7, pp. 637-640, April 2014.
This paper presents a visible light communication (VLC) system based on a single 50-μm gallium nitride light emitting diode (LED), exhibiting a 3-dB modulation bandwidth of at least 60 MHz. Pre- and post-equalization techniques, as well as adaptive data loading, are applied to achieve a demonstration of wireless communication at speeds exceeding 3 Gb/s.

D. Tsonev, S. Videv, and H. Haas, “Towards a 100 Gb/s Visible Light Wireless Access Network,” Optics Express, vol. 23, no. 2, pp. 1627-1637, January 2015.
This paper demonstrates the feasibility of 100 Gb/s visible-light communication using off-the-shelf laser diodes with illumination constraints and in a number of scenarios.

J. R. D. Retamal, et al., “4-Gbit/s Visible Light Communication Link Based on 16-QAM OFDM Transmission Over Remote Phosphor-Film Converted White Light by Using Blue Laser Diode,” Optics Express, vol. 23, no. 26, pp. 33656-33666, December 2015.
This paper presents a 4 Gbit/s visible-light communication system using a coherent blue laser diode and a remote phosphor-film to generate white light. The visible-light communication link is blue filter-free due to enhanced blue light transmission in the forward direction.

Y. Wang, L. Tao, X. Huang, J. Shi, and N. Chi, “8-Gb/s RGBY LED-Based WDM VLC System Employing High-Order CAP Modulation and Hybrid Post Equalizer,” IEEE Photonics Journal, vol. 7, no. 6, pp. 1-7, December 2015.
This paper experimentally demonstrates the feasibility of visible-light communication based on a hybrid post-equalizer and a high-order carrierless-amplitude-and-phase modulation. A commercially available red-blue-green-yellow light-emitting diode is utilized for four-wavelength multiplexing, and an aggregate data rate of 8 Gb/s is experimentally achieved.

Topic: Terrestrial FSO Communication Systems

W. Popoola, Z. Ghassemlooy Z, J. Allen, E. Leitgeb, and S. Gao, “Free-Space Optical Communication Employing Subcarrier Modulation and Spatial Diversity in Atmospheric Turbulence Channel,” IET optoelectronics, vol. 2, no. 1, pp. 16-23, February 2008.
This paper considers spatial diversity techniques to mitigate scintillation caused by atmospheric turbulence and derives an expression for the bit error rate of a multiple subcarrier intensity-modulated atmospheric optical communication system employing spatial diversity. The performance of on–off-keying is also presented and compared with the subcarrier intensity modulation under the same atmospheric conditions.

N. Cvijetic, D. Qian, J. Yu, Y. K. Huang, and T. Wang, “100 Gb/s Per-Channel Free-Space Optical Transmission with Coherent Detection and MIMO Processing,” in Proc. 35th European Conference on Optical Communication, Vienna, September 2009.
This paper experimentally demonstrates a 100 Gb/s per-channel free-space optical transmission suitable for short-distance fiber backhaul. The authors use polarization-multiplexed quadrature phase shift keying, coherent detection, and multiple-input multiple-output processing.

E. Ciaramella, Y. Arimoto, G. Contestabile, M. Presi, A. D'Errico, V. Guarino, and M. Matsumoto, “1.28 Terabit/s (32x40 Gbit/s) WDM Transmission System for Free Space Optical Communications,” IEEE Journal on Selected Areas in Communications, vol. 27, no. 9, pp. 1639-1645, December 2009.
This paper demonstrates a free-space optical system allowing a direct and transparent optical connection to single-mode fibers supporting wavelength-division multiplexing and 32 (wavelengths) x 40 Gbit/s transmission. The system has a dedicated electronic control unit that tracks signal beam wandering due to atmospheric turbulence and mechanical vibrations.

H. Huang, et al., “100 Tbit/s Free-Space Data Link Enabled by Three-Dimensional Multiplexing of Orbital Angular Momentum, Polarization, and Wavelength,” Optics letters, vol. 39, no. 2, pp. 197-200, January 2014. 
This paper demonstrates a free-space optical data link combining orbital angular momentum, polarization, and wavelength-division multiplexing, and providing an aggregate data-rate of 100.8 Tbit/s. The demonstration considers 1008 data channels encoded with 100 Gbit/s quadrature phase shift keying data, carried on 12 orbital angular momentum beams, 2 polarizations, and 42 wavelengths.

Topic: Deep-Space FSO Communication Systems

V. W. S. Chan, “Optical Satellite Networks,” Journal of Lightwave Technology, vol. 21, no. 11, pp. 2811 - 2827, 2003.
This paper explores the architectural implications of the construction of an optical satellite network as part of a larger integrated space-terrestrial network. The author explains how satellite network performance and cost can undergo quantum-leap improvements, affect space system architectures, and enable novel user applications.

M. Toyoshima, et al., “Ground-to-Satellite Laser Communication Experiments,” IEEE Aerospace and Electronic Systems Magazine, vol. 23, no. 8, pp. 10-18, August 2008.
This paper presents ground-to-satellite laser communication experiments between the optical ground station and a low earth orbit (LEO) satellite. The results demonstrate the applicability of free-space laser communication for geostationary earth orbit-LEO optical links and ground-to-LEO optical links.

H. Hemmati, A. Biswas, and I. B. Djordjevic, “Deep-Space Optical Communications: Future Perspectives and Applications,” Proceedings of the IEEE, vol. 99, no. 11, pp. 2020-2039, November 2011.
This paper presents the current status of optical communications with an emphasis on deep space. Future perspectives and applications of optical communications related to near-Earth and interplanetary communications are addressed.

Topic: Hybrid RF/VLC Systems

M. B. Rahaim, A. M. Vegni, and T. D. C. Little, “A Hybrid Radio Frequency and Broadcast Visible Light Communication System,” in Proc. of 2nd IEEE GLOBECOM Workshop on Optical Wireless Communications, pp. 792-796, December 2011.
This paper presents analytical and simulation results that characterize the aggregate throughput and delay performance of an indoor hybrid WiFi/VLC system and compares the obtained results with WiFi and VLC systems acting alone.

X. Li, R. Zhang, and L. Hanzo, “Cooperative Load Balancing in Hybrid Visible Light Communications and WiFi,” IEEE Transactions on Communications, vol. 63, no. 4, pp. 1319-1329, April 2015.
This paper investigates various VLC cell formation schemes, presents a heterogeneous system consisting of WLANs and VLC networks, and solves a load-balancing problem in the context of the proposed VLC/WiFi hybrid system.

Y. Wang and H. Haas, “Dynamic Load Balancing with Handover in Hybrid Li-Fi and Wi-Fi Networks,” Journal of Lightwave Technology, vol. 33, no. 22, pp. 4671-4682, November 2015.
This paper proposes and analyzes dynamic load balancing in a hybrid Li-Fi/Wi-Fi network by taking into account user mobility and handover signalling overheads, where the utility function considers system throughput and fairness.

M. Ayyash, et al., “Coexistence of WiFi and LiFi Toward 5G: Concepts, Opportunities, and Challenges,” IEEE Communications Magazine, vol. 54, no. 2, pp. 64-71, February 2016.
This article describes the general characteristics of WiFi and visible-light communications and demonstrates a practical framework for both technologies to coexist. It articulates current and future research challenges.

Topic: Niche Environments

H. Elgala and T. D. C. Little, “Reverse Polarity Optical-OFDM (RPO-OFDM): Dimming Compatible OFDM for Gigabit VLC Links,” Optics Express, vol. 21, no. 20, pp. 24288-24299, October 2013.
This paper proposes the reverse polarity concept, applies the concept to the well-known orthogonal frequency division multiplexing (OFDM) and evaluates the performance. The proposed system offers a practical approach to utilize off-the-shelf LED drivers.

J. Gancarz, H. Elgala, and T. D. C. Little, “Impact of Lighting Requirements on VLC Systems,” IEEE Communications Magazine, vol. 51, no. 12, pp. 34-41, December 2013.
This paper focuses on the impact of lighting requirements on VLC systems, especially as found in indoor deployment scenarios and considers dimming control and its impact on color quality in the context of measured vs. perceived light levels.

N. Hamedazimi, et al., “Firefly: A Reconfigurable Wireless Data Center Fabric Using Free-Space Optics,” ACM SIGCOMM Computer Communication Review, vol. 44, no. 4, pp. 319-330, August 2014.
This paper presents an inter-rack network solution using free-space optics, and demonstrates the viability of this architecture by building a proof-of-concept prototype and developing practical heuristics to address algorithmic and system-level challenges in network design and management.

I. Takai, T. Harada, M. Andoh, K. Yasutomi, K. Kagawa, and S. Kawahito, “Optical Vehicle-to-Vehicle Communication System Using LED Transmitter and Camera Receiver,” IEEE Photonics Journal, vol. 6, no. 5, pp. 1-14, October 2014.
This paper introduces an optical vehicle-to-vehicle communication system using a light emitting diode transmitter and a camera receiver. The setup is capable of achieving 10 Mb/s.

H. M. Oubei, et al., “4.8 Gbit/s 16-QAM-OFDM Transmission Based on Compact 450-nm Laser for Underwater Wireless Optical Communication," Optics Express, vol. 23, no. 18, pp. 23302-23309, September 2015. 
This paper experimentally demonstrates underwater OWC at 4.8 Gbit/s over a distance of 5.4 meters, by employing orthogonal frequency division multiplexed quadrature amplitude modulation.