Majumdar / Ricklin Free-Space Laser Communications

Principles and Advances
1. Auflage 2010
ISBN: 978-0-387-28677-8
Verlag: Springer US
Format: PDF
Kopierschutz: 1 - PDF Watermark

E-Book, Englisch, Band 2, 418 Seiten, eBook

Reihe: Optical and Fiber Communications Reports

Free-space laser communications, also referred to as optical communica tions, is a popular subject in today's technological marketplace. A number of conferences on this subject have been organized by professional societies such as SPIE (the International Society of Photo Optical and Instrumenta tion Engineering), OSA (Optical Society of America), and IEEE (Instituteof Electrical and Electronics Engineers). The evolving technology of free-space laser communications is emerging as an appealing alternative to RF com munications for links between satellites, as well as a promising addition to terrestrial applications such as video or computer linkups between buildings. There is a pressing need for more information on laser communications that is comprehensive enough to provide in-depth knowledge of free-space com munications, and that can satisfy the current demands of the research and commercial needs. This book has been designed to provide a comprehensive, unified tutorial to further understanding of the fundamental techniques for laser communi cations through the earth's atmosphere. The driving force behind free-space laser communications is the continuous demand for higher bandwidth to deliver high-capacity voice, data, and images to the customer. Free-space propagation distances include ranges that encompass a few millimeters (for example between optical interconnects in a computer using photonics to replace metal interconnects), a fewmeters (such as indoor communications), a fewkilometers (between buildings, campuses, and hospitals), and even up to thousands of kilometers (such as from an aircraft or satellite to the ground).

Zielgruppe

Research

Autoren/Hrsg.

Majumdar, Arun K.

Ricklin, Jennifer C

Inhaltsverzeichnis

Atmospheric channel effects on free-space laser communication.- Free-space laser communication performance in the atmospheric channel.- Laser communication transmitter and receiver design.- Free-space laser communications with adaptive optics: Atmospheric compensation experiments.- Optical networks, last mile access and applications.- Communication techniques and coding for atmospheric turbulence channels.- Optical Communications in the mid-wave IR spectral band.- Quantum cascade laser-based free space optical communications.- All-weather long-wavelength infrared free space optical communications.

Leseproben

"Communication techniques and coding for atmospheric turbulence channels (p. 303-304)

Abstract. In free -space optica l communication link s, atmo spheri c turbulence causes fluctuations in both the inten sity and the phase of the received light signal, impairing link performance. In this paper , we describe severa l communication techniques to mitigate turbulence-induced intensity fluctuation s, i.e., signal fading . The se techniques are applicable in the regime in which the receiv er aperture is smaller than the correlation length of the fading, and the observation interval is shorter than the correlation time of the fading. We assume that the receive r has no knowledge of the instantaneous fading state . The techniques we con sider are based on the stati stical properties of fading, as functions of both temporal and spatial coordinates. Our approaches can be divided into two categories : temporal domain techniques and spatial domain techniques.

In the spatial domain techniques, one must employ at least two receivers to collect the signal light at different positi ons or from different spatial angle s. Spatial diver sity reception with mult iple recei vers can be used to overcome turbulence-induced fading. When it is not possible to place the receivers sufficiently far apart, the fading at different receivers is correl ated , redu cing the diversity gain . We descr ibe a ML dete ction techn ique to reduce the diver sity gai n penalty caused by such fadin g correl ation.

In the temporal domain techniques, one empl oys a single receiver. When the receiver knows only the marginal statistics of the fading , a symbol-by-symbol ML dete ctor can be used to optimize perform ance. When the receiver also knows the temporal correlation of the fadin g, maximum -likelihood sequence detection (MLSD) can be employed, yielding a further perform ance improvement, but at the cos t of very high complexity. We descri be two reduced-compl exity implementations of the MLSD, which make use of a single-s tep Markov chain model for the fading co rrelation in conjunction with per-survivorprocessing. Next,we also investigate the performance of using error-control codingand pilotsymbol-assisted detectionschemesthroughatmospheric turbulence channels.

1. Introduction

Recently, free-space optical communication has attracted considerable attention for a variety of applications [1-8] . Because of the complexity associated with phase or frequency modulation, current free-space optical communication systems typically use intensity modulation with direct detection (IMIDO). However, in practice, the performance of free-space optical communication systems can be degraded by many effects, such as fog, obstruction of the line-of-sight path, atmospheric turbulence and the nonideal characteristics of optical transmitters and receivers. In this chapter, we focus on communication techniques and coding schemes to counter the degradation caused by atmospheric turbulence in IMIDO links."

Über Autor(innen)

Arun K. Majumdar

Ph.D., is Director of Research at LCResearch, Inc. in California. He has more than 23 years of experience from Industry, University and National Laboratory settings in the areas of atmospheric turbulence effects on laser propagation, imaging and communications. He received his Ph.D. in Electrical Engineering from the University of California, Irvine.

Jennifer C. Ricklin

received her Ph.D. in electrical engineering from the Johns Hopkins University. She has been with the Army Research Laboratory since 1983. Since that time her research interests have included a number of topical applications of laser beam propagation in the atmosphere. She is now a Program Manager at DARPA / ATO.