Optical and Wireless Communications

Next Generation Networks

Matthew N.O. Sadiku

• Publisher: CRC Press
• Year: 2018
• eBook ISBN: 9781351991896
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Optical and wireless technologies are being introduced into the global communications infrastructure at an astonishing pace. Both are revolutionizing the industry and will undoubtedly dominate its future, yet in the crowded curricula in most electrical engineering programs, there is no room in typical data communications courses for proper coverage of these "next generation" technologies.Optical and Wireless Communications: Next Generation Networks covers both types of networks in a unique presentation designed for a one-semester course for senior undergraduate or graduate engineering students. Part I: Optical Networks covers optical fibers, transmitters, receivers, multiplexers, amplifiers, and specific networks, including FDDI, SONET, fiber channel, and wavelength-routed networks. Part II: Wireless Networks examines fundamental concepts and specific wireless networks, such as LAN, ATM, wireless local loop, and wireless PBXs. This section also explores cellular technologies and satellite communications.Eventually, next generation networks will be as ubiquitous as traditional telephone networks, and today's engineering students must be prepared to meet the challenges of optical and wireless systems development and deployment. Filled with illustrations, examples, and end-of-chapter problems, Optical and Wireless Communications: Next Generation Networks provides a brief but comprehensive introduction to these technologies that will help future engineers build the foundation they need for success.

part 1

Optical networks

chapter one

Optical fibers

There is one thing stronger than all the armies in the world, and that is an idea whose time has come.

— Victor Hugo

Within a short period of time, the volume of data traffic transported across communications networks has grown rapidly and now exceeds the volume of voice traffic. This situation is forcing service providers to design, build, and add capacity to their networks. Optical networks are providing the necessary infrastructure to meet the need. Due to their high efficiency and straightforward architecture, optical networks can carry large amounts of data over long distances at a reduced cost. This allows network operators to offer more value-added services, such as video conferencing, real-time video on demand, and other high-bandwidth applications, thereby making it easier for the world to communicate at the speed of light.

This chapter begins by giving the motivation for studying optical fibers and looks at how modern optical communication began. It then introduces some basic properties associated with the propagation of light through optical fibers using geometrical-optics description.

1.1 Why optical fiber?

In the mid 1970s, it was recognized that the existing copper technology would be unsuitable for future communication networks. Inherent in copper wire are some problems, including the following:¹

• Its bandwidth is limited due to physical constraints.

• It is susceptible to radio, electrical, and crosstalk interference, which can garble data transmission.

• Its electromagnetic emissions compromise security.

• Its reliability is reduced in the presence of a harsh environment.

In light of these problems, the telecommunications industry invested heavily in research into optical fibers. Today, optical fiber is becoming the medium of choice for the following reasons:^2,3,4

• High bandwidth: The quantity of information that can be transmitted by electromagnetic waves increases in proportion to its frequency; therefore, by using light four or five orders of magnitude can be gained in the amount of information transmitted. Light has an information-carrying capacity (or bandwidth) 10,000 times greater than that of the highest radio frequencies. Therefore, optical fiber provides a very high capacity for carrying information; it can be made to carry 10 Tbps. It also has sufficient bandwidth that bit-serial transmission can be used, thereby considerably reducing the size, cost, and complexity of the hardware. The high bandwidth of fiber makes it a perfect candidate for transmitting bandwidth-hungry signals, such as images.

• High transmission rate: Fiber optics transmit at speeds much higher than copper wire. Although the current Gbps network is regarded as a milestone compared with the existing Mbps networks, its rate is only a small fraction of the rates possible with fiber optics technology — fiber is capable of transmitting three TV episodes in one second and will be able to transmit the equivalent of an entire 24-volume encyclopedia in one second.

• Attenuation: Fiber optics have low attenuation and are therefore capable of transmitting over a long distance (up to 80 km) without the need of repeaters. This low attenuation allows one to extend networks to large campuses or a city and its suburbs.

• Electromagnetic immunity: Fiber is a dielectric material. Therefore, it neither radiates nor is affected by electromagnetic interference (EMI), lightning strikes, or surges. The benefits of such immunity include the elimination of ground loops, signal distortion, and crosstalk in hostile environments.

• Security: Telecommunication companies need secure, reliable systems to transfer information between buildings and around the world. A fiber-optic network is more secure from malicious interception because the dielectric nature of optical fiber makes it difficult to tap a fiber-optic cable without interrupting communication. Accessing the fiber requires an intervention that is easily detectable by security surveillance. Fiber-optic systems are also easy to monitor. Fiber-optic cables are virtually unaffected by atmosphere conditions. Because the basic fiber is made of glass, it will not corrode or be affected by most chemicals. It can be buried directly in most kinds of soil or exposed to corrosive atmospheres without significant concern. This property of fiber makes it attractive to governments, banks, and others with security concerns.

Figure 1.1 A typical optical communication system.

• Cost: Glass fibers are made from silica sand, which is more readily available than copper. The cost of optical fibers has fallen considerably over the last few years and will continue to fall. The cost of related components, such as optical transmitters and receivers, is also falling.

These impressive advantages of fiber optics over electrical media have made optical fiber the replacement for copper for fast transmission of enormous amounts of information from one point to another.

However, optical fiber has its drawbacks. First, electrical-to-optical conversion at the sending end and optical-to-electrical conversion at the receiving end is costly. Second, optical fiber suffers the same fate as any wired medium — cable must be buried along the right of way. Third, special installation and repair techniques are required.

A fiber-optic system is similar to a conventional transmission system. As shown in Figure 1.1, a fiber-optic system consists of a transmitter, propagation medium, and receiver. The transmitter accepts and converts input electrical signals in analog or digital form to optical signals and then sends the optical signal by modulating the output of a light source (usually an LED or a laser) by varying its intensity. The optical signal is transmitted over the optical fiber (made of glass or plastic) to a receiver. At the receiver, the optical signal is converted back into an electrical signal by a photodiode.

1.2 A glimpse of history

Guided light has been used for communication purposes for ages. For example, Claude Chappe, the French engineer, invented the “optical telegraph.” The advantages of light as a transmission medium were also apparent in the time of Alexander Bell. In fact, Bell invented an optical telephone system known as the Photophone in 1880. However, modern optical communications began with the discovery of the ruby laser in 1960 by T. H. Maimon at Hughes Laboratories in the U.S. This discovery, m...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Table of Contents
• Part 1: Optical networks
• Part 2: Wireless networks
• Bibliography
• Glossary and acronyms
• Appendix — Physical constants
• Index