wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

2
Media
Herbert Schweinzer
Vienna University
of Technology
Saleem Farooq
Shaukat
COMSATS Institute of
Information Technology
Holger Arthaber
Vienna University
of Technology
2.1 Introduction....................................................................................... 2-1
2.2 Wired Links........................................................................................ 2-1
Physical Properties. •. Cable Types and Operational
Characteristics. •. Single-Ended and Differential
Transmission. •. Simplex and Duplex Communication. •
Bit Encoding. •. Standards. •. Data Transmission Utilizing Existing
Cable Infrastructure
2.3 Optical Links...................................................................................... 2-7
Physical Properties. •. Types and Media Access. •. Transmitters and
Receivers. •. Multiplexing. •. Implementations and Standards
2.4 Wireless Links.................................................................................. 2-11
Physical Properties. •. Types and Media Access. •. Modulation. •
Bit Coding, Multiplexing. •. Realizations and Standards
References.................................................................................................... 2-17
2.1 Introduction
This chapter discusses physical mechanisms for transferring digital data. The three dominant media
types and their applications are presented: data transmission over cable, over optical links, and over
wireless radio frequency (RF) links. Properties of each medium are concisely introduced with respect
to physical characteristics, alternatives of realization, topologies, bit coding, and standards. Media for
special local data exchange, e.g., infrared transmission, are not contained in this chapter.
2.2 Wired Links
2.2.1 Physical Properties
Data transmission of digital signals over cables is based on electromagnetic wave propagation, which is used
for moving data from one location to another. Data bits are coded as short pulses or fast changing modulations
of wave properties (amplitude, frequency, phase). The fundamental relation of wave propagation is
where
v is the phase velocity of a sinusoidal electromagnetic wave
f is the frequency
λ is the wavelength
v
= f ⋅ λ (2.1)
Each cable has a characteristic impedance Z W and has to be matched at both ends with equal terminating
resistors R E . Mismatch at an end leads to a reflection where the wave front, e.g., a pulse, is traveling back
2-1
© 2011 by Taylor and Francis Group, LLC