Wireless Transceiver Design - Ariel Luzzatto - ebook

Wireless Transceiver Design ebook

Ariel Luzzatto

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Building upon the success of the first edition (2007), Wireless Transceiver Design 2nd Edition is an accessible textbook that explains the concepts of Wireless Transceiver Design in detail. The architectures and the detailed design of both traditional and advanced all-digital wireless transceivers are discussed in a thorough and systematic manner, while carefully watching out for clarity and simplicity. Many practical examples and solved problems at the end of each chapter allow students to thoroughly understand the mechanisms involved, to build confidence, and enable them to readily make correct and practical use of the applicable results and formulas. From the instructors' perspective, the book will enable the reader to build courses at different levels of depth, starting from the basic understanding, whilst allowing them to focus on particular elements of study. In addition to numerous fully-solved exercises, the authors include actual exemplary examination papers for instructors to use as a reference format for student evaluation. The new edition has been adapted with instructors/lecturers, graduate/undergraduate students and RF engineers in mind. Non-RF engineers looking to acquire a basic understanding of the main related RF subjects will also find the book invaluable.

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Table of Contents

Cover

Title Page

Foreword

To the Instructor

About the Authors

Acknowledgment

1 Introduction

1.1 Radio Frequency Systems

1.2 Detailed Overview of Wireless Systems and Technologies

Bibliography

2 Transceiver Architectures

2.1 Receiver Architectures

2.2 Superheterodyne Receiver

2.3 Direct Conversion Receiver

2.4 Direct RF Sampling Receiver

2.5 Transmitter Architectures

2.6 Two Step Conversion Transmitter

2.7 Direct Launch Transmitter

2.8 Direct RF Sampling Transmitter

2.9 Transceiver Architectures

2.10 Full Duplex/Half‐duplex Architecture

2.11 Simplex Architecture

2.12 Solved Exercises

2.13 Theory Behind Equations

Bibliography

3 Receiving Systems

3.1 Sensitivity

3.2 Co‐channel Rejection

3.3 Selectivity

3.4 Blocking

3.5 Intermodulation Rejection

3.6 Image Rejection

3.7 Half‐IF Rejection

3.8 Dynamic Range

3.9 Duplex Desense

3.10 Other Duplex Spurs

3.11 Other Receiver Interferences

3.12 Solved Exercises

3.13 Theory Behind Equations

3.14 Extension to Direct RF Sampling Receivers

Bibliography

4 Transmitting Systems

4.1 Peak to Average Power Ratio

4.2 Nonlinearity in RF Power Amplifiers

4.3 Transmitter Specifications

4.4 Enhancement Techniques

4.5 Solved Exercises

4.6 Theory Behind Equations

Bibliography

5 Synthesizers

5.1 Integer‐N Synthesizer

5.2 Fractional‐N Synthesizer

5.3 Direct Digital Synthesizer

5.4 Integer‐N/DDS Hybrid Synthesizer

5.5 Solved Exercises

5.6 Theory Behind Equations

Bibliography

6 Oscillators

6.1 Low‐power Self‐limiting Oscillators

6.2 Oscillators Using Distributed Resonators

6.3 Solved Exercises

6.4 Theory Behind Equations

Bibliography

7 Functional RF Blocks

7.1 Antenna

7.2 Low Noise Amplifier

7.3 Filters

7.4 Power Amplifier

7.5 Mixer

Bibliography

8 Useful Reminders

8.1 The RF Channel

8.2 Noise

8.3 Propagation

8.4 Path loss

8.5 Modulation

8.6 Multiple Input Multiple Output

Bibliography

Appendix – Exemplary Exams

Exam 1

Exam 2

Index

End User License Agreement

List of Tables

Chapter 02

Table 2.1 Typical subsystem values for a high‐tier SHR.

Table 2.2 Typical subsystem values for a DCR.

Chapter 04

Table 4.1 Measured values of output power versus input power.

Table 4.2 Measured values of output power versus input power.

Appendix

Figure A2.1 RF PA laboratory measurement results.

List of Illustrations

Chapter 01

Figure 1.1 One‐way RF system.

Figure 1.2 Two‐way RF system.

Figure 1.3 Limited capacity RF system.

Figure 1.4 The cellular principle.

Chapter 02

Figure 2.1 SHR block diagram.

Figure 2.2 SHR spectral pictures: (a) RF level, (b) IF level, (c) baseband level.

Figure 2.3 DCR block diagram.

Figure 2.4 DRFS receiver block diagram.

Figure 2.5 (a) Spectrum of the desired signal and interferers at antenna. (b) Spectrum of the sampled signal after preselector filtering.

Figure 2.6 In‐principle TSCT architecture.

Figure 2.7 TSCT spectral pictures: (a) backend level, (b) exciter level, (c) PA level.

Figure 2.8 In‐principle DLT architecture.

Figure 2.9 In‐principle DRFS transmitter architecture.

Figure 2.10 Spectral pictures: (a) analog IF signal, (b) IF signal sampled at

.

Figure 2.11 DAC: (a) input sample value versus sample number, (b) output voltage versus time.

Figure 2.12 (a) |

X

d

(

ω

)| and |

H

DAC

(

ω

)|, (b) |

X

ZOH

(

ω

)|, |

X

a

(

ω

)| and |

X

0

(

ω

)|.

Figure 2.13 Typical full duplex subscriber architecture.

Figure 2.14 DCR/DLT simplex subscriber architecture.

Figure 2.15 Spectrum of the sampled signal: (a) for

, (b) for

.

Chapter 03

Figure 3.1 (a) Two cascaded stages. (b) Composite single‐stage equivalent.

Figure 3.2 Computing SHR sensitivity.

Figure 3.3 Sensitivity measurement with digital modulation.

Figure 3.4 Measurement of CCR with digital modulation.

Figure 3.5 (a) Ideal oscillator carrier. (b) Phase noise modulated oscillator carrier.

Figure 3.6 Spectral shape of phase noise in the offset range relevant to selectivity.

Figure 3.7 The spectral picture at mixer input.

Figure 3.8 The spectral picture at mixer output.

Figure 3.9 The spectral picture when increasing interferer power.

Figure 3.10 (a) LO reference spurs, (b) Spurious transfer to an adjacent interferer.

Figure 3.11 Spectral picture at mixer output in a blocking scenario.

Figure 3.12

IMR

3 products in a SHR receiver.

Figure 3.13 (a) The receiver of Figure 3.2. (b) The modified receiver.

Figure 3.14 Measurement of

IMR

3 with digital modulation.

Figure 3.15 Worst‐case image rejection in a lower‐side injection SHR receiver.

Figure 3.16 Worst‐case half‐IF attenuation in a lower‐side injection SHR receiver.

Figure 3.17 A frequently used duplexer architecture.

Figure 3.18 Measurement of duplex desense.

Figure 3.19 The receiver of Exercise 6.

Figure 3.20 The lineup of Exercise 8.

Figure 3.21 Attenuation curves of the filters of Figure 3.17.

Figure 3.22 Rotating filter impedance to open circuit: (a) BPF

R

, (b) BPF

T

.

Figure 3.23 Spectral density of jitter‐induced noise samples.

Chapter 04

Figure 4.1 Samples of a typical digitally modulated RF signal.

Figure 4.2 (a) 16 QAM constellation, (b) Time domain symbol.

Figure 4.3 Measurement of PAPR with digital modulation.

Figure 4.4 Typical spectral picture of an unfiltered PA output.

Figure 4.5 16QAM constellation: (a) undistorted, (b) distorted.

Figure 4.6 Computed values of relative gain versus input power.

Figure 4.7 Time domain plot of the input signal.

Figure 4.8 Frequency domain plot of the input signal.

Figure 4.9 Frequency domain plot of third‐order dominated PA output.

Figure 4.10 Frequency domain plot of fifth‐order dominated PA output.

Figure 4.11 SPICE circuit for the RF amplifier under test.

Figure 4.12 SPICE simulation of two‐tone test signal at the amplifier input.

Figure 4.13 SPICE simulation of the output spectrum with low‐level two‐tone input.

Figure 4.14 SPICE simulation of the output spectrum with medium‐level two‐tone input.

Figure 4.15 SPICE simulation of the output spectrum with high‐level two‐tone input.

Figure 4.16 Spectral picture of third‐ and fifth‐order intermodulation distortion.

Figure 4.17 SPICE and coefficient‐based spectral re‐growth simulations superimposed.

Figure 4.18 Spectral re‐growth versus backoff.

Figure 4.19 Measurement of

IMDN

.

Figure 4.20 Graphical description of the

N

‐th order intercept point.

Figure 4.21 Typical spectral mask structure.

Figure 4.22 Error vector in a 16 QAM constellation.

Figure 4.23 Corrupted symbols due to transmitter lineup imperfections.

Figure 4.24 ACPR definition.

Figure 4.25 Setup for the measurement of attack time.

Figure 4.26 Setup for the measurement of conducted emission.

Figure 4.27 Typical shape of a spectral bump.

Figure 4.28 Cartesian feedback.

Figure 4.29 In‐principle implementation of feed‐forward.

Figure 4.30 Real‐life implementation of feed‐forward.

Figure 4.31 Possible pre‐distortion architecture.

Figure 4.32 Envelope‐tracking supply.

Figure 4.33 Approximation using Stirling formula.

Figure 4.34 Saleh model.

Figure 4.35 16 QAM constellation distortion using Saleh model.

Figure 4.36 cardinal B‐splines of order 1, 2, 3, 4.

Figure 4.37 Spectral re‐growth bound versus normalized bandwidth.

Chapter 05

Figure 5.1 Integer‐N block diagram and related waveforms: (a) steering voltage, (b) charge pump current, (c) reference oscillator waveform, (d) divided VCO waveform.

Figure 5.2 Charge pump, loop filter, and VCO interconnection.

Figure 5.3 Integer‐N waveforms of Figure 5.1 under lock‐up conditions: (a) steering voltage, (b) charge pump current, (c) reference oscillator, (d) divided VCO.

Figure 5.4 Reference spurs.

Figure 5.5 Phase‐frequency detector modes: (a) steering voltage, (b) charge pump current, (c) reference oscillator waveform, (d) divided VCO waveform.

Figure 5.6 Fractional‐N block diagram.

Figure 5.7 DDS architecture: 24

N

48, 12

K

19 (msb out of

N

), 10

J

14.

Figure 5.8 Detailed PLL diagram functionality.

Figure 5.9 Normalized plot of

Δω

/

ΔNω

ref

versus

ω

n

t

.

Chapter 06

Figure 6.1 Self‐limiting oscillator mechanism.

Figure 6.2 A practical resonant

π

‐topology filter.

Figure 6.3 In‐principle ac equivalent of a

π

‐topology oscillator.

Figure 6.4 NAND gate‐driven oscillator with

π

‐topology.

Figure 6.5

π

‐Topology NAND gate oscillator ac equivalent.

Figure 6.6 NAND gate output current versus input voltage.

Figure 6.7 Parallel–serial bidirectional transformation.

Figure 6.8 Bipolar transistor‐driven oscillator in Colpitts configuration.

Figure 6.9 The ac equivalent of the circuit of Figure 6.8.

Figure 6.10 The model for the oscillator of Figure 6.9.

Figure 6.11 The serial equivalent of the 1.5 kΩ resistor in Figure 6.10.

Figure 6.12 Final oscillator equivalent.

Figure 6.13 Crystal symbol and fundamental‐mode lumped equivalent.

Figure 6.14 Typical crystal oscillator in Pierce configuration.

Figure 6.15 Lumped equivalent of an open‐ended resonant transmission line.

Figure 6.16 A typical open‐ended coaxial line oscillator in Clapp configuration.

Figure 6.17 The oscillator of Exercise 1.

Figure 6.18 Exercise 1 parallel transformation of the serial 50 Ω/15 pF combination.

Figure 6.19 The Colpitts oscillator of Exercise 2.

Figure 6.20 Exercise 2: ac equivalent of Figure 6.19.

Figure 6.21 Lumped equivalent of the Pierce oscillator of Exercise 6.

Figure 6.22 Close approximation to the circuit of Figure 6.21.

Figure 6.23 Final approximation to the circuit of Figure 6.21.

Figure 6.24 The lumped equivalent of the coaxial line Clapp oscillator in Figure 6.16.

Figure 6.25 The ac equivalent of Figure 6.24.

Figure 6.26 The circuit of Exercise 9.

Figure 6.27 The approximation to the circuit in Figure 6.26.

Figure 6.28 The modified oscillator of Exercise 10.

Figure 6.29 Norton’s ac equivalent of the buffered gate with added resistor.

Figure 6.30 The oscillator of Figure 6.28 with the resistor

R

transformed.

Figure 6.31 General

π

‐topology filter.

Figure 6.32 Oscillator model.

Figure 6.33 Phasor diagram of a pure carrier with a noise component at offset

ω

m

.

Figure 6.34 Low‐loss resonant transmission line.

Figure 6.35 The oscillator of Figure 6.16 modified to work as a VCO.

Chapter 07

Figure 7.1 2D examples of (a) directional and (b) bidirectional radiation patterns (

E

‐plane).

Figure 7.2 Simulation of antenna reflection coefficient

ρ

(S11).

Figure 7.3 Antenna beamwidth.

Figure 7.4 Symmetrical dipole.

Figure 7.5 Radiation pattern of a short dipole in the elevation plane.

Figure 7.6 PIFA structure (cross section).

Figure 7.7 Array of slots on a waveguide wall.

Figure 7.8 Microstrip antenna.

Figure 7.9 Resistances in the dipole of Exercise 2.

Figure 7.10 Input‐referred noise model in classical noise analysis.

Figure 7.11 Drain noise current in MOSFETs: (a) noisy MOSFET, (b) noiseless MOSFET.

Figure 7.12 The MOSFET gate noise model.

Figure 7.13 MOSFET small signal noise model.

Figure 7.14 LNA with resistor termination.

Figure 7.15 LNA with shunt series feedback.

Figure 7.16 LNA based on common gate configuration.

Figure 7.17 Inductive source degeneration and its small signal model.

Figure 7.18 The cascode LNA.

Figure 7.19 The frequency response of ideal filters: (a) LPF, (b) HPF, (c) BPF, (d) BSF.

Figure 7.20 Frequency magnitude response (dB).

Figure 7.21 Inductor coupled power amplifier.

Figure 7.22

i‐v

conduction angle of class B/AB/C PA.

Figure 7.23 Constant output power contours (load–pull technique).

Figure 7.24 The circuit of Exercise 7.4.1.

Figure 7.25 The matching circuit of Exercise 7.4.3.

Figure 7.26 The output characteristics of the MOSFET in Exercise 7.4.3.

Figure 7.27 MOSFET mixer.

Figure 7.28 Bipolar mixer.

Chapter 08

Figure 8.1 The overall NF of two cascaded components.

Figure 8.2 Two‐ray model.

Figure 8.3 NBFM modulator.

Figure 8.4 Phase noise associated with a carrier.

Figure 8.5 Spatial channels.

Figure 8.6 MIMO system structure.

Appendix

Figure A1.1 The SHR receiver of Q1(b).

Figure A1.2 The output spectrum of the PA in Q2(a).

Guide

Cover

Table of Contents

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Wireless Transceiver Design

Mastering the Design of Modern Wireless Equipment and Systems

Second Edition

Dr. Ariel Luzzatto

L&L Scientific Ltd.Israel

Prof. Motti Haridim

Holon Institute of Technology (HIT)Israel

This edition first published 2017 © 2017 John Wiley & Sons, Ltd

Registered OfficeJohn Wiley & Sons, Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, United Kingdom

For details of our global editorial offices, for customer services and for information about how to apply for permission to reuse the copyright material in this book please see our website at www.wiley.com.

The right of the author to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act 1988.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the publisher.

Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.

Designations used by companies to distinguish their products are often claimed as trademarks. All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners. The publisher is not associated with any product or vendor mentioned in this book.

Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. It is sold on the understanding that the publisher is not engaged in rendering professional services and neither the publisher nor the author shall be liable for damages arising herefrom. If professional advice or other expert assistance is required, the services of a competent professional should be sought.

Library of Congress Cataloging‐in‐Publication Data

Names: Luzzatto, Ariel, 1951– author. | Haridim, Motti, 1959– author.Title: Wireless transceiver design : mastering the design of modern wireless equipment and systems / Dr. Ariel Luzzatto, Prof. Motti Haridim.Description: Second edition. | Chichester, UK ; Hoboken, NJ : John Wiley & Sons, 2016. | sIncludes bibliographical references and index.Identifiers: LCCN 2016022671 | ISBN 9781118937402 (cloth)Subjects: LCSH: Radio–Transmitter‐receivers–Design and construction. | Wireless communication systems–Design and construction.Classification: LCC TK6561 .L878 2016 | DDC 621.3841/31–dc23LC record available at https://lccn.loc.gov/2016022671

Cover image credit: John Lund/Gettyimages

A catalogue record for this book is available from the British Library.

Ariel LuzzattoTo my brother Kfir.

 

Motti HaridimTo my father Shalom, of blessed memory, who inspired all of his children with the light of knowledge and love of learning.

Foreword

Following the advances in large‐scale and radio frequency (RF) semiconductor technology, the world is really “going wireless.” Almost everything we used to see connecting with plugs and wires is now being turned into a wireless connection. More and more commercial products include wireless Internet connection capabilities, either for the purpose of management, setup, or inclusion as a part of larger systems. The number of wireless technologies, protocols, physical layers, frequency bands, and implementations is exploding. The growing availability of low current‐drain Giga‐sample/s A/D converter circuits at commercially viable prices and the constantly increasing higher rate signal processing and computational capability now allow more and more hardware RF blocks within transceiver chains to be replaced with the corresponding software algorithms. However, from the architectural standpoint, the RF blocks and chain lineup, as well as the RF system design, remain essentially similar, regardless of the way of implementation. As a result, we are witnessing the evolution of a specialized field of signal processing which requires understanding and skills in both RF design techniques at the system, sub‐system and RF block level, together with advanced knowledge and skills in specific RF‐related signal processing techniques. This evolution calls for a field of expertise, which we may call either “signal processing‐oriented RF engineer” or “RF‐oriented signal processing engineer.” Still there are RF blocks that cannot be implemented in software and will likely remain in hardware form for the time being. Either way, this book is concerned with both hardware‐based approaches and all‐digital techniques such as direct RF sampling (DRFS). Moreover, we focus on system design for the blocks that we believe will be available as off the shelf components or fit for signal processing implementation, and we discuss detailed hardware design only for specific functions which we believe will remain mostly in hardware form for the time being.

To the Instructor

This book is a teaching‐oriented evolution of the first edition of Wireless Transceiver Design, published in 2007, and is intended to be a guide textbook for instructors, third and fourth year undergraduate engineering students, graduate students, and R&D engineers.

The material and its presentation have been prepared according to what the authors, based on their wide teaching experience, perceive as well adapted for teaching purposes, and in particular for effectively assisting instructors in the preparation of related courses.

The book comprises a large number of fully solved exercises and examples to help in building confidence all along the way. The Appendix presents exemplary two‐hour exams in a suitable format which has been actually implemented, and students have been able to successfully cope with.

With the purpose to provide a really friendly, “nonscary,” and self‐contained guide, the format of this teaching‐oriented textbook includes, in each main chapter body, detailed heuristic explanations together with final applicable results and detailed examples. These heuristic explanations and examples allow the reader to thoroughly understand and feel the mechanisms involved, to help build confidence, to enable the students to make correct use of the applicable results and formulas (still without requiring them to “dig” into complex mathematical developments), and to assist the instructors in keeping the discussion flowing smoothly and uninterrupted. The detailed mathematical proofs and formulations, and the more complex and sophisticated discussions, are provided with rigor. However, they are not a “must read” in order to allow a practical and educated use of the theory, and they are deferred to the end of the chapters in an appendix‐like way, to allow the interested reader to go over the details only when desired.

From the teacher’s perspective, the above format is helpful in preparing courses at different levels of depth, starting from the basic understanding, yet allowing the instructor to “zoom in” selectively whenever desired.

The last two chapters include basic theory and useful reminders on relevant background topics, to help fill‐in gaps, sparing both instructors and students the daunting task of searching over many sources in order to refresh subjects or fill‐in “holes.”

About the Authors

Ariel Luzzatto has over 35 years of R&D experience, most of them designing commercial and industrial communication and RF products. Ariel was the Chief Scientist of Motorola Israel Ltd. until 2009, and he is presently the CEO of L&L Scientific Ltd., and a lecturer of communication circuits and systems with several major academic institutes in Israel. He holds a PhD and a MSc in applied mathematics, and a BSc in electronic engineering, all from Tel Aviv University.

Motti Haridim received his PhD degree from Technion, Israel Institute of Technology, Haifa, and is a Professor of Electrical Engineering at Holon Institute of Technology (HIT), Israel. His research interests and accomplishments are mainly in the physical layer of communication systems, including optical communications, RF communications, antennas, and electromagnetic radiation. He is the author of more than 100 technical papers on theoretical and applied aspects of antennas, radiation, RF communications, and optical communications. Since 2014, he serves as the Vice President for academic development at HIT.

Acknowledgment

The authors wish to thank Mr. Gadi Shirazi for his contribution as the co‐author of the first edition of this book, published in 2007 in cooperation with Dr. Ariel Luzzatto.

1Introduction

1.1 Radio Frequency Systems

Radio frequency (RF) systems are an essential part of our everyday life. They provide wireless connectivity for diversified applications, such as short‐range car/door openers and wireless earphones, medium‐range digital systems such as routers for computer data links, and remote‐piloted vehicle controls, or long‐distance communication systems such as cellular phones, and satellite networks. The required characteristics of wireless transceivers, however, are strongly dependent on the nature of the target system in which the equipment is intended to operate. In this introductory chapter, we provide a detailed overview of several important RF systems, with the purpose to provide the reader with a basic background on the different architectural and operational requirements, which directly dictate the various transceiver design strategies discussed in the chapters to follow.

1.1.1 Conceptual RF system

An RF system consists essentially of five major components, as shown in Figure 1.1.

Transmitter

: Accepts at its input the information to be transmitted. Generates an RF signal embedding the input information. “Boosts” the RF signal to a suitable power level. The RF signal is routed to the antenna port.

Transmit antenna

: Serves as the mediator between the transmitter and the transmission medium. Its purpose is to make sure that all the RF signal power present at the antenna port, leaves the transmitter, enters the transmission medium, and propagates in the desired direction.

Transmission channel

: Is the medium separating the transmitter from the receiver. The RF signal must cross it in order to reach the receiving antenna. Usually the transmission medium consists of air or vacuum, but it may be solid or liquid as well. While propagating through the transmission medium, the RF signal loses its strength, and becomes weaker and weaker as it proceeds through the medium.

Receive antenna

: Serves as the mediator between the transmission medium and the receiver. Its purpose is to capture as much as possible of the incident (weak) RF signal power remaining after crossing the medium, and convey it to the input of the receiver.

Receiver

: Accepts the RF signal captured by the antenna. Extracts the information embedded in it. The information is routed to the receiver output.

Figure 1.1 One‐way RF system.

The system of Figure 1.1 is one‐way. However, adding an identical RF system in the opposite direction yields a two‐way RF system, as shown in Figure 1.2. The transmitter/receiver combination is termed a “transceiver”. The antenna may transmit and receive simultaneously, while the transmitter and receiver are operating independently from each other.

Figure 1.2 Two‐way RF system.

1.1.2 The frequency spectrum

For various reasons, not all RF frequencies are equally well‐fit for implementing different RF systems. For instance, since the optimum physical dimensions of transmit and receive antennas are directly related to the frequency and must be made larger as the frequency becomes lower, it follows that at low frequencies the antenna size becomes impractical for use in mobile systems such as cellular. In contrast, as the frequency becomes higher, the antennas may be made smaller, but the power losses and Doppler fading through the medium increase, which limits the transmission range and the travelling speed. It follows that choice of the RF frequency range is application dependent and the number of useful RF channels is limited. Several RF system architectures, such as the cellular architecture, have been developed in order to overcome the frequency shortage.

1.1.3 Cellular concept

The cellular concept is of great importance. Many modern RF system architectures are based on it, thus we find it appropriate to discuss it briefly here. As pointed out in the previous section, the number of available frequencies for mobile applications is limited. With reference to Figure 1.3, assume that a multitude of mobile users are found simultaneously in the region of area A. Further assume that there are N available RF channels and all the users connect to each other through a central base station that is located at a favorably high spot to provide appropriate geographical coverage. It follows that the system capacity is limited to simultaneous users per square meter. Clearly such an architecture is limited and cannot support large communication systems in large coverage areas.

Figure 1.3 Limited capacity RF system.

Now, with reference to Figure 1.4, assume that we divide the same area A into separate sub‐areas, named “cells”. At the center of each cell we place a base station that transmits with power sufficient to cover its own cell, but low enough so that it cannot be received in the adjacent cells. The base stations are all connected to each other by physical lines interconnected by a central computer that acts as a switch. Now, assume that we arrange the cells in regular patterns of cells, called clusters, each consisting of K adjacent cells.

Figure 1.4 The cellular principle.

Since, there is virtually no interference between cells belonging to different clusters, we can use all the N frequencies within each cluster. If the whole coverage area consists of M clusters, it follows that now the system capacity increases to C = N/(A/M) = MN/A, a factor of M. However, the problem remaining is how to prevent the mobile users from losing communication when passing from cell to cell. To see how the issue is solved, assume that the base stations in the various cells continuously report to the central computer how well they receive the mobile subscribers passing nearby. Assume now that a mobile subscriber is connected to the base station of cell #1 and is approaching cell #2, while travelling away from cell #1. At a certain point the user will begin to lose communication with cell #1, while the link with cell #2 becomes stronger. Since the central computer is aware of the scenario, at a certain point it will instruct the mobile user to leave the channel of cell #1 and connect to a free channel of cell #2. This process is called a “handoff” and allows the mobile subscribers to pass from cell to cell without losing communication. The cellular architecture was made possible by the advent of microprocessor components, which allowed introducing enough intelligence within the mobile equipment so to be able to instruct it how to handle the handoff process.

1.2 Detailed Overview of Wireless Systems and Technologies

1.2.1 System types

Wireless communications using electromagnetic waves began at the end of the nineteenth century with Tesla, Popov, and Marconi. Marconi sent the first wireless signals (Morse code). In his first experiments, Marconi used a wavelength (λ) much longer than 1 km, and it was in 1920 that he discovered short waves with λ ≈ 100 m.

World War 2 gave rise to many advances in development of wireless communication systems, especially in the fields of RADAR (RAdio Detecting And Ranging), wireless data transmission, and remote sensing. Since then, wireless communication has been evolving continuously, significantly affecting many different aspects of our life. Standardization of the communication technologies, an important step in development of communication systems and services, started with the advent of commercial TV in the 1940s, when the first TV standards were introduced. The development of mobile communications was rather slow till the 1970s, when enabling technologies were developed for reliable, compact RF circuits and modules.

Today, wireless communication systems are very ubiquitous, providing a wide variety of highly reliable services. A broad range of systems and services have been developed, paving the way for implementation of wireless communication systems: satellite communications, radio and TV broadcasting systems, mobile phones, wireless LANs, wireless sensor networks, and so on.

The rapid growth of wireless systems implies an increased demand for spectrum, making spectrum allocation a key issue for the further extension of existing communication services and the development of new ones.

The challenge in the design of communication systems is the efficient use of the allocated resources, that is, power budget and available bandwidth, to provide high‐quality communications in terms of bit error rate (BER) and data rate (measured in bits per second, bps). In the case of wireless communications, the design of such systems is even more challenging due to the fact that wireless channels are subject to dynamic fast environmental changes.

No single technology can provide a proper and optimal solution for all desired wireless applications. Wireless communication systems/networks can be generally divided into three main categories, where each category aims to address specific needs. The division is based on the coverage range: wireless personal area network (WPAN), wireless local area network (WLAN), and wireless wide area network (WWAN). The system’s range determines its latency.

WPANs, such as Bluetooth, provide wireless communication in short ranges of a few centimeters up to several meters. In these systems, the communication is mostly a point to point communication. Point to multipoint communication is also possible, for example PicoNET (a network generated by two or more Bluetooth enabled devices). The data rate in WPAN is rather low, limited to a few 100s of kbps.

WLAN is a medium‐range wireless network covering areas up to 100s of meters. Examples include Wi‐Fi and DECT (Digital Enhanced Cordless Telecommunications). The data rate is high, that is up to 20 Mbps.

WWANs are aimed at providing high speed long‐distance links extending to several thousand kilometers. Examples include cellular phones, satellite communications, and WiMAX. Beside the geographical scope, the wireless networks WLAN and WWAN differ in data delivery scheme, data rate limitations, and spectrum regulation.

One important distinction between small and large networks corresponds to the ownership of the networks. Small networks are owned and operated by the users. Large networks are owned and operated by service providers that are not necessarily the main users of the network.

The IEEE 802 family of standards governs the physical layer (PHY) specifications and datalink aspects of networking (both wired and wireless networks). Among other IEEE 802 standards, the most widely used standard for wired LANs are IEEE 802.3 (called Ethernet) and 802.5 (Token Ring). The popular standards for wireless networks are 802.15 (Wireless PAN), 802.11 (Wireless LAN), and 802.16 (WiMAX).

A detailed description of these systems is given in the following sections.

1.2.2 Wireless network architectures

1.2.2.1 Wireless Personal Area Network

WPANs are small‐scale wireless networks providing low‐cost, power‐efficient connectivity between a small group of private devices located in proximity to a person, and between these devices and the external world. A WPAN covers the personal space surrounding a person in the range of 10s of meters and can be thought of as a complementary communication capability for longer range networks, such as WLANs and cellular networks. WPANs allow removing the need for fixed cabled connections. They need no infrastructure or direct connectivity to external world, and hence help to increase the mobility. Personal devices that can be networked by WPANs include: laptops, handheld computers, personal digital assistants, tablets, and cameras.

WPANs are standardized by the IEEE 802.15 group that focuses on standards governing short‐distance wireless networks. The IEEE 802.15 standard group is divided into four main task groups:

Task Group 1 (TG1) is devoted to standards for Bluetooth operating in the 2.4 GHz unlicensed ISM (

I

ndustrial,

S

cientific, and

M

edical) band.

Task Group 1 (TG2) is devoted to the coexistence of devices that operate in unlicensed spectra.

Task Group 3 (TG3) is devoted to high data rate WPAN standards, that is UWB (

U

ltra

W

ide

B

and) WPAN.

Task Group 4 (TG4) is devoted to a low data rate, low power WPAN standards.

Here we will describe three standards implemented by IEEE 802.15: Bluetooth (IEEE 802.15.1), UWB (IEEE 802.15.3), and ZigBee (IEEE 802.15.4). The standards are to create harmony in technologies from different industrial manufacturers.

Bluetooth (IEEE 802.15.1)

Bluetooth is a widely used WPAN technology that provides ad hoc wireless networking in short‐distance stationary and/or mobile environments. It is intended to convey both voice and data using inexpensive and low‐power devices. It was proposed by Ericsson in 1994 and originally aimed at eliminating the need for cabling between PCs and their peripherals, such as printers and keyboards.

In 1998, the Bluetooth special interest group (SIG) was established to foster further development of the Bluetooth concept and applications. The SIG was first formed by five companies (Ericsson, Intel, IBM, Nokia, and Toshiba) and later thousands of companies joined this group. The SIG focused on three applications of Bluetooth: (i) cable replacement, (ii) formation of ad hoc networks in a small area called piconet, and (iii) providing voice and data access point to wide‐area networks, both wired and wireless. The first Bluetooth standard was released in 1999, and in 2000 there were mobile phones with Bluetooth capabilities.

The Bluetooth topology is based on the Piconet/Scatternet scheme. Piconets are the basic networking units formed by ad hoc detection of nearby (Bluetooth enabled) devices. The Bluetooth Scatternets are extended networks allowing the participation and coexistence of multiple piconets.

A piconet is a small cell consisting of two or more Bluetooth devices that share the same medium using a master‐slave mechanism. In other words, a piconet is a WPAN, in which one device acts as a master, that is it initiates and manages the communication with the other (slave) devices. A master device can communicate with the slaves either in point to point or point to multipoint modes. But, slaves are restricted to point to point communication with the master. A master device of one piconet can be slave of other piconets. Each device may belong to a number of piconets at the same time, thus allowing for data to flow beyond the range of a piconet. Over the time, the roles of master and slave devices can change, from master to slave and vice versa. All devices in a piconet are synchronized by the master's clock.

In order to allow for power conservation, each slave device can work in either one of the following modes: active, sniff, hold, park, and standby. A slave device can communicate with the master only in the active mode. The number of active slaves is limited to seven. In the other three modes, the “listening” time of the slave is reduced to different degrees. Master devices are always active. Each piconet can accommodate one master, up to seven active slaves, and up to 255 standby slaves.

Bluetooth uses the FHSS (Frequency Hopping Spread Spectrum) modulation method to combat interference from other sources, either narrow or wide band, such as other Bluetooth devices, hence allowing for concurrent communication between several Bluetooth devices located in close vicinity of each other. As shown later in this Chapter, in the FHSS technique, the carrier frequency hops from one frequency to another following a certain pseudo‐random sequence, to produce a spread spectrum signal, with a small power spectral density. Using FHSS, tens of piconets can overlap in the same coverage space, so that the throughput can be very high (exceeding 1 Mbps). Data is transmitted in packets.

In Bluetooth, each piconet is assigned a unique pseudo‐random hopping sequence determined by the master’s identity. The hopping phase is determined by the master’s system clock. Bluetooth uses 79 RF channels covering the whole bandwidth of 83.5 MHz from 2400.0 MHz to 2483.5 MHz. The RF channels are 1 MHz apart, the hopping rate is 1600 hops per second, and the hop dwell time is 0.625 ms. The 79 hops are arranged in even and odd numbered slots. The master transmits over the even slots and the slaves use the odd slots.

One drawback of using FHSS is the relatively long time (up to 5s) needed to set the Bluetooth connections.

Standard Bluetooth uses digital communication with a GFSK (Gaussian binary Frequency Shift Keying) modulation scheme. The Gaussian shape of the FSK signals produces signals with a narrow power spectrum and hence decreases high power consumption. Recently, other modulation schemes besides GFSK have been also adopted.

Bluetooth MAC (Medium Access Control) is based on TDD (Time Division Duplex) to allow for full duplex transmission and elimination of crosstalk between the transmitter and receiver. In this scheme the time is divided into slots where the duration of each slot is 0.625 ms. As mentioned above, data is transmitted through packets carrying either synchronous information (voice) or asynchronous information (data). The packets are transmitted over different hop frequencies (subcarriers). The data rate in the voice channels is 64 kbps, and in the asynchronous data channels data rates can reach 723.2 kbps asymmetric and 433.9 kbps symmetric.

Simultaneous participation of a Bluetooth device in multiple piconets is enabled by TDM (Time Division Multiplexing) and allows multiple voice and data stations to participate in a piconet.

Bluetooth uses low‐power signals of 1 mW (0 dBm) for ranges up to 10 m. The transmitting power can be increased to up to 100 mW (20 dBm) in order to extend the coverage range up to 100 m. The Bluetooth standard specifies three classes of transmitting power levels: 100 mW (class 1), 2.5 mW (class 2), and 1 mW (class 3). Bluetooth receivers are required to have a sensitivity of –70 dBm or better.

New releases of Bluetooth foster further developments of this technology. In particular the Bluetooth technology is used to explore the growing field of Internet of Things.

UWB (IEEE 802.15.3)

Bluetooth’s data rate is not high enough to support the high data rates required in multimedia applications. UWB WPAN technology has been developed to address the ever‐growing demand for high data rate WPANs, with higher capacity, high quality of service (QoS), low power consumption, and low cost. Thanks to its great bandwidth, UWB WPAN can provide data rates over 110 Mbps, sufficiently high for audio and video delivery in small areas.

USB is well suited for home multimedia wireless networks, as it can provide more than 110 Mbps for distances up to 10 m, and 480 Mbps for a distance of 2 m. UWB WPAN can also replace high speed cables such as USB 2.0.

The UWB WPAN technology has been standardized by the IEEE 802.15.3 standard group. It is intended to interconnect devices confined to a small coverage area of up to 10 m (e.g. home or office) for streaming high data rate multimedia, such as high‐definition video. However, unlike the 802.15.1 standard that completely governs Bluetooth technology for short‐range communications, the UWB standard pertains only to a certain part of such communication standard.

UWB is not a new technology, as it has been used in different applications such as sensing and localization. In recent years, UWB was applied to wireless data transmission.

According to the FCC, any signal with a relative (fractional) bandwidth exceeding 20% or an absolute bandwidth greater than 500 MHz is considered a UWB signal.

UWB (absolute) bandwidth is commonly defined as the frequency band bounded by points 10 dB below the peak emission. The UWB signals’ relative bandwidth is the ratio between the absolute bandwidth and the center frequency.

The Shannon capacity formula for an AWGN channel, showing the direct proportion of the channel capacity and the signal bandwidth, reflects the potential for high data rates in UWB‐WPANs.

UWB signals are characterized by very high bandwidth, very low power spectral density, and low transmitting power (less than 1 mW). It uses low energy RF pulses of different shapes of extremely short duration, with no specific carrier frequency. There are different UWB pulse shapes, such as Gaussian, chirp, wavelet, and Hermite‐based short‐duration pulses.

The low power and broadband features of the UWB signals result in important advantages, including high throughput, jamming mitigation, and coexistence with other radio links. It can provide data rates up to 480 Mbps. The low energy density property minimizes interference to other services. It also enables the usage of a spectrum being used by other services, hence increasing the spectral efficiency. Other advantages include multipath immunity, low cost, and all digital architecture.

UWB radios must allow for co‐existence with narrow‐band licensed signals, such as GSM (Global System for Mobile communications) and GPS (Global Positioning System) that use the same spectrum, without causing intolerable interferences.

In 2002, the Federal Communications Commission (FCC) approved, for the first time, the unlicensed deployment of UWB under a strict spectral mask for indoor and outdoor applications in the United States. The low transmitting power levels (–41.3 dBm/MHz) are meant to ensure that UWB coexists with existing (licensed) communication links, with minimal interference. The allocated band is the 3.1–10.6 GHz frequency band, that is a bandwidth of 7.5 GHz.

The first UWB communication systems were implemented using very short pulses, which is a carrier‐less modulation scheme, and can be considered as a baseband signal. This is a single‐band modulation technique that is known also as an impulse radio (IR) modulation. The short duration impulses (less than 1 ns) have a very wide spectrum and very low power spectral density levels.

Since the allocation of the 3.1–10.6 GHz frequency band by FCC in 2002, some other wireless communication technologies have been proposed for UWB transmission. These include multiband (MB) techniques such as multiband orthogonal frequency division multiplexing (MB‐OFDM) in which the UWB frequency band is divided into multiple sub‐bands, and data is independently encoded in different bands. MB‐OFDM was supported by the WiMedia Alliance and considered by IEEE 802.15 task group 3a. In addition to MB‐OFDM, the IEEE 802.15.3a standard group considered the direct sequence UWB (DS‐UWB) that was developed by the UWB Forum. In DS‐UWB, a single pulse of short duration is used that occupies the whole bandwidth of 7.5 GHz. The DS‐UWB uses DSSS (Direct Sequence Spread Spectrum) techniques with variable‐length spreading codes and either BPSK (Binary Phase Shift Keying) or quadrature biorthogonal keying (4‐BOK) signals. This technique can reach high data rates up to 1.32 Gbps.

In the MB‐OFDM approach the spectrum is divided into 14 bands of bandwidth 528 MHz, whereby in each band a 128‐point OFDM signal using QPSK (Quadrature Phase Shift Keying) modulation is implemented.

UWB WPANs use a topology based on small networks called piconets, like in the case of Bluetooth. However, in 802.15.3 networks piconets are controlled by a dedicated device called the PicoNet coordinator. The network is formed in an ad hoc manner, where devices may dynamically join and leave the network. Unlike Bluetooth (and other WPANs) UWB allows for direct link between devices in a piconet.

UWB uses ARQ (Automatic Repeat Query, or automatic repeat request) aimed at improving the data transmission reliability. ARQ is an error control method, in which the receiver can detect an error in a certain packet. It automatically informs the transmitter to retransmit the corrupted packet, hence reducing the error rate significantly.

ZigBee (IEEE 802.15.4)

Bluetooth and UWB WPANs provide short‐range device connectivity and wire replacement. The former has a moderate data rate (up to 1 Mbps), and the latter provides high data rates (110 Mbps). With the availability of these WPANs, a question may arise as what would be the drive to develop ZigBee as another WPAN standard? What added value does it have?

ZigBee, based on the IEEE 802.15.4 standard, has gained its popularity mainly due to its low power consumption and low cost. The nominal transmitting power is from –25 dBm to 0 dBm. Other advantages include ease of installation (joining time for a new slave is typically 30 ms), reliability (mesh networking architecture), greater range (using multi‐hop and mesh networking), and a simple and flexible protocol.

The long battery life (typically measured in years, while operating by an AA cell) implies almost no constant maintenance. The low power consumption is a key feature of ZigBee, and this comes at the price of a low data rate (about one‐fourth of Bluetooth's 1 Mbps data rate). However, there are many applications in which the advantages of ZigBee, especially the extremely low power consumption, are more important than the data rate capabilities. Thus, ZigBee is better suited for applications that need only small data packets to be transmitted over large networks (mostly static ones) consisting of a large number of devices. Each ZigBee network has the capacity to support more than 65 000 active devices (compared to eight devices in Bluetooth). ZigBee can be embedded in many applications, such as remote controls, sensors, monitoring services, home automation, and toys. Using a ZigBee network of embedded nodes it is possible to tie together a whole factory, office, or home for safety, automation, and security.

The ZigBee standard for PHY specifies three license‐free bands: the 2.4 GHz band, the 915 MHz band, and the European 868 MHz band. The 2.4 GHz band uses the 2.4–2.4835 GHz spectrum with 16 channels and maximum (ideal) data rate of 250 kbps. It can be used worldwide. The 915 MHz refers to the 902–928 MHz band with 10 channels for North America. The data rate is 40 kbps. The 868 MHz band refers to the 868–870 MHz band with one channel for Europe. The data rate is 20 kbps. DSSS techniques are used in all bands.

The 915 and 868 MHz bands use BPSK modulation, and the 2.4 GHz band uses offset QPSK.

Each ZigBee network’s node (or device) consists of a transceiver, a microcontroller, and an antenna.

The devices are classified into three categories: PAN coordinator, router, and end device. They are further distinguished as either a full‐function device (FFD) or a reduced‐function device (RFD). Any FFD can act as either of three device (node) types: a PAN coordinator, a router, or an end device. An RFD can operate merely as an end device. FFDs can communicate with both RFDs and other FFDs.

The PAN coordinator is a smart FFD that initiates the formation of a new PAN, and serves as a bridge to other networks. There is only one coordinator in each ZigBee network. The coordinator should find a suitable RF channel to avoid interfering with WLAN channels operating in the same frequency bands (2.4 GHz bands). After formation of a network by the coordinator, other ZigBee devices can join it.

A router is an FFD that links devices and groups together and allows for multi‐hopping from a source device to a destination device.

The ZigBee end devices are either an FFD or RFD that can communicate with the coordinator and routers, but are not involved in the routing process.

Unlike coordinators and routers, the end devices are battery powered and can be in sleep mode in order to minimize battery consumption. These devices have 64 bit addresses. If necessary, the address size can be shortened to 16 bits in order to reduce packet size.

ZigBee supports three network topologies: star, tree, and mesh. Star network is the simplest topology in which messages are exchanged between end devices in two hops. In this configuration, devices communicate via a central node, called the PAN coordinator, through which all messages are passed. The reliability of the star topology is relatively low as there is only one path between each node pair.

A tree network starts with a top node (root tree) below which branches evolve via a net of routers to the end devices. The routers extend the network coverage area. The tree network is a multi‐hop network in which messages travel up and down the tree to reach destination. One drawback of the tree topology is its low reliability due to lack of alternative paths if a router is disabled.

A mesh (or peer to peer) topology is a multi‐hop network with a structure similar to a tree topology, in which there is a direct path between some branches. Data packets are routed to their destination across the tree through an available route.

The mesh topology is characterized with high reliability, as there exist different routes between each device pair. This topology allows for network extension by amending new devices and routers to the network.

There exist other topologies, such as the cluster tree or clustered star networks that are based on a combination of the above‐mentioned topologies.

The ZigBee technology is based on a standardized set of layers. IEEE 802.15.4 standard defines only the characteristics of the PHY and MAC layers, and the ZigBee Alliance specifies network and application layers.

The functions provided by the PHY layer are the modulation and transmission of the signal at source, and the reception and demodulation of the received signals at the destination.

The MAC layer accesses the network and provides synchronization and coding to increase reliability of data exchange. Access to the network is based on carrier sense multiple access with collision avoidance (CSMA‐CA).

The network layer performs the functions of network initiation, detection of neighbor devices, adding/dropping of devices to the network, and route discovery.

A ZigBee network can operate in either the beacon mode, or the nonbeacon mode of communication to enable data exchange between devices. The beacon mode is employed in battery activated coordinators in order to minimize power consumption. The nonbeacon mode is preferable when the coordinator is operated by mains.

In the beacon mode, devices become active when a beacon is transmitted, so they all know when to communicate with each other. In this mode a coordinator periodically sends beacons to the routers in the network. Upon receiving a beacon, devices “wake up” and look for incoming messages. After a message is completely transmitted to a certain device, the coordinator sets a time for the next beacon, and the device and the coordinator enter the sleep mode till the next beacon.

In the nonbeacon mode, the coordinator and routers are always active. In this mode every device must know the schedule for communication. This requires a precise timing system in each device, increasing its power consumption level. It should be noted that, even though the power consumption level in the nonbeacon mode is higher than its level in the case of beacon mode, the power consumption in the former mode is also low since devices are mostly in inactive “sleep” mode.

1.2.3 Wireless local area network

Local area networks (LANs) emerged during the 1970s out of a desire to share resources such as printers and storage devices, at first as a wired means to connect computers located in a small area such as an office. The networking between PCs allowed each user to access resources (data and services) residing on other computers. LANs have a limited geographic extent in a fixed location, for example an office building or a university campus. The physical reach of LANs is between a few 100s of meters to a few kilometers. LANs provide reliable, high speed, secure, and low‐cost connectivity between users, who are usually the owner of the network. In the first LANs of the 1970s, computers were interconnected by coaxial cables or shielded twisted‐pair lines. Unshielded twisted‐pair and optical fibers were used in later stages. The structure and protocols of LANs are based on packet communication. Since the 1970s, LANs have evolved in line with the growing demand for high speed and low‐cost communication between PCs. Ethernet, invented in 1973, has become the predominant wired LAN. Ethernet is an asynchronous technology, that is no system level timing is required. The Ethernet standard was developed by the IEEE 802.3 working group in the 1970s. It is a CSMA/CD protocol based on carrier sensing, collision detection, and random time delay before resending a packet corrupted upon collision with another packet.

Wireless LAN (WLAN) technology was envisioned as an extension of wired LAN technology: users are able to move around in the coverage area with their laptop (or other portable devices) with no need to deal with cabling. In 1971, a packet‐switched wireless communication network called Alohanet was developed. This pioneer WLAN provided communication between seven computers at the University of Hawaii.

The first WLANs were deployed in 1990s and as expected had lower performance than wired LANs. For example data rates of only a few Mbps, compared to data rates of 100 Mbps in wired LANs. Since then, much effort has been devoted to improve the WLANs’ performance, functionality, and compatibility to a level similar to wired LANs.

WLANs mark the beginning of the era in which the dream of connectivity at anytime and anywhere became reality. Many WLANs are deployed as an extension to existing wired LANs, increasing the users’ capabilities for mobility and Internet access.

The WLAN has good flexibility, that is it allows adding many different devices very easily, and facilitates the deployment of hot spot‐like and ad hoc networks (e.g. mesh networks), otherwise requiring costly and complicated cable installation. WLANs are now well established and almost all laptops, smartphones, tablet computers have built‐in capability for wireless networking.

WLANs use the unlicensed ISM bands. This fact had a great impact on the successful development of WLANs, and is considered as a great strength of this technology as it removes the need for any regulation and restrictions.

The first wireless standards were based on the Ethernet standard (IEEE 802.3), even though the performance of WLANs was not up to the level of Ethernet at that time. All WLANs are governed by the IEEE 802.11 standards family developed since 1997. The first standard was IEEE 802.11a issued in 1997. It specified a center frequency of 5 GHz, and a maximum (raw) data rate of 54 Mbps, with ranges of 35 m indoors and 115 m outdoors. This standard uses the OFDM (Orthogonal Frequency Division Multiplexing) modulation method. IEEE 802.11a was not as widely accepted as IEEE 802.11b, apparently due to the use of the rather incompatible 5 GHz band, as compared to the 2.4 GHz band of the IEEE 802.11b standard.

IEEE 802.11b was the first WLAN standard widely used. Its range is 38 m indoors, and 125 m outdoors. IEEE 802.11b uses a modulation technique called Complimentary Code Keying (CCK) with a center frequency of 2.4 GHz. The maximum data rate is 11 Mbps, much lower than that of IEEE 802.11a.

In 2003, the IEEE 802.11g standard was introduced, based on the 2.4 GHz band (like IEEE 802.11b) and offering a bit rate of 11 Mbps (like IEEE 802.11b). The coverage range of this standard is 38 m indoors and 125 m outdoors.

In 2009, two versions of the IEEE 802.11n standard were developed, one operating in the 2.4 GHz band and the other in the 5 GHz band. This standard offers high data rates up to about 150 Mbps, an indoor range of 70 m and outdoor range of 1125 m. IEEE 802.11b and IEEE 802.11n are the most popular standards.

In the standards using the 2.4 GHz band, there are two power limits. For IEEE 802.11b using CCK modulation the maximum EIRP is 18 dBm (63 mW) set by the spectral power mask of 10 dBm/MHz (10 mW/MHz). For IEEE 802.11 g and IEEE 802.11n standards that use OFDM modulation, the limit is 20 dBm (100 mW). Since the 5 GHz band is divided into two bands, namely 5150–5350 MHz and 5470–5725 MHz, each band can have different power limits.

WLANs use spread spectrum and OFDM, in which the available spectrum is divided into many small bands, and each band uses a different subcarrier.

The very first WLANs operated in the unlicensed frequency band of 902–928 MHz. Over time, the interference level in this band grew as many other unlicensed devices started using this band. To mitigate the interference, spread spectrum techniques were used. The data rate with the spread spectrum was 500 kpbs.

The next generations of WLANs used the 2.4–2.483 GHz ISM band. However, the potential of interference from nearby systems such as MW ovens, cordless telephones, garage door openers operating in the 2.4 GHz ISM band led to using spread spectrum techniques that are less sensitive to such interference and noise sources. The data rate was increased to 2 Mbps, that is four times faster than the first generation.

The more recent WLANs allow for data rates up to 10 Mbps, operating at 5 GHz ISM band of 5.775–8.85 GHz, and an additional frequency band around 5.2 GHz.

1.2.3.1 Wi‐Fi

Wi‐Fi refers to WLAN devices based on the IEEE 802.11 standards and approved by the Wi‐Fi Alliance. The term Wi‐Fi was originally used for the 802.11b standard, considered as a fast standard (11 Mbps). Later, the Wi‐Fi Alliance extended Wi‐Fi to include other standards as well.

The main application of Wi‐Fi is to enable mobile users to access Internet easily. Users of portable devices, such as a cellular phone or a laptop, with Wi‐Fi capability, can access the Internet when being within the coverage range of a Wi‐Fi access point.