80,99 €
Mehr erfahren.
- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Wireless Connectivity: An Intuitive and Fundamental Guide Wireless connectivity has become an indispensable part, a commodity associated with the way we work and play. The latest developments, the 5G, next-generation Wi-Fi and Internet of Things connectivity, are the key enablers for widespread digitalization of practically all industries and public sector segments. This immense development within the last three decades have been accompanied by a large number of ideas, articles, patents, and even myths. This book introduces the most important ideas and concepts in wireless connectivity and discusses how these are interconnected, whilst the mathematical content is kept minimal. The book does not follow the established, linear structure in which one starts from the propagation and channels and then climbs up the protocol layers. The structure is, rather, nonlinear, in an attempt to follow the intuition used when one creates a new technology to solve a certain problem. The target audience is: * Students in electronics, communication, and networking * Wireless engineers that are specialized in one area, but want to know how the whole system works, without going through all the details and math * Computer scientists that want to understand the fundamentals of wireless connectivity, the requirements and, most importantly, the limitations * Engineers in energy systems, logistics, transport and other vertical sectors that are increasingly reliant on wireless technology
Sie lesen das E-Book in den Legimi-Apps auf:
Seitenzahl: 855
Veröffentlichungsjahr: 2020
Ähnliche
Table of Contents
Cover
Foreword
Acknowledgments
Acronyms
1 An Easy Introduction to the Shared Wireless Medium
1.1 How to Build a Simple Model for Wireless Communication
1.2 The First Contact
1.3 Multiple Access with Centralized Control
1.4 Making TDMA Dynamic
1.5 Chapter Summary
1.6 Further Reading
1.7 Problems and Reflections
2 Random Access: How to Talk in Crowded Dark Room
2.1 Framed ALOHA
2.2 Probing
2.3 Carrier Sensing
2.4 Random Access and Multiple Hops
2.5 Chapter Summary
2.6 Further Reading
2.7 Problems and Reflections
Note
3 Access Beyond the Collision Model
3.1 Distance Gets into the Model
3.2 Simplified Distance Dependence: A Double Disk Model
3.3 Downlink Communication with the Double Disk Model
3.4 Uplink Communication with the Double Disk Model
3.5 Unwrapping the Packets
3.6 Chapter Summary
3.7 Further Reading
3.8 Problems and Reflections
4 The Networking Cake: Layering and Slicing
4.1 Layering for a One-Way Link
4.2 Layers and Cross-Layer
4.3 Reliable and Unreliable Service from a Layer
4.4 Black Box Functionality for Different Communication Models
4.5 Standard Layering Models
4.6 An Alternative Wireless Layering
4.7 Cross-Layer Design for Multiple Hops
4.8 Slicing of the Wireless Communication Resources
4.9 Chapter Summary
4.10 Further Reading
4.11 Problems and Reflections
5 Packets Under the Looking Glass: Symbols and Noise
5.1 Compression, Entropy, and Bit
5.2 Baseband Modules of the Communication System
5.3 Signal Constellations and Noise
5.4 From Bits to Symbols
5.5 Symbol-Level Interference Models
5.6 Weak and Strong Signals: New Protocol Possibilities
5.7 How to Select the Data Rate
5.8 Superposition of Baseband Symbols
5.9 Communication with Unknown Channel Coefficients
5.10 Chapter Summary
5.11 Further Reading
5.12 Problems and Reflections
6 A Mathematical View on a Communication Channel
6.1 A Toy Example: The Pigeon Communication Channel
6.2 Analog Channels with Gaussian Noise
6.3 The Channel Definition Depends on Who Knows What
6.4 Using Analog to Create Digital Communication Channels
6.5 Transmission of Packets over Communication Channels
6.6 Chapter Summary
6.7 Further Reading
6.8 Problems and Reflections
Note
7 Coding for Reliable Communication
7.1 Some Coding Ideas for the Binary Symmetric Channel
7.2 Generalization of the Coding Idea
7.3 Linear Block Codes for the Binary Symmetric Channel
7.4 Coded Modulation as a Layered Subsystem
7.5 Retransmission as a Supplement to Coding
7.6 Chapter Summary
7.7 Further Reading
7.8 Problems and Reflections
8 Information-Theoretic View on Wireless Channel Capacity
8.1 It Starts with the Law of Large Numbers
8.2 A Useful Digression into Source Coding
8.3 Perfectly Reliable Communication and Channel Capacity
8.4 Mutual Information and Its Interpretations
8.5 The Gaussian Channel and the Popular Capacity Formula
8.6 Capacity of Fading Channels
8.7 Chapter Summary
8.8 Further Reading
8.9 Problems and Reflections
9 Time and Frequency in Wireless Communications
9.1 Reliable Communication Requires Transmission of Discrete Values
9.2 Communication Through a Waveform: An Example
9.3 Enter the Frequency
9.4 Noise and Interference
9.5 Power Spectrum and Fourier Transform
9.6 Frequency Channels, Finally
9.7 Code Division and Spread Spectrum
9.8 Chapter Summary
9.9 Further Reading
9.10 Problems and Reflections
10 Space in Wireless Communications
10.1 Communication Range and Coverage Area
10.2 The Myth about Frequencies that Propagate Badly in Free Space
10.3 The World View of an Antenna
10.4 Multipath and Shadowing: Space is Rarely Free
10.5 The Final Missing Link in the Layering Model
10.6 The Time-Frequency Dynamics of the Radio Channel
10.7 Two Ideas to Deal with Multipath Propagation and Delay Spread
10.8 Statistical Modeling of Wireless Channels
10.9 Reciprocity and How to Use It
10.10 Chapter Summary
10.11 Further Reading
10.12 Problems and Reflections
11 Using Two, More, or a Massive Number of Antennas
11.1 Assumptions about the Channel Model and the Antennas
11.2 Receiving or Transmitting with a Two-Antenna Device
11.3 Introducing MIMO
11.4 Multiple Antennas for Spatial Division of Multiple Users
11.5 Beamforming and Spectrum Sharing
11.6 What If the Number of Antennas is Scaled Massively?
11.7 Chapter Summary
11.8 Further Reading
11.9 Problems and Reflections
12 Wireless Beyond a Link: Connections and Networks
12.1 Wireless Connections with Different Flavors
12.2 Fundamental Ideas for Providing Wireless Coverage
12.3 No Cell is an Island
12.4 Cooperation and Coordination
12.5 Dissolving the Cells into Clouds and Fog
12.6 Coping with External Interference and Other Questions about the Radio Spectrum
12.7 Chapter Summary
12.8 Further Reading
12.9 Problems and Reflections
Bibliography
Index
End User License Agreement
List of Tables
Chapter 3
Table 3.1 Specification of the reception outcomes at Yoshi when Zoya and poss...
Chapter 6
Table 6.1 A random sample of five consecutive channel uses.
Table 6.2 Possible mapping of three data bits into two ternary symbols.
Chapter 7
Table 7.1 Encoding rule for the simple code of rate
.
Chapter 9
Table 9.1 Orthogonal codes allocated to the terminals.
List of Illustrations
Chapter 1
Figure 1.1 Communication model used in this chapter, referred to as a collisio...
Figure 1.2 Illustration of two essential wireless features captured by the col...
Figure 1.3 The problem of first contact when the mobile device Zoya is in the ...
Figure 1.4 Rendezvous protocol for Zoya and Yoshi where both of them use half-...
Figure 1.5 Downlink time division multiple access (TDMA). (a) Periodic equal a...
Figure 1.6 Introduction of a header in the TDMA frame. (a) Periodic TDMA syste...
Figure 1.7 Illustration of several ingredients required in a simple wireless T...
Figure 1.8 Uplink transmission with a reservation frame. (a) Case when the all...
Figure 1.9 Overlapped downlink and uplink frame for a full-duplex base station...
Chapter 2
Figure 2.1 Canonical scenario for random access protocols, where a number of u...
Figure 2.2 An example of random access with probing. (a) Representation with a...
Figure 2.3 A simple scenario for sharing the wireless spectrum between two col...
Figure 2.4 Illustration of randomized spectrum sharing between two interfering...
Figure 2.5 Transmission of a feedback packet
from Yoshi to Zoya for (a) a sl...
Figure 2.6 Different multi-hop configurations that can arise if not all nodes ...
Chapter 3
Figure 3.1 Zoya and Xia communicate simultaneously with Basil. The left side d...
Figure 3.2 Enhanced communication model with a strong and weak region. (a) Dep...
Figure 3.3 Communication system with a strong/weak region around the base stat...
Figure 3.4 Illustration of the use of SIC in the collision model. (a) Collisio...
Figure 3.5 Strategies for communication in a collision channel without feedbac...
Chapter 4
Figure 4.1 Introducing layering for a one-way wireless link. (a) Diagram of a ...
Figure 4.2 Illustration of how layering deals with packets that can get out of...
Figure 4.3 A simple layered model for two-way communication. Note that the arr...
Figure 4.4 Packet exchange when the black box of the lower layer provides (a) ...
Figure 4.5 An example of a layered structure for multiple terminals sending da...
Figure 4.6 Scenario in which Zoya can establish a multi-hop connection to Xia....
Figure 4.7 Protocol stacks: OSI versus TCP/IP.
Figure 4.8 Example of clustered wireless networks. Each car represents a clust...
Figure 4.9 Illustration of the points of convergence in different types of sys...
Figure 4.10 A primer on wireless slicing for two services, broadband and low l...
Chapter 5
Figure 5.1 A look inside the black boxes of the TXmodule and RXmodule. TXbaseb...
Figure 5.2 Effect of the additive noise complex baseband symbols. (a) Three di...
Figure 5.3 The QPSK constellation. All constellation points lie on a circle su...
Figure 5.4 Bit-to-symbol mapping for two constellations of power
. (a) BPSK. ...
Figure 5.5 (a) The noise cloud is a circle in two dimensions and becomes an in...
Figure 5.6 Higher-order constellations. Axis labels: I (in-phase) and Q (quadr...
Figure 5.7 Received constellation from two interfering transmitters, each usin...
Figure 5.8 Curves of the goodput
for three different modulations BPSK, QPSK,...
Figure 5.9 Three superposed packets with powers
, and
, while
is the ...
Figure 5.10 Received constellations of Zoya and Xia when Basil broadcasts two ...
Figure 5.11 Illustration of non-coherent communication with linear sub-spaces....
Chapter 6
Figure 6.1 The general model of communication system considered by Shannon.
Figure 6.2 Three baseband communication channels between Xia and Yoshi with ad...
Figure 6.3 Distribution of the received/output signal at Yoshi's side...
Figure 6.4 Creating digital channels from Xia to Yoshi by using BPSK or QPSK m...
Figure 6.5
-QAM constellation with Gray mapping.
Figure 6.6 Difference between Gray mapping and the bit-to-symbol mapping obtai...
Figure 6.7 Layered representation of communication channels.
Figure 6.8 The binary erasure channel where Yoshi knows for sure if an error h...
Figure 6.9 Layered model for asynchronous packet transmission.
Figure 6.10 An illustration of the frame synchronization problem with packets ...
Figure 6.11 Description of the channel with ternary inputs and outputs, where ...
Chapter 7
Figure 7.1 Binary symmetric channel (BSC) between Xia and Yoshi and three chan...
Figure 7.2 Comparison of the normalized goodput
for each of the four communi...
Figure 7.3 Expected number of erased symbols for the
-channel and the
-chann...
Figure 7.4 The main plot in error correction coding. (a) The original communic...
Figure 7.5 Representation of coding and modulation as a concatenation of two c...
Figure 7.6 Example of a trellis code with two states. On the left is the trell...
Figure 7.7 Comparison of full and partial retransmission. In both cases the pa...
Chapter 8
Figure 8.1 Entropy of a binary random variable with probability of
equal to
Figure 8.2 Diagram of the source coding problem.
Figure 8.3 Communication through a Z-channel. (a) Z-channel with perfectly rel...
Figure 8.4 Two wireless communication setups for interpretation of mutual info...
Figure 8.5 Illustration of data processing inequality for a layered communicat...
Figure 8.6 Illustration of water filling for two channels, where channel
is ...
Figure 8.7 Water filling in fading channels with known CSI at the transmitter....
Figure 8.8 Representation of the good and the bad states for a binary channel ...
Figure 8.9 Equivalent representation of the channel with two states, when the ...
Figure 8.10 Illustration of the equivalent fast fading channel between Xia and...
Chapter 9
Figure 9.1 A simple example that illustrates how to create a discrete communic...
Figure 9.2 (a) The periodic waveform with a period of
sent by Zoya. (b) Yosh...
Figure 9.3 Zoya uses the frequency
to transmit the complex symbol
at time
Figure 9.4 Number of channel uses in a given bandwidth
. Each vertical arrow ...
Figure 9.5 Interference between signals with different frequencies. (a) Observ...
Figure 9.6 Signals with finite duration and the Fourier Transform. (a) Possibl...
Figure 9.7 Illustration of chip synchronous, but not symbol synchronous, trans...
Figure 9.8 An illustration how CDMA works and why the effect of a spread spect...
Chapter 10
Figure 10.1 Electromagnetic radiation of the base station Basil at a distance
Figure 10.2 Definition of a coverage area, represented by gray shading. (a) As...
Figure 10.3 Illustration of radiation patterns of the antennas used by Zoya an...
Figure 10.4 Yoshi tries to orient his antenna in a way in which the interferen...
Figure 10.5 Change in the coverage area depending on the directivity of the an...
Figure 10.6 An example of an object that causes diffraction at low frequency, ...
Figure 10.7 Illustration of the two-ray propagation from the sender Zoya to th...
Figure 10.8 A detailed diagram of the LLCHannel (low layer channel) that shows...
Figure 10.9 An example of a channel impulse response defined for the channel b...
Figure 10.10 Illustration of the frequency selectivity in multipath channels. ...
Figure 10.11 Scenario in which the direct path between Zoya and Yoshi is block...
Figure 10.12 Illustration of the Doppler shift when Zoya transmits a sinusoida...
Figure 10.13 Yoshi moves towards Zoya at a speed
, but the speed along the di...
Figure 10.14 Illustration of the ideas to combat the multipath propagation. (a...
Figure 10.15 A physical setup that corresponds to: (a) Rayeigh fading, without...
Chapter 11
Figure 11.1 Use of multiple antennas to support the communication between Zoya...
Figure 11.2 Illustration of the propagation effects when the transmitter and t...
Figure 11.3 Coverage area with directed antennas. (a) Passive directed antenna...
Figure 11.4 Illustration of the distribution of the signals and interference w...
Figure 11.5 Difference between superposition coding and nonlinear precoding. T...
Figure 11.6 Example of spectrum sharing among three links by using digital bea...
Figure 11.7 Illustration of a massive MIMO. Basil and Bastian are base station...
Chapter 12
Figure 12.1 Illustration of different use cases for connections that are fully...
Figure 12.2 Communication scenario built around monitoring of a physical pheno...
Figure 12.3 Illustration of the basic coverage options. BS1, BS2, and BS3 are ...
Figure 12.4 Wireless mobile coverage achieved by cellular networks. Each base ...
Figure 12.5 Macrocell versus small cell coverage. (a) The area of a macrocell ...
Figure 12.6 One-way communication via a wireless relay that provides a backhau...
Figure 12.7 Two-way communication via a wireless relay that provides a backhau...
Figure 12.8 Two-way relaying that uses network coding. (a) Digital network cod...
Figure 12.9 Yoshi performs a soft handover by being simultaneously served by B...
Figure 12.10 Wireless coverage with cooperation and coordination among BSs int...
Figure 12.11 Cooperative wireless communications. (a) Cooperative downlink tra...
Figure 12.12 Providing wireless coverage through a system of interconnected BS...
Figure 12.13 Illustration of three different architectures in the case of upli...
Figure 12.14 Competition for wireless communication resources. Only desired li...
Figure 12.15 Coexistence and spectrum sharing in unlicensed frequency bands. (...
Guide
Cover
Table of Contents
Begin Reading
Pages
iii
iv
v
xv
xvi
xvii
xix
xx
xxi
xxii
1
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
51
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
73
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
103
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
145
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
175
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
273
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
Wireless Connectivity
An Intuitive and Fundamental Guide
Petar Popovski
Department of Electronic SystemsAalborg University, Denmark
This edition first published 2020© 2020 John Wiley & Sons Ltd
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 law. Advice on how to obtain permission to reuse material from this title is available at http //www.wiley.com/go/permissions.
The right of Petar Popovski to be identified as the author of this work has been asserted in accordance with law.
Registered OfficesJohn Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USAJohn Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK
Editorial OfficeThe Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK
For details of our global editorial offices, customer services, and more information about Wiley products visit us at www.wiley.com.
Wiley also publishes its books in a variety of electronic formats and by print-on-demand. Some content that appears in standard print versions of this book may not be available in other formats.
Limit of Liability/Disclaimer of WarrantyWhile the publisher and authors have used their best efforts in preparing this work, they make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives, written sales materials or promotional statements for this work. The fact that an organization, website, or product is referred to in this work as a citation and/or potential source of further information does not mean that the publisher and authors endorse the information or services the organization, website, or product may provide or recommendations it may make. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for your situation. You should consult with a specialist where appropriate. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this work was written and when it is read. Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.
Library of Congress Cataloging-in-Publication Data applied for
HB ISBN: 9780470683996
Cover Design & Image: © Peter Gregson
In memory of my father, the unshakeable optimist.
Foreword
First: But, Why?
Why should one dare to write a relatively long book in a digital age, where everything seems to be quickly found online and watching video tutorials is used as a substitute for reading? Why read, let alone write, a long text when a single tweet results in thousands of workers getting laid off or somebody becoming a millionaire in a day? And, last, but not least, why put in so much effort, knowing that, eventually, despite all the measures, the PDF of the book will be available for illegal download at a phony website?
A book or a textbook still has its role in the digital age, but this role is significantly different from the times when books were the ultimate source of information and knowledge. It should rather be understood as a gateway to knowledge, a gadget that helps to make sense of the massive amount of online data, a hitchhiker's guide for receiving, filtering, and learning from the overwhelming waves of information. As for the illegal copies: if you are reading this on an illegal copy, then it is fair to tell you that it is getting really boring from now on, so you can stop reading.:)
Wireless became Huge and Complex
This role of a “gateway to knowledge” was one of the motivations behind writing this book. The area of wireless communications has developed immensely over the last three decades, generating a large number of concepts, ideas, articles, patents, and even myths. Identifying the crucial ideas and their interconnection becomes increasingly difficult. The area of wireless connectivity grew to be very complex, to the level where the specialists working in one part of the system, say hardware, did not know much about the functioning of the high layer protocols, and vice versa. In the extreme case, this ignorance about the concepts and functioning of the other parts of the communication system led to the “only-my-part-of-the-system-matters” attitude, sometimes resulting in disastrously sub-optimal designs.
In order to see how much wireless communication has developed in volume and complexity, here is an ultra-short overview of the generations of wireless mobile communication systems. It started with the “modest” ambition of 2G being reachable for a phone call wherever you are moving, but the unlikely hero was the short message service (SMS) that brought texting as a new social phenomenon. It was perhaps this unlikely hero that planted the obsession with the “killer application” during the development of 3G. The advent of the smartphone has shown that there was not a single killer application, but a gateway to the internet, a gadget with many apps, a hitchhiker's guide to multiple applications [sic]. Only with the data speeds offered by 4G did the smartphone start to reach its full potential, completely transforming work and play. At the time of writing, we are at the dawn of the deployment of 5G, still with a lot of predictions, enthusiasm, and skepticism. The working version of the 5G ambition is to offer truly ubiquitous and reliable coverage to the humans, but also wirelessly connect machines and physical objects.
Note that this ultra-short overview is unfair to a lot of other wireless technologies that are omnipresent and play a crucial role in daily life, such as Wi-Fi and Bluetooth. The tone in the book is leaning towards mobile wireless cellular networks, but the overall discussion is kept generic, not tied to a particular wireless system or technology.
How this Book is Structured
The book does not follow the established, linear structure in which one starts from the propagation and channels and then climbs up the protocol layers. Here the approach has been somewhat nonlinear in an attempt to follow the intuition used when one creates a new technology to solve a certain problem. With this approach, we state a problem from the real world and create a model that reflects the features of the problem. The model is a simplification, a caricature of the reality, but as every good caricature, it captures the essential features. A certain model (for example, a collision model of a wireless channel), allows the system designer to propose solutions that reside within a subspace of the space of all possible solutions to the real communication problem. By enriching the model (for example, adding a capture and interference cancellation to the collision model), the system designer can devise solutions that go beyond the boundaries of the previously mentioned subspace. Practically each new chapter brings enrichment of the models, presenting system/algorithm designs that extend the ones developed for the simpler system models.
Each chapter starts with a cartoon that carries the main message of the chapter. The narrative in the book uses characters as it facilitates the discussion about communication between different parties. This is inspired by the security literature, which deals with Alice, Bob, etc. Here I have started from the other side of the alphabet, which is populated by the letters commonly used in communication theory. The characters are Zoya, Yoshi, Xia, Walt, Victoria (which happens to be the name of my mom) and Umer, and, yes, they are more international compared to Alice and Bob. The base stations are named Basil and Bastian for obvious reasons.
Among the references in “further reading”, I have inserted references to some of the research works co-authored by me. This is not to boost my citations by a self-citation (which is, righteously, often not counted in the academic record), but rather to offer a reference that shows that I, the author, have made an actual research contribution to the area. This can only increase the credibility of what is written in the chapter.
Objectives and Target Audience
When I started the book, the objective was to make it suitable for casual reading and use almost no equations. In the meantime, the number of equations increased, but still far below the number in standard textbooks on wireless communications, such that there is still hope that the reader can read it casually. Yet, the fact that there are five problems after each chapter indicates that the book can also be used as a textbook. However, for in depth reading, the reader should rely on the literature in “further reading”.
The target audience is:
Students in electronics, communication and networking. Some of the problems at the end of the chapters are actually mini-projects, which the students can do over an extended time. This is suitable for both graduate and undergraduate courses. Clearly, if used as a graduate course, then there is more reliance on external literature.
Wireless engineers that are specialists in one area who want to know how the whole system works, without going through all the detail and math.
Computer scientists that want to understand the fundamentals of wireless connectivity, the requirements. and, most importantly, the limitations.
As wireless connectivity starts to play a big role in a large number of cyber-physical systems, such as smart grids, transport, logistics or similar, the engineers specializing in those areas can obtain an insight into some of the essential wireless concepts.
As a supplement to other books on wireless connectivity that deal with the detail of analysis and design of specific technologies.
Acknowledgments
Even when a book has a single author, a large part of the authorship goes to the colleagues, friends, and family that provided inspiration, criticism, a gentle push when things looked impossible and a reminder that Sisyphus was only a mythical creature.
I am deeply grateful to Osvaldo Simeone (King's College London) for enormous support during the preparation of this book. The credit for the idea of using cartoons should go to him. He could absolutely always find the time to read the chapters that I was asking him to check, and provide prompt and rich feedback. I have been fortunate to have him, an exemplary erudite researcher, as a collaborator over many years.
Three people stood out in encouraging me throughout the long writing of the book. Jørgen Bach Andersen (Aalborg University), Angel Lozano (Pompeu Fabra University) and Hiroyuki Yomo (Kansai University). Jørgen provided me with very valuable feedback on Chapter 10 (Space in Wireless Communications). Angel removed my doubts about the usefulness of Chapter 9 (Time and Frequency in Wireless Communications). Hiroyuki decided to use this as a textbook in the early stages, when I presented him with the book concept.
I am very thankful for the feedback I got on specific chapters. Two members of my research group provided me with feedback in the early stage of writing and removed some of the doubts I had about the style. Čedomir Stefanović (Aalborg University) read the first chapters and Nuno Pratas (now with Nokia) read Chapter 6 (A Mathematical View on a Communication Channel). Anna Scaglione (Arizona State University), Emil Björnson (Linköping University) and Elisabeth de Carvalho (Aalborg University) were very kind to read Chapter 11 (Using Two, More, or a Massive Number of Antennas) and provide me with prompt and useful feedback.
A big thank you goes to the members of my research group, who had to be patient with my rants about the book throughout all these years. After one of my lectures for the master students, Rocco Di Taranto (now with Ericsson), at that time my PhD student, asked me: “Where can I read these topics explained in a way in which you did it at the lecture?”. The book idea had been cooking in the background for some time, but this was perhaps the decisive push to write it. Marko Angjelichinoski (now with Duke University) was convinced that the style and the whole book project were very original and I needed to hurry up. I would like to thank Kasper Fløe Trillingsgaard (now with InCommodities) for many stimulating discussion on the information-theoretic aspects. Alexandru-Sabin Bana (Aalborg University) and Radoslaw Kotaba (Aalborg University) helped to prepare a course based on this book and spotted several errors and inconsistencies. While this book was in the final stages, I was teaching a course at Aalborg University and several students were kind to correct errors in the chapters: Andreas Engelsen Fink, Jonas Ingerslev Christensen, Taus Mortensen Raunholt, Jeppe Thiellesen and Simon Kallehauge.
The cartoons, the cover page, as well as the clipart used to make the figures, were made by Peter Gregson Studio from Novi Sad, Serbia. This is a team of immensely creative people, Jovan Trkulja, Velimir Andrejević and Milan Letić, whose ideas play a significant role in the final look of the book. I would also like to thank Aleksandar Sotirovski for making the first version of the cartoons for some of the chapters, but due to objective reasons could not continue. Thanks to Kashif Mahmood (Telenor) for suggesting Umer as a Pakistani name starting with “U”. I would also like to thank the team at Wiley for being patient and supportive throughout the years, but especially in the final stage: Sandra Grayson, Louis Manoharan, Adalfin Jayasingh, and Tessa Edmonds.
My biggest support through these years came from my family: my wife Iskra, my children Andrej and Erina, as well as our extended family. Family was always there to take the blame when I was performing poorly on time management and planning of the writing. In its most severe form, that blame was ending with a threat that I was going to write something similar to the dedication written by a mathematician, who dedicates his book to his wife and children “without whom this book would have been completed two years earlier”. I am obviously not doing it and, instead, I want to thank them for absolutely always being there for me. I am hoping that some of them will read the book and get to know what I am actually working with. Unfortunately, my father passed away before this book was finished. I am dedicating this book to him.
P. P.
Acronyms
ACK
Acknowledgement
AF
Amplify and forward
ARQ
Automatic retransmission request
ASK
Amplitude shift keying
AMC
Adaptive modulation and coding
AWGN
Additive white Gaussian noise
BBU
Baseband processing unit
BPSK
Binary phase shift keying
BS
Base station
BSC
Binary symmetric channel
CDMA
Code division multiple access
CoMP
Coordinated multipoint
C-RAN
Cloud radio access network
CRC
Cyclic redundancy check
CRDSA
Contention resolution diversity slotted ALOHA
CSI
Channel state information
CSIT
Channel state information at the transmitter
CSMA
Carrier sensing multiple access
D2D
Device to device
DBPSK
Differential binary phase shift keying
DoF
Degree of freedom
EGC
Equal gain combining
FDD
Frequency division duplex
FDMA
Frequency division multiple access
FEC
Forward error correction
GF
Galois field
GPS
Global positioning system
HARQ
Hybrid automatic retransmission request
IoT
Internet of Things
ISI
Intersymbol interference
LBT
Listen before talk
LDPC
Low-density parity check
LEO
Low Earth orbit
LLN
Law of large numbers
LoS
Line of sight
MAC
Medium access control; also multiple access channel
MEC
Mobile edge computing
MIMO
Multiple input multiple output
MISO
Multiple input single output
MMSE
Minimum mean squared error
mmWave
Millimeter wave
MPR
Multi-packet reception
MRC
Maximum ratio combining
NACK
Negative acknowledgement
NOMA
Non-orthogonal multiple access
OFDM
Orthogonal frequency division multiplexing
OFDMA
Orthogonal frequency division multiple access
PAM
Pulse amplitude modulation
PAPR
Peak-to-average power ratio
probability density function
PHY
Physical layer
PSK
Phase shift keying
QAM
Quadrature amplitude modulation
QPSK
Quaternary phase shift keying
RF
Radio frequency
RNC
Radio network controller
RRH
Remote radio head
SC
Selection combining
SDMA
Space division multiple access
SIC
Successive interference cancellation
SIMO
Single input multiple output
SINR
Signal-to-interference-and-noise ratio
SNR
Signal-to-noise ratio
TDD
Time division duplex
TDMA
Time division multiple access
UEP
Unequal error protection
UWB
Ultra wideband
ZF
Zero rorcing
1An Easy Introduction to the Shared Wireless Medium
We start by describing wireless communication through an analogy with a conversation within a group of people, named Zoya, Yoshi, and Xia. We will refer to these and some other characters throughout the book; the characters will stand for wireless devices, base stations, or similar. The data that they want to communicate to each other is the content of their speech, which is part of the conversation. Regardless of the speech content, the conversation can only take place if the participants follow some conversation protocol, such that at a given time only one person speaks while the others listen. How do they agree who gets to speak and who gets to listen? One way would be, before starting the actual conversation, to have them agree upon which conversation protocol should be followed. In that case the information exchanged in that preliminary conversation cannot be regarded as useful data, but rather as metadata, also called protocol information or control information. The metadata is necessary in order to enable the conversation to take place. But then, how do they agree on the protocol for exchanging the metadata?
These questions can go on to infinity, but in a normal situation the communication protocol is agreed upon by either sticking to certain rules of politeness or following visual cues and gestures that facilitate the conversation. In other words, the metadata is exchanged by using a visual communication channel that is different from the speech communication channel. However, in a commonly encountered wireless communication system there is only one communication channel through which both the data and the metadata should be sent. This is not to say that it is not possible to have one wireless communication channel for data and a separate one for metadata; even if such separation exists, then what is the protocol for exchanging the meta-metadata that is used to agree how to send the metadata?
This gets obviously complicated, but the bottom line is that we will always hit the problem of communicating over a single shared wireless channel. Now, taking the fact that there is a single channel for communicating both the data and the metadata, the key point of the analogy with the conversation is to put Zoya, Yoshi, and Xia in a dark room, such that they have only speech as a means of communicating (we exclude tactile communication) and no visual cues can be of help. In that setting, the audio channel should be used both to coordinate the conversation and to carry the actual content of the conversation.
This is the common situation in which wireless communication systems operate and will be the subject of this chapter. Here are some examples of the questions that will be discussed. If Zoya and Yoshi want to talk to each other, how do they agree who talks first and who listens first? If both Xia and Yoshi want to talk to Zoya, how should they agree who takes a turn to speak at a given time, so that they don't all talk simultaneously? Solutions to these problems are provided by various protocols for controlling the access to the medium; hence the name MAC (medium access control) protocols, and they are of central importance in wireless communication systems.
1.1 How to Build a Simple Model for Wireless Communication
1.1.1 Which Features We Want from the Model
The main feature of the wireless communication medium is the fact that the medium is shared, in the same way in which the air through which the sound propagates is shared among the people having a conversation. MAC protocols enable multiple wireless communication users and devices to share the medium and send/receive data.
First, we must agree on how the system operates and what it takes to have a signal from one communication node received correctly at another node. In other words, we need to settle on a suitable system model: a set of assumptions that will allow us to talk about communication protocols and principles in a setting that is simple, but sufficient to contain the necessary properties of a shared wireless medium. We build the initial model by relying on a common sense analogy with the spoken conversation, as it captures three fundamental properties of wireless communication: broadcast, interference, and half-duplex operation. We illustrate these features by observing a conversation between Zoya, Yoshi, and Xia:
Half–duplex
: A given person, e.g. Zoya, cannot speak and listen at the same time.
Broadcast
: If Zoya has information to convey to Yoshi and Xia, then, provided that both Yoshi and Xia are listening, Zoya needs to say her message only once, and not repeat it individually to Yoshi and to Xia.
Interference
: If Yoshi and Xia speak simultaneously, Zoya will not understand either of them.
The descriptions above are arguably not always correct, but they do represent what is common sense for a conversation. Furthermore, the analogy of the communication problems with the conversation between Zoya, Yoshi, and Xia is useful, but it has its limitations, which will be pointed out when necessary.
1.1.2 Communication Channel with Collisions
For the purpose of this chapter, we define a communication channel to be the physical resource that is used for a wireless transmission. In that sense, in spoken communication, the channel is created by the audible vibrations that take place in air or even another sound-propagating medium. It is useful to note that the communication channel is not the whole physical medium with all the vibrations, since there are vibrations that cannot be registered by ear and thus do not carry useful audio information. Furthermore, spoken communication uses a single communication channel: one cannot switch to another channel, such as in a TV receiver, in order to listen to the desired speaker and avoid the undesired one.
As already stated above, our discussion will be limited to the case in which all nodes use a single communication channel. In reality that can be, for example, a certain frequency to which all the nodes are “tuned”. Here we use the term “frequency” as it is used in a common language for, say, a TV frequency. One may argue that Zoya and Yoshi can agree to one frequency, while Xia and Walt can agree to tune to another frequency and in this way they do not need to share the channel with the link Zoya–Yoshi. This is indeed possible and we will discuss it in later chapters, when we introduce the notion of separation in frequency. On the other hand, it is also true that Zoya and Yoshi should first use some communication channel to agree upon which frequency they will use for communication. This agreement is, again, metadata or control information, such that the corresponding channel is often denoted as a control channel and can be shared by multiple nodes to come to an agreement about the frequency. For example, if Zoya decides to communicate with Xia, then she knows that she should try to find Xia at the control channel and, upon contacting her, use the control channel to decide which channel/frequency they should both be tuned to in order to communicate the useful data. However, the control channel is a common, shared communication channel and therefore the question of how to share that channel to send metadata remains valid.
The communication model used in this chapter is called a collision model. This is because the central assumption of the model is that if two or more nodes transmit simultaneously, then the interference that they cause to each other is manifested as a collision at the receiver. Upon collision, the receiver does not manage to retrieve any data successfully. Another assumption in the model, not really related to the issue of collision, is that a node operates in a half-duplex manner and cannot receive while transmitting. Most of the wireless systems that we encounter today are not full-duplex, that is, do not transmit and receive simultaneously at the same frequency channel. However, although technologically more complex, it is also possible to have full-duplex operation. Therefore, throughout the chapter we will occasionally revise the half-duplex assumption and discuss the changes that the full-duplex can bring into the design of a specific protocol or algorithm.
The communication between the wireless nodes is based on data packets. A transmitting node is capable of sending bits per second (bps) such that a packet of duration contains bits. All packets have the same duration, unless stated otherwise. In the collision model, a packet is treated as the smallest, atomic unit of information, such that either the whole packet is received correctly or it is lost. In other words, it is not possible to receive only some bits of the packet correctly. A packet sent by Zoya to Yoshi is received correctly if:
Yoshi is in the communication range of Zoya such that the distance between them is less than
m;
No other communication node that is within
m of Yoshi transmits while Yoshi is receiving the packet from Zoya.
The first condition above indicates that each transmission is omnidirectional. Due to the basic property of reciprocity in electromagnetic/radio propagation (see Section 10.9), each reception in our model is also omnidirectional. From this it follows that Yoshi receives a signal as long it is sent from a distance less than m, regardless of the actual position. The ingredients of the collision model are illustrated in Figure 1.1. Specifically, Figure 1.1(a) depicts the data rate of an idealized single link as a function of the distance between two communicating nodes. An example communication scenario is depicted in Figure 1.1(b), where two nodes are connected by a line if the distance between them is less than , indicating the possibility of having a link between them. Figure 1.1(c) exemplifies a possible time evolution of a process of packet transmission in the framework of the collision model. The packet from Zoya to Yoshi is received correctly, while the packet is not, due to collision with the packet sent simultaneously by Xia. Note that, by treating a packet as an atomic unit of information, even a partial overlap of and causes packet loss. On the other hand, Walt is outside the range of Zoya, such that he can receive without being interfered with by .
Figure 1.1
Communication model used in this chapter, referred to as a collision model. (a) Simplified dependence between the data rate and the distance, denoting a communication range
. (b) An example topology with possible wireless links among devices. The distance between two connected devices is at most
. (c) Collision model at work for the topology in (b).
The assumptions of fixed-length packets and always-destructive collisions are weakening the analogy with a conversation. If we think to relate a packet to a spoken word, then not all words have the same length and missing some letters of a word may still not destroy its comprehensibility. In fact, the collision model is rather pessimistic. In reality, one expects a certain continuity in comprehensibility/correctness of a packet: if the packets and from Figure 1.1 have only a tiny overlap, then both would have to be received correctly by Yoshi. So, why are we not accounting for such a phenomenon and remain pessimistic about the collision? This is for pedagogical reasons in order to have a gradual path to system design and optimization. At the first step, make a system that works when every collision is identical and deemed destructive. In the next step, pose the question: what if not all collisions are identical? This leads to a refinement of the communication model by entering “inside the collision” and analyzing the different types of collision, which we will do in the later chapters. Notably, some types of collision will not be destructive and some collided packets can be received correctly, which sets the basis for optimizing the protocols further.
1.1.3 Trade-offs in the Collision Model
The basis of any good engineering is identification of the trade-off points that exist in a system: which benefits versus which costs are associated with given decisions on a system design. Even before discussing concrete techniques for accessing the shared medium, we can try to assess the limitations and the opportunities for protocol designs offered by the collision model. In that sense, it is at first instructive to look at the engineering trade-offs by contrasting the collision model with a model for wired communication.
For the problem of establishing and maintaining links, the obvious advantage offered in the wireless setting is that the communication is untethered and links can be established flexibly between any two nodes that come into spatial proximity. The price of this flexibility is twofold:
Resources (time, battery) need to be consumed in order to establish the link between two nodes.
The link is not exclusively reserved for use between the two nodes, as a third nearby node may transmit on the same channel and thus cause interference.
In contrast, in a wired model Zoya and Yoshi are connected by a dedicated cable. Precisely the lack of flexibility gives an advantage to the wired setting in certain scenarios. For example, consider the case in which Zoya and Yoshi are static devices and need to be able to reliably exchange extremely secure data, such as control data pertaining to a power plant. Then an investment in such a cable may be fully justified, despite the fact that the cable may be severely underutilized due to only occasional transmission of critical data.
The collision model captures the two essential wireless features, broadcast and interference. In Figure 1.2(a), Zoya, Yoshi, and Xia communicate with the base station (sometimes shortened to BS) named Basil. A base station can be seen as an entry point to an infrastructure through which Zoya, Yoshi, and Xia are connected to their communication peers. For example, consider the case in which Zoya wants to communicate with Walt. Zoya is in the range of the Basil, while Walt is in the range of a different base station, named Bastian. Then, Basil and Bastian are interconnected, most likely through a wired networking infrastructure, which allows transfer of data from Zoya to Walt and vice versa. In the sequel we will implicitly consider the fact that our users may want to communicate to their peers that are in the range of other base stations, but our focus will be on the communication between the users and a single base station.
Figure 1.2
Illustration of two essential wireless features captured by the collision model. (a) Broadcast. (b) Interference.
If Basil wants to send the same information to all three devices, a single transmission would suffice, since the three devices are within a distance smaller than . By contrast, if there were a wire between each device and Basil, then Basil should have sent each packet three times. Hence, wireless broadcast is cheap and this feature has been termed the wireless broadcast advantage. When we want to emphasize that the same message is sent to several devices, we will sometimes use the term multicast1. Clearly, if Basil has different information for each device, the broadcast advantage disappears, at least in our simple communication model.
When the communication takes part in the opposite direction, Figure 1.2(b), then the wireless broadcast advantage of the shared medium turns into a problem of interference. If the three devices transmit simultaneously, collision occurs and Basil does not receive anything useful. Therefore the devices should be coordinated in order not to transmit simultaneously and avoid collisions. This incurs certain coordination cost, spent on exchanging metadata. By contrast, the coordination cost is absent if each device has a dedicated wire to Basil, since he receives each signal over the wire. However, when calculating the grand total of costs, one has to account for the capital expenses incurred by installing the wires and, of course, the lack of flexibility inherent to a wired connection.
In summary, in the collision model broadcast can be an advantage, as all nodes in the range will perfectly receive the packet, while interference is always a disadvantage. In later chapters we will enhance the communication model by taking a magnifying glass and look what happens inside a collision. This will lead to a somewhat surprising conclusion that interference can be very useful.
1.2 The First Contact
Back to the dark room analogy, we ask the question: how do two people, who have never met before, start to communicate when placed in a dark room? Reformulating this question in terms of wireless communication, we can ask: how do two wireless devices start to communicate? Who speaks first and who listens first? This is an important issue when the devices operate in a half-duplex manner, since a device cannot transmit and receive simultaneously. Before a packet from Zoya is sent to Yoshi, each of them needs to know that Zoya is about to transmit and Yoshi is about to receive. This may sound trivial and indeed it is, provided that we somehow let Zoya know in advance that she should take the transmitter role and Yoshi should take the role of a receiver. For example, if they have communicated in the past, then they may agree that, next time they are placed together in a dark room, Zoya takes the role of the one that starts to talk first. But, how do they know the roles if they have never communicated before? Let us explore this problem of first contact or rendezvous between two wireless nodes.
1.2.1 Hierarchy Helps to Establish Contact
In many cases the rendezvous problem can be solved by relying on a pre-established hierarchy or context. For example, in a conversation Basil can be the boss and Zoya an employee in a company that follows a (ridiculously) strict hierarchy. In that case, both of them know that Basil should start speaking and Zoya should listen before making any attempt to talk. Translating this idea of pre-established hierarchy into a wireless communication setting, Zoya can be a device/phone that wants to connect to the base station Basil. Then the phone can be preprogrammed to be in receiving mode and wait for an invite packet from a base station. Note that in this case the context breaks the symmetry between Zoya and Basil and thus pre-assigns the role that a device will have in trying to access the wireless medium. Basil can label the invite packet with his name or unique address, such that Zoya knows who sends the invite packet and can decide whether she wants to respond and connect to Basil.
In a more involved case, Zoya may be also in the communication range of another base station, named Bastian, see Figure 1.3(a). This second base station serves as an alternative to which Zoya can connect to in order to get access to the overall wired infrastructure and the internet. But what if Basil and Bastian send the invitation packets simultaneously? Then, following the rules of the collision model, Zoya experiences collision and she does not receive anything useful. An easy fix could be to have both Basil and Bastian to be part of a the same communication infrastructure, which makes it viable to assume that they can communicate and coordinate over a wired channel and thus agree not to send the invite packets simultaneously.
However, there may be cases in which Basil and Bastian cannot coordinate through the wired connection, since, for example, they belong to networks with different owners. Hence, the problem of collision over a shared medium remains. If both Basil and Bastian go on to persistently send invitation packets over regular time intervals, then it can happen that they are synchronized in an unfortunate way. This is illustrated in Figure 1.3(b), where it can be seen that Zoya will not ever receive an invitation. One quasi-solution that Zoya might contemplate would be the following. The clocks of Basil and Bastian cannot be perfectly synchronized, so if Zoya patiently waits, at some point in the future the regular packet transmissions from Basil and Bastian will avoid overlapping. We dedicate space to this quasi-solution in order to show why is it not a usable one and thereby illustrate an important engineering point. Namely, a good algorithmic design cannot rely on randomization that is not controlled in any way by the participants in the system. Instead, the (pseudo-)random choice used in the protocol should be deliberately invoked by the participating actors in the system. In this example, imperfect synchronization is due to random deficiency in the production process of the clocks and it thus represents an uncontrolled random factor.
Figure 1.3
The problem of first contact when the mobile device Zoya is in the range of two base stations, Basil and Bastian. (a) Illustration of the scenario. (b) The invite packets of Basil and Bastian are persistently colliding. (c) Solution of the problem of collision between Basil and Bastian by using randomization.
Let us now assume that the clocks of the two base stations are perfectly synchronized and they are both dividing the time into identical slots, as in Figure 1.3(c), where each slot is sufficient to send an invitation packet or receive a packet termed invitation_accepted from Zoya. Before the start of a slot, each base station flips a coin and decides randomly to transmit or stay silent in that slot. As shown in Figure 1.3(c), some invite packets will still collide, but some will be sent free of collision. Hence, the use of coin flipping leads to randomization of the transmission time between two invite packets. This randomization is the key to finalize the establishment of a contact, with high probability, within a reasonably short time.
1.2.2 Wireless Rendezvous without Help
Things get more complicated when the roles of the devices are not predefined. This is the situation in establishing ad hoc links between two devices that belong to the same hierarchical level, as in device-to-device (D2D) communication. For example, Zoya, Yoshi, and Xia can be three mobile phones that want to start communication, but have never communicated with each other before. The last assumption is important, since if Yoshi and Xia have already communicated in the past, they may have agreed who should be the one sending the invite packet next time they need to communicate. In the absence of such a context, it is impossible to predefine the roles. For example, if Zoya and Yoshi are predefined to be the ones sending invite packets, while only Xia is waiting to receive them, then Zoya and Yoshi cannot establish a link between them. The problem of first contact when devices are symmetric is exacerbated by the half-duplex nature of devices: if Zoya and Yoshi are continuously sending invitations to each other, then neither of them is able to receive the invitation from the other one.
Coin flipping again helps to resolve this situation. Let us assume that Zoya and Yoshi have a common time reference for a slotted channel, as in the case with Basil and Bastian. Achieving the required synchrony is harder to justify in this case, compared to the example in which a device establishes connection with a base station. Nevertheless, for the purpose of this example, one can assume that both Zoya and Yoshi have GPS receivers that can be used for clock synchronization. Let both Zoya and Yoshi be quiet in the
