Cambridge University Press
9781107016767 - Next Generation Wireless LANs - 802.11n and 802.11ac - Edited by Eldad Perahia and Robert Stacey
Frontmatter/Prelims

Next Generation Wireless LANs

If you’ve been searching for a way to get up to speed on IEEE 802.11n and 802.11ac WLAN standards without having to wade through the entire 802.11 specification, then look no further.

This comprehensive overview describes the underlying principles, implementation details, and key enhancing features of 802.11n and 802.11ac. For many of these features, the authors outline the motivation and history behind their adoption into the standard. A detailed discussion of the key throughput, robustness, and reliability enhancing features (such as MIMO, multi-user MIMO, 40\80\160 MHz channels, transmit beamforming, and packet aggregation) is given, in addition to clear summaries of the issues surrounding legacy interoperability and coexistence.

Now updated and significantly revised, this 2nd edition contains new material on 802.11ac throughout, including revised chapters on MAC and interoperability, as well as new chapters on 802.11ac PHY, and multi-user MIMO, making it an ideal reference for designers of WLAN equipment, network managers, and researchers in the field of wireless communication.

Eldad Perahia is a Principal Engineer in the Standards and Technology Group at Intel Corporation. He is Chair of the IEEE 802.11 Very High Throughput in 60 GHz Task Group (TGad), the IEEE 802.11 Very High Throughput in <6 GHz Task Group (TGac) Coexistence Ad Hoc Co-Chair, the IEEE 802.11 liaison from the IEEE 802.19 Wireless Coexistence Working Group, and the former Chair of the IEEE 802.11 Very High Throughout Study Group. He was awarded his Ph.D. in Electrical Engineering from the University of California, Los Angeles and holds 21 patents in various areas of wireless communications.

Robert Stacey is a Wireless Systems Architect at Apple, Inc. He is the IEEE 802.11 Very High Throughput in <6 GHz Task Group (TGac) Technical Editor and MU-MIMO Ad Hoc Co-Chair. He was a member of the IEEE 802.11 High Throughput Task Group (TGn) and a key contributor to the various proposals, culminating in the final joint proposal submission that became the basis for the 802.11n draft standard. He holds numerous patents in the field of wireless communications.


“The authors are renowned experts in the field. The book is a must read for engineers seeking knowledge of recent advances in WLAN technologies.”

Dr Osama Aboul-Magd; IEEE 802.11ac Task Group Chair.

“First edition of the book “Next Generation Wireless LANs” by Eldad and Robert is excellent and very popular. The second edition adds newly developed IEEE 802.11ac standard with the same excellence in addressing technical features and easy to read writing style.”

Vinko Erceg, Broadcom Corporation

“The 802.11 standard has been evolving for over 20 years and now contains nearly 3000 pages of information. The authors have had direct involvement in writing many of those pages. This book represents a significant accomplishment in conveying and explaining the engineering behind the features for two of the most important radio options provided by the standard. Radio engineers approaching the standard for the first time as well as those already engaged in product development will find this text remarkably rewarding.”

Bruce Kraemer, Marvell Semiconductor and Chair, IEEE 802.11 Working Group

This endorsement solely represents the views of the person who is endorsing this book and does not necessarily represent a position of either the company, the IEEE or the IEEE Standards Association.


Next Generation Wireless LANs

802.11n and 802.11ac

Edited by

Eldad Perahia

Intel Corporation

Robert Stacey

Apple Inc.


CAMBRIDGE UNIVERSITY PRESS
Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, São Paulo, Delhi, Mexico City

Cambridge University Press
The Edinburgh Building, Cambridge CB2 8RU, UK

Published in the United States of America by Cambridge University Press, New York

www.cambridge.org
Information on this title: www.cambridge.org/9781107016767

© Cambridge University Press 2008, 2013

This publication is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press.

First published 2008
Reprinted with corrections 2010

Second edition 2013

Printed in the United Kingdom at the University Press, Cambridge

A catalog record for this publication is available from the British Library

Library of Congress Cataloging-in-Publication Data

Perahia, Eldad, 1967 – author.
Next generation wireless LANs : 802.11n, 802.11ac, and Wi-Fi direct / Eldad Perahia, Intel Corporation,
Robert Stacey, Apple Inc. – Second edition.
pages cm
ISBN 978-1-107-01676-7 (hardback)
1. Wireless LANs. I. Stacey, Robert, 1967 – author. II. Title.
TK5105.78.P47 2013
621.39′8–dc23
2012033809

ISBN 978-1-107-01676-7 Hardback

Cambridge University Press has no responsibility for the persistence or accuracy of URLs for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate.


To my wife Sarah and our son Nathan

— Eldad Perahia

To my wife Celia and son Zachary

— Robert Stacey


Contents

Foreword by Dr. Andrew Myles
xv
Preface to the first edition
xix
Preface to the second edition
xxi
List of abbreviations
xxii
Chapter 1     Introduction
1
1.1           An overview of IEEE 802.11
3
1.1.1         The 802.11 MAC
3
1.1.2         The 802.11 PHYs
4
1.1.3         The 802.11 network architecture
6
1.1.4         Wi-Fi Direct
6
1.2           History of high throughput and 802.11n
7
1.2.1         The High Throughput Study Group
7
1.2.2         Formation of the High Throughput Task Group (TGn)
8
1.2.3         Call for proposals
10
1.2.4         Handheld devices
11
1.2.5         Merging of proposals
11
1.2.6         802.11n amendment drafts
11
1.3           Environments and applications for 802.11n
12
1.4           Major features of 802.11n
14
1.5           History of Very High Throughput and 802.11ac
17
1.6           Outline of chapters
20
References
22
Part I        Physical layer
25
Chapter 2     Orthogonal frequency division multiplexing
27
2.1           Background
27
2.2           Comparison to single carrier modulation
29
References
31
Chapter 3     MIMO/SDM basics
32
3.1           SISO (802.11a/g) background
32
3.2           MIMO basics
32
3.3           SDM basics
34
3.4           MIMO environment
36
3.5           802.11n and 802.11ac propagation model
38
3.5.1         Impulse response
39
3.5.2         Antenna correlation
42
3.5.3         802.11n Doppler model
45
3.5.4         802.11ac Doppler model
46
3.5.5         Physical layer impairments
47
3.5.6         Path loss
50
3.6           Linear receiver design
51
3.7           Maximum likelihood estimation
54
References
56
Appendix 3.1  802.11n channel models
57
Chapter 4     PHY interoperability with 11a/g legacy OFDM devices
62
4.1           11a packet structure review
62
4.1.1         Short Training field
62
4.1.2         Long Training field
65
4.1.3         Signal field
68
4.1.4         Data field
69
4.1.5         Packet encoding process
70
4.1.6         Receive procedure
72
4.2           Mixed format high throughput packet structure
74
4.2.1         Non-HT portion of the MF preamble
75
4.2.2         HT portion of the MF preamble
81
4.2.3         Data field
88
4.2.4         HT MF receive procedure
96
References
102
Appendix 4.1  20 MHz basic MCS tables
103
Chapter 5     High throughput
105
5.1           40 MHz channel
105
5.1.1         40 MHz subcarrier design and spectral mask
106
5.1.2         40 MHz channel design
108
5.1.3         40 MHz mixed format preamble
108
5.1.4         40 MHz data encoding
113
5.1.5         MCS 32: high throughput duplicate format
116
5.1.6         20/40 MHz coexistence with legacy in the PHY
119
5.1.7         Performance improvement with 40 MHz
120
5.2           20 MHz enhancements: additional data subcarriers
121
5.3           MCS enhancements: spatial streams and code rate
122
5.4           Greenfield (GF) preamble
127
5.4.1         Format of the GF preamble
128
5.4.2         PHY efficiency
130
5.4.3         Issues with GF
130
5.4.4         Preamble auto-detection
134
5.5           Short guard interval
136
References
140
Appendix 5.1  Channel allocation
141
Appendix 5.2  40 MHz basic MCS tables
141
Appendix 5.3  Physical layer waveform parameters
146
Chapter 6     Robust performance
147
6.1           Receive diversity
147
6.1.1         Maximal ratio combining basics
148
6.1.2         MIMO performance improvement with receive diversity
149
6.1.3         Selection diversity
152
6.2           Spatial expansion
152
6.3           Space-time block coding
152
6.3.1         Alamouti scheme background
153
6.3.2         Additional STBC antenna configurations
156
6.3.3         STBC receiver and equalization
159
6.3.4         Transmission and packet encoding process with STBC
161
6.4           Low density parity check codes
164
6.4.1         LDPC encoding process
165
6.4.2         Effective code rate
175
6.4.3         LDPC coding gain
176
References
177
Appendix 6.1  Parity check matrices
177
Chapter 7     Very High Throughput PHY
182
7.1           Channelization
182
7.2           Single user (SU) VHT packet structure
184
7.3           VHT format preamble
185
7.3.1         Non-VHT portion of the VHT format preamble
185
7.3.2         VHT portion of the VHT format preamble
191
7.3.3         VHT data field
200
7.4           Modulation coding scheme
212
References
217
Part II       Medium access control layer
219
Chapter 8     Medium access control
221
8.1           Protocol layering
222
8.2           Finding, joining, and leaving a BSS
223
8.2.1         Beacons
223
8.2.2         Scanning
224
8.2.3         Authentication
224
8.2.4         Association
225
8.2.5         Reassociation
226
8.2.6         Disassociation
226
8.2.7         802.1X Authentication
226
8.2.8         Key distribution
227
8.3           Distributed channel access
228
8.3.1         Basic channel access timing
229
8.4           Data/ACK frame exchange
231
8.4.1         Fragmentation
232
8.4.2         Duplicate detection
233
8.4.3         Data/ACK sequence overhead and fairness
234
8.5           Hidden node problem
234
8.5.1         Network allocation vector (NAV)
235
8.5.2         EIFS
236
8.6           Enhanced distributed channel access
236
8.6.1         Transmit opportunity
238
8.6.2         Channel access timing with EDCA
239
8.6.3         EDCA access parameters
239
8.6.4         EIFS revisited
240
8.6.5         Collision detect
240
8.6.6         QoS Data frame
241
8.7           Block acknowledgement
241
8.7.1         Block data frame exchange
243
8.8           Power management
243
8.8.1         AP TIM transmissions
244
8.8.2         PS mode operation
244
8.8.3         WNM-Sleep
246
8.8.4         SM power save
246
8.8.5         Operating Mode Notification
246
References
247
Chapter 9     MAC throughput enhancements
248
9.1           Reasons for change
248
9.1.1         Throughput without MAC changes
248
9.1.2         MAC throughput enhancements
250
9.1.3         Throughput with MAC efficiency enhancements
251
9.2           Aggregation
253
9.2.1         Aggregate MSDU (A-MSDU)
254
9.2.2         Aggregate MPDU (A-MPDU)
255
9.2.3         Aggregate PSDU (A-PSDU)
257
9.2.4         A-MPDU in VHT PPDUs
258
9.2.5         VHT single MPDU
259
9.3           Block acknowledgement
259
9.3.1         Immediate and delayed block ack
259
9.3.2         Block ack session initiation
260
9.3.3         Block ack session data transfer
261
9.3.4         Block ack session tear down
262
9.3.5         Normal ack policy in a non-aggregate
262
9.3.6         Reorder buffer operation
263
9.4           HT-immediate block ack
264
9.4.1         Normal Ack policy in an aggregate
264
9.4.2         Compressed block ack
265
9.4.3         Full state and partial state block ack
265
9.4.4         HT-immediate block ack TXOP sequences
269
9.5           HT-delayed block ack
269
9.5.1         HT-delayed block ack TXOP sequences
270
References
270
Chapter 10    Advanced channel access techniques
271
10.1          PCF
271
10.1.1        Establishing the CFP
271
10.1.2        NAV during the CFP
272
10.1.3        Data transfer during the CFP
272
10.1.4        PCF limitations
273
10.2          HCCA
274
10.2.1        Traffic streams
274
10.2.2        Controlled access phases
276
10.2.3        Polled TXOP
276
10.2.4        TXOP requests
277
10.2.5        Use of RTS/CTS
277
10.2.6        HCCA limitations
277
10.3          Reverse direction protocol
277
10.3.1        Reverse direction frame exchange
278
10.3.2        Reverse direction rules
279
10.3.3        Error recovery
279
10.4          PSMP
280
10.4.1        PSMP recovery
281
10.4.2        PSMP burst
281
10.4.3        Resource allocation
282
10.4.4        Block ack usage under PSMP
283
References
283
Chapter 11    Interoperability and coexistence
284
11.1          Station capabilities and operation
284
11.1.1        HT station PHY capabilities
285
11.1.2        VHT station PHY capabilities
285
11.1.3        HT station MAC capabilities
286
11.1.4        VHT station MAC capabilities
286
11.1.5        Advanced capabilities
286
11.2          BSS operation
287
11.2.1        Beacon transmission
288
11.2.2        20 MHz BSS operation
289
11.2.3        20/40 MHz HT BSS operation
289
11.2.4        VHT BSS operation
293
11.2.5        OBSS scanning requirements
294
11.2.6        Signaling 40 MHz intolerance
298
11.2.7        Channel management at the AP
299
11.2.8        Establishing a VHT BSS in the 5 GHz band
300
11.3          A summary of fields controlling 40 MHz operation
300
11.4          Channel access in wider channels
301
11.4.1        Overlapping BSSs
302
11.4.2        Wide channel access using RTS/CTS
303
11.4.3        TXOP rules for wide channel access
304
11.4.4        Clear channel assessment
304
11.4.5        NAV assertion in an HT and VHT BSS
306
11.5          Protection
306
11.5.1        Protection with 802.11b stations present
307
11.5.2        Protection with 802.11g or 802.11a stations present
307
11.5.3        Protection for OBSS legacy stations
308
11.5.4        RIFS burst protection
308
11.5.5        HT Greenfield format protection
309
11.5.6        RTS/CTS protection
309
11.5.7        CTS-to-Self protection
310
11.5.8        Protection using a non-HT, HT mixed, or VHT PPDU with non-HT response
311
11.5.9        Non-HT station deferral with HT mixed and VHT format PPDUs
311
11.5.10       L-SIG TXOP protection
312
11.6          Phased coexistence operation (PCO)
314
11.6.1        Basic operation
314
11.6.2        Minimizing real-time disruption
315
References
316
Chapter 12    MAC frame formats
317
12.1          General frame format
317
12.1.1        Frame Control field
317
12.1.2        Duration/ID field
321
12.1.3        Address fields
321
12.1.4        Sequence Control field
321
12.1.5        QoS Control field
322
12.1.6        HT Control field
324
12.1.7        Frame Body field
327
12.1.8        FCS field
327
12.2          Format of individual frame types
327
12.2.1        Control frames
327
12.2.2        Data frames
336
12.2.3        Management frames
337
12.3          Management frame fields
342
12.3.1        Fields that are not information elements
344
12.3.2        Information elements
344
References
361
Part III      Transmit beamforming, multi-user MIMO, and fast link adaptation
363
Chapter 13    Transmit beamforming
365
13.1          Singular value decomposition
366
13.2          Transmit beamforming with SVD
369
13.3          Eigenvalue analysis
370
13.4          Unequal MCS
376
13.5          Receiver design
378
13.6          Channel sounding
379
13.7          Channel state information feedback
381
13.7.1        Implicit feedback
382
13.7.2        Explicit feedback
386
13.8          Improved performance with transmit beamforming
393
13.9          Degradations
399
13.10         MAC considerations
406
13.10.1       Sounding PPDUs
407
13.10.2       Implicit feedback beamforming
410
13.10.3       Explicit feedback beamforming
413
13.11         Comparison between implicit and explicit
416
13.12         Transmit beamforming in 802.11ac
417
13.12.1       VHT sounding protocol
418
References
419
Appendix 13.1 Unequal MCS for 802.11n
420
Unequal MCS for 20 MHz
420
Unequal MCS for 40 MHz
422
Chapter 14    Multi-user MIMO
424
14.1          MU-MIMO pre-coding
426
14.2          Receiver design
427
14.3          PHY considerations
428
14.3.1        VHT MU preamble
430
14.3.2        VHT MU data field
432
14.3.3        Compressed beamforming matrices
435
14.4          Group ID
435
14.4.1        Receive operation
435
14.4.2        Group ID management
435
14.5          MAC support for MU-MIMO
436
14.5.1        MU aggregation
436
14.5.2        MU acknowledgements
437
14.5.3        EDCA TXOPs for MU sequences
437
14.5.4        TXOP sharing
438
14.6          VHT sounding protocol for MU-MIMO
438
14.6.1        The basic sounding exchange
438
14.6.2        Support for fragmentation
439
References
439
Chapter 15    Fast link adaption
440
15.1          MCS feedback
441
15.2          MCS feedback mechanisms
442
15.3          MCS feedback using the HT variant HT Control field
442
15.4          MCS feedback using the VHT variant HT Control field
443
Index
445



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