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.”
“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.”
“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.”
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.
CAMBRIDGE UNIVERSITY PRESS
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Cambridge University Press
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Published in the United States of America by Cambridge University Press, New York
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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
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
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 |