Next Generation Wireless LANs If you’ve been searching for a way to get up to speed quickly on IEEE 802.11n without having to wade through the entire standard, then look no further This comprehensive overview describes the underlying principles, implementation details, and key enhancing features of 802.11n 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, 40 MHz channels, and packet aggregation) is given, in addition to a clear summary of the issues surrounding legacy interoperability and coexistence Advanced topics such as beamforming and fast link adaption are also covered With numerous MAC and physical layer examples and simulation results included to highlight the benefits of the new features, this is an ideal reference for designers of WLAN equipment, and network managers whose systems adopt the new standard It is also a useful distillation of 802.11n technology for graduate students and researchers in the field of wireless communication Eldad Perahia is a member of the Wireless Standards and Technology group at Intel Corporation, Chair of the IEEE 802.11 Very High Throughput Study Group, and the IEEE 802.11 liaison to IEEE 802.19 Prior to joining Intel, Dr Perahia was the 802.11n lead for Cisco Systems He was awarded his Ph.D in Electrical Engineering from the University of California, Los Angeles, and has fourteen patents in various areas of wireless communications Robert Stacey is a member of the Wireless Standards and Technology group at Intel Corporation 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, and has numerous patents filed in the field of wireless communications Next Generation Wireless LANs Throughput, Robustness, and Reliability in 802.11n ELDAD PERAHIA AND ROBERT STACEY CAMBRIDGE UNIVERSITY PRESS Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, São Paulo 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/9780521885843 © Cambridge University Press 2008 This publication is in copyright Subject to statutory exception and to the provision of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press First published in print format 2008 ISBN-13 978-0-511-43823-3 eBook (NetLibrary) ISBN-13 978-0-521-88584-3 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 father, who nurtured and guided an inquiring mind – Robert Stacey Brief contents Foreword by Dr Andrew Myles Preface List of abbreviations Introduction page xix xxiii xxv Part I Physical layer Orthogonal frequency division multiplexing 23 MIMO/SDM basics 29 PHY interoperability with 11a/g legacy OFDM devices 58 High throughput 101 Robust performance 142 Part II Medium access control layer Medium access control 181 MAC throughput enhancements 203 Advanced channel access techniques 225 10 Interoperability and coexistence 238 11 MAC frame formats 266 Part III Transmit beamforming 12 Transmit beamforming 307 Index 368 Contents Foreword by Dr Andrew Myles Preface List of abbreviations Introduction 1.1 History of IEEE 802.11 1.2 History of high throughput and 802.11n 1.2.1 The High Throughput Study Group 1.2.2 Formation of the High Throughput Task Group (TGn) 1.2.3 Call for proposals 1.2.4 Handheld devices 1.2.5 Merging of proposals 1.2.6 802.11n amendment drafts 1.3 Environments and applications for 802.11n 1.4 Major features of 802.11n 1.5 Outline of chapters References xix xxiii xxv 5 10 10 11 15 17 19 Part I Physical layer Orthogonal frequency division multiplexing 2.1 Background 2.2 Comparison to single carrier modulation References MIMO/SDM basics 3.1 3.2 3.3 3.4 3.5 SISO (802.11a/g) background MIMO basics SDM basics MIMO environment 802.11n propagation model 3.5.1 Impulse response 23 23 25 27 29 29 29 31 33 35 36 Index Block Acknowledgement Request (BAR) Acknowledgement Policy subfield, 277 Block Acknowledgement Request (BAR) Control field, 277 Block Acknowledgement Request Acknowledgement Policy subfield, 277 Multi-traffic Identifier subfield, 277 Starting Sequence Control field, 277 block acknowledgement session data transfer, 215 block acknowledgement session initiation, 213–15 block acknowledgement sessions, delayed, 214 immediate, 214 block acknowledgement session tear down, 215–16 block acknowledgement timeout value, 214 block data frame exchange, 201–2 block data transfer, mechanisms, 200–1 BPSK (binary phase shift keying), 64, 67, 70, 78, 317–18 Broadcom, 2–3 BSSID (BSS identifier), 184 BSSs see basic service sets (BSSs) Buffer Size field, 214 Buffer State Indicated subfield, 272–3 burst protection, reduced interframe space, 259 calibration errors, 347–50 implicit feedback beamforming, 352–4 null data packets for, 351 transmit beamforming, 325–7, 345–6 Calibration Control subfields, 275 calibration exchange, 353 using null data packets, 353–4 Calibration Position field, 273–5 Calibration Sequence field, 273–5 Capability Information field, 288–9 CAPs see controlled access phases (CAPs) carrier sense multiple access with collision avoidance (CSMA/CA), 4, 181 carrier sense, 186 mechanisms, 185 principles, 181 carrier sense multiple access with collision detect (CSMA/CD), 3–4, 181 carrier sense multiple access (CSMA), 3–4 CCA see clear channel assessment (CCA) CCDF (complementary cumulative distribution function), 34 CCK see complementary code keying (CCK) CF-Ack see contention free acknowledgement (CF-Ack) CF-End (contention free end), frame format, 281 CFPMaxDuration parameter, 226 CF-Poll see contention free poll (CF-Poll) CFPs see contention free periods (CFPs) 371 channel access priorities, 197 channel allocation, 135–9 20 MHz channels, 101, 136 40 MHz channels, 101, 137, 138 channel estimation, 62 generation, 68 multiple-input, multiple-output, 94–6 noise reduction, 64 channel fading coefficient, 29 channel management, at access points, 253–4 channel models, 36 A, 36, 52 B, 36, 53, 120, 132, 144, 145, 148, 149, 151, 152 C, 53 D, 36, 54, 74, 75, 121, 128, 133 development, 35–6 E, 36, 55, 122, 134 F, 41–2, 56, 57 IEEE 802.11n, 52 K-factor, 37–8 overview, 36 channel sounding PHY protocol data units, 350 transmit beamforming, 321–3 see also staggered sounding channel state information (CSI) feedback, 323–34, 355–6 explicit, 328–34 implicit, 323–8 Channel State Information (CSI)/Steering field, 273–5 Channel Switch Announcement elements, 253–4 Channel Switch Announcement frames, 253–4 Channel Switch Count field, 254, 288–90 Channel Switch Mode field, 288–90 clear channel assessment (CCA), 185, 245–6 in 20 MHz channels, 247 in 40 MHz channels, 247 clear to send (CTS), 193 frame format, 276 usage, 231 cluster models, 36 code rate, modulation and coding schemes, 116–21 code words number of, 161–3 size of, 161–3 coexistence, 19, 238–65 20 MHz channels, 241–54 20/40 MHz stations, 102–4, 114, 241–54 basic service sets, 238–40 phased coexistence operation, 255–7 protection mechanisms, 257–65 stations, 238–40 see also phased coexistence operation (PCO) collision detect, 199 and transmit opportunity, 199 372 Index communication systems, basics, 29 complementary code keying (CCK), 40 MHz, 238–40 complementary cumulative distribution function (CCDF), 34 compressed beamforming, 355–6 weights, explicit feedback, 330–4, 345 Compressed Beamforming Action frames, 356 compressed beamforming matrices, angles, 334 compressed bitmaps, 277, 279–80 contention-based access protocol, 18–19 contention free acknowledgement (CF-Ack), 227 frame format, 281 contention free end (CF-End), frame format, 281 contention free periods (CFPs), 225–6 CFPMaxDuration parameter, 226 data transfer during, 226–7 establishment, 225–6 length, 226 network allocation vector during, 226 repetition intervals, 225–6 contention free poll (CF-Poll), 227, 230–1, 289, 290 contention free poll request, 289, 290 contention window (CW), 188, 195–6 control frames, format, 276–81 controlled access phases (CAPs), 230 hybrid coordinated channel access function, 230 control wrapper frame, 267 format, 281 correlation coefficient, antenna correlation, 39–41 CRCs (cyclic redundancy checks), High Throughput Signal field, 79–80, 93 CSI (Channel State Information)/Steering field, 273–5 CSMA/CA see carrier sense multiple access with collision avoidance (CSMA/CA) CSMA (carrier sense multiple access), 3–4 CSMA/CD (carrier sense multiple access with collision detect), 3–4, 181 CTS see clear to send (CTS) CTS-to-self overhead, 261 protection, 261 CW (contention window), 188, 195–6 cyclic permutation matrices, 173 cyclic redundancy checks (CRCs), High Throughput Signal field, 79–80, 93 cyclic shifts, 73, 82 legacy devices, 73 mixed format preamble, legacy portion, 72–3, 75 DA (destination address), 184 Data/ACK frame exchange, 189–92 data transfer, 189–90 duplication detection, 191–2 fairness, 192 fragmentation, 191 sequence overhead, 192 Data field, 65–6 bit string, 84 cyclic shifts, 82 definition, 65 descrambling, 70 encoding, 85 interleaving, 86–7 in mixed format high throughput packet structure, 84–91 modulation mapping, 87 pilot subcarriers, 88, 96 receive processing, 68 reception, 96–7 block diagram, 69 scrambling, 85 space-time block coding, 158–9 spatial expansion, 89, 91 stream parsing, 85–6 structure, 65–6 transmission in 20 MHz high throughput format, 88–9 block diagram, 66 see also high throughput data field (HT-DATA), Data frames, format, 282 data subcarriers, additional, 116 data transfer during contention free periods, 226–7 traffic streams, 229 DCF (distributed coordination function), 40, 185–6, 225 DCF interframe space (DIFS), 185, 188 deauthentication frame, format, 284 degradation and feedback overhead, 345 and quantization, 343–4 sources, 345–6 transmit beamforming, 342–9 zero-forcing receivers, 51 see also interference; noise delayed block acknowledgement, 200, 213 see also high throughput delayed block acknowledgement DELBA Request, 200, 213 delivery traffic indication message (DTIM), 225–6 destination address (DA), 184 DIFS (DCF interframe space), 185, 188 Direct Link Session (DLS) Action frames, 285–6 direct sequence spread spectrum (DSSS), 4, 260, 261 40 MHz, 238–40 disassociation, 185 Disassociation frame, format, 284 Index distributed channel access, 185–9 basic channel access timing, 186–9 see also enhanced distributed channel access (EDCA) distributed coordination function (DCF), 40, 185–6, 225 distribution systems (DSs), 11, 183, 267 concept of, 12 DLS (Direct Link Session) Action frames, 285–6 Doppler model, 41–2, 342–5 modified, for channel model F, 41–2 Doppler spectra, 41–3 DSSS see direct sequence spread spectrum (DSSS) DTIM (delivery traffic indication message), 225–6 Duration/ID field, 270 EDCA see enhanced distributed channel access (EDCA) EIFS see extended interframe space (EIFS) eigenvalue analysis, transmit beamforming, 312–16 End of Service Period (EOSP), subfield, 271 enhanced distributed channel access (EDCA), 194–9, 225 access categories, 194–5 access functions, 195 access parameters, 197–8 channel access timing, 197 collision detect, 199 implementation, 196 transmit opportunity, 197, 233–4 Enhanced Wireless Consortium (EWC), establishment, 10 enterprise environments, 11–12 enterprise usage model, 13 concept of, 14 EOSP see End of Service Period (EOSP) equalizers multiple-input, multiple-output/spatial division multiplexing systems, 33 single-input, single-output systems, 33 weights, 47–8 see also zero-forcing (ZF) equalizers error recovery, 234 error vector magnitude (EVM), 44–5 ESSs see extended service sets (ESSs) Ethernet, 3–4 channel access protocol, 181 wireless, 181 EVM (error vector magnitude), 44–5 EWC (Enhanced Wireless Consortium) establishment, 10 explicit feedback, 358–9 channel state information, 328–34 compressed beamforming weights, 330–4, 345 non-compressed beamforming weights, 329, 344 explicit feedback beamforming, 355–8 373 sequences, 357 extended channel switch announcement elements, 254, 288–90 Extended Channel Switch Announcement frames, 254 Extended Channel Width Switch Announcement element, 255 extended interframe space (EIFS), 194, 198 usage, 195 extended service sets (ESSs), 11, 183 concept of, fast Fourier transforms (FFTs), 24–5, 27, 29 inverse, 27 fast link adaptation, 19 and modulation and coding scheme feedback, 361 and packet error rate, 359–60 and transmit beamforming, 359 FCC see Federal Communications Commission (FCC) FCS (frame check sequence), 194 FCS (Frame Check Sequence) field, 275 FDM see frequency division multiplexing (FDM) Federal Communications Commission (FCC) (US), 1, feedback channel state information, 355–6 explicit, 328–34, 344, 358–9 overhead and degradation, 345 explicit vs implicit, 359 see also explicit feedback; implicit feedback FFTs see fast Fourier transforms (FFTs) FHSS (frequency hopped spread spectrum), file transfer protocol (FTP), 232 Fourier transforms, 23–4 see also fast Fourier transforms (FFTs) fragment burst, 191 Frame Body field, 275 frame check sequence (FCS), 194 Frame Check Sequence (FCS) field, 275 Frame Control field, 266–70 Action Management frame, 267 Control Wrapper frame, 267 From Distribution System field, 267, 269 To Distribution System field, 267, 269 More Data field, 269 More Fragments field, 267 Order field, 269–70 Power Management field, 269 Protected Frame field, 269 Protocol Version field, 266 Retry field, 267 Subtype field, 266–8 Type field, 266–8 374 Index frequency division multiplexing (FDM) principles, 23 waveforms, 24 see also multiple-input, multiple-output/orthogonal frequency division multiplexing (MIMO/OFDM) systems; orthogonal frequency division multiplexing (OFDM) frequency hopped spread spectrum (FHSS), From Distribution System field, 267, 269 FTP (file transfer protocol), 232 full state block acknowledgement, 219–22 operation, 219 gain error distortion, 346 Gaussian distribution, 29 GF-HT-SIG see Greenfield High Throughput Signal field (GF-HT-SIG) GF-HT-STF see Greenfield High Throughput Short Training field (GF-HT-STF) GF preambles see Greenfield (GF) preambles GIs see guard intervals (GIs) Givens rotation matrix, 330–4 goodput, definition, 7–8 Greenfield deployments, use of term, 121–2 Greenfield format PHY protocol data units, 238–9 Greenfield (GF) preambles, 15, 18, 121–3 auto-detection, 129–31 format, 122–5 implementation issues, 129 interoperability issues, 127–30 issues, 125 length, 125 and network efficiency, 125–7 and physical layer efficiency, 125 protection, 259–60 space-time block coding, 159 throughput improvement, 127 timing, 129–30 transmit time, 130–1 Greenfield High Throughput Short Training field (GF-HT-STF) spatial streams, 123 waveform, 122–3 Greenfield High Throughput Signal field (GF-HT-SIG), 123–4 waveforms, 124 guard intervals (GIs), 23–4 short, 18, 131–5, 238–9 handheld devices, 9–10 Wi-Fi, HCCA function see hybrid coordinated channel access (HCCA) function HCF (hybrid coordination function), 228 Hertz, Heinrich Rudolf (1857–94), hidden node problem, 192–4 network allocation vector, 193 Highest Priority Buffered Access Category subfield, 272–3 high throughput (HT), 18, 101–39 40 MHz channel, 101–16 historical background, 5–11 packet formats, 70 High Throughput (HT) Action frames, 285, 287 High Throughput (HT) Capabilities elements, 238, 240, 290–1 advanced, 240 High Throughput (HT) Capabilities Information field, 290, 292 High Throughput (HT) Extended Capabilities field, 290, 293 high throughput control (HTC), 239 High Throughput Control field, 270, 273–5 Access Category Constraint field, 273–5 Antenna Selection Control subfield, 273–5 Calibration Control subfields, 275 Calibration Position field, 273–5 Calibration Sequence field, 273–5 Channel State Information/Steering field, 273–5 Link Adaptation Control field, 273–5 MAI subfields, 273–5 modulation and coding scheme feedback using, 361 Null Data Packet Announcement subfield, 273–5 RGD/More PPDU field, 273–5 High Throughput Data field (HT-DATA), 88–9 transmitter block diagram, 85, 109 waveform equations, 106–7 high throughput delayed block acknowledgement, 213, 223–4, 239 transmit opportunity sequences, 224 high throughput duplicate format 40 MHz channels, 111–14, 140 waveforms, 113–14 high throughput immediate block acknowledgement, 213, 217–23 normal acknowledgement policy, 217–18 transmit opportunity sequences, 222–3 High Throughput Information element, 291, 298, 299 High Throughput Long Training field (HT-LTF), 77, 82–4 construction, 83 cyclic shifts, 82 legacy portion, 113–14 receive procedures, 94–6 space-time block coding, 158 subcarrier sequence, 107 Index symbols, 82–4, 322–3 waveform equations, 106–7 high throughput protection, 240–1 field encoding, 240–1 High Throughput Short Training field (HT-STF), 77, 81–2 cyclic shifts, 82 receive procedures, 94–6 space-time block coding, 157 subcarrier sequence, 107 time domain waveforms, 82 waveform equations, 106–7 see also Greenfield High Throughput Short Training field (GF-HT-STF) High Throughput Signal field (HT-SIG), 77–81 auto-detection algorithms, 80–1 binary convolution encoding, 80 cyclic redundancy checks, 79–80, 93 data subcarrier constellations, 80 decoding, 104–5, 321 format, 78 legacy portion, 113–14 modulation and coding schemes, 78 receive procedures, 93–4 space-time block coding, 157–8 symbols, 80 transmission, block diagram, 77 and transmit beamforming, 78–9 waveform equations, 105–6 see also Greenfield High Throughput Signal field (GF-HT-SIG) high throughput stations, medium access control capabilities, 239 physical layer capabilities, 238–9 High Throughput Study Group (HTSG), 5–6 criteria forms, establishment, High Throughput Task Group (TGn) comparison criteria, definitions, establishment, formation, 6–8 functional requirements, proposals, 8–9 merging, 10 teams, hotspot environments, 11–12 hotspot usage model, 13–15 HT see high throughput (HT) HT Capabilities elements see High Throughput (HT) Capabilities elements HTC (high throughput control), 239 HT-DATA see High Throughput Data field (HT-DATA) HT (High Throughput) Action frames, 285, 287 375 HT-LTF see High Throughput Long Training field (HT-LTF) HTSG see High Throughput Study Group (HTSG) HT-SIG see High Throughput Signal field (HT-SIG) HT-STF see High Throughput Short Training field (HT-STF) HTTP see hypertext transfer protocol (HTTP) hybrid coordinated channel access (HCCA) function, 19, 225, 228–32, 234 advantages, 228 controlled access phases, 230 limitations, 231–2 polled transmit opportunity, 230–1 traffic streams, 228–30 hybrid coordination function (HCF), 228 hypertext transfer protocol (HTTP), 232 IBSS (independent basic service set), 183 IEEE 802.11, 1, 181 adoption, completion, 3–4 historical background, quality of service, IEEE 802.11a, 24–5 development, 4–5 packet structure, 58–9 protection, 258–9 sampling rate, 23 transmit waveform, 59 IEEE 802.11b, devices, 4–5 protection, 258 IEEE 802.11e, 7, 18–19, 203 block acknowledgement, 212 IEEE 802.11g development, protection, 258–9 IEEE 802.11 MAC, 3–4, IEEE 802.11n amendment drafts, 10–11 applications, 11–15 backward compatibility, 58 channel models, 52 coexistence, 238–65 drafts, 2–3 environments, 11–15 goodput, handheld devices, high input amendment, 101 historical background, 5–11 interoperability, 238–65 link robustness, 142 major features, 15–17 market segmentation, 238 operating modes, 376 Index IEEE 802.11n (cont.) primary environments, 11–12 propagation model, 35–47 robustness improvements, 15 scanning issues, 252–3 transmit beamforming, 307 IEEE 802.3, 181 IEEE see Institute of Electrical and Electronic Engineers (IEEE) IFFTs (inverse fast Fourier transforms), 27 immediate block acknowledgement, 200, 213, 220 see also high throughput immediate block acknowledgement implementation margin, determination, 117–18 implicit beamforming sequences, 354 implicit feedback, 323–8, 347–50, 358–9 early studies, 323–4 sequences using, 354–5 implicit feedback beamforming, 348–55 calibration, 352–4 relaxed timing, 355 sequences, 354 impulse response, 36–8 independent basic service set (IBSS), 183 industrial, scientific and medical (ISM) radio bands, infrared (IR), infrastructure basic service sets, 183 Institute of Electrical and Electronic Engineers (IEEE), see also IEEE 802.11 interference inter-symbol, 23–4 out-of-band, 103–4 and reciprocity, 324 see also adjacent channel interference Internet, free access, 1–2 interoperability, 238–65 20 MHz channels, 241–54 20/40 MHz stations, 241–54 basic service sets, 238–40 Greenfield preambles, 127–30 medium access control, 19 phased coexistence operation, 255–7 physical layers, 18, 58–100 protection mechanisms, 257–65 stations, 238–40 inter-symbol interference (ISI), 23–4 inverse fast Fourier transforms (IFFTs), 27 IR (infrared), ISI (inter-symbol interference), 23–4 ISM (industrial, scientific and medical) radio bands, K-factor, 38 channel models, 37–8 Ricean, 36–7, 47 LANs (local area networks), standards, 3–4 LAPACK, 311 L_DATARATE, 262–3 LDPC see low density parity check (LDPC) legacy devices, 128 compatibility issues, 122, 238 cyclic shifts, 73 orthogonal frequency division multiplexing, 73 Legacy Long Training field (L-LTF), 70–1, 76 applications, 71 symbols, 123 transmission, 114 waveform equations, 105–6 legacy preambles, 71–2, 92–3 interoperability issues, 127–9 timing, 81, 129–30 Legacy Short Training field (L-STF), 70–1, 75–6 applications, 71 power, 72–4 transmission, 114 transmission issues, 72 waveform equations, 105–6 Legacy Signal field (L-SIG), 70–1, 76–7 data subcarrier constellations, 80 decoding, 71, 104 parity bits, 93 protection, 264 transmission, 114 transmission block diagram, 77 waveform equations, 105–6 Legacy Signal field transmit opportunity (L-SIG TXOP) protection, 239, 263–5 disadvantages, 265 full support, 240–1 legacy stations, protection, 259 linear receiver design, 47–9 line-of-sight (LOS) paths, 36–7, 47 link adaptation processes, 359–60 see also fast link adaptation Link Adaptation Control field, 273–5 link budgets, 111–13 link robustness, 142 LLC (logical link control), 3, 182 L_LENGTH, 262–3 L-LTF, see Legacy Long Training field (L-LTF) local area networks (LANs), standards, 3–4 logical link control (LLC), 3, 182 Long Training field (LTF), 58, 61–4 and channel estimation, 62, 68 correlation, 61–3 definition, 61 Index see also High Throughput Long Training field (HT-LTF); Legacy Long Training field (L-LTF) Lorentz, Hendrik Antoon (1853–1928), 323–4 LOS (line-of-sight) paths, 36–7, 47 low density parity check (LDPC) and binary convolution code compared, 171 code bit repetition, 168–9 codes, 15, 142, 159–72 discovery, 159 code words number of, 161–3 size of, 161–3 coding, 238–9 coding gain, 172 effective code rate, 170–1 encoding, 18, 79 process, 160–70 parity bits generation, 164 puncturing, 167–8 shortening zero bits, number of, 163–4 stream parsing, 170 symbol packing, 166–9 L-SIG, see Legacy Signal field (L-SIG) L-SIG TXOP protection see Legacy Signal field transmit opportunity (L-SIG TXOP) protection L-STF see Legacy Short Training field (L-STF) LTF see Long Training field (LTF) MAC see medium access control (MAC) MAC frame formats see Medium Access Control (MAC) frame formats MAC protocol data units (MPDUs), 182 spacing constraints, 211–12 see also aggregate MAC protocol data units (A-MPDUs) MAC service data units (MSDUs), 7–8, 182, 200–1 fragmentation, 191 reorder buffer behavior, 217 retransmission attempts, 190 see also aggregate MAC service data units (A-MSDUs) MAI subfields, 273–5 Management frames fields, 288–302 information elements, 288–302 non-information elements, 288 format, 282–8 MANs (metropolitan area networks), standards, Marconi, Guglielmo (1874–1937), margin relative to minimum sensitivity, 118–19 market segmentation, 238 MATLAB, 11, 311 377 matrix notation, 32 maximal-ratio combining (MRC) basics, 143–4 receivers, 30–1, 142 maximum likelihood (ML) decoding, advantages, 50–1 disadvantages, 51 estimation, 49–51, 69–70 sub-optimal implementations, 51 MCSs see modulation and coding schemes (MCSs) mean-square-error (MSE), 47–8 and zero-forcing algorithm compared, 48 medium access control (MAC), 3–4, 6, 12, 181–202, 301 block acknowledgement protocol, 199–202 changes, 19 throughput without, 203–5 characteristics, 16–17 coexistence, 19 criteria, Data/ACK frame exchange, 189–92 distributed channel access, 185–9 efficiency, 15, 204, 208 decrease, 203 improvements, 205 efficiency enhancements, 206–7 Enhanced Distributed Channel Access, 194–9 enhancements, 17, 207, 208 functions, 181 hidden node problem, 192–4 interoperability, 19 management functions, 183–5 association, 184–5 authentication, 184 beacons, 183 disassociation, 185 reassociation, 185 scanning, 183–4 network simulations, 36 overview, 18–19 power efficiency, 225 protocol layering, 182–3 Response frames, 187 simulations, 125–6 throughput, throughput enhancements, 203–24 aggregation, 19, 207–12 block acknowledgement, 212–17 overview, 205–6 reasons, 203–7 and transmit beamforming, 349–58 Medium Access Control (MAC) frame formats, 19, 266–302 Address fields, 270 Control frames, 276–81 378 Index Medium Access Control (MAC) (cont.) Data frames, 282 Duration/ID field, 270 Frame Body field, 275 Frame Check Sequence field, 275 Frame Control field, 266–70 general, 266–75 High Throughput Control field, 273–5 individual types, 276–88 Management frames fields, 288–302 format, 282–8 Quality of Service Control field, 271–3 Sequence Control field, 270 metropolitan area networks (MANs), standards, MF see mixed format (MF) MFB see modulation and coding scheme feedback (MFB) MF preamble see mixed format (MF) preamble MIMO see multiple-input, multiple-output (MIMO) MIMO/OFDM systems see multiple-input, multiple-output/orthogonal frequency division multiplexing (MIMO/OFDM) systems MIMO receivers see multiple-input, multiple-output (MIMO) receivers MIMO/SDM systems see multiple-input, multiple-output/spatial division multiplexing (MIMO/SDM) systems MIMO systems see multiple-input, multiple-output (MIMO) systems minimum mean-square-error (MMSE) estimate, 47–8 signal-to-noise ratio, 48 minimum mean-square-error (MMSE) receivers, capacity, 48–50 filtering, 320–1 limitations, 50–1 signal-to-noise ratio, 49, 312–14 mixed format (MF), 18, 58 two spatial streams, 71 mixed format (MF) preamble, 71 40 MHz channels, 104–9 auto-detection, 129 high throughput portion, 70, 77–84 legacy portion, 70–7, 104, 106–7, 113–14 compatibility, 73 cyclic shifts, 72–3, 75 receive procedures, 93 transmission, 71–2 null data packets, 322 structure, 64–5 timing, 81, 129–30 mixed format high throughput packet structure, 70–98 data field, 84–91 mixed format preamble, high throughput portion, 70, 77–84 non-high throughput portion, 70–7 receive procedures, 91–8 decoding, 97 deinterleaving, 97 demapping, 97 descrambling, 97 legacy portion, 93 RF front end, 92–3 ML see maximum likelihood (ML) MMSE estimate see minimum mean-square-error (MMSE) estimate MMSE receivers see minimum mean-square-error (MMSE) receivers mobile handsets Wi-Fi, worldwide shipments, modulation and coding scheme feedback (MFB), and fast link adaptation, 361 using High Throughput Control field, 361 modulation and coding scheme feedback sequence identifier (MFSI), 362 modulation and coding scheme request (MRQ), 362 modulation and coding schemes (MCSs), 18, 78 20 MHz basic rates, 98–100, 318 40 MHz channels, 102, 109, 111–14, 139, 140, 319 code rate, 116–21 definitions, 18, 117 MCS 0, 150 MCS 7, 150 MCS 15, 102, 145, 155–6, 161–3 code words, 163, 165, 168, 169 MCS 23, 156 NCS 32, 111–14 parameters, 99, 100 symbols, 139, 363 selection, 360 and signal-to-noise ratio, 315 spatial streams, 116–21 symbols, 99, 139 time offset sensitivity, 132–4 see also unequal modulation and coding schemes Monte Carlo simulations, 340–5, 347–9 More Data field, 269 More Fragments field, 267 more PHY protocol data units (more PPDUs), 232–4 MPDUs see MAC protocol data units (MPDUs) MRC see maximal-ratio combining (MRC) MRQ (modulation and coding scheme request), 362 MSDUs see MAC service data units (MSDUs) MSE see mean-square-error (MSE) multipath fading, 33–4 frequency selective, 27 models, Index multiple antennas, 9, 29 advantages, 142, 150 space-time block coding, 142 multiple-input, multiple-output (MIMO), 2, 18, 29 basics, 29–31 channel estimation, 94–6 definition, 29 environment, 33–5 implementations, 2–3 performance improvement, 144–7 receive diversity, 143–7 signal-to-noise ratio, 35, 144–7, 315–16 spatial multiplexing, 15 multiple-input, multiple-output (MIMO) receivers, 142 antenna configurations, 143, 145–6 block diagrams, 92 multiple receive antennas, 93 multiple-input, multiple-output (MIMO) systems, 30 antenna correlation, 38–41 capacity, 34–5, 317 gain, 34 modified, 307 multipath fading models, 6, 34 robustness, 31 with transmit beamforming, 309 multiple-input, multiple-output/orthogonal frequency division multiplexing (MIMO/OFDM) systems performance, 35 power amplifier non-linearity, 45 signal-to-noise ratio, 312 multiple-input, multiple-output/spatial division multiplexing (MIMO/SDM) systems, 31, 101 data rates, 31–2 equalizers, 33 limitations, 33 mathematical representation, 32 schematics, 32 multi-TID BA see multi-traffic identifier block acknowledgement (multi-TID BA) multi-TID BAR see multi-traffic identifier block acknowledgement request (multi-TID BAR) multi-traffic identifier block acknowledgement (multi-TID BA) Block Acknowledgement Control field, 280 frame format, 280 subfields, 280 multi-traffic identifier block acknowledgement request (multi-TID BAR) field format, 278 Per TID Info field, 278 Multi-traffic Identifier (Multi-TID) subfield, 277, 279–80 379 NAV see network allocation vector (NAV) NDP (Null Data Packet) Announcement subfield, 273–5 NDPs see null data packets (NDPs) Netalink, 11 network allocation vector (NAV), 186, 193, 225 in 20/40 MHz basic service sets, 248 during contention free periods, 226 extended interframe space, 194 RTS/CTS frame exchange, 193 network efficiency, and Greenfield preambles, 125–7 New Channel Number field, 288–90 New Regulatory Class field, 288–90 NLOS environments see non-line-of-sight (NLOS) environments no acknowledgement, 199 no explicit acknowledgement, 199 noise phase, 43–4 see also additive white Gaussian noise (AWGN); signal-to-noise ratio (SNR) noise reduction, in channel estimation, 64 in Signal field, 64–5 non-compressed beamforming, 355–6 weights, explicit feedback, 329, 344 Non-Compressed Beamforming Action frames, 356 non-Greenfield high throughput stations present, 240–1 non-line-of-sight (NLOS) environments, 34–7, 47 channel model B, 120, 132, 144, 145, 148, 149, 151, 152 channel model D, 121, 128, 133 channel model E, 122, 134 normal acknowledgement, 199 policy in aggregates, 218 in non-aggregates, 216, 218 Not Sounding field, 322 Null Data Packet (NDP) Announcement subfield, 273–5 null data packets (NDPs), 321 for antenna selection, 351 for calibration, 351 calibration exchange using, 353–4 frame sequence, 351 mixed format preamble, 322 sounding, 357 as sounding PHY protocol data units, 351 and staggered sounding compared, 357–8 Number of Extension Spatial Streams field, 322 OBO (output backoff), 45 OBSSs see overlapping basic service sets (OBSSs) 380 Index OFDM see orthogonal frequency division multiplexing (OFDM) Open Systems Interconnection (OSI) Reference Model, Order field, 269–70 orthogonal frequency division multiplexing (OFDM), 4, 23–7, 32 advantages, 23 frequency selective multipath fading resistance, 27 inter-symbol interference, 23–4 legacy devices, 73, 104 limitations, 26–7 minimum number of symbols, 160–1 overview, 18 physical layer interoperability, 18, 58–100 sensitivity, 27 and single carrier modulation compared, 26 symbol packing, 166–9 waveforms, construction, 23 power spectra, 25 wideband, 34 OSI (Open Systems Interconnection) Reference Model, out-of-band interference 40 MHz, 103–4 output backoff (OBO), 45 overlapping basic service sets (OBSSs) legacy stations, protection, 259 non-high-throughput stations present, 240–1 scanning during 20/40 MHz basic service set operation, 250–1 parameters, 251–2 requirements, 248–53 scan parameters element, 302 packet decoding, 68–70 performance, 69 packet encoding, interleaving, 67 modulation formats, 67 processes, 66–8 pulse shaping functions, 67 space-time block coding, 156–9 packet error rate (PER), 8, 18, 36 and fast link adaptation, 359–60 performance, 118 vs signal-to-noise ratio, 101–2, 338 packet receive, procedures, 68–70 packet structure Data field, 65–6 IEEE 802.11a, 58–9 Long Training field, 58, 61–4 Short Training field, 58–61 Signal field, 58, 64–5 see also mixed format high throughput packet structure PAR see project authorization request (PAR) parallel–serial conversion, 68–9 parity bits generation, 164 puncturing, 167–8 parity check matrices, 172–7 partial state block acknowledgement, 219–22 motivation for, 219–21 operation, 221–2 PAs see power amplifiers (PAs) PAS (power angular spectrum), 39 passive scanning, 184 path loss, 46–7 path loss models development, 35–6 parameters, 47 PCF see point coordination function (PCF) PCF interframe space (PIFS), 188 PCO see phased coexistence operation (PCO) PC (point coordinator), 225 PDUs see protocol data units (PDUs) PER see packet error rate (PER) Per TID Info field, 278 phased coexistence operation (PCO), 16, 256 coexistence, 255–7 interoperability, 255–7 mechanisms, 256–7 real-time disruption minimization, 257 support, 239–40 phase noise, physical layers, 43–4 phase noise power spectral density (PSD), 43–4 PHY protocol data units (PPDUs), 182, 261 20 MHz, short guard intervals, 238–9 40 MHz, short guard intervals, 238–9 channel sounding, 350 null data packets as, 351 Greenfield format, 238–9 high throughput mixed format, 262, 263 more, 232–4 non-high throughput format, 260, 262 non-high throughput station deferral, 262–3 protection, 261–2 staggered sounding, 358 calibration exchange, 353 PHYs see physical layers (PHYs) PHY service data units (PSDUs), 110, 182, 207–9 see also aggregate PHY service data units (A-PSDUs) physical layers (PHYs), 2–4, 177 characteristics, 4, 16–17 criteria, data rates, 15, 204, 207, 208 increase, preamble overheads, 205 Index efficiency, 204 and Greenfield preambles, 125 improvements, 126 enhancements, 203 impairment, 43–5 interoperability, with orthogonal frequency division multiplexing devices, 18, 58–100 legacy in 20/40 MHz coexistence, 114 overview, 5, 15–16 phase noise, 43–4 power amplifier non-linearity, 44–5 preamble lengths, 125–6 response frames, 187 techniques, 18 throughput, 6, 340–2 waveform parameters, 141 PIFS (PCF interframe space), 188 pilot subcarriers, 88, 96 40 MHz channels, 107–8 space-time block coding, 159 point coordination function (PCF), 19, 225–8 limitations, 227–8 point coordinator (PC), 225 power amplifiers (PAs), models, 45 non-linearity, 44–5 power angular spectrum (PAS), 39 power management field, 269 power-save multi-poll (PSMP), 16–17, 19, 225, 234 advantages, 234 block acknowledgement under, 237 burst, 236 definition, 234 frames, 234 recovery, 236 resource allocation, 237 sequences, 234–5 support, 239–40 power-save multi-poll downlink transmission time (PSMP-DTT), 234–5 power-save multi-poll uplink transmission time (PSMP-UTT), 234–5 Power Save Poll (PS-Poll), frame format, 280–1 PPDUs see PHY protocol data units (PPDUs) preamble performance, 75 Primary Channel field, 240 primary environments, 11–12 usage models, 12 probability density function, 69–70 Probe Request frame, 184, 251 format, 284 Probe Response frame, 240, 251 format, 284 product development, vs standardization, 2–3 project authorization request (PAR), acceptance, 6–7 381 propagation models, antenna correlation, 38–41 development, 35–6 Doppler model, 41–2 IEEE 802.11n, 35–47 impulse response, 36–8 path loss, 46–7 physical layer impairments, 43–5 Protected Frame field, 269 protection burst, reduced interframe space, 259 coexistence, 257–65 CTS-to-self, 261 Greenfield format, 259–60 with IEEE 802.11a stations present, 258–9 with IEEE 802.11b stations present, 258 with IEEE 802.11g stations present, 258–9 interoperability, 257–65 PHY protocol data units, 261–2 RTS/CTS frame exchange, 260–1 see also high throughput protection; Legacy Signal field transmit opportunity (L-SIG TXOP) protection protection overlapping basic service set legacy stations, protection, 259 protocol data units (PDUs), 182 see also MAC protocol data units (MPDUs); PHY protocol data units (PPDUs) protocol layering, 182–3 concepts of, 182 protocol version field, 266 PSD (phase noise power spectral density), 43–4 PSDUs see PHY service data units (PSDUs) PSMP see power-save multi-poll (PSMP) PSMP-DTT (power-save multi-poll downlink transmission time), 234–5 PSMP-UTT (power-save multi-poll uplink transmission time), 234–5 PS-Poll (Power Save Poll), frame format, 280–1 Public Action frames, 288 pulse shaping functions, 67 QoS see quality of service (QoS) QoS Control field see Quality of Service (QoS) Control field QoS (Quality of Service) Action frames, 285–6 QPSK (quadrature phase shift keying), 67, 78, 317–18 quadrature phase shift keying (QPSK), 67, 78, 317–18 quality of service (QoS), 194–5, 203, 289, 290 Data frames, 199 extensions, 18–19 parameterized, 228 standards, traffic streams, 228 Quality of Service (QoS) Action frames, 285–6 382 Index Quality of Service (QoS) Control field, 271–3 Access Point Power Save Buffer State subfield, 272–3 Acknowledgement Policy subfield, 271–2 Aggregate MAC Service Data Unit Present subfield, 271 End of Service Period subfield, 271 Queue Size subfield, 271–2 Traffic Identifier subfield, 271 Transmit Opportunity Duration Requested subfield, 272 Transmit Opportunity Limit subfield, 271 quantization, and degradation, 343–4 Queue Size subfield, 271–2 random backoff procedure, 189 random backoff time, 188 Rapp PA model, 45–6 RA (Receiver Address) field, 279, 282 Rayleigh distribution, 36–7 Rayleigh fading, 29, 34 RDG (reverse direction grant), 232–3 reassociation, 185 Reassociation Response frame, 240 format, 283 receive antennas, number of, 32 receive diversity, 18, 31, 142–7 multiple-input, multiple-output, 143–7 throughput vs range comparison, 146 Receiver Address (RA) field, 279, 282 receiver design, for transmit beamforming, 320–1 reciprocity, and interference, 324 reduced interframe space (RIFS), 15, 234–5, 240–1 burst protection, 259 reorder buffer flushing, 218 operation, 216–17 request to send (RTS), 193 frame format, 276 usage, 231 residential environments, 11–12 residential usage model, 12–13 Retry field, 267 reverse direction frame exchange, 232–3 reverse direction grant (RDG), 232–3 reverse direction protocol, 15, 225, 232–4, 239 reverse direction rules, 233–4 RF chains, and selection diversity, 147 RF distortion, 324, 345–6 RGD/more PPDU field, 273–5 Ricean distribution, 36–7 Ricean K-factor, 36–7, 47 RIFS see reduced interframe space (RIFS) robustness, 18 improvements, 15 robust performance, 142–77 RTS/CTS frame exchange, 193, 201–2 protection, 194, 260–1 RTS see request to send (RTS) SAPs (service access points), 7–8 scanning, 183–4 active, 184 issues, 252–3 passive, 184 types of, scoreboard operation, 222 SDM see spatial division multiplexing (SDM) SDUs see service data units (SDUs) SE see spatial expansion (SE) secondary channel offset field, 240 selection diversity, 147 Sequence Control field, 270 service access points (SAPs), 7–8 service data units (SDUs), 182 see also MAC service data units (MSDUs); PHY service data units (PSDUs) service set identifier (SSID), 184 shadow fading, 46–7 Shannon capacity, 50 limit, 48–9 Shannon capacity formula, 29, 48–9 generalization, 32–3 shortening zero bits, number of, 163–4 short interframe space (SIFS), 15, 186–7, 234–5 Short Training field (STF), 58–61 correlation, 59–62 with delayed response, 62 definition, 58–9 receive processing, 68 see also High Throughput Short Training field (HT-STF); Legacy Short Training field (L-STF) short training symbols, construction, 60 SIFS (short interframe space), 15, 186–7, 234–5 SIG see Signal field (SIG) Signal field (SIG), 58, 64–5 definition, 64 noise reduction, 64–5 parity, 64–5 rate information, 64 receive processing, 68 structure, 64 see also High Throughput Signal field (HT-SIG); Legacy Signal field (L-SIG) signal-to-noise ratio (SNR), 29 40 MHz channels, 114–15 additive white Gaussian noise, 18 minimum mean-square-error estimate, 48–9 minimum mean-square-error receivers, 312–14 and modulation and coding schemes, 315 Index multiple-input, multiple-output, 35, 144–7, 315–16 multiple-input, multiple-output/orthogonal frequency division multiplexing systems, 312 and packet decoding, 69 single-input, single-output, 35 and singular value decomposition, 314 transmit beamforming, 315–16 vs packet error rate, 101–2, 338 waterfall curves, 18 zero-forcing equalizers, 48 zero-forcing receivers, 49, 312–14 SIMO (single-input, multiple-output), definition, 30–1 simulation scenarios, 12 single antennas, 29 single carrier modulation, and additive white Gaussian noise compared, 25–7 and orthogonal frequency division multiplexing compared, 26 single-input, multiple-output (SIMO), definition, 30–1 single-input, single-output (SISO), 142 basics, 29 definition, 29 equalizers, 33 signal-to-noise ratio, 35 system, 30 capacity, 29 limitations, 33 singular value decomposition (SVD), 308–11 and signal-to-noise ratio, 314 transmit beamforming with, 311–12 SISO see single-input, single-output (SISO) slot time, 187 SM (spatial multiplexing), power save mode, 239 SNR see signal-to-noise ratio (SNR) sounding packets, transmit beamforming, 327–8 space-time block coding (STBC), 15–16, 18, 79, 147–59 Alamouti scheme, 147–8 background, 149 antenna configurations, 151–5 comparisons, 155–7 data symbols, 159 disadvantages, 148 equalization, 154–6 Greenfield preambles, 159 multiple antennas, 142 packet encoding process, 156–9 performance, 151, 152 pilot subcarriers, 159 receivers, 154–6 reception, 238–9 383 transmission, 156–9, 238–9 block diagram, 158 and transmit beamforming compared, 336–42 transmit time, 159 spatial division multiplexing (SDM), 15, 18, 29 basics, 31–3 definition, 31 and transmit beamforming compared, 335–6, 339, 342 see also multiple-input, multiple-output/spatial division multiplexing (MIMO/SDM) systems spatial expansion (SE), 18, 147 benefits, 148, 149 matrices, 91 and transmit beamforming compared, 336–42 spatial multiplexing (SM), power save mode, 239 spatial streams definition, 31 modulation and coding schemes, enhancements, 116–21 parameters, 99, 100 use of term, 15–16 spectral flatness, 315 spectral masks 20 MHz channels, 117 40 MHz channels, 102–4 design, 102 Spectrum Management Action frames, 285–6 spherical decoding, 51 spread spectrum technology, SSC (Starting Sequence Control) field, 200–1, 277–9 SSID (service set identifier), 184 SSN (start sequence number), 215 staggered sounding, calibration exchange, 353 and null data packets compared, 357–8 standardization vs product development, 2–3 wireless local area network devices, wireless local area networks, starting sequence control (SSC) field, 200–1, 277–9 start sequence number (SSN), 215 STAs see stations (STAs) station channel width field, 255 stations (STAs) access competition, 192 and basic service sets, 183 behavior control, 241 channel width, 240 coexistence, 238–40 interoperability, 238–40 use of term, 182–3 see also 20/40 MHz stations; high throughput stations 384 Index STBC see space-time block coding (STBC) STF see Short Training field (STF) stream parsing, 86, 318 40 MHz channels, 110–11 data field, 85–6 low density parity check, 170 Subtype field, 266–8 Supported Channel Offset field, 255 supported channel width set, 238–40 Supported Channel Width Set field, 254–5 Supported Modulation and Coding Scheme Set field, 291, 294 SVD see singular value decomposition (SVD) target beacon transmission times (TBTTs), 183, 254 TA (Transmitter Address) field, 279, 282 TBTTs (target beacon transmission times), 183, 254 TCLAS (Traffic Classification) elements, 229 TCM (trellis coded modulation), 68 TCP see transmission control protocol (TCP) TGn see High Throughput Task Group (TGn) TGn Draft 1.0, 10 TGn Draft 2.0, 10–11 TGn Draft 3.0, 10–11 TGn Sync team, proposals, throughput data rates, 204, 207 issues, see also high throughput (HT) TID see traffic identifier (TID) TID/NumTIDs field, 277, 279–80 To Distribution System field, 267, 269 Traffic Classification (TCLAS) elements, 229 Traffic Identifier (TID), 199–200, 214 subfield, 271, 279–80 traffic specifications (TSPECs), 228, 237 applications, 229 traffic stream identifiers (TSIDs), 228 traffic streams (TSs) data transfer, 229 definition, 228 deletion, 229–30 hybrid coordinated channel access function, 228–30 maintenance, 229 quality of service, 228 setup, 229 training requests (TRQs), 355 transmission control protocol (TCP), 232 traffic, 126–7 transmit antennas configurations, 18, 31–2 number of, 32 transmit beamforming (TxBF), 15–17, 19, 31, 307–65 advantages, 307–8 and antenna configurations, 327 applications, 29–30 calibration, 325–7, 345–6 errors, 347–9 capacity, 317 channel sounding, 321–3 channel state information feedback, 323–34 degradation, 342–9 eigenvalue analysis, 312–16 fast link adaptation, 359 feedback explicit, 328–34, 344, 345, 358–9 implicit, 323–8, 348–50, 358–9 and High Throughput Signal field, 78–9 medium access control issues, 349–58 in multiple-input, multiple-output systems, 309 performance, 338, 340–2 improvement, 335–42 receiver design, 320–1 signal-to-noise ratio, 315–16 with singular value decomposition, 311–12 sounding packets, 327–8 and space-time block coding compared, 336–42 and spatial division multiplexing compared, 335–6, 339, 342 and spatial expansion compared, 336–42 standards, 307 system models, 307 and unequal modulation and coding schemes, 316–20 transmit beamforming capabilities field, 291, 295, 356 transmit opportunity (TXOP), 197, 203, 225 capacity, delay effects, 343 and collision detect, 199 concept of, 196–7 duration requested, 231 forward direction, 232 polled, 230–1 protection, Legacy Signal field, 239 queue size, 231 requests, 231 reverse direction, 232 sequences high throughput delayed block acknowledgement, 224 high throughput immediate block acknowledgement, 222–3 usage, 197, 232 Transmit Opportunity Duration Requested subfield, 272 Transmit Opportunity Limit subfield, 271 transmit power, total, 32 Transmitter Address (TA) field, 279, 282 transmitter weighting matrix, determination, 307 Index transmit time (TXTIME), 93–4 Greenfield preambles, 130–1 space-time block coding, 159 transmit waveform, IEEE 802.11a, 59 trellis coded modulation (TCM), 68 TRQs (training requests), 355 TSIDs (traffic stream identifiers), 228 TSPECs see traffic specifications (TSPECs) TSs see traffic streams (TSs) TxBF see transmit beamforming (TxBF) TXOP see transmit opportunity (TXOP) TXTIME see transmit time (TXTIME) Type field, 266–8 UDP see user datagram protocol (UDP) unequal modulation and coding schemes, 363–5 20 MHz, 317–19, 363–4 40 MHz, 317–18, 365–7 date rate grouping, 318 and transmit beamforming, 316–20 usage models enterprise, 13–14 hotspot, 13–15 primary environments, 12 residential, 12–13 user datagram protocol (UDP), throughput improvement, 127 traffic, 126–7 virtual private networks (VPNs), 1–2 Viterbi decoders, 68–9 VPNs (virtual private networks), 1–2 waterfall curves, 18, 338 waveform equations, 105–7, 131 waveform parameters, physical layers, 141 WEP (Wired Equivalent Privacy) protocol, 184 WFA see Wi-Fi Alliance (WFA) Wi-Fi handheld devices, hotspots, 13–15 IC shipments, mobile handsets, Wi-Fi Alliance (WFA), establishment, 385 WinEnd, 219, 221 WinSize, 219 WinStart, 219, 221 Wired Equivalent Privacy (WEP) protocol, 184 wireless Ethernet, 181 wireless fidelity see Wi-Fi wireless local area networks (WLANs), adoption, advantages, developments, early, free access, 1–2 overview, packet-based, standardization, wireless local area network (WLAN) devices, development, standards, wireless medium, characteristics, 181–2 Wireless Next Generation Standing Committee (WNG SC), 5–6 WLAN devices see wireless local area network (WLAN) devices WLANs see wireless local area networks (WLANs) WNG SC (Wireless Next Generation Standing Committee), 5–6 World Wide Spectral Efficiency (WWiSE) team, proposals, WWiSE team see World Wide Spectral Efficiency (WWiSE) team zero-forcing (ZF) algorithm, 47 and mean-square-error compared, 48 zero-forcing (ZF) equalizers, 47 signal-to-noise ratio, 48 zero-forcing (ZF) receivers capacity, 48–50 degradation, 51 filtering, 320–1 performance, 70 signal-to-noise ratio, 49, 312–14 ZF algorithm see zero-forcing (ZF) algorithm ZF equalizers see zero-forcing (ZF) equalizers ZF receivers see zero-forcing (ZF) receivers ... the technology continued to develop and in 2002 the IEEE 802. 11 Working Group started defining the next generation of PHY and MAC features as part of 802. 11n 802. 11n will define mechanisms to... combination of greater throughput, longer range and increased reliability, using mandatory and optional features in the PHY (including MIMO technology and 40 MHz channels) and the MAC (including... Throughput, Robustness, and Reliability in 802. 11n ELDAD PERAHIA AND ROBERT STACEY CAMBRIDGE UNIVERSITY PRESS Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, São Paulo Cambridge University