IEEE 802.11ac协议详解：超高速WiFi规范

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"802.11ac是无线局域网（WLAN）标准的一个重要修订版，专注于提升在低于6GHz频段的极高数据传输速率。此规范由IEEE LAN/MAN Standards Committee赞助，主要涉及到MAC（介质访问控制）和PHY（物理层）两部分的增强。该标准是对802.11-2012标准的修正，同时也考虑了802.11ae、802.11aa和802.11ad等其他修正案的影响。" 802.11ac协议规范是Wi-Fi技术发展的一个里程碑，它的目标是在家庭、办公室和公共场所提供比802.11n更快的数据传输速度。以下是802.11ac协议的一些核心知识点： 1. **多输入多输出（MIMO）技术**：802.11ac引入了更高阶的MIMO技术，支持最多8条空间流，相比于802.11n的4条空间流，极大地提高了无线网络的容量和速度。 2. **更宽的信道带宽**：802.11ac使用了80MHz和160MHz的信道带宽，而802.11n只使用了40MHz，更宽的带宽使得数据传输速率有了显著提升。 3. **正交频分多址（OFDM）**：802.11ac继续采用OFDM调制技术，但改进了子载波的密度和编码率，以提高频率效率和数据吞吐量。 4. **高阶调制**：802.11ac支持高达256-QAM的调制方式，与802.11n的64-QAM相比，每个符号可以携带更多信息，从而增加了数据传输速率。 5. **beamforming技术**：通过定向波束成形，802.11ac能够更精确地定位和优化信号传输，减少干扰并提高信号质量，尤其是在多用户环境中。 6. **VHT（Very High Throughput）增强**：802.11ac被称为VHT标准，意在提供极高的传输速率，理论最高速度可达1.3Gbps，实际应用中也远超过802.11n的最高速度。 7. **兼容性与向后兼容性**：尽管802.11ac提供了更高的性能，但它仍然保持与802.11a/b/g/n设备的兼容性，确保旧设备能够在新的Wi-Fi环境中正常工作。 8. **低延迟**：802.11ac通过优化协议设计和传输策略，降低了数据传输的延迟，这对于实时应用如视频流和在线游戏至关重要。 9. **设备密集环境的优化**：考虑到现代环境中无线设备数量的急剧增加，802.11ac规范也对设备密度和共存问题进行了优化，提高了网络的稳定性和可靠性。 802.11ac协议规范是Wi-Fi技术的一次重大飞跃，它通过技术创新极大地提升了无线网络的速度和容量，为用户带来了更快、更稳定的上网体验。在家庭、商业和公共Wi-Fi网络中，802.11ac已经成为主流标准，为高清视频流、大数据传输和物联网应用提供了强有力的支持。

8.5.4 DLS Action frame details............................................................................................ 106

8.5.4.2 DLS Request frame format........................................................................ 106

8.5.4.3 DLS Response frame format ..................................................................... 106

8.5.8 Public Action details.................................................................................................... 106

8.5.8.3 Measurement Pilot frame format............................................................... 106

8.5.8.7 Extended Channel Switch Announcement frame format .......................... 107

8.5.8.16 TDLS Discovery Response frame format ................................................. 107

8.5.13 TDLS Action frame details.......................................................................................... 108

8.5.13.2 TDLS Setup Request Action field format ................................................. 108

8.5.13.3 TDLS Setup Response Action field format............................................... 108

8.5.13.4 TDLS Setup Confirm Action field format................................................. 109

8.5.13.7 TDLS Channel Switch Request Action field format ................................. 109

8.5.14 WNM Action fields ..................................................................................................... 110

8.5.14.24 Channel Usage Response frame format..................................................... 110

8.5.16 Self-protected Action frame details............................................................................. 110

8.5.16.2 Mesh Peering Open frame format ............................................................. 110

8.5.16.3 Mesh Peering Confirm frame format......................................................... 111

8.5.23 VHT Action frame details ........................................................................................... 111

8.5.23.1 VHT Action field....................................................................................... 111

8.5.23.2 VHT Compressed Beamforming frame format ......................................... 112

8.5.23.3 Group ID Management frame format........................................................ 112

8.5.23.4 Operating Mode Notification frame format............................................... 113

8.6 Aggregate MPDU (A-MPDU)................................................................................................... 113

8.6.1 A-MPDU format.......................................................................................................... 113

8.6.3 A-MPDU contents ....................................................................................................... 116

9. MAC sublayer functional description................................................................................................... 118

9.2 MAC architecture ...................................................................................................................... 118

9.2.1 General......................................................................................................................... 118

9.2.4 Hybrid coordination function (HCF)........................................................................... 118

9.2.4.1 General....................................................................................................... 118

9.2.4.2 HCF contention-based channel access (EDCA)........................................ 119

9.2.7 Fragmentation/defragmentation overview................................................................... 119

9.3 DCF............................................................................................................................................ 120

9.3.1 General......................................................................................................................... 120

9.3.2 Procedures common to both DCF and EDCAF........................................................... 120

9.3.2.3 IFS ............................................................................................................. 120

9.3.2.5a VHT RTS procedure.................................................................................. 121

9.3.2.6 CTS and DMG CTS procedure ................................................................. 121

9.3.2.7 Dual CTS protection.................................................................................. 122

9.3.2.9a MU acknowledgment procedure ............................................................... 122

9.3.4 DCF access procedure ................................................................................................. 124

9.3.4.4 Recovery procedures and retransmit limits ............................................... 124

9.3.7 DCF timing relations ................................................................................................... 124

9.5 Fragmentation ............................................................................................................................ 124

9.7 Multirate support........................................................................................................................ 125

9.7.1 Overview ..................................................................................................................... 125

9.7.4 Basic Rate Set and Basic MCS Set for mesh STA ...................................................... 125

9.7.5 Rate selection for data and management frames ......................................................... 125

9.7.5.3 Rate selection for other group addressed data and management frames ... 125

9.7.5.5a Rate selection for data frames sent within an FMS stream ....................... 125

9.7.5.6 Rate selection for other individually addressed

data and management

frames ........................................................................................................ 126

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9.7.6 Rate selection for control frames................................................................................. 127

9.7.6.1 General rules for rate selection for control frames .................................... 127

9.7.6.2 Rate selection for control frames that initiate a TXOP ............................. 128

9.7.6.4 Rate selection for control frames that are not control response frames..... 128

9.7.6.5 Rate selection for control response frames................................................ 129

9.7.6.6 Channel Width selection for control frames.............................................. 132

9.7.8 Modulation classes ...................................................................................................... 134

9.7.9 Non-HT basic rate calculation..................................................................................... 135

9.7.10 Channel Width in non-HT and non-HT duplicate PPDUs .......................................... 135

9.7.11 Rate selection constraints for VHT STAs ................................................................... 136

9.7.11.1 Rx Supported VHT-MCS and NSS Set..................................................... 136

9.7.11.2 Tx Supported VHT-MCS and NSS Set ..................................................... 136

9.7.11.3 Additional rate selection constraints for VHT PPDUs.............................. 137

9.9 HT Control field operation ........................................................................................................ 138

9.11 A-MSDU operation.................................................................................................................... 138

9.12 A-MPDU operation.................................................................................................................... 139

9.12.2 A-MPDU length limit rules ......................................................................................... 139

9.12.3 Minimum MPDU Start Spacing field.......................................................................... 140

9.12.4 A-MPDU aggregation of group addressed data frames............................................... 140

9.12.5 Transport of A-MPDU by the PHY data service......................................................... 141

9.12.6 A-MPDU padding for VHT PPDU ............................................................................. 141

9.12.7 Setting the EOF field of the MPDU delimiter............................................................. 142

9.12.8 Transport of VHT single MPDUs ............................................................................... 143

9.15 STBC operation ......................................................................................................................... 143

9.16 Short GI operation ..................................................................................................................... 143

9.17a Group ID and partial AID in VHT PPDUs................................................................................ 145

9.18 Operation across regulatory domains ........................................................................................ 146

9.18.5 Operation with operating classes and the VHT Transmit Power Envelope element

... 146

9.19 HCF............................................................................................................................................ 147

9.19.2 HCF contention-based channel access (EDCA).......................................................... 147

9.19.2.2 EDCA TXOPs ........................................................................................... 147

9.19.2.3 Obtaining an EDCA TXOP ....................................................................... 148

9.19.2.3a Sharing an EDCA TXOP........................................................................... 149

9.19.2.4 Multiple frame transmission in an EDCA TXOP...................................... 149

9.19.2.5 EDCA backoff procedure .......................................................................... 151

9.19.2.6 Retransmit procedures ............................................................................... 153

9.19.2.7 Truncation of a TXOP ............................................................................... 154

9.19.2.8 EDCA channel access in a VHT BSS ....................................................... 154

9.19.3 HCCA .......................................................................................................................... 155

9.19.3.2 HCCA procedure ....................................................................................... 155

9.19.3.5 HCCA transfer rules .................................................................................. 155

9.21 Block Acknowledgment (Block Ack)........................................................................................ 156

9.21.10 GCR Block Ack........................................................................................................... 156

9.21.10.3 GCR Block Ack BlockAckReq and BlockAck frame exchanges ............. 156

9.23 Protection mechanisms .............................................................................................................. 156

9.23.5 L-SIG TXOP protection .............................................................................................. 156

9.23.5.3 L-SIG TXOP protection rules at the TXOP responder.............................. 156

9.23.6 Protection Rules for VHT STAs.................................................................................. 156

9.25 Reverse Direction Protocol........................................................................................................ 156

9.25.1 Reverse direction (RD) exchange sequence ................................................................ 156

9.25.3 Rules for RD initiator .................................................................................................. 157

9.25.4 Rules for responder...................................................................................................... 157

9.26 PSMP operation ......................................................................................................................... 157

9.26.1 Frame transmission mechanism during PSMP............................................................ 157

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9.26.1.2 PSMP downlink transmission (PSMP-DTT)............................................. 157

9.27 Sounding PPDUs ....................................................................................................................... 158

9.28 Link adaptation .......................................................................................................................... 158

9.28.2 Link adaptation using the HT variant

HT Control field .............................................. 158

9.28.3 Link adaptation using the VHT variant HT Control field ........................................... 159

9.29 Transmit beamforming .............................................................................................................. 162

9.29.1 General

HT steering matrix calculations ..................................................................... 162

9.29.2 HT t

Transmit beamforming with implicit feedback.................................................... 162

9.29.2.1 General....................................................................................................... 162

9.29.2.3 Bidirectional implicit transmit beamforming ............................................ 164

9.29.2.4 Calibration ................................................................................................. 164

9.29.3 Explicit feedback beamforming................................................................................... 164

9.29.4 VHT MU beamforming ............................................................................................... 165

9.30 Antenna selection (ASEL)......................................................................................................... 165

9.30.1 Introduction ................................................................................................................. 165

9.31 Null data packet (NDP) sounding.............................................................................................. 165

9.31.1 NDP rules .................................................................................................................... 165

9.31.2 Transmission of an HT

NDP ....................................................................................... 167

9.31.3 Determination of HT

NDP destination........................................................................ 167

9.31.4 Determination of HT

NDP source ............................................................................... 167

9.31.5 VHT sounding protocol............................................................................................... 168

9.31.5.1 General....................................................................................................... 168

9.31.5.2 Rules for VHT sounding protocol sequences ............................................ 168

9.31.5.3 Rules for fragmented feedback in VHT sounding protocol sequences ..... 172

9.31.6 Transmission of a VHT NDP ...................................................................................... 173

10. MLME .................................................................................................................................................. 174

10.1 Synchronization ......................................................................................................................... 174

10.1.3 Maintaining synchronization ....................................................................................... 174

10.1.3.2 Beacon generation in non-DMG infrastructure networks ......................... 174

10.2 Power management.................................................................................................................... 174

10.2.1 Power management in a non-DMG infrastructure network ........................................ 174

10.2.1.17 TIM broadcast............................................................................................ 174

10.2.1.19 VHT TXOP power save ............................................................................ 175

10.3 STA authentication and association........................................................................................... 176

10.3.5 Association, reassociation, and disassociation ............................................................ 176

10.3.5.3 PCP/AP association receipt procedures..................................................... 176

10.3.5.5 PCP/AP reassociation receipt procedures.................................................. 176

10.8 TPC procedures.......................................................................................................................... 176

10.8.2 Association based on transmit power capability ......................................................... 176

10.8.3a Interpretation of transmit power capability ................................................................. 177

10.8.4 Specification of regulatory and local maximum transmit power levels ...................... 177

10.9 DFS procedures.......................................................................................................................... 178

10.9.3 Quieting channels for testing....................................................................................... 178

10.11 Radio measurement procedures................................................................................................. 179

10.11.9 Specific measurement usage........................................................................................ 179

10.11.9.1 Beacon Report ........................................................................................... 179

10.11.9.3 Channel Load Report................................................................................. 180

10.11.9.4 Noise Histogram Report ............................................................................ 181

10.11.18AP Channel Report...................................................................................................... 181

10.15 20/40 MHz BSS operation......................................................................................................... 181

10.15.2 Basic 20/40 MHz BSS functionality ........................................................................... 181

10.15.8 Support for DSSS/CCK in 40 MHz............................................................................. 182

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10.15.9 STA CCA sensing in a 20/40 MHz BSS ..................................................................... 182

10.15.12Switching between 40 MHz and 20 MHz ................................................................... 182

10.16 Phased coexistence operation (PCO).........................................................................................182

10.16.1 General description of PCO......................................................................................... 182

10.17 20/40 BSS Coexistence Management frame usage ................................................................... 183

10.22 Tunneled direct link setup.......................................................................................................... 183

10.22.1 General......................................................................................................................... 183

10.22.6 TDLS channel switching ............................................................................................. 184

10.22.6.3 TDLS channel switching and power saving .............................................. 184

10.22.6.4 Setting up a wide bandwidth off-channel direct link................................. 184

10.25 Quality-of-Service management frame (QMF) ......................................................................... 185

10.25.1 General......................................................................................................................... 185

10.25.1.2 Default QMF policy................................................................................... 185

10.39 VHT BSS operation................................................................................................................... 186

10.39.1 Basic VHT BSS functionality...................................................................................... 186

10.39.2 Channel selection methods for a VHT BSS ................................................................ 187

10.39.3 Scanning requirements for VHT STA ......................................................................... 188

10.39.4 Channel switching methods for a VHT BSS ............................................................... 188

10.39.5 NAV assertion in a VHT BSS ..................................................................................... 191

10.39.6 VHT STA antenna indication ...................................................................................... 191

10.39.7 BSS basic VHT-MCS and NSS set operation ............................................................. 191

10.40 Group ID management operation ..............................................................................................191

10.41 Notification of operating mode changes.................................................................................... 192

11. Security................................................................................................................................................. 195

11.4 RSNA confidentiality and integrity protocols ........................................................................... 195

11.4.3 CTR with CBC-MAC Protocol (CCMP)..................................................................... 195

11.4.3.1 General....................................................................................................... 195

11.4.3.2 CCMP MPDU format................................................................................ 195

11.4.3.3 CCMP cryptographic encapsulation.......................................................... 196

11.4.3.4 CCMP decapsulation ................................................................................. 196

11.4.4 Broadcast/Multicast Integrity Protocol (BIP).............................................................. 196

11.4.4.1 BIP overview ............................................................................................. 196

11.4.4.5 BIP transmission........................................................................................ 197

11.4.4.6 BIP reception ............................................................................................. 197

11.4.5 GCM with Galois Message Authentication Code (GMAC) Protocol (GCMP) .......... 198

11.4.5.1 GCMP overview ........................................................................................ 198

11.5 RSNA security association management................................................................................... 198

11.5.3 RSNA policy selection in an ESS................................................................................ 198

11.5.5 RSNA policy selection in an IBSS and for DLS ......................................................... 198

11.5.7 RSNA policy selection in an MBSS............................................................................ 199

11.6 Keys and key distribution .......................................................................................................... 199

11.6.1 Key hierarchy .............................................................................................................. 199

11.6.1.2 PRF ............................................................................................................ 199

11.6.1.3 Pairwise key hierarchy............................................................................... 200

11.6.1.7 FT key hierarchy........................................................................................ 202

11.6.2 EAPOL-Key frames .................................................................................................... 204

11.6.3 EAPOL-Key frame construction and processing ........................................................ 205

11.7 Mapping EAPOL keys to IEEE 802.11 keys............................................................................. 205

11.7.7 Mapping IGTK to BIP keys......................................................................................... 205

13. MLME mesh procedures ...................................................................................................................... 206

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13.2 Mesh discovery.......................................................................................................................... 206

13.2.4 Mesh STA configuration ............................................................................................. 206

13.2.7 Candidate peer mesh STA ........................................................................................... 206

18. Orthogonal frequency division multiplexing (OFDM) PHY specification .......................................... 207

18.2 OFDM PHY specific service parameter list .............................................................................. 207

18.2.2 TXVECTOR parameters ............................................................................................. 207

18.2.2.1 General....................................................................................................... 207

18.2.2.7 TXVECTOR CH_BANDWIDTH_IN_NON_HT .................................... 207

18.2.2.8 TXVECTOR DYN_BANDWIDTH_IN_NON_HT ................................. 207

18.2.3 RXVECTOR parameters ............................................................................................. 208

18.2.3.1 General....................................................................................................... 208

18.2.3.7 RXVECTOR CH_BANDWIDTH_IN_NON_HT .................................... 208

18.2.3.8 RXVECTOR DYN_BANDWIDTH_IN_NON_HT ................................. 208

18.3 OFDM PLCP sublayer............................................................................................................... 208

18.3.2 PLCP frame format...................................................................................................... 208

18.3.2.2 Overview of the PPDU encoding process ................................................. 208

18.3.5 DATA field.................................................................................................................. 209

18.3.5.5 PLCP DATA scrambler and descrambler ................................................. 209

18.3.9 PMD transmit specifications ....................................................................................... 211

18.3.9.3 Transmit spectrum mask............................................................................ 211

18.3.9.7 Modulation accuracy ................................................................................. 211

19. Extended Rate PHY (ERP) specification ............................................................................................. 212

19.3 Extended Rate PLCP sublayer................................................................................................... 212

19.3.3 PLCP data modulation and rate change....................................................................... 212

19.3.3.4 Long and short DSSS-OFDM PLCP format ............................................. 212

20. High Throughput (HT) PHY specification........................................................................................... 213

20.1 Introduction................................................................................................................................ 213

20.1.1 Introduction to the HT PHY ........................................................................................ 213

20.3 HT PLCP sublayer..................................................................................................................... 213

20.3.10 Transmission of NON_HT format PPDUs with more than one antenna

transmit

chain............................................................................................................................. 213

20.3.11 Data field ..................................................................................................................... 213

20.3.11.3 Scrambler................................................................................................... 213

20.3.20 PMD transmit specification ......................................................................................... 213

20.3.20.1 Transmit spectrum mask............................................................................ 213

20.3.20.7 Modulation accuracy ................................................................................. 213

22. Very High Throughput (VHT) PHY specification ............................................................................... 214

22.1 Introduction................................................................................................................................ 214

22.1.1 Introduction to the VHT PHY ..................................................................................... 214

22.1.2 Scope ........................................................................................................................... 215

22.1.3 VHT PHY functions .................................................................................................... 215

22.1.3.1 General....................................................................................................... 215

22.1.3.2 PHY management entity (PLME) ............................................................. 215

22.1.3.3 Service specification method..................................................................... 215

22.1.4 PPDU formats..............................................................................................................215

22.2 VHT PHY service interface....................................................................................................... 216

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