IEEE802.11n：提升无线局域网性能的标准

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"IEEE802.11n是Wi-Fi联盟推出的一种无线传输标准协议，旨在提高无线局域网（WLAN）的性能，使之达到以太网的水平，提供高带宽和高质量的服务。该标准是802.11系列协议的扩展，包括了对802.11a/b/g的增强。" IEEE 802.11n标准详细介绍了如何提升无线网络的数据传输速率，主要通过以下技术实现： 1. **MIMO (Multiple-Input Multiple-Output)**：802.11n引入了MIMO技术，允许路由器和设备同时发送和接收多个数据流，显著提高了无线网络的吞吐量。通过利用空间多样性和多路信号合并，MIMO能够减少错误并增强信号强度。 2. **OFDM (Orthogonal Frequency Division Multiplexing)**：802.11n采用了OFDM调制技术，将宽带信号分解成多个窄带子信道，每个子信道独立调制，降低了干扰，提高了数据传输效率。 3. **40 MHz频宽**：相比802.11a/b/g的20 MHz频宽，802.11n支持双信道操作，使用40 MHz的总带宽，从而实现更高的传输速率。 4. **帧聚合**：802.11n允许将多个较小的数据包打包成一个更大的帧进行传输，减少了传输开销，提高了网络效率。 5. **Short Guard Interval (SGI)**：通过缩短保护间隔，进一步提升了数据传输速率，但可能牺牲了部分远距离连接的稳定性。 6. **Channel Bonding**：结合两个非重叠的20 MHz信道，形成一个40 MHz的信道，提供了两倍于20 MHz信道的带宽。这些技术的结合使得802.11n标准在理想条件下可以达到理论最高速度接近600 Mbps，实际应用中通常可达到几十兆比特每秒的传输速率，远超之前的802.11a/b/g标准。此外，802.11n标准还兼容前向纠错（Forward Error Correction, FEC），这有助于在网络条件较差时恢复丢失的数据，增强了网络的可靠性。同时，802.11n也考虑到了与其他802.11标准的互操作性，如802.11k（漫游优化）、802.11r（快速漫游）、802.11y（对5 GHz频段的扩展）以及802.11w（管理帧保护）等。 IEEE 802.11n标准是无线通信领域的一次重大进步，它通过技术创新显著提升了WLAN的性能，满足了用户对于高速、稳定无线网络的需求。在家庭、办公室和公共场所的无线网络部署中，802.11n标准起到了关键作用，为后来的802.11ac和802.11ax等更高速率标准奠定了基础。

8.3.3 CTR with CBC-MAC Protocol (CCMP)............................................................... 94

8.3.3.3 CCMP cryptographic encapsulation .................................................. 94

8.3.3.3.2 Construct AAD .......................................................... 94

8.3.3.3.5 CCM originator processing........................................ 95

8.3.3.4 CCMP decapsulation ......................................................................... 95

8.3.3.4.3 PN and replay detection............................................. 95

8.4 RSNA security association management............................................................................... 95

8.4.3 RSNA policy selection in an ESS.......................................................................... 95

8.4.4 RSNA policy selection in an IBSS and for DLS

................................................... 96

8.7 Per-frame pseudo-code .......................................................................................................... 96

8.7.2 RSNA frame pseudo-code ..................................................................................... 96

8.7.2.1 Per-MSDU/Per-A-MSDU Tx pseudo-code ....................................... 96

8.7.2.2 Per-MPDU Tx pseudo-code............................................................... 97

8.7.2.4 Per-MSDU/A-MSDU Rx pseudo-code ............................................. 98

9. MAC sublayer functional description................................................................................................ 99

9.1 MAC architecture ..............................................................................................................

.... 99

9.1.3 Hybrid coordination function (HCF) ..................................................................... 99

9.1.3.1 HCF contention-based channel access (EDCA) ................................ 99

9.1.5 Fragmentation/defragmentation overview............................................................. 99

9.1.6 MAC data service ................................................................................................ 100

9.2 DCF...................................................................................................................................... 100

9.2.2 MAC-Level acknowledgments ............................................................................ 100

9.2.3 IFS........................................................................................................................100

9.2.3.0a Overview.......................................................................................... 100

9.2.3.0b RIFS ................................................................................................. 101

9.2.3.1 SIFS ................................................................................................. 101

9.2.3.2 PIFS ................................................................................................. 101

9.2.3.5 EIFS ................................................................................................. 102

9.2.4 Random backoff time........................................................................................... 102

9.2.5 DCF access procedure ......................................................................................... 102

9.2.5.1 Basic access ..................................................................................... 102

9.2.5.3 Recovery procedures and retransmit limits ..................................... 102

9.2.5.4 Setting and resetting the NAV ......................................................... 103

9.2.5.5a Dual CTS protection ........................................................................ 103

9.2.5.5a.1 Dual CTS protection procedure ............................... 103

9.2.5.5a.2 Dual CTS protection examples................................ 105

9.2.5.7 CTS procedure ................................................................................. 105

9.2.6 Individually addressed MPDU transfer procedure .............................................. 105

9.2.7 Broadcast and multicast MPDU transfer procedure ............................................ 106

9.2.8 ACK procedure .................................................................................................... 106

9.2.8a BlockAck procedure ............................................................................................ 106

9.2.9 Duplicate detection and recovery ........................................................................ 106

9.2.10 DCF timing relations ........................................................................................... 107

9.2.10a Signal Extension .................................................................................................. 107

9.6 Multirate support.................................................................................................................. 107

9.6.0a Overview.............................................................................................................. 107

9.6.0b Basic MCS Set field............................................................................................. 108

9.6.0c Basic STBC MCS ................................................................................................ 108

9.6.0d Rate selection for data and management frames ................................................ 108

9.6.0d.1 Rate selection for non-STBC Beacon and non-STBC PSMP

frames............................................................................................... 108

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9.6.0d.2 Rate selection for STBC group-addressed data and management

frames............................................................................................... 109

9.6.0d.3 Rate selection for other group-addressed data and management

frames............................................................................................... 109

9.6.0d.4 Rate selection for polling frames ..................................................... 109

9.6.0d.5 Rate selection for +CF-Ack frames ................................................. 109

9.6.0d.6 Rate selection for other data and management frames .................... 109

9.6.0e Rate selection for control frames ......................................................................... 110

9.6.0e.1 General rules for rate selection for control frames .......................... 110

9.6.0e.2 Rate selection for control frames that initiate a TXOP.................... 111

9.6.0e.3 Rate selection for CF_End control frames....................................... 111

9.6.0e.4 Rate selection for control frames that are not control response

frames............................................................................................... 112

9.6.0e.5 Rate selection for control response frames ...................................... 112

9.6.0e.5.1 Introduction.............................................................. 112

9.6.0e.5.2 Selection of a rate or MCS....................................... 112

9.6.0e.5.3 Control response frame MCS computation ............. 113

9.6.0e.5.4 Selection of an alternate rate or MCS for a control

response frame ......................................................... 115

9.6.0e.5.5 Control response frame TXVECTOR parameter

restrictions................................................................ 115

9.6.0e.6 Channel Width selection for control frames .................................... 115

9.6.0e.7 Control frame TXVECTOR parameter restrictions......................... 116

9.6.1 Modulation classes............................................................................................... 116

9.6.2 Non-HT basic rate calculation ............................................................................. 117

9.7 MSDU transmission restrictions.......................................................................................... 118

9.7a HT Control field operation ..................................................................................................118

9.7b Control Wrapper operation .................................................................................................. 119

9.7c A-MSDU operation.............................................................................................................. 119

9.7d A-MPDU operation.............................................................................................................. 119

9.7d.1 A-MPDU contents ............................................................................................... 119

9.7d.2 A-MPDU length limit rules ................................................................................. 120

9.7d.3 Minimum MPDU Start Spacing field .................................................................. 120

9.7d.4 A-MPDU aggregation of group-addressed data frames ...................................... 120

9.7d.5 Transport of A-MPDU by the PHY data service ................................................. 121

9.7e PPDU duration constraint ....................................................................................................121

9.7f LDPC operation ................................................................................................................... 121

9.7g STBC operation ................................................................................................................... 121

9.7h Short GI operation ............................................................................................................... 121

9.7i Greenfield operation ............................................................................................................ 122

9.9 HCF...................................................................................................................................... 122

9.9.1 HCF contention-based channel access (EDCA) .................................................. 122

9.9.1.2 EDCA TXOPs.................................................................................. 122

9.9.1.4 Multiple frame transmission in an EDCA TXOP............................ 123

9.9.1.5 EDCA backoff procedure ................................................................ 124

9.9.1.6 Retransmit procedures ..................................................................... 125

9.9.1.7 Truncation of TXOP ........................................................................ 126

9.9.2 HCCA .................................................................................................................. 127

9.9.2.1 HCCA procedure ............................................................................. 127

9.9.2.1.3 Recovery from the absence of an expected

reception................................................................... 127

9.9.2.2 TXOP structure and timing.............................................................. 127

9.9.2.3 HCCA transfer rules ........................................................................ 128

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9.10 Block Acknowledgment (Block Ack).................................................................................. 128

9.10.1 Introduction.......................................................................................................... 128

9.10.2 Setup and modification of the Block Ack parameters ......................................... 128

9.10.3 Data and acknowledgment transfer using immediate Block Ack policy and

delayed Block Ack policy.................................................................................... 129

9.10.4 Receive buffer operation...................................................................................... 132

9.10.6 Selection of BlockAck and BlockAckReq variants............................................. 132

9.10.7 HT-immediate Block Ack extensions.................................................................. 133

9.10.7.1 Introduction to HT-immediate Block Ack extensions..................... 133

9.10.7.2 HT-immediate Block Ack architecture............................................ 133

9.10.7.3 Scoreboard context control during full-state operation ................... 134

9.10.7.4 Scoreboard context control during partial-state operation............... 135

9.10.7.5 Generation and transmission of BlockAck by an HT STA ............. 136

9.10.7.6 Receive reordering buffer control operation.................................... 137

9.10.7.6.1 General..................................................................... 137

9.10.7.6.2 Operation for each received data MPDU................. 137

9.10.7.6.3 Operation for each received BlockAckReq ............. 138

9.10.7.7 Originator’s behavior ....................................................................... 138

9.10.7.8 Maintaining BlockAck state at the originator.................................. 139

9.10.7.9 Originator’s support of recipient’s partial state ............................... 139

9.10.8 HT-delayed Block Ack extensions ...................................................................... 140

9.10.8.1 Introduction...................................................................................... 140

9.10.8.2 HT-delayed Block Ack negotiation ................................................. 140

9.10.8.3 Operation of HT-delayed Block Ack............................................... 140

9.10.9 Protected Block Ack Agreement ......................................................................... 140

9.12

Frame exchange sequences.................................................................................................. 141

9.13 Protection mechanisms for non-ERP receivers

.................................................................. 141

9.13.1 Introduction.......................................................................................................... 141

9.13.2 Protection mechanism for non-ERP receivers ..................................................... 141

9.13.3 Protection mechanisms for transmissions of HT PPDUs .................................... 142

9.13.3.1 General............................................................................................. 142

9.13.3.2 Protection rules for HT STA operating a direct link ....................... 144

9.13.3.3 RIFS protection................................................................................ 144

9.13.3.4 Use of OBSS Non-HT STAs Present field ...................................... 144

9.13.4 L_LENGTH and L_DATARATE parameter values for HT-mixed format

PPDUs.................................................................................................................. 145

9.13.5 L-SIG TXOP protection....................................................................................... 146

9.13.5.1 General rules .................................................................................... 146

9.13.5.2 L-SIG TXOP protection rules at the TXOP holder ......................... 148

9.13.5.3 L-SIG TXOP protection rules at the TXOP responder.................... 149

9.13.5.4 L-SIG TXOP protection NAV update rule ...................................... 149

9.15 Reverse Direction Protocol .................................................................................................150

9.15.1 Reverse direction (RD) exchange sequence ........................................................ 150

9.15.2 Support for RD..................................................................................................... 150

9.15.3 Rules for RD initiator .......................................................................................... 150

9.15.4 Rules for RD responder ....................................................................................... 151

9.16 PSMP Operation .................................................................................................................. 153

9.16.1 Frame transmission mechanism during PSMP .................................................... 153

9.16.1.1 PSMP frame transmission (PSMP-DTT and PSMP-UTT).............. 153

9.16.1.2 PSMP downlink transmission (PSMP-DTT)................................... 154

9.16.1.3 PSMP uplink transmission (PSMP-UTT)........................................ 154

9.16.1.4 PSMP burst ...................................................................................... 156

9.16.1.5 Resource allocation within a PSMP burst........................................ 157

9.16.1.6 PSMP-UTT retransmission.............................................................. 158

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9.16.1.7 PSMP acknowledgment rules .......................................................... 158

9.16.1.8 PSMP group-addressed transmission rules...................................... 160

9.16.1.8.1 Rules at the AP ........................................................ 160

9.16.1.8.2 Rules at the STA...................................................... 160

9.16.2 Scheduled PSMP.................................................................................................. 160

9.16.3 Unscheduled PSMP ............................................................................................. 161

9.17 Sounding PPDUs ................................................................................................................. 161

9.18 Link adaptation .................................................................................................................... 162

9.18.1 Introduction.......................................................................................................... 162

9.18.2 Link adaptation using the HT Control field......................................................... 162

9.19 Transmit beamforming ........................................................................................................164

9.19.1 General................................................................................................................. 164

9.19.2 Transmit beamforming with implicit feedback ................................................... 165

9.19.2.1 General............................................................................................. 165

9.19.2.2 Unidirectional implicit transmit beamforming ................................ 166

9.19.2.3 Bidirectional implicit transmit beamforming .................................. 167

9.19.2.4 Calibration ....................................................................................... 168

9.19.2.4.1 Introduction.............................................................. 168

9.19.2.4.2 Calibration capabilities ............................................ 169

9.19.2.4.3 Sounding exchange for calibration .......................... 170

9.19.2.4.4 CSI reporting for calibration.................................... 172

9.19.3 Explicit feedback beamforming........................................................................... 173

9.20 Antenna selection (ASEL) ................................................................................................... 177

9.20.1 Introduction.......................................................................................................... 177

9.20.2 Procedure ............................................................................................................. 177

9.21 Null data packet (NDP) sounding........................................................................................ 181

9.21.1 NDP rules............................................................................................................. 181

9.21.2 Transmission of an NDP...................................................................................... 182

9.21.3 Determination of NDP destination ...................................................................... 182

9.21.4 Determination of NDP source.............................................................................. 183

10. Layer management...............................................................................................................

............ 184

10.3 MLME SAP interface ..........................................................................................................1

10.3.2 Scan......................................................................................................................184

10.3.2.2 MLME-SCAN.confirm.................................................................... 184

10.3.2.2.2 Semantics of the service primitive........................... 184

10.3.3 Synchronization ................................................................................................... 187

10.3.3.1 MLME-JOIN.request....................................................................... 187

10.3.3.1.2 Semantics of the service primitive........................... 187

10.3.3.1.4 Effect of receipt ....................................................... 187

10.3.6 Associate.............................................................................................................. 188

10.3.6.1 MLME-ASSOCIATE.request.......................................................... 188

10.3.6.1.2 Semantics of the service primitive........................... 188

10.3.6.2 MLME-ASSOCIATE.confirm ........................................................ 189

10.3.6.2.2 Semantics of the service primitive........................... 189

10.3.6.3 MLME-ASSOCIATE.indication ..................................................... 190

10.3.6.3.2 Semantics of the service primitive........................... 190

10.3.6.4 MLME-ASSOCIATE.response ....................................................... 191

10.3.6.4.2 Semantics of the service primitive........................... 191

10.3.7 Reassociate........................................................................................................... 192

10.3.7.1 MLME-REASSOCIATE.request .................................................... 192

10.3.7.1.2 Semantics of the service primitive........................... 192

10.3.7.2 MLME-REASSOCIATE.confirm ................................................... 193

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10.3.7.2.2 Semantics of the service primitive........................... 193

10.3.7.3 MLME-REASSOCIATE.indication ................................................ 194

10.3.7.3.2 Semantics of the service primitive........................... 194

10.3.7.4 MLME-REASSOCIATE.response .................................................. 195

10.3.7.4.2 Semantics of the service primitive........................... 195

10.3.10 Start...................................................................................................................... 196

10.3.10.1 MLME-START.request................................................................... 196

10.3.10.1.2 Semantics of the service primitive........................... 196

10.3.10.1.4 Effect of receipt ....................................................... 197

10.3.15 Channel switch..................................................................................................... 198

10.3.15.1 MLME-CHANNELSWITCH.request ............................................. 198

10.3.15.1.2 Semantics of the service primitive........................... 198

10.3.15.3 MLME-CHANNELSWITCH.indication......................................... 199

10.3.15.3.2 Semantics of the service primitive.......................... 199

10.3.15.4 MLME-CHANNELSWITCH.response........................................... 199

10.3.15.4.2 Semantics of the service primitive........................... 199

10.3.24 TS management interface .................................................................................... 200

10.3.24.5 MLME-DELTS.request ................................................................... 200

10.3.24.5.2 Semantics of the service primitive........................... 200

10.3.24.7 MLME-DELTS.indication............................................................... 200

10.3.24.7.2 Semantics of the service primitive........................... 200

10.3.25 Management of direct links ................................................................................. 201

10.3.25.2 MLME-DLS.confirm....................................................................... 201

10.3.25.2.2 Semantics of the service primitive........................... 201

10.3.25.3 MLME-DLS.indication.................................................................... 201

10.3.25.3.2 Semantics of the service primitive........................... 201

10.4 PLME SAP interface ........................................................................................................... 202

10.4.3 PLME-CHARACTERISTICS.confirm ............................................................... 202

10.4.3.2 Semantics of the service primitive................................................... 202

10.4.6 PLME-TXTIME.request...................................................................................... 205

10.4.6.1 Function ........................................................................................... 205

10.4.6.2 Semantics of the service primitive................................................... 205

10.4.6.3 When generated ............................................................................... 205

11. MLME .........................................................................................................................

.................... 206

11.1 Synchronization .............................................................................................................

...... 206

11.1.2 Maintaining synchronization ............................................................................... 206

11.1.2.1 Beacon generation in infrastructure networks ................................. 206

11.1.3 Acquiring synchronization, scanning .................................................................. 206

11.1.3.4 Synchronizing with a BSS ............................................................... 206

11.1.4 Adjusting STA timers .......................................................................................... 207

11.1.6 Supported rates and extended supported rates advertisement ............................. 207

11.2 Power management.............................................................................................................. 208

11.2.1 Power management in an infrastructure network ................................................ 208

11.2.1.1 STA Power Management modes ..................................................... 209

11.2.1.2 AP TIM transmissions ..................................................................... 209

11.2.1.3 TIM types......................................................................................... 209

11.2.1.4 Power management with APSD ...................................................... 209

11.2.1.5 AP operation during the CP ............................................................. 210

11.2.1.6 AP operation during the CFP........................................................... 212

11.2.1.7 Receive operation for STAs in PS mode during the CP .................. 213

11.2.1.8 Receive operation for STAs in PS mode during the CFP................ 213

11.2.1.9 Receive operation for non-AP STAs using APSD .......................... 214

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