HT Features in Mesh Network Feb, 2008 doc.: IEEE 802.11-07/xxxx September 2008 HT Features in Mesh Network Date: 2008-11-11 Authors: L. Chu et al Liwen Chu, STMicroelectronics

HT Features Being Included in 11S Easily September 2008 HT Features Being Included in 11S Easily The following features can be used in a mesh network without any change after HT capability element being added to Beacon frame, Peer Link action frames A-MSDU A-MPDU Enhanced BlockAck RD (reverse direction) Beamforming ASEL (antenna selection) L. Chu et al

Unclear HT Features in 11S September 2008 Unclear HT Features in 11S It is also not clear if and how the following features are used in a mesh network: PSMP (power save multi-poll) HT protection STBC operation Transition between 20/40MHz channel and 20MHz channel in 20/40MHz operation PCO (phased coexistence operation) L. Chu et al

September 2008 PSMP Mechanism PSMP sequence allows the AP to create effective service periods for S-APSD Multiple-TID blockAck allows for single frame to respond to (implicit) BAR for multiple TID 2-hop MP (mesh point) may create more collision if EDCA method is used for PSMP in a mesh network No RTS/CTS protection for the downlink burst can be used PSMP- DTT1 (STA1) PSMP- DTT2 (STA2) PSMP- DTT3 (STA3) PSMP- DTT4 (STA4) PSMP AP STA PSMP- UTT1 (STA1) PSMP- UTT2 (STA2) PSMP- UTT3 (STA3) PSMP- DTT4 (STA4) PSMP Sequence L. Chu et al

PSMP Mechanism (Cont’d) September 2008 PSMP Mechanism (Cont’d) What happens if we combine MDA and PSMP This combination may increase link efficiency But this combination is different from the original MDA in that An MP will use PIFS or the EDCA mechanism of the highest AC of the data waiting to be transmitted Multiple AC’s frames will be transmitted in a MDA txop An MP will send unicast frames to more than one destination MP in a MDA OP. PSMP MDA OP should be reserved in the same way as multicast MDA OP So 11s should disallow the PSMP mechanism. PSMP- DTT1 (STA1) PSMP- DTT2 (STA2) PSMP- DTT3 (STA3) PSMP- DTT4 (STA4) PSMP AP STA PSMP- UTT1 (STA1) PSMP- UTT2 (STA2) PSMP- UTT3 (STA3) PSMP- DTT4 (STA4) PSMP Sequence L. Chu et al

HT Protection Mechanism September 2008 HT Protection Mechanism HT transmission will be protected based on the following fields: HT Protection Non-green-field HT STAs Present OBSS Non-HT Present L-SIG TXOP Protection Full Support In a infrastructure HT BSS, HT protection field may be set to one of the following modes HT no protection mode HT non-member protection mode HT 20MHz protection mode HT non-HT mixed mode L. Chu et al

HT Protection Mechanism (Cont’d) September 2008 HT Protection Mechanism (Cont’d) In a IBSS, the HT Protection field is reserved, but an HT STA shall protect HT transmissions as though the following fields have the settings indicated: The HT Protection field set to non-HT mixed mode The RIFS mode field of the HT Information element set to 1 The Non-Greenfield HT STAs present field set to 1 The L-SIG TXOP Full Support field set to 0 The OBSS Non-HT STAs present field set to 1 The PCO Active field set to 0 In a non-HT BSS, An HT STA operating a direct link with another HT STA shall operate as though the following fields have the settings indicated: The Basic MCS Set field set to all zeros L. Chu et al

HT Protection Mechanism (Cont’d) September 2008 HT Protection Mechanism (Cont’d) It is not clear how to protect HT transmission in a mesh network Solution 1: Mesh network uses whatever methods defined for IBSS HT protection It is easy to be defined It is inefficient especially when there are no legacy MP in the future Solution 2: Mesh network defines new HT protection methods An HT MP sets its protection mode according to the capabilities of its neighbor MPs and STAs in the primary channel or the secondary channel in 20/40 MHz mesh network When selecting the protection mode, its neighbor MPs in the same mesh network have the same roles as the STAs in the same BSS. L. Chu et al

HT Protection Mechanism (Cont’d) September 2008 HT Protection Mechanism (Cont’d) Solution 2: Mesh network defines new HT protection methods (Cont’d) When two peer MPs report the same protection mode in HT protection field, the protection methods of the related mode will be used When two peer MPs report different protection modes, If one MP reports non-HT mixed mode, the protection methods of non-HT mixed mode will be used for the transmission between these two MPs If one MP reports non-member protection mode and non-HT mixed mode is not reported by any MP, the protection methods of non-member protection mode will be used for the transmission between these two MPs If one MP report 20 MHz protection mode and neither non-HT mixed mode nor non-HT mixed mode is reported by any MP, the protection methods of 20 MHz protection mode will be used for the transmission between these two MPs L. Chu et al

HT Protection Solution 2: Example September 2008 HT Protection Solution 2: Example Non-member protection mode No protection mode MP1 MP2 MP3 MP4 MP5 No protection mode No Non-HT mixed mode STA1 STA1 and MP3 interfere with each other AP1 Non-HT MP or non-HTSTA 20MHz HT MP in Non-HT mixed mode 20MHz HT MP in Non-member protection mode 40MHz HT MP in 20MHz protection mode 20MHz HT MP in no protection mode L. Chu et al

September 2008 STBC Operation STBC achieves significant error rate improvements over single-antenna systems STBC related operations includes: Dual Beacon Dual CTS Protection Non-AP STA STBC Null RTS DATA CF-End SIFS SIFS SIFS SIFS SIFS SIFS SIFS SIFS STBC frame Optional AP CTS CTS ACK CF-End CF-END Non-STBC frame NAV for 3-party STBC STA near non-AP STA NAV for 3-party STBC STA near AP NAV for 3-party STBC STA near AP Dual CTS Mechanism L. Chu et al

STBC Operation (Cont’d) September 2008 STBC Operation (Cont’d) It is not clear if STBC operation is allowed in mesh network. Dual CTS protection needs master/client relationship. It is possible to use STBC transmission through indicating a master (ownership of a TXOP) between two peer MPs. But this may make protocol complicated: Two STBC capable peer MPs may have different rules comparing with only one peer MP with STBC capability. So 11s should disallow the STBC transmission. L. Chu et al

20/40MHz Operation Channel scanning and channel management September 2008 20/40MHz Operation Channel scanning and channel management An AP can switch the infrastructure BSS between 20/40MHz BSS and 20MHz BSS A 20/40MHz IBSS can not be changed to a 20MHz IBSS and a 20MHz IBSS can not be changed to a 20/40MHz BSS 40MHz transmission restriction STA CCA sensing in a 20/40MHz BSS NAV assertion in 20/40 MHz BSS Switching between 40 MHz and 20 MHz L. Chu et al

20/40MHz Operation (Cont’d) September 2008 20/40MHz Operation (Cont’d) 11s should support 20/40MHz operation 11s should allow a mesh network to switch between 20/40MHz mode and 20MHz mode 11s defines a robust distributed channel switch mechanism which can support When a mesh network switch between 20/40MHz mode and 20MHz mode, peer MPs may renegotiate MDA duration parameters When a mesh network switch between 20/40MHz mode and 20MHz mode, each MP may do path maintenance to find the optimized path. L. Chu et al

PCO Operation AP Establishes separate 20MHz and 40MHz operating phases September 2008 PCO Operation AP Establishes separate 20MHz and 40MHz operating phases 20MHz phase: allows independent BSS activity on control channel and OBSS on extension channel 40MHz phase: 40MHz transmissions across 40MHz channel with no 20MHz interference Beacon Or Set PCO Phase CTS2self CF-End 40MHz phase Set PCO Phase CF-End 20MHz phase Ch_a (primary) Ch_b (secondary) 20MHz STA in ch_a NAV 20MHz STA in ch_b NAV PCO active STA NAV NAV L. Chu et al

PCO Operation (Cont’d) September 2008 PCO Operation (Cont’d) 40MHz HT frames in 40MHz phase are not protected perfectly with 20MHz hidden MP. Undetectable duration in 20MHz MP may create more collision. The new rules need to be defined if two neighbour MPs are allowed to have overlap target 40MHz phase: 20Mz frames are allowed to be transmitted in a 40Mz phase. If MP1 and MP2 have overlapped 40MHz phases, when MP1 ends its 40MHz phase using CF-end, MP2’s MP 40MHz phase may also be ended. So 11s should disallow the PCO operation. MP0 MP1 MP2 MP3 MP4 40MHz PCO Capable MP 20MHz HT MP Duration MP1 40MHz HT Data 40MHz HT Data 40MHz Phase Duration MP2 ACK MP3 Data to MP2 EIFS Backoff Backoff L. Chu et al

September 2008 Conclusion After 11s HT capability element being added to Beacon frame, Peer Link action frames, the following features can be used in a mesh network without further work: A-MSDU A-MPDU Enhanced BlockAck RD (reverse direction) Beamforming ASEL (antenna selection) 11s should define new rules to decide how to use the following HT features if the following features are allowed in 11s mesh network HT protection, STBC operation, Transition between 20/40MHz channel and 20MHz channel in 20/40MHz operation. 11s should disallow the following HT features to be used in a mesh network PSMP, PCO Operation. L. Chu et al

September 2008 Straw Poll Do you think 11s should add more text to integrate HT features in its draft? Yes No Do not know Do you think 11s should use whatever HT features used by IBSS in its draft? Do you think 11s should define new rules to integrate HT features into 11s draft? Yes No Do not know L. Chu et al