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HT Features in Mesh Network

HT Features in Mesh Network. Authors:. Date: 2008-11-11. 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

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HT Features in Mesh Network

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  1. HT Features in Mesh Network Authors: Date: 2008-11-11 L. Chu et al

  2. 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

  3. 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

  4. 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 Mechanism PSMP- DTT3 (STA3) PSMP- DTT4 (STA4) PSMP- DTT1 (STA1) PSMP- DTT2 (STA2) PSMP AP PSMP- UTT3 (STA3) PSMP- DTT4 (STA4) PSMP- UTT1 (STA1) PSMP- UTT2 (STA2) STA PSMP Sequence L. Chu et al

  5. 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 Mechanism (Cont’d) PSMP- DTT3 (STA3) PSMP- DTT4 (STA4) PSMP- DTT1 (STA1) PSMP- DTT2 (STA2) PSMP AP PSMP- UTT3 (STA3) PSMP- DTT4 (STA4) PSMP- UTT1 (STA1) PSMP- UTT2 (STA2) STA PSMP Sequence L. Chu et al

  6. 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 HT Protection Mechanism L. Chu et al

  7. 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 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 OBSS Non-HT STAs present field set to 1 The L-SIG TXOP Full Support field set to 0 The PCO Active field set to 0 The Basic MCS Set field set to all zeros HT Protection Mechanism (Cont’d) L. Chu et al

  8. 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. HT Protection Mechanism (Cont’d) L. Chu et al

  9. 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 HT Protection Mechanism (Cont’d) L. Chu et al

  10. HT Protection Solution 2: Example Non-member protection mode No protection mode MP3 MP4 MP5 MP2 MP1 No Non-HT mixed mode No protection 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 inNon-member protection mode 40MHz HTMP in 20MHz protection mode 20MHz HT MP in no protection mode L. Chu et al

  11. STBC achieves significant error rate improvements over single-antenna systems STBC related operations includes: Dual Beacon Dual CTS Protection STBC Operation STBC Non-AP STA CF-End RTS DATA Null SIFS SIFS SIFS SIFS SIFS SIFS SIFS SIFS STBC frame Optional CTS ACK CF-END CTS AP 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

  12. 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. STBC Operation (Cont’d) L. Chu et al

  13. 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 20/40MHz Operation L. Chu et al

  14. 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. 20/40MHz Operation (Cont’d) L. Chu et al

  15. 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 PCO Operation Beacon Or Set PCO Phase 20MHz phase 40MHz phase Set PCO Phase CF-End CTS2self CF-End 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

  16. 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. PCO Operation (Cont’d) MP2 MP3 MP4 MP1 40MHz PCO Capable MP MP0 20MHz HT MP Duration 40MHz HT Data MP1 40MHz HT Data 40MHz Phase Duration ACK MP2 Data to MP2 MP3 EIFS Backoff Backoff L. Chu et al

  17. 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, 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 STBC operation, PSMP, PCO Operation. Conclusion L. Chu et al

  18. 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? Yes No Do not know Do you think 11s should define new rules to integrate HT features into 11s draft? Yes No Do not know Straw Poll L. Chu et al

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