doc.: IEEE /0798r3 Submission September 2008 L. Chu Etc.Slide 1 HT Features in Mesh Network Date: Authors:

doc.: IEEE /0798r3 Submission September 2008 L. Chu Etc.Slide 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)

doc.: IEEE /0798r3 Submission September 2008 L. Chu Etc.Slide 3 HT Information Element in a WLAN FieldReserved in IBSS Primary ChannelN Secondary Channel OffsetN STA Channel WidthN RIFS ModeY S-PSMP SupportY Service Interval GranularityY HT ProtectionY Non-green-field HT STAs PresentY FieldReserved in IBSS OBSS Non-HT STAs PresentY Dual BeaconY Dual CTS ProtectionY STBC BeaconY L-SIG TXOP Protection Full SupportY PCO ActiveY PCO PhaseY Basic MSC SetN HT Information element controls the operation of HT STAs in the BSS –An infrastructure BSS uses all fields in HT Information element to define the operation of HT STAs –An IBSS uses fields which are not reserved to define the operation of HT STAs It is not clear which fields will be used (or reserved) in a mesh network 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 –20/40MHz operation –PCO (phased coexistence operation)

doc.: IEEE /0798r3 Submission September 2008 L. Chu Etc.Slide 4 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 PSMP- DTT1 (STA1) STA PSMP Sequence AP PSMP- DTT2 (STA2) PSMP- DTT3 (STA3) PSMP- DTT4 (STA4) PSMP- UTT1 (STA1) PSMP- UTT2 (STA2) PSMP- UTT3 (STA3) PSMP- DTT4 (STA4)

doc.: IEEE /0798r3 Submission September 2008 L. Chu Etc.Slide 5 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 PSMP- DTT1 (STA1) STA PSMP Sequence AP PSMP- DTT2 (STA2) PSMP- DTT3 (STA3) PSMP- DTT4 (STA4) PSMP- UTT1 (STA1) PSMP- UTT2 (STA2) PSMP- UTT3 (STA3) PSMP- DTT4 (STA4)

doc.: IEEE /0798r3 Submission September 2008 L. Chu Etc.Slide 6 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

doc.: IEEE /0798r3 Submission September 2008 L. Chu Etc.Slide 7 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 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

doc.: IEEE /0798r3 Submission September 2008 L. Chu Etc.Slide 8 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.

doc.: IEEE /0798r3 Submission September 2008 L. Chu Etc.Slide 9 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

doc.: IEEE /0798r3 Submission September 2008 L. Chu Etc.Slide 10 HT Protection Solution 2: Example MP2 MP3MP4 MP1 MP5 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 Non-HT MP or non-HTSTA STA1 No protection mode Non-member protection mode No Non-HT mixed mode No protection mode AP1 STA1 and MP3 interfere with each other

doc.: IEEE /0798r3 Submission September 2008 L. Chu Etc.Slide 11 STBC Operation STBC achieves significant error rate improvements over single-antenna systems STBC related operations includes: –Dual Beacon –Dual CTS Protection Null RTS CTS SIFS Optional NAV for 3-party STBC STA near non-AP STA NAV for 3-party STBC STA near AP SIFS CTS NAV for 3-party STBC STA near AP DATA SIFS ACK SIFS CF-End SIFS CF-End SIFS CF-END STBC frame Non-STBC frame STBC Non-AP STA AP Dual CTS Mechanism

doc.: IEEE /0798r3 Submission September 2008 L. Chu Etc.Slide 12 STBC Operation (Cont’d) It is not clear if STBC operation is allowed in mesh network Possible solution to use STBC in mesh networks is: –A STBC MP sends out non-STBC beacon and STBC beacon if indicated in HT Information element –If both peer HT MPs set the Dual CTS Protection field of the HT Operation element to 1 in the mesh Beacon frames, the transmitter may act as AP with the Dual CTS Protection field of the HT Operation element has value 1 for dual CTS protection procedure. The transmitter may also act as the STA with the capacity to receive and transmit STBC frames using a single spatial stream –If a HT MP sets the Dual CTS Protection field of the HT Operation element to 1 in the mesh Beacon frames and its peer HT MP does not the Dual CTS Protection field of the HT Operation element to 1 in the mesh Beacon frames, it shall act as AP with the Dual CTS Protection field of the HT Operation element being set to 1 for dual CTS protection procedure when communicate with this peer MP

doc.: IEEE /0798r3 Submission September 2008 L. Chu Etc.Slide 13 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

doc.: IEEE /0798r3 Submission September 2008 L. Chu Etc.Slide 14 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.

doc.: IEEE /0798r3 Submission September 2008 L. Chu Etc.Slide 15 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 NAV Ch_a (primary) Ch_b (secondary) CTS2selfCF-End 40MHz phase Set PCO Phase CF-End 20MHz phase NAV 20MHz STA in ch_a 20MHz STA in ch_b PCO active STA

doc.: IEEE /0798r3 Submission September 2008 L. Chu Etc.Slide 16 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. MP1 MP2 MP3 MP1 MP2MP3 MP0 MP4 40MHz PCO Capable MP 20MHz HT MP ACK EIFS Backoff Data to MP2 40MHz HT Data Duration 40MHz Phase Duration

doc.: IEEE /0798r3 Submission September 2008 L. Chu Etc.Slide 17 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, –20/40MHz operation sections. 11s should disallow the following HT features to be used in a mesh network –PSMP, –PCO Operation.

doc.: IEEE /0798r3 Submission September 2008 L. Chu Etc.Slide 18 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? –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