doc.: IEEE /0798r1 Submission July 2008 L. Chu Etc.Slide 1 HT Features in Mesh Network Date: Authors:

doc.: IEEE /0798r1 Submission July 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 /0798r1 Submission July 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 /0798r1 Submission July 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 in a mesh network –No RTS/CTS protection for the downlink burst can be used It is possible to combine MDA and PSMP –This combination can increase link efficiency –But this combination is different from the original MDA in that A 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 –So it may be a good idea to disallow combination of MDA and PSMP 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 /0798r1 Submission July 2008 L. Chu Etc.Slide 5 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 /0798r1 Submission July 2008 L. Chu Etc.Slide 6 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 /0798r1 Submission July 2008 L. Chu Etc.Slide 7 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 –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 /0798r1 Submission July 2008 L. Chu Etc.Slide 8 STBC Operation STBC achieves significant error rate improvements over single-antenna systems STBC related operations includes: –Dual Beacon –Dual CTS Protection –STBC Beacon

doc.: IEEE /0798r1 Submission July 2008 L. Chu Etc.Slide 9 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 dual beacon and STBC beacon if indicated in HT Information element –A receiving MP acts as an AP when using 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 /0798r1 Submission July 2008 L. Chu Etc.Slide 10 20/40MHz Operation 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 It is not clear if a mesh network can switch between 20/40MHz mode and 20MHz mode –It seems to me that the answer is yes If the answer is yes, MDA should be updated accordingly –When a mesh network switch between 20/40MHz mode and 20MHz mode, peer MPs should renegotiate MDA duration parameters If the answer is yes, routing protocol should be updated accordingly –When a mesh network switch between 20/40MHz mode and 20MHz mode, each MP should do path maintenance to find the optimized path

doc.: IEEE /0798r1 Submission July 2008 L. Chu Etc.Slide 11 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 /0798r1 Submission July 2008 L. Chu Etc.Slide 12 PCO Operation (Cont’d) PCO operation can not be used in mesh network –20MHz MP2 in the following example will have little chance to get medium access right MP1 MP2 MP3 MP1 MP2MP3 40MHz phase NAV for MP3 NAV for MP1 NAV for MP3 NAV for MP1 NAV for MP3 NAV for MP1

doc.: IEEE /0798r1 Submission July 2008 L. Chu Etc.Slide 13 Conclusion To enable HT features in a mesh network, more work need to be done –HT protection, –STBC operation, –20/40MHz operation sections.

doc.: IEEE /0798r1 Submission July 2008 L. Chu Etc.Slide 14 Straw Poll 1 Do you think 11s should do more work to integrate 11n features in a mesh network? –Yes –No –Do not know