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Project: IEEE P802.11 Working Group for Wireless Local Area Networks (WLANs)

Project: IEEE P802.11 Working Group for Wireless Local Area Networks (WLANs) Submission Title: [ STMicroelectronics MAC Proposal for 802.11n CFP ] Date Submitted: [ 13 August 2004 ] Source: [ Liwen Chu, Gabriella Convertino, Mike Moreton, Vincenzo Scarpa, George Vlantis ]

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Project: IEEE P802.11 Working Group for Wireless Local Area Networks (WLANs)

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  1. Project: IEEE P802.11 Working Group for Wireless Local Area Networks (WLANs) Submission Title: [STMicroelectronics MAC Proposal for 802.11n CFP] Date Submitted: [13 August 2004] Source: [Liwen Chu, Gabriella Convertino, Mike Moreton, Vincenzo Scarpa, George Vlantis] Company [STMicroelectronics, N.V.] Address [1060 East Brokaw Road, San Jose, CA 95131-2309, California, USA] Voice: [+1 (408) 451-8109], FAX: [+1 (408) 452-0278] E-Mail: [{liwen.chu, gabriella.convertino, mike.moreton, vincenzo.scarpa,george.vlantis}@st.com] Re: [This submission presents the MAC recommendations of STMicroelectronics to the 802.11n Call For Proposals (Doc #11-03/0858r5) that was issued on 17 May 2004.] Abstract: [This presentation details STMicroelectronics’ MAC partial proposal for IEEE 802.11 TGn. Enhancements to the 802.11-1999 (Reaff 2003) MAC are presented, in order to achieve a higher MAC efficiency, while maintaining backward compatibility with the 802.11-1999 (Reaff) and 802.11e Draft 9.0 where possible. ] Purpose: [STMicroelectronics offer this contribution to the IEEE 802.11n task group for its consideration as the solution for standardization.] Notice:This document has been prepared to assist the IEEE P802.11. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release:The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.11. G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  2. ST Microelectronics MAC Partial Proposal for 802.11n CFP Presenters: Gabriella Convertino, Vincenzo Scarpa, George Vlantis STMicroelectronics, Inc ({Gabriella.Convertino, Vincenzo.Scarpa, George.Vlantis}@ST.com) G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  3. Main Features: Enhancements to the 802.11e MAC • 802.11e Draft 9.0 Compatible: • Mandatory features: EDCA • Optional operation: HCCA and DLP • Enhancements: • MSDU aggregation (mandatory) • Enhanced Block ACK for PPDU bursting (mandatory) • Piggybacking (optional) • Neighbor-list LC-EDCA (optional) • Super-frame LC-EDCA (optional) G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  4. Queue (TID,RA) (1,1) (1,2) (2,2) (1,1) (1,1) (1,1) 2 MPDUs created (1,2) (2,2) t AMSDU Enhancements to the 802.11e MAC • MSDU Aggregation • Multiple MSDUs in a single AMSDU (as in the WWiSE proposal) • No changes to MAC-PHY interface • Increased MPDU sizes (max size = 8K) • An ACK for each aggregated MPDU Preamble + PLCP header Pad Bits + Tail MAC header FCS (TID,RA) (1,1) . MSDU MPDU/PSDU PPDU Sub-Frame header Sub-Frame header: G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  5. (1,1) (1,2) (1,2) (1,3) Enhancements to the 802.11e MAC • Enhanced Block Ack (EBA) for PPDU bursting • Block Ack as in IEEE P802.11e/D9.0 but with: • Reduced 2us IFS (RIFS) for multiple destinations that require power adaptation • Zero IFS (ZIFS) for single destinations or when power amplifier is unchanged Preamble + PLCP header Pad Bits + Tail MAC header FCS (TID,RA) Queue (1,1) . (1,3) MSDU (1,2) MPDU/PSDU (1,2) PPDU (1,1) PHY Preamble+ PLCP header Reduced or Zero IFS = 2 or 0 ms All TIDs of the same AC may be concatenated. BlockReq at the end of the last PPDU burst. G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  6. Multiple Frame Transmissions (1/3)Tested alternatives (1) “HTP Burst”: multiple MPDUs in a single A-PPDU Frame 0 Frame 1 Frame 2 Frame 3 Frame 4 Frame 5 A-PPDU(01) (2) “Enhanced Block Ack”: multiple PPDUs burst with RIFS or ZIFS Frame 0 Frame 1 Frame 2 Frame 3 Frame 4 Frame 5 PPDU(4) PPDU(5) PPDU(2) PPDU(3) PPDU(0) PPDU(1) S/P/D/AIFS ZIFS or RIFS ZIFS or RIFS ZIFS or RIFS ZIFS or RIFS ZIFS or RIFS G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  7. Multiple Frame Transmissions(2/3)Tested Burst Policies: Single Destination Burst Same RA QoS Data RA=1 Seq=1495 QoS Data RA=1 Seq=1496 QoS Data RA=1 Seq=1497 QoS Data RA=1 Seq=1498 QoS Data RA=1 Seq=1499 QoS Data RA=1 Seq=1500 QoS Data RA=1 Seq=1501 QoS Data RA=1 Seq=1502 QoS Data RA=1 Seq=1503 QoS Data RA=1 Seq=1504 QoS Data RA=2 Seq=1506 QoS Data RA=2 Seq=1507 QoS Data RA=2 Seq=1508 RTS RTS BlockAckReq Starting Seq=1495 BlockAckReq Starting Seq=1500 BlockAckReq Starting Seq=1506 RTS Originator TXOP TXOP BlockAckAck CTS CTS CTS BlockAckAck Recipient RA1 BlockAckAck Recipient RA2 G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  8. Multiple Frame Transmission(3/3)Tested Burst Policies: Multiple Destination Burst Different RA BlockAckReq RA=1 Starting Seq=1500 RTS QoS Data RA=1 Seq=1500 QoS Data RA=1 Seq=1501 QoS Data RA=2 Seq=2000 QoS Data RA=1 Seq=1502 QoS Data RA=2 Seq=2001 BlockAckReq RA=2 Starting Seq=2000 RTS QoS Data RA=1 Seq=1503 QoS Data RA=1 Seq=1504 QoS Data RA=2 Seq=2002 QoS Data RA=2 Seq=2003 Originator TXOP TXOP CTS CTS BlockAckAck Recipient RA1 BlockAckAck Recipient RA2 Immediate BA with multiple RAs over a single TXOP G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  9. Simulation Conditions • Simulations include: • HTP Burst Transmission with A-PPDU • Enhanced Block Ack Transmission with reduced or zero inter-frame spacing (RIFS/ZIFS) without A-PPDU • Two burst aggregation policies simulated : • Single destination: each burst contains frames destined to the same Recipient Address (RA) • Multiple destination: a burst may contain frames destined to different RA. G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  10. TxOPLim aCWmin aCWmax AIFSN nBurst MAX MSDU Size 3008/1504* 8k AC_BK 31 1023 7 Y AC_BE 31 1023 3 Y 3008 8k AC AC_VI 15 31 2 Y 3008 8k AC_VO 7 15 2 Y 1504 1k Simulation Environment • NS2 has been used as simulation environment, with real PHY and TGn channel models • PHY • Appropriate 802.11n channel model used with real PHY • 20MHz MIMO 2x2 64QAM 3/4 (121.5Mbits/s) / 40MHz MIMO 2x2 64QAM 3/4 (243Mbits/s) • Preamble: 16us • MAC features • 802.11e Features • EDCA • Continuation TxOP • Direct Link • MSDU Aggregation (up to 8k, depends on AC) • Multiple Frame Transmissions: • Immediate ACK policy • Single/multiple destination • “HTP Burst” and “Enhanced Block Ack” • Traffic features • For UDP used CBR source • For TCP: TCP Sack • Miscellaneous • RTS/CTS protection mechanism used * 1504 used for scenario1 tests G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  11. Metrics • Metric 1 is defined as the sum of goodput across all flows in the simulation scenario. • Metric 2 is defined as the aggregate number of bits in MSDUs that are delivered at the Rx MAC SAP within the specified delay bound of the flow’s defined QoS, divided by the simulation duration. • Metric 3 is defined as the sum of goodput across all flows that meet their QoS objective in the simulation scenario. • MAC efficiency is defined as the aggregate Metric 2 goodput in CC20 divided by the average physical layer data rate. G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  12. Scenario #1 – Target Values • Aggregated Throughput: 84.604 Mbps • QoS throughput: 53.604 Mbps G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  13. Scenario #1Single Destination Results G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  14. Scenario #1Multiple Destination Results G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  15. Scenario #4 – Target Values • Aggregated Throughput: 451 Mbps • QoS throughput: 9.152 Mbps G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  16. Scenario #4Single Destination Results G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  17. Scenario #4Multiple Destination Results G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  18. Enhancements to the 802.11e MAC • MSDU Aggregation + Enhanced Block Ack: Conclusions • These two features are consistent with the WWiSE consortium proposal, but restrict the aggregation and bursting to the same Access Category, as in 802.11e D9.0. • The choice of either approach is a trade-off between data throughput and QoS. • The penalty for the extra preamble replication for the Enhance Block Ack burst is not significant, but adds the capability to adjust power levels in the case of multiple destinations and adds robustness to errors. • The combination of deciding the length of the aggregated MSDU and deciding the burst policy (i.e. single vs. multiple destinations) is key to the scheduler. G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  19. UDP 1 2 UDP DTA ACK+DTA ACK+DTA ACK DTA DTA ACK+DTA ACK+DTA ACK DTA SIFS SIFS SIFS SIFS DIFS DIFS SIFS SIFS Enhancements to the 802.11e MAC • Piggybacking mode (1/5) • Consider the following scenario: • Receiving STA could send the ACK for the successfully received packet together with a DTA packet . G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  20. Enhancements to the 802.11e MAC • Piggybacking mode (2/5) • A PB session must not exceed the TXOP limit (i.e. the recipient must ensure that the piggybacking data plus any required acknowledgement do not exceed the limit). The following case is not allowed: TxOP limit ACK+DTA DTA ACK+DTA ACK+DTA ACK ACK+DTA ACK+DTA ACK+DTA • PB should coexist with the Block Acknowledgement procedure. • The station which gains the medium access should allow piggybacking at the recipient side whenever it has insufficient packets to exhaust the TXOP limit. G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  21. Enhancements to the 802.11e MAC • A piggyback time value is transmitted (and updated) in each DTA (and ACK+DTA). This value is set by the station which gains access to the medium. • The value indicates the time available (in the current TXOP) for the receiving station to do piggyback plus the time to receive the ACK (if expected). • The value of 0 indicates that the data cannot be piggybacked (e.g. all frames sent using BA/noACK policy must have a zero value). • Each recipient can request to the originator a new PB opportunity by indicating the time needed in the current DataAck frame. • Piggybacking mode (3/5) bool Mac802_11e::is_Pbable(Packet* toSend, Packet* rcvd){ int time_available = rcvd->PB_duration; int time_needed = ACKTimeout(toSend); if ( time_needed < time_available){ toSend->PB_duration = time_available - Data_time(toSend) + ACKtime +SIFS); return true; } else return false; } G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  22. Enhancements to the 802.11e MAC • Piggybacking mode (4/5) • When piggybacking is not allowed, receiving station must send ACK only. TxOP limit DTA ACK+DTA ACK ACK+DTA Time needed Time available time time time time Here PB is not allowed G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  23. Originator DATA CTSn DataAck DataAck Recipient ACK DataAck DataAck NAV at legacy STAs NAV at other .11n STAs “CTSn to self” protection mechanism Enhancements to the 802.11e MAC • Piggybacking mode (5/5) • “CTSn to self” allows the originator to protect its transmissions from legacy devices for the entire TXOP duration • .11n devices will not update their NAV so they consequently can do piggybacking G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  24. UDP 1 1 2 UDP 2 Enhancements to the 802.11e MAC • Piggybacking mode simulation results (1/2) • Simple scenario For this simple scenario, PB allows a MAC efficiency of about 90% G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  25. Enhancements to the 802.11e MAC • Piggybacking mode simulation results (2/2) • Scenario 1 • PHY rate has been set to 121.5 Mbps, and we simulated with a real channel as defined in the STM simulation methodology document. • For both Single Destination (SD) and Multi Destination (MD) block ack we used 2us reduced IFS G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  26. Enhancements to the 802.11e MAC • Piggybacking mode: Conclusions • Piggybacking mode performance heavy depends on the simulation scenarios. • Piggybacking is most effective when “symmetric” flows with QoS constraints (e.g. VoIP flows) occur in a congested network. • The “CTSn to self” protection mechanism allows piggybacking to be used even in mixed mode, thus granting backward compatibility with legacy devices but could cause unfairness in case the protected period is much greater than the required one to piggyback all the data. • The HC can disallow the .11n stations to use piggybacking in mixed mode at any time by appropriately setting the PB field in the Capability Information field in the beacon frame G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  27. Enhancements to the 802.11e MAC • Neighbor-List LC-EDCA • Neighbor-list LC-EDCA is only used in an independent BSS. • A neighbor list is maintained in each STA. • Each STA allocates one weight to each of its neighbors. • Two STA priorities are used to lower the collision probability • One STA has highest priority (it can transmit the first frame after a shorter LCIFS idle medium time) • Other STAs have low priority (they use the standard EDCA medium access method) • The TXOP owner (the highest or low priority STA) selects the next highest priority STA (NHPS). This adds robustness and quick recovery in a scenario where packets are lost. G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  28. NHPS: Next Highest Priority STA LCTXOP: LC-EDCA TXOP LCIFS: LC-EDCA IFS AIFS[j] Backoff Window LCIFS LCIFS AIFS[i] Backoff Window Backoff Window EDCA TXOP EDCA TXOP LCTXOP LCTXOP STA_m STA_n STA_o LCIFS STA_p NHPS is STA_n Lose NHPS info or Error frame transfer STA_p gets access right NHPS is STA_o STA_m gets access right Enhancements to the 802.11e MAC • Neighbor-List LC-EDCA (Medium Access Method) • The highest priority STA • Services more than one Access Category • Gets the medium access right after the medium is idle for LCIFS • Switches to the low priority state when the LCTXOP ends • The last frame of its LCTXOP carries NHPS information • The low priority STAs • Use EDCA medium access method to access the medium • The last frame of a TXOP carries NHPS information G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  29. Enhancements to the 802.11e MAC • Neighbor-List LC-EDCA (NHPS selection) • The NHPS is selected in a round-robin fashion • In the neighbor-list, each entry is of the form (STA ID, weight) NHPS: Next Highest Priority STA LCTXOP: LC-EDCA TXOP LCIFS: LC-EDCA IFS NHPS: 3 NHPS: 2 LCTXOP LCTXOP LCTXOP STA_1 NHPS: 1 NHPS: 3 NHPS: 1 TXOP LCTXOP LCTXOP STA_2 NHPS: 2 NHPS: 1 LCTXOP LCTXOP STA_3 LCIFS LCIFS LCIFS LCIFS LCIFS LCIFS LCIFS G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  30. Type value b3 b2 Type description Subtype value b7 b6 b5 b4 Subtype description 00 Management 0110 Super-Frame 01 Control 0000 Block Acknowledgement Request (BlkAckReq) with NHPS information 11 Data 1000 QoS Data with NHPS information To DS From DS Address1 Address2 Address3 Address4 Usage 0 0 DA SA BSSID N/A or NHPS STA to STA traffic in an IBSS and QSTA-to-QSTA traffic in a QBSS Frame control Duration RA TA NHPS BAR Control Block Ack Starting Sequence Control FCS Enhancements to the 802.11e MAC • Neighbor-List LC-EDCA (New Frames) • The following new frames shall be added: • The QoS data frame with NHPS use address 4 to indicate next highest priority STA information • The BlockAckReq with NHPS Frame Format Octets: 2 2 6 6 6 2 2 4 G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  31. Enhancements to the 802.11e MAC • Super-Frame LC-EDCA • Used in a BSS only • The AP allocates the service period to each STA according to each STA’s load estimation • Two STA priorities are used • Highest priority in its own service period (SP) • Low priority in other STA’s service period • A more effective power saving mode can be used • A non-AP STA becomes active in its own SP and in AP’s SP • The AP is always in active mode SP: service period LCSI: LC-EDCA service interval AP’s SP STA1’s SP STA2’s SP STAn’s SP LCSI The Service Interval of Super-Frame LC-EDCA G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  32. Enhancements to the 802.11e MAC • Super-Frame LC-EDCA (Medium Access Method 1/2) • STA in its own SP • Services more than one Access Category • Gets the first medium access right after the medium is idle for LCIFS • Uses the highest priority backoff timer (LCIFS, LCCACWmin, LCCACWmax) to get back the medium access right with high probability again • Transmits the next frame at a SIFS period following the successful transmission of a frame if the remaining SP allows the next frame transmission • STA in other STA’s SP • Uses the EDCA medium access method to access the medium. G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  33. Enhancements to the 802.11e MAC • Super-Frame LC-EDCA (Medium Access Method 2/2) AIFS Backoff Window Backoff Window TXOP STA_o Backoff Window Backoff Window Backoff Window STA _o’s SP TXOP STA_n Backoff Window TXOP TXOP STA_m LCIFS No frame available in STA_m LCIFS LCIFS STA _m’s SP G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  34. Element ID (47) rsrv Length (6* STA_Num +6) LC-EDCASI High Priority STA SP High Priority STA SP High Priority STA SP AID start time stop time Enhancements to the 802.11e MAC • Super-Frame LC-EDCA (New Frames) • The service period (SP) information element shown in the following figure contains the service period information allocated to each high priority STA by the AP Octets: 1 1 2 2 6 6 6 • The structure of the high priority STA SP field is defined in the following figure: Octets: 2 2 2 G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  35. Enhancements to the 802.11e MAC • Neighbor-List LC-EDCA and Super-frame LC-EDCA: Conclusions • Collisions can be reduced in a distributed way for an IBSS using Neighbor-list LC-EDCA • Similarly, collisions can be reduced in a centralized way for a BSS using Super-frame LC-EDCA • Both techniques reduce the wasted deferring time of EDCA • A simple round robin scheduler can be implemented. • A weighting algorithm is demonstrated for selecting the Next-Highest Priority Station (NHPS). • In super-frame LC-EDCA, when the highest priority station has no packets to send, the EDCA mechanism allows all the other low priority stations to contend for the media, thus reducing unused time. G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

  36. References • [1] IEEE P802.11e/D9.0, “Draft Amendment to STANDARD [for] Information Technology – Telecommunications and Information Exchange Between Systems – LAN/MAN Specific Requirements – Part 11: wireless Medium Access Control (MAC) and Physical Layer (PHY) specifications: Medium Access Control (MAC) Quality of Service (QOS) Enhancements”, February 2004 • [2] IEEE 802 11-03/802, “TGn Usage Models” • [3] IEEE 802 11-03/813, “TGn Functional Requirements” • [4] IEEE 802 11-04/897, “STMicroelectronics MAC Partial Proposal Specification” G.Convertino, V.Scarpa, G.Vlantis STMicroelectronics

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