Update of Interference Management Using Beamforming Technique in OBSS Environment

1. Update of Interference Management Using Beamforming Technique in OBSS Environment Authors: Yusuke Asai (NTT)

2. Abstract • This submission shows the update topics for the interference management technique in OBSSs environment [1][2]. • Frame sequence and contents of control / management frames • Security class change • Throughput evaluation Yusuke Asai (NTT)

3. Overview of interference management using beamforming in OBSS environment • Some degrees of freedom on antennas at an AP can be used to mitigate interference to the STAs associated with other BSSs to form null to them. • When two APs mutually form null beams to the STAs associating to the partner’s AP, spatial multiplexing transmission between APs is possible. AP1 AP2 STA1 STA2 Null beams to the STA on the other BSS Yusuke Asai (NTT)

4. Merits and requirements of the proposed interference management technique Merits: • Simple implementation: Null-beams can be easily configured because each AP supporting MU-MIMO inherently has a transmit beamforming function. • Throughput improvementMore than 50% throughput improvement is achived. • Smaller latency: Frequency to access medium for AP will increase, which makes QoS data transmission more reliable. Requirements: • Frame sequence: to form beamforming weight and preparation for spatial multiplexing transmission • Control frame should be extended to call APs / STAs and exchange information between APs. Yusuke Asai (NTT)

5. Update Points • Frame sequence and contents of control / management frames • New type of control frame to initiate the sequence of spatially multiplexing transmission between APs is proposed. • Required actions for APs and STAs on the sequence is also updated. • Security class • We propose that security class of CSI feedback frame is changed 3 to 1. • Brief throughput evaluation including channel life time • When CSI reuse is used, throughput gain reaches up to 50%. Yusuke Asai (NTT)

6. Frame Sequence for Spatial Multiplexing Transmission between APs • The frame sequence for the spatially multiplexing transmission between APs comprises three phases: • Initiation phase Initiator AP calls the responder AP and STAs on its BSS. Responder AP responds to the initiator AP and calls STAs on its BSS. • CSI feedback phase Either implicit or explicit feedback is used. If CSI has been already exchanged, this phase may be skipped. • DATA transmission phase Spatial multiplexing transmission between APs and Block ACK transmission • Prior to “b. CSI feedback phase” and “c. DATA transmission phase,” “a. Initiation phase is run to establish the frame sequence. Yusuke Asai (NTT)

7. a. Initiation phase When an AP obtains a chance to access medium, the AP can start the sequence for spatial multiplexing transmission between APs. • AP1 (initiator) transmits a CTS-to-Self frame to set the NAV to all STAs associated in AP1. • AP1 transmits an OBSS Control frame (newly defined )to call AP2 (responder) and the destination STAs. • AP2 (responder) transmits a CTS-to-Self frame to set the NAV to all STAs associated in AP2. • AP2 transmits an OBSS Control frame to respond to AP1’s call and to call it’s destination STAs. CS : CTS-to-Self frame : OBSS control frame : Null Data Packet : Block ACK frame AP1 (initiator) CS OC 1. 2. OC STA1 NDP CS OC AP2 (responder) BA 3. 4. time STA2 a. Yusuke Asai (NTT)

8. OBSS Control Frame • An OBSS control frame informs parameters of the spatial multiplexing transmission between APs. • APs and STAs synchronize frame timing from the OBSS control frame. • An OBSS Control frame carries the following information: • For the responder AP: • MAC address of the responder AP • The number of available SS (spatial streams) for responder AP’s transmission • The number of spatial streams which the responder AP must form NULLs • For the initiator AP: • MAC address of the initiator AP • The number of • For the STAs associated to AP1 • Group ID corresponding to the STAs group • The numbers of spatial streams for STAs • The need of CTS-to-self protection for CSI feedback by STAs • For the all of receivers • Type of the frame sequence Yusuke Asai (NTT)

9. An example of frame format for OBSS Control (1/2) Octet: 2 2 6 6 6 Frame Control Duration Receiver Address 1 MAC address for Tx AP MAC address for Rx AP 1 1 2 1 1 4 (continued) Initiation / Response Group ID # of SSs for STAs # of available SSs for Tx AP CTS protection FCS • Frame Control Type/Subtype： (01) Control frame / (0110) OBSS Control • Duration Length of duration depends on the pattern of the following sequence. • Receiver Address 1 Group address (assigned for this frame) STAs and APs that support the spatial multiplexing transmission between APs shall recognize the content of the frame. • MAC address for Tx / Rx AP (Tx AP, Rx AP) = (initiator AP, responder AP) or (responder AP, initiator AP) Yusuke Asai (NTT)

10. An example of frame format for OBSS Control (2/2) Octet: 2 2 6 6 6 Frame Control Duration Receiver Address 1 MAC address for Tx AP MAC address for Rx AP 1 1 2 1 1 4 (continued) Initiation / Response Group ID # of SSs for STAs # of available SSs for Tx AP CTS protection FCS • Initiation / Response indicates whether this OBSS Control frame is initiation or response message. • Group ID (assigned for this frame) indicates the Group ID that corresponds a group of STAs in initiator / responder AP to join the spatial multiplexing transmission between APs. • # of SSs for STAs informs the numbers of spatial streams for STAs in the Group ID. The Rx AP must form NULL streams as many as summation of “# of SSs for STAs.” • # of available SSs for Tx AP The number of spatial streams that Tx AP can handle. (the maximum # of SSs for Rx AP’s STAs) = (the # of available SSs for Tx AP) – (summation of “# of SSs for STAs.”) • CTS protection Tx AP can order it’s STAs to use protection of CTS-to-Self frames by using this field (bitmap based). Yusuke Asai (NTT)

11. OBSS Control frame as Control Wrapper frame Octet: 2 2 6 2 4 18 4 Frame Control Duration Receiver Address 1 Carried Frame Control HTC Carried Frame FCS When CSI feedback sequence between APs, OBSS Control frame as Control Wrapper frame is used. • Frame Control Type/Subtype： Control frame/Control Wrapper • Duration Length of duration depends on the existence of CSI feedback (implicit/explicit), CTS frames from STAs and DATA transmission. • Receiver Address 1 Group address • Carried Frame Control Subtype: 0110 (OBSS Control frame) • HTC field Specify the type of CSI feedback scheme (implicit or explicit or “no use”.) • Carried frame is identical to OBSS Control frame without “Frame Control,” “Duration,” “Receiver Address 1.” Yusuke Asai (NTT)

12. Sequence Types (1/4) AP1 (initiator) CS OC Data for STA1 • DATA transmission only (“a. Initiation” + “c. Data transmission”) • OBSS Control frame is not Control Wrapper. • This sequence can be used only when transmit beam for spatial multiplexing transmission between APs is prepared on each AP prior to the sequence. BA STA1 AP2 (responder) CS OC Data for STA2 BA time STA2 a. c. (by CS from AP1) (by OC from AP1) NAV settings (by CS from AP2) (by OC from AP2) Yusuke Asai (NTT)

13. Sequence Types (2/4) AP1 (initiator) CS OC • The OBSS Control frames are Control Wrapper frames and HTC field is set to implicit feedback. • Implicit feedback only (“a. Initiation” + “b. CSI feedback”) NDP STA1 OC MR AP2 (responder) NDP time STA2 a. b. (by CS from AP1) (by OC from AP1) NAV settings (by CS from AP2) (by OC from AP2) Yusuke Asai (NTT)

14. Sequence Types (3/4) AP1 (initiator) CS CS OC OC Data for STA1 • Implicit feedback + DATA transmission • The 1st OCs are Control Wrapper frames • The 2nd OC are not Control Wrapper frames. NDP BA STA1 CS OC CS OC Data for STA2 AP2 (responder) NDP BA time STA2 a. b. c. (by the 1st CS from AP1) (by 2nd CS from AP1) NAV settings (by 2nd OC from AP1) (by 2nd CS from AP2) (by the 1st OC from AP1) (by 2nd OC from AP2) (by 1st OC from AP2) (by 1st CS from AP2) Yusuke Asai (NTT)

15. Sequence Types (4/4) AP1 (initiator) CS OC NDP • Explicit feedback only • Implicit feedback + DATA transmission CSI FB CSI FB STA1 • The OBSS Control frames are Control Wrapper frames and HTC field is set to explicit feedback. CS OC NDP AP2 (responder) CSI FB CSI FB time STA2 a. b. AP1 (initiator) CS OC NDP CS OC Data for STA1 time BA CSI FB CSI FB STA1 CS OC NDP CS OC Data for STA2 AP2 (responder) BA CSI FB CSI FB STA2 a. b. c. Yusuke Asai (NTT)

16. CTS protection • Initiator/responder AP can request STAs to transmit additional CTS-to-self frame prior to their transmission. AP1 (initiator) CS OC CS OC Data for STA1 STA1 (w/ CTS) NDP CS BA CS CS OC CS OC AP2 (responder) Data for STA2 NDP BA time STA2 a. b. c. (by 1st CS from AP1) (by 2nd CS from AP1) (by 1st OC from AP1) (by 2nd OC from AP1) NAV settings (by 2nd CS from AP2) (by 1st CS from AP2) (by 2nd OC from AP2) (by OC from AP2) (by 2nd CS from STA1) (by 1st OC from STA1) Yusuke Asai (NTT)

17. Security Class Change AP1 AP2 Three types of connections are used for the proposed sequences. • The connections between an AP and an STAs within a BSS: State 3 (Authenticated, Associated ) • CTS-to-Self frame (Class 1) • OBSS Control frame (control frame: Class 1) • NDP (just a preamble signal) • DATA frame (Class 3) • BlockACK frame (Class 3) • The connections between initiator and responder APs: State 1 (Unauthenticated, Unassociated) • CTS-to-Self frames (Class 1) • OBSS Control frames (Class 1) • The connections between an AP and an STA associated to the other AP: State 1 • NDP (just a preamble signal) • CSI feedback frames (management frame: Class 3) (defined as no “Robust” management frame in 7.3.1.11) Figure 11-6 - Relationship between state variables and services STA1 STA2 b. a. c. a. c. To establish CSI feedback connection between an AP and an STA associated to the Other AP, it is proposed that the class of CSI feedback frames is changed from Class 3 to Class 1. (This change does not degrade security level specified in 11w.) Yusuke Asai (NTT)

18. Throughput Evaluation • Evaluation Parameters Yusuke Asai (NTT)

19. Frame sequence without interference management (implicit feedback) • One user per AP case, an AP transmits SU-MIMO frames. (SU-MIMO without CSI feedback is assumed Data for STA1 (medium busy) AP1 (SU-MIMO) BA (medium busy) STA1 Data for STA2 (medium busy) AP2 (SU-MIMO) BA (medium busy) STA2 Data transmission from AP1 to STA1 Data transmission from AP2 to STA2 (Channel access phase based on DCF) Yusuke Asai (NTT)

20. Frame sequence without interference management (implicit feedback) • Two users per AP case, an AP transmits DL MU-MIMO frames. HTC+ Data for STA1/2 (medium busy) AP1 (DL MU-MIMO) NDP BA (medium busy) STA1 NDP BA (medium busy) STA2 HTC+ Data for STA3/4 (medium busy) AP2 (DL MU-MIMO) NDP BA (medium busy) STA3 BA NDP (medium busy) STA4 Data transmission from AP1 to STAs1 and 2 Data transmission from AP2 to STAs3 and 4 (Channel access phase based on DCF) Yusuke Asai (NTT)

21. Throughput Evaluation • Implicit feedback and CSI feedback per 10ms are assumeded. • Through improvement reaches 48% when the number of STAs per AP is 2 by spatial multiplexing transmission between twp APs. • It can saturate throughput even when traffic per AP is not saturated. 48% Normalized throughput The number of STAs per AP Yusuke Asai (NTT)

22. Throughput Improvement as a function of CSI lifetime 40-58% improvement • Throughput improvement depends on the length of CSI lifetime. • When CSI lifetime is longer, less frequent CSI feedback is required. • 40-58% throughput performance improvement can be achieved by the proposed scheme. Normalized Throughput Improvement The number of STAs per AP Yusuke Asai (NTT)

23. Summary • This submission shows the update points for the interference management technique in OBSS environment in terms of following topics: • Frame sequence and contents of control / management frames • Security class change • Throughput evaluation • Throughput evaluation shows that the proposed interference management using transmit beamforming improves throughput performance in OBSS environment by up to 58%. Yusuke Asai (NTT)

24. References [1] Yusuke Asai, “Interference Management Using Beamforming Technique in OBSS Environment,” Doc. IEEE802.11-10/0585r4. [2] Yusuke Asai, “Frame Sequence of Interference Management Using Beamforming Technique in OBSS Environment,” Doc. IEEE802.11-10/0831r0. Yusuke Asai (NTT)