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Frame Sequence of Interference Management Using Beamforming Technique in OBSS Environment

Frame Sequence of Interference Management Using Beamforming Technique in OBSS Environment. Date: 2010-07-12. Authors:. Background. In May IEEE meeting, we have made a presentation on the interference management using beamforming technique for OBSS environment [1].

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Frame Sequence of Interference Management Using Beamforming Technique in OBSS Environment

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  1. Frame Sequence of Interference Management Using Beamforming Technique in OBSS Environment Date: 2010-07-12 Authors: Yusuke Asai (NTT)

  2. Background • In May IEEE meeting, we have made a presentation on the interference management using beamforming technique for OBSS environment [1]. • This technique enables two APs to transmit data frames simultaneously by nullsteering to STAs associate with the other AP. • Brief evaluation for throughput performance shows that the proposed technique enhances throughput. Yusuke Asai (NTT)

  3. Abstract • This submission introduces the detail of the frame sequence for the proposed interference management technique in OBSSs environment. • Throughput evaluation shows that the proposed interference management technique is effective for both implicit and explicit feedback cases. Yusuke Asai (NTT)

  4. Basic concept of interference management using beamforming in OBSS environment • In dense OBSSs environment (ex. typical apartment scenario in Japan [2]), neither power control scheme frequency channel selection is effectivefor improve throughput performance [1]. • 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 between two APs is possible. AP1 AP2 STA1 STA2 Null steering to the STAs on the other BSS Yusuke Asai (NTT)

  5. Summary of the proposed interference management technique [1] Merits of the proposed interference management technique: • Simple implementation: Each AP inherently has a transmit beamforming function because DL MU-MIMO transmission will mandatory feature in TGac. • Throughput performance improvement: The proposed interference management technique improves throughput performance up to 53% when two APs are collaborate with each other. Yusuke Asai (NTT)

  6. Update Points • More details on frame sequence is introduced. • Two sets of frame sequence for implicit and explicit feedback • The details of NAV setting (MAC level protection against hidden nodes) • Throughput performance for both implicit and explicit feedback cases is evaluated. Yusuke Asai (NTT)

  7. Implicit / explicit beamforming [2] Yusuke Asai (NTT)

  8. Frame sequence using implicit feedback (1/8) AP1 (initiator) R R Data for STA1 Frame sequence: Sequence initiation CSI acquisition NAV setting data transmission (spatially multiplexing using beamforming) BA transmission (scheduled) Medium is released. S BA STA1 AP2 (responder) C C Data for STA2 S BA STA2 1. 2. 3. 4. 5. 6. Legend: R: RTS frame C: CTS frame S: Sounding frame Data: A-MPDU Data frame (beamformed) BA: BlockAck frame Omni-directional transmission Beamformed transmission Yusuke Asai (NTT)

  9. Frame sequence using implicit feedback (2/8) AP1 (initiator) R R Data for STA1 NAV S BA STA1 AP2 (responder) C C Data for STA2 S BA STA2 1. 2. 3. 4. 5. 6. • AP1 transmits an RTS frame: • - to invite AP2 to cooperate spatially multiplexed transmission by AP1 and AP2. • - to inform AP2 the available number of spatial streams used by AP2. • - to request STA1 to transmit sounding frame after AP2’s response. • This RTS frame sets the NAV until the end of final sounding frame sent by STA2. Yusuke Asai (NTT)

  10. Frame sequence using implicit feedback (3/8) AP1 (initiator) R R Data for STA1 NAV S BA STA1 AP2 (responder) C C Data for STA2 NAV S BA STA2 1. 2. 3. 4. 5. 6. • When AP2 accepts AP1’s invitation, it responds by a CTS frame. (Otherwise, AP2’s CTS frame contains the information to refuse cooperation.) The CTS frame includes the number of spatial streams used by AP2. • The CTS frame also requests STA2 to transmit a sounding frame after the sounding frame from STA1. • This CTS frames set the NAV until the end of final sounding frame from STA2. Yusuke Asai (NTT)

  11. Frame sequence using implicit feedback (4/8) AP1 (initiator) R R Data for STA1 NAV S BA STA1 AP2 (responder) C C Data for STA2 NAV S BA STA2 1. 2. 3. 4. 5. 6. • STA1 and STA2 transmit sounding frames (NDP) for AP1 and AP2 • to estimate CSI between STA1/STA2 and AP1/AP2. • (It is assumed that calibration among APs/STAs is established prior to this sequence.) Yusuke Asai (NTT)

  12. Frame sequence using implicit feedback (5/8) AP1 (initiator) R R Data for STA1 NAV NAV S BA STA1 AP2 (responder) C C Data for STA2 NAV S BA STA2 1. 2. 3. 4. 5. 6. • AP1 transmits RTS frame to protect the data and the BlockACK frames by setting NAV. • In addition, the RTS frame informs the length of the data frame to AP2. • (This frame also provides enough time for AP1/AP2 to calculate beamforming weight.) Yusuke Asai (NTT)

  13. Frame sequence using implicit feedback (6/8) AP1 (initiator) R R Data for STA1 NAV NAV S BA STA1 AP2 (responder) C C Data for STA2 NAV NAV S BA STA2 1. 2. 3. 4. 5. 6. • AP2 transmits a CTS frame to inform it is ready for the multiplexed transmission using • beamforming. • In addition, this frame sets appropriate length of NAV for the next data frame and • BlockAck frame. • AP2 set the duration of its data frame less than the data frame of AP1. • AP1 and AP2 may request STAs to transmit CTS frame when there are STAs which • are affected by hidden nodes[3]. Yusuke Asai (NTT)

  14. Frame sequence using implicit feedback (7/8) AP1 (initiator) R R Data for STA1 NAV NAV S BA STA1 (Null beam) (Null beam) AP2 (responder) C C Data for STA2 NAV NAV S BA STA2 1. 2. 3. 4. 5. 6. • AP1 and AP2 transmit the beamformed data frames simultaneously. STA1 and STA2 can receive its frame without interference because of null-steering by AP1 and AP2. Yusuke Asai (NTT)

  15. Frame sequence using implicit feedback (8/8) AP1 (initiator) R R Data for STA1 NAV NAV S BA STA1 AP2 (responder) C C Data for STA2 NAV NAV S BA STA2 1. 2. 3. 4. 5. 6. • STA1 and STA2 transmit BlockAck frame in scheduled manner. • After BlockAck transmission, medium is released. Yusuke Asai (NTT)

  16. Frame sequence using explicit feedback (1/6) AP1 (initiator) R S R Data for STA1 F F BA STA1 AP2 (responder) S C C Data for STA2 F F BA STA2 3. 1. 2. 4. 5. 6. 7. Frame sequence: Sequence initiation CSI acquisition for AP1 CSI acquisition for AP2 NAV setting data transmission (spatially multiplexing using beamforming) BA transmission (scheduled) Medium is released. Legend: R: RTS frame C: CTS frame S: Sounding frame F: CSI feedback frame Data: A-MPDU data frame (beamformed) BA: BlockAck frame Yusuke Asai (NTT)

  17. Frame sequence using explicit feedback (2/6) AP1 (initiator) R S R Data for STA1 NAV F F BA STA1 AP2 (responder) S C C Data for STA2 F F BA STA2 3. 1. 2. 4. 5. 6. 7. Omni-directional transmission Beamformed transmission • AP1 transmits an RTS frame to invite AP2 for multiplexed transmission by AP1 and AP2. • The number of available spatial streams used by AP2 is sent to AP2 by the RTS frame. • This RTS frame sets the NAV until the end of final sounding frame sent by STA2. Yusuke Asai (NTT)

  18. Frame sequence using explicit feedback (3/6) AP1 (initiator) R S R Data for STA1 NAV F F BA STA1 AP2 (responder) S C C Data for STA2 NAV F F BA STA2 3. 1. 2. 4. 5. 6. 7. • When AP2 accepts AP1’s invitation, it responds a CTS frame to inform the acceptance. • (Otherwise, AP2 responds to refuse cooperation.) • The CTS frame also informs the number of spatial streams used by AP2 to AP1. • This CTS frame set the NAV until the end of final CSI feedback frame from STA2. Yusuke Asai (NTT)

  19. Frame sequence using explicit feedback (4/6) AP1 (initiator) R S R Data for STA1 NAV F F BA STA1 AP2 (responder) S C C Data for STA2 NAV F F BA STA2 3. 1. 2. 4. 5. 6. 7. • AP1 transmits a sounding frame to STA1 and STA2 for explicit CSI feedback. • STA1 and STA2 estimate CSI and feedback the estimated CSI to AP1 in scheduled • manner. • (In the proposed interference management technique, STAs need transmit CSI • feedback frame to both of two APs, which increase overhead. • Some kinds of CSI compression scheme are useful for the proposed technique[4].) Yusuke Asai (NTT)

  20. Frame sequence using explicit feedback (5/6) AP1 (initiator) R S R Data for STA1 NAV F F BA STA1 AP2 (responder) S C C Data for STA2 NAV F F BA STA2 3. 1. 2. 4. 5. 6. 7. • AP2 carries out explicit CSI feedback as well as AP1. Yusuke Asai (NTT)

  21. Frame sequence using explicit feedback (6/6) AP1 (initiator) R S R Data for STA1 NAV NAV F F BA STA1 AP2 (responder) S C C Data for STA2 NAV NAV F F BA STA2 3. 1. 2. 4. 5. 6. 7. • After APs obtain complete CSI, the remaining sequence is identical to • implicit feedback case. Yusuke Asai (NTT)

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

  23. Frame sequence without interference management (implicit /explicit feedback) • One user per AP case, an AP transmits SU-MIMO frames. • In this case, neither sounding frame nor CSI feedback is transmitted. 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)

  24. Frame sequence without interference management (implicit feedback) Data for STA1 R (medium busy) Data for STA2 AP1 (DL MU-MIMO) S BA (medium busy) STA1 S BA (medium busy) STA2 Data for STA3 R (medium busy) Data for STA4 AP2 (DL MU-MIMO) S BA (medium busy) STA3 BA S (medium busy) STA4 Data transmission from AP1 to STA1/2 Data transmission from AP2 to STA3/4 (Channel access phase based on DCF) Yusuke Asai (NTT)

  25. Frame sequence without interference management (explicit feedback) Data for STA1 S (medium busy) Data for STA2 AP1 F BA (medium busy) STA1 F BA (medium busy) STA2 Data for STA3 S (medium busy) Data for STA4 AP2 BA F (medium busy) STA3 F BA (medium busy) STA4 Data transmission from AP1 to STA1 and 2 Data transmission from AP2 to STA3 and 4 Channel access phase based on DCF Yusuke Asai (NTT)

  26. Throughput Evaluation • Implicit Feedback case • 52% of throughput improvement is • achieved when the number of STAs • per AP is two. • In this case, throughput performance of • the proposed technique is saturated • because both AP uses all of degrees of • freedom at antenna for DL MU-MIMO • beamforming and nulling not to radiate • interference to the STAs on the other AP. • When the number of STA per AP is four, • there is nodegrees of freedom at antenna. 52% Normalized throughput The number of STAs per AP Yusuke Asai (NTT)

  27. Throughput Evaluation • Explicit Feedback case • Although overhead due to CSI feedback • increases in explicit feedback, the • proposed scheme achieves 37% of • throughput improvement when the • number of STAs per AP is two. 37% Normalized throughput The number of STAs per AP Yusuke Asai (NTT)

  28. Summary • Frame sequence for the proposed interference management technique in OBSS environment is presented. • Implicit feedback case • Explicit feedback case • Throughput evaluation shows that the proposed interference management using transmit beamforming improves throughput performance in OBSS environment in both implicit and explicit feedback cases. Yusuke Asai (NTT)

  29. References [1] Yusuke Asai, “Interference Management Using Beamforming Technique in OBSS Environment,” Doc. IEEE802.11-10/0585r4. [2] Kentaro Nishimori, "Measurement results for OBSS in home network scenarios,"Doc. 11-09/1031r0 [3] Yuichi Morioka, “Why Implicit TxBF is better for TGac,” Doc. IEEE802.11-10/0818r0. [4] Michelle Gong, “DL MU MUMO Analysis and OBSS Simulation Results,” doc.: IEEE 802.11-10/0567r1. [5] Koichi Ishihara, “CSI Feedback Scheme using DCT for Explicit Beamforming,” Doc. IEEE802.11-10/0806r1. Yusuke Asai (NTT)

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