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doc.: IEEE 802.11-10/0831r0
Submission
July 2010
Yusuke Asai (NTT)Slide 1
Frame Sequence of Interference Management Using Beamforming Technique
in OBSS Environment
Authors: Name Affiliations Address Phone email
Yusuke Asai NTT 1-1 Hirkarinooka, Yokosuka-shi, Kanagawa, Japan, 239-0847
+81 46 859 3494
Takeo Ichikawa NTT 1-1 Hirkarinooka, Yokosuka-shi, Kanagawa, Japan, 239-0847
+81 46 859 3079
Shoko Shinohara
NTT 1-1 Hirkarinooka, Yokosuka-shi, Kanagawa, Japan, 239-0847
+81 46 859 5107
Riichi Kudo NTT 1-1 Hirkarinooka, Yokosuka-shi, Kanagawa, Japan, 239-0847
+81 46 859 3140
Koichi Ishihara NTT 1-1 Hirkarinooka, Yokosuka-shi, Kanagawa, Japan, 239-0847
+81 46 859 4233
Masato Mizoguchi
NTT 1-1 Hirkarinooka, Yokosuka-shi, Kanagawa, Japan, 239-0847
+81 46 859 3758
Date: 2010-07-12
doc.: IEEE 802.11-10/0831r0
Submission
July 2010
Slide 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 null steering to STAs associate with the other AP.
• Brief evaluation for throughput performance shows that the proposed technique enhances throughput.
Yusuke Asai (NTT)
doc.: IEEE 802.11-10/0831r0
Submission
July 2010
Slide 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)
doc.: IEEE 802.11-10/0831r0
Submission Slide 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 effective for 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.
Yusuke Asai (NTT)
July 2010
STA1 STA2
AP1 AP2
Null steering to the STAs on the other BSS
doc.: IEEE 802.11-10/0831r0
Submission
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.
July 2010
Yusuke Asai (NTT)Slide 5
doc.: IEEE 802.11-10/0831r0
Submission Slide 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)
July 2010
doc.: IEEE 802.11-10/0831r0
Submission Slide 7
Implicit / explicit beamforming [2]
Yusuke Asai (NTT)
July 2010
Pros. Cons.
Implicit beamforming
It has small overhead to obtain CSI. After calibration, only sounding frame transmission is required, which leads to higher throughput performance. (small overhead)
Calibration function must be supported on PHY layer. Additional signal processing and memory are required. (increased implementation complexity)
Explicit beamforming
There is no need to equip calibration function on AP/STASignal processing in PHY layer is much simpler than implicit case. (simple implementation)
In addition to sounding frame transmission, it requires CSI feedback from each STA. (large overhead)
doc.: IEEE 802.11-10/0831r0
Submission Slide 8
Legend: R: RTS frameC: CTS frameS: Sounding frameData: A-MPDU Data frame (beamformed)BA: BlockAck frame
Frame sequence:1. Sequence initiation2. CSI acquisition3. NAV setting4. data transmission (spatially
multiplexing using beamforming)
5. BA transmission (scheduled)6. Medium is released.
Frame sequence using implicit feedback (1/8)
Yusuke Asai (NTT)
July 2010
AP1(initiator)
STA1
AP2(responder)
STA2
2.1. 3. 4. 5. 6.
C
BA
BA
C Data for STA2
R
S
R
S
Data for STA1
Omni-directional transmission Beamformed transmission
doc.: IEEE 802.11-10/0831r0
Submission
NAV
Slide 9
Frame sequence using implicit feedback (2/8)
Yusuke Asai (NTT)
July 2010
AP1(initiator)
STA1
AP2(responder)
STA2
2.1. 3. 4. 5. 6.
C
BA
BA
C Data for STA2
R
S
R
S
Data for STA1
• 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.
doc.: IEEE 802.11-10/0831r0
Submission
NAV
Slide 10
Frame sequence using implicit feedback (3/8)
Yusuke Asai (NTT)
July 2010
AP1(initiator)
STA1
AP2(responder)
STA2
2.1. 3. 4. 5. 6.
C
BA
BA
C Data for STA2
R
S
R
S
Data for STA1
• 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.
NAV
doc.: IEEE 802.11-10/0831r0
Submission
NAV
Slide 11
Frame sequence using implicit feedback (4/8)
Yusuke Asai (NTT)
July 2010
AP1(initiator)
STA1
AP2(responder)
STA2
2.1. 3. 4. 5. 6.
C
BA
BA
C Data for STA2
R
S
R
S
Data for STA1
• 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.)
NAV
doc.: IEEE 802.11-10/0831r0
Submission
NAV
Slide 12
Frame sequence using implicit feedback (5/8)
Yusuke Asai (NTT)
July 2010
AP1(initiator)
STA1
AP2(responder)
STA2
2.1. 3. 4. 5. 6.
C
BA
BA
C Data for STA2
R
S
R
S
Data for STA1
• 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.)
NAV NAV
doc.: IEEE 802.11-10/0831r0
Submission
NAV
Slide 13
Frame sequence using implicit feedback (6/8)
Yusuke Asai (NTT)
July 2010
AP1(initiator)
STA1
AP2(responder)
STA2
2.1. 3. 4. 5. 6.
C
BA
BA
Data for STA2
R
S
S
Data for STA1
• 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].
NAV NAV
NAV
R
C
doc.: IEEE 802.11-10/0831r0
Submission
NAV
Slide 14
Frame sequence using implicit feedback (7/8)
Yusuke Asai (NTT)
July 2010
AP1(initiator)
STA1
AP2(responder)
STA2
2.1. 3. 4. 5. 6.
C
BA
BA
Data for STA2
R
S
S
Data for STA1
• 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.
NAV NAV
NAV
R
C
(Null beam)(Null beam)
doc.: IEEE 802.11-10/0831r0
Submission
NAV
Slide 15
Frame sequence using implicit feedback (8/8)
Yusuke Asai (NTT)
July 2010
AP1(initiator)
STA1
AP2(responder)
STA2
2.1. 3. 4. 5. 6.
C
BA
BA
Data for STA2
R
S
S
Data for STA1
• STA1 and STA2 transmit BlockAck frame in scheduled manner. • After BlockAck transmission, medium is released.
NAV NAV
NAV
R
C
doc.: IEEE 802.11-10/0831r0
Submission Slide 16
Legend: R: RTS frameC: CTS frameS: Sounding frameF: CSI feedback frameData: A-MPDU data frame (beamformed)BA: BlockAck frame
Frame sequence:1. Sequence initiation2. CSI acquisition for AP13. CSI acquisition for AP24. NAV setting5. data transmission (spatially multiplexing using beamforming)6. BA transmission (scheduled)7. Medium is released.
Frame sequence using explicit feedback (1/6)
Yusuke Asai (NTT)
July 2010
AP1(initiator)
STA1
AP2(responder)
STA2
2.1. 4. 5. 6.
C
BA
BA
Data for STA2
R S
F
Data for STA1R
C
F
3.
S
F
F
7.
doc.: IEEE 802.11-10/0831r0
Submission Slide 17
Frame sequence using explicit feedback (2/6)
Yusuke Asai (NTT)
July 2010
AP1(initiator)
STA1
AP2(responder)
STA2
2.1. 4. 5. 6.
C
BA
BA
Data for STA2
R S
F
Data for STA1R
C
F
3.
S
F
F
7.
• 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.
NAV
Omni-directional transmission Beamformed transmission
doc.: IEEE 802.11-10/0831r0
Submission Slide 18
Frame sequence using explicit feedback (3/6)
Yusuke Asai (NTT)
July 2010
AP1(initiator)
STA1
AP2(responder)
STA2
2.1. 4. 5. 6.
C
BA
BA
Data for STA2
R S
F
Data for STA1R
C
F
3.
S
F
F
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.
NAV
NAV
doc.: IEEE 802.11-10/0831r0
Submission Slide 19
Frame sequence using explicit feedback (4/6)
Yusuke Asai (NTT)
July 2010
AP1(initiator)
STA1
AP2(responder)
STA2
2.1. 4. 5. 6.
C
BA
BA
Data for STA2
R S
F
Data for STA1R
C
F
3.
S
F
F
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].)
NAV
NAV
doc.: IEEE 802.11-10/0831r0
Submission Slide 20
Frame sequence using explicit feedback (5/6)
Yusuke Asai (NTT)
July 2010
AP1(initiator)
STA1
AP2(responder)
STA2
2.1. 4. 5. 6.
C
BA
BA
Data for STA2
R S
F
Data for STA1R
C
F
3.
S
F
F
7.
• AP2 carries out explicit CSI feedback as well as AP1.
NAV
NAV
doc.: IEEE 802.11-10/0831r0
Submission Slide 21
Frame sequence using explicit feedback (6/6)
Yusuke Asai (NTT)
July 2010
AP1(initiator)
STA1
AP2(responder)
STA2
2.1. 4. 5. 6.
C
BA
BA
Data for STA2
R S
F
Data for STA1R
C
F
3.
S
F
F
7.
NAV
NAV NAV
• After APs obtain complete CSI, the remaining sequence is identical to implicit feedback case.
NAV
doc.: IEEE 802.11-10/0831r0
Submission Slide 22
Throughput Evaluation
Parameter Value
# of APs 2
# of Tx/Rx antennas per AP 8
# of Tx/Rx antennas per STA 2
# of STAs per AP 1 / 2 / 3 / 4
# of subcarrier per spatial stream 234
Frequency bandwidth 80 MHz
MCS 64QAM, R=5/6
MSDU size 1500 Byte
A-MPDU size 64kByte
Yusuke Asai (NTT)
July 2010
• Evaluation Parameters
doc.: IEEE 802.11-10/0831r0
Submission Slide 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.
AP1
STA1
AP2
STA2
Data for STA1
Data transmission from AP1 to STA1
(Channel access phase based on DCF)Yusuke Asai (NTT)
July 2010
(medium busy)
(medium busy)
(medium busy)
(medium busy)
BA
BA
Data for STA2
Data transmission from AP2 to STA2
(SU-MIMO)
(SU-MIMO)
doc.: IEEE 802.11-10/0831r0
Submission Slide 24
Frame sequence without interference management (implicit feedback)
AP1
STA1
AP2
STA3
Data transmission from AP1 to STA1/2
Data transmission from AP2 to STA3/4
(Channel access phase based on DCF)Yusuke Asai (NTT)
July 2010
(medium busy)
(medium busy)
(medium busy)
(medium busy)
STA4(medium busy)
Data for STA4
S
S
R
BA
BA
BA
BA
S
S
R
(medium busy)STA2
(DL MU-MIMO)
(DL MU-MIMO)
Data for STA3
Data for STA2
Data for STA1
doc.: IEEE 802.11-10/0831r0
Submission Slide 25
Frame sequence without interference management (explicit feedback)
AP1
STA1
AP2
STA3
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)
July 2010
(medium busy)
(medium busy)
(medium busy)
(medium busy)
STA2
STA4
F
(medium busy)
(medium busy)
BA
BA
BA
BA
S
F
F
S
F
Data for STA4
Data for STA3
Data for STA2
Data for STA1
doc.: IEEE 802.11-10/0831r0
Submission
The number of STAs per AP
Nor
mal
ized
thro
ughp
ut
Slide 26
Throughput Evaluation
Yusuke Asai (NTT)
July 2010
• 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 no degrees of freedom at antenna.
52%
doc.: IEEE 802.11-10/0831r0
Submission
The number of STAs per AP
Nor
mal
ized
thro
ughp
ut
Slide 27
Throughput Evaluation
Yusuke Asai (NTT)
July 2010
• Explicit Feedback case
37%
• 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.
doc.: IEEE 802.11-10/0831r0
Submission
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.
July 2010
Yusuke Asai (NTT)Slide 28
doc.: IEEE 802.11-10/0831r0
Submission Slide 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)
July 2010
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