doc.: ieee 802.11-10/1123r0 submission september 2010 zhu/kim et al 1 date: 2010-09-13 authors:...

doc.: IEEE 802.11-10/1123r0

Submission

September 2010

Zhu/Kim et al1

Date: 2010-09-13

Authors:

Name Affiliations Address Phone email

Allan Zhu Samsung 75 W Plumeria Dr. San Jose CA 95134, USA

+1-408-544-5667

[email protected]

Youngsoo Kim Samsung Mt. 14-1 Nongseo-Ri, Giheung-Eup, Yongin-Si, Gyeonggi-Do, Korea 449-712

+82-31-280-9614

[email protected]

Matt Fischer Broadcom 190 Mathilda Place, Sunnyvale, CA 94040 +1-408-543-3370

[email protected]

Yong Liu Marvell 5488 Marvell Lane, Santa Clara, CA 95054, USA

+1-408-222-8412

[email protected]

Robert Stacey Intel 2111 NE 25th Ave Hillsboro, OR 97124, USA

+1-503-724-0893

[email protected]

Hemanth Sampath Qualcomm QRC224J, 5665 Morehouse Dr. San Diego, CA 92121-1714, USA

[email protected]

James Cho Atheros 5480 Great America Parkway, Santa Clara, CA 95054, USA

[email protected]

Jae Seung Lee ETRI 161 Gajeong-dong, Yuseong-gu, Daejeon, Korea

+82 42 860 1326

[email protected]

Yongho Seok LG Electronics, Inc.

533, Hogye-1dong, Dongan-Gu, Anyang-Shi, Kyungki-Do, 431-749, Korea

+82-31-450-1947 [email protected]

[TXOP Sharing for DL MU-MIMO Support]

doc.: IEEE 802.11-10/1123r0

Submission

September 2010

Zhu/Kim et al2

Abstract

• A Multi-User Transmit Opportunity (MU-TXOP) mechanism (i.e. TXOP sharing) is proposed to extend the existing 802.11 TXOP concept to support DL MU-MIMO.

doc.: IEEE 802.11-10/1123r0

Submission

September 2010

Zhu/Kim et al3

The Limitation of Current 802.11 TXOP

• The current EDCA TXOP mechanism is per AC based.– A TXOP obtained by a STA can only be used to transmit frames

belonging to the AC that won the TXOP.– A STA may initiate multiple frame exchange sequences to

transmit MMPDUs and/or MSDUs during a TXOP, but only within the same AC.

– Internal contention among EDCAFs of different ACs allows only one EDCAF to win the internal competition for the TXOP.

• These rules would not allow multiple frames belonging to different ACs to be transmitted simultaneously.– They need to be modified or enhanced to support DL MU-MIMO

transmission.

doc.: IEEE 802.11-10/1123r0

Submission

September 2010

Zhu/Kim et al4

Definitions

• The following terms are defined for the TXOP sharing mechanism.

– Primary AC: the AC that wins the TXOP for channel access after both external and internal competition. There is only one primary AC at any time.

– Secondary AC: an AC that does not win a TXOP but wants to share the TXOP obtained by the primary AC for simultaneous transmissions. There could be multiple secondary ACs at any time.

– Primary Destinations: destinations targeted by the frames belonging to the primary AC. There could be one or more primary destinations at any time.

– Secondary Destinations: destinations targeted by the frames belonging to secondary ACs. There could be one or more secondary destinations at any time.

doc.: IEEE 802.11-10/1123r0

Submission

September 2010

Zhu/Kim et al5

Main Ideas

• Each EDCAF of the AP’s MAC layer competes for TXOP as in current spec.

• Once an EDCAF wins a TXOP it becomes the owner of the TXOP.– its corresponding AC becomes Primary AC, and

– Its corresponding destination(s) become Primary Destination(s).

• The Primary AC can share the TXOP with other ACs which did not win the medium access – the TXOP becomes MU-TXOP.– These other ACs become Secondary ACs and their corresponding destinations

become Secondary destinations.

– The AP then groups the Secondary Destinations together with the Primary Destination(s) for simultaneous transmission (e.g. using GroupID).

• When sharing, a secondary AC may transmit even though that AC has not won contention and the backoff counter for that AC is not zero.

doc.: IEEE 802.11-10/1123r0

Submission

September 2010

Zhu/Kim et al6

TXOP Modes

• Current EDCA TXOP has two modes

– the initiation of the EDCA TXOP • occurs when the EDCA rules permit access to the medium• this is kept the same as in the current spec

– the multiple frame transmission within an EDCA TXOP• occurs when an EDCAF retains the right to access the medium.• this needs to be enhanced to allow multiple, simultaneous frame exchange

sequences.

• To support DL MU-MIMO transmissions, we propose to add a Share mode between the current two modes– the sharing of the EDCA TXOP

• occurs after the initiation mode , and before the multiple frame transmission mode.

doc.: IEEE 802.11-10/1123r0

Submission

September 2010

Zhu/Kim et al7

Mode #1: Initiation

• As specified in the current spec, at each of the slot boundaries, each EDCAF shall initiate a transmission sequence if(a) There is a frame available for transmission at that EDCAF, and(b) The backoff timer for that EDCAF has a value of zero, and(c) Initiation of a transmission sequence is not allowed to commence at this time for an EDCAF of higher UP.

• In this case, the AC becomes the Primary AC and the owner of the TXOP. Other ACs become secondary ACs.

• Note there is no change to current spec in this mode.

doc.: IEEE 802.11-10/1123r0

Submission

September 2010

Zhu/Kim et al8

Mode #2: Sharing

• Once a TXOP is obtained by the primary AC, the AP can decide whether and how to share it with other ACs, subject to the restrictions described in Slide 10.

• The AP determines which secondary ACs and secondary destinations can share the TXOP, and in what order. – How to pick a secondary AC/secondary destination is an implementation issue.

• This Share mode occurs after the initiation mode and before the Multiple Frame Transmission.

• Frames may be transmitted from a secondary AC queue if that queue is sharing the TXOP, even if the backoff counter for that secondary AC is not at zero.

• Internal competition for TXOP is resolved by allowing secondary ACs transmit in the same TXOP of the primary AC.

doc.: IEEE 802.11-10/1123r0

Submission

September 2010

Zhu/Kim et al9

Illustration: Sharing the TXOP

STA-A(AP)

AC_VI (1)

AC_BE (2)

AC_BE (1) AC_VO (2)

STA-B(Primary Dst)

STA-C(Secondary

Dst)

STA-D(Primary Dst)

AC_VI (2)AC_VO (1)

MU-TXOP

Time

EDCAF EDCAF EDCAF EDCAF

(MSDU, UP)

AC_VO AC_VI AC_BE AC_BK

(1)

(2)

(1)

(2)

(1)

(2)

A-MPDU boundaries

This figure shows how frames in different ACs can share the MU-TXOP.

In the figure, we assume AC_VI is the primary AC. It has two blocks of MSDU frames to transmit, one for STA-1 and the other for STA-3. So both STA-1 and STA-3 are primary destinations. AC_VO and AC_BE are secondary ACs, and STA-2 is secondary destination.

MSDUs in the buffer may be fragmented or aggregated into multiple A-MPDUs, each being transmitted in one downlink phase.

Among secondary ACs, higher priority traffic gets transmitted earlier; e.g. AC_VO is transmitted earlier than AC_BE.

Note this figure does not show the frame exchange sequence; it only shows the transmission arrangement and order. The frame exchange sequence will be shown in Figure 2.

Figure. 1

doc.: IEEE 802.11-10/1123r0

Submission

September 2010

Zhu/Kim et al10

Mode #3: Multiple Frame Exchange

• During a MU-TXOP won by an EDCAF, the AP may initiate multiple frame exchange sequences for frames belonging to the same or different ACs.

• The TXOP duration is determined by the TXOP limit of the primary AC.– In addition, at least one stream set* in each DL MU-MIMO PPDU shall

contain only MSDU(s) corresponding to the primary AC.

– This is to ensure fairness to other non-AP stations

• Inside one A-MPDU, AP transmits frames of only one AC to a STA.– No mixed ACs in one A-MPDU

* A stream set is defined as a group of spatial streams of a DL MU-MIMO PPDU that are all intended for reception by a single recipient.

doc.: IEEE 802.11-10/1123r0

Submission

September 2010

Zhu/Kim et al11

Illustration: Frame Exchanges

Figure. 2

AP

STA-1

RA = STA-1, AC_VI (1)


BA1

BA3

RA=STA-2, AC_VO (2)

BA2STA-2

STA-3

Downlink Phase Uplink Phase

pad

padPream

ble

Time

BA1

BA3


BA1


MU-TXOP


RA = STA-3, AC_VO (1)

STA-2, AC_VO (2)

pad

pad

Preamble


RA = STA-3, AC_BE (2)

STA-2, AC_BE (1)Preamble

BA2

BA3

BA2

A-MPDU boundaries

- The assumptions of the figure are the same as in Figure 1.- Additional assumption: scheduled Block Acknowledgement scheme is used. But this does not prevent other acknowledgements schemes to be used.- Padding fields are for illustration only.

pad

doc.: IEEE 802.11-10/1123r0

Submission

September 2010

Zhu/Kim et al12

Summary

• MU-TXOP breaks the current limitation of TXOP and enables simultaneous transmissions of multiple traffic streams at the MAC layer.

• Expand current two EDCA TXOP modes to three– A “share” mode is added after the initiation of the TXOP.

• ACs are divided into two classes, primary AC and secondary AC for each obtained MU-TXOP.

• Destinations are also divided into two classes, primary destinations and secondary destinations.

• MU-TXOP is obtained using EDCA parameters of the primary AC but may be shared by multiple traffic streams, which may or may not belong to the same AC.

• Internal collision can be resolved by TXOP sharing (except some special cases).

• The TXOP duration is determined by the TXOP limit of the primary AC.

• When transmitting, at least one stream set in each DL MU-MIMO PPDU shall contain only MSDU(s) corresponding to the primary AC.

doc.: IEEE 802.11-10/1123r0

Submission

September 2010

Zhu/Kim et al13

Straw Poll #1

• Do you support adding the following new section to the Proposed Specification Framework for TGac (11-09/992) to introduce the new mode of TXOP operation – TXOP sharing?– Section 6.4 TXOP Sharing

• Yes:

• No:

• Abstain:

doc.: IEEE 802.11-10/1123r0

Submission

September 2010

Zhu/Kim et al14

Straw Poll #2

• Do you support adding the following four definitions (as described in Slide #4) to Section 1 of the Proposed Specification Framework for TGac (11-09/992)?– Primary AC / Secondary AC

– Primary Destination / Secondary Destination

• Yes:

• No:

• Abstain:

doc.: IEEE 802.11-10/1123r0

Submission

September 2010

Zhu/Kim et al15

Straw Poll #3

• Do you support the following rules to be included in Section 6.4 of the Proposed Specification Framework for TGac (11-09/992), for VHT DL MU TXOP sharing?– The TXOP duration is determined by the TXOP limit of the primary AC.

– At least one stream set in each DL MU-MIMO PPDU shall contain only MSDU(s) corresponding to the primary AC, where a stream set is defined as a group of spatial streams of a DL MU-MIMO PPDU that are all intended for reception by a single recipient.

• Yes:

• No:

• Abstain:

doc.: IEEE 802.11-10/1123r0

Submission

September 2010

Zhu/Kim et al16

Reference

[1] IEEE Doc 11-10/0591r00, TXOP Enhancement for DL MU-MIMO Support

doc.: ieee 802.11-10/1123r0 submission september 2010 zhu/kim et al 1 date: 2010-09-13 authors:...

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