1 / 16

TXOP Sharing for DL MU-MIMO Support

This paper proposes a TXOP sharing mechanism to support DL MU-MIMO in 802.11 networks by allowing simultaneous transmission of frames belonging to different ACs.

lawsonj
Download Presentation

TXOP Sharing for DL MU-MIMO Support

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Date: 2010-09-13 [TXOP Sharing for DL MU-MIMO Support] Authors:

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Illustration: Sharing the TXOP Figure. 1

  10. 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.

  11. Illustration: Frame Exchanges Figure. 2

  12. 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.

  13. 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:

  14. 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:

  15. 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:

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

More Related