1. Fair and protected DLS July 2007 Date:2007-07-17 LG Electronics
Notice: This document has been prepared to assist IEEE It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.
Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE
Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures < ieee802.org/guides/bylaws/sb-bylaws.pdf>, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE Working Group. If you have questions, contact the IEEE Patent Committee Administrator at
LG Electronics

2. Outline Intuitive motivation of direct link protection
July 2007
Outline
Intuitive motivation of direct link protection
Substantiation: simulation results
RTS/CTS approach
DL protection – only the tip of the iceberg
Towards protection, spatial reuse and fairness
LG Electronics

3. QSTAs use 11e tools We assume legacy AP and QSTAs
July 2007
QSTAs use 11e tools
We assume legacy AP and QSTAs
QSTAs use state-of-the-art 11e data transmission scheme: QSTAs get TXOPs to transmit data and use Block ACK mechanism with Immediate ACK policy
LG Electronics

4. Intuitive motivation of direct link protection
July 2007
Intuitive motivation of direct link protection
3->4 RTS
4->3 CTS
1 heard nothing
2 heard RTS but not CTS
While 3->4 DATA:
1->2 RTS
2 doesn’t reply
CW of 1 increases
1->2 retry RTS, no answer
CW of 1 increases again …
In contention between 3 and 1, 3 wins almost always
3->4 DATA:
1 drops the packet (lifetime)
LG Electronics

5. We are going to consider the following cases
July 2007
We are going to consider the following cases 2 1 3 4
LG Electronics

6. Simulation assumptions
July 2007
Simulation assumptions
QSTAs use:
legacy data transmission mechanism
11e block data transmission mechanism
Initiators of direct transmissions (QSTAs 1 and 3) work in saturation
11a PHY, 54 Mbps
LG Electronics

7. Case 1 July 2007 All four QSTAs are in TX-range of one another
LG Electronics

8. Case 2 July 2007 QSTAs 1 and 4 are in CS-range of one another
LG Electronics

9. July 2007
Case 3
QSTAs 1 and 4 don’t hear one another
LG Electronics

10. Case 4 July 2007 QSTAs 1 and 4 don’t hear one another
QSTAs 1 and 3, and 2 and 4 are in CS-range of one another
LG Electronics

11. Case 5 July 2007 QSTAs 2 and 3 are in TX-range of one another
LG Electronics

12. Case 6 July 2007 QSTAs 2 and 3 are in CS-range of one another
LG Electronics

13. Case 7 July 2007 Two pairs of QSTAs cannot hear one another
LG Electronics

14. RTS/CTS approach July 2007 It’s a good approach: RTS CTS But… DATA
Simple
Standard frames
Reliable protection of direct links
RTS
CTS
But…
DATA
LG Electronics

15. RTS/CTS approach July 2007 But it allows NO spatial reuse 3->AP RTS
AP->3 CTS (broadcast)
The CTS from AP prohibits all other transmissions
However, transmissions 1->2 and 3->4 would be possible at the same time
Solution?
LG Electronics

16. Another problem: unfairness
July 2007
Another problem: unfairness
Non-direct:
AP queues DATA
First contention: 1->AP
Queueing delay at AP
Second contention: AP->2
AP is a bottleneck for several non-direct links 2
Direct:
The only contention 3->4
So, direct link gets much more of total throughput at the expense of non-direct link
Solution?
LG Electronics

17. Unfairness: Case A Simulation results: Links: July 2007
In non-saturation:
See Figure below
In saturation:
Link 3->4 throughput: 27.2 Mbps
Links 1->2 and 5->6 throughput: 0.7 Mbps each
Reasons:
The same as in Case 5
AP is a bottleneck
Links:
DL connection: 3->4
Non-DL connections:
1->AP->2 and 5->AP->6
LG Electronics

18. Unfairness: Case B Simulation results: July 2007 Links:
DL connection 3->4
Non-DL connections between legacy stations:
1->AP->2 and 5->AP->6
No obstacles
Simulation results:
In non-saturation:
See Figure below
In saturation
Link 3->4 throughput: 7.5 Mbps
Links 1->2 and 5->6 throughput: 3.4 Mbps each
Reason:
AP is a bottleneck
LG Electronics

19. Solution towards protection, spatial reuse and fairness
July 2007
Solution towards protection, spatial reuse and fairness
We propose to introduce a special Direct Link Announcement (DLA) action frame
Basic idea: the source QSTA shall broadcast/multicast the DLA frame over the AP
LG Electronics

20. DLA payload Direct transmission source and its destination
July 2007
DLA payload
Direct transmission source and its destination
Duration of the planning direct transmission (a-lá NAV)
DLA expiration time; after the time, DLA should be ignored
LG Electronics

21. Our approach: Scheme 1 July 2007 AP queues the DLA Protection:
All QSTAs are informed of the planning direct transmission and its duration
Upon receiving DLA back, QSTA 3 starts DATA after PIFS without contention
Fairness:
It takes two contention phases and queueing delay at the AP to start transmissions, equally direct or non-direct
DLA
DLA
ACK
DATA
LG Electronics

22. Our approach: Scheme 1(continue)
July 2007
Our approach: Scheme 1(continue)
Spatial reuse :
During DL Setup or by other radio measurement procedures, QSTAs collect a list of neighbors which it may interfere with
The list is included into the DLA
QSTAs which are not in the list may communicate during the direct transmission without sending DLA frames
DLA
DATA 5
DATA
LG Electronics

23. Our approach: Scheme 2 July 2007 Spatial reuse :
QSTAs don’t need to rely on knowledge of the list of neighbors which it may interfere with
Upon receiving DLA back from the AP, 3 starts RTS/CTS with 4 without contention
QSTAs which heard DLA, but neither RTS nor CTS, may communicate during the direct transmission
DLA
DATA 5
CTS
DATA
RTS
LG Electronics

24. Combination with RTS/CTS approach
July 2007
Combination with RTS/CTS approach
DLA timeout:
RTS/CTS approach upon DLA timeout expiration
Protection from legacy STAs
LG Electronics

25. Our approach: Scheme 3 July 2007
Combination of Scheme 1 and RTS/CTS approach
Aim: to improve the direct link protection from legacy STAs
DLA
DATA 5
RTS
CTS
DATA
LG Electronics

26. Our approach: Scheme 4 July 2007
Combination of Scheme 2 and RTS/CTS approach
Aim: to improve the direct link protection from legacy STAs
DLA
DATA 5
RTS
CTS
CTS
DATA
RTS
LG Electronics

27. Thanks for your kind attention!
July 2007
Thanks for your kind attention!
LG Electronics

28. July 2007
Call for interest
Who’s interested in getting together to work on this?
What should be the next steps:
Preparation the normative text ?
LG Electronics