VHT Metrics Considerations

1. VHT Metrics Considerations Authors: Date: 2008-04-18 Darwin Engwer, Nortel Networks

2. Abstract This presentation reviews some important considerations in the development of an analytical framework for VHT. In particular, relevant metrics are discussed. Please view in slideshow mode to see animations. Darwin Engwer, Nortel Networks

3. Outline • Objectives • Definition • Analytical Framework – Part I • BSS Maximum Throughput Metric (M1) • Analytical Framework – Part II • Multiple BSS Maximum Throughput Metric (M2) • Analytical Framework – Part III • Maximum BSS Throughput Metric in space (M1) • … Darwin Engwer, Nortel Networks

4. Metrics Objectives • Devise key metrics for characterization and comparison of different wireless systems. Darwin Engwer, Nortel Networks

5. What are metrics, and how do they differ from system measurement and performance reports? • Metrics characterize a given system in terms of the abstract entities operating in a perfect environment. • Metrics are computations that expose the capabilities of a given system. • Performance reports (TGT) are the outcomes of specific tests run on a real world implementation operating in a specific, constrained environment for a specific set of use case scenarios. • Measurement reports (802.11k) indicate the current state of an operating network implementation in the real world. Darwin Engwer, Nortel Networks

6. Analytical Framework – Part I • Consider a universe; a void with nothing in it. • In the middle of this void, place an AP with a set of associated STAs communicating with the AP. • The AP is a point of access to a non-802.11 LAN of infinite capacity (through a DS and portal, not shown). • A constellation of n STAs is associated with the AP. • Each STA is attempting to exchange a maximum amount of data with an entity x on the non-802.11 LAN. The entity x has infinite throughput capacity. Darwin Engwer, Nortel Networks

7. STA STA STA STA STA A single AP in a void AP Darwin Engwer, Nortel Networks

8. BSSThroughput Max 1 2 3 4 5 STAs BSS Maximum Throughput (M1) • Now consider that collectively the AP and the set of STAs are capable of some MAXIMUM throughput. Note: Data is for illustration purposes only. Darwin Engwer, Nortel Networks

9. BSS Maximum Throughput where, i = index of current STA n = number of associated and active STAs T = throughput at MAC SAP of STA i of n Darwin Engwer, Nortel Networks

10. Analytical Framework – Part II • Consider a universe; a void with nothing in it. • In the middle of this void, place a set of APs with a set of associated STAs communicating with each AP. • Each AP is a point of access to a non-802.11 LAN of infinite capacity (through a DS and portal, not shown). • A constellation of n STAs is associated with each AP. • Each STA is attempting to exchange a maximum amount of data with an entity x on the non-802.11 LAN. The entity x has infinite throughput capacity. • The APs are collocated. • The APs operate on different channels within a set of k channels. Darwin Engwer, Nortel Networks

11. STA STA STA STA STA STA AP AP AP STA STA STA STA STA STA STA STA STA A set of collocated APs in a void Darwin Engwer, Nortel Networks

12. Max ESS Throughput(Mbps) APs Multiple BSS Maximum Throughput (M2) • Now consider that collectively the set of APs and the associated sets of STAs are capable of some MAXIMUM throughput. Note: Data is for illustration purposes only. Darwin Engwer, Nortel Networks

13. Multiple BSS Maximum Throughput (M2) where, i = index of current STA n = number of associated and active STAs j = index of current AP m = number of APs k = number of channels T = throughput at MAC SAP of STA i of n wrt AP j of m (j, m, k determine number of APs on current channel) Darwin Engwer, Nortel Networks

14. Max Max ESSThroughput(Mbps) APs M2 examples Mbps 802.11a 802.11b APs Note: Data is for illustration purposes only. Darwin Engwer, Nortel Networks

15. Space • The metrics M1 and M2 seek to quantify aspects of the maximum throughput capability of the system. • In doing so, the M1 and M2 metrics ignore any consideration of space (or range) of the APs wrt the STAs. Darwin Engwer, Nortel Networks

16. Analytical Framework – Part III • Consider a universe; a void with nothing in it. • In the middle of this void, place an AP with a set of associated STAs communicating with the AP. • The AP is a point of access to a non-802.11 LAN of infinite capacity (through a DS and portal, not shown). • A constellation of n STAs is associated with the AP. • Each STA is attempting to exchange a maximum amount of data with an entity x on the non-802.11 LAN. The entity x has infinite throughput capacity. • The data rate varies depending on the distance between the AP and each STA. Darwin Engwer, Nortel Networks

17. STA STA STA STA STA An AP in a void, with zones at different rates AP Darwin Engwer, Nortel Networks

18. M1 in space • The M1 metric now expands from a single value to array of values, one per supported MCS, M1□. • Each value in the array represents the maximum throughput achievable using the corresponding MCS, and hence reflects the maximum throughput within an abstract range boundary. Darwin Engwer, Nortel Networks

19. Energy • The metric M1□ seeks to quantify one aspects of the maximum throughput capability of the system. • However, the M1□ metric ignores any consideration of the energy required to lift the bits into a space. Without this correlation the ability of a system to fill a given space with data in unknown. Darwin Engwer, Nortel Networks

20. Energy Factor • [add energy factor notes here, see file 38] • When we consider energy we usually do so in terms of the transmit power (EIRP), but from a system level perspective the amount of work required to actually “lift” the bits into the space is a much more valuable metric. Work is measured in units of Watt seconds, aka Joules. • … Darwin Engwer, Nortel Networks

21. Latency • [Add latency metric notes here] Darwin Engwer, Nortel Networks

22. Metrics Sub-summary • M1 – max BSS throughput • M2 – max ESS throughput • M1□ - max BSS throughput vs MCS • M1□e – max BSS throughput vs MCS vs energy • L1 – latency metric • Given those we can begin to consider parallel communications … Darwin Engwer, Nortel Networks

23. Direction Factor • [add direction factor notes here] • Uplink traffic • Downlink traffic • Combination of both uplink and downlink • (show effect on the formulas) • STA-to-STA traffic Darwin Engwer, Nortel Networks

24. Parallel Communications Metrics • [add parallel communications metrics notes here] • How to quantify various aspects of the system when parallel communications techniques are in use. • Filling a room with data • Note that with VHT we need to move away from a device centric view and instead look at what’s happening in the air. Our objective is to maximize utilize of the air (time, space, energy and frequency). Darwin Engwer, Nortel Networks

25. Impact of various parallel communications techniques • Multi-user MIMO • Downlink metric increases by number of independent streams factor • Network coding • Metric increases by total number of bits delivered, i.e. this includes the coded data • Max value is 1.5x ?? • Broadcast of group addressed data • Metrics are unaffected; same data to same recipients yields no advantage • Single hop relay • Contribution to metrics is constrained to the min() of the inputs to and outputs from the relay station. • MG ? Darwin Engwer, Nortel Networks

26. Conclusion • Metrics are helpful to quantify various approaches. • More work is needed … Darwin Engwer, Nortel Networks

27. References • 11-07-0412-01-0wng-looking-ahead-to-future.ppt • 11-07-0419-01-0000-very-high-throughput-study-group.ppt • 11-07-0574-01-0000-draft-par-and-5criteria-gigabit-tg.doc • 11-07-0724-01-0vht-vht-study-group-thoughts.ppt • 11-07-2863-00-0vht-how-should-we-manage-the-process-for-the-proposed-vht-activity.ppt • 11-07-2866-00-0vht-vht-possibilities.ppt • “Mobile Cooperation Usage Models”, IEEE 802.11 submission, 2008-01-13, Marc de Courville (Motorola) et al.11-08-0081-02-0vht-mobile-cooperation.ppt • “Below 6 GHz 11VHT PAR&5C’s Proposal”, IEEE 802.11 submission, 2008-03-17, Marc de Courville, Darwin Engwer et al.11-08-0219-04-0vht-below-6ghz-11vht-par-5c-s-proposal.ppt • “Infrastructure Mesh Broadband Wireless System: Example of Cooperative Wireless”, Intel Cooperative Wireless Workshop, 2007-04, N. K. Shankaranarayanan (AT&T) Darwin Engwer, Nortel Networks

28. Revisions • r0 – 2008-04-16 For first presentation to VHT SG. • r1 – 2008-04-18 s3, s10, s12, s13: Changed “ESS” to “Multiple BSS”. s8, s12, s14: Added “illustrative data only” notes. s28: Added list of revisions. s30: Added equation for c. Darwin Engwer, Nortel Networks

29. Backup Slides Darwin Engwer, Nortel Networks

30. Multiple BSS Maximum Throughput (M2) where, i = index of current STA n = number of associated and active STAs j = index of current AP m = number of APs k = number of channels c = number of APs on channel of AP j of m APs T = throughput at MAC SAP of STA i of n with c APs on the channel Darwin Engwer, Nortel Networks

31. Technology axes for VHT to consider Darwin Engwer, Nortel Networks

32. Technology axes for VHT to consider Darwin Engwer, Nortel Networks