1. Recommendation for EDCA Bandwidth Factor
April 2010
doc.: IEEE /0457r0
April 2010
Recommendation for EDCA Bandwidth Factor
Date: 2010, April 26
Authors:
Graham Smith, DSP Group
Graham Smith, DSP Group

2. Abstract 0304r1 presented “Empirical Formula for EDCA Overhead Factor”
April 2010
doc.: IEEE /0457r0
April 2010
Abstract
0304r1 presented “Empirical Formula for EDCA Overhead Factor”
The resulting formulas, and some new work are examined to see what information would be required in order to use then in an OBSS situation, i.e. in the QLoad information.
Suggestions are made as to how to resolve the problem
A recommendation is made.
Graham Smith, DSP Group
Graham Smith, DSP Group

3. April 2010
EDCA Overhead Factor
The Medium Access Time includes SIFS, AIFSN and the Contention Window value
As the number of streams increases, each stream is held up in the contention window while another stream is transmitting.
The total time required for EDCA streams is therefore greater than the Medium Time and it varies with the number of streams.
This total required time compared to the Medium Time is termed the EDCA Overhead Factor.
Graham Smith, DSP Group

4. Summary 11a/g EDCA Overhead Factor F
April 2010
Summary 11a/g EDCA Overhead Factor F
AC_VI Basic Formula
1 stream F = R For 1< Sequ<2 = S R
2 streams F = R For 2< Sequ<3 = S R
3 to 10 streams F = S R
>10 streams, S = 10
For Mixed Data Rates and PHY Rates
Sequ = x Total Medium Time of all streams
Medium Time of stream with least Medium Time
R = PHY Rate of the stream with least Medium Time
AC_VO Basic Formula
1 to 10 stream F = S R
For Mixed VO and VI Just count the AC_VO streams
For mixed PHY Rates
R = Highest PHY Rate of the VO streams
Graham Smith, DSP Group

5. SUMMARY 11n Equal VI Streams, no aggregation
April 2010
SUMMARY 11n
R = PHY Rate, S = number of streams,
A = 8, 16, 32 or 64 (corresponding to 8k, 16k, 32k, 64k)
Equal VI Streams, no aggregation
1 stream F = R
2 streams F = R
3 to 10 streams F = S R (>10 streams, S = 10)
VO Bi-directional streams (no aggregation)
1 to 10 stream F = S R (>10 streams, S = 10)
Equal VI streams, same aggregation
For Streams F = S R/A
For Streams F = S R/A
For Streams F = S R/A (>10 streams, S = 10)
Mixed streams, same Aggregation
S = Sequ = 0.5 x MT Total/MTmin
Mixed Streams, mixed Aggregation
F = [ (Amax/Amin)] r
Where r = Total MT of Amin aggregation streams Total Medium Time
Graham Smith, DSP Group

6. 11a/g VI examples To accurately calculate F, we need to know:
April 2010
11a/g VI examples
3 to 10 streams F = S R
For S or Sequ >10 streams, S = 10
For Mixed Data Rates and PHY Rates
Sequ = x Total Medium Time of all streams
Medium Time of stream with least Medium Time
R = PHY Rate of the stream with least Medium Time
To accurately calculate F, we need to know:
The Medium Time of the stream with the least medium time
and
The PHY Rate of that stream
Or, if equal streams, how many
Graham Smith, DSP Group

7. 11n VI example Mixed Streams, mixed Aggregation
April 2010
11n VI example
Mixed Streams, mixed Aggregation
F = [ (Amax/Amin)] r
Where r = Total MT of Amin aggregation streams Total Medium Time
To accurately calculate F, we need to know:
Total Medium Time
Amax
Amin
Sum of Medium times of Amin streams
Graham Smith, DSP Group

8. Mixed VI Scenarios 11a/g, 11n, aggregation, no aggregation, PHY Rates
April 2010
Mixed VI Scenarios 11a/g, 11n, aggregation, no aggregation, PHY Rates
Basic formula seems to hold across
Mixed PHY rates, 11n, 11a/g, aggregation , no aggregation*
F = [ (Amax/Amin)] r
Where r = Total MT of Amin aggregation streams Total Medium Time
And Amin = 1.4 if no aggregation (or 11a/g)*
To accurately calculate F, we need to know:
Amax, Amin, Sum of Medium Time of Amin streams
* New work not included in 0314r1.
Graham Smith, DSP Group

9. Option 1 – Add required fields to QLoad
April 2010
Option 1 – Add required fields to QLoad
Qload traffic element is presently 5 Octets
Octet 2 1
Mean
Stdev
Rsvd
AC3 Streams
AC2 Streams
Bits 16 14 4
QLoad traffic element would be increased to 11 Octets
Octets 2 1
Mean
Stdev
Rsvd
AC3 Streams
AC2 Streams
Amax
Amin MT
PHY Rate least MT
Bits 16 14 4 8
Graham Smith, DSP Group

10. Full QLoad traffic element
April 2010
Full QLoad traffic element
Octets 2 1
Mean
Stdev
Rsvd
AC3 Streams
AC2 Streams
Amax
Amin
MTmin
PHY Rate least MT
Bits 16 14 4 8
VI cases
Amax
Amin
MTmin
PHY Rate least MT, R
Interpretation
11a/g
Mean MT of stream with least MT
Rate of stream with least MT, R
Uses R to recognize 11/g
Sequ = Mean/Amin MT
(even if equal streams)
F= S+.0025R
11n
No Agg
Uses R to recognize
F= S+.0015R
equal
8,16,32, or 64
Same as Amax
If Amax=Amin,
F= S+.0041R/A
Mixed
0,8,16,32, or 64
Note:
0 = 1.4
SUM of mean MTs of ALL steams at Amin
Not used
Identifier is that Amax and Amin differ
r = MTmin/Mean
F=1.12+( Amax/Amin)r
Graham Smith, DSP Group

11. Alternative – simple worse case
April 2010
Alternative – simple worse case
TSPECs use the ‘safe’ minimum PHY rate, so we want to assume a high, safe minimum rate, e.g.:
11a/g, assume 36Mbps and 10 streams, F = 1.26
11n no agg, assume 52Mbps and 10 streams, F = 1.27
Mixed, assume Amax/Amin = 8, r = 0.5, F = 1.28
Worse case mixed, assume Amax= 64, Amin=1.4 (0), r = F = 1.43
Could simply recommend that F = 1.3 is used always for VI
Note:
Could delete Number of AC2 streams from QLoad
Graham Smith, DSP Group

12. April 2010
VO Traffic
If a value for AC3 streams is present, then ideally need to know highest PHY Rate specified. 11octet QLoad can do this.
F = S R 11a/g
F = S R 11n
Alternative:
Assuming S = 10 and R = 36Mbps or 52Mbps
F = 1.33 (11a/g) and (11n)
Could simply use a blanket F = 1.34 for everything, VO and VI
Graham Smith, DSP Group

13. April 2010
Summary
If ‘accurate’ calculation required for F, then QLoad needs to be increased to 11 octets
Alternative is to simply recommend that F = 1.34
Straw Poll approach A or B
Graham Smith, DSP Group

14. If Straw Poll B - Proposed new text for Annex aa 2.2 - EDCA BW Factor
April 2010
If Straw Poll B - Proposed new text for Annex aa EDCA BW Factor
Second paragraph, delete “The recommended EDCA Bandwidth overhead factor is given in Table aa1” and the Table.
Simple version, insert: “It is recommended that a fixed value of 1.34 is used for EDCA Overhead Factor.”
Explanatory version, insert: “In order to calculate a reasonably accurate estimate of EDCA Overhead Factor, more parameters than those provided in the QLoad Element are required. The benefits of a more accurate estimate as against the use of a fixed value are not considered to be highly significant. Therefore it is recommended that a fixed value of 1.34 is used for EDCA Overhead Factor.”
See over
Graham Smith, DSP Group

15. Proposed new text for Annex aa 2.2 - EDCA BW Factor
April 2010
Proposed new text for Annex aa EDCA BW Factor
More explanatory version, insert: “It has been established that the value of the EDCA Overhead Factor is dependent upon many factors, including:
Number and mix of streams, voice and video
Mixture of PHY Rates and PHYs
Mixture of streams’ data rates
Use and mix of aggregated MSDUs
For video streams a typical ‘high’ value has been estimated at For voice streams, a typical ‘high’ value has been estimated at This typical ‘high’ value is based upon the assumption of 10 streams for non-aggregated streams, or a mixture of non-aggregated and maximum aggregated streams. An overall upper limit of 1.43 has been estimated. In order to calculate a reasonably accurate estimate of EDCA Overhead Factor for each scenario, more parameters than those provided in the QLoad Element are required. The benefits of a more accurate estimate as against the use of a fixed value are not considered to be highly significant. Therefore it is recommended that a fixed value of 1.34 is used for EDCA Overhead Factor.”
Graham Smith, DSP Group

16. Straw Poll Straw poll which text is preferred, 1, 2 or 3? April 2010
Graham Smith, DSP Group

17. April 2010
doc.: IEEE /0457r0
April 2010
Motion
Amend text in Annex aa 2.2, as per text option (insert 1, 2 or 3 as per result of straw poll)
Graham Smith, DSP Group
Graham Smith, DSP Group