1. Response to Reasons and Cures related to ICB/DCB frames
doc.: IEEE /0396r0
May 2005
May 2005
Response to Reasons and Cures related to ICB/DCB frames
Date:
Authors:
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Tomoko Adachi, Toshiba Corporation
Tomoko Adachi, Toshiba Corporation

2. Authors (continued): May 2005 doc.: IEEE 802.11-05/0396r0 May 2005
Tomoko Adachi, Toshiba Corporation
Tomoko Adachi, Toshiba Corporation

3. Abstract Resolution to comments toward ICB/DCB frames are provided.
doc.: IEEE /0396r0
May 2005
May 2005
Abstract
Resolution to comments toward ICB/DCB frames are provided.
Shown that the 20 MHz-Base Managed Mixed Mode is robust even when these frames are missed because of its recovery mechanism.
Some supplementary explanation to rate selection for these frames added.
Reviews the benefit of the 20 MHz-Base Managed Mixed Mode.
Flexibility and ease of scheduling at AP explained.
Tomoko Adachi, Toshiba Corporation
Tomoko Adachi, Toshiba Corporation

4. Comment toward ICB/DCB frames (1)
doc.: IEEE /0396r0
May 2005
May 2005
Comment toward ICB/DCB frames (1)
4 comments claiming that ICB/DCB frames are unreliable
“The ICB/DCB frame types and related functionality should be removed. Dynamically changing bandwidth with broadcast frames is a bad idea because it can create unpredictable interference when stations don't receive these frames. Also, the benefit of such dynamic change is not clear at all.” (ID#43)
“ICB/DCB - This mechanism introduces a real risk of service interruptions, because it is entirely based on multicast frames. Loss of a single ICB or DCB frame may result in a significant service interruption, which will be particularly apparent in remote stations. Therefore, this mechanism should be removed.” (ID#63)
“The Increase/Decrease Channel Bandwidth mechanism is based on multicast frames, making it unreliable.” (ID#76.2)
Similar one in ID#51
Tomoko Adachi, Toshiba Corporation
Tomoko Adachi, Toshiba Corporation

5. Comment toward ICB/DCB frames (1) – cont’d
doc.: IEEE /0396r0
May 2005
May 2005
Comment toward ICB/DCB frames (1) – cont’d
Unreliable because of being broadcast frames?
Rate selection? ... Sent in stable rate from AP (not in beamforming)
Rate of ICB and DCB frames is selected from the BSS basic rate set and 40 MHz Basic MCS set, respectively. Typo in (R4) said as SCB frame instead of ICB. Missed explanation for DCB frame. -> corrected and added
Unexpected timing? ... But gives flexibility and has automatic timeouts for recovery
Beacon can be sent instead of ICB but ICB gives more flexibility to start 40 MHz phase. Note: There are recovery mechanisms when missing ICB/DCB as discussed next.
Tomoko Adachi, Toshiba Corporation
Tomoko Adachi, Toshiba Corporation

6. Comment toward ICB/DCB frames (1) – cont’d
doc.: IEEE /0396r0
May 2005
May 2005
Comment toward ICB/DCB frames (1) – cont’d
Unreliable because of having the danger of being lost?
STAs missing ICB stay and operate in 20 MHz
When STAs miss ICB, they stay in 20 MHz and contend in CSMA/CA with those successfully shifted to 40 MHz.
There is automatic timeout to recover from missing DCB
DCB is used to terminate the 40MHz period earlier
When 40 MHz capable HT STAs miss DCB, they switch back to 20 MHz mode on the control channel by timer set by Beacon or ICB frame. ( r4 clause )
In the worst case scenario,
a loss of ICB and/or DCB can be recovered in the next cycle
and therefore service interruption may only last for one cycle
Effect on missing these frames is minimum.
Tomoko Adachi, Toshiba Corporation
Tomoko Adachi, Toshiba Corporation

7. Examination of Acquisition Failure in ICB/DCB
doc.: IEEE /0396r0
May 2005
May 2005
Examination of Acquisition Failure in ICB/DCB
Conditions
No OBSS
Load per STA: Mbps
Acquisition failure of ICB/DCB frames
PER by distance in Channel Model B
Works even under severe condition!
Throughput vs. number of nodes
Tomoko Adachi, Toshiba Corporation
Tomoko Adachi, Toshiba Corporation

8. Examination of Acquisition Failure in ICB/DCB
doc.: IEEE /0396r0
May 2005
May 2005
Examination of Acquisition Failure in ICB/DCB
Conditions
Number of nodes: in target BSS, in OBSS
Load per STA: Mbps for target BSS, 5Mbps for OBSS
Acquisition failure of ICB/DCB frames
PER by distance in Channel Model B
Throughput vs. distance between OBSS
Tomoko Adachi, Toshiba Corporation
Tomoko Adachi, Toshiba Corporation

9. If you compare 10% acquisition failure probability with PER...
doc.: IEEE /0396r0
May 2005
May 2005
If you compare 10% acquisition failure probability with PER...
ex. in Channel Model B
SS6 : Hot Spot
(Scenario with largest range in 11n Usage Models) !
(Farthest STA from AP in SS6)
90[m]
30[m]
STA AP
STA1
PER = 0.1%
(SNR = 21 [dB])
PER = 10%
(SNR = 4 [dB])
Tomoko Adachi, Toshiba Corporation
Tomoko Adachi, Toshiba Corporation

10. Comment toward ICB/DCB frames (2)
doc.: IEEE /0396r0
May 2005
May 2005
Comment toward ICB/DCB frames (2)
6 comments claiming from the perspective of many new control frames
Remove frames
ID#20.2
ID#26.2
ID#32
ID#45.1
ID#69
ID#80
Those also adding to remove associated functionality
ID#33
Tomoko Adachi, Toshiba Corporation
Tomoko Adachi, Toshiba Corporation

11. Comment toward ICB/DCB frames (2) – cont’d
doc.: IEEE /0396r0
May 2005
May 2005
Comment toward ICB/DCB frames (2) – cont’d
Why do we need to control 20 MHz and 40 MHz access?
Coexistence with 20 MHz devices is a must when considering 40 MHz operation.
From the expect of marketing expansion in the near future, channels will be crowded and become difficult to keep clear extension channel.
Unmanaged CSMA/CA operated across the entire 40MHz has the following issues:
While waiting the other channel to be idle, a 20 MHz STA may start to use the channel which was idle. -> phased protection in two channels
To acquire both channels at HT STAs, contention probability will increase to double. -> divide the contention phase between 20 MHz and 40 MHz
Need to keep the benefit of 40 MHz even under this hard situation
or less meaning to support 40 MHz!
Tomoko Adachi, Toshiba Corporation
Tomoko Adachi, Toshiba Corporation

12. Comment toward ICB/DCB frames (2) – cont’d
doc.: IEEE /0396r0
May 2005
May 2005
Comment toward ICB/DCB frames (2) – cont’d
Effect of using ICB/DCB frames
Shown in doc.s r0 and r0 as performance of 20 MHz-base managed mixed mode.
TGn Sync 20-base
ex. when coexist with legacy devices within BSS
(throughput)
TGn Sync 20-base
Throughput vs. No. of 20 MHz legacy STAs
Tomoko Adachi, Toshiba Corporation
Tomoko Adachi, Toshiba Corporation

13. Comment toward ICB/DCB frames (2) – cont’d
doc.: IEEE /0396r0
May 2005
May 2005
Comment toward ICB/DCB frames (2) – cont’d
Delay is critical to
handheld devices!
ex. when coexist with legacy devices within BSS
(delay)
TGn Sync
20-base
Delay in 40 MHz vs. No. of 20 MHz legacy STAs
Tomoko Adachi, Toshiba Corporation
Tomoko Adachi, Toshiba Corporation

14. Comment toward ICB/DCB frames (2) – cont’d
doc.: IEEE /0396r0
May 2005
May 2005
Comment toward ICB/DCB frames (2) – cont’d
TGn Sync 20-base
ex. when there is also OBSS in the extension channel
(throughput)
TGn Sync 20-base
Throughput vs. No. of 20 MHz legacy STAs
Tomoko Adachi, Toshiba Corporation
Tomoko Adachi, Toshiba Corporation

15. Comment toward ICB/DCB frames (2) – cont’d
doc.: IEEE /0396r0
May 2005
May 2005
Comment toward ICB/DCB frames (2) – cont’d
ex. when there is also OBSS in the extension channel
(delay)
TGn Sync 20-base
Delay in 40 MHz vs. No. of 20 MHz legacy STAs
Tomoko Adachi, Toshiba Corporation
Tomoko Adachi, Toshiba Corporation

16. Comment toward ICB/DCB frames (2) – cont’d
doc.: IEEE /0396r0
May 2005
May 2005
Comment toward ICB/DCB frames (2) – cont’d
20 MHz-Base Managed Mixed mode works without ICB/DCB frames (see slide 6) But
They give flexibility in changing the phase
Scheduling the ratio between 20 and 40 MHz phases at the AP will be easier by using these frames than without them, because accurate setting for duration will not be required --- Needed for real world
Tomoko Adachi, Toshiba Corporation
Tomoko Adachi, Toshiba Corporation

17. Comment toward ICB/DCB frames (3)
doc.: IEEE /0396r0
May 2005
May 2005
Comment toward ICB/DCB frames (3)
1 comment referring to hidden-node problem in beam forming
“The MAC design is too complicated with too many new frame formats to fix beam forming hidden-node problem. Suggest removing IAC/RAC and ICB/DCB mechanisms.” (ID#46)
ICB/DCB frames are aimed to realize the coexistence between 20 and 40 MHz devices.
Note that these frames are not beam-formed.
The effect is shown in the previous slides.
The new control frames including ICB/DCB frames are not only to fix the hidden-node problem of beam forming.
Tomoko Adachi, Toshiba Corporation
Tomoko Adachi, Toshiba Corporation

18. doc.: IEEE /0396r0
May 2005
May 2005
Conclusion
Some supplementary explanation to rate selection for these frames has been added to the spec.
There are robust mechanisms with ICB/DCB
STAs missing ICB stay in 20 MHz
STAs missing DCB switch back to 20 MHz (automatic timeout)
Simulation results with severe acquisition failure show that 20 MHz-Base Managed Mixed Mode does not suffer from service interruption even with the loss of these frames.
Reviews the benefit of the 20 MHz-Base Managed Mixed Mode which uses ICB/DCB.
ICB/DCB give flexibility and ease scheduling at AP.
Tomoko Adachi, Toshiba Corporation
Tomoko Adachi, Toshiba Corporation

19. References 11-04-0889-04 TGn Sync Proposal Technical Specification
doc.: IEEE /0396r0
May 2005
May 2005
References
TGn Sync Proposal Technical Specification
TGn Sync Complete Proposal
Comparison of 20/40 MHz coexistence methods
Performance Analysis on 20/40 MHz coex. methods taking in legacy in BSS
Tomoko Adachi, Toshiba Corporation
Tomoko Adachi, Toshiba Corporation