1. Channel Selection and Management for 11ac
May 2010
Channel Selection and Management for 11ac
Date:
Authors:
Name
Affiliation
Address
Phone
Yujin Noh
LG Electronics, Inc.
LG R&D Complex 533, Hogye-1dong, Dongan-Gu, Anyang-Shi, Kyungki-Do, , Korea
Daewon Lee
Yongho Seok
Bonghoe Kim

2. Outlines Background and Motivation
40MHz channel access for 11n
80MHz channel access for 11ac
Channel Selection and Management for 80MHz channel bandwidth for 11ac
Channel allocation for 80MHz operation
The Primary channel allocation

3. Background 1
Up to 40MHz channel bandwidth which is composed of primary channel and secondary channel for 11n
Primary channel is located on the boundary over 40MHz channel bandwidth
Secondary channel is selected and indicated with the offset value relative to the primary channel
Above/Below the primary channel
No secondary channel

4. Background 2 40MHz channel operation for 11n
CSMA/CA approach for the primary channel
The secondary channel has been idle for at least a PIFS interval prior to the expiry of backoff counter

5. Motivation Two OBSS scenarios in framework document
In-home entertainment application
Enterprise network
Support up to at least 80MHz channel bandwidth
The well-designated 80MHz channel allocation will be useful for efficient channel management of 11ac

6. Channel Allocation for 80MHz operation
May 2010
Channel Allocation for 80MHz operation
Non-overlapping channel allocation
Overlapping channel allocation

7. Channel Allocation for 11ac 40MHz
40MHz operation based on two adjacent 20MHz channels in the same way of 11n
The position of the primary/secondary channels has patterns
The permissible 40MHz channel allocation options are defined in terms of the designated primary/secondary channel
Non-overlapping channel allocation for each 40MHz channel

8. Channel Allocation for 80MHz 1
80MHz operation with four 20MHz channels in a row based on the framework document
Option 1: non-overlapping channel allocation
Simple extension from 40MHz channel allocation
There may be limited numbers of 80MHz channel to support 80MHz operation
Two 80MHz channel allocations through 5.4GHz band

9. Channel Allocation for 80MHz 2
Option 2: overlapping channel allocation
Overlapping channel allocation by 40MHz shift
Four 80MHz channel allocations through 5.4GHz band
Overlapping channel allocation by 20MHz shift
Eight 80MHz channel allocations through 5.4GHz band
Increase the number of 80MHz allocation channels to be used

10. Favorable circumstance with overlapping channel allocation 1
OBSS circumstance
AP with 80MHz capability is surrounded by 40MHz capable APs in home entertainment system like the HD video streaming.
Non-overlapping channel allocation
According to OBSS scanning rule, 11ac 80MHz channels are recommended to share the same 2x20MHz channels
Time division multiplexing to support 80MHz channel operation
Overlapping channel allocation
It will be good to leave enough chances to allocate 80MHz channels
Throughput enhancement possibly with efficient channel utilities

11. Favorable circumstance with overlapping channel allocation 2
Unexpected interference circumstance
It will be useful in case of AP detecting some unexpected interference like a radar

12. Concerns on overlapping channel allocation
It is assumed that CH3 and CH4 are shared 40MHz channels of both AP1 and AP2 according to the OBSS scanning rule of 11n
AP3 starts scanning idle channels to establish a 80MHz BSS newly
In case AP2 is hidden node in AP3 point of view
CH5 and CH6 are scanned as idle states
Unexpected interference on CH5 and CH6 between AP2 and AP3

13. Comparison between non-overlapping and overlapping channel allocations 1
20/40MHz channel pairing for 80MHz operation in 5 GHz band
Available number of 80MHz channel depending on the channel allocation option
GHz
GHz
GHz
Non-overlapping 2 1
Overlapping by 40MHz 3 4
Overlapping by 20MHz 5 8

14. Comparison between non-overlapping and overlapping channel allocations 2
If weak points of overlapping channel allocation is significant, only non-overlapping channel allocation can be supported
Concern on the limited number of 80MHz channel
Need to increase the efficiency of non-overlapping 80MHz channel
Strength
Weakness
Non-overlapping
Simple
Extension from 40MHz channel allocation
Allocate limited number of 80MHz channels
Restricted performance depending on different circumstance
Overlapping
Allocate enough number of 80MHz channels
Possibly sustained performance in different circumstance
Increased protocol complexity to arrange overlapping channels
Hidden node problem

15. The Primary channel allocation

16. 80MHz operation for 11ac Support up to 80MHz channel bandwidth
The primary channel can be allowed to be set to any 20MHz subchannel over 80MHz channel bandwidth for some 11ac configurations
CSMA/CA approach for the primary channel
The rest of subchannels have been idle for at least a PIFS interval prior to the expiry of backoff counter

17. Efficient 80MHz Channel Allocation
Non-overlapping channel allocation
It is assumed that 11ac AP/STA follow the OBSS scanning rule of 11n

18. Example of 80MHz Channel Allocation
Overlapping channel allocation
Overlapping channel allocation by 40MHz shift

19. Example of 80MHz Channel Allocation
Overlapping channel allocation by 20MHz shift

20. Summary
Follow the 40MHz channel allocation rule of 11n for 80MHz channel allocation
Non-overlapping channel allocation for 11ac
To increase the number of possible 80MHz channel allocation
Option 1
Overlapping channel allocation can be one of good candidates
Option 2
Non-overlapping channel allocation with any location of the primary channel over 80MHz channel
Open the possibility to select the primary channel which is allocated in the middle of entire channel bandwidth

21. Straw Poll
Do you support “the location of the Primary channel concept” described on page 16 by inclusion of the following section and text in the Tgac spec framework document
5 Coexistence 
R5.C:The Primary Channel may be designated to any 20MHz subchannel over 80MHz channel bandwidth, where Primary Channel designation is subject to co-existence(OBSS) rules yet to be defined.
Yes No
Abstain