1. 40 MHz Operation in 2.4 GHz Date: 2006-11-11 Authors: November 2006
Month Year
doc.: IEEE yy/xxxxr0
November 2006
40 MHz Operation in 2.4 GHz
Date:
Authors:
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Richard van Nee, Airgo Networks
John Doe, Some Company

2. Month Year
doc.: IEEE yy/xxxxr0
November 2006
Abstract
In this presentation, we recap the co-existence issues regarding 20/40 MHz operation in both the 2.4 Ghz and 5 GHz band.
A proposed set of solutions for 20/40 MHz operation in the 5 GHz band and 2.4 GHz band are described.
Normative text has been prepared for these solutions
Richard van Nee, Airgo Networks
John Doe, Some Company

3. Month Year
doc.: IEEE yy/xxxxr0
November 2006
CID’s Addressed
Subset of CIDs addressed related to 40 MHz operation in 2.4 GHz band
104, 258, 286, 288, 430, 431, 689, 705, 706, 1493, 1560, 1558, 1728, 2848, 3006, 3010, 3471, 3501, 3502, 3602, 4570, 4571, 7010, 7195, 7312, 7313, 7314, 7376, 7871, 7925, 8138, 8282, 8186, 8194
Richard van Nee, Airgo Networks
John Doe, Some Company

4. Further definition of the 20/40 MHz Issues in Draft 1.0
Month Year
doc.: IEEE yy/xxxxr0
November 2006
Further definition of the 20/40 MHz Issues in Draft 1.0
There are two separate, but related issues:
The current draft does not define normative behavior for CSMA/CA (i.e. ‘listen before your talk’) for the ‘extension channel’ in 40 MHz operation
This issue will lead to interoperability problems with legacy a/b/g and other .11n equipment
The channel bonded, 2x20 MHz mode as specified leads to a misaligned use of channels with the majority of the installed base of legacy .11b/g (which is typically deployed based on a 25 MHz channel spacing)
This issue will lead to interoperability problems with legacy b/g installed base, even if issue #1 is fixed
Richard van Nee, Airgo Networks
John Doe, Some Company

5. Month Year
doc.: IEEE yy/xxxxr0
November 2006
2.4 GHz Installed base interoperability problematic with 20/40 .11n Operating Modes
Both the Primary and Secondary channel cannot be centered on the widely-used adjacent 2.4 GHz channels (e.g. channel 1 and 6 or channel 6 and 11)
The Primary and Secondary channels would be 1 and 5, or 6 and 2 for example; i.e. misaligned by 5 MHz
In the misaligned channel, there will be no proper defer behavior leading to a high collision rate
Richard van Nee, Airgo Networks
John Doe, Some Company

6. Requirements for a Proposed Solution
Month Year
doc.: IEEE yy/xxxxr0
November 2006
Requirements for a Proposed Solution
CCA sensing on both Primary and Secondary Channel
Address the 5 MHz offset issue, to ensure ‘good neighbor’ behavior with the fast majority of the legacy installed base of .11b/g devices
Litmus test for Proposed Solutions:
“Will the solution protect a single .11g VOIP call in an OBSS that overlaps in the Secondary channel?”
Richard van Nee, Airgo Networks
John Doe, Some Company

7. Overview of the Proposed Solution for 5 GHz band (1/2)*
Month Year
doc.: IEEE yy/xxxxr0
November 2006
Overview of the Proposed Solution for 5 GHz band (1/2)*
Before commencing any 40MHz transmission, a STA shall sense CCA on both Primary channel and Secondary channel
Secondary Channel CCA shall be deemed busy during Tx or Rx of a 20 MHz frame in Primary Channel
TX of 40 MHz frame only if Secondary channel has been idle for at least a DIFS
When TXOP obtained for a 20 MHz transmission, STA shall not transmit 40 MHz frames during this TXOP
* A key strawpoll in Melbourne showed strong support for this proposed solution
Richard van Nee, Airgo Networks
John Doe, Some Company

8. Overview of the Proposed Solution for 5 GHz Band (2/2)*
Month Year
doc.: IEEE yy/xxxxr0
November 2006
Overview of the Proposed Solution for 5 GHz Band (2/2)*
CCA sensitivity
Receiver of a 20/40 MHz STA shall provide CCA on both the primary and secondary channels
CCA busy for:
Start of a valid 20 MHz transmission** in the Primary channel at Rx level > -80dBm; primary CCA busy
Start of a valid 40 MHz transmission in the Primary and Secondary channel at Rx level > -77 dBm; both primary and secondary CCA busy
20 MHz primary CCA for any signal > -60 dBm (ED)
When primary CCA Idle, Secondary Channel CCA for any signal > -60 dBm (ED)
For a 40 MHz transmission, both primary and secondary channel CCA for any signal level > -57 dBm (ED)
* A key strawpoll in Melbourne showed strong support for this proposed solution
** Valid transmission = A transmission that is detected as a .11 waveform, and for which a preamble has been decoded
Richard van Nee, Airgo Networks
John Doe, Some Company

9. Month Year
doc.: IEEE yy/xxxxr0
November 2006
The Proposed Solution for 2.4 GHz Includes an Optional Legacy Duplicate DSSS Mode
Can be used to transmit a CTS-to-self or RTS-CTS that can be received by legacy 11g devices, even with a carrier offset of 5 or 10 MHz
This will ensure proper defer behavior in the 2.4 GHz band regardless what channels are used
Duplicate DSSS signal uses a 20 MHz spacing just like the existing duplicate non-HT OFDM rates.
Richard van Nee, Airgo Networks
John Doe, Some Company

10. Example Transmitter For Duplicate DSSS
Month Year
doc.: IEEE yy/xxxxr0
November 2006
Example Transmitter For Duplicate DSSS
DAC
Generate baseband legacy DSSS signal
Shift by +10 MHz
Shift by
-10 MHz
To RF j
This is exactly the same structure that can be used for the existing duplicate non-HT OFDM rates
Richard van Nee, Airgo Networks
John Doe, Some Company

11. Duplicate DSSS Spectrum
Month Year
doc.: IEEE yy/xxxxr0
November 2006
Duplicate DSSS Spectrum
Spectrum falls well within 11n 40 MHz mask
No changes required in filtering
Richard van Nee, Airgo Networks
John Doe, Some Company

12. Proposed Additions* for 2.4 GHz operation (1/2)
Month Year
doc.: IEEE yy/xxxxr0
November 2006
Proposed Additions* for 2.4 GHz operation (1/2)
For 20/40 MHz operation:
Mandatory sensing of transmissions in the Secondary channel that are not part of a 40 MHz operation in the same BSS
Per CCA sensitivity levels as described in the slide summarizing the consensus solution for the 5 GHz band
If secondary channel is not idle, STA shall immediately do one of the following:
For Non-AP STAs, either:
Switch to 20 MHz only mode Or:
Use MAC Protection Frame (RTS/CTS, CTS-to-self) at a 40 MHz-duplicate-DSSS rate prior to any 40 MHz transmission (to set NAV of devices operating in Secondary channel)
When secondary “channel busyness” persisted for a configured percentage value (e.g. 10, 20, 40%) over a configured time then non-AP STA SHOULD switch to 20 MHz only mode
* In addition to the solution as described in the slide summarizing the consensus solution for the 5 GHz band (i.e., a device operating in 2.4 GHz band should behave according to elements described for 5 GHz band + contents of this slide).
Richard van Nee, Airgo Networks
John Doe, Some Company

13. Proposed Additions* for 2.4 GHz operation (2/2)
Month Year
doc.: IEEE yy/xxxxr0
November 2006
Proposed Additions* for 2.4 GHz operation (2/2)
For AP STAs, either:
Switch the BSS:
Switch BSS to 20MHz only mode
Remain in 20/40 mode but switch BSS to different 40 MHz channel set
Or:
Use MAC Protection Frame (RTS/CTS, CTS-to-self) at a 40 MHz-duplicate-DSSS rate prior to any 40 MHz transmission
When secondary “channel busyness” persisted for a configured percentage value (e.g. 10, 20, 40%) over a configured time then AP STA SHOULD switch to 20 MHz only mode
STA may switch back from 20 MHz only mode to full 20/40 MHz mode after the duration of ‘dot 11SecondaryOBSSSwitchTime’ (configurable parameter)
* In addition to the solution as described in the slide summarizing the consensus solution for the 5 GHz band (i.e., a device operating in 2.4 GHz band should behave according to elements described for 5 GHz band + contents of this slide).
Richard van Nee, Airgo Networks
John Doe, Some Company

14. Month Year
doc.: IEEE yy/xxxxr0
November 2006
“Will the solution protect a single .11g VoIP call in an OBSS that overlaps in the Secondary channel?”
Proposed solutions:
Immediately switch back to 20 MHz only or switch BSS to another 40 MHz channel:
Yes it will protect VoIP call, but may not always be the most efficient solution
Use MAC Protection Frame (RTS/CTS, CTS-to-self) at a 40 MHz-duplicate-DSSS rate prior to 40 MHz transmissions:
Yes, it will protect VoIP call in secondary channel (even at an offset of 5 or 10 MHz), and benefits of using 40 MHz modes in the 2.4 GHz channel can be achieved.
An alternative solution may be to exclude the use of 40 MHz modes in the 2.4 GHz band in the standard altogether. However, it appears unrealistic to assume that this will prevent the marketplace proliferation of products which operate in 40 MHz modes in the 2.4 GHz band.
Richard van Nee, Airgo Networks
John Doe, Some Company

15. BACKUP SLIDES November 2006 Month Year doc.: IEEE 802.11-yy/xxxxr0
Richard van Nee, Airgo Networks
John Doe, Some Company

16. 11b rates With Channel Offset
Month Year
doc.: IEEE yy/xxxxr0
11b rates With Channel Offset
November 2006
Two 1 Mbps networks on Channel 1, second network turned on after 20 seconds
Two 1 Mbps networks on Channels 1 and 2, second network turned on after 20 seconds
Networks properly defer in the presence of a channel offset
when using 11b Barker rates – they share fairly
Richard van Nee, Airgo Networks
John Doe, Some Company

17. Channel Utilization USA
Month Year
doc.: IEEE yy/xxxxr0
November 2006
Channel Utilization USA
Total of 1088 Access Points
Measurements taken in San Francisco and Silicon Valley using the Netstumbler tool
Richard van Nee, Airgo Networks
John Doe, Some Company

18. Channel Utilization Europe
Month Year
doc.: IEEE yy/xxxxr0
November 2006
Channel Utilization Europe
Total of 1722 Access Points
Measurements taken in Netherlands, Belgium and Italy
Richard van Nee, Airgo Networks
John Doe, Some Company