1. Additional 40 MHz Scanning Proposal
September 2008
doc.: IEEE /1101r1
September 2008
Additional 40 MHz Scanning Proposal
Date:
Authors:
John R. Barr, Motorola, Inc.
John R. Barr, Motorola, Inc.

2. September 2008
doc.: IEEE /1101r1
September 2008
Abstract
Due to the number of negative comments that have been cast in the recent letter ballot regarding use of 40 MHz channels in 2.4 GHz spectrum, it is proposed to add scanning requirements to clause for FC HT AP 19 and FC HT ATA 19 devices to detect presence of non radios operating in 2.4 GHz spectrum and set the Forty MHz Intolerant field to 1 in transmitted HT Capabilities elements if detection is positive. This should be sufficient to resolve all of the latest negative comments (9304, 9044, 9041, 9009, and unresolved comments from earlier ballots).
John R. Barr, Motorola, Inc.
John R. Barr, Motorola, Inc.

3. Coexistence with other IEEE 802 Standards
September 2008
Coexistence with other IEEE 802 Standards
Current draft n provides substantial coexistence language for legacy IEEE devices via mandatory scanning prior to enabling operation of 40 MHz channels.
40MHzIntolerant bit is used to inform other devices in BSS that operation of 40 MHz channels is not allowed.
Adding mandatory scanning for non-IEEE devices operating in 2.4 GHz should satisfy negative letter ballot comments and improve the draft.
John R. Barr, Motorola, Inc.

4. Current Coexistence Language
September 2008
Current Coexistence Language
Normative:
: “An FC HT AP 19 that detects either of the BSS channel width trigger events TE-B or TE-C or that determines that the value of its variable 20/40 Operation Permitted has changed from TRUE to FALSE shall set the Secondary Channel Offset field to SCN in transmitted HT Operation elements beginning at the next DTIM or next TBTT if no DTIMs are transmitted to indicate that no secondary channel is present (i.e., that the BSS operating width is 20 MHz).”
Informative:
T.5.2: “Before starting a 20/40 MHz BSS, an 40 MHz capable HT AP is required by the rules defined in to examine the channels of the current regulatory domain to determine whether the operation of a 20/40 MHz BSS might unfairly interfere with the operation of existing 20 MHz BSSs. The AP (or some of its associated HT STAs) is required to scan all of the channels of the current regulatory domain in order to ascertain the operating channels of any existing 20 MHz BSSs and 20/40 MHz BSSs.”
John R. Barr, Motorola, Inc.

5. Current Coexistence Language (2)
September 2008
Current Coexistence Language (2)
Informative:
T.5.2: “An additional constraint on establishing a 20/40 MHz BSS includes the allowance for any device to explicitly prohibit the operation of the 20/40 BSS mode due to other considerations. For example, if an WPAN device is operating in the area, that device is likely to be unable to communicate successfully with a paired receiver if the number of available WPAN channels falls below a given threshold. Operation of a 20/40 MHz BSS in the 2.4 GHz band can contribute to the reduction of the number of available WPAN channels, possibly pushing the available channels below that threshold.”
John R. Barr, Motorola, Inc.

6. September 2008
doc.: IEEE /1101r1
September 2008
Over the Air Measurements Confirms that devices are negatively affected
Number of retransmissions for A2DP increase by a factor of 15. (Increases energy requirements)
Number of error free packets reduced by a factor of 2. (Reduces throughput)
Number of available hopping channels reduced to 27% of normal (79 to 22 channels). (Reduces noise immunity and ability to share channel)
Results in numerous stereo audio drop outs.
Adaptive Frequency Hopping (AFH) enabled, but typical detection algorithms can’t handle 100% larger channels and intermittent use of that channel.
John R. Barr, Motorola, Inc.
John R. Barr, Motorola, Inc.

7. Current Negative Comments Suggest
September 2008
Current Negative Comments Suggest
Resolution:
Clause , line 22, replace "When using 40 MHz channels, it can operate in the channels defined in and " to "When using 40 MHz channels, it can operate in the channels defined in "
Rationale:
Due to the large number of devices based on IEEE Std ™-2005 (e.g., > TWO Billion Bluetooth wireless devices), the probability of sharing the spectrum with n devices will be high.
John R. Barr, Motorola, Inc.

8. 40 MHz Effect on IEEE Std 802.15.1™-2005
September 2008
40 MHz Effect on IEEE Std ™-2005
Two interference measurement tests have shown that it is necessary to remove close to 75% of the available 2.4 GHz spectrum to allow devices to operate without interference from 40 MHz channels in 2.4 GHz:
n mhz-11n-interference-on-bluetooth.ppt
n-11n-40-mhz-and-bt-coexistence-test-results.ppt
This does not reflect reasonable coexistence per accepted IEEE 802 definitions.
IEEE and should have equal protection from 40 MHz operation as does legacy BSSs.
John R. Barr, Motorola, Inc.

9. Alternative Proposal Add clause to 11.14 20/40 MHz BSS Operation:
September 2008
Alternative Proposal
Add clause to /40 MHz BSS Operation:
FC HT AP 19 and FC HT STA 19 devices shall perform a “non radio scan” (TBD) prior to establishing/joining a 20/40 MHz or 40 MHz BSS and at least once per dot11BSSWidthTriggerScanInterval seconds during operation of a 20/40 MHz or 40 MHz BSS. A positive scan result shall cause the 20/40 Operation Permitted local variable to be set to FALSE in an FC HT AP 19 and the dot11FortyMHzIntolerant MIB attribute set to TRUE. A negative scan result shall have the opposite effect.
Note that the exact integration of scan event results may be best integrated into clause
John R. Barr, Motorola, Inc.

10. September 2008
“non radio scan”
Front end of n radio can be used to detect features of and radios with minimal cost impact.
IEEE (Bluetooth) wireless devices utilize a low cost scanning mechanism to detect presence of frequency hopping signals with pseudo-random hopping sequences.
IEEE (Zigbee) wireless devices use energy detection and feature recognition to detect devices.
A combination of these methods can be used to define the “non radio scan” algorithm and detection limits.
Similar to DFS algorithm used for radar detection
Detection limits based on expected signal level of non radio within range of likely interference by 40 MHz n transmissions (e.g., 2-3m).
Confirmation of algorithm and detection limits from at least Bluetooth SIG and Zigbee Alliance.
John R. Barr, Motorola, Inc.

11. September 2008
Process
TGn develops language for insertion of “non radio scan” into clause and other clauses as necessary.
Bluetooth SIG and Zigbee Alliance provide details on detection of their radios and recommended detection limits.
TGn approves detection method clause referenced by changes to clause for inclusion in n draft.
Sponsor Ballot...
John R. Barr, Motorola, Inc.

12. September 2008
References
Draft P802.11n_D6.0
pdf
pdf
John R. Barr, Motorola, Inc.

13. 802.11n Transmit Spectral Mask
September 2008
802.11n Transmit Spectral Mask
Skirts detected by AFH.
John R. Barr, Motorola, Inc.

14. Coexistence Alternatives
September 2008
Coexistence Alternatives
Fair and reasonable cooperative solution allows reasonable sharing of 2.4 GHz spectrum with multiple radio systems:
802.11n 40 MHz BSSs provide advertised performance when possible.
Consumers have no complaints about devices failing to work at odd times.
Everyone for themselves:
802.11n only protects legacy devices
Other radio systems adapt to increased levels of interference:
devices raise transmitted power level and turn off AFH to maintain necessary QoS. Allowed to transmit up to 100mW.
devices would increase frequency of transmissions due to larger number of retransmissions required to get message passed.
802.11n 40 MHz BSSs fail to provide advertised performance due to increased levels of interference.
John R. Barr, Motorola, Inc.