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Additional 40 MHz Scanning Proposal

Additional 40 MHz Scanning Proposal. Authors:. Date: 2008-09-09. Abstract.

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Additional 40 MHz Scanning Proposal

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  1. Additional 40 MHz Scanning Proposal Authors: Date: 2008-09-09 John R. Barr, Motorola, Inc.

  2. 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 11.14 for FC HT AP 19 and FC HT ATA 19 devices to detect presence of non-802.11 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.

  3. Coexistence with other IEEE 802 Standards • Current draft 802.11n provides substantial coexistence language for legacy IEEE 802.11 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 802.11 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 • Normative: • 11.14.12: “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 11.14.5 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) • Informative: • T.5.2: “An additional constraint on establishing a 20/40 MHz BSS includes the allowance for any 802.11 device to explicitly prohibit the operation of the 20/40 BSS mode due to other considerations. For example, if an 802.15.1 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 802.15.1 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 802.15.1 WPAN channels, possibly pushing the available channels below that threshold.” John R. Barr, Motorola, Inc.

  6. Over the Air Measurements Confirms that 802.15.1 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.

  7. Current Negative Comments Suggest • Resolution: • Clause 20.3.25, line 22, replace "When using 40 MHz channels, it can operate in the channels defined in 20.3.15.1 and 20.3.15.2." to "When using 40 MHz channels, it can operate in the channels defined in 20.3.15.2." • Rationale: • Due to the large number of devices based on IEEE Std 802.15.1™-2005 (e.g., > TWO Billion Bluetooth wireless devices), the probability of sharing the spectrum with 802.11n devices will be high. John R. Barr, Motorola, Inc.

  8. 40 MHz Effect on IEEE Std 802.15.1™-2005 • Two interference measurement tests have shown that it is necessary to remove 67% of the available 2.4 GHz spectrum to allow 802.15.1 applications to operate without degradation from 40 MHz channels in 2.4 GHz: • 11-08-0992-01-000n-20-40-mhz-11n-interference-on-bluetooth.ppt • 11-08-1140-00-000n-11n-40-mhz-and-bt-coexistence-test-results.ppt • This does not reflect reasonable coexistence per accepted IEEE 802 definitions. • IEEE 802.15.1 and 802.15.4 should have equal protection from 40 MHz operation as does legacy 802.11 BSSs. John R. Barr, Motorola, Inc.

  9. Alternative Proposal • Add clause to 11.14 20/40 MHz BSS Operation: • FC HT AP 19 and FC HT STA 19 devices shall perform a “non-802.11 radio scan” 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. FC HT STA 19 devices that already have the dot11FortyMHzIntolerant MIB attribute set or are exempt from OBSS scanning (11.14.6) are not required to perform this scan. • Note that the exact integration of scan event results may also be integrated into clause 11.14.12. John R. Barr, Motorola, Inc.

  10. “non-802.11 radio scan” • Add clause defining “non-802.11 radio scan”: • The “non-802.11 radio scan” shall be able to detect presence of 1 MHz GFSK transmissions in channels centered on f=2402+k MHz for k=0..78 with a power level greater than –35 dBm that appear on at least 20 channels in a 10 mSec time period, and 5 MHz DSSS O-QPSK transmissions with a 2 MHz chip rate in channels centered on f=2405 + 5(k-11) MHz for k=11-26 with a power level greater than –38 dBm that appear on channels affected by the proposed 40 MHz channel in a 10 mSec time period. If either transmissions are detected “non-802.11 radio scan” result is positive otherwise it is negative. John R. Barr, Motorola, Inc.

  11. Background - “non-802.11 radio scan” • Front end of 802.11n radio can be used to detect features of 802.15.1 and 802.15.4 radios with minimal cost impact. • IEEE 802.15.1 (Bluetooth) wireless devices utilize a low cost scanning mechanism to detect presence of frequency hopping signals with pseudo-random hopping sequences. • IEEE 802.15.4 (Zigbee) wireless devices use energy detection and feature recognition to detect 802.15.4 devices. • A combination of these methods can be used to define the “non-802.11 radio scan” algorithm and detection limits. • Similar to DFS algorithm used for radar detection • Detection limits based on expected signal level of non-802.11 radio within range of likely interference by 40 MHz 802.11n transmissions (e.g., 2-3m). • Confirmation of algorithm and detection limits from at least Bluetooth SIG and Zigbee Alliance. John R. Barr, Motorola, Inc.

  12. Process • TGn develops language for insertion of “non-802.11 radio scan” into clause 11.14 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 11.14 for inclusion in 802.11n draft. • Sponsor Ballot... John R. Barr, Motorola, Inc.

  13. References • https://mentor.ieee.org/802.11/file/08/11-08-0962-01-000n-tgn-lb134-coex-comments.xls • https://mentor.ieee.org/802.11/file/08/11-08-0779-01-000n-coex-40-mhz-comments.doc • https://mentor.ieee.org/802.11/file/08/11-08-0992-01-000n-20-40-mhz-11n-interference-on-bluetooth.ppt • Draft P802.11n_D6.0 • 802.15.1-2005.pdf • 802.15.4-2003.pdf John R. Barr, Motorola, Inc.

  14. 802.11n Transmit Spectral Mask Skirts detected by AFH. John R. Barr, Motorola, Inc.

  15. 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 802.11 devices • Other radio systems adapt to increased levels of interference: • 802.15.1 devices raise transmitted power level and turn off AFH to maintain necessary QoS. Allowed to transmit up to 100mW. • 802.15.4 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.

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