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Optional Scanning Proposal for 40MHz Channels in 2.4GHz Spectrum

This proposal suggests adding optional scanning requirements to detect non-802.11 radios before allowing transmission of 40MHz channels in the 2.4GHz spectrum. It aims to address negative comments received in letter ballots regarding the use of 40MHz channels.

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Optional Scanning Proposal for 40MHz Channels in 2.4GHz Spectrum

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  1. Additional 40 MHz Scanning Proposal Authors: Date: 2008-10-06 John R. Barr, Motorola, Inc.

  2. Abstract Due to the number of negative comments that have been cast in the recent letter ballots regarding use of 40 MHz channels in 2.4 GHz spectrum, it is proposed to add optional scanning requirements to clause 11.14 for FC HT AP 2G4 and FC HT STA 2G4 devices to detect presence of non-802.11 radios operating in 2.4 GHz spectrum before allowing transmission of 40 MHz PPDUs and set the Forty MHz Intolerant field to 1 in transmitted HT Capabilities elements if scanning is not implemented. 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. • Note recommending not using 40 MHz channels when non-802.11 devices are “in the area”. • Adding optional scanning for non-IEEE 802.11 devices operating in 2.4 GHz should satisfy negative letter ballot comments and improve the draft as long as 40 MHz channels not allowed if optional scanning not implemented. John R. Barr, Motorola, Inc.

  4. D 7.0 Comment 10025 (10027 and 10029) • Proposed changes: • 1) In subclause 7.32.57.5, use the reserved bit B3 of the Extended Capabilities field for the HT AP or HT STA to declare its support for non-802.11 radio scans. • 2) In subclause 11.14.3.2, insert after line 12 , page 223: • Before an AP or IDO STA that is capable of detecting non-802.11 radios (bit B3 of the Extended capabilities field is set to 1) starts a 20/40 MHz BSS, it shall perform overlapping BSS scans to search for non-802.11 radios. • 3) In subclause 11.14.3.2, insert after line 65 , page 223, the following: • An FC HT AP 2G4 that is capable of detecting non-802.11 radios shall keep the value of 20/40 Operation Permitted to FALSE if a presence of non-802.11 radio is detected. • 4) Insert the following paragraph at the end of subclause 11.14.5, page 230, after line 13 • An FC HT STA 2G4 that is associated with an FC HT AP 2G4 and is capable of performing non-802.11 radio scans (bit B3 of the Extended Capability field is set to 1) shall perform at least one non 802.11 radio scan every dot11BSSWidthTriggerScanInterval seconds., unless the FC HT STA 2G4 satisfies the conditions described in 11.14.6. John R. Barr, Motorola, Inc.

  5. D 7.0 Comment 10047 • Promote the Note 2 recommendation in 11.14.4.1 to the main body of the subclause. Add the following normative sentence: "If a STA is operating in the 2.4GHz ISM band and has no mechanism to know whether any non-802.11 communication devices are operating in the area or has knowledge that a non-802.11 communication device is operating in the area, then it shall assert the 40MHz Intolerant bit in its HT Capabilities IE." John R. Barr, Motorola, Inc.

  6. “non-802.11 radio scan update” • 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 100 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 100 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.

  7. Situation • 40 MHz 802.11n channels in 2.4 GHz significantly interfere with other 802.11 standard implementations: • Legacy 802.11 radios (protection required in D 7.0) • IEEE Std 802.15.1™-2005 (Bluetooth) • Reduction of available channels from 79-27 • Increased OOC noise due to 802.11n skirts • Mandatory Scanning for legacy 802.11 radios in D 7.0 • Note recommending not to use 40 MHz channels when non-802.11 radios also present in D 7.0 • Comments recommending non-802.11 radio scan from LB 136 • Motion from 802.11 WG for conditional approval for sponsor ballot as “WG11 balloters are largely satisfied with the draft and its time for the transition to the next phase.” John R. Barr, Motorola, Inc.

  8. Proposed Text • In subclause 7.32.57.5, use the reserved bit B3 of the Extended Capabilities field for the HT AP or HT STA to declare its support for non-802.11 radio scans. • In subclause 11.14.3.2, insert after line 12 , page 223: • Before an AP or IDO STA that is capable of detecting non-802.11 radios (bit B3 of the Extended capabilities field is set to 1) starts a 20/40 MHz BSS, it shall perform a non-802.11 radio scan to search for non-802.11 radios. • In subclause 11.14.3.2, insert after line 65 , page 223, the following: • An FC HT AP 2G4 that is capable of detecting non-802.11 radios shall keep the value of 20/40 Operation Permitted to FALSE if presence of non-802.11 radio is detected. • Insert the following paragraph at the end of subclause 11.14.5, page 230, after line 13 • An FC HT STA 2G4 that is associated with an FC HT AP 2G4 and is capable of performing non-802.11 radio scans (bit B3 of the Extended Capability field is set to 1) shall perform at least one non 802.11 radio scan every dot11BSSWidthTriggerScanInterval seconds., unless the FC HT STA 2G4 satisfies the conditions described in 11.14.6. • In subclause 11.14.11, change “dot11FortyMHzIntolerant is TRUE” to “dot11FortyMHzIntolerant is TRUE or dot112G4RadioScanEnabled is FALSE” • TBD - Add dot112G4RadioScanEnabled in appropriate places and define as performance of non-802.11 radio scan John R. Barr, Motorola, Inc.

  9. Proposal • Acceptable text necessary to add optional non-802.11 radio scanning and setting of 40MHzIntolerant to TRUE when scanning not enabled be prepared for consideration in November. • IEEE 802.19 TAG and 802.15 WG strongly recommend that proposed text be incorporated in D 8.0 prior to conditional approval for sponsor ballot of 802.11n. John R. Barr, Motorola, Inc.

  10. References • 11-08-0779-01-000n-coex-40-mhz-comments.doc • 11-08-0962-01-000n-tgn-lb134-coex-comments.xls • 11-08-0992-01-000n-20-40-mhz-11n-interference-on-bluetooth.ppt • 11-08-1101-03-000n-additional-40-mhz-scanning-proposal.ppt • 11-08-1140-00-000n-11n-40-mhz-and-bt-coexistence-test-results.ppt • 11-08-1174-07-000n-lb134-cid-9044.doc • 11-08-1208-00-000n-tgn-lb136-composite-comments.xls • Draft P802.11n_D6.0 and P802.11n_D7.0 • 802.15.1-2005.pdf • 802.15.4-2003.pdf John R. Barr, Motorola, Inc.

  11. 802.11n Transmit Spectral Mask Skirts detected by AFH. John R. Barr, Motorola, Inc.

  12. John R. Barr, Motorola, Inc.

  13. 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.

  14. Draft 6.0 Comments Follow • Comments for Draft 6.0 proposed to prevent operation of 40 MHz channels in 2.4 GHz spectrum. • Not fully considered to to lack of time to prepare suggested text. • Note added to Draft 7.0 to recommend not using 40 MHz channels in 2.4 GHz when presence of non-802.11 radios “known”. John R. Barr, Motorola, Inc.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  21. “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.

  22. 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.

  23. 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.

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