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Fast Moving Scan Channel

This presentation suggests a method to reduce the scanning time on unused channels in the 2.4GHz ISM band. It proposes an improvement to the active scanning mechanism, which can significantly speed up the scanning process.

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Fast Moving Scan Channel

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  1. Fast Moving Scan Channel Authors: Date: 2013-01-07 YonghoSeok, LG Electronics

  2. Abstract • The presentation proposes an improvement to the Active Scanning mechanism in 2.4GHz ISM band to reduce the scanning time on unused channels. Yongho Seok, LG Electronics

  3. Conformance w/ TGai PAR & 5C Yongho Seok, LG Electronics

  4. Motivation • In 2.4GHz ISM band, a STA scans the channel from Channel Number 1 to Channel Number 13. • For each channel to be scanned: • Wait until the ProbeDelay time has expired or a PHYRxStart.indication primitive has been received. • Perform the Basic Access procedure as defined in 9.3.4.2. • Send a probe request to the broadcast destination address, with the SSID and BSSID from the MLME-SCAN.request primitive. When the SSID List is present in the MLME-SCAN.request primitive, send one or more probe request frames, each with an SSID indicated in the SSID List and the BSSID from the MLME-SCAN.request primitive. • Set to 0 and start a ProbeTimer. • If PHY-CCA.indication (busy) primitive has not been detected before the ProbeTimer reaches MinChannelTime, then set NAV to 0 and scan the next channel, else when ProbeTimer reaches MaxChannelTime, process all received probe responses. • Set NAV to 0 and scan the next channel. Yongho Seok, LG Electronics

  5. Motivation • If other BSSs occupy adjacent channels of a scan channel, the transmission from other BSSs may trigger the PHY-CCA.indication (busy) primitive. • If there is no BSS occupying the current scan channel, the scan time overhead is increased to MaxChannelTime - MinChannelTime. Yongho Seok, LG Electronics

  6. Proposed FILS Active Scanning Procedure • For each channel to be scanned: • Wait until the ProbeDelay time has expired or a PHYRxStart.indication primitive has been received. • Perform the Basic Access procedure as defined in 9.3.4.2. • Send a probe request to the broadcast destination address, with the SSID and BSSID from the MLME-SCAN.request primitive. When the SSID List is present in the MLME-SCAN.request primitive, send one or more probe request frames, each with an SSID indicated in the SSID List and the BSSID from the MLME-SCAN.request primitive. • Set to 0 and start a ProbeTimer. • If PHY-CCA.indication (busy) primitive has not been detected before the ProbeTimer reaches MinChannelTime, then set NAV to 0 and scan the next channel, else when ProbeTimer reaches MaxChannelTime, process all received probe responses. • If PHY-RxStart.indication primitive has not been received before the ProbeTimer reaches MinChannelTime, then STAs with dot11FILSActivated equal to true sets NAV to 0 and scans the next channel • Set NAV to 0 and scan the next channel. Yongho Seok, LG Electronics

  7. Probe Request PHY-CCA.indication (busy) • If PHY-CCA.indication (busy) primitive has been detected before the ProbeTimer reaches MinChannelTime, then STA scans the channel until ProbeTimer reaches MaxChannelTime. DATA MinChannelTime ACK MaxChannelTime Probe Request PHY-RxStart.indication& PHY-CCA.indication (busy) • If PHY-CCA.indication (busy) primitive has been detected before the ProbeTimer reaches MinChannelTime, then STA scans the channel until ProbeTimer reaches MaxChannelTime. DATA MinChannelTime ACK Probe Response MaxChannelTime <Current Scanning Procedure> Yongho Seok, LG Electronics

  8. Probe Request PHY-CCA.indication (busy) • If PHY-RxStart.indication primitive has not been received before the ProbeTimer reaches MinChannelTime, then STAs with dot11FILSActivated equal to true sets NAV to 0 and scans the next channel DATA MinChannelTime ACK Probe Request PHY-RxStart.indication& PHY-CCA.indication (busy) • If PHY-RxStart.indication primitive has been received before the ProbeTimer reaches MinChannelTime, then STA scans the channel until ProbeTimer reaches MaxChannelTime. DATA MinChannelTime ACK Probe Response MaxChannelTime <Proposed FILS Scanning Procedure> Yongho Seok, LG Electronics

  9. Proposed FILS Active Scanning Procedure • In many countries, the non-overlapping channel set (1, 5, 9, 13 or 1, 6, 11) is recommended. • When only 1, 5, 9, 13 channels are occupied, the proposed FILS active scanning procedure can reduce the scanning time from MaxChannelTime*13 to MaxChannelTime*4 + MinChannelTime*9 • MinChannelTime: 5ms • MaxChannelTime: 10ms • The gain of the scanning time is about 34% (from 130ms to 85ms) Yongho Seok, LG Electronics

  10. Conclusion • In 2.4GHz ISM band, as IEEE 802.11n 40MHz BSS is more crowded, PHY-CCA.indication (busy) probability on adjacent channels is more increasing. • This presentation proposes to scan the next channel if a STA does not receive a valid PLCP header during MinChannelTime. Yongho Seok, LG Electronics

  11. Straw Poll • Do you support to include the following condition in FILS active scanning procedure for fast moving scan channel? • If PHY-RxStart.indication primitive has not been received before the ProbeTimer reaches MinChannelTime, then STAs with dot11FILSActivated equal to true sets NAV to 0 and scans the next channel Yongho Seok, LG Electronics

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