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Fast Active Scan Proposals

Fast Active Scan Proposals. Moo Ryong Jeong, Fujio Watanabe, Toshiro Kawahara DoCoMo USA Labs mrj@ieee.org Zhun Zhong Philips zhun.zhong@philips.com. Background. 03/416r0 presented an active scanning scheme having short scanning time*. *: Excludes time for sending probe request

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Fast Active Scan Proposals

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  1. Fast Active Scan Proposals Moo Ryong Jeong, Fujio Watanabe, Toshiro Kawahara DoCoMo USA Labs mrj@ieee.org Zhun Zhong Philips zhun.zhong@philips.com Moo Ryong Jeong, DoCoMo USA Labs.

  2. Background • 03/416r0 presented an active scanning scheme having short scanning time* *: Excludes time for sending probe request †: Varies depending on the size of SSID field and Supported Rates field • The cost of the short scanning time is increased implementation complexity Moo Ryong Jeong, DoCoMo USA Labs.

  3. Goal of This Presentation • This presentation provides: • Three schemes (modification to 03/416r0) that make trade-off between scanning time and implementation complexity at different levels Moo Ryong Jeong, DoCoMo USA Labs.

  4. Current Active Scanning Procedure • Use of DCF in probe response transmission is source of time-consumption • DCF is used in current standard on assumption that • STA has no knowledge about neighbor APs • STA wants to obtain information on all neighbor APs • Probe request is broadcast so that any AP can hear and respond by sending probe response Moo Ryong Jeong, DoCoMo USA Labs.

  5. Assumptions Changed • STA may have knowledge on possible neighbor APs • Site report, previous scanning results • STA may be interested only in specific APs • APs chosen from site report or previous scanning results • Probe request can be a directed frame (by standard modification) to a desired AP so that the AP can hear and respond within SIFS • We present fast active scanning methods which fits with changed assumptions Moo Ryong Jeong, DoCoMo USA Labs.

  6. Basic Ideas of Fast Active Scan • Probe request is sent as directed frame to a specific AP on the AP’s operation channel with BSSID in DA field and BSSID field • AP responds to directed probe request after SIFS • Response may be a probe response or an ACK • If the response is an ACK, AP sends probe response later • STA can learn availability/unavailability of AP after SIFS • If STA receives ACK, STA stay on the channel unlit it receives probe response Moo Ryong Jeong, DoCoMo USA Labs.

  7. Original scheme (03/416r0) • AP sends probe response with broadcast destination address after SIFS deferral • Probe response is fast transmitted with high probability of success • Probe response considered as ACK to probe request • No retransmission of probe response MinChannelTime Scanning Station Probe to APi APi P Response SIFS Moo Ryong Jeong, DoCoMo USA Labs.

  8. Original scheme (03/416r0) • Shortest scanning time • ≈ 10 sec when AP is unavailable • SIFS plus transmission time of probe response ( 898 sec) when AP is avaiable • Most demanding in implementation Moo Ryong Jeong, DoCoMo USA Labs.

  9. Alternative Scheme 1 • AP sends ACK after SIFS period • When probe response is ready, send it with DIFS deferral (and random backoff) • Probe response is retransmitted unless ACK is received MaxChannelTime MinChannelTime Scanning Station Probe to APi Ack APi P Response Ack Other frames SIFS SIFS DIFS Random Backoff Moo Ryong Jeong, DoCoMo USA Labs.

  10. Alternative Scheme1 • Scanning time • For unavailable AP, as short as in 03/416r0 • For available AP, longer than 03/416r0 but shorter than conventional active scanning (collocated APs do not respond to probe request) • Least demanding in implementation Moo Ryong Jeong, DoCoMo USA Labs.

  11. Alternative Scheme 2 • AP sends ACK after SIFS period • When probe response is ready, send it with PIFS deferral • Facilitates fast and safe transmission of probe response • Probe response is retransmitted with DIFS and random backoff unless ACK is received MaxChannelTime MinChannelTime Scanning Station Probe to APi Ack APi P Response Other frames Ack SIFS SIFS PIFS Moo Ryong Jeong, DoCoMo USA Labs.

  12. Alternative Scheme 2 • Scanning time • For unavailable AP, as short as in 03/416r0 • For available AP, longer than 03/416r0 but shorter than alternative scheme 1 (priority access of probe response) • Less demanding than 03/416r0 but more demanding than alternative scheme 1 Moo Ryong Jeong, DoCoMo USA Labs.

  13. Knowledge on Neighbor AP • Collection of neighbor AP information • Offline collection by operator • Realtime collection by AP • Reassociation message (TGf) • Beacon report from associated STAs (TGk) • Exchange neighbor AP information among access point • Realtime collection by STA • Results from previous scanning (passive or conventional active) • Delivery of neighbor AP information • Initial setup • Site Report request • Beacon • Probe response Moo Ryong Jeong, DoCoMo USA Labs.

  14. Indicating Probe Request with Fast Active Scan • Use current probe request • AP’s MAC address in DA and BSSID fields in probe request as indication of fast active scan • Define new management frame subtype for probe request with fast active scan • Define new action category for probe request with fast active scan Moo Ryong Jeong, DoCoMo USA Labs.

  15. Indicating Fast Active Scanning Capability of AP • Require all STAs capable of radio measurement be also capable of fast active scanning • Set B12 (radio measurement) in capability information field • Non-AP STA shall be compatible with all schemes • AP shall implement at least one of the three schemes • Implementation changes according to the fast active scanning needs • Define new bit in capability information field to indicate fast active scanning capability Moo Ryong Jeong, DoCoMo USA Labs.

  16. Modification Required • Addressing • Directed frame for probe request (all schemes) • Broadcast frame for probe response (03/416r0) • IFS • SIFS between probe request and probe response (03/416r0) • PIFS deferral in sending probe response (alternative 2) • ACK • Immediate probe response considered as ACK to probe request (03/416r0) • MaxChannelTime • Ignored if probe response is received Moo Ryong Jeong, DoCoMo USA Labs.

  17. Conclusion • We considered improvement of active scanning • Our schemes speed up active scanning process when there is prior knowledge on neighbor APs (e.g. site report) • Proposed active scanning schemes are effective for: • Reducing overhead in active scan-based measurement • Fast handoff • AP implements one of the three schemes according to the fast active scanning needs Moo Ryong Jeong, DoCoMo USA Labs.

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