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Cooperative AP Discovery

Cooperative AP Discovery. Authors:. Date: 2012-1 -16. Abstract. This document describes a technical proposal for TGai which addresses the following phase. AP Discovery. Conformance w/ TGai PAR & 5C. Background.

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Cooperative AP Discovery

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  1. Katsuo Yunoki, KDDI R&D Laboratories Cooperative AP Discovery Authors: • Date: 2012-1-16

  2. Katsuo Yunoki, KDDI R&D Laboratories Abstract • This document describes a technical proposal for TGai which addresses the following phase. • AP Discovery

  3. Katsuo Yunoki, KDDI R&D Laboratories Conformance w/ TGai PAR & 5C

  4. Katsuo Yunoki, KDDI R&D Laboratories Background • We assume a scenario with multiple APs in a channel and a large number of STAs concurrently attempting to find an appropriate AP for association in that channel. • Other submissions have presented results on the amount of channel time needlessly spent on Probe Request / Response and waiting for Beacons (see 11-11/1413, for example.). • STAs are assumed to only support legacy 802.11 protocols. Reduced FILS latency through modification of AP protocol behavior is the goal of this work.

  5. Wang and Yee, MediaTek Observations • Scanning across multiple channels is very time consuming with STA implementation-specific delays. We assume the operating channel is fixed. • STAs typically first scan for Beacons from known APs. Some STAs perform Probe Request by default. • Operating independently, APs transmit Beacons at random time intervals. Most APs set their BI = 100ms. • Operating independently, APs will respond to a received Probe Request without considering if another AP is more suitable.

  6. Wang and Yee, MediaTek Coordinated AP Behavior • If APs coordinate their Beacon intervals in order to uniformly distribute the beacon transmission times of all APs, the average beacon wait time of a STA can be reduced. • If APs exchange BSS load information and defer to other suitable AP with lighter load to respond to Probe Requests, channel time can be better utilized.

  7. Wang and Yee, MediaTek Proposed Protocol Mechanisms - Summary • Coordinated Beaconing among Neighboring APs • Goal: The APs of a Hot-Spot take turns to transmit beacon frames in a deterministic order • AP Self-Censorship based on system loading • Goal: Only one AP, the active responder, responds to broadcast probe request in order to avoid probe response storm. • Deferred Beacon Transmission for next scheduled beaconing AP • Goal: The active responder AP updates its loading information in the next scheduling time. The next scheduled beaconing AP defers transmitting of its beacon frame to avoid collision.

  8. Wang and Yee, MediaTek Proposed Protocol Mechanisms (1) • Coordinated Beaconing among Neighboring APs • Option 1: re-use MBSS mechanisms such as Mesh Beacon Collision Avoidance (MBCA). • Option 2: a distributed beaconing synchronization algorithm (No need to define new protocol element, only new behavior. May re-use some of the MBSS protocol element)

  9. Wang and Yee, MediaTek Proposed Protocol Mechanisms (2) • AP self-censorship by using system loading • Every AP sends its loading information by carrying BSS Load and multiple BSSID information element in beacon frames • All AP learns the system loading of other APs • Only the AP with the lightest load, active responder AP, responds to broadcast probe request. Other AP remain silent • The active responder AP will be the one responding to probe requests till another AP resumes the role of active responder • (No need to define new protocol element, need to define new behavior)

  10. Wang and Yee, MediaTek Proposed Protocol Mechanisms (3) • Deferred Beacon Transmission • The active responder sends a beacon frame at the next scheduled beaconing time • The scheduled beaconing AP defers transmitting its beacon frame by using random backoff. • If no beacon frame from active responder AP is received at the scheduled beaconing time, the scheduled beaconing AP transmits a beacon frame after backoff timer expired (No need to define new protocol element if using the new distributed beaconing algorithm. May need new protocol element if using MBSS protocol )

  11. Wang and Yee, MediaTek FILS latency reduction and efficiency improvement using these mechanisms • Assuming there are n APs with BI= 100 ms in a channel • Baseline Link Setup Delay • Passive scanning: Worst case delay is 100ms regardless of n. • Active scanning: • Average delay = (Probe_Req Tx Time)+ n*((ProbeResp Tx time)/2 + AP system and channel access delay) • Expected FILS latency • Beacon coordination time • A generic distributed algorithm should complete one-time beacon coordination log (n) BIs, • Scanning time • Passive scanning: A STA will receive a beacon frame in 100/n ms • Active scanning: Avoid unicast probe responses storm • Delay after Load Balancing = (Probe_Req Tx Time)+(ProbeResp Tx time) + AP system and reduced channel access delay • Load balancing overhead • Periodic BSS Load update time

  12. Wang and Yee, MediaTek Further Improvement of these mechanisms • Information which will further improve the FILS performance • Beacon Transmit Power • The receiving STA can check SNR against Tx power to estimate the channel • Additional information complicates the algorithm for selecting the best AP. The cost and effect should be evaluated carefully

  13. Wang and Yee, MediaTek Simulation Results • - Work in Progress

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