802.11ai – Improving WLAN System Performance

1. Hiroshi Mano (ATRD) 802.11ai – Improving WLAN System Performance Date: 2013-11-06 Authors:

2. Hiroshi Mano (ATRD) Agenda • Introduction to IEEE802.11ai, FILS • Use case • 802.11ai features in details • Trial report of the FILS feasibility study • Current status of IEEE802.11ai • Note: • This presentation has not been approved by IEEE802.11ai task group as an official overview document. It has been proposed by the authors based on the approved submissions as of Nov 2013.

3. Hiroshi Mano (ATRD) Introduction to IEEE802.11ai, Fast Initial Link Setup (FILS) • The initial link setup includes all operations required to enable IP packets exchange: • Network and BSS discovery • Authentication and association • IP address configuration • 802.11ai focuses to an environment where mobile users are constantly entering and leaving the coverage area of an existing extended service set (ESS). Every time the mobile device enters an ESS, the mobile device has to do an initial link set-up. This requires efficient mechanisms that: • (a) scale with a high number of users simultaneously entering an ESS • (b) minimize the time spent within the initial link set-up phase • (c) securely provide initial authentication.

4. Hiroshi Mano (ATRD) Today’s Market Trends • Growth of portable device market • Majority of the Wi-Fi devices are portable • New application’s request (Twitter, Facebook…) • Push Notification Service • Quick updates • High bandwidth • Very SMALL CELL of each AP • True mobile usage • Users frequently pass through (isolated) hot spots while on the move • The dwell time of an user within a cell is short • Isolated hot spots cause frequent initial association / authentication (link setup) • Always-on connectivity is a must

5. Hiroshi Mano (ATRD) Hot Spot Environment 1/2 • Dense deployment: The famous ”Tokyo Metro Station” • Increased amount of spectrum & number of networks & number of devices • Signaling overhead, exchange of Unnecessary information • QoS violation • Use of WLAN offloading is increasing • It is equally important to shorten the link setup time as it is to shorten the data transmission time • Shorter scanning reduces power consumption of the device

6. Hiroshi Mano (ATRD) Hot Spot Environment 2/2 • Most of air time is occupied by control frame • Especially undesired Probe Response frames are overflowing • KDDI’s report • Understanding the current situation of public Wi-Fi usage. • 13/11-13-0523-02 • hew-understanding-current-situation-of-public-wifi-usage.pptx Frame type profile at metro station Breakdown of Management frames

7. Hiroshi Mano (ATRD) Features of IEEE802.11ai (Scan) • More control to scanning procedures: • Terminating the ongoing scan • More reporting options of the scanning result • Immediate reporting • Reporting after a channel is scanned • Legacy, reporting after scanning is completed • Announcing one or more neighbor BSS or channel information in Beacon, Probe Response and Fast Discovery (FD) frame • Avoids scanning of channels with no AP • BSSID of neighbor AP enables more precise active scanning • Additional parameters may be included to provide more information of the neighbor BSSs

8. AP1 Hiroshi Mano (ATRD) AP1 AP2 AP2 AP3 AP3 Probe Request STA 1 STA 2 STA 2 Delay probe request transmission Abort probe request transmission Probe Response STA 1 Active Scanning, Expedited Scanning Procedure • If device has received a probe request, it should avoid transmitting the same probe request as transmitted

9. Hiroshi Mano (ATRD) AP1 AP1 AP2 AP2 AP3 AP3 Probe Request STA 1 STA 2 STA 2 STA2 misses the probe request transmission Receive probe responses Probe Response STA 1 Active Scanning, Probe Response Collision Avoidance • The APs avoids sending unnecessary copies of probe responses • Single copy of probe response or beacon frame is enough AP1 AP2 AP3 Probe Request STA 1 STA 2

10. Hiroshi Mano (ATRD) Chn 1 Chn 6 Chn 1 Chn 6 Probe Response + Neighbor List Probe Request Contains information of itself (AP 2), as well as AP 1 and AP 3 or channel 6 Request for information of other BSSs STA 1 STA 1 AP1 AP1 AP2 AP2 AP3 AP3 Active Scanning, Comprehensive Response • One probe response may contain information of multiple APs • The total number of responses is reduced

11. AP1 AP1 Hiroshi Mano (ATRD) AP2 AP2 AP3 AP3 Probe Request Probe response is transmitted if all the criteria are met Criteria for AP delay performance & RSSI STA 1 Probe Response STA 1 Active scanning, New Response Criteria • Probe Request contains criteria to transmit Probe Response. Response is transmitted only if the criteria is met • Criteria include: • Reception power • AP’s channel access delay • Vendor specific information • AP capabilities

12. Hiroshi Mano (ATRD) Active scanning, Probe Response Reception Time Element • The transmitters of the Probe Request may indicate how long the transmitter will be available to receive Probe Responses • Probe Response Reception Time is set to MAX_Probe_Response_Time

13. Hiroshi Mano (ATRD) Passive Scanning, Key Enhancements • FILS Discovery (FD) frame: a new public action frame • Small-size: 30-byte MAC headers + 10 to about 25 bytes FD frame body, i.e., 40 to 55 bytes for typical uses; • One mandatory information element: SSID; • Optional information items: AP’s Next TBTT, AP-CCC, Access Network Options, Capability, Security, Neighbor AP information. • FD frame is transmitted between Beacon frames, for a fast AP/Network discovery; • FD frame may be transmitted as a non-HT duplicate PPDU, enabling a larger channel than 20MHz; Beacon Example #1 FD frame Primary channel of the transmitter Preamble Payload of FD Frame T1 time Preamble Payload of FD Frame Example #2 Preamble Payload of FD Frame T2 time Preamble Payload of FD Frame Example #3 T3 time

14. Hiroshi Mano (ATRD) Reducing Sizes of the Responses • AP Configuration Change Count (CCC) keeps count of changes of the parameters in Probe Response and Beacon • One octet in length • AP-CCC does not consider changes of BSS Load, Average Access Delay and other rapidly changing parameters

15. Hiroshi Mano (ATRD) Network Discovery, Key Enhancements • GAS query enhancement by using an AP white-list • A new IE with one or multiple 6-byte BSSIDs in GAS request to indicate the AP(s) that the requesting STA wants to query. • GAS traffic reduction by using GAS Configuration Sequence Number • A new IE with an 1-byte unsigned integer: • indicating the version number of AP’s GAS configuration information set; • monotonically incrementing whenever there is any change in the AP’s GAS configuration information set; • Used in Beacon and/or Probe Response.

16. Hiroshi Mano (ATRD) Feature of IEEE802.11ai (Higher layer setup) • Reduce the number of packet exchanges during initial link setup. • All of necessary information are exchanged in 2 to 3 round trip of packet exchanges. • Note: IEEE802.11ai achieves to have an established IP-Link after the set-up (ready to use for higher layer protocols / applications) This is a major difference from what we have today (IP-setup follows afterwards) and saves lots of time.

17. Hiroshi Mano (ATRD) Link Setup States per 802.11ai

18. Hiroshi Mano (ATRD) Trial report of FILS feasibility study • The effect of reducing packet exchange was evaluated by field test in Japan • The details are reported in IEEE802.11 as, https://mentor.ieee.org/802.11/dcn/13/11-13-0323-02-00ai-tgai-experimental-test-report-of-fils.pptx • FILS STAs completed the association process in significantly less time than WPA STAs •  More time within the AP coverage for (user) data exchange • The large number of link setup frame exchanges for WPA2 STAs (as compared to FILS STAs) made them vulnerable. • If retransmission of a lost frame did not succeed after three attempts, the association process had to restart from the beginning • This field trial did only consider the higher layer set-up features while using legacy scanning. We expect FURTHER performance improvement when the FILS scanning features are in use

19. Hiroshi Mano (ATRD) Trial report of feasibility study with FILS 2/2 • 20 FILS and 20 WPA2 are entering the service area. • Measured the distance of STA and AP where STA establish link successfully and received http contents. • Measured the time from Association/FILS request to IP address assignment propriety application. • http://www.youtube.com/watch?v=xOKaVOPWXTU • 90% (18/20) FILS STA established link before arriving at in the front of AP • 85% (17/20) WPA2 established link since they passed in the front of AP • Average link setup time from FILS request to IP address assignment is 0.742 Sec • Average link setup time from Association request to IP address assignment is 21.599 Sec Established Link Point FILS 非接続 歩きながら移動 非接続 Service Area WPA2

20. Hiroshi Mano (ATRD) Annex, use case examples that benefit from FILS

21. Hiroshi Mano (ATRD) Alternative Use Cases • Automatic metering • Power electric • Water meter • Gas meter • etc.. • Drive through • Digital Signage • V2V,V2X

22. Hiroshi Mano (ATRD) Feasibility Study of Automobile Application • Fast initial link setup enables opportunistic vehicle to vehicle communication. • Toyota InfoTechnology Center measured the number of user text message exchanges during specific time period. • Assumption • Air coverage: 50m • Vehicle speed: 40km/h（11m/Sec） • Available communication time : 5Sec • WPA2: More than 4Sec communication time is required to exchange messages. • FILS: it is available to exchange messages under short communication time. • Y: Number of exchanged messages • X: Communication time • This measurement did only consider the higher layer set-up features while using legacy scanning. • We expect FURTHER performance increase if the stations implemented the new scanning features.