1. 802.11ai – Improving WLAN System Performance
1Page 1
John Doe, Some Company
Month Year
doc.: IEEE yy/xxxxr0
Nov 2013
802.11ai – Improving WLAN System Performance
Date:
Authors:
Hiroshi Mano (ATRD)

2. Introduction to IEEE802.11ai, FILS Use case
Nov 2013
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.
Hiroshi Mano (ATRD)

3. Introduction to IEEE802.11ai, Fast Initial Link Setup (FILS)
Nov 2013
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.
Hiroshi Mano (ATRD)

4. Today’s Market Trends Majority of the Wi-Fi devices are portable
Nov 2013
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
Hiroshi Mano (ATRD)

5. Hot Spot Environment 1/2 Nov 2013
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
Hiroshi Mano (ATRD)

6. Nov 2013
Hot Spot Environment 2/2
Most of air time is occupied by control frame Especially undesired Probe Response frames are overflowing
Frame type profile at metro station
KDDI’s report Understanding the current situation of public Wi-Fi usage. 13/ hew-understanding- current-situation- of-public-wifi- usage.pptx
Breakdown of Management frames
Hiroshi Mano (ATRD)

7. Features of IEEE802.11ai (Scan)
Nov 2013
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
Hiroshi Mano (ATRD)

8. Active Scanning, Expedited Scanning Procedure
doc.: IEEE yy/xxxxr0
Month Year
Nov 2013
Active Scanning, Expedited Scanning Procedure
If device has received a probe request, it should avoid transmitting the same probe request as transmitted
STA 1
Probe Request
STA 2
Delay probe request transmission
AP1
AP2
AP3
STA 1
Probe Response
STA 2
Abort probe request transmission
AP1
AP2
AP3
Hiroshi Mano (ATRD)
John Doe, Some Company

9. Active Scanning, Probe Response Collision Avoidance
doc.: IEEE yy/xxxxr0
Month Year
Nov 2013
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
STA 1
Probe Request
STA 2
STA2 misses the probe request transmission
AP1
AP2
AP3
STA 1
Probe Request
STA 2
AP1
AP2
AP3
STA 1
Probe Response
STA 2
Receive probe responses
AP1
AP2
AP3
Hiroshi Mano (ATRD)
John Doe, Some Company

10. Active Scanning, Comprehensive Response
doc.: IEEE yy/xxxxr0
Month Year
Nov 2013
Active Scanning, Comprehensive Response
One probe response may contain information of multiple APs
The total number of responses is reduced
STA 1
Probe Request
Chn 1
Chn 6
Request for information of other BSSs
AP1
AP2
AP3
Probe Response + Neighbor List
Contains information of itself (AP 2), as well as AP 1 and AP 3 or channel 6
Hiroshi Mano (ATRD)
John Doe, Some Company

11. Active scanning, New Response Criteria
doc.: IEEE yy/xxxxr0
Month Year
Nov 2013
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
STA 1
Probe Request
Criteria for AP delay performance & RSSI
AP1
AP2
AP3
STA 1
Probe Response
Probe response is transmitted if all the criteria are met
AP1
AP2
AP3
Hiroshi Mano (ATRD)
John Doe, Some Company

12. Active scanning, Probe Response Reception Time Element
Nov 2013
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
Hiroshi Mano (ATRD)

13. Passive Scanning, Key Enhancements
Nov 2013
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;
Example #1
Beacon
FD frame
Primary channel of the transmitter T1
Preamble
Payload of FD Frame
time
Preamble
Payload of FD Frame
Example #2
Preamble
Payload of FD Frame T2
time
Preamble
Payload of FD Frame
Example #3 T3
time
Hiroshi Mano (ATRD)

14. Reducing Sizes of the Responses
Nov 2013
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
Hiroshi Mano (ATRD)

15. Network Discovery, Key Enhancements
Nov 2013
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.
Hiroshi Mano (ATRD)

16. Feature of IEEE802.11ai (Higher layer setup)
Nov 2013
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.
Hiroshi Mano (ATRD)

17. Link Setup States per 802.11ai
Nov 2013
Link Setup States per ai
Hiroshi Mano (ATRD)

18. Trial report of FILS feasibility study
Nov 2013
Trial report of FILS feasibility study
The effect of reducing packet exchange was evaluated by field test in Japan The details are reported in IEEE as, ai-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
Hiroshi Mano (ATRD)

19. Trial report of feasibility study with FILS 2/2
Nov 2013
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.
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 Sec Average link setup time from Association request to IP address assignment is Sec
Established Link Point
FILS
非接続
歩きながら移動
非接続
Service Area
WPA2
Hiroshi Mano (ATRD)

20. Annex, use case examples that benefit from FILS
Nov 2013
Annex, use case examples that benefit from FILS
Hiroshi Mano (ATRD)

21. Nov 2013
Alternative Use Cases
Automatic metering Power electric Water meter Gas meter etc.. Drive through Digital Signage V2V,V2X
Hiroshi Mano (ATRD)

22. Feasibility Study of Automobile Application
Nov 2013
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.
Hiroshi Mano (ATRD)