Interference Signalling Enhancements

1. Interference Signalling Enhancements Authors: Date: 2010-03-xx Allan Thomson, Cisco Systems

2. Abstract As part of the implementation evaluation of the current collocated interference feature in TGv SB, several significant issues were raised about the viability of the feature This proposal highlights a solution to resolve TGv SB Recirc #1 CIDs 2 and 13 Allan Thomson, Cisco Systems

3. An Example Use Case: WiFi Voice Client with BT Headset The client wants to use voice over wifi and BT headset at the same time. BT is periodic at 3.75ms intervals with 1.25ms active and 2.5ms silence, AP has to transmit after the U-APSD trigger frame and before the BT transmission by the handset Client U-APSD Trigger Frame Client 3.75ms AP U-APSD Voice Frames AP Allan Thomson, Cisco Systems

4. Problem The currently defined collocated interference feature has the following issues: 1) Requires the AP implement some form of scheduling and when combined with all interactions and services the AP has to provide for BSS operation becomes a significantly complex task 2) Does not make use of existing 802.11 frames and AP interactions and therefore requires additional complexity on both AP and client 3) Does not take into account important state such as power save provided by U-APSD Allan Thomson, Cisco Systems

5. AP Guiding Principles/Objectives • Maximize over-the-air throughput in the BSS • Minimize wasted transmissions to absent clients • Provide scalable solution for up to 100’s of clients in the BSS • Provide solution such that existing performance is not negatively impacted • Transmit packets in order received subject to priority • Don’t give devices reporting collocated interference greater priority than devices without interference • Minimize development

6. Solution Introduction Extend the U-APSDsignalling that takes place to allow the client to report interference free intervals and have the AP integrate that logic into the delivery of frames Provide two mechanisms 1) Immediate AP transmission based on trigger frames 2) Absolute AP transmission based on TSF offset to 0 Solution aspects: • Advertisement • Client Reporting Mechanism • AP Mediation Mechanism Allan Thomson, Cisco Systems

7. Example #1: WiFi Voice Client with Periodic BT Interference every 3.75ms with 1.25ms active BT Client setup (not shown): Sends ADDTS coexistence for 2ms duration Client sends U-APSD trigger frame after each BT interference period AP transmits buffered frames to client after receiving trigger frame until end of duration Client U-APSD Trigger Frame Client BT Frames 1.25 1.25 3.75ms AP U-APSD Voice Frames Optional AP EOS U-APSD Frame AP Allan Thomson, Cisco Systems

8. Example #2: WiFi Voice Client with Periodic BT Interference every 3.75ms with 1.25ms active BT Client setup (not shown): Sends ADDTS coexistence for 3.75ms interval with TSF 0 Offset = 2 Client sends U-APSD trigger frame after each BT interference period AP transmits buffered frames to client after receiving trigger frame until end of adjusted duration calculated based on interval of interference and offset from TSF

9. Advertisement • Add new bit to Extended Capabilities IE to indicate U-APSD Coexistence service • Both AP and non-AP STA would set the bit when supporting the feature • If either does not support the feature then coexistence while using U-APSD is not available Allan Thomson, Cisco Systems

10. Client Reporting Mechanism • Include in ADDTS Request frame an optional “coexistence” IE • The client receives a ADDTS response that acknowledges positive acceptance by the AP that coexistence will be provided for the Duration requested Allan Thomson, Cisco Systems

11. Coexistence IE • TSF 0 Offset only used if non-AP STA wants AP to adjust for TSF drift of interference • Interval/Duration defines how long the AP is able to transmit to the non-AP STA after receiving a U-APSD trigger frame • TSF 0 Offset field is microseconds since TSF time 0 • 0 indicates unused • Interval/Duration field is measured in microseconds and defined in 4 octets • 0 is a reserved value Allan Thomson, Cisco Systems

12. Client Advertisement Behavior • If the non-AP STA has advertised support for U-APSD Coexistence feature in the Extended Capabilities IE then it has the capability to detect interference and request use of the coexistence feature • The non-AP STA shall not include the Coexistence IE in the ADDTS frame unless the AP has also advertised support for the Coexistence feature in the Extended Capabilities IE Allan Thomson, Cisco Systems

13. Client Behavior – Interference Detected • Upon determination that interference is occurring the non-AP STA shall include the Coexistence IE in the ADDTS frame indicating the preferred Duration when the AP should transmit frames to the non-AP during the U-APSD service period • ADDTS frame with Coexistence requested: Allan Thomson, Cisco Systems

14. Client Behavior – Interference Changes • Upon determination that interference is changing, the non-AP STA may issue another ADDTS frame to update the Duration field as necessary • ADDTS frame with Coexistence modified: Allan Thomson, Cisco Systems

15. Client Behavior – No Interference Detected • Upon determination that interference has stopped and the non-AP STA no longer needs the AP to provide coexistence protection but continues to use QoS Services for U-APSD SP the non-AP STA may transmit a ADDTS frame without the Coexistence IE • ADDTS frame sent to stop interference protection without CoexistenceIE Allan Thomson, Cisco Systems

16. Client Behavior – No QoS Required & No Interference Detected • Upon determination that interference has stopped and the non-AP STA no longer needs the AP to provide QoS services or coexistence protection for U-APSD SP the non-AP STA may transmit a DELTS frame without the Coexistence IE • DELTS frame sent to stop interference protection without CoexistenceIE Allan Thomson, Cisco Systems

17. AP Behavior • If the AP has advertised support for U-APSD Coexistence feature in the Extended Capabilities IE then it shall process U-APSD Coexistence IE otherwise it shall ignore • AP should never receive a Coexistence IE from a non-AP STA is the AP has not already advertised support for this feature • Upon reception the AP shall associate the Duration field for the non-AP STA such that any frames transmitted during the U-APSD SP to that non-AP STA should be transmitted during that period Allan Thomson, Cisco Systems

18. U-APSD SP Termination • Normal behavior for AP is that it sets the EOSP bit in the last frame transmitted in the U-APSD service period • If the AP determines that the frame to be transmitted cannot be transmitted before the Duration field expires then it needs to notify the non-AP STA somehow • Explicit Termination: • New normative behavior required to define that the AP transmits a QoS null frame in this circumstance with the EOSP bit set to terminate the U-APSD SP • Implicit Termination: • New normative behavior required to defined that both the AP and non-AP STA will implicitly terminate the SP after the Duration time has expired after reception of the U-APSD Trigger frame at the AP Allan Thomson, Cisco Systems

19. Questions ? Allan Thomson, Cisco Systems