Presentation to accompany IEEE 802.11-08/0233r2

1. Presentation to accompany IEEE 802.11-08/0233r2 Authors: Date: 2008-05-12 Jon Rosdahl, CSR

2. Abstract This presentation was prepared to accompany IEEE 802.11-08/0233r2. This presentation looks at the following questions: 1. What is transmit inhibition interference? 2. What can be done with knowledge of transmit inhibition interference? 3. What is the cost of the proposed changes? The proposed text is then described. Jon Rosdahl, CSR

3. What is transmit inhibition interference? • In our context this occurs when an IEEE 802.11 STA is required to be silent to protect a high priority reception at a co-located receiver. • It is often enforced by coexistence signalling between the co-located and (possibly mutually) interfering transceivers. • In some cases transmit inhibition of 802.11 may also be necessary to protect the (remote) reception of a transmission made by the co-located transceiver. Jon Rosdahl, CSR

4. What is transmit inhibition interference? (cont) • Transmit inhibition interference is a relaxed case of interference in comparison to receive de-sense interference • In the 802.11 protocol, receive interference at a STA precludes any communication initiated by a peer STA. • In contrast, a transceiver subject to only transmit inhibition interference is still able to receive. • If the initiator does not require a response then the communication will be successful. • Though STAs can choose to schedule transmissions to be made through the DCF or EDCF, such flexibility is not afforded for control responses, e.g. • Basic automatic control responses such as ACK or CTS. • Block acknowledgements where an immediate block acknowledgement policy is in use. Jon Rosdahl, CSR

5. Some examples of relevant use cases:IEEE 802.11 co-located with… • IEEE 802.16(e) – WiMAX, Mobile WiMAX or WiBro • Operation in licensed (i.e. paid-for) spectrum means unlicensed technologies must defer • FCH, DL-MAP, UL-MAP are important WiMAX downlink messages and can occur with periodicity 5 ms and instance duration on the order of 1 ms. • Bulk data downlink activity may have periodicity 5 ms and instance duration of up to 3 ms. • VoIP activity may cause two patterns of transmit inhibition interference, each with period 20 ms and instance duration 1-3 ms. These two patterns have phase offset of 5 ms. • Bluetooth (or 802.15.1) • Common use case sees Synchronous Connection-Oriented (SCO) transport carrying voice with little FEC and no retransmission • Any packet loss results in immediate user impact (audio distortion) thus SCO is given very high priority • This would cause transmit inhibition interference with period 3.75 ms and instance duration on the order of 0.4 ms. • Ultra-Wide Band (UWB) • A UWB receiver will likely be blocked by a collocated with IEEE 802.11 transmitter operating near 5 GHz (either through direct interference or through inter-modulation distortion) • UWB beacon period must be protected. This will have periodicity of 65 ms and instance duration on the order of 0.5-1 ms. Jon Rosdahl, CSR

6. What can be done with knowledge of transmit inhibition interference? • Some frames do not require an immediate response from the recipient • Multicast and broadcast frames from a STA in an IBSS or an AP • Unicast frames with a QoSNoAck policy • Unicast frames with a delayed block acknowledgement policy • A STA in an IBSS or an AP may schedule frames which do not require a response if the peer STA(s) is(are) known to be subject only to transmit inhibition interference. • For longer frames, a STA in an IBSS or an AP may be able to commence transmission of a frame that does require a response if it determines that the instance of transmit inhibition interference will have ended by the time that response is required. Jon Rosdahl, CSR

7. What does it cost? • Note that all statements in the previous slide are MAYs – not SHALLs. • No requirements are placed on an implementation. • A single bit in the Co-located Interference Response frame is needed to indicate transmit inhibition interference • For STAs choosing not to use such functionality this bit is treated as reserved. • We propose this bit be inserted in the Interference Level Accuracy/Interference Index field. Jon Rosdahl, CSR

8. Specifically… • Modify Figure v93 as shown: Figure v93 – Interference Level Accuracy/Interference Index field format Jon Rosdahl, CSR

9. Specifically – part 2 • Insert the following text in the draft amendment in Section 7.4.11.15 following the paragraph describing the Expected Accuracy field: The Interference Type bit indicates the nature of co-located interference. If set, the bit indicates that the interference causes transmit inhibition only, meaning that the transmitting STA can be addressed while subject to the interference, but will be unable to respond. Jon Rosdahl, CSR

10. Conclusion • The situations this mechanism proposes to address exist and are relevant. • The proposal places no requirement on anyone implementing the specification. • The proposal provides an avenue for product differentiation. • The proposed specification changes are minor. • In coexistence scenarios such performance gains can add up to make a major difference. Jon Rosdahl, CSR