Listen interval for sensor devices

1. Listen interval for sensor devices Date: 2012-05-14 Authors: Jinsoo Choi, LG Electronics

2. Jinsoo Choi, LG Electronics

3. Introduction • Some sensor devices are likely to wake up periodically and rarely receive a downlink traffic of a low duty cycle • For this type of devices, it might be efficient not to indicate their paged status through the TIM signaling [1] • Can save the TIM overhead • Based on that, this contribution investigates how we can operate that mechanism efficiently Jinsoo Choi, LG Electronics

4. Investigation • Some challenge • AP cannot know transmission time of a polling or trigger frame from the STA, so AP may need to buffer the DL traffic of the STA (for a long time in some case) to guarantee the successful data reception in STA • Considering this situation with existing lots of devices, it would be a burden on the buffer management <Example of power save polling w/o TIM listening> Jinsoo Choi, LG Electronics

5. Proposal (1/2) • This type of devices can transmit PS-POLL or trigger frame as following • A transmission interval can be established between AP and a STA • For this purpose, Listen Interval field can be reused • “The Listen Interval field is used to indicate to the AP how often a STA in power save mode wakes to listen to Beacon management frames”, fromIEEE 802.11-2012 • “The STA shall wake up early enough to be able to receive the first Beacon frame scheduled for transmission at the time corresponding to the last TBTT plus the Listen Interval”, fromIEEE 802.11-2012 • Because original meaning of Listen Interval field is based on listening a beacon frames, a little modification might be required on this field for this type of devices • After possible negotiation in advance about the proposed usage between AP and this type of device, this Listen interval field can be applied with following modification • The Listen Interval field is used to indicate to the AP how often a STA in power save mode wakes to listen to Beacon management frames or transmit a polling or trigger frame to check the buffered DL traffic • The STA shall wake up early enough to be able to receive the first Beacon frame scheduled for transmission or transmit a polling or trigger frame to check the buffered DL traffic at the time corresponding to the last TBTT plus the Listen Interval Jinsoo Choi, LG Electronics

6. Proposal (2/2) • AP may buffer and discard the DL traffic for the STA based on the Listen Interval, i.e., the life time of the frames that buffered for the STA can be determined by the Listen Interval information (from IEEE 802.11-2012) • While non-TIM STA is not required to wake to receive a beacon each listen interval, the STA shall transmits at least one polling or trigger frame every Listen interval for checking the buffered DL traffic <Example of proposed method w Listen Interval> Jinsoo Choi, LG Electronics

7. Summary • For sensor devises that wake up with a low duty cycle, AP may not include their paged status in TIM signaling • Without TIM indication, these devices transmit a frame to check the buffered DL traffic (e.g. PS-POLL or trigger frame) based on a Listen Interval established through the management procedure (e.g. association request/response procedure) in advance Jinsoo Choi, LG Electronics

8. References [1] 11-12-0610-00-00ah-Non_TIM_Stations [2] Specification framework for TGah, 11-11/1137r6 [3] Draft P802.11-2012 Jinsoo Choi, LG Electronics

9. Straw Poll • Do you support the concept that non-TIM STA shall transmit at least one PS-POLL or trigger frame every listen interval and non-TIM STA is not required to wake to receive a beacon each listen interval? Jinsoo Choi, LG Electronics