Low Energy Subgroup Report

1. Low Energy Subgroup Report Wei Hong (Arch Rock Corp.) Wei Hong, Arch Rock Corporation

2. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: Low Energy Subgroup Report Date Submitted: 21 September, 2009 Source: Wei Hong Company: Arch Rock Corporation Address: 501 2nd Street, Suite 410, San Francisco, CA 94707, USA Voice: 415-692-0828, FAX: 415-278-0441, E-Mail: whong@archrock.com Re: Subgroup status report for 802.15.4e Abstract: Proposal review and subgroup status update. Purpose: Subgroup update for 802.15.4e Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15. Wei Hong, Arch Rock Corporation

3. Status • All required changes are included in combined draft doc 604 rev3 except for • Changes between doc 427 rev5 and rev4 • Will communicate with Ludwig to include them Wei Hong, Arch Rock Corporation

4. Major Changes Since SF Meeting • Added Receiver Initiated Transmission (RIT) as an alternative low-energy mechanism to Coordinated Sampled Listening (CSL) • Clarified how the upper layer can turn off and on sampled listening to reduce latency for urgent messages Wei Hong, Arch Rock Corporation

5. Coordinated Sampled Listening (CSL) Review • Receiver periodically performs channel sampling for radio traffic • Every macCSLPeriod (ms) • Sender transmits wakeup frame sequence prior to payload frame • Full wakeup sequence (macCSLMaxPeriod) if unsynchronized with receiver, i.e., first time to send to the receiver • Short wakeup sequence for guard time if synchronized with receiver • Set frame pending bit for streaming traffic

6. Note on Channel Occupancy and Latency • Channel Occupancy • Unsynchronized transmissions are rare • First time communication between nodes • Broadcast traffic • Synchronized transmissions have minimal channel overhead • Latency • Frame pending bit can be set for low latency streaming • Upper layer has the option to turn off sampled listening temporarily • Setting macCSLPeriod to zero on receiver • Setting macCSLMaxPeriod to zero on the sender • Coordination between sender and receiver Wei Hong, Arch Rock Corporation

7. Receiver Initiated Transmission (RIT) Review • Receiver periodically broadcasts datareq frames and listen for a short amount of time (macRitDataWaitPeriod) for incoming transmissions every macRitPeriod • Sender waits until receiving datareq frame from receiver then immediately transmit payload frame • Broadcast not directly supported • Simulated by a sequence of unicasts

8. Tradeoff between CSL and RIT • CSL • Channel sample typically takes 0.5ms • Idle listen duty cycle = 0.05% when macCSLPeriod = 1000ms • Achieves low energy with <= 1s per-hop latency • Tradeoff between latency and energy consumption • RIT • Datareq frame transmission typically takes 10ms • Idle listen duty cycle = 0.05% when macRitPeriod = 20s • Works better when higher latency can be tolerated • Works with regulations which limit continuous transmission duration (e.g., Japan) Wei Hong, Arch Rock Corporation

9. Informative Annex • If link latency needs to be less than a second, use CSL. • If link latency can be greater, consider RIT • Best with 10s of seconds of latency to reduce datareq overhead • If regulation limits continuous transmission duration, use RIT Wei Hong, Arch Rock Corporation

10. Thanks You • Questions? Wei Hong, Arch Rock Corporation