Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Slot Based Link Access for Low-Energy Wide Area Monitoring] Date Submitted: [Sep 15, 2011] Source: [Seong-Soon Joo, Tae-Wook Heo, Jong-Arm Jun] Company: [ETRI] Address: [161 Gajeong-dong, Yuseong-gu, Daejeon, KOREA] Voice: [+82-42-860-6333], FAX: [+82-42-860-4197], E-Mail: [ssjoo@etri.re.kr] Re: [IEEE 802 TG4k issues a call for proposal] Abstract: [Global time synchronization for low-energy wide area monitoring is proposed.] Purpose: [Tocontributethe initial process of preparing draft for TG4k] 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.

2. Slot Based Link Accessfor Low-Energy Wide Area Monitoring Seong-Soon Joo*, Tae-Wook Heo, Jong-Arm Jun ETRI

3. LECIM MAC Design • Major design goals for LECIM MAC • long lived infra  low energy consumption • ease maintained infra  carrier grade network management • Design considerations • low energy consumption • find a balance between data transmission throughput and duration of sleep • carrier grade network management • light and a certain level of reliable & real-time downward link • upward link for supporting alarming events

4. MAC Design Criteria • Measuring the energy efficiency of MAC • energy consumption on LECIM network • sum of active working duration of nodes in network • LECIM network throughput • sum of the frame length of successfully transmitted frames in network • efficiency = energy consumption/network throughput • Measuring the availability of upward and downward link • delay time to obtain the access right to a link • energy consumption for getting an access right • link availability = delay time * energy consumption

5. Energy Consumption on a Device (I) • Active working duration in RF PHY • sleep to active • time to activate regulator, stabilize the XOSC • wait for signal (synch) • varying on the MAC algorithm • receiving • length in bit from preamble to FCS * symbol/bit • transition from receiving to transmitting or vice versa • turnaround time • transmitting • length in bit from preamble to FCS * symbol/bit • active to sleep • Device power states • MCU • active mode • standby mode • RF PHY • low power mode • active mode • wait for sync • receiving • transmitting

6. Energy Consumption on a Device (II) • energy consumption on RF PHY • consumed energy (J) for 1hr duration in a device = (∑ duration * current for sleep + ∑ duration * current for transition + ∑ duration * current for waiting+ ∑ duration * current for receiving + ∑ duration * current for transmitting) * voltage • Ref.: power consumption MCU and RF PHY • MSP430x5xx Family typical current consumption • Active Mode : • Flash program execution : 230uA/MHz at 8MHz • RAM program execution : 110uA/MHz at 8MHz • 165uA/MIPS • Standby mode, LPM3 (CPU, MCLK, SMCLK, FLL off) : 2.1uA RTC with Crystal • CC2520 typical current consumption • TA =25°C, VDD=3.0V, fc=2440MHz • Low Power Mode Current • LPM1 (XOSC off, digital regulator on): 175uA • LPM2 (XOSC off, digital regulator off): 30nA • Receive current • wait for frame : 22.3mA • receiving frame (-50dBm input) : 18.5mA • Transmit current • 0 dBm TX : 25.8mA • 5 dBm TX : 33.6mA

7. Energy Consumption on a Device (III) • energy consumption on a device • energy consumption on LECIM network • sum of active working duration of nodes in network • reduce waiting time as possible as can • for transmitting 128byte PPDU on 40kbps link, 25.6ms • reduce retrials on RX and TX as possible as can • do not make a situation that RX or TX is interrupted 25.8mA 25.8mA 22.3mA 22.3mA 18.5mA 175uA sleep waiting RX TX TX waiting

8. Link Access for LECIM • reduce waiting time • devices aware when wake up to receive or transmit • link access for RX • waiting until event happened • request to send frame, and wait for limited time • wake up for receiving • reduce retrials on RX and TX • preemptive RX or TX • time slot based link resource allocation • need time synchronization processing • need prior time slot allocation processing • how to minimize overhead ?

9. Slot Based Access for LECIM (I) • slots for LECIM network • to assign a preemptive slot for a device, need over 1,000 time slots • for ease manageable network, require ease to increase time slots • Multi-frame Order in DSME of TG4e • repeat the superframe in beacon interval • max number of slot in beacon interval • with CAP reduction mode, 16*214 = 262,144 slots • base slot duration = 60 symbols • base slot length (sec) = 60symbols/symbol rate BI = 2BO *aBaseSuperframeDuration SD=2SO *aBaseSuperframeDuration 2BO-SO th superframe beacon beacon beacon beacon TS 0x01 TS 0x0f TS 0x00 TS 0x10 TS 0x11 TS 0x1f 16*2BO-SO-1

10. Slot Based Access for LECIM (II) • slot length • minimum length for RX/TX a frame with max PPDU • 128byte PPDU on 40kbps link, 25.6ms • need longer slot length • for receiving ACK within the same slot • multiple frames RX/TX in a slot • Superframe Order • superframe order determines the length of time slot • BPSK, data rate 20kbps • base slot length = 3ms • SO > 5 for RX/TX a frame with 128byte PPDU • 8, 192 slots available, when BO is 14 • enough slots for assigning to each LECIM devices • But, how to minimize the allocation overhead • in DSME, exchange DSME-GTS request and response commands • prior to request the time slot allocation, need association completed.

11. Slot Based Access for LECIM (III) • implicit slot allocation • need no command frames exchange • slot number can assigned off-line, or calculated on-line • based upon the device identifier • manufacture's product sequential # • IEEE OUI, 64bit address • if available time slot is larger than the number of devices • device identifier modulo number of time slots • else, provides prioritized multiple slots • hashing function 1 (device identifier) % number of time slot • hashing function 2 (device identifier) % number of time slot • … • assigned slot number • superframe ID + time slot ID

12. Slot Based Link Access (I) • slots for devices • BPSK, data rate 20kbps • BO = 14, SO = 5, MO = 9 • 512 superframes, 8,192 slots • slot length = 96ms, BI = 786,432ms • length of superframe = 1,536ms • number of master beacons in 24hour = 457 • total number of beacons in 24hour = 2,343 • a device has 457 chances to access a slot every 1,536ms per a day B B B B B B B B 2,343 beacons in 24 hours 512 superframes, 8,192 slots assigned to device i assigned to device i assigned to device i

13. Slot Based Link Access (II) • upward link access • three grades of up-link access • grade 0: real-time transmission (emergent access) • grade 1: reliable transmission • grade 2: loss tolerant transmission • grade 2 • MCU on, find the coming nearest master beacon • wake up at the start of assigned slot of superframe • transmit a frame without CCA, and sleep beacon beacon beacon beacon coordinator TS 0x01 TS 0x0f TS 0x00 TS 0x10 TS 0x11 TS 0x1f 16*2BO-SO-1 wakeup device gr2 access data TS 0x01 TS 0x0f TS 0x00 TS 0x10 TS 0x11 TS 0x1f 16*2BO-SO-1 sleep

14. Slot Based Link Access (III) • grade 1 • step1: MCU on, find the coming nearest master beacon • step2: wake up at the start of assigned slot of superframe • step3: transmit a frame with CCA, and sleep to next beacon or device management slot • step4: wake up at beacon slot or management slot, check ACK/NACK • step5: if failed, retry transmission with CCA on next candidate slot • repeat steps 2~5 until retrial counter is over beacon beacon TS 0x01 TS 0x01 beacon beacon coordinator TS 0x1f TS 0x00 TS 0x0f TS 0x10 TS 0x11 16*2BO-SO-1 wakeup wakeup data data beacon beacon device gr1 link TS 0x1f TS 0x0f TS 0x00 sleep sleep TS 0x10 TS 0x11 16*2BO-SO-1 wakeup sleep

15. Slot Based Link Access (IV) • grade 0 • step1: wake up, transmit a frame without CCA, wait ACK • step2: if failed, sleep to the nearest slot of all the assigned slots • step3: wake up at the start of assigned slot, transmit a frame without CCA, and wait ACK • repeat steps 2~3 until retrial counter is over beacon beacon beacon coordinator beacon TS 0x01 TS 0x01 TS 0x1f TS 0x0f TS 0x00 TS 0x10 TS 0x11 16*2BO-SO-1 wakeup wakeup device gr1 link dACK dACK data data TS 0x1f TS 0x0f TS 0x00 TS 0x10 TS 0x11 16*2BO-SO-1 sleep sleep

16. Slot Based Link Access (V) • downward link access • broadcast down-link • unicast down-link • broadcast down-link • beacon slot • management slot • bidirectional link • number of slots are predefined • unicast down-link • assigned slot to a device • periodic open or device/coordinator request based open beacon beacon TS 0x01 BS MS1 MS2 BS BS beacon beacon coordinator TS 0x1f TS 0x0f TS 0x00 TS 0x10 TS 0x11 16*2BO-SO-1

17. Amendment to TG4e • MAC PIB • add macUplinkGrade • MAC primitive & command • add MCPS-LECIM-DATA • MAC frame format • short frame header • consecutive multiple frames

18. Thanks for your Attention! ssjoo@etri.re.kr