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

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [MAC Proposal for Low-Energy Wide Area Monitoring] Date Submitted: [ Sep 15, 2011] Source: [Seong-Soon Joo, Jong-Arm Jun, Cheol-Sig Pyo] Company: [ETRI]

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

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  1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [MAC Proposal for Low-Energy Wide Area Monitoring] Date Submitted: [Sep 15, 2011] Source: [Seong-Soon Joo, Jong-Arm Jun, Cheol-Sig Pyo] 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: [A MAC 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. MAC Proposal for Low-Energy Wide Area Monitoring Seong-Soon Joo*, Jong-Arm Jun, Cheol-Sig Pyo ETRI

  3. Requirements on LECIM MAC • Design goals of wide area monitoring • long lived infra • more than 10 years life like network carrier’s infra • ease maintained monitoring network • high degree of freedom to start the monitoring/maintenance business • Design requirements on LECIM MAC • guaranteed link access on low duty cycle with low energy • minimize contention on a link • support to fair access between near and far nodes • time-stamping • support to ease installation • support to ease maintenance • support to make network structure simple • optimized to network configuration near node coordinator hidden node far node contention node

  4. Major Contribution • Provide a tool for time-stamping • global time synchronization • adjust clock drift with light overhead • Contention-free low energy link access • distribute access loads on slotted link • three grades of link access • Extend reaches of link • echo back a frame • two modes of link repeater • Low-energy link management • management frame from coordinator for optimized configuration and ease maintenance • link power management

  5. Contention-free Low Energy Link Access (11-0599-00-00k)

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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 ?

  12. 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

  13. 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.

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

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

  21. Provide a Tool for Time-Stamping (11-0598-00-00k)

  22. Time and Low Energy Wide Area Monitoring (I) • synchronized measuring • the times of occurrence of physical events • often crucial for the observer • to associate event reports with the originating physical events • need accurate time-stamping of measured quantities • acoustic leak detection mechanisms • that can pinpoint the location of a leak given a known speed-of-sound through a pipe. • synchro-phasor measurements • relative phase relationship between current and voltage at various locations can be measured • if an absolute time basis is communicated to multiple end-points. • determining location of sensor nodes • based on the measurement of time of flight or difference of arrival time of certain signals also require finely synchronized time. • distributed observations into a coherent estimate of the original phenomenon • requires accurate time-stamping. source: Mark Wilbur, IEEE 15-11-0397-00-004k, “Time Synchronization in Wireless Sensor Networks”

  23. Time and Low Energy Wide Area Monitoring (II) • global time synchronization for time-stamping • need global master time clock • for synchronizing distributed devices’ local time clock • periodical time synchronization for compensating local clock drift • over-the-air time synchronization • coordinator is power-free • may have high precision clock • afford to transmit clock information periodically in any time scale • adjust clock drift of a local device based upon coordinator master clock • beacon frame as a global clock tick • need a message to broadcast global clock time • beacon interval can be clock leap second • use sequence number of beacon frame for clock sampling

  24. Time and Low Energy Wide Area Monitoring (III) • time expression in LECIM network • multi-superframe of TG4e DSME MAC • sequence # of master beacon • superframe ID • slot ID • precision of clock tick • length of slot • BPSK, data rate 20kbps (BO = 14, SO = 5, MO = 9) • 96ms 2,343 beacons in 24 hours B B B B B B B B 512 superframes, 8,192 slots assigned to device i assigned to device i assigned to device i

  25. Time and Low Energy Wide Area Monitoring (IV) • time synchronization • initiate time synchronization • in phase with the global time clock • recover from the loss of time synchronization • how to achieve low energy time synchronization? • advantage of power-free coordinator • balancing the energy consumption with precision of clock • virtue of multi-superframe structure

  26. Level 0 Time Synchronization • initiate time synchronization • two options • find beacon • request global time • dependent on PHY • power consumption on RX and TX • symbol rate • request global time • device requests synchronized global time • use grade 0 link • LECIM MAC management command frame: SyncReq • coordinator responds with current global time • ACK frame (seq. # of master beacon, superframe ID, slot ID) coordinator wake up SyncReq ACK device sleep

  27. Level 1 Time Synchronization (I) • clock drift compensation • two options • periodical wake up • request global time • dependent on usage of links • need operation and maintenance command and control for LECIM • frequency of measuring events coordinator SyncReq ACK wake up device sleep

  28. Level 1 Time Synchronization (II) BI BI*2Wo coordinator device adjust clock adjust clock

  29. Level 1 Time Synchronization (III) device device adjust clock adjust clock adjust clock

  30. Level 2 Time Synchronization • implicit exchange of time information • frame from the coordinator • receive management frame transmitted on management slot • compensate clock drift with estimated time of management slot • device : (estimated current seq. # of master beacon, superframe ID, slot ID) • received: (seq. # of master beacon, superframe ID, slot ID) • frame from a device • receive data frame, command frame transmitted on device slot • save the time of slot at which frame is received coordinator management data device

  31. Amendment to TG4e • MAC PIB • extend macBSN • add macWakeupOrder • MAC management primitive & command • add MLME-TIME-SYNC • add Time synchronization request command • MAC frame format • short frame header • beacon format

  32. Low-energy Link Management (11-0600-00-00k)

  33. LECIM Network Reference Model • Components of LECIM network • coordinator, device • repeater • Topology of LECIM network • near node, far node • linear, group, distributed • range near node linear far node group coordinator repeater distributed device

  34. LECIM Network Data Model (I) • Traffic in a device • upward • sensing data • device status report • device join • device alarming • downward • data ACK • time synchronization • device management command • Traffic in LECIM network • attributes • number of devices • feature of device: data size, frequency • interference model, contention probability • traffic in busy hour • traffic in off hour

  35. LECIM Network Data Model (II) • Data in LECIM network • sensing/measuring data • contents • device/location ID : 2 ~ 4 bytes • time stamp : 2 ~ 4 bytes, (NTP : 8~ 16 bytes) • monitoring data • vector data : 1 ~ 100 bytes • stream data : 4 Kbyte x n frame/s • frequency in appearance • periodic data : 1 ~ 1,440 event/day • occasional data : • operation & management data • device maintenance data • device installation • device fault diagnosis & maintenance • network operation data • global clock time synchronization • device status check

  36. Possible Infra Structures • Star topology • power free collector • multi-channel transceivers in a collector • synchronized/asynchronous resource allocation • power management on end point • identify operators at PHY or MAC layer • Multi-hop topology with repeater • synchronized resource allocation for each hop • upward/downward forwarding at the MAC layer operator 1 operator n

  37. Link Repeater • Extend reaches of link • varying RF environment from/to coordinator • devices are located sparsely • extend reaches of link from/to coordinator • Link repeater • echo back a frame after receiving a frame from the coordinator or devices • link repeater is power-free or located at ease maintainable place • two modes of link repeater according to the limitation on power resource coordinator repeater device

  38. Power Management • Link power management • reduce interference range • adaptable to radio environmental variance • extend life of near end device • Power control procedure • measure the distance to coordinator • detectradio energy from coordinator • adjust TX power level • reply back to coordinator • feedback from coordinator • adjust TX power level near node coordinator hidden node far node contention node coordinator device DeviceStausRepReq measure RSSI, LQI adjust TX power level DeviceStausRep DeviceStausRepReq (RSSI, LQI) adjust TX power level DeviceStausRep

  39. Link for Management • management links • broadcast down-link • bidirectional management slot link • bidirectional device owned slot link • broadcast down-link • management data on beacon • bidirectional management slot link • bidirectional link • number of slots are predefined • bidirectional device owned slot 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

  40. LECIM MAC Procedure coordinator device Beacon get BO, SO, MO, set WO estimate next beacon arrival time i) join to LECIM network Beacon adjust clock drift sleep Beacon wakeup at BI*2WO wait beacon adjust clock drift Beacon DeviceStatusRepReq/ DeivceLinkControl ii) link management manage device link infor DeviceStausRep sleep Data wakeup at device time slot tx data with grade0 link wait ACK ACK iii) data transmission Data wakeup at device time slot tx data with grade2 link sleep

  41. Amendment to TG4e • MAC PIB • add macLECIMlinkInfor • MAC management primitive & command • add MLME-LECIM-STATUS • add MLME-LECIM-LINK • add device status report command • MAC frame format • beacon format

  42. Next Steps • Agree to move forward (include in baseline) • Explore and validate • light overhead frame format • optimal wake up order based upon the TG4k PHY • link repeater • power management • Begin drafting

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

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