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Actis: WBAN Demo Emil Jovanov Electrical and Computer Engineering Department University of Alabama in Huntsville.

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Presentation on theme: "Actis: WBAN Demo Emil Jovanov Electrical and Computer Engineering Department University of Alabama in Huntsville."— Presentation transcript:

1 Actis: WBAN Demo Emil Jovanov Electrical and Computer Engineering Department University of Alabama in Huntsville

2 Outline Introduction WBAN System Architecture TinyOS environment Actis application WBAN Wireless Communications Time Synchronization Data format and processing … play time

3 WBAN for Health Monitoring Wireless Body Area Network for Ambulatory Health Monitoring Mobility / Ubiquitous System Real-time on-sensor processing Warnings Increased Quality of Life Multisensor Monitoring (Synergy) Hierarchical Multi-tier Telemedicine System

4 WBAN Implementation WBAN for ambulatory health monitoring Activity Monitor / Motion Sensor ECG Sensor Network Coordinator Personal Server Challenges Sensor Fusion On-Sensor Processing Ubiquitous Communications Power Efficiency/Battery Life

5 Outline Introduction WBAN System Architecture TinyOS environment Actis application WBAN Wireless Communications Time Synchronization Data format and processing … play time

6 User 2 nc Interne t Tier 1: WBAN A A A E Tier 2: PS Tier 3: MS WBAN WWAN (GPRS) Emergency Informal caregiver Healthcare provider User N Medical Server WWAN WLAN WLAN (Wi-Fi) … User 2 User 1 User N … System Architecture ZigBee or Bluetooth User 1 A. Milenkovic, C. Otto, E. Jovanov, "Wireless Sensor Networks for Personal Health Monitoring: Issues and an Implementation," Computer Communications, Vol. 29, No , August 2006, pp

7 Outline Introduction WBAN System Architecture TinyOS environment Actis application WBAN Wireless Communications Time Synchronization Data format and processing … play time

8 TinyOS An open-source OS designed for embedded WSN (limited resources) Component-based architecture application = scheduler + graph of components event-driven architecture NO kernel, process/memory management, virtual memory Component A Component B Component D Component C Application configuration Component E Component F

9 Components A component has: Frame (internal state) Tasks (computation) Interface (events, commands) Frame: one per component statically allocated fixed size Tasks Component Frame EventsCommands Commands and Events are function calls Application: linking/gluing interfaces (events, commands)

10 Commands/Events commands: deposit request parameters into the frame are non-blocking need to return status => postpone time consuming work by posting a task can call lower level commands events: can call commands, signal events, post tasks, can not be signaled by commands preempt tasks, not vice-versa interrupt trigger the lowest level events deposit the information into the frame

11 Scheduler two level scheduling: events and tasks scheduler is simple FIFO a task can not preempt another task events preempt tasks (higher priority) Hardware Interrupts events commands FIFO Tasks POST Preempt Time commands

12 Outline Introduction WBAN System Architecture TinyOS environment Actis application WBAN Wireless Communications Time Synchronization Data format and processing … play time

13 Network Coordinator

14 Sensor Nodes

15 Typical Message Flow

16 Typical Message Flow (2)

17 Feature Extraction

18 Raw data Events MS Internet Gateway PS Sensors NC WBAN WLAN/ WAN SSS Interne t WBAN Messaging Session Files Database Data Flow and Analysis Healthcare Access EMR

19 Outline Introduction WBAN System Architecture TinyOS environment Actis application WBAN Wireless Communications Time Synchronization Data format and processing … play time

20 Typical WSN Application Periodic Data Collection Network Maintenance Majority of operation Triggered Events Detection/Notification Infrequently occurs But… must be reported quickly and reliably Long Lifetime Months to Years without changing batteries Power management is the key to WSN success sleep wakeup processing data acquisition communication Power Time From Polastre et al: The Mote Revolution: Low Power Wireless Sensor Network Devices Hot Chips 2004 : Aug 22-24, 2004

21 Overhead of switching from Sleep to Active Mode Wakeup Microcontroller Radio (FSK) 10ns – 4ms typical 1– 10 ms typical 2.5 ms 292 ns From Polastre et al: The Mote Revolution: Low Power Wireless Sensor Network Devices Hot Chips 2004 : Aug 22-24, 2004

22 Power Efficient TDMA 85% Sensor Power from Radio Significant Power Savings From Disabling Radio Timeslots for Communication Distributed Events Concentrated Bursts Allows Radio to be disabled Extended Battery Life / Lower Weight

23 TDMA Means Low Power Deterministic RF timeslots Radio can be disabled Extend battery life

24 ZigBee An industry consortium that promotes the IEEE standard (www.zigbee.org)www.zigbee.org Low-cost, low-power features for multi-year operation on standard batteries Low data throughput (250 kbps) Star and peer-to-peer network topologies

25 Design Principles Key to Low Duty Cycle Operation: Sleep – majority of the time Wakeup – quickly start processing Active – minimize work & return to sleep

26 Sleep Majority of time, node is asleep Typically >99% Minimize sleep current through Isolating and shutting down individual circuits Using low power hardware Need RAM retention Run auxiliary hardware components from low speed oscillators (typically 32kHz) Shut down all unused clocks Perform ADC conversions, DMA transfers, and bus operations while microcontroller core is stopped

27 Active Microcontroller Fast processing, low active power Avoid external oscillators Radio High data rate, low power tradeoffs Narrowband radios Low power, lower data rate, simple channel encoding, faster startup Wideband radios More robust to noise, higher power, high data rates External Flash (stable storage) Data logging, network code reprogramming, aggregation High power consumption Long writes Radio vs. Flash 250kbps radio sending 1 byte Energy : 1.5 J Duration : 32 s Atmel flash writing 1 byte Energy : 3 J Duration : 78 s From Polastre et al: The Mote Revolution: Low Power Wireless Sensor Network Devices Hot Chips 2004 : Aug 22-24, 2004

28 Outline Introduction WBAN System Architecture TinyOS environment Actis application WBAN Wireless Communications Time Synchronization Data format and processing … play time

29 Time Synchronization Crucial service in WSNs Group operations Source localization Data aggregation Distributed sampling Communication channels sharing Metrics for synchronization protocols Precision Longevity of synchronization Time and power budget available for synchronization Geographical span Size and network topology ? ? ? ? ?

30 Time Synchronization - Motivation Wall Clock versus WBAN (Jiffy) Time Two Issues Offset Drift TDMA Efficient Sharing of Communication Channels Timeslot Assignments Beacon Prediction (Maximize Radio off) Correlating Intra-WBAN events Relative timing is important Synchronizing start time

31 Offset 2 Skew Offset 2 Sending Time Receiving Time Time Synchronization - Issues

32 Time Synchronization #2 Propagation Data transmitted over RF PreambleSFDLengthMAC Protocol Data SFD Capture Timer Timestamp PreambleSFDLengthMAC Protocol Data Timestamp Data received over RF SFD Capture Timer Synchronize local time (TinyOS) Network Coordinator

33 Inserting the Timestamp Network coordinator Starts the transmission (time sync header) Captures timer and converts to a global timestamp Inserts it into the message (sends over SPI) Is this enough time not to underrun the TxFIFO in CC2420? Time capture and calculate timestamp: 150 s Send timestamp: 300 s Sync header transmission: 700 s

34 Outline Introduction WBAN System Architecture TinyOS environment Actis application WBAN Wireless Communications Time Synchronization Data format and processing … play time

35 Demonstration System configuration Position sensor (3 ACC axes – raw data) Values Acc = acc_comp*2000 Heart rate sensor RR intervals in ticks (32 KHz – jiffy periods) Heart rate – 60 * / RRint

36 EMR … Update Session 1 Update Session 2 Contiguous Data Blocks System organization - Sessions

37 Accelerometer sensor X Y Z Acc = acc_comp*2000

38 Session file format Byte Field Description 4 Timestamp 32-bit global jiffy time 2 numValues Number of values used in data field 2 Not used Reserved for future param. 2 LastSampNum 4 SessionSignalID Unique identifier formed from concatenation of session number with signal type 20 data Signal dependent for raw data this is bit samples AEE, the first 4 bytes are little endian AEE Total: 34 bytes/record

39 Test data Web page: Experimental data Example processing (.M) What information can you extract? Change of position Classification of the physical activity HR as a function of physical activity

40 Outline Introduction WBAN System Architecture TinyOS environment Actis application WBAN Wireless Communications Time Synchronization Data format and processing … play time


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