Actis: WBAN Demo Emil Jovanov emil.jovanov@uah.edu Electrical and Computer Engineering Department University of Alabama in Huntsville

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

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

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

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

System Architecture WWAN WLAN WBAN … WWAN (GPRS) Tier 3: MS Tier 2: PS User1 User2 UserN WBAN … WWAN (GPRS) ZigBee or Bluetooth Tier 3: MS E A Medical Server nc A A Tier 2: PS Tier 1: WBAN Internet Healthcare provider WLAN (Wi-Fi) User2 User1 UserN … Informal caregiver A. Milenkovic, C. Otto, E. Jovanov, "Wireless Sensor Networks for Personal Health Monitoring: Issues and an Implementation," Computer Communications, Vol. 29, No. 13‑14, August 2006, pp. 2521-2533. Emergency

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

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 B D C Application configuration E F

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

Commands/Events commands: events: 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

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

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

Network Coordinator

Sensor Nodes

Typical Message Flow

Typical Message Flow (2)

Feature Extraction

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

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

Typical WSN Application processing data acquisition communication 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 Power wakeup sleep Time From Polastre et al: “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004

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

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

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

ZigBee An industry consortium that promotes the IEEE 802.15.4 standard (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

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

Sleep Majority of time, node is asleep Minimize sleep current through 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

Active Microcontroller Radio External Flash (stable storage) 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 : 1.5mJ Duration : 32ms Atmel flash writing 1 byte Energy : 3mJ Duration : 78ms From Polastre et al: “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004

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

Time Synchronization Crucial service in WSNs ? 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 ? ? ? ?

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

Time Synchronization - Issues Offset2 Skew Sending Time Receiving Time

Time Synchronization #2 SFD  Capture Timer Data transmitted over RF Preamble SFD Length MAC Protocol Data Timestamp Propagation Data received over RF Preamble SFD Length MAC Protocol Data Timestamp SFD  Capture Timer Synchronize local time (TinyOS) Network Coordinator

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

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

Demonstration System configuration Position sensor (3 ACC axes – raw data) Values Acc = 8000 + acc_comp*2000 Heart rate sensor RR intervals in ticks (32 KHz – jiffy periods) Heart rate – 60 * 32768 / RRint

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

Accelerometer sensor Z X Y Acc = 8000 + acc_comp*2000

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 10 16-bit samples AEE, the first 4 bytes are little endian AEE Total: 34 bytes/record

Test data Web page: Experimental data Example processing (.M) http://www.ece.uah.edu/~jovanov/whrms/data_proc.html 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

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