1. Actis: WBAN Demo Emil Jovanov emil.jovanov@uah.edu
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 Challenges
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. 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
Emergency

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 B D C
Application
configuration E F

9. 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)

10. 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

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

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. 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

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
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

21. 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

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 (
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 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

27. 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

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?
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. Time Synchronization - Issues
Offset2
Skew
Sending Time Receiving Time

32. 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

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

37. Accelerometer sensor Z X Y
Acc = acc_comp*2000

38. Session file format Byte Field Description
4 Timestamp 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)
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 