Full Life Cycle Analysis
for Wireless Sensor Networks
Jack Stankovic
Computer Science
University of Virginia
January 10 , 2007
University of Virginia
Main Themes of Talk
• Require design time analysis to obtain approximate
system design – do this with few assumptions
• Redo analysis as a function of subsequent design
choices
– Specific routing protocol
• Analysis of various types required at all phases of
system design, implementation, and operation
• Require a tool/framework for combining multi-stage
analysis
University of Virginia
VigilNet - Power Aware Surveillance
• Acoustic
• Magnetometer
• Four 90 degree motion sensors
• XSM motes - Crossbow
ACM TOSN, Feb. 2006
University of Virginia
Energy Efficient Surveillance System
1. An unmanned plane (UAV) deploys motes
Zzz...
Sentry
3.Sensor network detects
vehicles and wakes up
the sensor nodes
2.
Motes establish an sensor network
with power management
University of Virginia
Tripwire-based Surveillance
• Self-organize (partition) sensor network into multiple
sections (one per base station).
• Turn off all the nodes in dormant sections.
• Apply sentry-based power management in tripwire
sections
• Flexible scheduling, sections rotate to balance energy.
Road
Dormant
Active
Dormant
Active
Dormant
Dormant
Active
Dormant
Active
University of Virginia
Sentry Duty-Cycle Scheduling
• A common period p and duty-cycle β is chosen for all
sentries, while starting times Tstart are randomly
selected
Non-sentries
Sentries
A
D
B
C
E
Target
Trace
A
t
B
t
C
t
D
t
E
0
p
Awake
University of Virginia
2p
t
Sleeping
VigilNet Architecture
University of Virginia
Life Cycle Analysis
• Design Time
– Analytical
• Programming Time
– Execution time, memory, delays, …
• Debugging Time
– Operational, fix bugs, race conditions
• Field Testing Time
– Overhear, replay
• System Lifetime
– Validation services
University of Virginia
ANDES
• Extensible Design Tool
– Model and analyze WSN “early”
– Iterate to obtain final configuration
• Integrate analysis into a design tool - Plug-ins
– Target tracking analysis
– Communication schedulability analysis
– …
• Extend AADL/OSATE framework
– Used extensively for real-time and embedded systems
– CMU/SEI
University of Virginia
Design Time
• Performance
Attributes
–
–
–
–
–
–
Lifetime
Sensing coverage
Communication Capacity
Reliability
QoS
Security
• System Parameters
–
–
–
–
–
–
Number of nodes
Density
Duty cycle
Sensing Range
Communication range
Bandwidth
University of Virginia
Example - Tracking Analysis
University of Virginia
Tracking Analysis
• First Level of Analysis
– Probability of detection
– Average detection delay
–
–
–
–
–
–
Density d
Duty cycle b
Period T
Sensing range R
Length of Path L
Speed of target v (stationary, slow, fast)
– Impact on lifetime
University of Virginia
Obtain Probability of Detection
R
Node
l
target locus
βT+l/v
βT
0
l/v
βT
l/v
T
t
Probability of detection
(βT+l/v ) /T
Time interval when the target is in the sensing area
Time interval when the node is awake in one period
University of Virginia
Consider All Possible Locations
For a fast target with velocity v
R
R
(x,y)
l
target locus
A
L
University of Virginia
Formulas for Detection Delay
Expected Detection Delay for Fast Targets:
Expected Detection Delay for Slow Targets:
where
* DCOSS paper
University of Virginia
Expected Delay vs. β
Expected Delay vs. beta (T=1s, R=5m, d=0.01/m*m)
1.8
v=5m/s
v=15m/s
v=25m/s
v=35m/s
1.6
expected delay (s)
1.4
1.2
Minimum energy gives
1.3s detection delay
1
0.8
0.6
0.4
0.2
0
0
0.1
0.2
0.3
0.4
0.5
duty cycle beta
0.6
0.7
0.8
0.9
University of Virginia
Realistic Sensing Areas
Formulas Validated
What do real
sensing areas look
like?
University of Virginia
Real-Time Communication Analysis
• Next level of analysis
– Are expected end-to-end data flows going to meet their
deadlines?
– Fn(bandwidth, deadlines, periods, workloads)
– Impact on lifetime
University of Virginia
Schedulability Analysis – Example
Network topology
Stream specification
stream 1
stream 2
stream 3
Stream
Message
Size
Period
Deadline
Start
time
1
2000b
100ms
1000ms
0
2
200b
20ms
100ms
0
3
40b
10ms
50ms
0
Communication parameters
Interference range
3m
Radio range
1m
Result: Schedulable
Communication Link from node 1 to 2 is assigned to stream 1 at time slot 1
Communication Link from node 3 to 5 is assigned to stream 3 at time slot 1
••••••
University of Virginia
RT Scheduling Analysis
• Analysis includes
– The impact of interference
– Streams’ time constraints
– Multi-hop communication
• Assumptions
–
–
–
–
Perfect collision-free MAC protocol
Fixed routing
Constant communication and interference range
No transmission failure
University of Virginia
Solution - Exact Characterization
• Analogous to real-time scheduling theory
• Prioritize streams (velocity)
• Schedule stream 1
• Schedule stream 2 assuming stream 1 exists
– Account for time, BW and interference
• Keep adding streams until
– All streams successfully scheduled
– All streams up to stream X successfully scheduled
University of Virginia
Analogy of Schedulability Problem to
Cylinder Packing
Time t
Y
DC
X
DB
DA
stream C
stream B
stream A
Stream A
Stream C
Stream B
University of Virginia
Implementation of Analysis
stream 1 (period: 4, deadline: 5, delay: 1, path: link 1,2,3,4)
stream 2 (period: 4, deadline: 6, delay: 1, path: link 5,6)
0 1 1 0 0 1
1 0 1 1 1 1 


1 1 0 1 1 1 
InterferenceMatrix  

0
1
1
0
1
0


0 1 1 1 0 1 


1 1 1 0 1 0 
link6
Input=>
link1
link2
link3
link4
link5
Output=>
link/time
1
2
3
4
5
6
1
1
link allocation table
2
3
4
...
...
1
1
1
2
2
Can be very
general
University of Virginia
VigilNet Surveillance System
1. An unmanned plane (UAV) deploys motes
Zzz...
Sentry
3.Sensor network detects
vehicles and wakes up
the sensor nodes
2.
Motes establish an sensor network
with power management
University of Virginia
Main Idea of EnviroLog
• A distributed service that achieves repeatability via
asynchronous event recording and replay
Input
Flash
Log
modules
EnviroLog
Target
modules
Output
Record Stage
University of Virginia
Main Idea of EnviroLog
• A distributed service that achieves repeatability via
asynchronous event recording and replay
Input
Flash
Log
modules
EnviroLog
Target
modules
Output
Replay Stage
University of Virginia
Uses of EnviroLog
• System evaluation
– Suite of real tests recorded and replayed
• Debugging
– Exact same tests
• Protocol comparison in real setting
– Exact same tests
• Parameter tuning
– Exact same tests
• Wider testing than possible with physical system (e.g.,
speed up capability exists)
• Valuable for rare, unsafe or hard to reproduce events
– Fire, explosion, …
University of Virginia
Summary
• Require Initial Analysis to Approximate Design
Parameters
• Refine Based on Design Decisions – analysis accounts
for those decisions
• Validation of the Early Analysis via Empirical Data
• Value of AADL basic features/analysis
• Integration among Life Cycle Analyses
– A comprehensive and consistent toolkit
University of Virginia
Acknowledgements
• VigilNet – large team at UVA (Tian He, …)
• ANDES – (Vibha Prasad, …)
• Tracking Analysis – (Ting Yan, …)
• Envirolog – (Liqian Luo, …)
• Papers available on each of these topics
University of Virginia