Post on 22-Jan-2016
description
Mobility Improves Coverage of Sensor Networks
Benyuan Liu*, Peter Brass, Olivier Dousse, Philippe Nain, Don Towsley
* Department of Computer ScienceUniversity of Massachusetts - Lowell
Outline
background and motivation
mobility improves coverage
summary and future work
What is coverage ?
coverage: quality of surveillance of sensor networkhow well sensors cover a region of interest ? how effective sensor network detect intruders ?many different measures: area coverage, barrier
coverage, detection coverage, etc
important for surveillance sensor net applicationsbattlefield, infrastructure security
Mobile sensor networks
coverage of stationary sensor network intensively studied
sensors can be mobile: mounted on robots or move with environments
Q: How does sensor mobility affect coverage?
Previous work[Howard 02, Zou04, Wang 04]
sensors move to reach stationary configuration with better area coverage
several approaches proposed, different in how to compute desired locations for sensors (e.g., potential field, virtual force, etc)
Our work different perspective: coverage resulting from
continuous movement of sensors
1. mobility increases covered area stationary sensors: covered area doesn’t change over time mobile sensors: uncovered area may be covered later, more area
covered over time
we are interested in area coveragearea covered at specific time instant tarea covered over time interval [0, t) fraction of time a location is covered
Our work2. mobility improves intrusion detection
stationary sensors: intruder won’t be detected if not move or moves along uncovered path
mobile sensors: may be detected by moving sensors
we are interested in detection time time before an intruder is first detected measure how quickly sensors detect intruders consider stationary and mobile intruders
Our work
3. how should sensors and intruder move? intruder moves to maximize its detection timesensors minimize the maximum detection time
we are interested in optimal mobility strategies for both sensors and intruders game theoretic approach
Network model
initial configuration sensors are deployed uniformly at random
sensor density: sensing range: r
mobility model each sensor chooses a random direction [0, 2)
according to distribution speed vs [0, vs
max] according to
)(f
)(vVf
simple model to obtain insight
Area coverage
area coverage at any given time instant unchanged
21 reaf
)][22(1)( tsVrEretif
t
uncovered region will be covered, more area will
be covered for a time interval [0,t)
Tradeoff: covered area and covered time
location alternates between covered and uncovered
)2exp(~ srVnT
21 retf
appropriate for delay-tolerant applications
fraction of time a point is covered
uncovered time:
covered time λr)/λπr(eTcE 212][
Detection time: stationary intruder
intruder can be detected by moving sensors
detection time: time before first being detected, X
divide sensors into different classes according to direction
time takes to be first hit (detected) by a class i sensor:
)2exp(~ srViiX
Vs
Detection time: stationary intruder
)2exp( srVX iXX min
to guarantee expected detection time smaller than T0
)2exp()( tsrVtXP
02/1 rTsV
can tradeoff sensor density with speed
detection time: smallest hit times among all classes
result:
Mobile intruder: detection time
20 )()(
22cos
2ˆ41)(
1ˆ,/
dftwcsvsV
uccuw
ccsvtvc
)2exp( sVrX
convert to reference system where intruder is stationary detection time:
),( ttv
speedsensor effective :sV
Mobile intruder: optimal strategy
target maximizes its lifetime
)],),(([,
max tvtfXEtvt
sensors minimize the maximum detection time
)],),(([,
max)(
min tvtfXEtvtf
a minimax optimization problem
Optimal strategy: special cases
sensors: move in same direction
intruder: moves in same direction with same speed as sensor
sensors: choose direction uniformly in [0, 2)
intruder: stay stationary intuition: if intruder moves,
will hit oncoming sensors sooner
Optimal strategy: solution
sensors choose direction uniformly target stay stationary
intuition: if not uniform, intruder will move in direction of highest probability density, resulting in longer detection time
21)( f
0tV
?
Summary and future work
define coverage resulting from sensor mobility
derive analytical results to provide insight
future work: more general mobility and detection model collaboration among sensors
Thank you!