Surviving Holes and Barriers in
Geographic Data Reporting for
Wireless Sensor Networks
Yangfan Zhou1, Michael R. Lyu1, and Jiangchuan Liu2
1Dept. of Comp. Sci. & Eng., The Chinese University of Hong Kong, Hong Kong
2School of Comp. Sci., Simon Fraser University, Canada
Mobile Ad Hoc and Sensor Systems, 2009, Macau, China
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Outlines
Outlines
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Background and motivations of this work
Our proposed waypoint-based geographic data reporting
protocol (GDRP)
Demonstration of GDRP
Simulation studies
Conclusions
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Background and Motivations
Geographic Forwarding
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Greedy forwarding
v
v
v
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A node finds out its nearest neighbor to the sink
If the neighbor is nearer to the sink than the
node, forward packet via it
Otherwise, ?? (Network holes or barriers)
Detour-mode forwarding
v
v
Planarize the network à planar graph
Route packets along the face of the graph
towards the sink
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Background and Motivations
Geographic Forwarding
The detour-mode forwarding tends to forward data
packets along the boundaries of holes.
à The path from the source to the destination is
much longer than the optimum.
à More energy consumption in data collection.
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Background and Motivations
Waypoint-based geographic forwarding
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Find a waypoint sequence [w(1), w(2), ..., w(M)] where
w(1) is the source and w(M) the destination
Forward packets via the waypoint sequence one by
one
v Packets are transported between two adjacent
waypoints with a geographic forwarding scheme.
■ Minimize the unnecessary detours so that the path can bypass
holes and barriers.
■ Waypoints: Calculated with a trial-and-error approach
- Better and better waypoint sequences will be worked out gradually
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Background and Motivations
d (destination)
d (destination)
u6
u5
u10
u4
Hole 2
u9
u3
Hole 1
u2
u1
u8
w(4)
Hole 3
w(1)
Hole 2
w(2)
Hole 1
w(3)
w(5)
u7
s (source)
(a). A network scenario where greedy
forwarding results in suboptimal path.
s (source)
(b). A network scenario where routing along
the convex hull causes suboptimal results.
Existing schemes may result in suboptimal paths
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Part II
GDRP: An Waypoint-based Geographic Data Reporting
Protocol for Wireless Sensor Networks
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Geographic Data Reporting Protocol (GDRP)
Waypoint-Based Geographic Forwarding
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When a Path is Acceptable
strongly perfect sequence
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It is a greedy-forwarding path from the first node to the last node
Given an x-y coordinate system with its x-axis passing the first and
the last nodes, the maximum difference of the y-coordinates between
any two nodes in the sequence is no more than d = a · r, where a is a
constant and r is the communication range.
Acceptable Path
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A path is acceptable when the path segments between
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two adjacent waypoints are strongly perfect sequence
Why?
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When a Path is Acceptable
Definition
The topological length of a path is the total
number of hops between the source and the
destination of the path
Energy consumption in data forwarding
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When a Path is Acceptable
Lemma
The topological length of a path is bounded by
times the Euclidean distance between the source and
the destination if the path is a strongly perfect
sequence
Corollary
If a path between two nodes is a strongly perfect
sequence, the topological length of the path is not larger
than
times that of their shortest path
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When a Path is Acceptable
Lemma
The topological length of a path is bounded by
times the Euclidean distance between the source and
the destination if the path is a strongly perfect
sequence
Strongly perfect sequence
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Suppose the path is [u0, u1, …, destination]
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Draw circles centered at uk when k is odd, with the radii being r/2
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These circles cannot intersect
These circles must be in the rectangle area with length and width
being l and (a+1)r
Maximum # of such circles
Topologic length of the path
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When a Path is Acceptable
Corollary
If a path between two nodes is a strongly perfect
sequence, the topological length of the path is not larger
than
times that of their shortest path
1. The topologic length of a strongly perfect sequence
2. The topologic length of the shortest path is lower-bounded by
Hence, the topologic length of a strongly perfect sequence will not be worse
than
times the shortest path
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Waypoint Calculation
Waypoint calculation
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In each round, based on the current knowledge of the holes and
barriers, find a best set of waypoints for the next round
Purpose: make the packets bypass the known holes and barriers so as
to minimize the topological length of the path found in the next round
How?
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Waypoint Calculation
When a path is not an acceptable path
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There are holes or barriers in between the source and
the destination
At least one path segment between a pair of adjacent
waypoints is not a strongly perfect sequence
The impact of holes or barriers can be modeled as how
they make the path segment “imperfect”
- Find which parts of the segment make it fail to be
a strongly perfect sequence
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Waypoint Calculation
Perfect sequence
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Similar to strongly perfect sequence
With only one difference: It is not necessary that
the last second node is connected with the last node.
- It is not necessary to be a “path”
perfect sequences:
[w, u1, u2,w’]
[u4, u5, u6,w’]
[u8, u9, u10, w’]
[u2, u3, u4] and [u6, u7, u8] make the whole path
segment fail to be a strongly perfect sequence
Holes and barriers
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Call these parts detour parts
Save these parts: they are the current
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Waypoint Calculation
Problem 1: Who should be the potential waypoints
1. The last node in a detour part
should be a potential waypoint
2. The first node in a detour part
should be a potential waypoint
Reason: The hole or barrier does not
influence the path any longer from
the node on
Reason: The node can avoid
the detour part by forwarding packets
to another direction
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Waypoint Calculation
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Now we have a set of the potential waypoints, how to select a waypoint sequence for
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the next round?
We expect in the next round, we can find an acceptable path
v
v
v
Construct a graph G(V, E)
- V: the set of the potential waypoints
- E: two nodes in G share an edge if the line segment between them does not
intersect a known detour part
The waypoint sequence should be a path for the source to the sink in G(V, E)
The waypoint sequence forms the shortest path from the source to the sink
Hence, the waypoint
sequence for the next
round is [w, u2, u8, w’]
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Geographic Routing between Waypoints
Routing between adjacent waypoints
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Geographic forwarding
- Detour-mode forwarding: routing along the face of the planar
graph counter-clockwise or clockwise
- Use one as default. Change if required by a waypoint (when it is
a starting node of a detour part)
Still a light-weighted protocol for sensor nodes
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Part III
A Case Demonstration
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GDRP Demo
A case demonstration: round 1
This path segment make
the whole path fail to be a
strongly perfect sequence
Nodes 1 and 2 are then
potential waypoints, because
they are the first node and the
last node of the detour part
Construct the waypoint graph
Find the shortest path from the
source to the sink. Hence, the new
waypoint for the next round is
[source, destination]
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GDRP Demo
A case demonstration: round 2
Again, we will reach this node,
since it is the starting node of
a detour part, it will route the
packet to another direction
This path segment make the
whole path fail to be a
strongly perfect sequence
Node 3 is then a potential waypoint.
Because node 1 is the first node of two
detour parts, it means it cannot bypass
a hole or barrier by routing packets to
another direction. So it is removed
from the potential waypoint set.
Construct the waypoint graph
Find the shortest path from the source to the
sink. Hence, the new waypoint for the next
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Mobile Ad Hoc and
Sensor
2009,
Macau,
China
round
isSystems,
[source,
node
3, destination]
GDRP Demo
A case demonstration: round 3
Now packets will be sent to
node 3 first.
This path segment make the
whole path fail to be a
strongly perfect sequence
Nodes 4 is then a potential
waypoint.
Construct the waypoint graph,
find the shortest path from the
source to the sink. Hence, the new
waypoint for the next round is
[source, node 2, destination]
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GDRP Demo
A case demonstration: round 4
Now packets will be sent to
node 2 first.
These path segments between
adjacent waypoints are both
strongly perfect sequences
We are done!
We can see that the
resulting path is comparable
to the shortest path
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Part IV
Simulation Results
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Simulation Studies
Protocols in simulation study
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GDRP (Geographic Data Reporting Protocol): Our protocol
GPSR (Greedy Perimeter Stateless Routing): Traditional geographic forwarding
CONVEX-W
- Waypoint-based geographic forwarding
- Packets are forwarded along the convex hull of the known holes
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Simulation Studies
Simulation settings
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Simulation Studies
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Simulation Studies
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Conclusions
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We propose a waypoint-based geographic forwarding
protocol
We prove the performance guarantee of our protocol
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Thank you!!!
Q&A
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