a robust interference model for wireless ad-hoc networks€¦ · interference 2 towards a robust...
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A Robust Interference Model for Wireless Ad-Hoc Networks
Pascal von RickenbachStefan Schmid
Roger WattenhoferAaron Zollinger
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WMAN 2005
Overview
• What is Topology Control?
• Context – related work
• A robust interference model
• Interference in known topologies
• The highway model– Exponential node chain– General highway
• Conclusions
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WMAN 2005
Topology Control
• Drop long-range neighbors: Reduces interference and energy!• But still stay connected
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WMAN 2005
Topology Control as a Trade-Off
Network Connectivity
Topology Control
Conserve EnergyReduce Interference
Sometimes also clustering, Dominating Set construction
Not in this presentation
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WMAN 2005
Overview
• What is Topology Control?
• Context – related work
• A robust interference model
• Interference in known topologies
• The highway model– Exponential node chain– General highway
• Conclusions
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WMAN 2005
Reducing Interference by Graph Sparseness or Bounded Degree
• Constructions from computational geometry
– Delaunay Triangulation [Hu 1993]– Minimum Spanning Tree [Ramanathan & Rosales-Hain INFOCOM 2000]– Gabriel Graph [Rodoplu & Meng J.Sel.Ar.Com 1999]
• Cone-Based Topology Control
– [Wattenhofer et al. INFOCOM 2000]– [Li et al. PODC 2001, Jia et al. SPAA 2003, Li et al. INFOCOM 2002]– [Wang & Li DIALM-POMC 2003]
local, planar, distance and energy spanner, constant node degree
Interference is consideredonly implicitly!
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WMAN 2005
Explicit Interference Definitions
• Diversity as an interference measure [Meyer auf der Heide et al. SPAA 2002]
– Interference between edges, time-step routing model, congestion– Trade-offs: congestion, power consumption, dilation– Interference model based on network traffic
• Link-based interference model [Burkhart et al. MobiHoc 2004]
– „How many nodes are affected by communication over a given link?“– Minimize the maximum interference & preserve connectivity– Graph sparseness or low node degree ; low interference
8
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WMAN 2005
Explicit Interference Definitions
• Diversity as an interference measure [Meyer auf der Heide et al. SPAA 2002]
– Interference between edges, time-step routing model, congestion– Trade-offs: congestion, power consumption, dilation– Interference model based on network traffic
• Link-based interference model [Burkhart et al. MobiHoc 2004]
– „How many nodes are affected by communication over a given link?“– Minimize the maximum interference & preserve connectivity– Graph sparseness or low node degree ; low interference
8
Sender-centric perspective
Interference occurs at the receiver
Susceptible to drastic changes
Interference ∈ O(1)Interference ∈ O(n)
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WMAN 2005
Overview
• What is Topology Control?
• Context – related work
• A robust interference model
• Interference in known topologies
• The highway model– Exponential node chain– General highway
• Conclusions
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WMAN 2005
Interference 2
Towards a Robust Interference Model
• Interference model– Node u disturbs all nodes closer than its farthest neighbor– Interference of node u =
#nodes whose distance to u is at most the distance to their farthest neighbors
• Problem statement– We want to minimize maximum interference– At the same time the topology must be connected
Interference occurs at the receiver
Susceptible to drastic changes
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WMAN 2005
Overview
• What is Topology Control?
• Context – related work
• A robust interference model
• Interference in known topologies
• The highway model– Exponential node chain– General highway
• Conclusions
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WMAN 2005
Let’s Study the Following Topology!
…from a worst-case perspective
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WMAN 2005
Topology Control Algorithms Produce…
• All known topology control algorithms (with symmetric edges) include the nearest neighbor forest as a subgraph and produce something like this:
The interference of this graph is Ω(n)!
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WMAN 2005
But Interference…
• Interference does not need to be high…
This topology has interference O(1)!!
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WMAN 2005
Overview
• What is Topology Control?
• Context – related work
• A robust interference model
• Interference in known topologies
• The highway model– Exponential node chain– General highway
• Conclusions
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WMAN 2005
The Highway – a High Interference Topology?
• Already 1-dimensional node distributions seem to yield inherently high interference... [Meyer auf der Heide et al. SPAA 2002]
• ...but the exponential node chain can be connected in a better way
Connecting linearly results in interference O(n)
3 3 2 2 1
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WMAN 2005
3 3 2 2 1
The Highway – a High Interference Topology?
• Already 1-dimensional node distributions seem to yield inherently high interference... [Meyer auf der Heide et al. SPAA 2002]
• ...but the exponential node chain can be connected in a better way
Connecting linearly results in interference O(n)
2 23 20
0
1
1
1
2
2 1
2
1
3
1
3
123 3
3
123
Nodes connecting to theright are called hubs
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WMAN 2005
3 3 2 2 1
The Highway – a High Interference Topology?
• Already 1-dimensional node distributions seem to yield inherently high interference... [Meyer auf der Heide et al. SPAA 2002]
• ...but the exponential node chain can be connected in a better way
Connecting linearly results in interference O(n)
4 3 2 5 4 1234 4 34
5
Interference =
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WMAN 2005
Can We Do Any Better?
• Observations– Interference ≥ #hubs - 1– Interference ≥ maximum degree
• Assumption– Optimum-interference topology yields interference <
⇒ #hubs · ⇒ max degree <
is a lower bound for the interference in the exponential node chain!
Resulting topology is not connected
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WMAN 2005
The General Highway Model
• Arbitrary distributed nodes in one dimension• Are there instances where a minimum-interference topology
exceeds interference ?
• Algorithm– Partition the highway into segments of unit length 1– Every -th node in a segment becomes a hub– Connect hubs linearly– Connect all other nodes to their nearest hub– Connect adjacent segments
∆ = maximum node degree in the UDG
hub = node with morethan one neighbor
segment
interval
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WMAN 2005
On the Highway…
• Observations– #hubs in a segment is in O( )– Regular nodes only interfere with nodes in the same interval– The interference range of a node is limited to adjacent segments
segment
interval
The resulting topology yields interference O( )
Algorithm is designed for the worst-case!
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WMAN 2005
Approximation Algorithm
• Idea– Only apply Algorithm to high interference instances…– …else connect nodes linearly
• Algorithm– Connect nodes linearly– If interference > ⇒ apply Algorithm
• Proof– Lower bound also applies to general highway
The resulting topology approximates the optimal interference up to a factor in O( )
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WMAN 2005
Conclusions
• Definition of an explicit interference model– Receiver-centric– Robust with respect to addition/removal of individual nodes
• All currently known topology control algorithms fail to confine interference at a low level
• Focusing on networks in one dimension– -approximation of the optimal connectivity-preserving topology
• Future work
Adaptation of our approach to higher dimensions
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