Transcript UWB Impact on WLAN (IEEE802.11b) Network

Ad Hoc Networking Course
Instructor: Carlos Pomalaza-Ráez
Geographical Routing
Using Partial Information for
Wireless Ad Hoc Networks
Rahul Jain, Anuj Puri, and Raja Sengupta
University of California, Berkeley
Published on IEEE Personal Communications, Vol.8, Issue 1, Feb2001
Presented by Jani Saloranta at Ad Hoc Networking Course 27.1.2004
Outline
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Introduction
Geograhical Routing Algorithm (GRA)
Algorithm
Related Issues
Teardown protocol
Performance
Simulation Results
Conclusion
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Introduction
• The algorithm for routing in wireless ad hoc
networks using information about
geographical location of the nodes.
• Why?
– Setting up a communication infrastructure
is difficult.
– Mobility
– Money
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The Geographical Routing
Algorithm
• Doesn’t assume any hierarchical network
architecure
• Doesn’t do source routing
• Assumes nodes position via global positioning
system (GPS) and existence of geographical
location service (GLS).
• Optimal power
• Symmetric links
• Medium access schedule such that each node
can transmit at a certain bit rate without
interference.
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• Wireless network can be modellad as a graph
G = ( N, L ),
where nodes N = {1, 2, ..., n} and edges
(links) L = { ( i, j ) | nodes i and j are
neighbours }.
• Each node knows about a small number of
nodes in the network. More about the those
who are nearer to it than those about those
further away.
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D
S
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The Algorithm
• Start point: Each node knows only about its
neighbours.
• Routing table for node S is a list <(pi, Si)>,
where pi is a geographical position and Si is
neighbour of S.
• Node S checks from its routing table which pi
is closest for packet destination D.
• Each node thus forwards the packet in the
same way till the packet reaches the
destination.
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• If node S discovers that it is closer to the destination
than any other pi we say the packet is ”stuck”. Route
discovery protocol handles these situations.
• Route discovery protocol:
– Finds a path from S to D.
( Path(S, D) = <k0, k1, ..., kl> ) and updates the
routing table of the node ki <Pos(D), ki+1 >.
D
S
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1) from A to E
2)
3)
C
D
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Related Issues
• Positional Errors
– Node i gets its position from GPS and there
is an error. i advertises wrong position pi
instead of correct position pi’.
– If error is big enough packet most propably
get ”stuck”  Route discovery protocol.
• Multiple Route Discoveries
– Avoided by timestamps.
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Teardown protocol
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Extension which tries to maintain the centers
property ans keep the routing tables consistent.
Node S updates its routing table:
1. S receives hello msg from node Ni
 it puts (Ni, pos(Ni), Ni)
2. If S doesn’t hear anything from node Ni for
certain time  it removes (Di, pos(Ni), Ni) for
every Di.
3. If Table(S) contains the entry (Di, pi, Ni) and S
receives Table(Ni) which contains the entry (Di,
pj, –), then S updates its entry to (Di, pj, Ni).
4. If Table(S) contains the entry (Di, pi, Ni) and S
receives Table(Ni) which does not contain an
entry (Di, –, –), then S removes the entry (Dii, pi,
Ni) from its table.
5. After any change to its routing table, S
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broadcasts the new Table(S).
Performance
• Convergence of Routing Tables
– One of the advantages of algorithm is that a node
does not need to have a routing entry for every
other node in the network.
• Number of route discoveries per node
– O (log n)
• Routing Table Size
– The mean routing table size is bounded above by
O ( L1 log n )), where L1 is the mean length of the
shortest path between any pair of nodes in an nnode random network.
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Assumption: network has n nodes in a unit area and
each node has transmission radius r.
• Overhead from a single link going down
– O ( L log(n) / r 2 )
• Number of links going down due to mobility
– O (r v n 2),
where v is speed of certain node.
 Total overhead
– O ( L v n 2 log(n ) / r ) packets get generated in
the network per unit time.
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Simulation Results
Figure 7a
Figure 7b
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Figure 8a
Figure 8b
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Figure 9a
Figure 9b
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Conclusions
• Algorithm is asynchronous, real-time,
distributed, and scalable. It does not require
an architecture or hierarchy to be imposed on
the network, but provides each node with a
distance-dependent aggregated view of the
network topology.
• Correctness of algorithm has been shown via
theoretic calculus and verified through
simulations.
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Teardown misspelling
Correct form can be
found from [19].
Says: (di, pi, ni)
Should say: (di, pj, ni)
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Blurry math
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”We assume the network has n nodes in a unit area and each node has
a transmission radius r.”
”On average, each node has nπr2 neighbors and cLlog(n) entries in its
routing table. So on average a = cLlog(n)/(nπr2) entries in the routing
table of A are using a link from node A to a neighbor B.”

nodes
radius
neighbours
entries
n
r
nπr2
cLlog(n)
0.1
1
10
10
10
10
31
314
3141
cL* (-1)
2
2
25
0
cL
cL* (0.3)
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