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Asymmetric Links in a Mobile Environment

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(X,Y) (NX,NY) Simulation Methodology. 1500 m. 300 m. Constant Speed (NX, ... What is the best definition for graph connectivity in the case of asymmetric links? ... – PowerPoint PPT presentation

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Title: Asymmetric Links in a Mobile Environment


1
Asymmetric Links in a Mobile Environment
  • By
  • Yaser Khamayseh
  • Kavita Jari

2
Agenda
  • Introduction
  • Motivation
  • Simulation Methodology
  • Results
  • Questions

3
Questions
4
Mobile Environment
  • Mobility
  • High packet loss
  • Lower Bandwidth
  • Power constraints
  • Range of cells
  • Interference

5
CSMA/CA
  • Carrier Sense Multiple Access/Collision Avoidance
  • Collision avoidance before transmission
  • Carrier sense
  • Each station listens for transmission before
    transmitting
  • Multiple access
  • Each station is free to transmit when it has
    data to send
  • Collision avoidance
  • Each station listens for any media activity
    start transmission if the channel is free

6
Hidden Node Problem
S2
S1
R
S3
7
RTS/CTS
  • Peer-to-Peer Protocol
  • The node sends an RTS to its neighbor and waits
    for a CTS.
  • Once it has received the CTS, it starts sending
    the data.
  • Wait for ACK.

8
RTS/CTS
RTS
DATA S1 ? R
R
S1
CTS
S1
ACK
R
Busy
S2
Busy
S3
9
Symmetric Links
Example of a connected graph
10
Symmetric Links
Example of a disconnected graph
11
Asymmetric Links
  • Each node has two radii (ranges)
  • Transmitting Radius
  • Receiving (sensing) Radius
  • Transmission radius ? Sensing radius
  • Two graphs to represent the state of the network

12
Asymmetric Links
Sensing Graph
Node 0
Node 1
Node 2
Node 1
Node 0
Transmitting Graph
Node 0
Node 1
Node 1
Node 0
13
Motivation
Does send/receive asymmetry
break our mobile protocols???
14
Simulation Methodology
  • Rectangular Area
  • Parameters and Factors
  • Random way-point movement model
  • Events
  • Performance Metrics

15
Parameters Factors
  • The size of the rectangular area is 1500 300
  • Number of Nodes are 10, 20 or 50
  • Different transmission and sensing radii
  • 50 .. 300
  • Different combinations will be tested
  • Node pause time based on exponential distribution
  • Node speed based on uniform distribution

16
Simulation Methodology
1500 m
(X,Y)
300 m
17
Simulation Methodology
1500 m
(NX,NY)
Constant Speed
(X,Y)
300 m
18
Simulation Methodology
1500 m
(NX,NY)
(tX,tY)
(tX,tY)
300 m
19
Simulation Methodology
1500 m
(NX,NY)
(tX,tY)
(tX,tY)
300 m
20
Simulation Methodology
1500 m
(NX,NY)
Pause Time
(tX,tY)
300 m
21
Events
  • Start moving
  • Nodes move to a new location with a specific
    speed
  • Stop moving
  • Nodes pause for a specific time
  • Add an edge
  • Connection is established between two nodes
  • Remove an edge
  • Connection is removed between two nodes

22
Performance Metrics
  • Graph Connectivity
  • Effect of different radii (Transmitting vs.
    Sensing)
  • What is the best definition for graph
    connectivity in the case of asymmetric links?
  • Each node in the graph can send and receive from
    every other node in the graph.

23
Expectations
  • With increase in sensing radius ? Better
    collision avoidance.
  • The graph connectivity maybe better !
  • With increase in transmitting radius ?
  • More collision

24
Previous Work
  • Increasing Transmission radius
  • Increased connectivity
  • Increase in interference
  • Loss of channel throughput
  • Decreasing Transmission radius
  • Increase number of hops to destination
  • Transmission radius covering 6 hops will achieve
    a throughput proportional to sqrt(No. of nodes).

25
Conclusion The Goals
  • Increasing connectivity
  • Maximizing throughput
  • Optimizing (minimizing) energy consumption
  • Decreasing the number of hops (delay)

26
References
  • 1 Kleinrock Silvester, Optimum transmission
    radii for packet radio networks, 1978
  • 2 Sanchez, Giles, Zander, CSMA/CA with beam
    forming antennas in multi-hop packet radio
  • 3 Ravi Prakash, Unidirectional links prove
    costly in Wireless Adhoc networks, 1999
  • 4 Sanchez, Manzoni, Determination of critical
    transmission range in ad-hoc networks
  • 5 Royer, Melliar-Smith, Moser, An analysis of
    the optimum node density for adhoc mobile
    networks

27
Questions
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