A Holistic Cross Layer Design Approach for MultiHop Mobile Ad Hoc Networks

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A Holistic Cross Layer Design Approach for
Multi-Hop Mobile Ad Hoc Networks
Communications Research Group

• Authors
• Danish Khan
• Peter Ball
• Geoff Childs

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Destination
Source
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Destination
Source
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Outline

• Design objective
• Cross layer design approach
• Minimum transmission power
• Battery life
• Throughput
• Conclusion

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Design objectives

• Primary objective is to establish a route between
  the source and destination.
• Maximise network lifetime (time when all nodes
  can communicate)
• Minimise the transmission power
• Avoid using nodes for relays that have low
  battery energy
• Avoid unacceptable interference to other active
  nodes
• Maintain performance
• Avoid excessive delay
• Maintain throughput

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Cross layer communication
Appropriate communication is needed between the
nodes to provide the information needed to
determine the best route.
Delay
Throughput
Intelligent Routing
Battery level
Available nodes
Modulation
Tx power
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Nodes available for multi hop route
BT

• Access method is needed (busy tone scheme) -
  determines the max amount of power that each node
  can transmit without causing an unacceptable
  interference at other nodes.

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Nodes available for multi hop route
Nodes D, E and H not available due to interference
BT
Available intermediate nodes

• This determines that nodes are available for
  communication between the source and destination.

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Nodes available for multi hop route
Available intermediate nodes
Large delay route

• First metric Discard all routes for which the
  delay is too large for the application.

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Nodes available for multi hop route
Two routes exist to the destination

• Second metric Minimum power route.
• Multi hop route provides multiple short links
  instead of a single point to point link.

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Nodes available for multi hop route
Two routes exist to the destination

• Assuming Free Space Path Loss Model between the
  nodes.
• As the number of hops between source and
  destination increases, the end to end tx power
  decreases.

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Nodes available for multi hop route
Two routes exist to the destination

• However as the number of hops increases, the
  processing power will increase proportionally and
  become increasingly important.

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To investigate Min Tx Power vs. Number of hops
vs. spatial position of accessible nodes
Single point to point link Comparison of power
requirement of p2p link with multi hop route
Lower power bound multi hop model
Upper power bound multi hop model
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Result MTP vs. number of hops vs. position
Relative gain vs number of hops with 1
processing power

• The result shows that if the processing power can
  be reduced to 1 of the transmission power, then
  a power saving of up to 12dB can be achieved for
  a straight line with 4 hops and 6dB for nodes on
  the arc of a circle.

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Battery life
Min power route
remaining battery

• In addition to minimising the power, the battery
  life of each node can be taken into account with
  the aim of maximising the lifetime of all nodes
  in the network.

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Battery life
remaining battery

• In addition to minimising the power, the battery
  life of each node can be taken into account with
  the aim of maximising the lifetime of all nodes
  in the network.

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Throughput

• Multi hop reduces the transmission power, but
  this also reduces the throughput.

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Throughput
X packets in time t
Frequency re-use depends upon the interference
range of the transmission assuming frequency
re-use is not possible for up to 4 hops.

• Single frequency channel is used on the basis
  that a node cannot transmit and receive at the
  same time on the same frequency channel.

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Throughput
X/2 packets in time t
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Throughput
X/4 packets in time t
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Throughput adaptive modulation
It is possible to recover some or all of the loss
in throughput if the link power budget can
support higher modulation scheme Higher order
modulation scheme requires greater carrier to
interference ratio (needs higher transmit power
for the same distance)
1 hop
2 hops
3/4 hops
5/6 hops
C/I for different modulation schemes relative to
BPSK
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Throughput - results
Resultant power saving with maintained throughput
using adaptive modulation.

• Result shows that a small power saving is
  possible with constant throughput for a small
  number of links and for nodes located close to
  the direct line from source to destination.

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Conclusions

• A procedure to select an optimum route in an ad
  hoc network has been described.
• The optimum routes are selected based on
  maximising the network lifetime, minimising
  interference, avoiding delay, and maintaining the
  throughput.
• Information from the Application, MAC and
  Physical layers is communicated to the network
  layer to determine the optimum route.
• The results shows that it is possible to
  establish a route with up to about four hops with
  the throughput maintained and no increase in the
  overall power consumption.