Adaptive Self-Configuring Sensor Network Topologies ns-2 simulation

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Adaptive Self-Configuring Sensor Network
Topologies ns-2 simulation performance analysis

• Zhenghua Fu
• Ben Greenstein
• Petros Zerfos

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Sensor Networks

• Advances in micro-sensor and radio technology
  will enable deployment of sensors for a range of
  environmental monitoring applications
• Due to the low cost per node, networks of sensors
  may be densely distributed

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Challenge

• Unattended sensor nets with limited energy often
  must be long-lived
• The network should be able to adaptively
  self-configure to maximize energy efficiency,
  while still achieving spatial coverage and
  robustness

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ASCENTAdaptive Self-Configuring sEnsor Networks
Topologies

• Answers how to form a multi-hop topology
• Developed by Alberto Cerpa, UCLA
• Protocol assumes dense distribution of nodes
• ASCENT leverages the redundancy imposed by high
  node density
• Each node assesses its connectivity and adapts
  its participation in the multi-hop network
  topology
• Network membership determined in a distributed
  fashion using measurements and calculations
  performed locally

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What is ASCENT?

• It is NOT a routing or data dissemination
  protocol
• ASCENT simply decides which nodes should join the
  routing infrastructure
• In this respect, routing protocols are
  complementary to ASCENT

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Why not use a central configuration node?

• Scaling and robustness considerations
• Nodes would need to communicate detailed
  connectivity state information to this central
  node

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Network Assumptions

• Ad-hoc deployment
• Energy constraints
• Unattended operation under dynamics
• In many such contexts, it will be easier to
  deploy large numbers of nodes initially rather
  than to deploy additional nodes or energy
  reserves at a later date.

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Effects of Node Density

• Too few nodes
• Larger inter-node distance
• Higher packet loss rate
• Too many nodes
• At best, unnecessary energy expenditure
• At worst, interfering nodes congest the channel
• Equilibrium
• Approximated using self-configuration

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ASCENT

• Initially, only nodes A and B are alive
• All other nodes are passively listening, but are
  not part of the network

B
A
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ASCENT

• A sends data to B
• Due to signal attenuation and random shadowing B
  detects high message loss
• Notion of high is application dependent

B
A
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ASCENT

• B attempts to remove this communication hole
• B requests additional nodes in the region to join
  the network to serve to relay messages from A to B

B
A
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ASCENT

• Additional node(s) join the network
• Alternatively, while passively listening, node C
  determines whether it would be helpful to join
  the multi-hop routing infrastructure

B
C
A
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Neighbor Discovery Phase

• A neighbor is defined as a node from which a node
  receives a certain percentage of messages over
  time
• The number of neighbors can greatly increase the
  energy consumption in contention for resources

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Neighbor Discovery Phase

• Entered at time of node initialization
• Using local measurements, each node obtains an
  estimate of the number of neighbors actively
  transmitting messages
• As the neighbor count increases, so too should
  the neighbors message loss threshold

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Join Decision Phase

• A node decides whether to join the multi-hop
  diffusion sensor network
• A node may temporarily join and test whether it
  contributes to improved connectivity
• The decision is based on message loss percentage
  and number of neighbors

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Active Phase

• A node enters the Active Phase from the Join
  Decision Phase when it decides to join the
  network for a long time
• Starts sending routing control and data messages

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Adaptive Phase

• When a node decides NOT to join the network
• A node has the option of either powering down for
  a period of time or reducing its transmission
  range

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Previous ASCENT Implementation

• PC-104 nodes
• RPC Radiometrix Radio
• Linux
• LECS barebones CSMA MAC
• Diffusion Routing
• ASCENT written on top of Diffusion
• ASCENT uses Diffusion for routing of its control
  messages

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ASCENT for NS

• Rewrote ASCENT for NS
• Placed the ASCENT code in the NS Link Layer
• Removed calls to Diffusion to route control
  packets
• Modified 802.11 and Link Layer code so that nodes
  could play dead
• Removed retransmit functionality of 802.11

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Motivation

• ASCENT has been tested on only 25 nodes. With NS
  it can be tested on hundreds
• Verify that NS models the real world well
• Confirm that ASCENT works

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Simulation Setup

• Communication within 1-hop distance
• 90 message loss at 1100m.
• One source (sending frequencies of 1p/sec and
  10p/sec CBR-like), one sink
• Densities of 3, 4, 5, 10, 30, 50, 75 and 100
  nodes, randomly distributed in a fixed area (800m
  x 800m)
• MAC layer IEEE 802.11 with no retransmissions -
  messages sent in broadcast
• Propagation model Shadowing (probabilistic)

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Metrics

• Message Loss
• End-to-end percentage of data packets created by
  source that were correctly received by sink
• Event Delivery Ratio
• Percentage of packets that could have been
  received that actually were received (at each
  node)
• Delay (end-to-end)
• Overhead
• Percentage of packets received (at each node)
  that were control packets

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Message Loss vs. Density
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Event Delivery vs. Density
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Delay vs. Density
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Overhead vs. Density
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Message Loss vs. Density
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Event Delivery vs. Density
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Delay vs. Density
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Overhead vs. Density
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Conclusions

• Our experiments (2Mbps), Previous experiments
  (13Kbps)
• Under-utilized channel
• Small vulnerable Period
• Propagation effects examined better than
  collision effects
• ASCENT performs well
• As nodes increases (scalability)
• As sending frequency increases our overhead
  remains low