Energy Aware Routing for Low Energy Ad Hoc Sensor Networks

1
Energy Aware Routing for Low Energy Ad Hoc Sensor
Networks

• Rahul C. Shah and Jan Rabaey
• Berkeley Wireless Research Center
• Dept. of EECS
• University of California, Berkeley

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Wireless Sensor Nodes Constraints

• Low Data Rates ltlt 10 kbps
• Self-configuring, maintenance-free and robust
• Aggressive networking protocol stack
• Redundancy in deployment
• Low cost lt 1
• Small size lt 1 cm3
• Low power/energy
• Long lifetime of product requires
  energy-scavenging
• Plausible scavenging level lt 100 ?W

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PicoNetwork Specifications

• Density of nodes 1 node every 1 to 20 sq. m.
• Radio range 3 to 10 m
• Average bit rate per node 100-500 bps
• Peak bit rate per node 10 kbps
• Very low mobility of nodes
• Loose QoS requirements
• Sensor data is redundant, so reliability is not
  required
• Most data is delay insensitive

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Protocol Stack

• Issues at the network layer
• Addressing
• Addressing will be class based
• ltlocation, node type, sub typegt
• Symbolic addressing may be supported
• Routing
• Should route packets to the destination
• Given
• Destination location
• Position of self
• Position of the neighbors

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Data Link Layer

• Maintains position of self and neighbors
• Main radio receiver
• Runs at 10 kbps
• Locally unique channel, globally reused
• Wake-up radio receiver
• Global broadcast channel
• Used to wake-up neighboring nodes

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Routing Protocol Characteristics

• Ensure network survivability
• Low energy (communication and computation)
• Tolerant and robust to topology changes
• Scalable with the number of nodes
• Light weight

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Network Survivability
Network survivability is application-dependent
coverage may also be an issue
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Proactive vs. Reactive Routing

• Proactive routing maintains routes to every other
  node in the network
• Regular routing updates impose large overhead
• Suitable for high traffic networks

• Reactive routing maintains routes to only those
  nodes which are needed
• Cost of finding routes is expensive since
  flooding is involved
• Good for low/medium traffic networks

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Traditional Reactive Protocols
Dest
Source

• Finds the best route and then always uses that!
• But that is NOT the best solution!
• Energy depletion in certain nodes
• Creation of hotspots in the network

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Directed Diffusion
Setting up gradients
Source
Destination

• Destination initiated
• Multiple paths are kept alive

C. Intanagonwiwat, R. Govindan and D. Estrin,
Directed Diffusion A scalable and robust
communication paradigm for sensor networks,
IEEE/ACM Mobicom, 2000
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Energy Aware Routing

• Destination initiated routing
• Do a directional flooding to determine various
  routes (based on location)
• Collect energy metrics along the way
• Every route has a probability of being chosen
• Probability ? 1/energy cost
• The choice of path is made locally at every node
  for every packet

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Setup Phase
Directional flooding
Sensor
Controller
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Data Communication Phase
Each node makes a local decision
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Whats The Advantage?

• Spread traffic over different paths keep paths
  alive without redundancy
• Mitigates the problem of hot-spots in the network
• Has built in tolerance to nodes moving out of
  range or dying
• Continuously check different paths

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Energy Cost

• The metric can also include
• Information about the data buffered for a
  neighbor
• Regeneration rate of energy at a node
• Correlation of data

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Simulation Setup

• Simulations done in Opnet
• 76 nodes in a typical office setup
• 47 light sensors
• 18 temperature sensors
• 7 controllers
• 4 mobile nodes
• Light sensors send data every 10 seconds, while
  the temperature data is sent every 30 seconds
• Comparison with directed diffusion routing

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Simulation Model
Network model
Office layout
Node layout
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Simulation Measurements

• Energy used is measured
• For reception 30 nJ/bit
• For transmission 20 nJ/bit 1 pJ/bit/m3
• Packet sizes are 256 bits
• 1 hour simulation time

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Energy Usage Comparison
Diffusion Routing
Energy Aware Routing
Peak energy usage was 50 mJ for 1 hour simulation
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Normalized Energy Comparison
Diffusion Routing
Energy Aware Routing
Energy of each node is normalized with respect to
the average energy
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Bit Rate Comparison
Diffusion Routing
Energy Aware Routing
Peak bit rate was 250 bits/sec. Average bit rate
was 110 bits/sec.
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Network Lifetime

• Nodes have fixed initial energy 150 mJ
• Measure the network lifetime until the first node
  dies out
• Diffusion 150 minutes
• Energy Aware Routing 216 minutes

44 increase in network lifetime
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Summary

• Mitigation of hot-spots is crucial in energy
  constrained networks
• Simulation results suggest that probabilistic
  routing increases time until the first node dies
  out
• Analysis is required to show the theoretical
  optimum
• Network performance is application dependent
  need to clearly identify metrics of interest