Experimental study of the effects of Transmission Power Control and Blacklisting in Wireless Sensor Networks

1
Experimental study of the effects of Transmission
Power Control and Blacklisting in Wireless Sensor
Networks

• Dongjin Son, Bhaskar Krishnamachari and John
  Heidemann
• Presented by Anandha Gopalan
• Nov. 3, 2004

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Outline

• Introduction
• Experiments
• Transmission Power Control (TPC) with
  blacklisting
• Conclusion and Future work

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Introduction

• Zikes !!! Yet another paper on power-management
• This one has a slightly different take about it
• ? Thank goodness for that ?
• So, whats different ???
• Simulations usually assume idealized link
  conditions
• Experimentally evaluate the effect of
  transmission power on link conditions
• Sometimes, increasing TP may help ? Aha !!!
  thats a bit different

4
Experiments

• Effects of unreliable wireless links
• Effects of TPC
• Experimental study of varying TP on a single
  wireless link
• One receiver and multiple transmitters
• One transmitter and multiple receivers
• Wireless link distance
• Node location (Multi-Path and Interference)
• Time (Environment change)

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Experiments

• Testbed
• PC104 testbed with mica2 motes
• Directed diffusion routing
• S-MAC MAC protocol
• Weak link
• Packet Reception Rate (PRR) lt Threshold
• Asymmetric link
• PRR gt Threshold in only one direction

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Experiments

• Effect of unreliable wireless links
• Having unreliable links is worse than having any
  links at all
• They tend to be utilized
• Convert unreliable links to good links or prevent
  them from being used

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Experiments

• Effects of TPC
• Increased TP leads to more good links
• Unreliable links can be converted to good links
• New communication links can be discovered and
  used for packet delivery
• Problem May lead to new unreliable links
• Taken care of by blacklisting
• Problem May use up more network capacity

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Experiments

• New definitions
• Weak link
• Packet Reception Rate (PRR) lt Threshold, even
  after TPC
• Asymmetric link
• PRR gt Threshold in only one direction, even after
  TPC

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Experiments

• One receiver and multiple transmitters
• Difference is not obvious at close distances
• Difference b/w node 27 and nodes (30,20) noticed
  after a distance of 17m
• Difference b/w nodes 30 and 20 noticed after a
  distance of 23m

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Experiments

• One transmitter and multiple receivers
• In the TP range b/w -3 and 6 dBm, the link
  quality is different at the same TP level, while
  different TP is required for each link to reach
  the same PRR level
• Range of TP that generates this kind of variation
  is called unreliable transmission power range
  (UTPR)
• UTPR can be avoided in two ways
• Assign a TP high enough for every link to be
  outside UTPR
• Assign a distinct TP for each link

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Experiments

• Effect of wireless link distance
• Clear line of sight b/w transmitter and receiver
• Distance b/w transmitter and receiver is varied
• Experiments show that new reliable, communication
  links that are not available at default TP can be
  generated with TPC

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Experiments

• Effect of node location
• No clear line of sight b/w the sender and
  receiver
• Receiver is placed in six different locations in
  the same indoor environment
• Results
• Multi-path interference effect are severe
  indoors, where signal is weak
• Severe link quality variation can be expected
  with small movement of sensor nodes

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Experiments

• Effect of surrounding environment change
• Variation in link quality is observed at
  different times of the day and night
• Results
• Variation in link quality observed during the day
  due to change in surrounding environment
• The difference in link quality is only b/w the TP
  of -7 to 2 dBm

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TPC with blacklisting (PCBL) - Characteristics

• TPC for link quality control
• Convert unreliable links to reliable links
• Packet-based TPC
• TP is assigned to each packet based on its
  destination and type of packet, considering link
  quality requirement
• Metric-based link quality estimation
• Link quality is measured based on PRR

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PCBL - Characteristics

• Blacklisting at adjusted TP level
• Not all links can be converted to a good link
  with TPC
• New weak or asymmetric links can be generated at
  adjusted TP level
• Blacklisting is used with TPC to remove remaining
  unreliable links after TPC

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PCBL - Algorithm

• 1. Collect link statistics in PRR metric
• 2. Select a unicast power for each link
• 3. Blacklist unreliable links
• 4. Select a broadcast power for each node

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PCBL - Algorithm

• 1. Collect link statistics
• PRRs at pre-selected transmission power levels
  are collected
• 2. Select a unicast power for each link
• Select a link quality control threshold (THLQ)
• Unicast power for each link is assigned such as
  Ui-gtj P where PRRpi gt THLQ and P min pi,
  otherwise Ui-gtj is set to maximum TP (Pmax)

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PCBL - Algorithm

• 3. Blacklist unreliable links
• Links that cannot be converted to good links
  based on the blacklist threshold (THBL) are
  blacklisted and not used for any packet
  transmission or reception
• 4. Select a broadcast power for each node
• Broadcast transmission power of node i (Bi) is
  selected to be max (Ui-gtj )
• Ensures that broadcast packets reach every node
  with a good wireless link

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PCBL Algorithm On-demand optimization for
Long-lived Routing

• 1. Collect link statistics only at the maximum
  transmission power level
• 2. Blacklist unreliable links before using a
  routing protocol
• 3. Find a delivery path with a routing protocol
• 4. Identify unicast transmission powers to use
  only for links in the delivery path

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PCBL Analysis for Single Data Flows

• Packet Delivery Rates
• PCBL is better than TPP-P0, TPP-P5 and TPP-P10,
  but worse than M-BL
• Energy Consumption
• PCBL consumes more than TPP-P0
• Energy consumption per packet
• PCBL consumes less than TPP-P0

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PCBL Analysis for Multiple Data Flows

• Packet Delivery Rates
• PCBL is better than M-BL for flows 12, but is
  slightly worse for flow 3
• Improvement in flows 12 due to the saturation of
  the wireless link around node 11 for M-BL

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Conclusion and Future work

• Presented an experimental study of the effects of
  TPC on wireless link quality
• A TPC scheme with blacklisting for link quality
  control was proposed
• Analysis of the proposed scheme was carried out
  using experiments
• Optimizations for the proposed algorithm is to be
  studied for future work

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Issues with the paper

• Overhead of collecting link statistics ???
• How are the statistics collected ???
• Comparing PCBL with TPP-P0, TPP-P5 and TPP-P10
  for multiple flows
• How do you get the threshold values ???
• Mistakes in the paper

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