Adaptive Power Aware Prefetch in Wireless Networks

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Adaptive Power Aware Prefetch in Wireless Networks

• IEEE TRANSACTION ON WIRELESS COMMUNICATIONS 2004
• Liangzhong Yin Student Member IEEE
• Guohong Cao Member IEEE

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System Model

• Pull based broadcasting model
• Single server and a number of client
• A database
• Asymmetric up/down link bandwidth of the wireless
  channel
• The server sends reply through the common
  broadcast channel

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Cache Invalidation Model

• The server broadcasts invalidation report (IRs)
  every L seconds .
• The IR consists of the current time-stamp Ti ,and
  a list of tuples (dx , tx) such that txgt(Ti
  wL) , where dx is the data item id,tx is the
  most recent update time-stamp of dx , w is the
  invalidation broadcast window size.

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Performance Metrics

• Response time , the time between sending a
  request and receiving the reply
• Stretch (of a request) , define to the ratio of
  the response time of a request to its service
  time ,note that (defined in other paper )in
  broadcast systems , the service time for a time
  for a request is the requested data size divided
  by the bandwidth
• stretch response time / service
  timeservice time requested data / bandwidth
• Various factors access rate, update rate, data
  size

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AVP Scheme (proposed)

• Part 1 . VP (Value - based)
• Part 2 . AVP ( Adaptive value - based)
• The ideal data for prefetching should have a high
  access probability , a low update rate,a small
  data size, and a high retrieval delay.

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VP scheme
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VP scheme (conti.)
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VP scheme (conti.)
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VP scheme (conti.)

• VP scheme is defined as follow Suppose a client
  can Np data items , the VP scheme prefetches the
  Np items which have highest value based on the
  value fucntion.

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AVP scheme

• Value of Np when Np 0 , there will be no
  prefetch. As Np increases , the number of
  prefetch increase and the power consumption also
  increase.
• Np controls the number of data to be prefetch and
  then affects the tradeoff between performance and
  power

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AVP scheme

• AVP_T Adapting Np to Reach a Target
  Battery Life
• AVP_P Adapting Np Based on the Power
  Level

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AVP_T
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AVP_P

• Let ak be the percentage of energy left in the
  client

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PERFORMANCE
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Energy-stretch

• A new metric called energy-stretch
• Define
• energy-stretch stretch energy-consumed