Bluetooth Scatternets: An Enhanced Adaptive Scheduling Schema

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Bluetooth ScatternetsAn Enhanced Adaptive
Scheduling Schema

• Simon Baatz
• Matthias Frank
• Carmen Kühl
• Peter Martini
• Christoph Scholz

presented by Metin Tekkalmaz
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Outline

• Introduction
• Related Bluetooth Topics
• Challenges in Scatternet Formation
• Credit Based Approach
• Performance Enhancements
• Conclusion

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Introduction

• The Goal is to schedule the data traffic in the
  scatternet
• Paper discusses one of the ways of this which,
• Adapts to varying traffic patterns
• Is based on sniff mode
• Does not need much modifications on current spec

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Related Bluetooth Topics

• Poll - Null messages
• Maximum Poll interval
• Sniff Mode

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Challanges (1/3)

• Scatternets need some nodes to be connected with
  multiple piconets
• different hop sequences
• different timing
• Single transceiver Single hopping schema at a
  time
• Switching is a necessity - in TDM

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Challanges (2/3)

• Different slot boundaries

• High vs. Low switching frequency
• Throughput vs. Delay

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Challanges (3/3)

• Scheduling Switches

• Switching but, when and to where
• How the coordination is achieved?
• Is Presence Schedule a solution?

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Credit Based Approach (1/5)Presence Point
Concept (lets call it PP)

• Presence Points (o/l) instead of Presence
  Schedules (a priori)
• PP is where communication on a link (between
  Master Slave) may start
• Quickly determine if peer is available
• Begin communication if available
• Try another PP otherwise
• Communication period is not predetermined

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Credit Based Approach (2/5)PP implementation w/
Sniff Mode

• Let the sniff slots be the PPs
• Maximize probability of a common sniff slot
• Continue sniff event until one or both sides
  decide to abort
• Max. poll interval provides QoS
• When and Where problem is still unsolved

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Credit Based Approach (3/5)The Solution Credit
Schema

• Devices assign priorities to each link, locally
• Priority is per peer, not per link
• i.e. Different devices may assign different
  priorities to the same link
• A link has a higher priority if it has been
  treated relatively unfair
• Assign credits to each link to keep track of
  relative fairness

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Credit Based Approach (4/5)Credit Schema

• One credit is charged from its credit account if
  that link is used
• If a slot is not used at all a special temporary
  account is debited
• To keep the system balanced increase the
  temporary if a credit is debited from a links
  account
• Redistribute temp accnts savings when it reaches
  n, which is of links (QoS charecteristics may
  be considered)

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Credit Based Approach (5/5)Credit Schema

• Abort an ongoing sniff event if link with
  upcoming sniff slot has a higher credit

• Poll Null Switch to next PP
• If max. poll interval exceeds give highest
  priority

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Performance Enhancementsto minimize of switches

• After communcation begins reserve some number of
  slots for that comm
• May lead to starvation

• Switch links only if the difference between the
  credits is higher that a threshold

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Performance Enhancementsfor better utilization
of Redistribution

• Redistribute a links credits if it doesnt use
  them
• Absolute vs. Relative distribution
• Relative distribution
• Triggered by Poll-Null

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Performance EnhancementsAdaptive Presence Point
Density (APPD)

• Do not waste credit with unseccessful sniff slots
  or Poll-Null sequences
• Double PP intervals for unsuccessfull tries
• Assure process is identical at both sides

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Conclusion

• Simulation results are in the paper
• Good for arbitrary topologies
• No need for scatternet-wide coordination
• Easily adapts to the traffic conditions
• QoS aspects are open problems
• I am impressed!!!