Handover procedures in a Bluetooth network

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Handover procedures in a Bluetooth network
Department of Information Engineering University
of Padova, Italy

• Roberto Corvaja

, Andrea Zanella
corvaja, zanella_at_dei.unipd.it
COST273 Sep. 19-20, 2002 Lisboa
TD (02)-146
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Outline of the contents

• Bluetooth basic
• Handover algorithms
• Table-based handover (TBH)
• On-demand handover (ODH)
• Simulation model
• Experimental results
• Conclusions and future work

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Bluetooth Technology

• What is Bluetooth?
• A wireless technology
• Proposed as cable replacement for portable
  electronic devices, BT provides short-range
  low-power point-to-(multi)point wireless
  connectivity
• A global industry standard in the making
• Initially developed by Ericsson, now BT is
  promoted by an industry alliance called Special
  Interest Group (SIG)

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Bluetooth piconet

• Two up to eight Bluetooth units sharing the same
  channel form a piconet
• In each piconet, a unit acts as master, the
  others act as slaves
• Channel access is based on a centralized polling
  scheme

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FH TDD

• Each piconet is associated to frequency hopping
  (FH) channel
• The pseudo-random FH sequence is imposed by the
  master
• Time is divided into consecutive time-slots of
  625 ?s
• Each slot corresponds to a different hop
  frequency
• Full-duplex is supported by Time-division-duplex
  (TDD)
• Master-to-slave (downlink) transmissions start on
  odd slots
• Slave-to-Master (uplink) transmissions start on
  even slots

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Bluetooth scatternets

• Piconets can be interconnected by Inter-piconet
  Units (IPUs)
• IPUs may act as gateways, forwarding traffic
  among adjacent piconets
• IPUs must time-division their presence among the
  piconets
• Time division can be realized by using SNIFF mode

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Next in the line

• Bluetooth basic
• Handover algorithms
• Table based handover (TBH)
• On-demand handover (ODH)
• Simulation model
• Experimental results
• Conclusions and future work

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Pure-Bluetooth Handover

• Scope
• Seamless transfer of slave connection from the
  origin master to the target master
• Hybrid networks (wired/wireless)
• Make use of the wired connection between masters
• Pure-Bluetooth network
• Make use of standard Inquiry/Page/Scan modes
• Handover-time can be of the order of seconds
• Make use of accurate Page/Scan modes
• Devices are acquainted with slaves clock BT
  address
• The accurate paging reduces the time to the order
  of milliseconds

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Table-based handover

• The slave issues an handover-request to its
  origin master and enters the page-scan mode
• The origin master forwards the request to the
  other masters and acquaints them with the slaves
  parameters
• The masters start paging on the basis of a
  paging-table
• Only one master at a time is allowed to page the
  slave
• The slave just listens but DOES NOT reply to any
  page
• Once the paging-table has been scanned, the slave
  can choose the best master and synchronize to it
• The sequence of masters (table) has to be
  repeated once more to allow the synchronization
  between the slave and the chosen master
• The new master that takes the slave in its
  piconet, finally, signals the end of the
  procedure to the origin master

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On-demand handover

• The slave issues an handover-request to its
  origin master and enters the page-scan mode
• The origin master forwards the request to the
  other masters and acquaints them with the slaves
  parameters
• The target masters begin an accurate page of the
  slave
• The slave replies to the first page packet it
  gets
• The corresponding master connects the slave
• The new master issues an handover-complete
  message
• The other masters stop paging

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Pros and Cons
On-demand (ODH)
Table-based (TBH)

• PROS
• Fast and simple
• Does not require any coordination
• Does not require the knowledge of the network
  topology
• CONS
• No control on the choice of the new master (the
  first paging)
• Failure in case of paging collisions

• PROS
• Allows the slave to choose the best master after
  receiving several paging from different masters
• Paging is collision-free
• CONS
• Needs coordination among masters
• Can take a long time for scanning the paging
  table

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Next in the line

• Bluetooth basic
• Handover algorithms
• Table-based handover (TBH)
• On-demand handover (ODH)
• Simulation model
• Experimental results
• Conclusions and future work

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Simulation platform

• Simulator Tool OPNET Modeler Ver. 8.0
• The simulator does support
• Baseband protocols
• Frequency Hopping, Paging, Inquiry, Scan
• Link manager (LM) protocol
• Link layer control and adaptation protocol
  (L2CAP)
• Connection setup/release, Sniff Mode
• Handover for Bluetooth slaves
• The simulator does not support
• Multi-slot data packets
• Handover for master and gateway units

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Model assumptions

• Pre-formed Scatternet
• Roles of master/slave/gateway are pre-assigned
• Pure Round Robin polling strategy
• Nodes have the same priority and get polled in
  cyclic order
• 2 piconets per gateway
• A gateway spends equal time in each one of its
  piconet
• Sniff mechanism is used to support inter-piconet
  switching
• Gateways are not coordinated

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Next in the line

• Bluetooth basic
• Handover algorithms
• Table-based handover (TBH)
• On-demand handover (ODH)
• Simulation model
• Experimental results
• Conclusions and future work

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TBH-time statistic

• Simulation parameters
• Scatternet with 3 masters
• 3 and 5 devices per piconet
• Sniff time N10 slots
• 2 table-scanning repetitions
• 12 paging slots per master
• Results
• Handover time less than 100 slots
• Small dispersion
• Limited impact of the of slaves

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ODH-time statistic

• Simulation parameters
• Scatternet with 3 masters
• 3 and 5 devices per piconet
• Sniff time N10 slots
• Results
• Handover time less than 25 slots
• Limited impact of the of slaves
• Handover time better than TBH

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Sniff-time

• Simulation parameters
• Scatternet with 3 masters
• 3 devices per piconet
• Variable Sniff time
• Results
• Handover-time grows linearly with the Sniff-time

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Number of devices

• Simulation parameters
• Scatternet with 3 masters
• Sniff time N100 slots
• Variable number of devices
• Results
• Handover-time is only marginally dependent on the
  number of devices per piconet

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Next in the line

• Bluetooth basic
• Handover algorithms
• Table-based handover (TBH)
• On-demand handover (ODH)
• Simulation model
• Experimental results
• Conclusions and future work

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Final Remarks

• Handover can be supported by an accurate paging
• Impact on the handover time
• Sniff time strong impact
• Number of devices per piconet weak impact
• Table-based handover
• Handover takes less than 100 slots
• Choice of optimum master is possible
• Exchange of information and coordination is
  required
• On-demand handover
• Handover takes less than 25 slots
• Choice of optimum master is NOT possible
• No coordination is required

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Future work

• Next in the line
• Simulator enhancements
• Multi-slot packets
• Physical channel characterization
• Implementation of dynamic scatternet formation
  algorithms
• Integration of handover and routing procedures
• Mathematical analysis of the scatternet capacity