Department of Information Engineering

University of Padova, Italy

COST273 Sep. 19-20, 2002 LisboaCOST273 Sep. 19-20, 2002 Lisboa TD (02)-146TD (02)-146

Handover procedures in a Handover procedures in a Bluetooth networkBluetooth network

Roberto Corvaja

{corvaja, zanella}@dei.unipd.it

, Andrea Zanella

Sep. 19-20, 2002 COST273 TD (02)-146 2

Outline of the contentsOutline of the contents

Bluetooth basic Handover algorithms

Table-based handover (TBH) On-demand handover (ODH)

Simulation model Experimental results Conclusions and future work

Sep. 19-20, 2002 COST273 TD (02)-146 3

Bluetooth TechnologyBluetooth 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)

Sep. 19-20, 2002 COST273 TD (02)-146 4

Bluetooth piconetBluetooth 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

active slavemaster

parked slavestandby

slave1

slave2slave3

master

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FH & TDDFH & 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

625 s

t

t

master

slave

f(2k) f(2k+1) f(2k+2)

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Bluetooth scatternetsBluetooth 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

Sep. 19-20, 2002 COST273 TD (02)-146 7

Next in the line…Next in the line…

Bluetooth basic Handover algorithms

Table based handover (TBH) On-demand handover (ODH)

Simulation model Experimental results Conclusions and future work

Sep. 19-20, 2002 COST273 TD (02)-146 8

Pure-Bluetooth Pure-Bluetooth HandoverHandover

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 slave’s clock & BT address The accurate paging reduces the time to the order of

milliseconds

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Table-based handoverTable-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 slave’s 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 handoverOn-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 slave’s 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 ConsPros and Cons

PROSPROS Fast and simple Does not require any

coordination Does not require the knowledge

of the network topology CONSCONS

No control on the choice of the new master (the first paging)

Failure in case of paging collisions

PROSPROS Allows the slave to choose the

best master after receiving several paging from different masters

Paging is collision-free CONSCONS

Needs coordination among masters

Can take a long time for scanning the paging table

On-demand (ODH)On-demand (ODH)Table-based (TBH)Table-based (TBH)

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Next in the line…Next in the line…

Bluetooth basic Handover algorithms

Table-based handover (TBH) On-demand handover (ODH)

Simulation model Experimental results Conclusions and future work

Sep. 19-20, 2002 COST273 TD (02)-146 13

Simulation platform 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 assumptionsModel 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

Sep. 19-20, 2002 COST273 TD (02)-146 15

Next in the line…Next in the line…

Bluetooth basic Handover algorithms

Table-based handover (TBH) On-demand handover (ODH)

Simulation model Experimental results Conclusions and future work

Sep. 19-20, 2002 COST273 TD (02)-146 16

TBH-time statisticTBH-time statistic Simulation parameters

Scatternet with 3 masters 3 and 5 devices per piconet Sniff time N=10 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 statisticODH-time statistic

Simulation parameters Scatternet with 3 masters 3 and 5 devices per piconet Sniff time N=10 slots

Results Handover time less than 25

slots Limited impact of the # of

slaves Handover time better than TBH

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Sniff-timeSniff-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 devicesNumber of devices

Simulation parameters Scatternet with 3 masters Sniff time N=100 slots Variable number of devices

Results Handover-time is only

marginally dependent on the number of devices per piconet

Sep. 19-20, 2002 COST273 TD (02)-146 20

Next in the line…Next in the line…

Bluetooth basic Handover algorithms

Table-based handover (TBH) On-demand handover (ODH)

Simulation model Experimental results Conclusions and future work

Sep. 19-20, 2002 COST273 TD (02)-146 21

Final RemarksFinal 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 workFuture 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