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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
slave2
slave3
master
Sep. 19-20, 2002 COST273 TD (02)-146 5
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)
Sep. 19-20, 2002 COST273 TD (02)-146 6
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
Sep. 19-20, 2002 COST273 TD (02)-146 9
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
Sep. 19-20, 2002 COST273 TD (02)-146 10
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
Sep. 19-20, 2002 COST273 TD (02)-146 11
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)
Sep. 19-20, 2002 COST273 TD (02)-146 12
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
Sep. 19-20, 2002 COST273 TD (02)-146 14
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
Sep. 19-20, 2002 COST273 TD (02)-146 17
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
Sep. 19-20, 2002 COST273 TD (02)-146 18
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
Sep. 19-20, 2002 COST273 TD (02)-146 19
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
Sep. 19-20, 2002 COST273 TD (02)-146 22
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