Department of Information Engineering
University of Padova, Italy
Handover procedures in a
Bluetooth network
Roberto Corvaja , Andrea Zanella
{corvaja, zanella}@dei.unipd.it
COST273 Sep. 19-20, 2002 Lisboa
TD (02)-146
Outline 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
2
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)
Sep. 19-20, 2002
COST273 TD (02)-146
3
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
Sep. 19-20, 2002
COST273 TD (02)-146
slave2
slave3
master
slave1
master
active slave
parked slave
standby
4
FH & TDD
f(2k)
f(2k+1)
f(2k+2)
master
t
slave
t
625 s


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
Sep. 19-20, 2002
COST273 TD (02)-146
5
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
Sep. 19-20, 2002
COST273 TD (02)-146
6
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
7
Pure-Bluetooth Handover

Scope:


Hybrid networks (wired/wireless)


Seamless transfer of slave connection from the origin master to
the target master
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
8
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 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
9
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 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
10
Pros and Cons
On-demand (ODH)
Table-based (TBH)

PROS


Allows the slave to choose the best

Fast and simple
master after receiving several

Does not require any coordination

Does not require the knowledge of
paging from different masters


PROS
Paging is collision-free
CONS

Needs coordination among masters

Can take a long time for scanning
the paging table
Sep. 19-20, 2002
the network topology

CONS

No control on the choice of the new
master (the first paging)

Failure in case of paging collisions
COST273 TD (02)-146
11
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
12
Simulation platform

Simulator Tool: OPNET Modeler Ver. 8.0

The simulator does support

Baseband protocols


Link manager (LM) protocol

Link layer control and adaptation protocol (L2CAP)



Frequency Hopping, Paging, Inquiry, Scan
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
13
Model assumptions

Pre-formed Scatternet


Pure Round Robin polling strategy


Roles of master/slave/gateway are pre-assigned
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
14
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
15
TBH-time statistic


Sep. 19-20, 2002
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
COST273 TD (02)-146
16
ODH-time statistic


Sep. 19-20, 2002
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
COST273 TD (02)-146
17
Sniff-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
18
Number 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
19
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
20
Final Remarks


Handover can be supported by an accurate paging
Impact on the handover time



Table-based handover




Sniff time: strong impact
Number of devices per piconet: weak impact
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
21
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
Sep. 19-20, 2002
COST273 TD (02)-146
22