Department of Information Engineering University of Padova, Italy COST273 Sep , 2002 Lisboa TD (02)-146 Handover procedures in a Bluetooth network Roberto Corvaja {corvaja, Andrea Zanella

Sep , 2002COST273 TD (02)-1462 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 , 2002COST273 TD (02)-1463 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 , 2002COST273 TD (02)-1464 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 active slave master parked slave standby slave1 slave2 slave3 master

Sep , 2002COST273 TD (02)-1465 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 625  s t t master slave f(2k)f(2k+1)f(2k+2)

Sep , 2002COST273 TD (02)-1466 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 , 2002COST273 TD (02)-1467 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 , 2002COST273 TD (02)-1468 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 slave’s clock & BT address The accurate paging reduces the time to the order of milliseconds

Sep , 2002COST273 TD (02)-1469 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 , 2002COST273 TD (02) 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 , 2002COST273 TD (02) Pros and Cons PROS PROS  Fast and simple  Does not require any coordination  Does not require the knowledge of the network topology CONS CONS  No control on the choice of the new master (the first paging)  Failure in case of paging collisions PROS PROS  Allows the slave to choose the best master after receiving several paging from different masters  Paging is collision-free CONS CONS  Needs coordination among masters  Can take a long time for scanning the paging table On-demand (ODH) Table-based (TBH)

Sep , 2002COST273 TD (02) 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 , 2002COST273 TD (02) 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 , 2002COST273 TD (02) 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

Sep , 2002COST273 TD (02) 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 , 2002COST273 TD (02) TBH-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 , 2002COST273 TD (02) ODH-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 , 2002COST273 TD (02) 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 , 2002COST273 TD (02) 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 , 2002COST273 TD (02) 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 , 2002COST273 TD (02) 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

Sep , 2002COST273 TD (02) 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