University of Padova Department of Information Engineering On

University of Padova Department of Information Engineering On the Optimal Topology of Bluetooth Piconets: Roles Swapping Algorithms Daniele Miorandi & Andrea Zanella {daniele. miorandi, andrea. zanella}@dei. unipd. it Med-Hoc-Net 2002 , Chia (Italy), 6 September 2002

Overview ØProblem definition: find efficient topologies for Bluetooth networks. ØFirst step: study of optimal piconet configurations. ØAssumption: knowledge of the end-to-end traffic matrix. ØStability issues & delay analysis (with Pure Round Robin and Poisson traffic). ØMetrics: average packet delay. ØOptimal criterion for off-line topologies design. ØSuboptimal criterion (lower computational complexity) for real-time network reconfiguration. ØConclusion & discussion. D. Miorandi & A. Zanella Med-Hoc-Net, Chia, 6 September 2002

Background: BT system architecture ØPiconet üTwo up to eight active Bluetooth devices sharing the same FH channel form a piconet. üIn each piconet, a unit acts as a master, the others act as slaves. üChannel access is based on a centralized polling scheme. üFull duplex is achieved by means of time division duplexing (TDD). ØScatternet: üPiconets may overlap and may be connected by means of a shared inter-piconet units (IPUs). üIPUs may be shared on a time-division basis, which may be realized using low-power SNIFF mode. D. Miorandi & A. Zanella slave 2 slave 3 master slave 1 master active slave parked slave standby Med-Hoc-Net, Chia, 6 September 2002

System Model ØCluster of (N+1) nodes ( ). ØAssumptions: ØEach node is in the coverage area of all other nodes; ØThe traffic flows may be modeled as independent Poisson processes. ØEnd-to-end traffic matrix (average packets generation rates). ØPiconet definition: ØEffective traffic pattern matrix (traffic actually flowing on the net): D. Miorandi & A. Zanella Med-Hoc-Net, Chia, 6 September 2002

System Model (2) ØStability condition for the PRR polling scheme: ØDefinition: A traffic matrix is admissible if there is a master choice k s. t. the stability condition holds (i. e. there is a stable topology). ØDefinition: A traffic matrix is fully admissible if the stability conditions hold for any choice of the master k. ØProposition: A traffic matrix following conditions hold: is fully admissible if and only if the ØProposition: A traffic matrix following conditions hold: is admissible if and only if the D. Miorandi & A. Zanella Med-Hoc-Net, Chia, 6 September 2002

Optimal Criterion ØLink delay: ØUp to a randomization of the polling order the average packet delay may be expressed as: ØDefining as the total offered traffic we have: ØCriterion I: choose k s. t. D. Miorandi & A. Zanella Med-Hoc-Net, Chia, 6 September 2002

Suboptimal Criterion ØThe effective offered traffic is given by: ØReasoning: üThe more the effective traffic, the closer we get to the stability limit. üThe closer to the stability limit, the higher the delay. ØCriterion II: choose k s. t. D. Miorandi & A. Zanella Med-Hoc-Net, Chia, 6 September 2002

Results (1) ØAt medium-to-high loads, both criterion offer a remarkable performance improvement. ØThe suboptimal criterion leads to results good, even if far from optimality. N=5, matrix entries uniformly distributed in (0, 1). D. Miorandi & A. Zanella Med-Hoc-Net, Chia, 6 September 2002

Results (2) ØThe delays are much lower in the sparse case. ØBoth criterion offer valuable performance improvement. N=5, matrix entries uniformly distributed in (0, 1), average density of 0. 4. D. Miorandi & A. Zanella Med-Hoc-Net, Chia, 6 September 2002

Applications ØOptimal design of a static Bluetooth piconet (e. g. , sensor networks). ØDynamic reconfiguration of a Bluetooth piconet: üEach node keeps an estimate of the traffic generated towards the other nodes. üThe suboptimal criterion is used to find “better” configurations. üConnection admission control: for each request the master checks for admissibility of the resulting traffic matrix; if the answer is negative the request is dropped. D. Miorandi & A. Zanella Med-Hoc-Net, Chia, 6 September 2002

Conclusion ØAn analytical settlement for the characterization of efficient piconet topologies has been proposed. ØTwo algorithms for the master choice (an optimal and a suboptimal with low computational complexity) have been presented. ØSimulation have been performed to show the impact on network performance. ØSome applications have been presented. ØNext step: towards efficient scatternet topologies. D. Miorandi & A. Zanella Med-Hoc-Net, Chia, 6 September 2002

Any Questions? D. Miorandi & A. Zanella Med-Hoc-Net, Chia, 6 September 2002