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University of Padova Department of Information Engineering On the Optimal Topology of Bluetooth Piconets: Roles Swapping Algorithms Daniele Miorandi & Andrea Zanella Med-Hoc-Net 2002, Chia (Italy), 6 September 2002 {daniele.miorandi, andrea.zanella}@dei.unipd.it
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Med-Hoc-Net, Chia, 6 September 2002 D. Miorandi & A. Zanella Overview Problem definition: find efficient topologies for Bluetooth networks. First step: study of optimal piconet configurations. Assumption: knowledge of the end-to-end traffic matrix. Stability issues & delay analysis (with Pure Round Robin and Poisson traffic). Metrics: average packet delay. Optimal criterion for off-line topologies design. Suboptimal criterion (lower computational complexity) for real-time network reconfiguration. Conclusion & discussion.
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Med-Hoc-Net, Chia, 6 September 2002 D. Miorandi & A. Zanella Background: BT system architecture Piconet Two up to eight active Bluetooth devices sharing the same FH channel form a piconet. In each piconet, a unit acts as a master, the others act as slaves. Channel access is based on a centralized polling scheme. Full duplex is achieved by means of time division duplexing (TDD). Scatternet: Piconets may overlap and may be connected by means of a shared inter-piconet units (IPUs). IPUs may be shared on a time-division basis, which may be realized using low-power SNIFF mode. active slave master parked slave standby slave1 slave2 slave3 master
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Med-Hoc-Net, Chia, 6 September 2002 D. Miorandi & A. Zanella System Model Cluster of (N+1) nodes ( ). Assumptions: Each node is in the coverage area of all other nodes; The traffic flows may be modeled as independent Poisson processes. End-to-end traffic matrix (average packets generation rates). Piconet definition: Effective traffic pattern matrix (traffic actually flowing on the net):
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Med-Hoc-Net, Chia, 6 September 2002 D. Miorandi & A. Zanella System Model (2) Stability condition for the PRR polling scheme: Definition : 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). Definition : A traffic matrix is fully admissible if the stability conditions hold for any choice of the master k. Proposition : A traffic matrix is fully admissible if and only if the following conditions hold: P roposition : A traffic matrix is admissible if and only if the following conditions hold:
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Med-Hoc-Net, Chia, 6 September 2002 D. Miorandi & A. Zanella Optimal Criterion Link delay: Up to a randomization of the polling order the average packet delay may be expressed as: Defining as the total offered traffic we have: Criterion I : choose k s.t.
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Med-Hoc-Net, Chia, 6 September 2002 D. Miorandi & A. Zanella Suboptimal Criterion The effective offered traffic is given by: Reasoning: The more the effective traffic, the closer we get to the stability limit. The closer to the stability limit, the higher the delay. Criterion II : choose k s.t.
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Med-Hoc-Net, Chia, 6 September 2002 D. Miorandi & A. Zanella Results (1) N=5, matrix entries uniformly distributed in (0,1). At medium-to-high loads, both criterion offer a remarkable performance improvement. The suboptimal criterion leads to results good, even if far from optimality.
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Med-Hoc-Net, Chia, 6 September 2002 D. Miorandi & A. Zanella Results (2) N=5, matrix entries uniformly distributed in (0,1), average density of 0.4. The delays are much lower in the sparse case. Both criterion offer valuable performance improvement.
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Med-Hoc-Net, Chia, 6 September 2002 D. Miorandi & A. Zanella Applications Optimal design of a static Bluetooth piconet (e.g., sensor networks). Dynamic reconfiguration of a Bluetooth piconet: Each node keeps an estimate of the traffic generated towards the other nodes. The suboptimal criterion is used to find “better” configurations. Connection admission control: for each request the master checks for admissibility of the resulting traffic matrix; if the answer is negative the request is dropped.
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Med-Hoc-Net, Chia, 6 September 2002 D. Miorandi & A. Zanella Conclusion An analytical settlement for the characterization of efficient piconet topologies has been proposed. Two algorithms for the master choice (an optimal and a suboptimal with low computational complexity) have been presented. Simulation have been performed to show the impact on network performance. Some applications have been presented. Next step: towards efficient scatternet topologies.
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Med-Hoc-Net, Chia, 6 September 2002 D. Miorandi & A. Zanella Any Questions?
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