1. 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

2. 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.

3. 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

4. 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):

5. 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:

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.

11. 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.

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