Bluetooth Scatternets: Enhanced Adaptive Scheduling Schema

1. Bluetooth Scatternets:An Enhanced Adaptive Scheduling Schema Simon Baatz Matthias Frank Carmen Kühl Peter Martini Christoph Scholz presented by Metin Tekkalmaz

2. Outline • Introduction • Related Bluetooth Topics • Challenges in Scatternet Formation • Credit Based Approach • Performance Enhancements • Conclusion

3. Introduction • The Goal is to schedule the data traffic in the scatternet • Paper discusses one of the ways of this which, • Adapts to varying traffic patterns • Is based on sniff mode • Does not need much modifications on current spec

4. Related Bluetooth Topics • Poll - Null messages • Maximum Poll interval • Sniff Mode

5. Challanges (1/3) • Scatternets need some nodes to be connected with multiple piconets • different hop sequences • different timing • Single transceiver: Single hopping schema at a time • Switching is a necessity - in TDM

6. Challanges (2/3) • Different slot boundaries • High vs. Low switching frequency • Throughput vs. Delay

7. Challanges (3/3) • Scheduling Switches • Switching but, when and to where • How the coordination is achieved? • Is “Presence Schedule” a solution?

8. Credit Based Approach (1/5)Presence Point Concept (let’s call it PP) • “Presence Points” (o/l) instead of “Presence Schedules” (a priori) • PP is where communication on a link (between Master & Slave) may start • Quickly determine if peer is available • Begin communication if available • Try another PP otherwise • Communication period is not predetermined

9. Credit Based Approach (2/5)PP implementation w/ Sniff Mode • Let the sniff slots be the PPs • Maximize probability of a common sniff slot • Continue sniff event until one or both sides decide to abort • Max. poll interval provides QoS • When and Where problem is still unsolved

10. Credit Based Approach (3/5)The Solution: Credit Schema • Devices assign priorities to each link, locally • Priority is per peer, not per link i.e. Different devices may assign different priorities to the same link • A link has a higher priority if it has been treated relatively unfair • Assign credits to each link to keep track of relative fairness

11. Credit Based Approach (4/5)Credit Schema • One credit is charged from its credit account if that link is used • If a slot is not used at all a special temporary account is debited • To keep the system balanced increase the temporary if a credit is debited from a link’s account • Redistribute temp accnt’s savings when it reaches n, which is # of links (QoS charecteristics may be considered)

12. Credit Based Approach (5/5)Credit Schema • Abort an ongoing sniff event if link with upcoming sniff slot has a higher credit • Poll – Null : Switch to next PP • If max. poll interval exceeds give highest priority

13. Performance Enhancementsto minimize # of switches • After communcation begins reserve some number of slots for that comm • May lead to starvation • Switch links only if the difference between the credits is higher that a threshold

14. Performance Enhancementsfor better utilization of Redistribution • Redistribute a link’s credits if it doesn’t use them • Absolute vs. Relative distribution • Relative distribution: • Triggered by Poll-Null

15. Performance EnhancementsAdaptive Presence Point Density (APPD) • Do not waste credit with unseccessful sniff slots or Poll-Null sequences • Double PP intervals for unsuccessfull tries • Assure process is identical at both sides

16. Conclusion • Simulation results are in the paper • Good for arbitrary topologies • No need for scatternet-wide coordination • Easily adapts to the traffic conditions • QoS aspects are open problems • I am impressed!!!