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Design and Analysis of Bluetooth Data Communication Issues

Explore Bluetooth protocol stack, piconet and scatternet problems, and propose a novel sniff scheduling protocol for power saving. Evaluate the impact on power consumption and throughput in experimental scenarios.

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Design and Analysis of Bluetooth Data Communication Issues

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  1. Design and Analysis of Data Communication Problems in Bluetooth Wireless Personal-Area Networks Ting-Yu Lin (林亭佑) Department of Electrical and Computer Engineering National Chiao Tung University, Bun Lab.

  2. Agenda • Bluetooth Standard Overview • Talk Structure • Piconet Issues Addressing (Parts I & II) • Scatternet Problems Resolving (Parts III & IV) • Conclusions • Future Directions • References

  3. Bluetooth Standard Overview • Master-driven short-range wireless radio technology • Operate at 2.4 GHz unlicensed ISM band • TDD/FHSS with nominal rate 1600 hops/sec and 23/79 frequencies available, each of 1 Mbps symbol rate • Transmission range: 10, up to 100 meters • Physical links: - SCO (Synchronous Connection-Oriented) for voice slot reservation at fixed intervals - ACL (Asynchronous ConnectionLess) for data polling access scheme

  4. Bluetooth Standard Overview • Bluetooth protocol stack • Addressing - 48-bit Bluetooth Device Address (BD_ADDR) - 3-bit Active Member Address (AM_ADDR) - 8-bit Parked Member Address (PM_ADDR) • Four operational modes - Active, Sniff, Hold, Park

  5. Bluetooth Network Topology • Piconet - Master can connect to at most 7 active/sniff/hold slaves simultaneously per piconet • Scatternet - Interconnecting multiple piconets to form a larger network Bridge Bridge

  6. MASTER ACL ACL ACL SCO SCO SCO SCO ACL SLAVE 1 SLAVE 2 SLAVE 3 Packets Exchange Scenario

  7. Bluetooth Frequency Hopping

  8. Talk Structure

  9. Part ISniff Scheduling for Power Saving < Low-power sniff mode in Bluetooth specification > Slot pair

  10. Sniff Scheduling • Problem Statement - Open issue: how to determine the sniff-related parameters based on different traffic loads? - Goal: balancing tradeoff between power conservation and traffic need • Deficiencies of Previous Works - Each slave is considered independentlyof others - Most works are restricted to a naive exponential adjustment in either sniff interval or active window - The placement of active windows on the time axis when multiple sniffed slaves are involved is ignored

  11. Sniff Scheduling • Architecture of Our Sniff Scheduling Protocol

  12. Evaluation Period Basic Idea • Sniff timing for slave k (unit = slot pair) • Slot occupancy = (active window size) / (sniff interval) • Our Evaluator is performed periodically to check the slot utilization status and determine an appropriate slot occupancy (reduction/increase/no change) for slave k = 20/60 = 1/3

  13. Evaluator • Uk: the slot utilization of the sniff-attempt slots assigned to slave k. • Bk: the buffer backlog for slave k, indicating the number of packets currently queued in the local Baseband buffer. • Wk: a weighted value derived from Uk and Bk to indicate the utilization ratio of time slots assigned to slave k. Bmax is the maximum buffer space and 0 ≦α≦ 1 Wk = βWk’ + (1-β) WkWk’is the history value, 0 ≦β ≦ 1 • Tk,Nk,Ok: the current sniff parameters (sniff interval, active window size, and offset, respectively) associated with slave k. • Sk: the desired slot occupancy of slave k derived by the following equation. This value is the expected ratio of the new Nk to the new Tk. where 0 < δ < 1

  14. Calculator X (factor α) Calculator Y (factor δ) Wk Sk • Example Evaluation Period α= 0.5 δ= 0.8 Evaluator for slave k Uk Bk/Bmax Uk= 16 (used) / 80 (reserved) = 0.2 Bk/Bmax= 7 (queued) / 50 (buffer size) = 0.14 Wk= 0.5 x 0.2 + 0.5 x 0.14 = 0.17 Sk= 0.17 x 1/3 (slot occupancy) / 0.8 = 0.07 = 1/15

  15. Evaluator for slave k • Possible sniff timings to satisfy 1/15 slot occupancy

  16. 120 (max. sniff interval) 2-D finite matrix M 15(min. sniff interval) Resource Pool (RP) 1-D infinite vector V

  17. Scheduling Policy • Recall that the Evaluator for Slave1 concludes that its slot occupancy should be reduced from 1/3 to 1/15 • Possible scheduling Slave1 must first give back the 1/3 slot occupancy Scheduler tries to find a sniff pattern satisfying 1/15 slot occupancy Or 2/30 Or 4/60 Or 8/120 • Two scheduling policies are proposed - LSIF (Longest Sniff Interval First), which starts searching with the longest interval - SSIF (Shortest Sniff Interval First), which starts searching with the shortest interval

  18. Experimental Environment • 2-state MMPP traffic model • 5 slaves in the piconet • α = 0.7 • δ = 0.5 • Resource Pool (RP) size = 100 x 4 = 400 (slot pairs)

  19. (a) Power Consumption With Buffer Size≧ 30 Our LSIF/SSIF achieve (Compared to AA) • 37 % reduction in power consumption • 16 % improvement in throughput AA: Always Active with Round Robin polling policy AS_VSI: Always Sniff Varying Sniff Interval AS_VAW: Always Sniff Varying Active Window Buffer Size Bmax (b) Throughput Buffer Size Bmax

  20. Summary of Contributions • Features of Proposed Solution - An adaptive sniff scheduling scheme is proposed to consider multiple slaves simultaneously. - Our scheduling is more accurate in determining the sniff- related parameters based on slaves’ traffic loads. - Our proposal includes the placement of active windows of sniffed slaves on the time axis.

  21. Part IILink Polling Policy by Pattern Matching • Observations • Few works consider the asymmetric up-/down-link traffics between master and slave. • The incorporation of packet type selection into polling policy remains unaddressed before this work.

  22. β Pattern Matching Polling (PMP) • This work focuses on the Bluetooth ACL link. • Assuming error-free, only DH1/3/5 are considered. • Bandwidth Efficiencyβ is defined as the number of payload bytesper non-empty slot.

  23. Motivation(A Naive Greedy Polling Example) β = (16*(20+2)) / (5+3) = 44 • Bandwidth Efficiency unit = bytes/slot

  24. Motivation(A Pattern Matching Polling Example) • Bandwidth Efficiency β = (26*(20+2)) / (5+3+1+1) = 57.2 (23% improvement)

  25. Pattern Matching Polling (PMP) • Two problems need further elaboration in PMP: • How to determine a most bandwidth efficientpolling pattern? 2. Given a most efficient pattern, how to schedule polling timings?

  26. Polling Patterns Parameters - Consider a master-slave pair with λM and λS (bytes/slot) as their traffic loads. - Let λH = max{λM , λS}, λL = min{λM , λS}, and ratio ρ = λH / λL. - Denote by NH and NL the units with loads λH and λL , respectively. - Use numbers 1/3/5 to represent DH1/DH3/DH5 packets. - A polling pattern is a sequence of packet types that will be exchanged by a master-slave pair.

  27. Polling Patterns • A length-k pattern (k is a positive integer) consists of two k-tuples: (H1, H2, …, Hk) and (L1, L2, …, Lk), where Hi , Li = 1, 3, or 5, each representing a packet type. • Intuitively, the sequence of packets (H1, L1, H2, L2, …, Hk, Lk) will be exchanged by NH and NL, and the sequence will be repeated periodically, as long as the ratio ρ is unchanged and there is no bursty traffic.

  28. Impact of Pattern Length • As k grows, the number of offered traffic ratios ρ will increase exponentially.

  29. Bandwidth Efficiency • Given traffic loads λH and λL of a master-slave pair, we propose to select the polling pattern that gives the highest bandwidth efficiency β for use.

  30. Γ1 Γ2 Γk Reference point Polling Timings • Let j be a positive integer ≦k(within one iteration of the pattern)

  31. Γ1 Γ2 Pattern Matching Polling Example • Based on λH and λL, the most efficient polling pattern (5, 3) (1, 1) is selected. • Γ1 = 16, Γ2 = 26, β = 57.2 (23% improvement) • Note thatan overflow bit is also implemented in our PMP policy to prevent buffer overloading when bursty traffic occurs.

  32. Experimental Environment • 7 active slaves in a piconet • Buffer size for each slave = 2048 bytes • Three other polling strategies are implemented - NGP: Naive Greedy Polling (p.23) - ERR: Exhaustive Round Robin (ref. A. Capone et. al.) - StickyAFP: StickyAdaptive Flow-based Polling (ref. A. Das et. al.)

  33. K: max. allowable • pattern length • Piconet Throughput • Average Delay When λ≧ 65 (bytes/slot) Our PMP achieves (Compared to NGP) • 17 % improvement in throughput • 14 % reduction in average delay

  34. Summary of Contributions • Features of Proposed Solution - An efficient Pattern Matching Polling (PMP) policy is proposed to handle asymmetric up-/down-link traffics and exploit different Bluetooth packet types. - The ultimate goal is to reduce the unfilled, or even null, payloads in each busy slot. • When multiple links (master-slave pairs) exist, bandwidth efficiency of each single link does determine the max. allowable throughput within a piconet (piconet capacity).

  35. Part IIIBlueRing:A New Scatternet Topology for Bluetooth

  36. BlueRing • Scatternet Structure • Routing Protocol • Topology Maintenance Mechanism

  37. Motivation • Deficiencies of Previous Works - Most star- or tree-shaped scatternet topologies suffer from a communication bottleneck at the root as the network enlarges. - How to route packets once the scatternet is formed remains unaddressed. - Topology maintenance (fault-tolerance) issues are not properly addressed.

  38. BlueRing Structure • Upstream/Downstream Piconet • Upstream/Downstream Master • Upstream/Downstream Bridge Master/Bridge interleaving

  39. BlueRing Routing Protocol • General baseband packet format • Payload header formats: (a) single-slot packets and (b) multi-slot packets

  40. BlueRing Routing Protocol • Payload formats in BlueRing: (a) single-hop unicast communication, (b) multi-hop unicast communication, and (c) scatternet broadcast communication • The fields in gray are what added by BlueRing

  41. BlueRing Recovery Protocol • We propose to use 2 DIACs (from 63 reserved DIACs), say DIAC1 and DIAC2, to facilitate BlueRing recovery/extension. • The general GIAC will be used to invite new hosts to join an existing BlueRing. • Bridge missing recovery: (a) DIAC1 discovering and (b) the reconnected BlueRing.

  42. BlueRing Recovery Protocol • Master missing recovery: (a) DIAC1 discovering and (b) the reconnected BlueRing.

  43. BlueRing Extension Protocol • In BlueRing, each master should execute GIAC inquiry from time to time. • When the number of slaves belonging to a master exceeds a certain limit, sayα(α≧ 4), we will split it into two piconets. • The master should send out a split_request token to obtain split permission from all other masters (concurrent splitting avoidance).

  44. Once the split request is approved by all piconets on the ring, the master detaches its upstream bridge and two non-bridge slaves. (b) (a) A BlueRing extension example with α= 4 (c)

  45. Experimental Environment • Only DH1 packets are simulated • No mobility is modeled • Each ACL connection could be intra- or inter-piconet communication with data rate of 256K bps

  46. Simulated topologies with 21 hosts • Star-shaped structure with a piconet as the central gateway • BlueRing with 3 piconets, each containing 7 slaves • Single-piconet structure containing all 21 nodes in a single piconet (park mode is used)

  47. (a) Throughput (21 % increased, compared to Star-shaped) (b) Average packet delays (38 % reduced, compared to Star-shaped)

  48. Summary of Contributions • Features of Proposed Solution - Routing on BlueRing is stateless. - BlueRing architecture is simple and scalable. - Maintaining a BlueRing is an easy job.

  49. Part IVCollision Analysisfor a Multi-Piconet Environment

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