Post on 20-Dec-2015
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Data Scheduling and SARfor Bluetooth MAC
Manish Kalia, Deepak Bansal, Rajeev Shorey
IBM India Research Laboratory
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Outline
• Medium Access Control in Bluetooth
• Problems & Restrictions faced in Bluetooth MAC
• Goals, Assumptions & Approaches
• Priority Policy (PP)
• K-Fairness Policy (KFP)
• Scheduling Data in Presence of Voice
• Bluetooth SAR Policy & Possible Improvements
• Results & Conclusion
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Medium Access Control in Bluetooth
• TDD slot structure with strict alternation of slots between the Master and the Slaves
• Single point of coordination (at Master)
• Polling based
• A slave transmits packets in the reverse slot only after the Master polls the slave in a forward slot
• Thus, Bluetooth is a Master driven, polling based TDD standard
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Problems & Restrictions
• Conventional scheduling policies such as Round Robin (RR) does not perform well
• Bluetooth MAC enforces tight coupling of uplink & downlink, which leads to slot wastage
• TDD structure also restricts the packet size (1,3 or 5)
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Goals, Assumptions & Approaches
• Parameters of interest:
• system throughput
• packet delays
• fairness
• packet drop probability
• simplicity
• satisfying the low cost objective of Bluetooth standard.
conflicting
objectives
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Goals, Assumptions & Approaches (Continues...)
Criterias that an efficient scheduling policy would depend on:
• state of the queues at the Master and the Slaves
• traffic arrival process at these queues
• packet length distributions
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Goals, Assumptions & Approaches (Continues...)
• N queues at the Master for a piconet with N slaves
• Each slave has a queue for its connection with the Master
• Binary information is used in order to represent the state of the queues:
• 1 : has data to send 0: has no data awaiting
• State of the queue at the Slave is available at the Master (requires only 1 bit of information to transfer)
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Priority Policy (PP)
• There are four possibilities for the state of the queues regarding a connection:
• 1-1: Both Master and Slave have data to send
• 1-0 or 0-1: Only one side has data awaiting
• 0-0: Neither of them has data to send• PP assigns different priorities to these:
• 1-1 > 1-0 = 0-1, 0-0 is not scheduled
• It is also argued that it could be 1-0 > 0-1(*)
* Master:1 – Slave:0 > Master:0 – Slave:1
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K-Fairness Policy (KFP)• Beyond optimization and system throughput:
Having a strict fairness bound• qmax: Master-Slave queue pair that has
received maximum excess service (service sacrified to it)
• qmin: Master-Slave queue pair that has sacrificed maximum service to other connections
• (Services of qmax – Services of qmin) can be at most K
• When K = 0, KFP tuns out to be pure Round Robin
• In order to prevent more sacrifices: Change 1-0 into 1-1
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Scheduling Data in Presence of Voice
• Extend PP (to HOL-PP) & KFP (to HOL-KFP)
• Consider slot utilization by using Head-of-the-line (HOL) packets (higher utilization -> higher priority)
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Bluetooth SAR Policy & Possible Improvements
•Bluetooth Segmentation and Reassembly (SAR):
• naive SAR is random: assigns data packet sizes (1, 3 or 5) probabilistically.
• Instead, data arrival rates at the Master and Slave queues can be used -> Intelligent SAR (ISAR) (?):
• Initially all queues have packet size of 1
• Packet sizes change according to the differences in arrival rates at the Master and Slave
• Binary information represent high/low data rates
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Results & Conclusion
• Simulation results (K=500 & P=4, for 5000 TDD slots):
• KFP > PP > RR in throughput
• KFP < PP < RR in average delay (units of slots)
• KFP gives better throughput than PP with more fairness
• ISAR > SAR by means of throughput
• Keep It Simple and Stupid!
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Interconnecting Bluetooth-like Personal Area Networks
Godfrey Tan
MIT Laboratory of Computer Science
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Outline
• Conclusion
• Challenges of Interconnecting Bluetooth-like PANS & proposed solutions for each:
• Scatternet topology formation
• Packet routing
• Channel or link scheduling
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Scatternet Formation• Decentralized and self-healing algorithm
• Unique address for each node that are connected in a tree structure (constructed incrementally)
• Loop-free
• No packet overhead
• No periodic routing messages
• New nodes join with search announcements (root or the new node can choose among possible points of attachement)
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Scatternet Formation (Continues...)
0N
0*
10N-1
1*
11*
110N-
2
10*
101*
100*
1010N-3
1011*
1010*
10110N-
4
• bk = k b’s, where
b = 0 or 1
• Each node holds the portion of the address space allocated to each child
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Packets Relaying & Channel Scheduling
• Relaying of packets are accomplished by means of a technique that is similar to forwarding of IP packets
• makes use of longest-prefix match• Channel scheduling problem is declared to be similar to the maximal matching problem for bi-partite graphs
• An upper-bound of ceiling(d/2)*MaxDegree(*) is given for an algorithm of which details are not given
* MaxDegree = depth of the tree, d = distance in hops
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Conclusion
• It is declared that the algorithms are implemented in ns-2 and give good performance but simulation results are not presented
• The key idea is to construct the scatternet as a tree
• makes other problems easy to keep track of
• If the root is the one that hadle new attachements, it would have large overhead
• Enforcement of tree structure may cause deficiencies
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Scatternet Structure and Inter-Piconet Communication in the Bluetooth System
Manish Kalia, Sumit Garg, Rajeev Shorey
IBM India Research Laboratory
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Outline
• Piconet models and possible scatternet structures
• Single Piconet Model (SPM)
• Scatternet Model
• Two-Level Hierarchy of Piconets (TLP)
• Shared Slave Piconets (SSP)• Performance Comparisons & Conclusion
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Single Piconet Model (SPM)
• Single piconet is used even if there exists more then seven slaves
• Model uses the “Park mode”
• Timestamps are used in order to determine the period in which a slave remained parked/unparked
• Periodically, parked Slave with the oldest timestamp is unparked and active Slave with oldest timestamp is parked
• Each Slave remains unparked for the same time period
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Scatternet Model
• Notion of a “Communicating Group” (CG): A group of mobile devices which have frequent data transfer in between
• When forming scatternets try to make members of a CG reside in the same piconet
• Start with a SPM, structure the scatternet by collecting traffic flow patterns
• Master can observe destination addresses (Efficient policies for discovering and updating CGs are not investigated)
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Two-Level Hierarchy of Piconets (TLP)
• Centralized design
• Notion of root & leaf piconets
• Masters of leaf piconets periodically become slaves of the root piconet (temporary Masters can be assigned)
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Shared Slave Piconets (SSP)
• Decentralized structure
• A Slave in between, periodically switchs to the hopping pattern of two different Masters.
• Better load balancing & robust
• Routing is more complex
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Performance Comparisons & Conclusion
• Simulation results with to piconets:
• System throughput: SSP > TLP > SPM
• Average System Delays SPM >> TLP > SSP
• Scatternet allows simultaneous communication in different piconets
• In TLP leaf piconets periodically suspend communication
• SPM can be improved by considering backlogged data at the Slave queues