Nov. 15 2002Chung-Hsien Hsu1 Round Robin with Look Ahead: A New Scheduling Algorithm for Bluetooth...
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Transcript of Nov. 15 2002Chung-Hsien Hsu1 Round Robin with Look Ahead: A New Scheduling Algorithm for Bluetooth...
Nov. 15 2002 Chung-Hsien Hsu 1
Round Robin with Look Ahead: A New Scheduling Algorithm for Bluetooth Daqing Yang, Gouri Nair, Balaji Sivaramakrishnan,
Harishkumar Jayakumar and Arunabha SenICPPW’02. 2002 IEEE
Speaker: Chung-Hsien Hsu
Nov. 15 2002 Chung-Hsien Hsu 2
Outline
Introduction Bin Packing Problem Scheduling Algorithm
– Look Ahead– Look Ahead Round Robin
Simulation Conclusion
Nov. 15 2002 Chung-Hsien Hsu 3
Introduction
SCO: Synchronous Connection Oriented
ACL: Asynchronous Connectionless Links
frame
Nov. 15 2002 Chung-Hsien Hsu 4
Introduction
Objective:– To achieve high channel utilization.
(throughput).
Nov. 15 2002 Chung-Hsien Hsu 5
Bin Packing Problem
Bin Packing Problem:– A set of objects L = { a1,…,an} with a size s(ai)
– A set of bins with a fixed capacity B– Objective:
• To pack the objects ai, 1<=i<=n, into as few bins as possible.
Nov. 15 2002 Chung-Hsien Hsu 6
Bin Packing Problem (cont.)
Off-line bin packing problem:– Have the complete knowledge of all elements
and their sizes.• Efficiently pack the objects in the bins.
Online bin packing problem:– Limited amount of future knowledge.– The scheduling algorithm for Bluetooth
Nov. 15 2002 Chung-Hsien Hsu 7
Bin Packing Problem (cont.)
M
S1 S2
MQ1 ( 5,5,5,5,5) MQ2 ( 1,1,1,1,1)
SQ1 ( 5,5,5,5,5) SQ2 ( 1,1,1,1,1)
CMSQ1 ( 10,10,10,10,10) CMSQ2 ( 2,2,2,2,2)
Bluetooth:
Nov. 15 2002 Chung-Hsien Hsu 8
Bin Packing Problem (cont.)
Supposition:– The number of slots between every SCO slot
pair is 10.• Frame size = 10
• As a bin with capacity 10.
The packets in the CMSQ can be viewed a objects.
Nov. 15 2002 Chung-Hsien Hsu 9
Scheduling Algorithm
Definition:– Asymptotic worst-case performance ratio
The minimum number of bins required to pack list L
The number of bins used by packing list L
Scheduling Algorithm AL = (a1,a2,…,an) : the packets being scheduled by algorithm A
Nov. 15 2002 Chung-Hsien Hsu 10
Scheduling Algorithm (cont.)
Theorem:– For the Round Robin scheduling algorithm A in
Bluetooth, RA = 5/3Proof:Bin sizes: 10Item sizes: 2, 4, 6, 8, 10.The Round Robin algorithm A guaranteed that any neighboring pair of bins packed item sizes at least 12.If OPT(L) = n the packets need to be packed have size at most 10n.A(L) <= 20n/12RA = 5/3
The Round Robin algorithm A compared with any scheduling algorithm B in Bluetooth, A is at most 5/3 worse than B.
Nov. 15 2002 Chung-Hsien Hsu 12
Look AheadStep 1: Examine the (Head-Of-the-Line) packets CMSQ1,…CMSQx for all the active slaves in the piconet.
Step 2: Prioritize slaves in order of non-increasing size of their HOL packets in CMSQ (the slave with the largest HOL packet has the highest priority).
Step 3: If possible, schedule the highest priority slave in the current frame.
Step 4: If HOL packet of the highest priority does not fit, search through HOL priority list for highest priority that will fit the current frame.
Step 5: If none fits, wait for the start of a new frame and put the HOL packet in the new frame. Repeat step 1 through 5.
Nov. 15 2002 Chung-Hsien Hsu 13
Look Ahead (cont.)
Drawback – Computational overhead may be unacceptably
high.• If N slaves, it can be computed in O(log N) amount
of computation.
– Starvation.
Nov. 15 2002 Chung-Hsien Hsu 14
Look Ahead Round Robin
Round Robin + Look Ahead.– To avoid the starvation.– To reduce the computational complexity.
Different from RR:– When the current packet does not fit,
the algorithm looks ahead and attempt to schedule a packet from next slave in line.
Nov. 15 2002 Chung-Hsien Hsu 15
Look Ahead Round Robin (cont.)
Step 1: The algorithm will fill the current frame with the HOL packets in a Round Robin fashion, if the HOL packet can fit in the frame.
Step 2: If the HOL packet of the queue being serviced is too large to fit in the current frame, following Round Robin fashion, find the queue whose HOL packet will fit in the current frame. If no such queue exists, wait for the start of a new frame and schedule the HOL packet in the new frame. Repeat steps 1 and 2.
Note:
The information (size of the HOL packet in the slave) may be conveyed to the master by slaves using the unused fields in the header of the immediately preceding packet.
Nov. 15 2002 Chung-Hsien Hsu 16
Look Ahead Round Robin (cont.)
Example 1:Support the number of packets in each queue is n.Queue 1: L1 = (6, 6, 6, 6, 6, …)Queue 2: L2 = (8, 8, 8, 8, 8, …)Queue 3: L3 = (4, 4, 4, 4, 4, …)Queue 4: L4 = (2, 2, 2, 2, 2, …)
Round Robin algorithm : 3n frames.Round Robin with 1-look-ahead algorithm : 2n frames.
Performance comparison ratio: 3/2
Nov. 15 2002 Chung-Hsien Hsu 17
Look Ahead Round Robin (cont.)
Example 2:Support the number of packets in each queue is n.Queue 1: L1 = (6, 6, 6, 6, 6, …)Queue 2: L2 = (6, 6, 6, 6, 6, …)……Queue 2k-1: L2k-1 = (6, 6, 6, 6, 6, …)Queue 2k: L2k = (8, 8, 8, 8, 8, …)Queue 2k+1: L2k+1 = (4, 4, 4, 4, 4, …)Queue 2k+2: L2k+2 = (4, 4, 4, 4, 4, …)……Queue 4k-1: L4k-1 = (4, 4, 4, 4, 4, …)Queue 4k: L4k = (2, 2, 2, 2, 2, …)
Round Robin algorithm : 3kn frames.Round Robin with (2k-1)-look-ahead algorithm : 2kn frames.
Performance comparison ratio: 3/2
Nov. 15 2002 Chung-Hsien Hsu 18
Look Ahead Round Robin (cont.)
Example 3:Support the number of packets in each queue is n.Queue 1: L1 = (6, 6, 6, 6, 6, …)Queue 2: L2 = (6, 6, 6, 6, 6, …)……Queue 2k: L2k = (6, 6, 6, 6, 6, …)Queue 2k+1: L2k+1 = (8, 8, 8, 8, 8, …)Queue 2k+2: L2k+2 = (4, 4, 4, 4, 4, …)Queue 2k+3: L2k+3 = (4, 4, 4, 4, 4, …)……Queue 4k+1: L4k+1 = (4, 4, 4, 4, 4, …)Queue 4k+2: L4k+2 = (2, 2, 2, 2, 2, …)
Round Robin algorithm : (3k+1)n frames.Round Robin with 2k-look-ahead algorithm : (2k+1)n frames.
Performance comparison ratio: (3k+1)/(2k+1)
Nov. 15 2002 Chung-Hsien Hsu 19
Simulation
Special situations– Round Robin with k-look-ahead can reduce the
number of frames by 50% over just Round Robin.
General situations:– Turned to simulation.
Nov. 15 2002 Chung-Hsien Hsu 20
Simulation (cont.)
Environment:– Developed in Java
• Create pseudo-parallel packet generation and scheduling.
• Assume packet arrival at the master and the slaves followed a Poisson process.
• Packet size: 1, 3, 5
• Packet be drawn from a uniform distribution.
Nov. 15 2002 Chung-Hsien Hsu 21
Simulation (cont.) Variables:
– The number of slaves in the piconet.• 1 ~ 7
– Packet arrival rate.• 0.1 ~ 1.0
The simulation was carried out for 1000 units of times.
Each experiment was repeated 500 times to compute average frame savings.
Nov. 15 2002 Chung-Hsien Hsu 22
Simulation (cont.)
Number of Slaves
Average % Savings from RR
LARR
LA
Nov. 15 2002 Chung-Hsien Hsu 26
Conclusion
Present two scheduling algorithms for BT.– Look Ahead algorithm– Look Ahead Round Robin algorithm.
LA and LARR perform significantly better than the RR algorithm.