Nov Chung-Hsien Hsu1 Round Robin with Look Ahead: A New Scheduling Algorithm for Bluetooth Daqing Yang, Gouri Nair, Balaji Sivaramakrishnan, Harishkumar Jayakumar and Arunabha Sen ICPPW’ IEEE Speaker: Chung-Hsien Hsu

Nov Chung-Hsien Hsu2 Outline  Introduction  Bin Packing Problem  Scheduling Algorithm –Look Ahead –Look Ahead Round Robin  Simulation  Conclusion

Nov Chung-Hsien Hsu3 Introduction SCO: Synchronous Connection Oriented ACL: Asynchronous Connectionless Links frame

Nov Chung-Hsien Hsu4 Introduction  Objective: –To achieve high channel utilization. (throughput).

Nov Chung-Hsien Hsu5 Bin Packing Problem  Bin Packing Problem: –A set of objects L = { a 1,…,a n } with a size s(a i ) –A set of bins with a fixed capacity B –Objective: To pack the objects a i, 1<=i<=n, into as few bins as possible.

Nov Chung-Hsien Hsu6 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 Chung-Hsien Hsu7 Bin Packing Problem (cont.) M S1S1 S2S2 MQ 1 ( 5,5,5,5,5)MQ 2 ( 1,1,1,1,1) SQ 1 ( 5,5,5,5,5) SQ 2 ( 1,1,1,1,1) CMSQ 1 ( 10,10,10,10,10)CMSQ 2 ( 2,2,2,2,2) Bluetooth:

Nov Chung-Hsien Hsu8 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 Chung-Hsien Hsu9 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 A L = (a 1,a 2,…,a n ) : the packets being scheduled by algorithm A

Nov Chung-Hsien Hsu10 Scheduling Algorithm (cont.)  Theorem: –For the Round Robin scheduling algorithm A in Bluetooth, R A = 5/3 Proof: Bin sizes: 10 Item 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/12 R A = 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 Chung-Hsien Hsu11 Scheduling Algorithm (cont.)  Look Ahead  Look Ahead Round Robin

Nov Chung-Hsien Hsu12 Look Ahead Step 1: Examine the (Head-Of-the-Line) packets CMSQ 1,…CMSQ x 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 Chung-Hsien Hsu13 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 Chung-Hsien Hsu14 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 Chung-Hsien Hsu15 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 Chung-Hsien Hsu16 Look Ahead Round Robin (cont.)  Example 1: Support the number of packets in each queue is n. Queue 1: L 1 = (6, 6, 6, 6, 6, …) Queue 2: L 2 = (8, 8, 8, 8, 8, …) Queue 3: L 3 = (4, 4, 4, 4, 4, …) Queue 4: L 4 = (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 Chung-Hsien Hsu17 Look Ahead Round Robin (cont.)  Example 2: Support the number of packets in each queue is n. Queue 1: L 1 = (6, 6, 6, 6, 6, …) Queue 2: L 2 = (6, 6, 6, 6, 6, …) …… Queue 2k-1: L 2k-1 = (6, 6, 6, 6, 6, …) Queue 2k: L 2k = (8, 8, 8, 8, 8, …) Queue 2k+1: L 2k+1 = (4, 4, 4, 4, 4, …) Queue 2k+2: L 2k+2 = (4, 4, 4, 4, 4, …) …… Queue 4k-1: L 4k-1 = (4, 4, 4, 4, 4, …) Queue 4k: L 4k = (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 Chung-Hsien Hsu18 Look Ahead Round Robin (cont.)  Example 3: Support the number of packets in each queue is n. Queue 1: L 1 = (6, 6, 6, 6, 6, …) Queue 2: L 2 = (6, 6, 6, 6, 6, …) …… Queue 2k: L 2k = (6, 6, 6, 6, 6, …) Queue 2k+1: L 2k+1 = (8, 8, 8, 8, 8, …) Queue 2k+2: L 2k+2 = (4, 4, 4, 4, 4, …) Queue 2k+3: L 2k+3 = (4, 4, 4, 4, 4, …) …… Queue 4k+1: L 4k+1 = (4, 4, 4, 4, 4, …) Queue 4k+2: L 4k+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 Chung-Hsien Hsu19 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 Chung-Hsien Hsu20 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 Chung-Hsien Hsu21 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 Chung-Hsien Hsu22 Simulation (cont.) Number of Slaves Average % Savings from RR LARR LA

Nov Chung-Hsien Hsu23 Simulation (cont.) Arrival rates Average % Savings from RR LARR LA

Nov Chung-Hsien Hsu24 Simulation (cont.) Arrival rates Average % Savings from RR LARR LA

Nov Chung-Hsien Hsu25 Simulation (cont.) Arrival rates Average % Savings from RR LARR LA

Nov Chung-Hsien Hsu26 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.

Nov Chung-Hsien Hsu27 Conclusion (cont.)  LARR better than LA –Computational complexity is smaller. –To avoid starvation.  Currently Examining the efficacy of these two algorithms from the power consumption point of view.