MAC Scheduling Policies for Power Optimization in Bluetooth: A Master Driven TDD Wireless System

1. MAC Scheduling Policies for Power Optimization in Bluetooth: A Master Driven TDD Wireless System Sumit Garg, Manish Kalia, Rajeev Shorey IBM India Research Laboratory. VCT 2000-Spring, Volume: 1, 2000 Page(s): 196 -200 vol.1 Speaker: Chung-Hsien Hsu Chung-Hsien Hsu

2. Outline • Introduction • The Bluetooth Standard • Power Optimization Parameter • Power Optimization Policies • Simulation • Conclusion Chung-Hsien Hsu

3. Introduction • Power at the mobile nodes is a limited resource. • Optimize power consumption at the nodes in a wireless network. • Propose and study policies that can be effectively employed in Master driven TDD based systems such as Bluetooth. • Study MAC scheduling algorithems with the aim of power optimization in Bluetooth. Chung-Hsien Hsu

4. The Bluetooth Standard • BT has four operational modes for a BT unit: • Active • Sniff • Hold • Park low power Chung-Hsien Hsu

5. The Bluetooth Standard (cont.) • Sniff mode even slots ( Slave listens for a Master transmission ) Chung-Hsien Hsu

6. The Bluetooth Standard (cont.) • In this paper, it propose policies that use the sniff mode at the Slaves to optimize power consumption. • Increasing system throughput. • Reducing system delays. • Hold mode: • Slots are wasted in deciding the hold mode parameter. • Park mode: • Slots are wasted in parking and unparking a Slave. Chung-Hsien Hsu

7. Power Optimization Parameter • Measuring only the total power consumed by a system without taking throughput into account does not give a true measure of power utilization of the system. Chung-Hsien Hsu

8. Power Optimization Parameter (cont.) • PPR (Power-Packet Ratio) • Power consumed by the Slave nodes in transmitting/receiving 1000 single slot length packets to/from the Master. • slot utilization • As a measure of backlog at a MSP inBluetooth • The ration of the slot-pairs used (for data transfer) by an MSP to the total slot-pairs alloted to the MSP. • Ex: slot utilization = 0.8 • MSP was able to utilize 80% of the slots allocated to it. Chung-Hsien Hsu

9. Power Optimization Policies • In naïve Round Robin (RR) : • Slave is always in active mode leading to a high power consumption. • Leading to slot wastage and a high PPR. • It proposes policies that modify two sniff mode parameters: • Tsniff (Sniff Interval) and Nsniff-Attempt (Serving Time) Chung-Hsien Hsu

10. Varying the Tsniff Varying the Nsniff-Attempt Varying the Tsniff and Nsniff-Attempt Power Optimization Policies (cont.) • Policies: • BRR (Batched Round Robin) • VSI (Variable Sniff Interval) • LBS (Load Based Service) • GBS (Group Based Service) Chung-Hsien Hsu

11. Power Optimization Policies (cont.) • It assumed: • Measuring the power consumption at the Slaves only. • All Slaves are in active mode ( no Slave in Hold/Park.) • The number of slaves in a pico-cell remains constant. • Do not take into account fading and interference in the wireless. Chung-Hsien Hsu

12. BBR (Batch Round Robin) • Serve MSPs in RR fashion. • Each MSP is served for Nbrr contiguous slots. • For every MSP, it maintains an average slot utilization parameter as a measure of data queues at MSP. • It doubles the Tsniff interval for a Slave with slot utilization below a threshold (Ulow) • MSP with slot utilization above a threshold, Uhigh, is served in the slots left vacant. Chung-Hsien Hsu

13. BBR (Batch Round Robin) (cont.) • This policy improves throughput (by minimizing wastage) as well as optimizes the power consumption at the Slaves. Chung-Hsien Hsu

14. VSI (Variable Sniff Interval) • To very the Tsniff interval of different Slaves according to the average slot utilization parameter. • The serving interval, Nvsi is kept constant. • The MSPs with low load are given higher Tsniff and vice-versa. • Tsniff of an MSP is determined independent of other MSPs. • Some slots exist when no Slave is in the active mode. • More than one Slave can be active at the same time. Chung-Hsien Hsu

15. VSI (Variable Sniff Interval) (cont.) • In the empty slots (no Slave active): • Continue serving the MSP last served. • More than one Slaves are active during a slot interval: • Serving these Slaves in RR. Chung-Hsien Hsu

16. LBS (Load Based Service) • To very the NSniff-Attempt. • It defines Cperiod as a slot interval of constant size. • All MSPs are alloted contiguous slots, Ni, in the interval Cperiod in proportion to their average slot utilization parameters. • This policy is similar to Max-Min Fair Share algorithm [7]. Chung-Hsien Hsu

17. LBS (Load Based Service) (cont.) • Slot utilization parameters of all MSPs are initialized to 0.5 and MSPs are alloted equal number of slots. • When the slot utilization parameter of a MSP falls below a threshold, the number of slots alloted to it are reduced. Chung-Hsien Hsu

18. LBS (Load Based Service) (cont.) • Number of slots alloted to a MSP is nearly in proportion to the utilization parameter. Chung-Hsien Hsu

19. GBR (Group Based Service) • To very both the parameters according to the backlog information. • It divides the set of Slaves into groups. • Each group is served for a fixed number (Ngbs) of contiguous slots. • Tsniff = Ngbs * (no of groups) Chung-Hsien Hsu

20. GBR (Group Based Service) (cont.) • Regulations: • Different groups in turn are served based upon the RR policy. • Slaves in a group are in active mode only when their group is being served. • Within each group, backlogged MSPs are served in RR. Chung-Hsien Hsu

21. GBR (Group Based Service) (cont.) • Group configuration depends on the slotutilization parameters of the MSPs. • Group split: • A group has more than one MSP with high slot utilization parameter. • A high slot utilization MSP is put in the new group. Chung-Hsien Hsu

22. GBR (Group Based Service) (cont.) • Group remove: • Any group has all MSPs with low slot utilization parameter. • The MSPs of this group are distributed among other groups. Chung-Hsien Hsu

23. Simulation • It studies the performance of the various scheduling policies with varying parameters. • GBS : Ngbs • BRR : Nbrr • VSI : Nvsi • LBS : Cperiod Chung-Hsien Hsu

24. Simulation (cont.) • It assumes: • Receiving a packet of one slot length, a Slave consumes 1 unit of power. • Transmission of a single slot length packet consumes 2 units of power. • Receiving the header consumes 1/6 units of power. • Transmitting the acknowledgement consumes 1/3 units of power. • Looking at a single pico-cell with no parked Slaves and do not take into account issues like fading, interference etc. Chung-Hsien Hsu

25. Simulation (cont.) • The total power consumption is reduced by more than 14%, with significant throughput increase as compared to RR. • The PPR reduces by more than 30% as compared to naïve RR. • It is incorrect to compare the four policies in terms of rate of degradation with the parameter. Chung-Hsien Hsu

26. Simulation (cont.) Chung-Hsien Hsu

27. Simulation (cont.) Chung-Hsien Hsu

28. Simulation (cont.) Chung-Hsien Hsu

29. Simulation (cont.) Chung-Hsien Hsu

30. Conclusion • It proposed new dynamic scheduling algorithms for MAC that attempt to optimize power consumption of Slaves in Master driven TDD pico-cellular wireless systems. • All algorithms take decisions on the basis of slot utilization at the Slaves. • The algorithms yield significant power optimization over the naïve policies such as RR. Chung-Hsien Hsu