2002/9/17 Chung-Hsien Hsu 1

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

System

Sumit Garg, Manish Kalia, Rajeev ShoreyIBM India Research Laboratory.

VCT 2000-Spring,Volume: 1, 2000 Page(s): 196 -200 vol.1

Speaker: Chung-Hsien Hsu

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Outline

Introduction The Bluetooth Standard Power Optimization Parameter Power Optimization Policies Simulation Conclusion

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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 po

wer optimization in Bluetooth.

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The Bluetooth Standard

BT has four operational modes for a BT unit:– Active

– Sniff

– Hold

– Park

low power

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The Bluetooth Standard (cont.)

Sniff mode

even slots ( Slave listens for a Master transmission )

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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.

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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.

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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 in Bluetooth– 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.

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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)

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Power Optimization Policies (cont.)

Policies:– BRR (Batched Round Robin)

– VSI (Variable Sniff Interval)

– LBS (Load Based Service)

– GBS (Group Based Service)

Varying the Tsniff

Varying the Nsniff-Attempt

Varying the Tsniff and Nsniff-Attempt

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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.

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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.

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BBR (Batch Round Robin) (cont.)

This policy improves throughput (by minimizing wastage) as well as optimizes the power consumption at the Slaves.

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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.

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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.

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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].

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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.

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LBS (Load Based Service) (cont.)

Number of slots alloted to a MSP is nearly in proportion to the utilization parameter.

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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)

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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.

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GBR (Group Based Service) (cont.)

Group configuration depends on the slot utilization 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.

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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.

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Simulation

It studies the performance of the various scheduling policies with varying parameters.– GBS : Ngbs

– BRR : Nbrr

– VSI : Nvsi

– LBS : Cperiod

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Simulation (cont.)

It assumes:– Receiving a packet of one slot length, a Slave consume

s 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.

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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.

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Simulation (cont.)

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Simulation (cont.)

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Simulation (cont.)

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Simulation (cont.)

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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.