energy-saving scheduling in ieee 802.16e networks chia-yen lin, and hsi-lu chao department of...

Energy-Saving Scheduling in IEEE 802.16e Networks

Chia-Yen Lin, and Hsi-Lu Chao

Department of Computer Science

National Chiao Tung University

< IEEE Conference on Local Computer Networks (LCN) 2008 >

Outline

• Introduction

• Related work– AS and Period algorithms

• Least-Awake-Frames Scheduling (LAFS)– System model

– Phase 1 for UGS connections

– Phase 2 for rtPS and nrtPS connections

– Phase 3 for MSS to determine sleep and awake frames

• Performance Evaluation

• Conclusion

Introduction

• The IEEE 802.16e standard defines three types of power saving classes.

Sleep Mode

Type 1 …

Type 2 …

Type 3 …

Normal Operation Sleep period Listen period

Introduction

• It is not efficient that MSS can only enters sleep mode when all connections have common sleep period.

Connection 1

Connection 2

Connection 3

MSS

Sleep period

Listen period

Related work

• Some papers were proposed to enhance the power saving mechanism in IEEE 802.16e standard.

– Energy-Efficient Sleep-Mode Operation for Broadband Wireless Access Systems. 【 AS】

• IEEE VTC 2006

• You-Lin Chen, and Shiao-Li Tsao

– A Maximal Power-Conserving Scheduling Algorithm for IEEE 802.16e Broadband Wireless Networks. 【 Period】

• IEEE WCNC 2008

• Hsin-Lung Tseng, Yu-Pin Hsu, Chung-Hsien Hsu, Po-Hsuan Tseng, and Kai-Ten Feng

Related work - AS

• The main concept is that choosing the connection with the minimum delay requirement to be the base, and adjusting other connections’ transmissions to reduce total power consumption, but still satisfy connections’ QoS demands.

Listen period Sleep period Listen period Sleep period

Packet Arrivals

Packets Scheduling

maximum delay : 3 frames

Related work - Period

• This algorithm maximizes the duration of the sleep interval based on the pre-defined QoS requirements by discovering a periodic pattern of sleep and awake intervals.

TS

TL

Frame Duration

Bandwidth constraint

Delay constraint

Related work

• The major drawback of AS and Period– they do not consider non-real time connections.

• Motivation and objectives– Design a power saving protocol which is

• suitable for UGS, rtPS, nrtPS and BE service classes,

• guaranteeing QoS demands,

• and lengthening sleep interval.

Least-Awake-Frames Scheduling (LAFS)

• Phase 1– determining awake-frame candidate sets for UGS connections

• Phase 2– determining sleep/awake intervals for connections of the remainin

g service classes, such as rtPS, nrtPS, and BE connections

• Phase 3– determining sleep and awake frames of an MSS

System model in LAFS

• QoS parameters :– p : grant period (frame)

– d : maximum grant delay (frame)

– r : allocated bandwidth per frame (bits/frame)

– μmin : minimum service rate per frame

– μmax : maximum service rate per frame

– d’ : maximum delay

• UGS : ( p , d , r )

• rtPS : (μmin , μmax , d’ )

• nrtPS : (μmin , μmax )

• BE : (μmax )

System model in LAFS

• LAFS operates in TDD mode.

• A connection admission control (CAC) mechanism is implemented in WiMAX system.– whether QoS requirement can be satisfied or not

– whether the rescheduled per-frame bandwidth allocation does not exceed the frame capacity or not

MSS ID connection ID Link capacity

frame duration

a constant within (0,1]

Phase 1 in LAFS

• Determination of awake-frame candidate set for UGS– those frames the MSS can delay its transmissions to.

r1 = 7 M / frame , r2 = 6 M / frame, r3 = 4 M / frame, C = 10 Mbps , t = 1 sec

2110/67 UGSN[3,4] or [4,5]

Phase 2 in LAFS

• Calculation of sleep/awake interval for other service types.– This paper assumes that

• an MSS will report the queue sizes of rtPS, nrtPS, and BE connections to its BS at the end of an awake-interval through polling and piggyback.

• packets arrived in current sleep and awake intervals (e.g., Si and Wi) will be transmitted in the following awake interval (Wi+1 )

Phase 2 in LAFS

• Li : the cumulated queue size of an MSS within Si and Wi.

• the maximum required number of frames for the (i+1)th awake interval Wi+1 is /iL

Phase 2 in LAFS

• An MSS has six connections (data rate, maximum delay)– (256 Kbps , 4 frames)

– (256 Kbps , 4 frames)



– ( 2 Mbps , 6 frames)

– ( 2 Mbps , 6 frames)

– S1 = W1 = 1 frame

– 1 frame = 1 sec

– C = 20 Mbps

( 256K * 2 + 512K * 2 + 2M * 2 ) * 2 = 11.072 Mbits

S2 ≤ 4 – 1 – 1 – = 1 20072.11

S2 ≤ 4 – 1 – = 2 20072.11

Phase 3 in LAFS

• Only UGS connections– BS informs the MSS of its awake frames being last NUGS frames wi

thin the awake-frame candidate set.

• Only rtPS and nrtPS connections– The sleep and awake intervals of the MSS is obtained from phase

2.

Phase 3 in LAFS

• All connections– awake-frame candidate set and sleep/awake interval have overlap.

Performance Evaluation

• 8Mbps Bandwidth

• Frame duration : 5 ms

• Time slot : 0.1 ms

• DL/UL-MAP occupies 2 slots

• One BS-MSS, MSS with multiple connections

• Data rate : [ 25Kbps , 56Kbps ]

• Packet arrivals occur at the beginning of a frame

• Simulation time : 25 secs


UGS connections

per-connection-basis


UGS connections


ALL connections

Conclusion

• The Least-Awake Frames Scheduling (LAFS) for IEEE 802.16e networks improves power saving efficiency.

• The major contribution of this paper is LAFS supports all service classes.

• The LAFS algorithm outperforms the power-saving mechanism defined in IEEE 802.16e and other existing power saving protocols.

The End

THANK YOUTHANK YOU

energy-saving scheduling in ieee 802.16e networks chia-yen lin, and hsi-lu chao department of...

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