A Delay-aware Auto Sleep Mode Operation for Power Saving WiMAX

1Shengqing Zhu, 1Xiaoyu Ma, and 2Lujian Wang

( 南京大學 . 計算機科學 ) ( 浙江大學城市學院 . 信息工程 )

1Department of Electronic and Information, Nanjing University, China2Department of Communication Engineering, Zhejiang University City College

<IEEE ICCCN 2007>

Outline

• Introduction

• Motivation

• Proposed algorithm– Dynamic Tuning of Initial Sleep Window (DTISW)

– Delay-aware Sleep Mechanism (DSM)

• Simulation

• Conclusion

Introduction

• Mobile stations are usually powered by battery, and therefore power saving is a critical concern in designing the medium access control.

• One of core techniques of WiMAX is a sleep mode operation, which is employed to save power in IEEE 802.16e.– type I : for BE and NRT-VR traffic.

– type II : for UGS and RT-VR traffic.

– type III : for multicast connections and management operations.

• This paper addresses only power saving class of type I.– only downlink (from BS to MS) is considered.

Introduction

new sleep window = min {2 × (previous sleep window), initial sleep window × 2(final sleep window exponent) }

normal operation

sleep windows

listening windows

…

MO

B_S

LP

-RE

Q

MO

B_S

LP

-RS

P

BS

MS

MO

B_T

RF

-IND

(-)

MO

B_T

RF

-IND

(-)

MO

B_T

RF

-IND

(-)

MO

B_T

RF

-IND

(+)

DA

TA

DA

TA

DA

TA

t

t

initial sleep window

DA

TA

Introduction

• To bound the delay in the required range, a heuristic algorithm is proposed to adapt the parameters of sleep mechanism to the traffic load and the delay requirement.– This paper describes the performance of WiMAX sleep mode oper

ation by means of a simple Markov chain model.

Motivation

• When the MS enters into sleep mode, the BS buffers all packets addressed to the MS until it wakes up.– Power consumption

– Delay

normal operation

sleep windows

listening windows

MO

B_S

LP

-RE

Q

MO

B_S

LP

-RS

P

BS

MS

MO

B_T

RF

-IND

(-)

MO

B_T

RF

-IND

(+)

DA

TA

t

t

DA

TA

MO

B_S

LP

-RE

Q

MO

B_S

LP

-RS

P

MO

B_T

RF

-IND

(-)

MO

B_T

RF

-IND

(+)

DA

TA

DA

TA

MO

B_S

LP

-RE

Q

MO

B_S

LP

-RS

P

…

Motivation

• When the MS enters into sleep mode, the BS buffers all packets addressed to the MS until it wakes up.– Power consumption

– Delay

normal operation

sleep windows

listening windows

t

t…

MO

B_S

LP

-RE

Q

MO

B_S

LP

-RS

P

BS

MS

MO

B_T

RF

-IND

(-)

MO

B_T

RF

-IND

(-)

MO

B_T

RF

-IND

(-)

MO

B_T

RF

-IND

(+)

DA

TA

DA

TA

delay

Motivation

• The size of initial sleep window and the traffic load influence the following sleep operation and efficiency.

Motivation

• The queuing length in the buffer increases with the sleep interval, and so that packets’ end-to-end delay increases with the sleep interval.

Motivation

• Initial sleep window is the key of tradeoff between power consumption and delay.

Dynamic Tuning of Initial Sleep Window (DTISW)

Markov Chain Model

• The ith sleep interval Ti = 2iTb, (Tb = initial sleep window) , 0 ≤ i ≤ M

• The behaviors of an MS working in power saving mode can be described with a bi-dimensional random process {s(t), b(t)}

s(t), b(t)

The MS stays in the ith sleep interval

The status of the MS0：MS is sleeping

s：MS is receiving packets from BS

normal operation

sleep windows

listening windows

MSt

T0 T1 T2 T3

sleep mode normal modenormal mode

Dynamic Tuning of Initial Sleep Window (DTISW)

Markov Chain Model

normal operation

sleep windows

listening windows

MSt

T0 T1 T2 T3

sleep mode normal modenormal mode

0, s i, s M, s

0, 0 i, 0 M, 0

1, s

1, 0

MOB_TRF-IND(-)

(-) (-) (-) (-)

(+) (+) (+) (+)1 1 1 1

…… …(-)

Tb

Dynamic Tuning of Initial Sleep Window (DTISW)

• βi: the transition probability from state (i ,0) to state (i+l,0) (or from (M,0) to (M,0) when i=M), where equal to the probability that no packets arrive in the ith sleep state

• 1- βi : the transition probability from (i ,0) to related serving state (i,s)

MSt

T0 T1 T2 T3

0, 0 1, 0 2, 0 3, 0 4, s

0, s 1, s i, s M, s

0, 0 1, 0 i, 0 M, 0β0 β1 βi-1 βi βM-1

1-β0 1-β1 1-βi 1-βM1 1 1 1

…… ……βM

Tb

T4

Dynamic Tuning of Initial Sleep Window (DTISW)

• The initial sleep window should depend on the number of packets j served in the ith serving state

0, s 1, s i, s M, s

0, 0 1, 0 i, 0 M, 0β0 β1 βi-1 βi βM-1

1-β0 1-β1 1-βi 1-βM1 1 1 1

…… ……βM

Tb

MSt

T0 T1 T2 Ti

2i

222120

…

Dynamic Tuning of Initial Sleep Window (DTISW)

• Ex ：有 5 個 packets 於 T3 到達，則下次的 initial sleep window

Tb* = 24 / (INT) (log2 5) = 24 / 2 = 12 (T2)

MSt

T0 T1 T2 Ti

2i

222120

…

MSt

T0

(3)T1

(6)T2

(12)T3

(24)

5

Dynamic Tuning of Initial Sleep Window (DTISW)

• Ex ：有 5 個 packets 於 T3 到達，則下次的 initial sleep window

Tb* = 24 / (INT) (log2 5) = 24 / 2 = 12 (T2)

MSt

T0

(3)T1

(6)T2

(12)T3

(24)

5

3, s

0, 0 1, 0 2, 0 3, 0β0 β1 β2

1-β31

Tb

3, s

0, 0 1, 0 2, 0 3, 0β0 β1 β2

1-β3

1

Tb

Delay-aware Sleep Mechanism (DSM)

• A high initial sleep window results in high delay, and thus the selection of the initial sleep window should take the effect of delay into account.

• θ is the initial sleep window corresponding to the delay requirement D0.

– with the delay requirement D0 given, θ can be computed with formula T*

b.

0, s 1, s i, s M, s

0, 0 1, 0 i, 0 M, 0β0 β1 βi-1 βi βM-1

1-β0 1-β1 1-βi 1-βM1 1 1 1

…… ……

βM

Tb

Delay-aware Sleep Mechanism (DSM)

在 Ti 中累積 j 個封包的機率

在 Ti 中， j 個封包的平均 delay

Ti (MS 收資料 ) 的機率

封包在 Ti (MS Sleep) 時到達的 delay 總和

0, s 1, s i, s M, s

0, 0 1, 0 i, 0 M, 0β0 β1 βi-1 βi βM-1

1-β0 1-β1 1-βi 1-βM1 1 1 1

…… ……

βM

Tb

Poisson 機率公式

Serving time per packet Packet arrival rate

封包到達總數

Simulation

StandardDTISWDSM

Simulation

StandardDTISWDSM

Conclusion

• The DSM adapts the initial sleep window to the traffic load and the delay requirement.

• A marked gain in the power consumption compared to the traditional sleep mechanism can be found.

The End

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