Adaptive Waiting Time Threshold Estimation Algorithm for Power Saving in Sleep Mode of I

EEE 802.16e

Khyati Sanghvi, Piyush Kumar Jain, Debabrata DasInternational Institute of Information Technology, India

Abhijit LeleMotorola India Research Labs, Bangalore, India

IEEE International Conference on Communication System Software and Middleware (COMSWA 2008)

Outline

Introduction Proposed Algorithm Example Analytical Model Simulation Conclusion

Introduction

Portable mobile devices are characterized by limited compute capacity and energy availability.

Sleep mode is a key feature introduced in IEEE 802.16e standard, which ensures power-efficient operation of battery operated mobile devices.

Introduction – 802.16e sleep mode operations

Power Saving Class of Type I

Power Saving Class of Type II

Power Saving Class of Type III

…

TS_init (Initial sleep window)

2 x TS_init TL

4 x TS_init TS_max

Incoming packet

TL TS

Incoming packets

…

Incoming packets Incoming packetsIncoming packets

TS

normal operation

sleep windows

listening windows

MOB_TRF-IND

Motivation

TRF-IND(-) TRF-IND(+)

Wakemode

Frame no.2 1 4 1

Listeningwindow

In PSC of type I, The 802.16e standard does not define when to take decision to trigger sleep mode.

Packet arrival times in non real time traffic are unpredictable.

4

DL Data arrival

DL

Sleeping Period Active Period

REQ REP

MS

BS

Waiting time threshold?

REQ REP

…

Motivation

Waiting time threshold– MSS wait for longer duration before switching to sleep mode at

low traffic, leading to less sleep duration.– MSS wait for lower duration before switching to sleep mode at

high traffic, leading to frequent sleep–active transitions.

Motivation

Waiting time threshold– MSS wait for longer duration before switching to sleep mode

at low traffic, leading to less sleep duration.– MSS wait for lower duration before switching to sleep mode at

high traffic, leading to frequent sleep–active transitions.

Frame no.

4

MSlonger Waiting time

threshold longer

TRF-IND(+)

DL

Frame no. 4

MSWaiting time

threshold longer

TRF-IND(+)

DL

Sleeping Period

Sleeping Period

Motivation Waiting time threshold

– MSS wait for longer duration before switching to sleep mode at low traffic, leading to less sleep duration.

– MSS wait for lower duration before switching to sleep mode at high traffic, leading to frequent sleep–active transitions.

Frame no.

4

MS W

TRF-IND(+)

DLFrame no. 4

MSWaiting time

threshold longer

TRF-IND(+)

DL DL

DL

TRF-IND(+)

W

DL

Active Period Active Period

Goal

This paper proposes a novel algorithm for estimating optimum waiting time threshold to reduce the energy consumption.

Definitions

Sleeping Period Active Period Sleeping Period

MS

S L S L A W A W REQ S L S L …

S: Sleep Window

L: listening window

A: Packets serving

W: Waiting time duration

Tth : Waiting time threshold

REQ : REQ/RSP message change

Tth

REQ

Example

Sleeping Period Active Period

MS

S L S L A W

TRF-IND(+) DL

UL

Tth

Tth_min is minimum limit of waiting time threshold.

REQ

Example

Active Period

S L S L A W

TRF-IND(+) DL

A

UL

MS

REQ

Sleeping Period

The MS will enter packet serving duration immediately

Example

Active Period

S L S L A W

TRF-IND(+) DL

A

UL

W

TthMS

REQ

Sleeping Period

When packet serving time is over, the Ms will estimate waiting time duration

Example

A W

β is a constant with unit sec-1. λnew is new arrival rate, λn is weighted arrival rate after n th packet arrival, λn-1 is weighted arrival rate after (n-1) th packet arrival

A W

DL

UL

REQ S L S L

Tth

Example

Active Period

S L S L A W

TRF-IND(+) DL

A

UL

W

Sleeping Period

REQ S L S

TthMS

REQ

Sleeping Period

The MS will wait the estimated waiting time duration

Valid Example

A

UL

W REQ S L S L

Tth

TRF-IND(+)

A W

DL

β = 4.865

α = 0.01

1/100

1/1000

0.00101

20ms

19.9567015 ms

REQ S LA …

Valid Example

A W

Tth

WA W

DL

UL UL

A

1/100

1/10

0.991

β = 4.865

α = 0.01

20.4334715 ms

20 ms

Analytical Model

Case 1: When UL or DL MAP arrives at MSS during waiting time threshold duration

Case 2: When UL MAP is present at MSS for transmission during n th sleep interval while there is no DL frame arrival at BS for MSS

Case 3: When DL MAP arrives at BS for MSS during n th sleep interval while there is no UL frame present at MSS

Case 4 When UL frame is present at MSS for transmission with at least one DL frame arrival at BS for the MSS in the nth sleep interval

Active Period Sleeping Period

L A W A W REQ S L S L …

CASE 1 CASE 2 CASE 3 CASE 4

Definitions

A W A W REQ S1 L S2 L …

λ = mean arrival rate λd = mean downlink arrival rate λu = mean uplink arrival rate

tt = arrival time of UL or DL frame

tn = sleep interval during n-th sleep cycle

Si = total sleep and listening interval till the i-th sleep cycle

Tth_mean = mean waiting time threshold Ei = energy consumption for case i where i= {1, 2, 3, 4} Di = average delay in transmission of DL frame at BS for MSS due to MSS being in sleep mode for case i where i={1, 2, 3, 4} Eth = energy consumption at MSS during waiting time threshold Es = energy consumption at MSS during sleep mode E = total energy consumption at MSS D = total average delay at MSS

Tint_mean = mean inter arrival time DL/UL MAP

Case 1: When UL or DL MAP arrives at MSS during waiting time threshold duration

Sleeping Period

A W REQ S1 L S2 L …

DL / UL MAP

tt

Tth_mean

tn = 0

Case 1: When UL or DL MAP arrives at MSS during waiting time threshold duration

Sleeping Period

REQ S1 L S2 L …A W

Tth_mean

DL / UL MAP

tt

tn = 0

Case 2: When UL MAP is present at MSS for transmission during n th sleep interval while there is no DL frame arrival at BS for MSS

Sn

A W REQ S1 L S2 …

UL MAP

tt

Sn-1 tnL

Sn

A W REQ S1 L S2 …

UL MAP

tt

Sn-1 tnL

Case 3: When DL MAP arrives at BS for MSS during n th sleep interval while there is no UL frame present at MSS

Sleeping Period

A W REQ S1 L S2 L …

DL MAP

Case 3: When DL MAP arrives at BS for MSS during n th sleep interval while there is no UL frame present at MSS

Sleeping Period

A W REQ S1 L S2 L …

DL MAP

Case 4 When UL frame is present at MSS for transmission with at least one DL frame arrival at BS for the MSS in the n th sleep interval

Sleeping Period

A W REQ S1 L S2 L …

UL MAPDL MAP

Case 4 When UL frame is present at MSS for transmission with at least one DL frame arrival at BS for the MSS in the n th sleep interval

Sleeping Period

A W REQ S1 L S2 L …

UL MAPDL MAP

Analytical Model

Active Period Sleeping Period

A W REQ S1 L S2 L …

CASE 1 CASE 2 CASE 3 CASE 4

Simulation

We have validated our simulation model with published simulation results performed on NS2 platform.

The total simulation time is 400 sec and results are obtained by taking average value of 100 samples of traffic sequence for each arrival rate λ.

Mean arrival rate λ varies from 0.05 to 1.0.

One frame duration= 5ms

α = 0.01,

β = 4.865,

listening duration L = 5ms,

initial sleep duration tmin = 10ms and

maximum sleep duration tmax = 160ms

Simulation

Energy consumption values for waiting time threshold duration and sleep duration is taken as Eth = 280mw and Es= 10mw, respectively

Furthermore, fixed waiting time threshold for existing algorithm is taken as Tth = 25ms and proposed algorithm uses minimum waiting time threshold Tth_min = 5ms and maximum waiting time threshold Tth_max = 50ms.

In case- I the ratio of DL versus UL traffic is taken as R = 4 where R = λd / λu

In case- II the ratio of DL versus UL traffic is taken as R = 1/4 where R = λ d / λu.

Simulation

Simulation

Simulation

Simulation

Simulation

Conclusion

This paper attempts to modify the existing constant waiting time threshold scheme by making it adaptive to the varying downlink and uplink traffic pattern.

We observe that traffic arrival pattern is an important factor for the

waiting time threshold control.