doc.: IEEE 802.11-12/0338r1

Submission

March 2012

Hung-Yu Wei, National Taiwan UniversitySlide 1

DeepSleep: Power Saving Mode to Support a Large Number of Devices

Date: 2012-03-16Authors:

Name Affiliations Address Phone email Hung-Yu Wei National Taiwan

University No. 1, Sec. 4, Roosevelt Road, Taipei, Taiwan

+886 2 33663700 hywei@cc.ee.ntu.edu.tw

Hsiang-Ho Lin National Taiwan University

Yan-Bin Chen National Taiwan University

doc.: IEEE 802.11-12/0338r1

Submission

Abstract

• In this contribution, we propose a power saving mechanism that supports low-power STAs in 802.11ah.

March 2012

Hung-Yu Wei, National Taiwan UniversitySlide 2

doc.: IEEE 802.11-12/0338r1

Submission

Motivation

• To save power, STAs could reduce the time in active state.

• To save power, a STA could spend a long time in power saving mode. Upon waking up, the STA wakes up to communication shortly and then goes back to power save mode as soon as possible.

March 2012

Hung-Yu Wei, National Taiwan UniversitySlide 3

doc.: IEEE 802.11-12/0338r1

Submission

Spend Less Time in Active State for Energy Efficiency

• Reducing backoff time and listening time could improve energy efficiency. – A STA with reduced CWmin has shorter contention time and

could go back to power saving mode sooner

– There are concerns about reducing CWmin• Fairness to contention

• Collision probability

• To be fair, only STAs that have been stay in sleep mode for a while should be qualified for setting small CWmin value.

March 2012

Hung-Yu Wei, National Taiwan UniversitySlide 4

doc.: IEEE 802.11-12/0338r1

Submission

Reduce Contention Nodes for Energy Efficiency

• With large number of devices, reducing channel contention improves energy efficiency

• A large percentage of STAs are configured to enter sleep mode to reduce contention and to save energy– Similar solutions to resolve issues caused by large number of

STAs have been proposed for 11ah [1][2]

March 2012

Hung-Yu Wei, National Taiwan UniversitySlide 5

doc.: IEEE 802.11-12/0338r1

Submission

802.11 Contention and Waste of Energy

March 2012

Hung-Yu Wei, National Taiwan UniversitySlide 6

Energy waste during this time period

doc.: IEEE 802.11-12/0338r1

Submission

Proposal Overview

• We propose an enhanced mechanism to save power for low-power 802.11ah STAs– The low-power STAs (which have been stayed in sleep mode for a

long time) has higher priority when it wakes up. These STAs could have shorter idle listening period and going back to power-saving mode sooner

• The channel access fairness is also considered.– Only STAs that do not access channel for a while are qualified for

high priority access because of fairness

March 2012

Hung-Yu Wei, National Taiwan UniversitySlide 7

doc.: IEEE 802.11-12/0338r1

Submission

Design Overview

1. STAs go to DeepSleep– Enter DeepSleep mode randomly

• If (P < Prob_Threshold)• Optional extension: a STA considers its energy status

– Stay in DeepSleep for a while (DeepSleep_Duration )

2. STAs wake up– If the STA has slept for a long enough time

• The wake-up STA applies smaller contention window to have high priority to transmit.

– Otherwise,• The wake-up STA operates in the original 802.11 mode

March 2012

Hung-Yu Wei, National Taiwan UniversitySlide 8

doc.: IEEE 802.11-12/0338r1

Submission

Our proposal• Algorithm:

– Randomly Enter DeepSleep Mode

if(P < Threshold)

then{

Enter DeepSleepMode (Stay in sleep for DeepSleep_Duration)

Bool_Sleep = TRUE;

}

– Wakeup

if (Bool_Sleep)

then{

CWmin = CW_Sleep;

Bool_Sleep = FALSE;

}

else{

CWmin = CW_Original;

}

March 2012

Hung-Yu Wei, National Taiwan UniversitySlide 9

doc.: IEEE 802.11-12/0338r1

Submission

Simulation Settings

March 2012

Hung-Yu Wei, National Taiwan UniversitySlide 10

• Use NS-2 simulator• Number of devices : 100• traffic interval: 1s• beacon period: 1s• TX power: 550 mW• RX power: 250 mW• Idle power: 200 mW• Sleep power: 40 mW • CWmin_Orignal: 31• CWmin_DeepSleep: 15• DeepSleep_Duration : 10 beacon periods

• Case 1: 100 devices use the proposed scheme• Case 2: 100 devices use default 802.11 scheme• Case 3: 50 devices with the proposed scheme, 50 default scheme

doc.: IEEE 802.11-12/0338r1

Submission

Better Energy Efficiency

March 2012

Hung-Yu Wei, National Taiwan UniversitySlide 11

doc.: IEEE 802.11-12/0338r1

Submission

Lower Collision Probability

March 2012

Hung-Yu Wei, National Taiwan UniversitySlide 12

doc.: IEEE 802.11-12/0338r1

Submission

Stay in Sleep Mode Longer

March 2012

Hung-Yu Wei, National Taiwan UniversitySlide 13

Sleep time rate is defined as the time ratio that a STA is stayed in PSM mode. For example, sleep time rate = 0.95 implies a STA operates in active mode 5% of time and stays in power save mode 95% of time.

doc.: IEEE 802.11-12/0338r1

Submission

Lower Retransmission Count

March 2012

Hung-Yu Wei, National Taiwan UniversitySlide 14

To successfully deliver a packet, how many time does a STA needs to transmit (e.g. transmission per packet delivered = 1, if there is no packet loss; transmission per packet delivered = 2, if the average re-transmission count is 1).

doc.: IEEE 802.11-12/0338r1

Submission

The Same Packet Delivery Ratio

March 2012

Hung-Yu Wei, National Taiwan UniversitySlide 15

doc.: IEEE 802.11-12/0338r1

Submission

Conclusions

• We proposed a power saving mechanism for the STAs.– Reducing the contention level caused by large number of devices. – Reducing the backoff time and channel listening time upon a STA wakes

up.

• Simulation results show the proposed mechanism effectively improve energy efficiency. – Better energy efficiency– Lower collision probability– Stay in doze time more often– Lower collision probability

• Suitable for scenarios with a large number of lower-power STAs

March 2012

Hung-Yu Wei, National Taiwan UniversitySlide 16

doc.: IEEE 802.11-12/0338r1

Submission

References

• [1] 11-11-1255-00-00ah-dcf-enhancements-for-large-number-of-stas

• [2] 11-12-0028-01-00ah-power-saving-possibilities-for-networks-supporting-a-large-number-of-stas

March 2012

Hung-Yu Wei, National Taiwan UniversitySlide 17

doc.: IEEE 802.11-12/0338r1

Submission

Straw Poll (1)

• Do you agree that a power saving mechanism to reduce the channel sensing period should be developed in Specification Framework?– Y

– N

– A

March 2012

Hung-Yu Wei, National Taiwan UniversitySlide 18

doc.: IEEE 802.11-12/0338r1

Submission

Straw Poll (2)

• Do you agree to use a smaller CWmin parameter when STAs wakes up after a long doze (e.g. with grouping)? – Y

– N

– A

March 2012

Hung-Yu Wei, National Taiwan UniversitySlide 19