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Energy-efficient Sleep-Energy-efficient Sleep-mode Operations for mode Operations for Broadband Wireless Broadband Wireless

Access SystemsAccess SystemsYou-Lin Chen and Shiao-Li TsaoYou-Lin Chen and Shiao-Li Tsao

IEEE 64th Vehicular Technology Conference, Sep. 2006

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OutlineOutline• Introduction• 802.16e sleep mode operations and

power consumption issues• Energy-efficient scheduler for sleep-

mode operations• Simulation results• Conclusions and future work

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IntroductionIntroduction• Mobile devises are normally battery-operated• IEEE 802.16e specifies three power-saving class for different applications• MSS should stay in sleep periods as much as possible but not to violate the QoS requirements

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802.16e sleep mode operations 802.16e sleep mode operations and power consumption issuesand power consumption issues

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Actual sleep periodsActual sleep periods

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Example of two scheduling Example of two scheduling schemesschemes

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Periodic on-off scheme (PS)Periodic on-off scheme (PS)• Sleep and listen for a fixed period in a round-robin basis• Based on IEEE 802.16e power-saving class of type-2• Schedule the packets in fewer OFDM frames without violating the QoS

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Example of periodic on-off Example of periodic on-off scheme (PS)scheme (PS)

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Maximal data transmit and Maximal data transmit and receive in a listen periodreceive in a listen period

Tframe: length of an OFDM frameBframe: BS can supply the maximal resources in an OFDM frameNS: number of OFDM frame in a sleep periodNA: number of OFDM frame in a listen periodQi {PSi , TIi, Di}: QoS parameters of connection i

PSi: average packet size for connection iTIi: average inter-packet arrive time for connection iDi: delay constraint of any two consecutive packets for connection i

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PS scheduling area under PS scheduling area under constraintconstraint

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Average power consumptionAverage power consumption

PS: power consumption of a MSS in sleep modePA: power consumption of a MSS in listen mode

Maximize here to reduce average power consumption

PA > PS

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Aperiodic on-off scheme (AC) Aperiodic on-off scheme (AC) • Using the type-3 power-saving class• First sorts all connections

– Tight delay constraint packet has higher priority• Connection i: The first priority connection• Bj,i: amount of data required by connection i in the jth OFDM frame• Bk: amount of data for other connections of the MSS has been scheduled in kth OFDM frame (k

>= j) ; (0 <= Bk <= Bframe)j

k

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Bandwidth and delay Bandwidth and delay constrains of ASconstrains of AS

• j

k

2

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If Bframe= 10 k

j = 2

k = 4(4-2+1)x10 <= 35

If Tframe= 10 k Di = 35

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Example of Aperiodic on-off scExample of Aperiodic on-off schemeheme

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Simulation resultsSimulation results• The length of an OFDM frame is 5 ms• The maximal data rate from BS to a

MS is 1600 kbps• Traditional scheme

– Assign OFDM frames to a MSS whenever the MSS needs to send or to receive packets

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QoS parameters of four different real-time connections

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Percentage of sleep periods of a MSS by different scheduling schemes

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Average packet delays for different scheduling schemes

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Percentage under the tight delay constraints

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Conclusion and future workConclusion and future work• Two scheduling schemes for sleep-mode in IEEE 802.16e• These schemes minimize the power consumption of a MSS under QoS • Increase 15% to 50% more sleep time than traditional approach• Applying to multiple-MSS and global optimization for a BS’s point of view

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Thank youThank you