A Power Saving MAC Protocolfor Wireless Networks

Technical Report July 2002

Eun-Sun Jung Texas A&M University, College Station

Nitin H. Vaidya University of Illinois at Urbana-Champaign

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Outline

• Introduction• Related Work• New Power Saving Mechanism

(NPSM)• Performance Evaluation• Conclusion

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Introduction

• Battery power in one of the critical resources in wireless networks• Battery management• Power control• Energy-efficient protocols using

directional antennas• Power saving mode

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Introduction

• Power saving mode• Awake states

• Transmit• Receive• idle

• Doze states• Transition delay ( 250uS ->800uS )• Additional energy consumption when

changes state from doe to awake

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Introduction

• 802.11• PCF Power saving mechanism• DCF Power saving mechanism

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Introduction• Significantly affected by ATIM window

size • Optimal ATIM window size

• Network load• Beacon interval size

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Related Work[ 3] B. Chen, K. Jamieson, H. Balakrishnan, and R. Morris,

“Span: An Energy-Efficient Coordination Algorithm for Topology Maintenance in Ad Hoc Wireless Networks,” in MOBICOM 2001

• Elects coordinators which periodically rotate their roles

• Coordinators stay awake and forward traffic for active connections

• Non-coordinators follow the power saving mechanism of IEEE 8012.11 DCF

[15] S. Singh, M. Woo, and C. S. Raghavendra, “Power-aware

Routing in Mobile Ad Hoc Networks,” in MOBICOM 1998.• Using control channel determines when and

for how long to power off

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Related Work

[20] Y.-C. Tseng, C.-S. Hsu, and T.-Y. Hsieh, “Power-Saving Proto-cols for IEEE 802.11-Based Multi-Hop Ad Hoc Networks,” in INFOCOM 2002,

• Multi-hop synchronization of beacon intervals solutions

[22] H. Woesner, J.-P. Ebert, M. Schlager, and A. Wolisz, “Power-Saving Mechanisms in Emerging Standards for Wireless LANs: The MAC Level Perspective,” IEEE Personal Communications, 1998.

• A mechanism to choose the ATIM window size dynamically

• Allows nodes to power off whenever they finish packet transmission

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Related Work[23] Y. Xu, J. Heidemann, and D. Estrin,

“Geography-informed En-ergy Conservation for Ad Hoc Routing,” in MOBICOM 2001,• Uses location information• All nodes in the same grid are equivalent in

terms of traffic forwarding• Guarantees that one node in each grid stays

awake in order to forward traffic

[24] W. Ye, J. Heidemann, and D. Estrin, “An Energy-Efficient MAC Protocol for Wireless Sensor Networks,” in INFOCOM 2002,

• Allows nodes to sleep during neighbors’ transmissions

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Related Work

[25] R. Zheng and R. Kravets, “On-demand Power Management for Ad Hoc Network,” Tech. Rep. UIUCDCS-R-2002-2280, Depart-ment of Computer Science, University of Illinois at Urbana-Champaign, 2002.

• Routing node stay awake reduce end-to-end delay

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New Power Saving Mechanism (NPSM)

• Removing the ATIM window• In order to reduce control overhead• Start of a beacon interval, every node

enters an awake state for a specified duration called DATA window

• Node transmits a packet to a destination it includes the number of pending packets in the packet

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Proposed Power Saving Mechanism

• Announcing pending packets• T(i) : number of packet transmits for node i• R(i) : number of packet receiver for node ii• Up(i) : number of packets that neighbor node I

needs to transmit or receive• R total : sum of R over all neighbors

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Proposed Power Saving Mechanism

• Extend Data window• Has not finished receiving all the packets• Infer the neighbors node i in awake and need

to transmit to node I

• 20ms < DATA window size < 100ms, step 5ms

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Performance Evaluation• Metrics are used to evaluate

• Aggregate throughput over all flows in the network

• Total data delivered per unit of energy consumption (K bits delivered per joule)

• Average packet delay over all flows in the network

• Simulation model• Used ns-2 • 11 Mbps bit rate, transmission range 250m• Transmit 1.65W, Receive 1.4W, Idle 1.15W,

Doze 0.045W• 800uS as the doze-to-awake transition time

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Simulation ResultsOne hop : varying the network load

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Simulation ResultsOne hop : varying the network load

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Simulation ResultsOne hop : varying packet size

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Simulation ResultsMulti-hop : varying the network load

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Simulation ResultsMulti-hop : varying the network load

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Conclusion

• Removing the ATIM window makes more bandwidth

• Better aggregate throughput and energy savings as compared to PSM

• NPSM saves energy at the cost of increasing the packet delay

• Trade-off between energy savings and packet delay

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Thank You !!