The Chinese Univ. of Hong KongDept. of Computer Science & Engineering

POWER-SPEED A Power-Controlled

Real-Time Data Transport Protocolfor Wireless Sensor-Actuator Networks

(Based on the work submitted to WCNC 2007)

Y. Zhou, E. Ngai, M. Lyu, and J. LiuGroup Meeting

2006-11-21

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Outline

Introduction Protocol Design Simulation Study Conclusions

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Introduction

An example wireless sensor network

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Introduction

An example wireless sensor-actuator network (WSAN)I, robot

I, robot

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Introduction

Features of WSANs• Real-time data transport

• Mobile data sinks, i.e., the actuator nodes• Stateless protocol is highly desired

• Battery-powered sensor nodes • Energy-efficiency is still a critical issue

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Introduction

Existing protocols for WSANs and WSNs• Timeliness-domain QoS-guaranteed protocols

• SPEED, MMSPEED

• PREI (in MASS’06, by us)

• Feedback control packets are required

• To select fitful paths

• If feedback control packets can be avoided, …

• It would be

• This is the focus of this work

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Introduction

Existing protocols for WSANs and WSNs• GRP: Geographic Routing Protocol

• No feedback packets are required.

• No QoS guarantee

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Outline

IntroductionProtocol Design Simulation Study Conclusions

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Protocol Design

Selecting next hop neighbor to which packets are forwarded• Guarantee in-time delivery

• Achieve energy-efficiency

Examples• GRP

• Shortest-path based protocol

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Protocol Design

Estimating QoS conditions of downstream links• No feedback packets

• unaware of real QoS data

• Perform estimation• Space domain: delay of upstream links

• Time domain: historical link delay

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Protocol Design

Observation• Encapsulate data in packet is more energy-

efficient than send them individually

• Example• Sending two 32-byte packets cost twice as much

energy as sending one 64-byte packet

• Data on upstream-link conditions can be easily encapsulated in sensor reporting packets

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Protocol Design

Part of POWER-SPEEDpacket header

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Protocol Design

Link delay estimation • Time domain

• Space domain

SPEED

Max hops

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Protocol Design Estimate the number of hops if delivering

packet to a specific neighbor

Candidate• Those

• Required energy to send a packet to this neighbor

Energy consumption estimation

So, next-hop neighbor is the one that achieves minimum

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Protocol Design

Summaries• POWER-SPEED selects the next-hop neighbor

based on the estimation of downstream path quality and the latency-bound requirement of packets. Adaptively it sends a packet • that will expire in a longer period of time with lower

transmitter power level to save energy

• that will expire sooner with higher transmitter power level, which results in fewer hop numbers between senders to destination actuators, and thus guarantees that the packet can reach its destination in a shorter period of time.

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Outline

Introduction Protocol Design Simulation Study Conclusions

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Simulations

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Simulations

Randomly place 100 nodes. Compare the performance of GRP and POWER-SPEED in terms of energy consumptions

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Simulations

Randomly place 100-250 nodes. Compare the performance of GRP and POWER-SPEED in terms of energy consumptions

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Simulations

Compare the performance of GRP and POWER-SPEED in terms of in-time packet delivery rate

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Outline

Introduction Protocol Design Simulation StudyConclusions

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Conclusion

We show a way to achieve real-time data transport without feed-back control packets

We propose POWER-SPEED and show the effectiveness of the protocol

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Q & A