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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