Optimizing Sensor Networks in the Energy-Latency-Density

Design Space

Curt Schurgers, Vlasios Tsiatsis,

Saurabh Ganeriwal, Mani Srivastava,

IEEE TRANSACTIONS ON MOBILE COMPUTING,2002

Speaker : hsiwei

Outline

INTRODUCTIONSTEMSIMULATIONCONCLUSIONS

INTRODUCTION

Sensor networks are made up of a large number of tiny devices,call sensor node

Sensor nodes have only a small battery as a power source

To achieve satisfactory network lifetime,energy efficiency is really a problem

Network communications as the radio is the main energy comsumer in a sensor node

INTRODUCTION(con.)

Monitoring state : The network is only sensing its environment.

Transfer state : Once an event happens, data needs to be forwarded to the data sink.

目的 : It reduces the energy consumption in the monitoring state to a bare minimum while ensuring satisfactory latency for transitioning to the transfer state.

INTRODUCTION(con.)

Sleep state:In the monitoring state, where there is no traffic to forward.

Working state: The radio is only turned on if the processor decides that the information needs to be communicated to other nodes.

To forward traffic, nodes on the multihop path need to be awakened, or,equivalently, transition from the monitoring to the transfer state.

INTRODUCTION(con.) Initiator node:The node that wants to communicate. Target node: initiator node polls the node it is trying to w

ake up. Once the link between nodes is activated data is transfer

red using a MAC protocol The reason is that MAC protocols are designed to organi

ze access to the shared medium. STEM offers an alternative by trading energy for latency.

STEM

Each node periodically turns on its radio for a short time to listen if someone wants to communicate with it.

Since this aggressive nature is needed to limit the wakeup latency

STEM

The solution : is to completely separate data transfer from wakeup. transfer stat

e

wakeup band

STEM

STEM-B : As soon as the target receives a beacon, it turns on its data radio in band f1 and also sends back an acknowledgment in band f2.

STEM-T : a target node never sends back an acknowledgment.

contains the MAC address of both the target and initiator node.

STEM

Target node has received the beacon correctly or seen a collided packet and turned on its data radio in either case.

If they do not receive any traffic in band f1 after some time, they time out and return to the monitoring state.

SETUP LATENCY

Fig. 11. Analysis of the setup latency of STEM-B without collisions.

SETUP LATENCY

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SETUP LATENCY

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SETUP LATENCY

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Beacon collision

SETUP LATENCY

Fig. 12. Analysis of the worst-case setup latency of STEM-T.

IRXS TTTT *2Tone -based

SIMULATION

Were written on the Parsec platform, an event-driven parallel simulation language

distribute N nodes in a uniformly random fashion over a field of size L x L

transmission range : R the average number of neighbors of a node:

The node turns its data radio back off if it has not received any traffic for 20 seconds.

20,100 N

22

* RL

N

SIMULATION

Setup latency of a link

ENERGY CONSUMPTION

1

2

P

P

1

2,1,

P

PP sleepsleep

burstwdata tft

t*

power of wakeup radio and data radio

sleep power for the data and wakeup radio

The average time the radio is on during one such data communication phase

The number of such transitions per second the node sets up a link

ENERGY CONSUMPTION

datawakeupnode EEE

setupsetupsetupnodewakeup tPttPE *)(* 2,2,

T

TPTTPP RXlistenRXsleepnode

*)(* 2,2,2,

datadatadatasleepdata tPttPE *)(* 1,1,

tPE originalnode *1

originalnode

node

E

E

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tPE originalnode *1there is only one radio that is never in the sleep state,

ENERGY CONSUMPTION

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sS TfE

E

SSsetup Tft

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其中Setup frequency

SIMULATION

SIMULATION

SIMULATION existing topology management schemes, such as GAF

and SPAN.

CONCLUSIONS

STEM: A topology management technique that trades power savings for path setup latency in sensor networks.

the combination of STEM and GAF can

reduce the energy to 1 percent or less of that of a network without topology management

Summary

利用兩個不的 channel,達到 sensor node 節省電力 .

透過數學的分析及模擬 ,得到不錯的省電效果