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SenCar: An Energy-EfficientData Gathering Mechanism forLarge-Scale Multihop Sensor Networks

Ming Ma, and Yuanyuan YangDepartment of Electrical and Computer Engineering, State

University of New York at Stony Brook

IEEE TRANSACTIONS ON PARALLEL AND DISTRIBUTED SYSTEMS 2007 (TPDS 2007)

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Outline

Introduction Motivations and main idea

Data gathering scheme for a connected network

Data gathering in a disconnected network Performance evaluation Conclusions

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Introduction Static network architecture

Sensors close to the BS consume much more energy than sensors at the margin of the network

SenCar network architecture: To balance loading of each sensor node by sensor car can prolong network lifetime

Base station

Base station

Static network architecture SenCar network architecture

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Data gathering scheme for a connected network

Assumption A SenCar will be sent out to gather data from sensors periodically. Each sensor may turn on their transceivers only when SenCar mov

es close to its cluster, all sensors belonging to the same cluster will be woken up and will send or relay packet

a moving path of SenCar consists of a series of connected line segments

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Data gathering scheme for a connected network

The problem is divided into three part:Load balancing v.s network lifetime

Given a moving path of SenCar, the load balancing alg. can calculate the network lifetime

Path planning algorithm v.s network lifetime Given set of candidate paths, we can choose the best path wit

h maximum network lifetime by load balancing alg.

Clustering v.s network lifetime The clustering algorithm is used to divide the network into cl

usters such that each node knows packet relaying path

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Data gathering scheme for a connected network – Load Balance

A sensor network can be modeled as a directed graph : :sensor set A: all directed link:

, if si can reach sj in 1-hop , if the moving path of SenCar traverses the transmi

ssion range of si, or, equivalently, si can reach SenCar in one hop while SenCar is moving

C: SenCar

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Load balancing A corresponding flow graph is

constructed as follows:

j

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Load balancing : data generating rate of node si : energy limit of node si :power consumption for generating a unit of traffic :power consumption for relaying a unit of traffic T : network lifetime

The number of unit of traffic that si can relay

Total generate unit of traffic

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Load balancing For any given T, this problem is a regular maximum flow prob

lem When maximum flow means:

Until time T, all generated traffic from n sensor nodes is received by SenCar

i.e., all sensors must be alive until T How to calculate network lifetime?

Incremental alg. to find max T: We can increase T until the maximum flow less than :

Some nodes have failed before time T How to increase T?

Since SenCar gathers data periodically, every time we can set at the beginning and increase T by every time

The value T of the last run, which the maximum flow = ,is the network lifetime of the corresponding SenCar path

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Path planning We assume that each sensor forwards one packet to SenCa

r, whereas SenCar moves from A to B Node 1 is bottleneck: it must forward 8 packet toSenCar

A straight path is not well enough (X)

How to find some turning points of SenCar such the network lifetime can be prolong?

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Path planningDetermining Turning Points of the Moving Path:

Given the starting point A to the end point B: To select a best path with the max network lifetime Grid size is a fixed parameter

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Path Planning Algorithm

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Clustering Clustering the Network along the Segments of the Moving Path:

To determine the direction of packet forwarding

Shortest path tree

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Moving path determination Merge the approach of the three part by divide and conquer

clustering determining the turning point An example of 4 iteration:

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Real world constraints

Constraint:• The sensed data must be gathered by SenCar before the

sensor’s buffer overflows.• the maximum moving distance of SenCar without rech

arging may be limited by its battery capacity.• Delay sensitivity application

Solution: For each turning point is added into path, all constraints m

ust be satisfied. The recursive moving path alg. could be terminated befor

e the above bound is reached.

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Avoiding Obstacles in the Sensing Field

For each candidate location of a turning point: If the next turning point are blocked by the obstacles, then the candidat

e location is not eligible to be the turning point.

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Data gathering in a disconnected network

Intra-cluster solutions + inter-cluster solution Inter-cluster problem is NP-Complete Inter-cluster solution can be found by exhaustive search or TSP solution

cluster1

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Performance Evaluation

800 sensor nodes Scheme 1—a static BS placed at the center of the

network (at point (500 m, 250 m)) Scheme 2—a SenCar moves alg. straight line betw

een (0 m, 250 m) and (1,000 m, 250 m) Scheme3-well-planned

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Performance evaluation

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Performance evaluation

X percent network lifetime

(100-x)percent sensors either run out of battery or cannot send the data to the sink due to the failure of the relaying nodes

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Performance evaluation

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Conclusion

This paper proposed a new data collection mechanism to prolong network lifetime

This paper presented a heuristic algorithm for planning the moving path/circle of SenCar and balancing the traffic load

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Thank You!!