1. On the Energy Hole Problem of Nonuniform Node Distribution in Wireless Sensor Networks
Xiaobing Wu, Guihai Chen
State Key Laboratory for Novel Software Technology
Nanjing University
Sajal K. Das
Department of Computer Science and Engineering
The University of Texas at Arlington
MASS 2006

2. Outline
Introduction
Theoretical Analysis of Nonuniform Node Distribution Strategy
Routing with A Nonuniform Node Distribution Strategy
Simulation Results
Conclusions

3. Introduction Nodes nearer the sink have to take heavier traffic load AB
Sink
Sensor

4. Introduction
Sensor nodes that are closer to sink consume their energy rapidly (Energy Hole Problem)
Network partition A B
Sink
Sensor

5. Motivation and Goal Motivation Goal
Explore the theoretical aspects of power balance problem in wireless sensor networks with nonuniform node distribution
Goal
Propose a node distribution strategy to achieve a suboptimal balanced energy depletion

6. Assumptions and Network Model
A circular area with a radius of R
Transmission range of all the nodes is fixed
Data can be transmitted to the next inner corona with one hop

7. Theoretical Analysis of Nonuniform Node Distribution Strategy
Ei : Energy consumed per unit time by the nodes in corona Ci
Ni : The number of nodes in the corona Ci
A node
Send one bit : e1 units of energy
Receive one bit : e2 units of energy
Generate and send L bits of data per unit time

8. The Impossibility of Balanced Energy Depletion of The Network
Initial energy
A perfect and maximum energy efficiency is not achievable
Nodes in the corona CR only need to transmit their own data

9. The Suboptimal Balanced Energy Depletion of The Network
Find that a balanced energy depletion among the coronas except the outmost one is possible

10. The Suboptimal Balanced Energy Depletion of The Network
The number of nodes in coronas varies with a geometric proportion from outer coronas to inner ones in the whole network

11. Routing with A Nonuniform Node Distribution Strategy
Assume the number of nodes in the coronas increases with geometric proportion
Each node in Ci+1 can communicate directly with q different nodes in Ci 32 16 8 64 4
q=2

12. Routing with A Nonuniform Node Distribution Strategy
In network initialization, nodes find their upstream node and their q relay candidates
The source node selects one relay node with maximum energy resource

13. Simulation Results

14. Simulation Results C6(4) C5(8) C4(16) C3(32) C2(64) C1 (128)
Most nodes have little energy wasted

15. Simulation Results
Small variances in the fragments

16. Simulation Results Simulated value q=2 Theoretical value q=2
Residual energy ratios of different values of network radius and q

17. Conclusions
With the number of nodes in the coronas increasing from outer areas to inner ones with geometric proportion
The network achieves a high energy efficiency