**3.4 Discussion**

454 Environmental Monitoring

applying our scheme are shown in Figs.7, 8 and 9, where the number of sensor nodes is 1000. In Figs.7, 8 and 9, *Te* was set to 0.0J, *E*×0.5J, and *E*×0.9J, where *E* indicates the battery capaci-ty of each sensor node. Of the 3000 data packets transmitted from the evaluation node, the r-outes used by the first 500 data packets are illustrated in Figs.7, 8 and 9(a), those used by the 1000 data packets are in Figs.7, 8 and 9(b), those used by the 2000 data packets are in Figs.7, 8 and 9(c), and those used by a total of 3000 data packets are in Figs.7, 8 and 9(d). From Figs. 7, 8 and 9, it can be confirmed that the effect of our scheme is extended by

(c) 1 to 2000 data packets (d) 1 to 3000 data packets

Next, it was assumed that data packets were periodically transmitted from a total of 20 sensor nodes placed in the set simulation area. In Figs.10, 11 and 12, the transition of the delivery ratio of the total number of data packets transmitted from a total of 20 randomly selected se-

(a) 1 to 500 data packets (b) 1 to 1000 data packets

*evaluation node*

*evaluation node*

*evaluation node*

*evaluation node*

Fig. 7. Routes used by applying our scheme (*Te* = 0.0J )

early switching to low power.

To facilitate ubiquitous information environments by wireless sensor networks, their control mechanisms should be adapted to the variety of types of communication, depending on ap-plication requirements and the context. Currently, adaptive communication protocols for the long-term operation of the above ubiquitous sensor networks (Intanagonwiwat et al., 20-03; Silva et al., 2004; Heidemann et al., 2003; Krishnamachari & Heidemann, 2003; Wakabay-ashi et al., 2007) are under study. In

Autonomous Decentralized Control Scheme for Long-Term

*NS*

*NS*

*Proposal* (*Te=* 0.0J) *Proposal* (*Te=E* ×0.5J) *Proposal* (*Te=E* ×0.9J)

Fig. 11. Transition of delivery ratio (The number of sensor nodes is 1000 )

*Proposal* (*Te=* 0.0J) *Proposal* (*Te=E* ×0.5J) *Proposal* (*Te=E* ×0.9J)

Fig. 10. Transition of delivery ratio (The number of sensor nodes is 750 )

*0%*

*0%*

*20%*

*40%*

*60%*

*Delivery ratio (%)*

*80%*

*100%*

*120%*

*20%*

*40%*

*60%*

*Delivery ratio (%)*

*80%*

*100%*

*120%*

Operation of Large Scale and Dense Wireless Sensor Networks with Multiple Sinks 457

P*roposal* )

*100% line* (*NS* ) *100% line* (

*0 1000 2000 3000 4000 5000 6000 7000 The total transmission number of data packets*

*100% line* (*NS* ) *100% line* (

P*roposal* )

*0 1000 2000 3000 4000 5000 6000 7000 The total transmission number of data packets*

addition, the advanced design schemes of wireless sens-or networks, such as sink node allocation schemes based on the particle swarm optimization algorithms aiming to minimize total hop counts in a network and to reduce the energy cons-umption of each sensor node (Kumamoto et al., 2008; Yoshimura et al., 2009; Taguchi et al., 2010), and forwarding node set selection schemes (Nagashima et al., 2009; Sasaki et al., 2010) and forwarding power adjustment scheme (Nagashima et al., 2011) for adaptive and efficie-nt query dissemination throughout a wireless sensor network, are positively researched. By coupling our scheme (Matsumoto et al., 2010) with the above advanced design schemes, it can be expected that the lifetime of a wireless sensor network is moreover prolonged.

Fig. 9. Routes used by applying our scheme (*Te* = *E*×0.9J )

addition, the advanced design schemes of wireless sens-or networks, such as sink node allocation schemes based on the particle swarm optimization algorithms aiming to minimize total hop counts in a network and to reduce the energy cons-umption of each sensor node (Kumamoto et al., 2008; Yoshimura et al., 2009; Taguchi et al., 2010), and forwarding node set selection schemes (Nagashima et al., 2009; Sasaki et al., 2010) and forwarding power adjustment scheme (Nagashima et al., 2011) for adaptive and efficie-nt query dissemination throughout a wireless sensor network, are positively researched. By coupling our scheme (Matsumoto et al., 2010) with the above advanced design schemes, it can be expected that the lifetime of a wireless sensor network is moreover

(c) 1 to 2000 data packets (d) 1 to 3000 data packets

(a) 1 to 500 data packets (b) 1 to 1000 data packets

*evaluation node*

*evaluation node*

*evaluation node*

*evaluation node*

Fig. 9. Routes used by applying our scheme (*Te* = *E*×0.9J )

prolonged.

Fig. 10. Transition of delivery ratio (The number of sensor nodes is 750 )

Fig. 11. Transition of delivery ratio (The number of sensor nodes is 1000 )

Autonomous Decentralized Control Scheme for Long-Term

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*ions on Fundamentals*, Vol.E92-A, No.2, 459-466

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Fig. 12. Transition of delivery ratio (The number of sensor nodes is 1250 )
