## 4 Description of MRP
### Phase II: Constructing Multipath
Although TEEN also belongs to a dynamically clustering algorithm, the structure of cluster in TEEN is not related to the event area. Therefore, the energy consumption of TEEN is higher than that of MRP. MACS is one of the most costly algorithms, because it fails to take advantage of the data correlation and clustering to remove the redundant information among neighboring nodes. Although

Figure 4: Performance in WSNs with same initial energy levels (scenario 1) (a) Average Energy. (b) Energy Consumption. (c) Standard Deviation. (d) Network Lifetime. MP is also a flat routing algorithm, the energy consumption of MP is less than that of TEEN and MACS. The reason is that the primary route in MP is formed according to some metrics, such as low energy consumption. Therefore, the energy consumption of MP is low when source nodes always use the primary route to transmit data. In Figure 4c, when compared with the other algorithms, MRP presents a significant reduction in the standard deviation. It indicates that MRP can efficiently balance the energy consumption on all nodes. Figure 4d shows the network lifetime for the four algorithms. It is evident that the network lifetime of MRP is almost twice of that obtained by the other algorithms. The network size influences MRP the least. The reason is that clustering and dynamically choosing one path to transmit data can greatly contribute to reducing energy consumption and achieving load balancing among all nodes. TEEN outperforms MACS because it can use clustering to transmit data. Among of the four algorithms, the performance of MP is the worst. The reason is that MP always uses the primary path to transmit data, which results in energy of the nodes in the primary route becoming depleted very soon. Figure 5: Performance in WSNs with different initial energy levels (scenario 2) (a) Average Energy. (b) Energy Consumption. (c) Standard Deviation. (d) Network Lifetime. The results illustrated in Figure 5 correspond to the second scenario. From Figure 5, we can see that the results are very similar to those of the first scenario. Although the initial energy of nodes is randomly distributed, MRP still presents the best results. That can be explained by the adaptability of the protocol, which can efficiently balance the energy consumption among nodes by dynamic clustering and using multiple paths to transmit data. The simulation results also illuminate that MRP is suitable for either the homogeneous network or the heterogeneous network. ## 6 Conclusion

For monitoring the burst events in WSNs, we have proposed a novel multipath routing protocol based on clustering and ACO. By introducing an objective function to carry out dynamic clustering, MRP improves the efficiency of data aggregation, thus, reducing the energy consumption. We also use an improved ACO algorithm to search for the optimal and suboptimal paths based on many metrics, which can balance the energy consumption among nodes. Furthermore, a load balancing function is presented for dynamically choosing one path to transmit data. Performance evaluation shows that MRP achieves better load balancing and lower energy consumption, and then, maximizes the network lifetime. As explained before, MRP has some parameters that need be set. The values of these parameters have a great impact on the performance of the algorithm. For future research, we plan on making the algorithm compatible with different networks by adaptively adjusting the value of these parameters. Furthermore, we intend to extend the algorithm to monitor the object with an appropriate speed. ## Acknowledgements

This work was supported by the National High-Tech Research and Development Plan of China under Grant No. 2007 AA10Z241 and 2006 AA10A301; the National Natural Science Foundation of China under Grant No. 60864003. We would like to thank the anonymous reviewers for their perspicacious comments. ## References and Notes

* (1) [PERSON] Using Sensor Networks for Highway and Traffic Applications. _IEEE Potentials_**2004**, \(3\), 13-16.