Visual sensor networks (VSNs) have been attracting more and more research attention nowadays. There are applications where the spatial density of sensors is a constraint. Assuming that with the current technology the cost of a sensor is tens of times greater than the cost of embedded batteries, it will be valuable to examine whether the lifetime of the network could be increased by simply distributing extra energy to some existing nodes without introducing new nodes. In this paper an improvement to LEACH protocol is done to increase the lifetime of network. CPA is heterogeneous-aware, in the sense that election probabilities are weighted by the initial energy of a node relative to that of other nodes in the network. This prolongs the time interval before the death of the first node (stability period), which is crucial for many applications where the feedback from the sensor network must be reliable.

1. Youssef Charfi, Bell Canada Naoki Wakamiya, Masayuki Murata, "Challenging issues in visual sensor networks", in IEEE Transaction on wireless communication, 2009.
2. W. R. Heinzelman, A. P. Chandrakasan, and H. Balakrishnan, "Energy efficient communication protocol for wireless microsensor networks," in Proceedings of the 33rd Hawaii International Conference on System Sciences (HICSS-33), January 2000.
3. "An application-specific protocol architecture for wireless microsensor networks," IEEE Transactions on Wireless Communications,no. 4, pp. 660–670, October 2002.
4. "Minimizing communication costs in hierarchically-clustered networks of wireless sensors," Computer Networks, vol. 44, no. 1, pp. 1–16, January 2004.
5. Akyildiz, I. ; Su, W. ; Sankarasubramaniam, Y. ; Cayirci, E. A survey on sensor networks. Comput. Netw. 2002, 38, 393-422.
6. Baronti, P. ; Pillai, P. ; Chook, V. ; Chessa, S. ; Gotta, A. ; Hu, Y. Wireless sensor networks: A survey on the state of the art and the 802. 15. 4 and ZigBee standards. Comput. Commun. 2006, 30, 1655-1695.
7. Yick, J. ; Mukherjee, B. ; Ghosal, D. Wireless sensor network survey. Comput. Netw. 2008, 52, 2292-2330.
8. Akyildiz, I. ; Melodia, T. ; Chowdhury, K. A survey on wireless multimedia sensor networks. Comput. Netw. 2007, 51, 921-960.
9. K. -Y. Chow, K. -S. Lui, and E. Y. Lam, "Maximizing Angle Coverage in visual sensor networks", in IEEE Wireless Communications & Networking Conference, March 2007.
10. W. Heinzelman, A. Chandrakasan, and H. Balakrishnan, "An application specific protocol architecture for wireless microsensor networks", IEEE Transactions on Wireless Communications, vol. 1, pp. 660-670, Oct 2002.
11. Stanislava Soro, Wendi B. Heinzelman, "Cluster head selection techniques for coverage preservation in wireless sensor networks", in Elsevier Ad hoc networks, vol. 7, August 2008, pp. 955-972.
12. F. Akyildiz et al. , "A Survey on Sensor Networks", IEEE Commun. Mag. , vol. 40, Aug. 2002, pp. 102–14.

Leach Cpa Vsn