Energy efficiency is the key requirement in wireless sensor network as sensors are small, cheap and are deployed in very large number in a large geographical area, so there is no question of replacing the batteries of the sensors once deployed. Different ways can be used for efficient energy transmission including Multi-Hop algorithms, collaborative communication, cooperativecommunication, Beam- forming, routing algorithm, phase, frequency and time synchronization. The paper reviews the need for time synchronization and proposed a BFS based synchronization algorithm to achieve energy efficiency. The efficiency of our protocol has been tested and verified by simulation
 Bheemidi, D.R.; Sridhar, N "A Wrapper-Based Approach to Sustained
Time Synchronization in Wireless Sensor Networks" Computer
Communications and Networks, 2008. ICCCN '08. Proceedings of 17th
International Conference on 3-7 Aug. 2008 Page(s):1 - 6 Digital Object
 J. Elson and D. Estrin, "Time synchronization for wireless sensor
networks," in Proc. of the 2001 International Parallel and Distributed
Processing Symposium (IPDPS), Workshop on Parallel and Distributed
Computing Issues in Wireless Networks and Mobile Computing, San
Francisco, CA, Apr. 2001.
 Sichitiu, M.L.; Veerarittiphan, C., "simple, accurate time
synchronization for wireless sensor," Proc. IEEE Intl. Conf. on Wireless
Communications and Networking, 2003 IEEE (ICASSP ), vol. 4, pp.
 M. Lemmon, J. Ganguly, and L. Xia, "Model-based clock
synchronization in networks with drifting clocks," in Proc. Of the 2000
Pacific Rim International symposium on Dependable Computing, Los
Angeles, CA, Dec. 2000, pp. 177-185.
 K. Romer, "Time synchronization in ad hoc networks," in Proceedings
of the 2nd ACM international symposium on Mobile ad hoc networking
and computing. 2001, pp. 173-182, ACM Press.
 Roberto Solis, V.S Borkar, P.R. Kumar, "A New Distributed Time
Synchronization Protocol for Multihop Wireless Networks" Decision
and Control, 2006 45th IEEE Conference on 13-15 Dec. 2006
Page(s):2734 - 2739
 B. Vukojevic, N. Goel, K. Kalaichevan, A. Nayak, I. Stojmenovic,.
"Power-aware Depth First Search based georouting in ad-hoc and sensor
 Mobile Wireless Communications Networks, 2007 9th IFIP International
 19-21 Sept. 2007 Page(s):141 - 145
 C.-Y. Chong and S. Kumar, "Sensor networks: evolution, opportunities,
and challenges," Proc. IEEE, vol. 91, no. 8, pp. 1247-1256, 2003.
 D. Estrin, L. Girod, G. Pottie, and M. Srivastava, "Instrumenting the
world with wireless sensor networks," Proc. IEEE Intl. Conf. on
Acoustics, Speech, and Signal Processing (ICASSP ), vol. 4, pp. 2033-
 A. Ephremides and B. Hajek, "Information theory and communication
networks: an unconsummated union," IEEE Trans. on Inform. Theory,
vol. 44, no. 6, pp. 2416-2434, 1998.