You can read "Intelligent Sleeping Mechanism for wireless sensor networks" by

Anar A Hady, Sherine M Abd, Hussein S Eissa

Egyptian Informatics Journal 04/2013; DOI:10.1016/j.eij.2013.03.002

Thank u madam

It really depends on what you want. Sometimes asynchronous duty-cycling is better, sometimes synchronous one is better (see our SenSys'13 paper for instance).

This mechanisms involves a tradeoff between energy consumption and wake up latency. The 'best' will be according to your research objective/need/environment. They can be classified as:

1. On demand (STEM / STEM-B/ STEM-T/ PTW / ...)

2. Synchronous (Fully Synchronized Pattern / Staggered Wakeup Pattern/ Forward Staggered Pattern/ Flexible Power Scheduling/ Shifted Even and Odd Pattern/ Two-Staggered Pattern/ Cross-Staggered Pattern...)

3. Asynchronous (Asynchronous Wakeup Protocol (AWP) / Random Asynchronous Wakeup (RAW) /... )