This book has been written by the author as a result of the research and development work done during his Ph.D. in the area of Wireless Sensor Networks. In his Ph.D. he worked upon various areas of IEEE 802.15.4 like: Topologies, Modulations, Motes, Frequencies, Packet Sizes etc. After working on these vast fields for few years, author realized that the results obtained can be presented in the form of a book.