Inwhee Joe Taewon Ahn An Efficient Bi-directional Routing Protocol for Wireless Sensor Networks. 1-4 2007 MobiQuitous http://dx.doi.org/10.1109/MOBIQ.2007.4451050 conf/mobiquitous/2007 db/conf/mobiquitous/mobiquitous2007.html#JoeA07