Liu Shengmei, born in 1977. She received her B.S. and M.S. degrees from Nanjing University of Posts and Telecommunications in 1999 and 2002, re- spectively, and her Ph. D. from Southeast University in 2005, all in Communication and Information System. She is currently an assistant professor of Nanjing Uni- versity of Posts and Telecommunications. Her research interests include vertical handoff technology for hetero- geneous networks.To whom correspondence should be addressed. E-mail: smliu@ njupt, edu. cn