A Marcinkiewicz integral type characterization of the Sobolev space
  In this paper we present a new characterization of the Sobolev space $W^{1,p}$, $1<p<\infty$ which is a higher dimensional version of a result of Waterman. We also provide a new and simplified proof of a recent result of Alabern, Mateu and Verdera. Finally, we generalize the results to the case of weighted Sobolev spaces with respect to a Muckenhoupt weight. 
Piotr Haj{\l}asz and Zhuomin Liu
math.FA