On weighted U-statistics for stationary processes
  A weighted U-statistic based on a random sample X_1,...,X_n has the form U_n=\sum_{1\le i,j\le n}w_{i-j}K(X_i,X_j), where K is a fixed symmetric measurable function and the w_i are symmetric weights. A large class of statistics can be expressed as weighted U-statistics or variations thereof.   This paper establishes the asymptotic normality of U_n when the sample observations come from a nonlinear time series and linear processes. 
Tailen Hsing and Wei Biao Wu