Zixiang Xiong Kannan Ramchandran Cormac Herley Michael T. Orchard Flexible tree-structured signal expansions using time-varying wavelet packets. 333-345 1997 45 IEEE Transactions on Signal Processing 2 http://dx.doi.org/10.1109/78.554299 db/journals/tsp/tsp45.html#XiongRHO97