Zipper VDSL: a solution for robust duplex communication over telephone lines

We overview a digital duplex scheme called Zipper, intended for DMT-based VDSL systems. The Zipper multicarrier duplex scheme represents a breakthrough toward digital implementation of frequency-division duplexing. A duplex scheme is a method to divide the capacity of a line between the upstream and downstream directions. Zipper divides the available bandwidth by assigning different subcarriers for the different directions. As a prerequisite, DMT symbols are extended with an additional cyclic suffix, and are shaped at both the transmitter and receiver. Zipper is characterized by high flexibility and high spectral compatibility with programmable spectrum usage, robustness against frequency-selective impairments such as radio frequency interference and bridge taps, interoperability with ADSL, and high spectral efficiency since no guard bands are needed.