Implementation of DMT: ADSL
John A. C. Bingham · 2001
A simple block diagram of an Asymmetric digital subscriber loop (ADSL) system is given in this chapter. It is important to note the two stages of “splitting”: from the line side the POTS and the xDSL (both bidirectional) are first separated by the low-pass and high-pass filters, and then the xDSL transmit and receive signals (unidirectional) may be separated by any combination of filters, 4W/2W hybrid, and echo canceler. In this chapter we describe most of the components and incorporated algorithms of such a system: Sections cover the transmitter, transmitter/receiver interconnection, the receiver, and the algorithms. Some of the components are generic to xDSL, some specific to DMT xDSL, and some even more specific to DMT ADSL or VDSL. Some components—POTS splitters, IFFTs and FFTs, and equalizers—however, deserve chapters or appendices of their own. In this chapter we deal with what has already been implemented; possible components of future xDSL modems—improved equalizers and RFI cancelers, and crosstalk cancelers—are discussed in Chapter 11.