VDSL, from concept to chips

Over the previous decades, successive DSL technologies have increased the transmission speeds over the telephone access network from 33.6 Kbit/s for analog modems to about 8 Mbit/s with ADSL. VDSL, or Very high-speed Digital Subscriber Line, puts the copper loop in an even higher gear. VDSL can transport data at tens of Megabits-per-second (Mbit/s) over conventional copper twisted pairs that have been used for more than a century - till the emergence of HDSL and ADSL - to carry only voice calls or low-speed data. Whereas ADSL (Asymmetric DSL) brings you Internet downloads at high speeds and good quality video, VDSL can deliver several films simultaneously. To enable such super-fast traffic, the frequency band over which the system operates has to be increased, from about 1 MHz for ADSL to over 10 MHz for VDSL. This requires faster digital signal processing and analog (integrated) components with higher bandwidths. In addition the system has to withstand loop impairments that were inexistent or less stringent for other DSL variants. Once again (as for ADSL) Discrete MultiTone (DMT) transmission turns out to deliver the required performance. If carefully implemented, DMT can be combined with frequency division duplexing (FDD) without requiring filters for up- and downstream frequency band separation, resulting in extreme flexibility for spectral shaping and band allocation, while simplifying the design. This paper takes you in a couple of pages from the concepts up to the implementation of a system on chip. It shows how a very performant and flexible FDD-DMT system can be integrated while meeting the requirements on power and size.