Alcatel-Lucent's research arm, Bell Labs, has achieved a broadband DSL download speed of 300Mbps at distances of up to 400 meters (or 100Mbps at 1km) over existing copper line infrastructure. Most of BT's telephone and broadband ISP network in the UK is still copper line based, where at present the best speeds available only go up to 40Mbps ( FTTC / VDSL2 ).

The technology itself is called DSL Phantom Mode and critically makes use of "two digital subscriber lines (DSL)" to achieve the speed. At its core, DSL Phantom Mode involves the creation of a virtual (phantom) channel that supplements the two physical wires that are the standard configuration for copper transmission lines.

The source of DSL Phantom Mode’s dramatic increase in transmission capacity lies in its application of analogue phantom mode technology in combination with industry-standard techniques: vectoring that eliminates interference (crosstalk) between copper wires, and bonding that makes it possible to take individual lines and aggregate them.


At these speeds ISPs could maximize the ability of existing copper infrastructure - widely deployed around the world - to satisfy demand for bandwidth-intense residential triple-play and business services and without the need to rollout a full fibre optic broadband network directly into homes and businesses ( e.g. FTTH ).

At present BT's new Fibre-to-the-Cabinet ( FTTC ) technology delivers a fast fibre optic link to the operators street level cabinets, while the remaining connection (between cabinets and homes) is done using VDSL2 (similar to current ADSL broadband but faster over short distances) through existing copper cable; FTTC will initially deliver speeds of up to 40Mbps (uploads should reach up to 10Mbps).

The VDSL2 part of this connection usually runs over a fairly short "last mile" distance and its conceivable that DSL Phantom Mode, which runs at its best within a similar environment, might one day replace that. Of course bonded services can be very expensive and Alcatel-Lucent admit that further research must first be conducted to refine the technology. In other words, don't expect to see this for awhile.

UPDATE 23rd April 2010

Speaking off the record to a BT technical rep, it is understood that transmission in 'Phantom Mode' is not new or novel and builds on ideas from the 90s. The operator points out that it is still in research phase and, while interesting, there remain some [technical] issues to overcome like EMC aspects.

Electromagnetic Compatibility (EMC) is the term used to describe how affectively a system is able to function in an electromagnetic environment without introducing EM disturbances that interfere with the operation of other electrical products in the environment. In other words it's a good idea but one that has yet to overcome some critical problems.