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The art of Spectral Management; Downstream power back-off for VDSL2 - Whitepaper DSL04


Author: Brink, R.F.M. van den
Publisher: TNO
Place: Delft
Institution: TNO Informatie- en Communicatietechnologie
Identifier: 348031
Report number: 35093


Spectral Management (SpM) involves managing an access network such that different systems can co-exist with each other. In relation to DSL systems, spectral management ensures that they can co-exist within the same cable. The use of spectral signal limits (specified via mandatory access rules) is necessary for all DSL deployments, and serves a common interest of all involved DSL operators. VDSL2 is a new technology, and can be deployed from remote locations such as street cabinets to shorten the loop to the home and thus increase the achievable bitrate. However, remote deployments can easily disturb legacy deployments (e.g. ADSL) from the central office if the transmit power is not reduced properly. This is called downstream power back-off (DPBO). Such reductions can only be effective if they are tailored to underlying business needs, installed base of legacy equipment selected degree of protection, and loop characteristics. These are all country or region specific, and cannot be copied blindly from neighbouring countries. This paper explains the need for DPBO, and shows that an effective amount of DPBO can protect legacy deployments at the cost of only a small penalty for the VDSL2 performance itself.