Full vectoring optimal power allocation in xDSL channels under per-modem power constraints and spectral mask constraints

摘要

In xDSL systems, crosstalk can be separated into two categories, namelyin-domain crosstalk and out-of-domain crosstalk. In-domain crosstalk is alsorefered to as self crosstalk. Out-of-domain crosstalk is crosstalk originatingfrom outside the multi-pair system and is also denoted as external noise (aliencrosstalk, radio frequency interference,...). While self crosstalk in itselfcan easily be canceled by a linear detector like the ZF detector, the presenceof external noise requires a more advanced processing. Coordination betweentransmitters and receivers enables the self crosstalk and the external noise tobe mitigated using MIMO signal processing, usually by means of a whiteningfilter and SVD. In this paper, we investigate the problem of finding theoptimal power allocation in MIMO xDSL systems in the presence of self crosstalkand external noise. Optimal Tx/Rx structures and power allocation algorithmswill be devised under practical limitations from xDSL systems, namely per-modemtotal power constraints and/or spectral mask constraints, leading to ageneralized SVD-based transmission. Simulation results are given for bondedVDSL2 systems with external noise coming from ADSL2+ or VDSL2 disturbing lines,along with a comparison between algorithms with one-sided signal coordinationeither only at the transmit side or the receive side.