Pilot-Based Crosstalk Channel Estimation for Vector-Enabled VDSL Systems

Recently, the International Telecommunication Union has consented the ITU-T G.993.5 recommendation on vectoring in VDSL2 technology, which specifies the required functionality for interoperability between chipsets of different vendors to achieve vectoring. This paper will briefly review the principles of vectoring and the underlying precoding and channel estimation techniques. This framework is then used to introduce mechanisms for crosstalk channel estimation that exploit channel smoothness with the aid of frequency-dependent pilot sequences, as well as mechanisms that allow fast and simultaneous initialization by targeted assignment of pilot sequences. A pilotbased technique is described that exploits the robustness of the synchronization symbols to estimate crosstalk emanating from "legacy" VDSL2 lines within a vectoring group. This allows cancellation of crosstalk from legacy lines without replacement of the installed VDSL2 customer premises equipment. Some of these techniques are compatible with the current version of ITU-T G.993.5 recommendation, while others require changes that are under consideration for possible inclusion in future amendments.