关键词: 第二代甚高速数字线, 信噪比, 星座映射, 近端串扰, 远端串扰

Abstract:

As broadband access network speed advances,VDSL2 technology has become the mainstream method of the last mile access.The dramatic increase in the number of user transmission makes the signal crosstalk an important factor between the transmissions lines, which restricts VDSL2 system performance. The crosstalk between the lines is divided into a nearend crosstalk (NEXT) and a farend crosstalk (FEXT).VDSL2 system uses DMT carrier modulation technique, and nearend crosstalk can be filtered out by the filter, but farend crosstalk cannot be eliminated. This paper mainly studies a method of farend crosstalk noise cancellation in VDSL2 system, proposes how farend crosstalk noise is evaluated and calculated, and derives the farend crosstalk offset formula.And it calculates the influence of crosstalk noise from other lines on each line.The receiver’s signal can eliminate the influence of crosstalk noise by the crosstalk noise preelimination algorithm at the transmitter.Therefore,SNR values of the receiver's signal and VDSL2 transmission rate are improved.

Key words: VDSL2, signal to noise ratio;constellation mapping;near-end crosstalk;far-end crosstalk