A hybrid precoding scheme for crosstalk cancelation in downstream VDSL system

At present, Vectored transmission technique has been widely used for the far-end crosstalk (FEXT) cancelation in digital subscriber line (DSL) system. To reduce the overhead due to SNR feedback for vectoring, a new FEXT cancelation scheme combining random codebook and channel quantization is proposed in this paper. In the scheme, a factor α_m is defined to indicate the degree of FEXT coupling loss. Random codebook is utilized when α_m is larger than the threshold which means FEXT is small. On the contrary, when the FEXT is serious and random codebook is not effective, the channel state information (CSI) which is quantized at receivers will be sent back to the transmitter. The amount of feedback is analyzed in the paper and it shows that the proposed method has reduced the overhead sharply compared to the current SNR-based method. Moreover, the proposed method has nearly the same performance as the scheme which requires perfect channel state information (PCSI).