A square distance-based byte-erasure method for reduced-delay protection of DSL systems from non-stationary interference

DSL systems achieve high rate transmission through copper pairs traditionally used for voiceband communication. In order to attain high rates, sophisticated system designs are employed to cope with both stationary and non-stationary disturbers. In current DSL systems, protection against nonstationary interference, comprising impulse noise and radio frequency ingress (RFI), is achieved using a forward error correction (FEC) scheme consisting of a Reed-Solomon (RS) code and interleaving. However, interleaving results in increased end-to-end delay. The end-to-end delay can be reduced by taking advantage of the erasure decoding property of RS codes. The paper presents a byte-erasure technique that allows erasure decoding to be employed. The method locates the possibly erroneous bytes in each RS codeword by comparing the square distance between each received carrier symbol of the interleaved stream and the closest point of the constellation to which the symbol belongs. Thus, the interleaving delay can be reduced by a factor up to 2 when impulse noise impairs transmission. The method can also be applied to systems affected by both impulse noise and RFI, since it can distinguish between the two sources of non-stationary interference. Finally, no change is required at the transmitter, and hence compatibility with currently deployed systems is guaranteed. A DMT-VDSL system is used as a particular example of the achieved reduction of the interleaving delay.