This paper presents the performance of various coding schemes for the asymmetrical digital subscriber line (ADSL) in an impulse-noise environment. Impulse noise is considered to be one of the most damaging impairments in the ADSL, in which compressed video signals are delivered to residential customers. The impulse noise used in this study was measured and collected in German telephone networks. Based on this measurement and the corresponding statistical modeling, a simulation model for impulse noise is proposed and its properties are outlined. The coding schemes considered here utilize burst-error correcting Reed-Solomon codes and/or random error correcting trellis codes as well as symbol interleaving between the two codes. It has been found through computer simulations that a proper concatenation of the two codes could increase the immunity against impulse noise compared to an uncoded scheme. Specifically, a concatenated code, using a 2-dimensional 8-state trellis code and a 4-error-correcting Reed-Solomon code with an interleaving depth of 18 symbols, was able to eliminate all the errors caused by the impulse noise used in the study. It has also been found that the trellis codes are not very effective against impulse noise, unless they are used in conjunction with Reed-Solomon codes and a proper symbol interleaving. Performance results of other coding configurations using Reed-Solomon codes with different error-correcting capabilities are also presented. In addition, we also show the performance results when simple array codes are used instead of the Reed-Solomon codes

A general-purpose modulation and coding implementation that is based on the quadrature amplitude modulation (QAM) family of modulation is described. The technique utilizes the 'superposed' property of certain rectangular QAM constellations, along with the fact that optimal four-state trellis codes for such constellations are essentially identical, to provide a single modem architecture capable of performing over a wide range of power and bandwidth efficient transmission using either an uncoded or a coded modulation scheme. While the specific modulation and coding techniques are not new, the authors believe that their intrinsic compatibility is not well known and provides attractive system flexibility.>

An analytical approach for investigating the effect of noise correlation on the performance of trellis-coded communication systems is described. Several trellis codes are investigated in the presence of colored noise, and computer simulation and real-time experimental results are given to confirm the analysis. In some practical cases, the actual coding gain could be as small as a fraction of 1 dB as opposed to the nominal 4-5 dB of coding gain that can be obtained on additive white Gaussian noise (AWGN) channels. A filter swapping technique which eliminates the performance degradation due to the effect of noise correlation is proposed. It is shown that if the equalizer is moved from the receiver to the transmitter and is scaled to satisfy an average power constraint, then the noise at the Viterbi decoder input is white and the signal-to-noise ratio remains the same. Doing this allows the nominal coding gain to be achieved.>