ADSL system for time periodic noise environments

xDSL (Digital Subscriber Line) is a group of technologies for transmitting high-speed digital signals over existing metallic cables. xDSL was original ly studied in the USA. These technologies have spread to other areas of the world, including Europe and Asia. In this process of introducing this tech nology to the different areas, several new local but critical problems have emerged, due to the local system and cable situations. In Japan, TCM (Time Compression Multiplex)-ISDN is widely used. This ISDN causes periodic cros stalk noise of Far End Crosstalk (FEXT) and Near End Crosstalk (NEXT) to xD SL. For the optimization of the transmission performance to this type of no ise, it is efficient to use different bit assignments corresponding to the FEXT period and NEXT period. NEC has proposed a solution of the optimizatio n for ADSL (Asymmetric DSL) transmission under the TCM-ISDN crosstalk noise environment. We have compared the following transmission methods, the exis ting ANSI-ADSL, Dual Bitmap (DBM)-ADSL, Single Bitmap (SBM)-ADSL and TCM-AD SL, with some simulation results. This shows that the performance of ANSI-A DSL is greatly degraded by ISDN crosstalk disturbance, and DBM-ADSL improve s the performance significantly. SBM and TCM-ADSL also have better performa nces in a long reach with small modifications. The study results are explai ned.