DESIGN OF DIGITAL TRANSMISSION SYSTEMS OPERATING ON PAIR CABLES

Digital transmission systems operating on multipair cables between exchanges in urban areas have been widely introduced in recent years. These systems operate at 2.048 Mbit/s (30 channel system) ._Because of the close proximity of the pairs in the cable and the unavoidable small imbalance in the geometries of pairs, coupled crosstalk inrerference between these
Systems occurs and limits the repeater span and/or the number of digital
systems that are carried in the cable. This paper addresses the general problem of estimating the maximum number of pcm systems allowed on one cable, given pcm repeater characteristics and cable data. Starting with a unified approach,the system parameters determining performance limitations due to near – end crosstalk (NEXT) and far- end crosstalk (FE:XT) are identified. to gaurantee the desired error rate for each repeater section, the minimum average NEXT and FEXT loss requirement at Nyquist freguency as a function of repeater spacin9,and number of PCM systems operating on the cable is obtained. Graphical results presented fore commonly used raised cosine channel shaping and different types of channel coding such as AMI, HDB3, 4B3T... will aid the system design with repeater spacing loss up to 50 tdB.