Statistical Behavior of Multipair Crosstalk

Baseband digital transmission systems,1"10 such as T l , TIC, SLCTM-40, SLCTM-96 and other similar systems,11"16 are being used increasingly on existing twisted multipair cables in short-haul trunk and subscriber loop networks as an economic alternative to analog voiceband transmission. This penetration will be further accelerated by the introductions of direct digital interfaces to ESS machines, digital central offices, and remote digital switching machines. New technologies, including large-scale integrated circuit and digital system approaches, and market growth in direct digital services to the customer premises17"19 will also enhance the use of digital transmission. It therefore becomes important to understand the performance and the 955 limitations of various existing and future digital transmission systems on twisted-pair cables. Crosstalk interference is a prime limitation on the transmission capacity and the repeater spacing of digital systems on twisted multipair cables. An important step in the design of digital systems and their associated engineering rules is the characterization of the power sums of pair-to-pair crosstalk losses.20'31 The crosstalk power sum is the total crosstalk interference which appears on a given pair as a result of coupling from all disturbers on other pairs in the cable. Development of an accurate crosstalk model will allow maximum exploitation of the transmission capability of the vast existing network of twisted, multipair cables. This may be achieved by operating a larger number of digital systems in a given cable, by using a longer repeater spacing, or by using higher bit rate systems.