Crosstalk theory is applied to the prediction of error rates in digital line systems due to analog telephony signaling events on adjacent pairs in the same cable. Measurements of the margin against impulsive noise at a given probability of error have been performed, and these show reasonable agreement with predictions based on crosstalk theory. For a simple switching event, the regenerator NEXT impulsive noise figure for the near-end crosstalk path is defined. Measurements of the mean and variance of near-end crosstalk attenuation are then used to calculate the maximum exchange section loss (from central office to first line regenerator) which satisfies a suggested error performance criterion.

This paper considers the cyclostationary nature of digital signals when determining crosstalk interference between such signals in multipair cable. This approach is necessary as the interference is only relevant at the decision instants in the receivers of the disturbed systems and any time variation of this interference with respect to the sampling instants changes the effect of this interference; previous studies in the area have ignored the cyclostationary nature of the digital signal. Expressions for the time-varying mean and variance of far-end and near-end crosstalk (FEXT and NEXT) have been derived. These expressions demonstrate the inherently smaller time variation of the NEXT interference when compared to the FEXT interference. An interesting result is that the calculation of the time-averaged value of the variance of FEXT and NEXT interference still requires the use of the cyclostationary properties of the digital signal. The results of this paper are extended and applied to various examples of the engineering of digital line systems in multipair cable in Part II of this paper.

In this paper, the results of Part I are applied to the engineering of primary-level digital line systems in multipair cable operating in either a nonsynchronous or a synchronous network. It is shown that the erstwhile incorrect assumption that crosstalk interference from digital line systems is wide sense stationary, and not cyclostationary, leads to an overestimation of system margin of less than 1 dB. It is also shown that the change from a nonsynchronous to a synchronous network leads to a reduction in system margin which is difficult to quantify exactly, but it is typically less than 2.5 dB for FEXT and 1.5 dB for NEXT. The paper concludes with a consideration of the cyclostationary nature of block,encoded digital signals such as 4B3T, MS43, etc., and extends some of the results of Part I.