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.

Compares two performance measures used to assess the immunity of PCM regenerators to near end crosstalk, viz. the NEXT noise figure and the input signal-to-NEXT noise ratio. The NEXT noise figure is shown to be the superior performance measure, and three methods of measuring this parameter are compared on the basis of their sensitivity to implementation imperfections. It is shown that although a similar test configuration is used for each method, measurement accuracy is dependent on an associated calibration procedure. Numerical simulations indicate that measurement error can be held to 0.5 dB when practical test equipment is used to measure the performance of different commercial regenerators.

The near end crosstalk (NEXT) model proposed by Cravis and Crater [1] is analyzed to give the covariance of NEXT, with good agreement between theory and measurements on multipair cable. The covariance of NEXT is then used to estimate the variance of the meansquare NEXT interference between PCM systems operating under the same cable sheath. These results are used to derive the required minimum mean NEXT loss\mu_{0}'as a function of the number of PCM systemsN, the NEXT loss standard deviation σ, and pertinent PCM system parameters. Comparisons with the minimum mean NEXT loss proposed in [4] and [5],\mu_{0}'', and that proposed in [1],\mu_{0}''', show that:-0.4 < \mu_{0}'' - \mu_{0}' < 2dB, for1 \leq N \leq 500and6 \leq \sigma \leq 14, while-16 < \mu_{0}''' - \mu_{0}' < 6dB, for25 \leq N \leq 500and6 \leq \sigma \leq 14, for all pertinent PCM system parameters.