On the capacity of a twisted-wire pair: peak-power constraint

The capacity of a twisted-pair channel (TPC) with a peak-power constraint imposed on the transmitted signal is considered. Bounds on the capacity are evaluated for two models of the near-end crosstalk (NEXT). The NEXT is modeled either by a peak-limited signal governed by the same probability law characterizing the transmitted signal, or by a Gaussian process possessing the same power spectral density as that of the transmitted signal. White Gaussian noise is also present in addition to the NEXT interference. The important case of NEXT-dominated interference for which the bounds do not depend on the specific pulse-shape used, and therefore apply also for the optimized pulse amplitude modulation (PAM) scheme, is particularly examined. Optimized channel symbol rates and bounds on the number of information bits per channel symbol are evaluated using a certain PAM format and a suboptimal receiver. A comparison between optimally coded and uncoded PAM schemes is performed for the NEXT-dominated TPC. The results presented extend those reported in a previous work by I. Kalet and S. Shamai (see ibid., vol.38, p.379-83, Mar. 1990) on the capacity of a TPC in which a Gaussian model for both the transmitted and the NEXT signals is adopted and only an average power constraint on both signals is imposed.<
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