Fext

Abstract: A scheme for compensating for both near-end (NEXT) and far-end (FEXT) crosstalk within a communication connector having first and second pairs of contact wires. A first stage of compensation includes capacitive coupling that corresponds in magnitude to a sum of offending capacitive and offending inductive crosstalk both of which originate from a mating connector. At a second stage of compensation, both (a) inductive coupling corresponding in magnitude to the offending inductive crosstalk, and (b) capacitive coupling corresponding in magnitude and of opposite polarity to the inductive coupling, are produced. In the disclosed embodiment, the first and the second compensation stages are implemented in an industry type RJ-45 communication jack to meet or surpass Category 6 NEXT/FEXT loss levels.

Abstract: Multi-tone transmission is a potentially viable technique for application on asymmetric digital subscriber lines (ADSLs). The results of a preliminary study on the performance of an ideal discrete multi-tone (DMT) signaling technique for a 1.6-Mb/s ASDL are presented. The performance margins using single-tone 16-point quadrature amplitude modulation (QAM) with ideal decision feedback equalization (DFE) are presented. The feedforward filter of the DFE is a quarter-baud spaced fractionally spaced equalizer (FSE). The interference is assumed to be the sum of far-end crosstalk (FEXT) and additive white Gaussian noise (AWGN). The subscriber loops are assumed to be in a plant environment where the maximum resistance does not exceed 1300 /spl Omega/. The projected performance of an ideal DMT with a sampling rate of 1.024 MHz and 256-subchannel segmentation offers potential margin enhancement up to 3 dB over a quarter baud-spaced FSE-based 16-QAM signaling. >

Abstract: A system and method for determining transmission characteristics for a communications channel and for transmitting data on the communications channel. In one embodiment, the method starts by determining the channel's transfer function and determining interference characteristics for the channel. The interference characteristics preferably include transfer functions describing the channel's susceptibility to cross talk from neighboring channels. The channel transfer function and the interference characteristics are then examined and a transmit spectrum (or power spectral density function) is constructed for the channel. The transmit spectrum preferably uses orthogonal separation of upstream and downstream communications to increase channel capacity. This method is useable in communicating data when the channel is subject to interference from one or more other communications channels, including near-end cross talk (NEXT) and far-end cross talk (FEXT), from other channels carrying the same service and/or different services. The present invention may be used in digital subscriber-line (xDSL) communications or in a variety of other applications, such as in well-logging and in systems involving multiple interfering radio transmitters.

Abstract: Methods, apparatus, techniques and computer program products for joint reduction of crosstalk in a synchronized, time division duplexed DSL systems use sequential removal of NEXT interference followed by removal of FEXT interference from a received DSL signal. Crosstalk is removed from a primary signal in a synchronized TDD DSL system having a primary channel that carries the primary signal, at least one NEXT generating channel that generates NEXT interference in the primary signal and at least one FEXT generating channel that generates FEXT interference in the primary signal. Signal data is acquired, where the signal data includes received signal data for the primary channel and at least one FEXT generating channel, transmitted signal data for at least one NEXT generating channel, and channel data comprising channel transfer function data and crosstalk coupling coefficient data for the primary channel, each NEXT generating channel and each FEXT generating channel. After the signal data is acquired, NEXT interference in the primary signal is then removed using the transmitted signal data and the channel data, followed by removal of FEXT interference in the primary signal using vectored DMT FEXT removal, the received signal data and the channel data. In another system in which FEXT generating received signals are not necessarily available, FEXT removal can be achieved using expectation cancellation, the primary signal and the channel data in connection with possible transmitted signal values.