Abstract: A receiver, comprising an adaptive filter, performs blind equalization using a modified form of the constant modulus algorithm (CMA). This modified form of CMA is referred to as symbol CMA (SCMA). SCMA utilizes both the constant R and the sliced symbols, Ân, in performing blind equalization. The constant R is statistically created to the sliced symbols, Ân. The adaptive filter is a two-filter structure. The SCMA blind equalization technique reduces the rate of occurrence of a diagonal solution.

Abstract: A receiver, comprising an adaptive filter, performs blind equalization using a modified form of the constant modulus algorithm (CMA). This modified form of CMA is referred to as phase compensating CMA (PC-CMA). PC-CMA includes a phase-compensating term in the tap updating algorithm of the equalizer such that convergence to a straight constellation is achieved without the need of a rotator.

Abstract: In an Asymmetric Digital Subscriber Loop (ADSL) Discrete Multi-Tone (DMT) system, a DMT receiver uses, during start-up, an automatic gain control (AGC) element and a rotator element in place of a one-tap complex finite impulse response (FIR) filter.

Abstract: A communications system employs frequency division duplexing to accommodate symmetric and asymmetric services, while substantially eliminating near-end cross talk. Upstream and downstream channels are separated by a guard band in order to insure that near-end cross talk is kept to a minimum. An asymmetric upstream channel is preferably located at a lower frequency range than that of the asymmetric downstream channel. The guard band between these asymmetric upstream and downstream channels shifts in frequency along with the shift in frequency of the respective upstream and downstream channels as a function of reach. This guard band shifting permits the communications systems to utilize a greater percentage of the frequencies available to it and to thereby substantially maximize the communications rate that it can support. Although the asymmetric guard band is allowed to shift in the manner described, it is not allowed to do so in a manner that would create a conflict with symmetric channels.

Abstract: A receiver, comprising an adaptive filter, performs blind equalization using a joint constant modulus algorithm—multimodulus algorithm (CMA-MMA) blind equalization algorithm. The adaptive filter is a two-filter structure. The receiver performs CMA-MMA blind equalization using asymmetric algorithms. This joint CMA-MMA blind equalization technique reduces the rate of occurrence of a diagonal solution.

Abstract: A communications system employs frequency division duplexing to accommodate symmetric and asymmetric services, while substantially eliminating near-end cross talk. Upstream and downstream channels are separated by a guard band in order to insure that near-end cross talk is kept to a minimum. An asymmetric upstream channel is preferably located at a lower frequency range than that of the asymmetric downstream channel. The guard band between these asymmetric upstream and downstream channels shifts in frequency along with the shift in frequency of the respective upstream and downstream channels as a function of reach. This guard band shifting permits the communications systems to utilize a greater percentage of the frequencies available to it and to thereby substantially maximize the communications rate that it can support. Although the asymmetric guard band is allowed to shift in the manner described, it is not allowed to do so in a manner that would create a conflict with symmetric channels.

Abstract: A receiver has a dual mode of operation—a carrierless amplitude modulation/phase modulation (CAP) mode and a quadrature amplitude modulation (QAM) mode-yet only requires a single equalizer structure for both the CAP mode of operation and the QAM mode of operation during blind start-up. The receiver uses the same blind equalization updating algorithm independent of the type of received signal for converging the equalizer structure. The blind equalization updating algorithm incorporates a constant R, whose value is a function of the type of received signal, e.g., a QAM signal or a CAP signal. The type of received signal is determined as a function of the in-phase component of the mean-squared error, E[e2n.

Abstract: A blind convergence technique is restricted to using a subset of equalizer output samples. Illustratively, a receiver implements a windowed MMA approach. In this windowed MMA approach, a sample window overlays the two-dimensional plane representing the set of equalizer output samples. Only those equalizer output samples appearing within the sample window are used during filter adaptation.

Abstract: A decision feedback equalizer (DFE) comprises a feed-forward filter and a feedback filter. Blind training of the DFE is performed using a statistical-based tap updating algorithm for the feed-forward filter, and a symbol-based type of tap updating algorithm for the feedback filter.

Abstract: The problem of tracking rapid changes in the echo signals associated with modems is eliminated by using an echo canceler consisting of cascaded adaptive filters. Each filter in the structure contributes to the modeling of the overall echo path impulse response, with a longer filter providing the ability to model long echo path impulse responses and a shorter filter providing the ability to track changes in the echo path impulse response over time.

Abstract: A generalized form of a multimodulus algorithm (GMMA) is described for use in blind equalization. A receiver uses a signal point constellation representing 256 levels. This signal space is divided into sample, or data, subsets. Cost function minimization is done with respect to each sample subset.

Abstract: The problem of error propagation is resolved by using the communications channel to adapt a pre-equalizer of a transmitter, in response to changes in the communications channel. In particular, the pre-equalizer adapts to changes in the communications channel by processing an error signal that is communicated over a reverse channel by a corresponding receiver.

Abstract: A blind equalization cost function called the "constrained Hilbert cost function" (CHCF) provides for reliable blind convergence of a two-filter equalizer structure. In particular, the CHCF cost function is designed in such a way that the two filters are constrained to be a Hilbert pair. Advantageously, this technique can be used with any blind equalization algorithms, such as RCA, CMA, and MMA.

Abstract: The problem of tracking rapid changes in the echo signals associated with modems is eliminated by using an echo canceler consisting of cascaded adaptive filters. Each filter in the structure contributes to the modeling of the overall echo path impulse response, with a longer filter providing the ability to model long echo path impulse responses and a shorter filter providing the ability to track changes in the echo path impulse response over time.

Abstract: A blind equalization technique uses both the "constant modulus algorithm" (CMA) and the "multimodulus algorithm" (MMA) during blind start-up. This approach provides the basis for a "transition algorithm." One example of a transition algorithm is the CMA-MMA transition algorithm in which an adaptive filter simply switches from CMA to MMA. Other examples are variations of the CMA-MMA transition algorithm and are illustrated by the "Constant Rotation CMA-MMA" transition algorithm and the "Dynamic Rotation CMA-MMA" transition algorithm.

Abstract: A device for providing conferencing communications. The device comprises: a summing circuit for forming a signal sum equal to a sum of signals received from at least three information signal sources along with an echo compensation signal, the signal received from each information source including echoes and the signal sum including an aggregation of such echoes; an adaptive filter having an input and an output, the input being solely responsive to the signal sum and the output being only coupled to the summing circuit, the filter forming the echo compensation signal which is an estimate of the aggregation of echoes; and a low level training sequence generator having an amplitude less than a predetermined level.

Abstract: A blind equalization technique--the multimodulus algorithm (MMA)--adapts coefficients of an equalizer so as to minimize dispersion of the output samples of the equalizer around piecewise linear contours of a signal space. The MMA technique is illustrated in the context of both square and non-square signal point constellations.

Abstract: Briefly, in accordance with one embodiment of the invention, an adaptive equalizer comprises: a digital filter including filter tap coefficients; a slicer; and a filter tap coefficient update block. The filter, slicer and coefficient update block are configured so as to perform at least one burst update of the filter tap coefficients. In accordance with another embodiment of the invention, a method of updating the filter tap coefficients of an adaptive equalizer comprises the step of: performing at least one burst update of the filter tap coefficients.

Abstract: Symbols which are representative of customer data are transmitted in bursts. In the idle mode, i.e., the time intervals between bursts, symbol sequences which are a priori known to the receiver are transmitted. Such idle mode symbols maintain adaptive apparatus, such as NEXT cancellers and equalizers, in their properly converged state. To reduce crosstalk and spectral emissions, the idle mode symbols are selected to be the innermost symbols in the signal constellation encompassing the ensemble of all symbols.

Abstract: Timing control resolution between two communications devices is provided by assigning each device to one of a plurality of priorities and by transmitting an identification of this priority to the other communications device. The determination of which device is the master and which device is the slave is then resolved by comparing the received and transmitted identifications from the contending devices to a predetermined ranking of identification signals. When such identifications signals are the same, each device randomly selects an identification signal from a group of such signals. Preferably this group includes all of the identification signals except that transmitted in the immediately prior contention round. The received and transmitted identifications signals from the contending devices are then compared to the predetermined ranking of identification signals.