We describe a system, a wireless overlay on existing hybrid fiber/coax digital packet-based networks, for high-speed, short-range wireless access to video programming services, to the Internet, and to the telephone, cellular mobile, and other communication networks. Wireless access may be provided to both fixed (residential) users and to passersby with portable devices. Smart transponder nodes and antennas are densely distributed along the access cable line for wireless communication with user nodes. The antennas along a cable access line form an adaptive "superantenna" that is excited, for downstream transmission, by short sequences of vector signals that cancel radio interference. These excitations can be derived from a stable adaptive process. Upstream transmission from a subscriber node is designed so that the vector received by the superantenna can be used to separate this signal from that of other users' transmitters. Cooperation among end users is not necessary but is possible. Antenna excitation signals are controlled from the system headend, based on processing that uses measured channel parameters between the sets of access line and user antennas. A program controller in the headend, responding to end user requests, manages delivery of selected program streams and other customer services through generation of superimposed superantenna excitation signals that target multiple end users. This model offers opportunities for flexible capacity allocations and a wide range of programming and customized private.

The author gives an overview of progress made in the evolution of technology to provide DS1 rate telephone access in a restricted segment of the loop plant without intermediate repeaters, loop conditioning, or pair selection in assignment. This technology is called the high bit rate digital subscriber line (HDSL). Discussed are background information on electronics in the loop plant and characterization of the tranmission environment in the relevant frequency band. The progress of HDSL study project of the American National Standards Institute (ANSI) is outlined. Analytical and theoretical studies to determine the limits on the transmission capabilities of the loop plant, motivated by the need to determine the feasibility limits of HDSLs, are reviewed. Also discussed is progress in technical work on suitable transmission formats. The possibility of an asymmetrical digital subscriber line (ADSL), transmitting at the DS1 rate from the central office to a remote distribution point, through the entire nonloaded loop plant is discussed.>

The performance of two-pair dual-duplex systems is substantially improved if the transmission on one pair is coordinated with that on the other, so that the transmitted signals are two-dimensional vector pulses. The advantages of coordination of transmission in an optimal way are quantified. Signal processing gains of 1.8 dB can be achieved in this way by averaging the SNRs on the two pairs constituting the high rate digital subscriber line (HDSL) and by canceling the near-end crosstalk (NEXT) between them. Exploitation of pair-to-pair correlation of NEXT voltages on the constituent pairs provides an additional source of processing gain. Under reasonable assumptions concerning the distribution of NEXT coupling coefficients between cable pairs, there is a better than 50% chance that the signal processing gain achieved by exploiting pair-to-pair NEXT correlation will be greater than 1.5 dB. Coordinated transmission requires the adaptation of four flat gain amplifiers in transmitters to achieve its optimum system configuration.>

An interpolation theorem is determined for the case when there are a finite number of arbitrarily placed sampling instants and the interpolation function is the output of a known filter. They are also the interpolation functions with the specified properties that have minimum energy. The theorem is used to determine the input to a communications channel given a finite number of samples of its output. This provides a generalization of matched filters and a perspective on the benefits of fractionally spaced equalization. The theorem is also used to construct masks of a family of pulses that are specified by the range of pulse voltages at a finite number of sampling instants. The theory determines how the pulse masks thus constructed is transformed when the pulse family is transmitted through a filter such as a length of transmission line.>

A determination is made of the combinations of transmitted block codewords and matching receiver filters that maximize the signal-to-noise ratio at the detector with arbitrary channel impulse response and arbitrary noise spectrum. This permits representing the channel as a set of parallel, uncoupled subchannels with uncorrelated noise; the representation is used to calculate the capacity of an arbitrary block coded, time discrete channel. It is shown that substantial coding gains, compared to symbol-by-symbol processing, can be achieved. The block code used can be concatenated with trellis-coded modulation so that the two coding gains are additive.>

This paper is a mathematical analysis of digital subscriber lines that use adaptive decision feedback equalization (DFE). Adaptive transversal feedforward filters (FFF) and feedback filters (FBF) with baud rate sampling are assumed. In order that all block codes are considered in the model, correlation between the values of the transmitted symbol values is included. Additionally, added noise is not assumed to be white, to permit the eyaluation of the effects of near end crosstalk and residual echo noise. It is shown that the correlation between the transmitted symbols causes the FBF to adapt differently than they usually do (i.e., cancel intersymbol interference within the range of the FBF) in two ways: the FBF uses the correlation between transmitted symbols to reduce the intersymbol interference outside of its range, and a bias vector is added to the FBF tap weights that adjusts future slicing levels to account for the variable likelihood of future transmitted symbol values. It is found that the received signal-to-noise ratio is approximately a linear function of loop insertion loss when the loss is high and noise is low.

The status of the formulation of standards for loop transmission to provide Basic Access in the North American loop plant is reviewed. The impact of loop plant bridged taps on performance is discussed, the reasons for preferring echo canceller technology over time compression multiplexing are reviewed, and issues involved in the specification of echo canceller requirements are discussed. This includes line code selection and receiver design, including linear and decision feedback equalizer design. Some of the possible methods of timing recovery are reviewed, and future directions for the evolution of Basic loop access are considered.

It is shown that the maximum instantaneous near-end crosstalk interference voltage on a cable pair can be constrained by restricting the energy transmitted in any time interval of a duration determined by the cable properties. The maximum interference is proportional to the sum of the energies in the impulse responses of the equalized near-end crosstalk paths to the disturbed pair.

Instantaneous near-end crosstalk interference depends only on the shape of the signals transmitted on the disturbing pairs during an interval of duration determined by cable properties that immediately precedes observation of the interference. It is shown that these shapes can be resolved into a linear combination of a finite number of orthonormal functions that cause significant crosstalk and a function that does not cause substantial crosstalk. The orthonormal functions are the solution of an equation that depends on the statistical properties of the crosstalk.

A previous paper showed that constraining the total energy transmitted on all pairs in a cable during any time interval of a specified duration limits the maximum instantaneous near-end crosstalk voltage on any pair. This paper determines a constraint on the energy that is the same for each pair and that guarantees the same limit on near-end crosstalk. While the new constraint permits less variation of transmitted power among the pairs, it permits greater average power per pair. Thus, the constraint developed herein would be particularly useful when a cable is used principally for one type of capability, e.g., ISDN basic access.