Abstract: A device (100) and method (400) are set forth that provide a parity check that utilizes a nonlinear dependence upon bits other than the parity bit alone. The 4D 16-state Wei trellis code is made transparent to m.multidot.90 degree rotations by utilizing a parity generating unit that generates a parity check bit based on at least a second rotationally significant label bit. The parity check bit allows detection of errors in a first rotationally-significant label bit, i.e., allows for achievement of a rotationally transparent parity check.

Abstract: A decoder including first and second decoding stages for selecting a codeword near to a given N-tuple r which is a sequence of N real values r.sub.i representing signals. The first stage includes substages associated respectively with sections r.sub.j of N-tuple r, each substage for evaluating distances between multiple sets of possible partial codewords and the section r.sub.j and for selecting a survivor from each of the multiple sets based on the distances. The second stage includes n-1 substages, each of which operates with respect to a supersection made up of a combination of two parts, each part being a section or a supersection combined in an earlier substage of the second stage and it includes a final substage which operates with respect to a final supersection whose parts make up the complete N-tuple r.

Abstract: A Voronoi signal constellation includes those points of a coset of a lattice .LAMBDA. that lie within a Voronoi region of a sublattice .LAMBDA.' of .LAMBDA., where .LAMBDA.' is other than a scaled version of .LAMBDA.. The Voronoi signal constellation is combined with a coset code. A method of mapping data words to Voronoi constellation points is described.

Abstract: An improvement to a modulation system of the kind in which the encoder selects a codeword corresponding to a plurality of modulation signal points on the basis of a block of digital data, the available codewords for a given block being independent of the signal points corresponding to the codeword selected for any other block. In the improvement a constellation of available signals comprises groups with equal numbers of signals, and an encoder is arranged so that the group from which at least one signal point for a block is drawn depends on the group from which at least one other signal point for the block is drawn. In another aspect, the constellation includes inner signals and outer signals, one bit of data determines whether any of the signal points will be outer signals, and if so at least one other bit determines which will be an outer signal point.

Abstract: In apparatus for transmitting digital symbols over a band-limited channel using a modulated carrier system by encoding the symbols into discrete signals selected by a finite state encoder from a signal alphabet comprised of subsets each corresponding to transitions from a particular previous state to a particular current state of the encoder, the improvement in which at least two of the subsets have a signal in common, and at least one signal belongs to only one of the two subsets.

Abstract: Locations of a desired number of signal points for a double side band-quadrature carrier modulation system occupy the inner intersections of a multiplicity of concentric rings with a triangular grid. The signal point locations of the desired number on the outer partially occupied ring are provided with additional signal points at positions selected to provide that the centroid of the set of locations is at the center of the rings.

Abstract: Modem receiver apparatus having circuitry for automatically adaptively equalizing received signals, including equalizer updating circuitry for updating coefficients stored in the equalizer, wherein the apparatus comprises circuitry for detecting the duration of periodicity in the received signals, circuitry for comparing the duration to a threshold, and circuitry for freezing the updating circuitry when the duration exceeds the threshold and for otherwise releasing the updating circuitry to permit updating of the coefficients.

Abstract: In a high speed QAM data communications receiver of the type adapted to receive bursts of signals having a bandwidth B Hz and sent at a predetermined rate of 1/T signals per second over a channel, wherein the receiver includes an automatic adaptive equalizer having taps spaced equally apart, tap coefficient circuitry for repeatedly multiplying the output of each tap by a respective tap coefficient, and adjustment circuitry for adjusting the tap coefficients, and output circuitry responsive to the equalizer for providing output signals at times kT + .tau., k = 0, 1, . . . , where .tau.

Abstract: Initial Adjustment of a receiver having an automatic adaptive equalizer in a modem communication system is accomplished by employing a data transmission rate lower than normal for an early segment of each burst of signals. At this lower rate, accurate reception is possible without complete adaptation of the equalizer. These same (early segment) signals are used to adapt the equalizer in a decision-directed mode. When the adaptation is completed the system switches to its normal higher rate of data transmission.

Abstract: Double side band-quadrature carrier modulation signal points as mapped on the complex plane are drawn from an alphabet consisting of at least 8 points, and are set up in concentric rings each rotated by 45.degree. with respect to adjacent rings. Differential encoding is shown encoding the phase components of the transmitted signals.