Racal Data Communications Inc.

Racal-Datacom, Inc.

Vedavalli G Krishnan

Rangarajan Srinivasagopalan

Luis V Farias

James D Pruett

Raj M Misra

The present invention helps derive accurate clock and carrier translation presets in the presence of noise and various line shapes. The invention provides an adaptive algorithm that optimizes the calculations of clock slew (.DELTA.T.sub.s) and frequency offset (.DELTA.f) over the specific line conditions encountered at each connection by choosing an optimal subset of the communication device's probing frequencies that minimizes the effect of line losses and noise.

Method and apparatus for estimating clock slew and carrier translation

The present invention is directed toward a method and apparatus in a communications device for mapping a selected group of data bits into a predetermined number of two-dimensional symbols selected from a minimized alphabet of M two-dimensional symbols forming a symbol constellation, with one of the two-dimensional symbols being transmitter during each symbol (i.e., baud) interval. A plurality of symbol mappers in an adaptive communications device use a superframe of bits per baud. Each superframe includes at least two groups of frames, a low bit frame and a high bit frame. The superframe has A) one of these two types of frames uses whole bits per baud and the other uses fractional bits per baud or B) both of these two types of frames will use fractional bits per baud.

Data bit to constellation symbol mapper

Superframes

Disclosed is a modem including a transmitter having a convolutional encoder for transforming each group interval digital data into an expanded bit sequence having symbol-selecting bits and a frame of subset-selecting bits forming a plurality of bit groups, with each bit group designating a 2-dimensional subset and the symbol-selecting bits being used to select one 2-dimensional symbol from each of the selected subsets, the transmitter further providing modulation of a carrier signal, and a receiver wherein a commonality-seeking, branch cost calculator determines the candidate branch associated with the minimum cost N-dimensional symbol subset for each coset and a Viterbi decoder which determines the maximum likelihood path from a plurality of surviving paths formed from branches selected from the candidate branches.

Modem and method using multidimensional coded modulation

Apparatus employing microprocessor control for reconfiguring the strapping status of local and remote data modems automatically through a front panel display built into the modem.

Automatic digital strapping apparatus for data modems

The presence of a predetermined pure sinusoidal signal is detected by periodically sampling the actual value of an input electrical signal and, based thereon, predicting what the expected value of the sinusoid would be at a next sampling instant if it is present. The actual and predicted future input signal values are then compared and a running average signal of the thus detected errors in predictions over plural such sampling and prediction cycles are compared to a preset threshold signal value to detect the presence of the predetermined tone. A modem receiver is turned off in the exemplary embodiment when the predetermined test tone is detected to prevent false data or 'garbage' being output therefrom.

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Miami Lakes, FL, United States of America

Vedavalli G Krishnan