Paradyne Corporation

Other

At&t Bell Laboratories

A.t. & T. Paradyne

Kenneth Martinez

William Lewis Betts

Gordon F Bremer

Edward S Zuranski

Kurt E Holmquist

Stanley Bottoms

Donald R Laturell

Gregory Mack

In the public switched telephone network, an originating modem can identify an answering modem, e.g., as to the type of modem it is, by detection of a low-level identification signal sent from the answering modem. The low-level identification signal is hidden within an industry standard 'answer tone,' e.g., a CCITT V.25 answer tone of 2100 Hz. If the low-level identification signal is detected by the originating modem, the industry standard 'handshaking' procedure is terminated and a non-standard handshaking procedure is implemented. If the identification signal is not detected by the originating modem, the industry standard handshaking procedure is simply completed.

Technique for automatic identification of a remote modem

An apparatus monitors the convergence of the equalization training sequence in a multipoint communication network. Various latches record the period of the incoming sequence and the time to convergence, if any. A counter records the number of periods free of convergence, and upon the counter exceeding a threshold, the network train time is doubled. A register records the longest required time to convergence. This value is periodically compared to the network train time, and, if less, substituted therefor.

Automatic equalizer initialization time control for multipoint networks

In a communication system, a plurality of remote modems send streams of data to a local modem, each remote modem preceding its transmission with a unique preamble consisting of phase reversed signals. At the local modem a preamble decoder detects the phase reversals of received signals without requiring channel equalization and the local modem uses this information for system setup.

Subrate preamble decoder for a high speed modem

In a system encompassing the transmission of high speed data over a communication channel, a circuit provides information as to whether the modems of the system are in synchronism. The circuit first determines the number of points being received within a given time at a certain inner location in the signal constellation and at another certain outer location in the signal constellation. The circuit includes an up/down counter which is incremented for each inner point received by the circuit and decremented for each outer point received. The counter output is conveyed to a comparator which determines whether the counter output has reached a preselected threshold. At the time that the counter output reaches the preselected threshold, the comparator outputs a signal which is indicative of the fact that the modems of the system are out of synchronism and retraining of the system is required.

Frequency of occurrence retraining decision circuit

A modem is operated in a half-duplex mode having various elements which are trained on data and which are locked up while data is not exchanged, thereby eliminating the need for a preamble. A preamble is used if the period between successive transmissions exceeds a preselected threshold. In addition, a parity encoder is used to calculate a parity word for each transmission, said parity word being inserted in the first baud period of the next transmission. This first baud period is usually empty because data signals have not been received yet from the corresponding data transmission equipment.

Transparent error detection in half duplex modems

A Viterbi decoder is disclosed particularly suited for implementation in a microprocessor-based modem. The decoder calculates the branch metric corresponding to each point of a signal constellation by calculating the Euclidean distance between a received point and a subset of constellation points. Prior to the metric calculations, each received point is translated to the first quadrant and, if necessary, truncated.

Viterbi decoder for wireline modems

In the transmitter of a data communication system using QAM, a plurality of trellis coders with delay units are used for forward error correction. The output of each encoder is modulated using QAM to generate sequential baud signal elements. The redundant data bits generated are distributed between several non-consecutive bauds. Likewise, at the receiver a plurality of distributed convolutional decoders are utilized to decode the received signal element. The distributed trellis decoder is self-synchronizing.

Distributed trellis encoder

In the transmitter of a data communication system using QAM, a plurality of trellis coders with delay units are used for forward error correction. The output of each encoder is modulated using QAM to generate sequential baud signal elements. The redundant data bits generated are distributed among several non-consecutive bauds. At the receiver a distributed convolutional decoder individually addressed having sectioned memory elements is utilized to decode the received signal element. The distributed trellis decoder is self-synchronizing.

Self-synchronizing de-interleaver for viterbi decoder used in wireline

In the transmitter of a data communication system using QAM, a trellis coder with k-baud delay units is used for forward error correction. The output of the encoder is modulated using QAM to generate sequential baud signal elements. The redundant data bits generated are distributed among several non-consecutive bauds. At the receiver a plurality of distributed convolutional decoders are utilized to decode the received signal element. The distributed trellis decoder is self-synchronizing.

Self-synchronizing interleaver for trellis encoder used in wireline

A modem is operated in a half-duplex mode having various elements which are trained on data and which are locked up while data is not exchanged, thereby eliminating the need for a preamble. A preamble is used only if the period between successive transmissions exceeds a preselected threshold.

Half-duplex modem without turnaround delay

In a QAM digital modem decoder section, the received signals (after equalization) are transposed to a preselected quadrant of the signal constellation to generate an index pointer. The index pointer and the actual quadrant are used to decode the QAM signals. The index pointer is also used to update the equalizer taps and to operate a phase tracking loop used to reduce or eliminate phase jitter.

Index decoder for digital modems

The present invention pertains to a digital modem utilizing QAM-type modulation having a signal-to-noise monitor which utilizes some of the components of a standard modem without interfering with its normal operation. The monitor averages the absolute value of the difference between the signal received by the modem and the ideal signal as represented on a typical signal constellation. In order to minimize the effect of phase and amplitude errors the monitor only handles the innermost signals of the constellation and ignores all the other signals.

Digital modem having a monitor for signal-to-noise ratio

In a receiver for multiplexed QAM/PSK signals which have been radial amplitude modulated for synchronization, an error signal is generated by each received signal to the corresponding ideal point as mapped in the complex plane. A synchronizing signal is generated and synchronized by the error signal and is used for both demultiplexing, and amplitude demodulating the signal.

Normalized error compensator for modems using radial amplitude

This invention provides a system which monitors the phase error signal generated by a phase tracking loop. The system includes a first circuit for averaging the phase error signal thus generating an uncorrected phase error, and a second signal for integrating the phase error to generate a corrected phase signal. The two generated signals are added together to yield a total phase error signal.

Phase tracking loop impairment monitor for modems

A phase tracking loop is provided for a digital modem. The phase tracking loop rotates the equalized output of the modem by a phase corrector angle generated by a phase error detector, frequency offset integrator and phase corrector integrator. The phase error is obtained by complex multiplexing the coordinates of the received signal with a phase corrector number. The first integrator operates on the sum of the detected phase error. The second integrator operates on the sum of the output of the phase detector and first integrator. The second integrator output comprises the phase corrector angle.

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Pinellas Park, FL, United States of America

Kenneth Martinez