Other

Case Communications Inc.

Paul E Treynor

Richard L Stuart

David Gordon-Smith

Steven A Tretter

Robert P Redick

A 14.4 kilobit/second modem uses an encoding scheme in which groups of five bits are encoded as one of thirty-two (2.sup.5) possible code groups. This is done by using quadrature amplitude modulation and a 6 by 6 space-state constellation which allows a maximum of thirty-six different points to be encoded. Since only thirty-two points are needed the four outer corner points of the constellation are not used. In order to achieve the desired 14.4 KBPS data rate the baud clock must run at 2880 Hz. However, this bandwidth is very close to the maximum bandwidth available on voice-grade telephone lines. Accordingly, data encoding and data recovery techniques must be used which maximize the probabilities of correctly receiving the encoded data signals. These techniques include (1) data scrambling/descrambling; (2) assigning groups of five bits to constellation points, including performing rotational and Gray encoding; (3) a baud clock recovery scheme at the receiver which is performed prior to partial response encoding; and (4) a start-up technique using a three-level partial response ideal reference sequence during initial training at the receiver. In addition, the invention uses passband equalization, class I partial response encoding accomplished by the passband equalizer, and independent inphase and quadrature Viterbi decoders at the receiver.

High speed data modem using multilevel encoding

An automatic transversal equalizer is provided wherein the input signal is sampled and stored on a series of capacitors. The capacitor voltages are sequentially recalled for application to an analog multiplier which also receives a sequence of coefficient voltages which have been stored by a second series of capacitors. The single analog multiplier performs the functions of the plural voltage controlled attenuators of prior art equalizers.

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New Carrollton, MD, United States of America

Paul E Treynor