Luis Carlos Farias

US Patent:

48918067, Jan 2, 1990

Filed:

Sep 18, 1987

Appl. No.:

7/098547

Inventors:

Luis V. Farias - Sunrise FL

Assignee:

Racal Data Communications Inc. - Sunrise FL

International Classification:

H04J 312
H04J 306
H04L 512
H04L 2302

US Classification:

3701101

Abstract:

A method of providing an inband secondary channel for a data modem includes encoding the main channel data using a convolutional encoder so that main channel data symbols are selected from a first constellation. The secondary channel data are encoded using a differential encoder and secondary channel data symbols are selected from a second constellation. The transmission of the main channel symbols takes place during 48 frames of a 49 frame master frame. The differentially encoded secondary channel data symbols are transmitted during the remaining frame. The symbols of the secondary channel constellation are selected to have a higher average energy than those of the main channel data so that the secondary channel is easily detected and may be used to obtain frame synchronization for the modem after brief dropouts without having to retrain the modem.

US Patent:

47617845, Aug 2, 1988

Filed:

Jan 15, 1987

Appl. No.:

7/004389

Inventors:

Rangarajan Srinivasagopalan - Coral Springs FL
James D. Pruett - Fort Lauderdale FL
Vedavalli G. Krishnan - Miami Lakes FL
Luis V. Farias - Sunrise FL

Assignee:

Racal Data Communications Inc. - Sunrise FL

International Classification:

G06F 1110

US Classification:

371 43

Abstract:

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.