04891806 is referenced by 101 patents and cites 18 patents.

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.

Title
Constellation multiplexed inband secondary channel for voiceband modem
Application Number
7/98547
Publication Number
4891806
Application Date
September 18, 1987
Publication Date
January 2, 1990
Inventor
Chin Pan Wong
Davie
FL, US
Vadavalli G Krishnan
Miami Lakes
FL, US
Luis V Farias
Sunrise
FL, US
Agent
Jerry A Miller
Assignee
Racal Data Communications
FL, US
IPC
H04L 23/02
H04L 5/12
H04J 3/06
H04J 3/12
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