Multiplex communications – Wide area network – Packet switching
Patent
1987-09-18
1990-01-02
Safourek, Benedict V.
Multiplex communications
Wide area network
Packet switching
375 39, 375106, 3701001, H04J 312, H04J 306, H04L 512, H04L 2302
Patent
active
048918067
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.
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Farias Luis V.
Krishnan Vadavalli G.
Wong Chin-Pan
Chin Wellington
Miller Jerry A.
Racal Data Communications Inc.
Safourek Benedict V.
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