Patents by Inventor Vadavalli G. Krishnan

Vadavalli G. Krishnan has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).

  • Constellation multiplexed inband secondary channel for voiceband modem
    Patent number: 4891806
    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.
    Type: Grant
    Filed: September 18, 1987
    Date of Patent: January 2, 1990
    Assignee: Racal Data Communications Inc.
    Inventors: Luis V. Farias, Vadavalli G. Krishnan, Chin-Pan Wong