Prabhat M Gupta

US Patent:

57347891, Mar 31, 1998

Filed:

Apr 18, 1994

Appl. No.:

8/229271

Inventors:

Kumar Swaminathan - Gaithersburg MD
Kalyan Ganesan - Germantown MD
Prabhat K. Gupta - Germantown MD

Assignee:

Hughes Electronics - Los Angeles CA

International Classification:

G10L 900

US Classification:

395 215

Abstract:

A bit rate Codebook Excited Linear Predictor (CELP) communication system which includes a transmitter that organizes a signal containing speech into frames of 40 millisecond duration, and classifies each frame as one of three modes: voiced and stationary, unvoiced or transient, and background noise.

US Patent:

55966764, Jan 21, 1997

Filed:

Oct 11, 1995

Appl. No.:

8/540637

Inventors:

Kumar Swaminathan - Gaithersburg MD
Kalyan Ganesan - Germantown MD
Prabhat K. Gupta - Germantown MD

Assignee:

Hughes Electronics - Los Angeles CA

International Classification:

G10L 912
G10L 914

US Classification:

395 217

Abstract:

A method for encoding a signal that includes a speech component is described. First and second linear prediction windows of a frame are analyzed to generate sets of filter coefficients. First and second pitch analysis windows of the frame are analyzed to generate pitch estimates. The frame is classified in one of at least two modes, e. g. voiced, unvoiced and noise modes, based, for example, on pitch stationarity, short-term level gradient or zero crossing rate. Then the frame is encoded using the filter coefficients and pitch estimates in a particular manner depending upon the mode determination for the frame, preferably employing CELP based encoding algorithms.

US Patent:

54917719, Feb 13, 1996

Filed:

Mar 26, 1993

Appl. No.:

8/037193

Inventors:

Prabhat K. Gupta - Germantown MD
Allan Lamkin - Arlington VA
Walter R. Kepley - Gaithersburg MD

Assignee:

Hughes Aircraft Company - Los Angeles CA

International Classification:

G10L 302
G10L 900

US Classification:

395 232

Abstract:

A codec uses low cost digital signal processors (DSPs) to implement the codebook excited linear prediction (CELP) algorithm. The flexible architecture provides a platform for implementing a family of CELP codecs. In a specific example, an 8 Kbps CELP codec is partitioned into parallel tasks for real time implementation on dual DSPs with flexible intertask communication, prioritization and synchronization with asynchronous transmit and receive frame timings. The two DSPs are used in a master-slave pair. Each DSP has its own local memory. The DSPs communicate to each other through interrupts. Messages are passed through a dual port RAM. Each dual port RAM has separate sections for command-response and for data.

US Patent:

57937559, Aug 11, 1998

Filed:

Jul 7, 1995

Appl. No.:

8/499421

Inventors:

Prabhat K. Gupta - Germantown MD
Sanjay Gupta - Germantown MD
Paul Gaske - Rockville MD
Bob Kepley - Gaithersburg MD

Assignee:

Hughes Electronics Corporation - El Segundo CA

International Classification:

H04B 320

US Classification:

370286

Abstract:

A signal classifier and a echo suppressor for a facsimile calls in an echo prone network. The signal classifier quickly and reliably differentiates facsimile calls from voice and modem calls. The echo suppressor suppresses echo and has a variable hangover time which avoids attenuating and distorting a return transmission signal.

US Patent:

56490127, Jul 15, 1997

Filed:

Sep 15, 1995

Appl. No.:

8/529042

Inventors:

Prabhat K. Gupta - Germantown MD
Sanjay Gupta - Germantown MD

Assignee:

Hughes Electronics - Los Angeles CA

International Classification:

H04B 323

US Classification:

379410

Abstract:

A method of synthesizing an echo path in an echo canceller is provided. The method includes the steps of obtaining near end and far end signal samples at an echo canceller, locating the echo in a background task using a whitened version of the signal, transferring the echo location information to a foreground task, and eliminating the echo in the incoming signals by filtering the signal in the location passed to the foreground task by the background task.

US Patent:

54598141, Oct 17, 1995

Filed:

Mar 26, 1993

Appl. No.:

8/038734

Inventors:

Prabhat K. Gupta - Germantown MD
Shrirang Jangi - Germantown MD
Allan B. Lamkin - Arlington VA
W. Robert Kepley - Gaithersburg, MD
Adrian J. Morris - Gaithersburg, MD

Assignee:

Hughes Aircraft Company - Los Angeles CA

International Classification:

G10L 900

US Classification:

395 242

Abstract:

A voice activity detector (VAD) which determines whether an input signal contains speech by deriving parameters measuring short term time domain characteristics of the input signal, including the average signal level and the absolute value of any change in average signal level, and comparing the derived parameter values with corresponding predetermined threshold values. In order to further minimize clipping and false alarms, the VAD periodically monitors and updates the threshold values to reflect changes in the level of background noise.

US Patent:

58094636, Sep 15, 1998

Filed:

Sep 15, 1995

Appl. No.:

8/528967

Inventors:

Sanjay Gupta - Germantown MD
Prabhat K. Gupta - Germantown MD

Assignee:

Hughes Electronics - Los Angeles CA

International Classification:

G10L 900

US Classification:

704233

Abstract:

A method of detecting double talk in an echo canceller is provided. The method includes determining far end, near end and echo signal cancelled power, determining the presence of near end, maybe near end and far end speech, and controlling an echo suppressor and filter coefficient updates in an echo canceller.

US Patent:

56895569, Nov 18, 1997

Filed:

Sep 15, 1995

Appl. No.:

8/528762

Inventors:

Prabhat K. Gupta - Germantown MD
Sanjay Gupta - Germantown MD

Assignee:

Hughes Electronics - Los Angles CA

International Classification:

H04B 323

US Classification:

379410

Abstract:

A method of detecting narrow-band signals in an echo canceller to control the coefficient update process, echo suppression process, and the disablement of the echo canceller is provided. The method includes the steps of searching for the presence of a generic tone, searching for DTMF tones, searching for a 2100 Hz tone and, if a generic tone is found, searching for a dial tone. If a generic tone is detected on the far end signal, a tone flag is set which triggers the disablement of the echo canceller coefficient update process and the enablement of the echo suppressor process. If a 2100 Hz tone is detected, the echo canceller is disabled. If a DTMF signal is detected, DTMF flags are set which are used by the echo suppressor for suppressing the near end echo. Finally, if a dial tone is detected, dial tone flags are set which cause the disablement of the echo suppressor.