Applied Signal Technology, Inc.

Wavetek Wandel Goltermann

Wavetek Wandell Goltermann, Inc.

Wavetek Wandell and Goltermann

Wavetek Wandel and Goltermann

Jeffrey Marc Kletsky

Ernest T Tsui

Method and apparatus for non-invasive testing of digital communications systems. Amplitude measurements are made for multiple frequencies of a multi-frequency communication system, converted to the time domain. An adaptive filter output is matched to the time domain representation to characterize the channel. Impedance mismatches may be precisely located using this technique. An error signal representing a difference between a signal transmitted through the channel and a received signal is estimated and analyzed. The error signal is separated into components corresponding to contributions by wide band noise, residual phase modulation, and residual amplitude modulation. Identification and removal of narrow-band interferers may occur prior to this separation. Bit error rate and system margin computations employ a Monte Carlo simulation of the various error sources. This provides a well refined estimate of bit error rate and system margin.

Non-invasive digital cable test system

Method and apparatus for non-invasively testing performance of a digital communication system. The test system finds particular application in digital broadcast systems where interruption of regular service for test purposes is impracticable. In one embodiment oriented to digital television cable broadcast systems, unwanted reflections due to loose connectors and other causes may be localized within a subscriber's home. The test system takes advantage of information typically generated by digital receivers to correct for communication channel imperfections. Examples of such information include current filter parameters computed for use in an internal adaptive equalizer, internal loop parameters, and the difference between the signal received and a reconstruction of that signal from the symbols estimated by the receiver.

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San Francisco, CA, United States of America

Jeffrey Marc Kletsky