Television – Monitoring – testing – or measuring – Transmission path testing
Reexamination Certificate
1998-11-10
2001-10-30
Peng, John K. (Department: 2714)
Television
Monitoring, testing, or measuring
Transmission path testing
C348S192000, C348S191000, C348S181000, C348S086000
Reexamination Certificate
active
06310645
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to measuring the quality of communication signals, and more specifically to a method and apparatus for measuring characteristics of a communication signal modulated by a video signal, such as a composite video signal, which is transmitted from one location to another, such as by a cable television (CATV) system.
Existing methods for measuring the quality of a communication signal modulated with a composite video signal in CATV systems require the use of a device connected to the channel that synchronizes to the composite video signal to identify a vertical blanking interval (VBI) where no visual carrier modulation occurs. Such a device is quite costly and cumbersome.
It is desirable to measure the quality of a signal, such as communication signal modulated with a composite video signal in a CATV system, in the presence of modulation, without the need for a synchronizing device.
SUMMARY OF THE INVENTION
According to the present invention, a method and apparatus are provided for measuring a characteristic of a communication signal modulated with a composite video signal by examining samples of an intermediate signal derived from the received communication signal that represents the power spectrum of the communication signal at different instants of time. From a priori knowledge of the spectral characteristics of the communication signal modulated with a composite video signal, predetermined features of the communication signal are identified based on the relative values of the samples collected over a period of time equal to an entire frame of the composite video signal. For example, the sample with the maximum sample value of a plurality of samples collected for one frame is coincident with the occurrence of a vertical synchronization pulse of the composite video signal, when no modulation is present. Therefore, the maximum sample is representative of the power of the communication signal at the visual carrier frequency. Moreover, once the sample with the maximum level is identified, the beginning of a frame is known, and therefore the power level of any other portion of the composite video signal can be measured based on the power level of the communication signal at a corresponding point in time.
In one embodiment, the samples of the intermediate signal are processed in digital form, and therefore, the present invention is well suited for implementation by digital signal processing techniques using any suitable processing device. Consequently, effective “synchronization” to the communication signal is achieved without the use of a costly synchronizing device.
The above and other objects of the present invention will become more readily apparent when reference is made to the following description, taken in conjunction with the accompanying drawings.
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Birger Alexander
Lapushin Semyon
Smychkovich Boris
Antec Corporation
Boss Gerald R.
Natnael Paulos
Peng John K.
Troutman Sanders LLP
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