Television – Monitoring – testing – or measuring
Reexamination Certificate
1998-08-07
2001-09-04
Eisenzopf, Reinhard J. (Department: 2614)
Television
Monitoring, testing, or measuring
C348S181000, C348S192000, C348S614000, C348S473000
Reexamination Certificate
active
06285396
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to apparatus and methods for detection of temporary interruptions of a television video signal, known as glitches, and particularly to glitch detection for subscriber satellite television transmission.
BACKGROUND OF THE INVENTION
Transmission of television video signals is sometimes momentarily or temporarily interrupted, such interruptions being referred to in the art by the term “glitch”. Glitches may be caused by a variety of factors, inter alia, environmental factors such as lightning or weather changes, interference from buildings, electrical/electronic failures during transmission, or satellite communication problems, such as poor placement of satellite dishes or temporary transmission or reception failures. In the case of encrypted transmissions which are deciphered by a decryption key, system “bugs” or failure may prevent reception of the decryption key.
Glitches may be perceived by a viewer as a shaking, blurring, fuzziness, halting, etc., of the picture on the television screen. In subscriber satellite television transmission, glitches can cause further problems. In such subscriber systems, an encrypted television signal is transmitted together with a conditional access stream which contains entitlement control messages (ECM's) which comprise, inter alia, decryption key information. Encrypted systems are described, for example, in U.S. Pat. Nos. 5,282,249 and 5,481,609 to Cohen et al. and assigned to the present assignee, the disclosures of which are incorporated herein by reference. An integrated receiver decoder (IRD) receives the encrypted signal and uses the decryption key information to decode the ECM's which determine whether the viewer is authorized to view the particular broadcast. If a glitch occurs in such an encrypted system, particularly a glitch in the ECM stream, the IRD is unable to interpret the signal and momentarily no picture at all is transmitted to the television set. Depending on the programming of the IRD, the momentary non-transmission of a picture may be perceived as a frozen or blue screen or a scrambled picture.
It is thus readily understood that detecting glitches is an important tool in providing reliable broadcasting service. By detecting glitches, it may be possible to discover their source and eliminate or at least cover up and/or mend the problem.
Glitch detectors are known in the art. U.S. Pat. No. 4,107,651 to Martin describes a glitch detector and circuit for detecting glitches upon a digital signal depending upon the digital signal level and the polarity of subsequent transitions within a discrete sampling period. U.S. Pat. No. 4,198,608 to Comley describes a glitch detector and trap circuit for removing a glitch generated by a D/A converter due to an error in one or more bits of an input digital signal. U.S. Pat. No. 4,353,032 to Taylor describes a system that employs two glitch detectors associated with complementary data signals that can detect either positive-going or negative-going glitches within a sample clock period. U.S. Pat. No. 4,495,621 to Nakagomi et al. describes a glitch detector which recognizes and measures the lengths of glitches by sampling an input signal at fractions of a sampling clock.
Published PCT patent application WO 96/34294 describes a method for non-invasively testing performance of a digital communication system. The test system takes advantage of information typically generated by digital receivers to correct for communication channel imperfections.
Other published patent documents attempt to detect glitches by transmitting a known test pattern which is viewed at the receiving end, any glitches in the received test pattern being readily detectable. An example of such art is Published PCT patent application WO 95/24101 which describes apparatus for creating video test patterns for outputting to a video test pattern generator, which test pattern is displayed to an operator in picture representation which simulates the appearance of a test pattern when displayed on a television receiver. European Patent Application EP 729280 A2 describes a transmission monitoring system which receives a test signal from a given source and provides a feedback indicative of the received test signal to the source via a standard voiceband telephone connection. EP 746168 A1 describes a test pattern generator which generates a test pattern that can be visually inspected by a test engineer to determine whether or not certain lines of the test pattern are being properly decoded by a television signal decoder. EP 746169 A1 describes a test pattern suitable for a television signal decoder which detects changes in the color content of a signal from frame to frame, and on the basis of these changes modulates certain parameters, such as attenuation of high frequency illuminance components. EP 757499 A2 describes a method of testing a compressed digital television signal decoder with a signal analyzer that checks whether the decoder provides an expected signature of bits from a test bit stream.
However, the above cited prior art does not provide a glitch detector for automatically detecting glitches in a test pattern that can efficiently be used for subscriber satellite television transmission.
SUMMARY OF THE INVENTION
The present invention seeks to provide improved apparatus and methods for glitch detection, particularly to glitch detection for subscriber satellite television transmission, both for analog and digital television signals.
The present invention employs a video inserter which generates and inserts a test pattern into a video transmission, particularly video for broadcasting to viewers, which can be multiplexed to a plurality of IRD's. A glitch detector can simultaneously sample and compare each video frame produced by each of the IRD's with a known pattern at a known time. A glitch is considered detected if the pattern differs from the known pattern. One particular feature of the present invention is that the video inserter can generate a dynamic test pattern which is particular useful with MPEG systems, as will be described in detail hereinbelow. Preferably a glitch is detected if the sampled pattern does not change in accordance with the known way that the known pattern changes.
It is known in the art that the uppermost and lowermost lines of home-user television screens are not generally viewable. Another particular feature of the present invention is to exploit this fact and send the test pattern on these “dead” lines of the television screen.
Unlike the prior art, the glitch detector of the present invention is capable of simultaneously monitoring pattern information from a multiplicity of channels comprising the video signals.
There is thus provided in accordance with a preferred embodiment of the present invention a method for detecting glitches in video signals, including the steps of humanlessly sampling pattern information from a frame of video signals, the frame being characterized by known pattern information, comparing sampled pattern information from the frame to the known pattern information, and detecting a glitch if the sampled pattern information differs from the known pattern information.
In accordance with a preferred embodiment of the present invention the method also includes modifying the known pattern information from one the frame to another the frame, and wherein the step of detecting includes detecting a glitch if the sampled pattern information does not change in accordance with the modifying of the known pattern information.
Further in accordance with a preferred embodiment of the present invention the method includes modifying the known pattern information from one the frame to another the frame so as to at least partially prevent diminishment of data of the known pattern information due to video compression. Preferably the known pattern information is generated by inserting a test pattern into the video signals.
Additionally in accordance with a preferred embodiment of the present invention the method incl
Chechik Dovid
Har Shoshanim Daniel
Desir Jean W.
Eisenzopf Reinhard J.
Ladas & Parry
NDS Limited
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