Abstract:
Detection of faults in a transmitted signal stream occurs by recovering, from the information stream, a water mark embedded in the stream prior to transmission. The embedded watermark has data characteristic of stream quality. Thereafter, the at least one watermark property is analyzed to detect faults in the received information stream.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit, under 35 U.S.C. §365 of International Application PCT/US2008/05798 and filed May 6, 2008, which was published in accordance with PCT Article 21(2) on Nov. 20, 2008, in English and which claims the benefit of U.S. Provisional Patent Application No. 60/928,566, filed on May 10, 2007, in English. 
    
    
     TECHNICAL FIELD 
     This invention relates to a technique for detecting a fault in connection with the transmission of information. 
     BACKGROUND ART 
     Typically, the distribution of digital video content occurs by first compressing the content at a head end for transmission, often via satellite, to a downstream station at which the content typically undergoes transcoding prior to further distribution. In the course of the transmission of content between the head end and a downstream station, one or more faults can occur which currently can only be detected via human monitoring of the transcoded content stream. Present day monitoring techniques involve manual inspection of a changed channel and the reporting of errors if any resulting from such manual inspection. Tools presently exist for monitoring link quality. However, link quality only provides an indirect indicator of problems associated with a satellite/channel switch but does not serve as a reliable indicator of other problems that can exist in the transport and upper signal layers that could potentially prevent receipt of the correct video signal. 
     BRIEF SUMMARY OF THE INVENTION 
     Briefly, in accordance with a first illustrative embodiment of the present principles, there is provided a method for detecting faults occurring in a transmitted signal stream. The method commences by recovering, from the information stream, a water mark embedded in the stream prior to transmission. The embedded watermark has data characteristic of stream quality. Thereafter, the at least one watermark property is analyzed to detect faults in the received information stream. For example, among its properties, the watermark could include a program identifier (e.g., a Program ID). By comparing the Program ID in the recovered watermark to an expected Program ID, a determination can be made whether the correct program is being received. Another possible watermark property would be a count that increases sequentially with each received frame or group of frames. Thus, a failure of the count to increase would indicate a decoding failure. Further, the signal strength of the watermark itself also can constitute a property indicative of the quality of the received signal stream. If the signal strength does not exceed a minimum value, then the received signal stream is likely corrupted. 
     In accordance with a second preferred embodiment of the present principles, there is provided a method for communicating an information stream to a downstream receiver. The method comprises the step of embedding in the information stream prior to transmission a watermark having data characteristic of stream quality. Recovering the watermark and analyzing the embedded watermark provides a mechanism for detecting faults in the information stream following reception. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a block schematic diagram of an information communication system; 
         FIG. 2  depicts a block schematic diagram of a transmission system according to the prior art that comprises part of the communication system of  FIG. 1 ; 
         FIG. 3  depicts a block schematic diagram of a first preferred embodiment of a transmission system for use with the communication system of  FIG. 1  for embedding a watermark in the transmitted signal stream to enable fault detection in accordance with the present principles; 
         FIG. 4  depicts a block schematic diagram of a first preferred embodiment of receiver for use with the communications system of  FIG. 1  for detecting faults in the received signal stream by analyzing the embedded watermark in accordance with the present principles; 
         FIG. 5  depicts a block schematic diagram of a second preferred embodiment of a transmission system for use with the communications system of  FIG. 1  for embedding a watermark in the transmitted signal stream to enable fault detection in accordance with the present principles; 
         FIG. 6  depicts a block schematic diagram of a second preferred embodiment a receiver for use with the communications system of  FIG. 1  for detecting faults in the received signal stream by analyzing the embedded watermark in accordance with the present principles; and 
         FIG. 7  depicts a block schematic diagram of a third preferred embodiment of a receiver for use with the communications system of  FIG. 1  for detecting faults in the received signal stream by analyzing the embedded watermark in accordance with the present principles. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an exemplary information communication system for practicing the fault detection technique of the present principles. As depicted in  FIG. 1 , a head end  100 , typically under the control of a content owner or its agent, transmits an information stream, typically in form of a stream of digitized content (video and/or audio and/or data), to a downstream station  102 . The downstream station  102  can take the form of an affiliated regional head that transcodes the content stream for subsequent distribution. Transmission of the content stream from the head end  100  to the downstream station  102  can occur via a satellite  104 . While the remainder of this application uses satellite transmission to describe the concept, the principles described herein extends to any transmission network that broadcasts/multicasts information. 
     Occasionally, a need exists to switch transmission of the content stream from the satellite  104  to another satellite  106  or from one transponder to a different transponder on the same satellite. In order to remain synchronized, the head end  100  will transmit certain information to the downstream station  102  some time prior to the switch. This information typically includes the exact time that the switch will occur, the identity of the new satellite and the particular channel on which the new satellite will transmit the stream. At an appointed time, both the head-end  100  and the downstream station  102  will simultaneously switch from the current channel on the satellite  104  to the specified channel on the satellite  106 . 
     A successful switch by the head-end  100  to the new channel on the new satellite  106  does not automatically assure that the downstream station  102  will successfully make the switch as well. Presently, a human operator must manually monitor the output of the downstream station  102  to verify decoding of the correct stream. Upon detecting a fault, the operator at the downstream  102  station typically will send a message to the head-end  100  via a low-bandwidth channel  108  requesting retransmission of the information on the new channel or a different channel if available. The low bandwidth channel  108  can take the form of an ordinary Plain Old Telephone Service (POTS) line for carrying voice messages, or a data channel for carrying digital voice or text messages. 
       FIG. 2  depicts a block schematic diagram of a prior-art transmission  200  system associated with the head end  100  of  FIG. 1 . The transmission system  200  includes a database  210  of stored content (e.g., programs). A control system  220  makes use of scheduling information to select one or more programs in the database  210  for transmission, and to select the satellite and the satellite channel that will transmit the selected program(s). The selected programs then undergo compression encoding by an encoder  230  which compresses the programs at a specified bitrate using a selected specified compression standard (e.g., MPEG-2). Finally, the compressed programs undergo transmission by transmitter  240 , which typically takes the form of an uplink station for transmitting the programs to a specified satellite, such satellite  104  or  106  of  FIG. 1 . 
     In accordance with a one aspect of the present principles, automated detection of faults can occur by using digital watermarking technology to embed in the transmitted content stream, e.g., the compressed program(s), a watermark containing certain information. Such information can include a Program ID. In practice, the Program ID undergoes a separate transmission from the content owner head-end  100  of  FIG. 1  to the downstream station  102  of  FIG. 1  either via satellite (the in-band channel) or out-of-band via the low bandwidth channel  108  of  FIG. 1 . Thus, the downstream station  102  of  FIG. 1  will know the Program ID apart from the Program ID embedded in the transmitted program. The downstream station  102  will recover the Program ID from the received program for comparison against the separately sent Program ID. If the separately transmitted Program ID and the Program ID recovered from the transmitted program do not match, then the program switch was not successful. 
     Digital watermarking comprises a collection of techniques for modifying the original content to embed to watermark data such that the modified content is perceptually similar to the original content and the watermark data can be subsequently recovered from the content as modified even if the content has been distorted. Watermarking systems include both an embedder for modifying the original content and one or more detectors for recovering the watermark data. Some embedders operate on baseband images while some operate on compressed content streams. Similarly, some detectors operate on baseband images and others operate on compressed streams. Some systems are designed such that the watermark data can be embedded in the compressed stream, but detected in baseband. Similarly, some systems allow the watermark embedding in the baseband and detection in a compressed stream. In accordance with the present principles, the watermarking of content occurs by watermarking the video portion of such content. Alternatively, the audio portion of the content could undergo watermarking in place of the video portion of the content. 
       FIG. 3  depicts a block schematic diagram of a transmission system  300  in accordance with a first embodiment of the present principles for incorporation within the head end  100  of  FIG. 1  for embedding a watermark in the content for fault detection purposes. The transmission system  300  of  FIG. 3  includes a database  310  of stored content (e.g., programs). A control system  320  makes use of scheduling information to select one of more programs in the database  310  for transmission, and to select the satellite and the satellite channel that will transmit the selected program(s). In addition to selecting the program(s) for ultimate transmission, the control system  320  also generates a program identifier, generally referred to by the term “Program ID,” that particularly identified each selected program. As depicted in  FIG. 3 , the Program ID undergoes storage in a memory or buffer  325 . Although the memory  325  that stores the Program ID appears as a separate element from the control system  320 , the memory could reside within the control system itself. 
     The program(s) selected by the control system  320  undergo processing by a watermark embedder  327  which embeds into each selected program a digital watermark containing the corresponding Program ID for that program. The watermark embedder  327  of  FIG. 3  inserts data (e.g., the Program ID) into the baseband video portion of the selected program, either in every frame or into a subset of frames. Preferably, the embedded data appears with some minimum frequency. After each program has its corresponding Program ID embedded therein, the program then undergoes compression encoding by an encoder  330  which compresses the program at a specified bitrate using a selected specified compression standard. Finally, the compressed program undergoes transmission by transmitter  340 , which typically takes the form of an uplink station for transmitting the programs to a specified satellite, such satellite  104  or  106  of  FIG. 1 . The transmitter  340  also receives the Program ID directly from the memory  325  for transmission to the downstream stations  102  of  FIG. 1 , either by multiplexing onto the transmitted content stream and/or by transmission via the low-bandwidth channel  108  of  FIG. 1 . This delivery of the Program ID occurs repeatedly on a periodic basis. 
       FIG. 4  depicts a block schematic diagram of a receiver system  400  in accordance with a first embodiment of the present principles for detecting faults based on recovered watermark data. In practice, the receiver system  410  of  FIG. 4  resides in the downstream station  102  of  FIG. 1 . The receiver system  400  of  FIG. 4  includes a receiver  410  tuned to a particular channel on a specified satellite, such as one of satellites  104  and  106  of  FIG. 1 . The receiver  410  possesses the capability of tuning a different channel on the same or a different satellite. The receiver  410  serves to recover both the transmitted content (including the embedded Program ID) as well as the separately provided Program ID multiplexed in the content stream or received via the low bandwidth channel. The separately provided Program ID undergoes storage in a memory  415  which can be integral with or separate from the receiver  410 . The content stream recovered by the receiver  410  undergoes compression transcoding via a compression transcoder  420  into a format for distribution to regional subscribers by at least one hub  430 . The compression transcoder  420  also decodes the content stream to obtain baseband video stored in a memory or buffer  440  for subsequent receipt by a watermark detector  450 . The watermark detector  450  recovers embedded data, including the Program ID, in the baseband video, and passes this data, along with a value indicating the strength of the detection, to a fault detector  460 . Since the embedded watermark data appears periodically in the baseband video, the watermark detector  450  will periodically recover such data for receipt by the fault detector  460 . 
     The fault detector  460  compares the Program ID held in the memory  415  to the Program ID recovered by the by the watermark detector  450 . If the two values do not match, then the fault detector  460  issues an alert indicating that the received content stream does not match the expected content stream. If the watermark strength, as reported by the watermark detector  450 , does not exceed a set threshold, then the fault detector  460  will also an alert indicating potential corruption of the received content stream. 
     The data embedded by in the video portion of the content stream by the watermark embedder  327  of  FIG. 3  can include a sequential count. In practice, each time the watermark detector  450  of  FIG. 4  passes recovered data to the fault detector  460 , the value of the count should increase as compared to the count detected on the previous recovery. Upon reaching a maximum value, the count resets to an initial value. If the fault detector  460  detects a count value that does not change, the fault detector issues an alert, indicating that the compression transcoder  420  has become “stuck” and currently outputs still frame. 
       FIG. 5  depicts a block schematic diagram of a transmitter system  500  in accordance with a second embodiment of the present principles for incorporation within the head end  100  of  FIG. 1  for embedding a watermark in the content for fault detection purposes. The transmission system  500  of  FIG. 3  includes a database  510 , a control system  520 , a Program ID memory  525 , a compression encoder  530 , a watermark embedder  535 , and a transmitter  540  which each perform substantially the same function as the database  310 , control system  320 , compression encoder  330 , watermark detector  330  and transmitter  340 , respectively, of the transmitter system  300  of  FIG. 3 . As compared to the transmitter system  300  of  FIG. 3  whose watermark embedder  327  inserts data (e.g., the Program ID and the sequential count) into the baseband video portion of the content, the watermark embedder  535  of the transmission system  500  inserts such data into the compressed video portion of the content. Otherwise, the transmitter system  500  of  FIG. 5  operates in the same manner as described with respect to the transmitter system  300  of  FIG. 3 . 
       FIG. 6  depicts a block schematic diagram of a receiver system  600  in accordance with a second embodiment of the present principles for detecting faults based on recovered watermark data. The receiver system  600  of  FIG. 6  includes a receiver  610 , a Program ID memory  615 , a compression transcoder  620 , a hub  630 , a watermark detector  650 , and a fault detector  660 , each performing substantially the same function as the receiver  410 , the Program ID memory  415 , the compression transcoder  420 , the hub  430 , the watermark detector  450  and the fault detector  460 , respectively. As compared to the receiver system  400  of  FIG. 4  in which the watermark detector  450  operates on baseband video, the watermark detector  650  of the receiver system  600  operates on the content stream prior to compression transcoding. While the input stream to the watermark detector  650  exists in a different format as compared to the input stream to the watermark detector  450  of  FIG. 4 , the output is the same. 
       FIG. 7  depicts a block schematic diagram of a receiver system  700  in accordance with a third embodiment of the present principles for detecting faults based on recovered watermark data. The receiver system  700  of  FIG. 6  includes a receiver  710 , a Program ID memory  715 , a compression transcoder  720 , a hub  730 , a watermark detector  750 , and a fault detector  760 , each performing substantially the same function as the receiver  410 , the Program ID memory  415 , the compression transcoder  420 , the hub  430 , the watermark detector  450  and the fault detector  460 , respectively. As compared to the receiver system  400  of  FIG. 4  in which the watermark detector  450  operates on baseband video, the watermark detector  750  of the receiver system  700  operates on the compressed transcoded content stream produced by the compression transcoder  720 . While the input stream to the watermark detector  750  exists in a different format as compared to the input stream to the watermark detector  450  of  FIG. 4 , the output of the watermark detector  750  is the same. 
     The foregoing describes a technique for detecting faults in an information communications system by examining watermarked data embedded in transmitted content. It must also be recognized that the watermark embedding technique for fail-safe program or context switching can be generalized to switching between multicast groups in an IP network. In other words, the technique of the present principles is not confined to a particular mode of transmission, but rather, but has applicability for detecting faults during content reception when transitioning among content sources.