Abstract:
Incoming digital video signals to a video system each undergo identification with specific identifier prior to receipt at a corresponding one of the video system inputs. At each of the video system outputs, the output signal undergoes decoding to obtain the identity of the signal to confirm proper routing of signals within the video system.

Description:
This application claims the benefit, under 35 U.S.C. §365 of International Application PCT/US2006/046853, filed Dec. 8, 2006, which was published in accordance with PCT Article 21(2) on Jun. 12, 2008 in English. 
     TECHNICAL FIELD 
     The invention relates to a technique for positive identification of digital video signals. 
     BACKGROUND ART 
     Identification of a serial digital video signal from a single source or even a few sources generally presents little difficulties. However, in a typical broadcast facility, many serial digital video signals exist, and identification of each signal often proves problematic, particularly as the signals undergo routing through one or more devices, such as a cross-point switcher, some times referred to as a cross-point matrix. Presently, to positively identify a given serial digital video signal during routing, descrambling and de-serialization of the signal must occur in order to decode the identification information. Carrying out these processes requires a significant amount of hardware. Thus, in a system having many serial digital video signals, providing the necessary descrambling and de-serialization hardware often proves impractical from a cost, space and power consumption perspective. For this reason, broadcast facilities typically rely completely on routing control system status information to determine which input connects to a given output in the cross-point matrix. Such reliance incurs the disadvantage that no automated method exists for checking the actual signal present at a given cross-point matrix output and alerting the user should the status information prove erroneous. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with an illustrative embodiment of the present principles, a method for identifying a digital video signal in a video system commences with the step of phase modulating the digital video signal with an identification signal at an input of the video system, thereby identifying that signal. The phase modulated digital video signal undergoes demodulation at an output of the video system to establish the identity of the video signal. In this way, verification of proper routing of the signal through video system can occur. 
    
    
     
       BRIEF SUMMARY OF THE DRAWINGS 
         FIG. 1  depicts a block schematic diagram of video system that identifies at least one digital video signals at an input for confirmation at an output in accordance with an illustrative embodiment of the present principles, 
         FIG. 2  depicts a block schematic diagram of one of the input circuits of the video system of  FIG. 1  to phase modulate an input signal to identify that signal; 
         FIG. 3  depicts a block schematic diagram of one of the output circuits of the video system of  FIG. 1  to demodulate an output signal for obtain the identification of that signal. 
     
    
    
     DETAILED DESCRIPTION 
     As described in greater detail hereinafter, in accordance with the present principles, the digital video input signal to a video system, gets identified to enable verification of signals at the system outputs. 
       FIG. 1  depicts a video system  10  which illustratively takes the form of cross-point matrix, some times referred to as a cross-point switcher or router, having the capability of routing a digital video signal at one or more of its inputs  12   1 - 12   n  to one or more of its outputs  14   1 - 14   m  where n and m are both integers greater than zero, but not necessarily equal to each other. The cross-point matrix  10  performs the routing of selected signals at its respective inputs  12   1 - 12   n  to selected ones of the outputs  14   1 - 14   m  under control of a routing control system (not shown). For a large video cross point matrix where n and m are both large, confirmation of the routing of a digital video signal from an input to any given output previously depended on status information provided by cross-point matrix or its control system. Since no mechanism heretofore existed for independent signal identification, an error in the status information thus could go undetected. 
     In accordance with the present principles, the cross-point matrix  10  has a plurality of input circuits  16   1 - 16   n  coupled to corresponding ones of the matrix inputs  12   1 - 12   n , respectively. Each input circuit such as input circuit  12   1  receives an incoming serial digital video signal destined from the cross-point matrix  10  and provides the signal with its own identification in a manner described hereinafter. In this way, each input signal routed through the cross-point matrix  10  to one or more outputs  14   1 - 14   m  carries its own unique identifier. 
     Each of the cross-point matrix  10  outputs  14   1 - 14   m  is coupled to a corresponding output circuit  18   1 - 18   m , respectively. Each output circuit, such as output circuit  18   1  serves to strip the identifier from the signal at the corresponding cross point matrix output. The identifier stripped from the output signal is decoded to verify that the output signal corresponds to the input signal routed from the intended input. In other words, if the signal at input  12   1  was to be routed to output  14   1 , the identifier associated with the output signal appearing at that output should match the identifier of the input signal at the corresponding cross-point matrix input. Thus, the combination of the input circuits  16   1 - 16   n  and output circuits  18   1 - 18   m  provide a mechanism for determining whether an error exists in the cross-point matrix  10  status information. 
       FIG. 2  depicts a block diagram of an exemplary input circuit, such as input circuit  16   1 , all of which share the same features. The input circuit  16   1  includes an equalizer and re-clocking circuit  20  for equalizing and re-clocking an incoming serial digital video signal. A phase modulator  22  phase modulates the output signal of the equalizer and re-clocking circuit  20  with a source identification information signal specific to the particular input circuit. In other words, each of the input circuits  16   1 - 16   n  makes use of a different source identification information signal to uniquely identify each incoming serial digital video signal. 
     The frequency of each source identification signal typically will lie above the pass band of a loop filter (not shown) in the output of the equalizer and re-clocking circuit  20 . In practice, the loop band pass bandwidth usually lies in the 100-200 kHz region. The frequency of the source identification signal is also chosen so that it is not an integer sub-multiple of the serial digital video data rate (i.e. 135 MHz, 90 MHz, 67.5 Hz etc. for a 270 Mb/s signal or 742.5 MHz, 495 MHz, 371.25 MHz etc. for a 1.485 Gb/s signal). Avoiding such frequencies avoids the large amounts of energy present at these frequencies in the serial digital video signal frequency spectrum. The depth of modulation is set so that the combined total of phase modulation and jitter from other sources is less than 20% of the unit interval for the data rate used. Setting the depth of modulation in this manner assures that signal recovery can occur without error by during re-clocking by one of the output circuits  18   1 - 18   m . 
       FIG. 3  depicts an exemplary output circuit, such as circuit  18   1 , all of which share the same features. The output circuit  18   1  includes a re-clocking flop-flop register  24  supplied at its D input with the serial digital video signal from the associated output of the cross-point matrix  10  of  FIG. 1 . A phase detector  26  within the output circuit  18   1  also receives the serial digital video signal at a first input from the cross-point matrix  10  of  FIG. 1 . The phase detector  26  has its second input supplied with the output signal of a voltage controlled oscillator  27  which serves as the clock signal generator for the re-clocking register  24 . 
     The phase detector  26  provides an output signal in accordance with the phase difference between the signals at its first and second inputs to both a loop filter  28  and a source identification decoder  30 . The source identification signal decoded by the decoder  30  allows the routing control system for the cross-point matrix  10  (not shown) to verify the correct routing path through the cross-point matrix. The source identification signal has a higher frequency than the pass band of the loop filter  28  so that the loop filter effectively rejects the source identification signal. In this way, the voltage controller oscillator  27 , driven at its input by the output signal of the loop filter  28 , will not track the source identification signal. 
     As indicated previously, the output signal of the voltage controlled oscillator  27  serves as the clock signal for the re-clocking register  24 . With the loop filter  28  filtering out the source identification signal from the voltage controlled oscillator  27 , the source identification effectively gets removed from the output of the re-clocking register  24 . In this way, the re-clocking register  24  can drive an output buffer  36  with re-clocked signal corresponding to the incoming serial digital video signal in a normal manner. 
     The foregoing describes a technique for identifying serial digital video signals in a video system, thereby enabling verification of the routing of such signals through the video system.