Abstract:
Society of Motion Picture and Television Engineers (SMPTE) video data is separated into first data and second data. A first signal is formed based on the first data. A second signal is formed based on the second data. The first signal is transported via a first Optical Carrier 3 (OC-3) channel. The second signal is transported via a second OC-3 channel.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to methods and systems for transporting high-quality video signals.  
         BACKGROUND OF THE INVENTION  
         [0002]    The video industry has adopted the Society of Motion Picture and Television Engineers (SMPTE) 259M (level C) standard almost exclusively for high quality video in studio and production applications. In some applications, a SMPTE 259M signal is to be transported to a remote location, which may be several miles away for example. Current methods of transporting SMPTE 259M signals or other professional quality video signals to remote locations use either dark fiber overlay networks or proprietary methods over very high bandwidth pipes. For example, an OC-12 channel may be used to transport an SMPTE 259M signal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0003]    The invention is pointed out with particularity in the appended claims. However, other features of the invention will become more apparent and the invention will be best understood by referring to the following detailed description in conjunction with the accompanying drawings in which:  
         [0004]    [0004]FIG. 1 is a block diagram of an embodiment of a system to transport high-quality video;  
         [0005]    [0005]FIG. 2 is a flow chart of an embodiment of a method performed at a transmitter end;  
         [0006]    [0006]FIG. 3 is a flow chart of an embodiment of a method performed at a receiver end;  
         [0007]    [0007]FIG. 4 illustrates the SMPTE 259M data structure;  
         [0008]    [0008]FIG. 5 is a block diagram illustrating an embodiment of an uncompressed signal based on a subframe of a SMPTE frame;  
         [0009]    [0009]FIG. 6 is a schematic block diagram of an embodiment of a video processor at the transmitter end;  
         [0010]    [0010]FIG. 7 is a schematic block diagram of an embodiment of a video processor at the receiver end;  
         [0011]    [0011]FIG. 8 is a block diagram of an embodiment of a system to provide timing information;  
         [0012]    [0012]FIG. 9 is a block diagram of an embodiment of a system to reconstruct the timing information at the receiver end; and  
         [0013]    [0013]FIG. 10 is a block diagram depicting a packing method for transmitting 10-bit word information using 8-bit bytes. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0014]    Briefly, embodiments of the present invention provide an improved process for transporting high-quality video. The process includes separating the video data into two sets of data, encapsulating each set of data into asynchronous transfer mode (ATM) cells, and transporting two ATM cell-based bit streams over dual, concatenated Optical Carrier 3 (OC-3) channels. Error checking and/or correction is used to reduce the probability of data errors during transport.  
         [0015]    Embodiments of the present invention are described with reference to FIG. 1, which is a block diagram of an embodiment of a system to transport high-quality video, FIG. 2, which is a flow chart of an embodiment of a method performed at a transmitter end  20 , and FIG. 3, which is a flow chart of an embodiment of a method performed at a receiver end  22 .  
         [0016]    As indicated by block  24 , the method comprises separating SMPTE video data  26 , such as SMPTE 259M video data, into first uncompressed data  30  and second uncompressed data  32 . Preferably, the act of separating the SMPTE video data comprises separating each frame of the SMPTE video data into a first subframe and a second subframe. The first subframe comprises even lines of active video from the frame, and the second subframe comprises odd lines of active video from the frame. In addition to active video, the first subframe and the second subframe may further comprise horizontal ancillary data, optional video data and/or vertical ancillary data.  
         [0017]    The SMPTE 259M standard is inherently suitable to separate video data because of its field and frame-oriented data structure. In addition, extraneous data can be eliminated since the timing signals are not necessary to carry along a transport stream.  
         [0018]    [0018]FIG. 4 illustrates the SMPTE 259M data structure. The data structure comprises active video fields  34  and  36 . The active video fields  34  and  36  contain component pixel data. The active video field  34  includes odd lines of active video from a frame, while the active video field  36  includes even lines of active video from a frame. Optional video fields  40  and  42  contain vertical blanking interval (VBI) data and non-critical data. Horizontal ancillary (HANC) data fields  44  and  46  contain audio, timing and control information. Vertical ancillary (VANC) data fields  48  and  49  contain special user information. A clear delineation between the fields is created by the inherent timing signals EAV  50  and SAV  52 .  
         [0019]    The aforementioned structure is exploited to separate the SMPTE video data into two equal blocks. The first uncompressed data includes data from the active video field  34 , the HANC data field  44 , and a portion of the data from the optional video field  40  and/or the VANC data field  48 . The second uncompressed data includes data from the active video field  36 , the HANC data field  46 , and a portion of the data from the optional video field  42  and/or the VANC data field  49 .  
         [0020]    Referring back to FIG. 2, the method comprises acts of forming a first uncompressed signal based on the first uncompressed data (block  54 ) and forming a second uncompressed signal based on the second uncompressed data (block  56 ). The first uncompressed signal is based on the each first subframe. The second uncompressed signal is based on the each second subframe.  
         [0021]    The act of forming the first uncompressed signal further comprises appending a corresponding first sequence number to each first subframe, and encapsulating each first subframe with its corresponding first sequence number into at least one asynchronous transfer mode (ATM) cell. Similarly, the act of forming the second uncompressed signal further comprises appending a corresponding second sequence number to each second subframe, and encapsulating each second subframe with its corresponding second sequence number into at least one ATM cell. The sequence numbers are appended to each subframe since traffic in most ATM networks can take any of several paths, each with a potentially different latency and cell delay variation. The sequence numbers are used at the receiving end  22  to order reconstructed frames.  
         [0022]    In one embodiment, each sequence number is defined by 20 bits. One bit of the sequence number is used to identify whether the field is field  1  or field  2 . Choosing 20 bits for the sequence number field allows sequence numbers up to 2^ (20−1)=524,288. For a frame rate of 30 frames per second, the maximum video length for 20 sequence number bits is (524,288 frames)/((30 frames per second)★(3600 seconds per hour)), which approximately equals 4.854 hours.  
         [0023]    [0023]FIG. 5 is a block diagram illustrating an embodiment of an uncompressed signal which results from the act of either block  54  or block  56  in FIG. 2. The uncompressed signal comprises a bit stream including a sequence number  60 , ancillary data  62 , and active video data  64  for a subframe from a first frame. Thereafter, the bit stream includes a sequence number  70 , ancillary data  72 , and active video data  74  for a subframe from a second frame. The pattern of including a sequence number, ancillary data and active video data for a subframe is repeated for each succeeding frame.  
         [0024]    The above-described encapsulation method distinguishes video data (e.g. field/frame data) from ancillary data to facilitate the SMPTE 259M video data being properly reconstructed at the receiver end  22 . Since timing relationships are well-defined in the SMPTE 259M standard, and since a fixed frequency of 270 Mbps is used, logic at the receiver end  22  can add the proper timing signals.  
         [0025]    The bandwidth required to transmit the above bit stream is calculated as follows. With respect to the active video bandwidth, each field has 244 active video lines. The number of words per line is 720 pixels★2(Cr, Y, Cb)=1440. Since each word consists of 10 bits, the number of bits per line is (1440 words per line)★(10 bits per word)=14,400. Thus, the total number of active video bits per field is (14,400 bits per line)★(244 active video lines per field)=3.5136 Mb. Since each frame is based on 2 fields, the total number of active video bits per frame is (3.5136 Mb per field)★(2 fields per frame)=7.0272 Mb. For a frame rate of 30 frames per second, the active video bit rate is (7.0272 Mb per frame)★(30 frames per second)=210.816 Mbps. Accounting for ATM overhead with a cell tax of 1.09433, the total active video bandwidth is 1.09433★210.816 Mbps=230.7043 Mbps.  
         [0026]    The bandwidth for the HANC data is determined as follows. The HANC bit rate is 30 Mbps. Accounting for ATM overhead with a cell tax of 1.09433, the HANC bandwidth is 1.09433★30 Mbps=32.8302 Mbps.  
         [0027]    The bandwidth for the VANC/optional data is determined as follows. Each frame has 20 lines allocated for VANC/optional data. The 20 lines comprise any 10 lines selected from lines  1 - 20 , and any 10 lines selected from lines  264 - 283 . Since the number of bits per line is 14,400, the total number of VANC/optional bits per frame is (14,400 bits per line)★(20 VANC/optional lines per field)=288,000. For a frame rate of 30 frames per second, the VANC/optional bit rate is (288,000 bits per frame)★(30 frames per second)=8.64 Mbps. Accounting for ATM overhead with a cell tax of 1.09433, the VANC/optional bandwidth is 1.09433★8.64 Mbps=9.4550112 Mbps.  
         [0028]    The total data rate is equal to the sum of the total active video bandwidth, the HANC bandwidth and the VANC/optional bandwidth. Thus, the total data rate is 230.7043 Mbps+32.8302 Mbps+9.4550112 Mbps, which equals 272.984612 Mbps. This is less than the 299.52 Mbps bandwidth available on two OC-3 links. Since the data is separated into two fields, the total data rate per field is 272.984612 Mbps/2, which approximately equals 136.4923 Mbps.  
         [0029]    Optionally, the act of forming the first uncompressed signal further comprises adding a first ATM adaptation layer (AAL) with either an error checking code or an error correcting code. Similarly, the act of forming the second uncompressed signal may optionally comprise adding a second ATM adaptation layer with either an error checking code or an error correcting code. A block coding algorithm such as Reed Solomon or another forward error correcting (FEC) code may be used.  
         [0030]    Referring back to FIGS. 1 and 2, the method comprises transporting  80  the first uncompressed signal via a first OC-3 channel  82 , and transporting  84  the second uncompressed signal via a second OC-3 channel  86 . The OC-3 channels  82  and  86  are provided by an ATM network  90 .  
         [0031]    The adaptation layers may be added because of additional bandwidth available on two OC-3 links beyond the 272.984612 Mbps required by the two bit streams. Either AAL- 1  with FEC or AAL- 5  with FEC may be used. The former is less efficient but more robust, and the latter is more efficient and slightly less robust. The selection of which of these two adaptations to use may be dictated by specifications of a specific application. Note that the FEC process is symmetrical, requiring processing the inverse algorithm at the receiver end  22 .  
         [0032]    Turning now to FIG. 3, a method performed at the receiver end  22  comprises receiving the first uncompressed signal via the first OC-3 channel (block  92 ), and receiving the second uncompressed signal via the second OC-3 channel (block  94 ). As described above, the first uncompressed signal comprises a bit stream of a first plurality of ATM cells, and the second uncompressed signal comprises a bit stream of a second plurality of ATM cells. The ATM cells are extracted from the incoming bit streams.  
         [0033]    As indicated by blocks  96  and  100 , the method optionally comprises performing error checking based on the first uncompressed signal, and performing error checking based on the second uncompressed signal. An inverse FEC block code algorithm is used for error checking and recovery. If an error is detected, the block code may provide correction depending on which block code is used and the type and number of errors.  
         [0034]    As indicated by block  102 , the method comprises extracting each first subframe and its corresponding first sequence number from the first plurality of ATM cells. As indicated by block  104 , the method comprises extracting each second subframe and its corresponding second sequence number from the second plurality of ATM cells. In these acts, the data payload is extracted from the AAL- 1  or AAL- 5  encapsulation.  
         [0035]    As indicated by block  106 , the method comprises reconstructing SMPTE video data  108 , such as SMPTE 259M video data. Each frame of the SMPTE video data is reconstructed based on a first corresponding subframe represented within the first uncompressed signal and a second corresponding subframe represented within the second uncompressed signal. Further, the EAV and SAV timing signals are added to reconstructed frames. The reconstructed frames are ordered based on each first sequence number and each second sequence number.  
         [0036]    One approach to ordering the frames comprises using a buffer management process to synchronize the arriving data based on the sequence numbers. A modified leaky bucket (LB) algorithm or similar technique can be used to synchronize the two fields. Optimization can be performed by varying the limit parameter based on the LB counter and the last compliance time. The arrival time is based on the arrival of the sequence number. This allows for a fast implementation in silicon, using the sequence number to direct data to the appropriate buffers.  
         [0037]    It is noted that some acts described with reference to FIGS. 2 and 3 need not be performed in the order shown in FIGS. 2 and 3. Further, some of the acts may be performed concurrently. For example, the act of transporting the first signal via the first OC-3 channel typically is performed concurrently with the act of transporting the second signal via the second OC-3.  
         [0038]    Referring back to FIG. 1, the transmitter end  20  comprises a video processor  110  which performs the method described with reference to FIG. 2. FIG. 6 is a schematic block diagram of an embodiment of the video processor  110  at the transmitter end  20 . Each video frame  120  within SMPTE 259M video data  122  is separated into two active video subframes. A temporary buffer  124  stores one of the two active video subframes. A temporary buffer  126  stores the other of the two active video subframes. The temporary buffers  124  and  126  may have equal sizes. Ancillary data  130  within the SMPTE 259M video data  122  is appended to outputs of the temporary buffers  124  and  126 . The resulting streams are applied to first-in-first-out (FIFOs)  132  and  134 . A sequence number is added to the FIFO stream  132  by tagging logic  136 . A sequence number is added to the FIFO stream  134  by tagging logic  140 . An AAL  142  applies FEC to the output of the tagging logic  136 . An AAL  144  applies FEC to the output of the tagging logic  140 . A physical layer  146  couples the AAL  142  to the OC-3 channel  82  in FIG. 1. A physical layer  150  couples the AAL  144  to the OC-3 channel  86  in FIG. 1. The aforementioned components of the video processor  110  are directed by system control logic  152 .  
         [0039]    Referring back to FIG. 1, the receiver end  22  comprises a video processor  158  which performs the method described with reference to FIG. 3. FIG. 7 is a schematic block diagram of an embodiment of the video processor  158  at the receiver end  22 . A physical layer  160  couples the OC-3 channel  82  in FIG. 1 to an AAL  162 . A physical layer  164  couples the OC-3 channel  86  in FIG. 1 to an AAL  166 . The physical layers  160  and  164  extract ATM cells from an incoming bit stream. The AALs  162  and  166  perform an inverse FEC block code algorithm for error checking and/or correcting, and extract the data payload from AAL-⅕ encapsulation.  
         [0040]    Tagging logic  170  is responsive to the AAL  162  to order each subframe based on its sequence number, and to remove the sequence number. Tagging logic  172  is responsive to the AAL  166  to order each subframe based on its sequence number, and to remove the sequence number. The resulting synchronized buffers are indicated by FIFOs  174  and  176 . Ancillary data  180  is extracted from each subframe. Temporary buffers  182  and  184  store the two active video portions which, when combined with EAV and SAV signals, form a video frame  186 . The video frame  186  is in accordance with an SMPTE standard such as SMPTE 259M. The aforementioned components of the video processor  158  are directed by system control logic  190 . The system control logic  190 , among other things, directs synchronization of data from the two separate fields.  
         [0041]    [0041]FIG. 8 is a block diagram of an embodiment of a system to provide timing information in addition to the sequence number. The timing information is based upon a first clock  200  and a second clock  202 . Preferably, the first clock  200  has a frequency of 90 kHz, and the second clock  202  has a frequency of 27 MHz.  
         [0042]    A first counter  204  is responsive to the first clock  200 . A second counter  206  is responsive to the second clock  202 . Preferably, the first counter  204  is a 23-bit counter and the second counter  206  is a 9-bit counter. The timing information has an upper portion  210  comprising bits from the second counter  206 , and a lower portion  212  comprising bits from the first counter  204 . The timing information is encapsulated as described above for the bit stream. The additional  32  bits keep the overall bandwidth within the bandwidth limit of the two OC-3 links.  
         [0043]    [0043]FIG. 9 is a block diagram of an embodiment of a system to reconstruct the timing information at the receiver end. A clock recovery module  214  outputs a first clock signal based on the lower portion  212  of the received timing information, and a second clock signal based on the upper portion  210 . The clock recovery module  214  may be embodied using a phase-locked loop circuit. Preferably, the first clock signal has a frequency of 90 kHz and the second clock signal has a frequency of 27 MHz.  
         [0044]    The clock signals can be useful in reducing jitter and synchronizing data. The use of field/frame counters allow better decisions to be made when reconstructing frames at the receiver. If link errors occur, the receiver can perform a first check on field number and decide what to do based thereupon. For example, the receiver may decide to use a previous frame and wait for the next consecutive frames to resynchronize.  
         [0045]    [0045]FIG. 10 is a block diagram depicting a packing method for transmitting 10-bit word information using 8-bit bytes. Four consecutive pixel samples  220 ,  222 ,  224  and  226  are packed into five consecutive bytes  230 ,  232 ,  234 ,  236  and  238 .  
         [0046]    Several embodiments including preferred embodiments of a method and system to transport high-quality video signals have been described herein.  
         [0047]    The herein-described methods and systems facilitate high bandwidth, real-time video signals to be transmitted over existing ATM infrastructure. Use of two OC-3 links rather than one OC-12 connection translates into a significant savings in bandwidth.  
         [0048]    It will be apparent to those skilled in the art that the disclosed invention may be modified in numerous ways and may assume many embodiments other than the preferred form specifically set out and described above.  
         [0049]    Accordingly, it is intended by the appended claims to cover all modifications of the invention which fall within the true spirit and scope of the invention.