Abstract:
A method and apparatus for broadcasting a data stream is disclosed. The method comprises the steps of inverse multiplexing the data stream into a first component data stream and a second component data stream and providing the first component data stream to a first transponder and providing the second component data stream to a second transponder. The apparatus comprises an inverse multiplexer, communicatively coupled to the data stream, for separating the data stream into a first component data stream and a second component data stream; an uplink transmitter, for providing the first component data stream to a first transponder and providing the second component data stream to a second transponder.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to systems and methods for transmitting information and in particular to a method and apparatus for transmitting data at high rates in systems having multiple transponders.  
           [0003]    2. Description of the Related Art  
           [0004]    Data objects can be transmitted from a location to another a variety of ways, including the use of the modems and public switched telephone network (PSTN), dedicated landlines, terrestrial microwave systems, and satellite systems.  
           [0005]    Satellite systems are particularly well suited for use in situations where the data is to be transmitted to multiple receivers or subscribers (e.g. “broadcasted” rather than just transmitted). In recent years, it has become increasingly desirable to transmit larger and larger data objects (high resolution movies suitable for public display, for example) from one place to multiple locations in a short amount of time.  
           [0006]    Data rates can be increased by using more powerful or wider bandwidth transponders. However, transmission bandwidth cannot be increased beyond assigned frequency bands, and highly powerful transponders are expensive or impossible to produce. Further, once deployed, satellite systems cannot be easily modified to permit higher data rate transmissions.  
           [0007]    There is therefore a need for a system and method for transmitting data at high rates to multiple receivers without requiring deployment of additional satellites or modifying the satellites. The present invention satisfies that need.  
         SUMMARY OF THE INVENTION  
         [0008]    To address the requirements described above, the present invention discloses a method and apparatus for transmitting a data stream. The method comprises the steps of inverse multiplexing the data stream into a first component data stream and a second component data stream and providing the first component data stream to a first transponder and providing the second component data stream to a second transponder.  
           [0009]    The apparatus comprises an inverse multiplexer, communicatively coupled to the data stream, for separating the data stream into a first component data stream and a second component data stream; an uplink transmitter, for providing the first component data stream to a first transponder and providing the second component data stream to a second transponder, and a receiver, which comprises a tuner for receiving the first component data stream from the first transponder and the second component data stream from the second transponder and a processor, communicatively coupled to the tuner. The processor reconstructs the data stream from the received first component data stream and the received second component data stream by interleaving the first component data stream and the second data stream. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    Referring now to the drawings in which like reference numbers represent corresponding parts throughout:  
         [0011]    [0011]FIG. 1 is a diagram illustrating an overview of the data distribution system;  
         [0012]    [0012]FIG. 2 is a diagram showing the transmission of a data stream using the data distribution system;  
         [0013]    [0013]FIG. 3 is a diagram illustrating one embodiment of the process of inverse multiplexing the input data stream into a plurality of contiguous component data streams;  
         [0014]    [0014]FIG. 4 is a diagram illustrating an alternative embodiment of the invention in which identifiers are transmitted in a map; and  
         [0015]    FIGS.  5 A- 5 D are flow charts illustrating exemplary method steps that can be used to practice the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0016]    In the following description, reference is made to the accompanying drawings which form a part hereof, and which is shown, by way of illustration, several embodiments of the present invention. It is understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.  
       Video Distribution System  
       [0017]    [0017]FIG. 1 is a diagram illustrating an overview of a data distribution system  100 . The video distribution system  100  comprises a control center  102  in communication with one or more uplink center(s)  104  via a ground or other link(s)  114  and with receivers  124  at receiver stations  122  such as theaters displaying program material to viewers  110  via a public switched telephone network (PSTN) or other link  120 . The control center  102  provides program material to the uplink center(s)  104 , coordinates with the receiver stations  122  to display audiovisual information to the viewers  110 . Associated functionality, including billing for video programs, encryption/decryption, and assuring the security of the video programs is also provided by the control center  102 .  
         [0018]    In the illustrated embodiment, the control center  102  and the uplink center  104  are shown as geographically separate entities. However, the functionality of the control center  102  and uplink center(s)  104  can be integrated within a single facility. Further, although FIG. 1 depicts that the program material is transmitted from the control center  102  to the uplink center  104  via a ground link  114 , the program material can be delivered to the uplink center  104  in tangible form by messenger, by satellite or terrestrial transmission, or by any secure means.  
         [0019]    The uplink center receives program material and program control information from the control center  102 , and using one or more uplink antennae  106  and transmitter module(s)  105 , transmits the program material and program control information to one or more satellite(s)  108 A and  108 B (hereinafter alternatively referred to as satellite or satellites  108 ).  
         [0020]    Collectively, the satellites  108  of the video distribution system  100  include a plurality of transmitters. In one embodiment, the transmitters comprise transponders  107 A 1 - 107 B 2 , which receive the signal from the uplink center  104  at a particular frequency, and transpond the signal to the receiver station(s)  122 . Since this involves minimal satellite  108  processing, this is sometimes referred to as a “bent-pipe” transmission system.  
         [0021]    Multiple transponders  107 A 1 - 107 B 2  can be implemented in the video distribution system  100  by including more than one transponder on a single satellite (e.g.  107 A 1  and  107 A 2  on satellite  108 A), or a single transponder on a plurality of satellites (e.g. transponder  107 A 1  on satellite  108 A and transponder  107 B 1  on satellite  108 B), or by including more than one transponder on more than one satellite (e.g. transponders  107 A 1  and  107 A 2  on satellite  108 A and transponders  107 B 1  and  107 B 2  on satellite  108 B).  
         [0022]    Each of the satellite transponders (hereinafter alternatively collectively referred to as transponder(s)  107 ) receives a signal from the uplink center  104  (via link  116 A or  116 B) transmits the signal to the subscribers  110 . The subscriber  110  receiving station receives this information using the subscriber antenna  112 .  
         [0023]    While the invention disclosed herein will be described with reference to a satellite based video distribution system  100 , the present invention may also be practiced with terrestrial-based transmission of program information, whether by broadcasting means, cable, or other means. Further, the different functions collectively allocated among the control center  102 , uplink center  104 , and/or the receiver stations  122  as described above, and can be reallocated as desired without departing from the intended scope of the present invention.  
         [0024]    Although the foregoing has been described with respect to an embodiment in which the program material delivered to the subscriber is video (and audio) program material such as a movie, the foregoing method can be used to deliver program material comprising purely audio information or computer data as well.  
         [0025]    [0025]FIG. 2 is a diagram showing the transmission of a data stream using the video distribution system  100 . The uplink center  104  includes an inverse multiplexor  202 . The inverse multiplexor  202  accepts an input data stream  210  and separates the input data stream into a plurality of component data streams  212 A- 212 F. This is accomplished by designating a first contiguous portion of the data stream  210 A as a member of the first component data stream  212 A, and designating a second contiguous portion of the data stream  210 B as a member of the second component data stream  212 B. In one embodiment, the each contiguous portion of the input data stream  210 A- 210 F is associated with an identifier before being separated into separate component data streams  212 A- 212 F. This permits the data in the component data streams  212 A to be reassembled in the proper temporal relationship compared to other data in the component data streams by the receiving station  122 . This process is described further below.  
         [0026]    The component data streams  212 A- 212 F are provided to the transmitter module(s)  105 . In one embodiment, each transmitter module  105  includes a plurality of transmitter channels  220 A- 220 F, each for transmitting one of the component data streams  212 A- 212 F. Each transmitter channel  212 A- 212 F includes an encryption module  222  for encrypting the component data stream  212 A- 212 F, a modulator  224  communicatively coupled to the encryption module  222 , transmitter  226 , and antenna  228 . Of course, the functionality of each of the encryption modules  222 , modulators  224 , transmitters  226  and antennae can be combined into a single unit (e.g. one encryption module  222 , one modulator  224 , one transmitter  226 , and or one antennae  228 ) operating on all component data streams  212 A- 212 F in parallel or series). For example, a widebeam antennae  228  can be used to transmit information from all component data streams to different satellites (e.g.  108 A and  108 B) if the beamwidth of the antennae  228  is wide enough to include both satellites  108 A and  108 B).  
         [0027]    The transmitted component data streams  212 A- 212 F are received and retransmitted (e.g. transponded) by transponders  107  to the receiver station  122 . The receiving station  122  includes a receiver module  124 . The receiver module  124  includes a plurality of channel receivers  230 A- 230 F. In one embodiment, the channel receivers  230 A- 230 F each include an antenna  112 , a tuner,  234  and a processor  236  for controlling the reception of the downlink signal from the satellites  108 . Each of the channel receivers  230 A- 230 F provides a received component signal  214 A- 214 F, respectively, which is provided to a multiplexor  206 .  
         [0028]    The multiplexor  206  assembles the receives the component data streams  214 A- 214 F to reconstruct the input data stream  210 A- 210 F. In one embodiment, this is accomplished using the identifiers included in each component data stream, as described further below. In another embodiment, the input data stream  210 A- 210 F is reconstructed from the received component data streams  214 A- 214 F in other ways, including a periodically transmitted map, or by inferring the order that the elements of the received component data streams  214 A- 214 F from the content of the data itself.  
         [0029]    While the foregoing has been described with respect to channel receivers  230 A- 230 F each having separate antennae  112 , tuners  234 , and processors  236 , operations performed by the receiver station  122  can be integrated into fewer elements. For example, the receiver station  122  may comprise two antennae (a first antenna oriented to receive communications from satellite  108 A and a second antenna oriented to receive communications from satellite  108 B), or an antenna with multiple sensing elements sharing a single reflector capable of collecting radiant energy transmitted from both the first satellite  108 A and the second satellite  108 B. Further, a single tuner  234  can be used to receive each of the component data streams, one at a time, or two tuners (one for each satellite  108 ) can be used. Finally, the receiver station  230  may include only a single processor  236  which performs all of the necessary functions, including the control of the tuners  234  and antennae  112  to receive the component data streams  214 A- 214 F.  
         [0030]    [0030]FIG. 3 is a diagram illustrating one embodiment of the inverse multiplexing of the input data stream  210  into a plurality of contiguous component data streams. As described earlier in FIG. 2, the input data stream  210  is separated into a plurality component data streams  212 A- 212 F. A first contiguous portion  210 A of the data stream is associated with a first identifier  302 A. In the illustrated the first identifier  302 A is added to the beginning of the payload (the first contiguous portion of the data stream  210 A), however, the first identifier  302 A could be appended to the end of the payload, placed within the payload, or coded into the payload, using techniques similar to those used in digital watermarking. It is noted that the identifier  302  used to reassemble the component data streams  214 A- 214 F can simply be a serial number, which can cycle up to a maximum value and repeat at the beginning. In this embodiment, the number of serial numbers in the period should be sufficient to assure unambiguous identification of the component data streams and reassembly to reconstruct the input data stream. Also, as shown in FIG. 3, each payload can include multiple data packets, each including a header  306 A as well as program material  308 A. In this way, the present invention can be implemented using a wide variety of transmission protocols without modification.  
         [0031]    [0031]FIG. 4 is an illustration of another embodiment of the present invention. In this embodiment, the identifiers  302  associated with the component data streams that are used to reassemble the input data stream  210  are assembled into a map  414  that is periodically transmitted to the receiver station  124 . In one embodiment, the map  414 A maps identifiers  302  with associated component data streams. In a second embodiment, the map  414 B is simply an ordered list of identifiers, thus indicating the order that the component data streams  214 A- 214 F should be reassembled. In this embodiment, the uplink center  104  includes a map generator or data mapper  402  which interfaces with the inverse multiplexor  202  to generate a data stream  404  including a map such as map  414 A and/or  414 B (hereinafter alternatively referred to as maps  414 ). In the illustrated embodiment, the maps  414  are transmitted to the receiver station  124  via one of the satellites  108 B using a separate channel transmitter  406 , transponder (e.g. transponder  107 B 4 ), and channel receiver  406 . In another embodiment, the map is transmitted via a different channel such as the PSTN, other land line, Internet, or dedicated communication link.  
         [0032]    The correlator  412  receives the map, and interfaces with the multiplexor  206  to reassemble the received component data streams  214 A- 214 F into the input data stream  210 .  
         [0033]    In one embodiment, the multiplexor  206  includes a buffer for buffering the received component data streams  214 A- 214 F to allow the portions of the component data stream to be reassembled in the proper order (e.g. saving a data portion until all of the data portions which preceded it before inverse multiplexing and transmission have been received and processed).  
         [0034]    [0034]FIG. 5 is a flow chart illustrating exemplary method steps that can be used to practice the present invention. The input data stream  210  is inverse multiplexed into a first component data stream  212 A and a second component data stream  212 B, as shown in block  502 . The first and second component data streams  212 A and  212 B are provided to a first and second transponder (e.g. separate transponders), as shown in block  504 . The first component data stream  212 A is then broadcast by a first transponder  107 A 1  and the second component data stream  212 B is broadcast by the second transponder (e.g.  107 A 2  or  107 B 1 ), as shown in block  506 . The first and second component data streams  214 A and  214 B are received at the receiver station  124 , as shown in block  508 , and the input data stream  210  is reconstructed, as shown in block  510 .  
         [0035]    [0035]FIG. 5B is a flow chart showing exemplary method steps that can be used to inverse multiplex the input data stream  210  into component data streams  212 A- 212 F. A first contiguous portion of the data stream  210 A is designated as a member of the first component data stream  212 A, and a second contiguous portion of the data stream  210 B is designated as a member of the second component data stream  212 B, as shown in blocks  512  and  514 . A first identifier ( 414 B 1 , for example) is associated with the first contiguous portion of the data stream  210 A and a second identifier ( 414 B 2 , for example) is associated with the second contiguous portion of the data stream  210 B, as shown in block  516 .  
         [0036]    [0036]FIG. 5C is a flow chart illustrating exemplary method steps that can be used to associate the first identifier and the second identifier with their respective component data streams. In this embodiment, a map that associates the first and second identifiers with the first and second contiguous portions of the data steam is generated, as shown in block  518 .  
         [0037]    [0037]FIG. 5D is a flow chart illustrating exemplary method steps that can be used to inverse multiplex the input data stream  210  into component data streams  212 A- 212 F. The available transmission capacity of the first transponder (e.g.  107 A 1 ) and the second transponder (e.g.  107 A 2 ) are determined in block  520 . In one embodiment, the available transmission capacity of the transponders  107  can be determined by measuring the throughput (instantaneous or averaged over a selectable period of time) and determining the difference between the measured throughput and the transmission capacity of the transponders  107 . In another embodiment, the throughput of the transponder is not measured, but estimated based on other factors that can either be predicted or measured. For example, throughput can be estimated based upon knowledge of the data supplied to the transponder  107 . Such knowledge can include data metrics commonly available in statistical multiplexing techniques and the like. In some cases, the transponder output nominally includes some number empty data packets. In such cases, the number of such data packets can be used to determine the available transmission capacity of the transponder.  
         [0038]    Further, in designating which data stream portions  210 A- 210 F should be assigned to which transponders  107 A 1 - 107 B 3 , the inverse multiplexor  202  may generate an optimized allocation of the available transmission capacity of all or a subset of the transponders  107 A 1 - 107 B 3 . This can be accomplished by comparing predictions of the future data throughput of each transponder with the predicted data throughput requirements for the input data stream  210 A- 210 F as well as other data streams of interest. Different data streams can be allocated according to customer priority, quality of service (QoS), or throughput requirements.  
       Conclusion  
       [0039]    This concludes the description of the preferred embodiments of the present invention. The foregoing description of the preferred embodiment of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. For example, while the foregoing has been described with respect to a video distribution system used primarily for purposes of distribution of films and the like to movie theaters, the video distribution system herein described can be used to transmit data of a variety of types, including software, audio, and electronic copies of books and/or other data. Further, while the foregoing has been described with respect to one way communications from the uplink center to the receiver station, the foregoing principles can be used to implement two way communications (e.g. from the receiver station to the uplink station or other ground station) by employing transmitter(s) and transmitting antennae at the receiver station and employing receiver(s) at the uplink center or ground station.  
         [0040]    It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto. The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.