Patent Publication Number: US-2001000457-A1

Title: Method and apparatus for dynamic allocation of transmission bandwidth resources and for transmission of multiple audio signals with a video signal

Description:
RELATED PROVISIONAL APPLICATION  
     1. The present application relates to, and claims priority from, provisional application Ser. No. 60/002,445, filed Aug. 16, 1995.  
    
    
     
       FIELD OF THE INVENTION  
       2. The present invention relates generally to a method and apparatus for dynamically allocating transmission bandwidth resources. Utilization of available bandwidth is maximized by a using a multiple channel, multiple carrier (MCMC) transmission scheme. The transmission rate capability of each carrier is parsed down into smaller slots which can be dynamically allocated and multiplexed to facilitate any sized user, from one slot to multiple slots. Multiple carriers are used to transmit the allocated data slots on available portions of the transmission spectrum. At least one slot of information on each carrier will be used for control information so that channels or services can be located on that particular carrier. Additionally, a separate service might be used to provide system-wide mapping or administrative functions. As a result, a user can find any service even if a channel or service location has changed. This transmission scheme allows for wide user flexibility, while also maximizing use of available transmission spectrum.  
       3. In an alternative embodiment, the present invention generally relates to a method and apparatus for transmitting at least one digitally encoded video signal with at least two digitally encoded audio signals related thereto. According to this alternative embodiment, the video and audio digital signals are combined through time division multiplexing to produce an aggregate audio/video bitstream containing data packets transmitted along at least two channels of fixed bandwidth, thereby maintaining a known fixed delay between packets of data in a given channel.  
       BACKGROUND OF THE INVENTION  
       4. Available bandwidth on transmission systems is a valuable commodity whose value continues to increase as more and more users and applications crowd the spectrum. As a result, maximizing the use of available bandwidth is an important concern for the industry. To date, systems have not adequately provided for user flexibility in conjunction with maximum use of available bandwidth.  
       5. Current technology permits modulation of a binary base band signal into a radio frequency (RF) signal for transmission and demodulation back into base band. As shown in FIG. 1, the base band signal  1  enters the modulator  3  and is converted into RF for transmission and receipt over antennas  5 ,  7 . Demodulator  9  converts the received signal back into a base band signal  11 . This transmission scheme is known as single channel per carrier (SCPC).  
       6. Modulators convert base band signals from binary into the frequency spectrum through a variety of modulation techniques. Common modulation techniques include binary phase shift keying (BPSK) and quadraphase shift keying (QPSK). BPSK has a conversion rate of approximately 1 kilohertz (KHZ) per 1 kilobit (KB). QPSK has a conversion rate of approximately 0.5 KHZ per 1 KB. Accordingly, QPSK is more efficient in that nearly twice as many bits of information can be transmitted over a similar frequency bandwidth. However, noise tradeoffs exist as data conversion rates increase. This limits the effectiveness of increasing bandwidth usage through modulation techniques with even higher data conversion rates.  
       7. As shown in FIG. 2, SCPC systems generate a separate RF carrier signal  13 ,  15  for each base band input signal  14 ,  16 . FIG. 3 shows a plot of power versus frequency for the carrier signals  13 ,  15  wherein each signal occupies a separate center frequency  17 ,  19  with a separate bandwidth  21 ,  23 . Since each channel—with a separate carrier—occupies different space on the frequency spectrum, such SCPC systems are inherently inefficient for multi-channeled systems.  
       8. Referring to FIG. 4, to maximize efficiency, the space  25  between each carrier signal must be minimized. However, as shown in FIG. 5, if this space is minimized too much, then the edges, or “skirts”  27 , of the carrier signals overlap and interfere with each other. This can lead to erroneous and noisy demodulation of the RF signal. Alternatively, as shown in FIG. 6, the skirts  27  can be truncated via filtering, but then part of the original carrier signal has been excluded. This again could appear as errors or noise upon demodulation.  
       9. Current technology also includes multiple channel per carrier (MCPC) systems as shown in FIG. 7. With this system, multiple binary base band signals (or channels)  31 ,  33  are multiplexed via a multiplexor  35  and then fed into a modulator  37 . The transmitted RF signal is then demodulated (via  39 ) and demultiplexed (via  41 ) into its component base band signals  43 ,  45 . As shown by FIGS.  8 ( a ) and  8 ( b ), separate carriers— that might be produced by signals  31 ,  33  in an SCPC system—would have the potentially noisy skirt overlap  49 , and a collective bandwidth  47 . By multiplexing the signals together, the resulting RF signal shown in FIG. 8( b ) would have a comparable bandwidth  51  and yet carry more information (e.g. up to 20% more bits), with less noise, due to more efficient use of the carrier signal across the corresponding bandwidth  51 . Accordingly, MCPC systems are inherently more efficient than SCPC systems.  
       10. While MCPC systems might be more efficient, they are often used in very inefficient ways due to the inflexibility of existing transmission systems. For instance, to gain the benefits of multiplexing two (or more) signals together, information must often be transported or transmitted back to the facility where the MCPC multiplexing and transmission ultimately occurs. This practice is known as “backhauling” information. Referring to FIG. 9( a ), an SCPC system  56  is shown with the resulting plot of carrier signal  57 . FIG. 9( b ) shows an MCPC system  58  which multiplexes the signal  57  with the backhauled signal  55  to produce the resulting MCPC carrier signal  59 . FIG. 10 demonstrates the relative inefficiency of backhauling; not only is the bandwidth of signal  59  being used on the frequency spectrum, the bandwidth of signal  55  is also being used. Hence, the use of multiple carriers to create an MCPC signal is relatively inefficient, particularly when backhauling is employed, because more frequency bandwidth is ultimately used than with the MCPC system alone.  
       11. The applicant has recognized the need for a multiple channel multiple carrier system (MCMC) which is more flexible and allows users of all sizes to access the system. Multiple carriers, each carrying multiple channels, can be spread out over the available frequency spectrum, thus maximizing bandwidth usage. Each carrier will carry control header information which will allow location and access to all possible channels spread out over all possible carriers.  
       12. Existing transmission systems transport audio and video data in satellite and cable TV applications. FIG. 23 illustrates an exemplary audio/video transmission system including an audio/video encoder  400  which communicates with a statistical remultiplexor  402  which in turn communicates with a modulator  404 . The encoder  400  receives audio and video signals along input lines  401  and  403  and outputs encoded packets of audio and video data along lines  406  and  408 , respectively. The statistical remultiplexor  402  combines the audio and video data packets (according to the format illustrated in FIG. 25) and outputs same as an aggregate bitstream along line  412 . The aggregate bitstream is transmitted to a remote destination via antenna  418  by the modulator  404 . Feedback lines  410  and  414  are provided to maintain a desired timing relation between the data transmission rates of the encoder  400 , remultiplexor  402  and transmit module  404 .  
       13. The transmitted bitstream is received by a demodulator and the audio and video data packets are demultiplexed and decoded into separate audio and video data streams. These decoded data streams are processed and displayed to end viewers. One such demultiplexor and decoding system has been proposed LSI Logic Corporation of California (Model No. L64007 MPEG-2 Transport Demultiplexor). The system proposed by LSI Logic complies with the international standard ISO/IEC 13818-1 MPEG-2 systems specification. As shown in FIG. 25, the aggregate bitstream  450  is composed of plurality of data packets  452 , each of which includes a data section  454  and a “presentation time stamp”  456  (explained below in more detail). As shown in FIG. 25, the statistical multiplexor  402  (FIG. 23) intersperses the audio and video packets in a non-uniform manner. By way of example, a single audio packet  458  may be followed by two video packets  460  and  462 , which are followed by alternating audio and video packets  464 - 472 . The statistical remultiplexor  402  controls the order in which the audio and video packets  458 - 472  are combined.  
       14. The presentation time stamps  456  are provided within each data packet  452  by the encoder  400  to enable synchronization and realignment, at the downstream end, between the audio and video signals. Each time stamp  456  represents a timing offset, with respect to a reference time Tr, at which corresponding audio or video packet is to be played/displayed.  
       15. However, conventional audio/video encoding and decoding have met with limited success. These existing systems have been unable to combine multiple audio and video signals into a single aggregate bitstream in an optimal manner. As explained above, conventional systems utilize statistical remultiplexors  402  to combine audio and video packets.  
       16.FIG. 26 illustrates an exemplary aggregate bitstream produced by a statistical remultiplexor which receives input signals from multiple audio and video encoders. In the example of FIG. 26, it is assumed that three audio and video encoders are utilized, denoted encoders A, B and C. According to the conventional technique, the statistical remultiplexor combines audio and video packets from these multiple encoders A-C in a statistical fashion (as shown in FIG. 26). Thus, packets pertaining to a particular video encoder or a particular audio encoder may be separated by several packets from different encoders. Time stamps generated by a single encoder represent an offset which is reset to a new reference time at time intervals of a duration only sufficient to account for the maximum delay between audio and video data packets for a single encoder. Hence, packets statistically multiplexed from two or more encoders exceed the time interval between reference times. Accordingly, the statistical remultiplexor must adjust each presentation time stamp to account for the increased delay due to the use of multiple encoders. These modified time stamps are denoted by reference numerals  480 - 494 .  
       17. However, the foregoing statistical multiplexing process is excessively complex, slow and undesirable.  
       OBJECTS OF THE INVENTION  
       18. The present invention has various embodiments that achieve one or more of the following features or objects:  
       19. It is an object of the present invention to provide a multiple channel, multiple carrier transmission system with dynamically allocable base band signal slots (or channels) to accommodate any sized service.  
       20. It is another object of the present invention to provide a multiple channel, multiple carrier transmission system wherein each carrier can by dynamically located to maximize bandwidth usage on the frequency spectrum.  
       21. It is a further object of the present invention to provide a multiple channel, multiple carrier transmission system wherein each carrier contains header information which can provide access to all services on the series of carriers.  
       22. It is yet a further object of the present invention to provide a multiple channel, multiple carrier transmission system wherein each carrier contains header information which can provide access to all services on the series of carriers, and wherein additional service space is allocated for such tasks as information transfer, service identification, and service control.  
       23. It is yet a further object of the present invention to provide a system for digitally encoding and transmitting at least one digital video signal along with multiple digital audio signals.  
       24. It is a corollary object of the present invention to provide an audio/video encoding and transmitting system which transmits multiple audio signals related to a single video signal in a time division multiplexed manner.  
       25. It is a further object of the present invention to provide a digital encoding and transmitting system which avoids the need to adjust presentation time stamps generated within each encoder by maintaining a fixed delay between data packets from different encoders.  
       26. It is yet a further object of the present invention to provide a digital encoding and transmitting system which assigns fixed bandwidths to each audio and video signal to be transmitted.  
       SUMMARY OF THE INVENTION  
       27. The disclosed invention overcomes the aforementioned inefficiencies of prior transmission systems by providing a transmission system that is flexible and efficient. The present invention provides a multiple channel, multiple carrier transmission system with dynamically allocable slots (or channels) that can be combined to form any sized service. Slots could be allocated sequentially or nonsequentially. The data rate of each slot is relatively small compared to the data rate of the whole system. This allows each user to purchase and use only the necessary number of bits for a particular application. As user needs change, the slots can be dynamically reallocated without affecting the efficiency of the system, the ease of use by the user without affecting other slots used by different users.  
       28. Each carrier signal contains reserved header data regarding all other carriers associated with the transmission system. This allows all services (e.g. allocated combinations of slots) to be located regardless of which carrier signal contains that service to be located. Accordingly, a plurality of services— each consisting of one or many slots—can be spread out over a plurality of carrier signals and so transmitted. When operating with a plurality of carriers, each carrier signal can be dynamically tuned to fill available spaces in the transmission frequency spectrum, thus maximizing use of all available transmission bandwidth.  
       29. In an alternative embodiment, a method and apparatus are provided for digitally encoding and transmitting at least one video signal and at least two related audio signals. According to this alternative embodiment, a video encoder is provided along with at least two audio encoders. The audio and video encoders generate corresponding audio and video bitstreams, each of which comprises a plurality of packets containing data sections. The audio and video bitstreams are delivered to a multiplexor which effects time division multiplexing upon to combine the audio and video bitstreams into an aggregate audio/video bitstream. The aggregate audio/video bitstream contains at least two independent channels of fixed bandwidth for separately transmitting designated ones of the video and audio bitstreams. A modulator transmits the aggregate audio/video bitstream. According to the above described alternative embodiment, fixed delays are maintained between packets within a single channel, thereby avoiding the need to adjust any presentation time stamps which may be generated by the encoders.  
       30. Additional features and advantages of the present invention will become apparent to one skilled in the art upon consideration of the following detailed description of the present invention.  
     
    
    
     BRIEF DESCRIPTIONS OF THE DRAWINGS  
     31.FIG. 1 is a block diagram illustrating a single channel per carrier (SCPC) transmission scheme.  
     32.FIG. 2 is a block diagram illustrating the generation of two separate carrier signals from two separate SCPC transmission schemes.  
     33.FIG. 3 is a plot of power versus frequency for the two carrier signals of FIG. 2.  
     34.FIG. 4 is a plot of power versus frequency for two example carrier signals showing the desire to minimize the frequency spacing between the two signals.  
     35.FIG. 5 is a plot of power versus frequency for two example carrier signals wherein the frequency spacing has been minimized to the point that the carrier signal skirts overlap.  
     36.FIG. 6 is a plot of power versus frequency for an example carrier signal wherein the skirts have been filtered off.  
     37.FIG. 7 is a block diagram illustrating a multiple channel per carrier transmission scheme.  
     38.FIG. 8( a ) is a plot of power versus frequency for two example carrier signals showing skirt overlap for a given bandwidth.  
     39.FIG. 8( b ) is a plot of power versus frequency for the two example carrier signals of FIG. 8( a ) which have been multiplexed before modulation.  
     40.FIG. 9( a ) shows a block diagram of an SCPC system and a resulting plot of power versus frequency for a carrier signal with a given bandwidth.  
     41.FIG. 9( b ) shows a block diagram of an MCPC system, along with an SCPC system for backhauling, and a resulting plot of power versus frequency for the MCPC generated signal.  
     42.FIG. 10 is a plot of power versus frequency for the MCPC signal and the SCPC signal of FIG. 9( b ).  
     43.FIG. 11 shows a block diagram of an MCPC system with a plurality of input and output channels.  
     44.FIG. 12 shows a block diagram of the multiplexor and demultiplexor sections of the MCPC system of FIG. 11, with different channels allocated for different services.  
     45.FIG. 13 a block diagram of the multiplexor and demultiplexor sections of the MCPC system of FIG. 11, with yet other channels allocated for other services.  
     46.FIG. 14 is a table showing the type of information which allows a user to locate and use a particular service on a system-wide basis.  
     47.FIG. 15 is a plot of power versus frequency for a carrier signal, with a given center frequency and bandwidth, which contains the services of FIGS. 13 and 14.  
     48.FIG. 16 is a block diagram illustrating an MCPC system with four slots and secondary multiplexors for services spanning more than one slot.  
     49.FIG. 17 is a table showing the bitstream patterns of the MCPC system of FIG. 16, and the resulting multi-slot service bitstream.  
     50.FIG. 18 is a plot of power versus frequency showing two unaccessible bandwidth areas and three carrier signals oriented in the available spaces between the unaccessible areas.  
     51.FIG. 19 is a block diagram illustrating a multiple channel, multiple carrier transmission scheme, with multiple services, corresponding to the carrier signals of FIG. 18.  
     52.FIG. 20 is a table showing the type of information which allows a user to locate and use a particular service on the MCMC system of FIGS. 18 and 19.  
     53.FIG. 21 is a block diagram of a multiplexor configuration as used in an embodiment of the MCMC system.  
     54.FIG. 22 is a block diagram of a receiver configuration as used in an embodiment of the MCMC system.  
     55.FIG. 23 illustrates a block diagram of an exemplary conventional audio/video encoding and transmitting system.  
     56.FIG. 24 illustrates a block diagram of an alternative embodiment of an audio/video encoding system according to the present invention.  
     57.FIG. 25 illustrates a portion of an aggregate audio/video bitstream transmitted by the conventional system of FIG. 23.  
     58.FIG. 26 illustrates an exemplary aggregate audio/video bitstream generated according to the system of FIG. 23 for multiple audio and video encoders.  
     59.FIG. 27 illustrates an exemplary aggregate audio/video bitstream generated by the system of the alternative embodiment of FIG. 24 of the present invention.  
     60.FIG. 28 illustrates a block diagram of an exemplary decoder for use in connection with the alternative embodiment of FIG. 24 of the present invention.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     61. Referring now to FIG. 11, an MCPC system  60  is shown with a plurality of input channels  61  and a plurality of output channels  63 . As with other MCPC systems a multiplexor  65  combines the various channels into a single bitstream which enters the modulator  67 . The modulator  67  converts the bitstream into an RF signal  69  which enters the demodulator  71  and is converted back into a binary signal. The binary signal enters the demultiplexor  73  which separates the signal back into its component channels  63 .  
     62. While each channel of an MCPC system  60  might handle a variety of data rates from large to small, the preferred embodiment uses a relatively small, fixed data rate for each channel. Referring to FIG. 12 the multiplexor and demultiplexor portion of the MCPC system  60  is shown is more detail. As shown for purposes of example, for the plurality of channels  61  (numbered 0 through N), each channel (or slot) operates at 8 kilobits per second (KBS). This allows for services  75  to be tailored to each user&#39;s size and data rate needs. For example, Service 1  utilizes four slots to give the user a 32 KBS capability. Service 2  utilizes only 1 slot for a 8 KBS capability. Similarly, Service 3  utilizes only 1 slot for a 8 KBS capability.  
     63. The allocation of slots for services does not have to be sequential. As shown in FIG. 13, Service N    81  spans slot  1  ( 83 ), slot  2  ( 85 ), slot  4  ( 89 ), and slot  6  ( 93 ) thus creating a service with a 32 KBS data rate capability. Service W    97  spans slot  3  ( 87 ) and slot  5  ( 91 ) thus creating a service with a 16 KBS data rate capability. The slot data then enters multiplexor  99  and is modulated into an RF signal and demodulated back to binary (not shown). The demodulated binary signal then enters demultiplexor  101  for separation back into the appropriate slot and service data.  
     64.FIG. 15 shows the resulting carrier signal  110  which is generated and transmitted by the MCPC system of FIG. 13. Signal  110  is centered about frequency f c    111  and has a bandwidth (bw) indicated by  113 . Carrier signal  110  contains all of the multiplexed slot information which can be extracted if the location of the services is known.  
     65.FIG. 14 shows a table of the type of information that would allow a user to locate and use a particular service on a system-wide basis (e.g. a slot allocation table, along with carrier center frequencies and bandwidths). It is preferable that the center frequency and bandwidth of a particular carrier be known to receive and demodulate the carrier signal. It is also preferable that the total number of multiplexed slots (for that particular carrier) be known to facilitate decoding of the demodulated bitstream. Optionally, the center frequency, bandwidth and/or the total number of multiplexed slots may be computed using related information, such as bandwidth and the like. For each service, the total number of slots used for that particular service should be known, as well as the particular slot numbers used. As FIG. 14 shows, Service N  can be located and demodulated at center frequency f c  with a bandwidth bw. The total number of slots in this MCPC system is eight. Service N  uses 4 total slots with slot numbers 1, 2, 4 and 6, for a 32 KBS data rate capability. Similarly, and as part of the same carrier, Service W  can be located and demodulated at center frequency f c  with a bandwidth bw. Again, the total number of slots in this MCPC system is eight. Service W  uses 2 total slots with slot numbers 3 and 5 for a data rate capability of 16 KBS.  
     66. With this table of information, the user can locate and use the services transmitted on a particular carrier signal. In the preferred embodiment, the slots used for each service on a particular carrier are transmitted as auxiliary header information on a designated, hardwired slot. While this designated slot might be any of the total number of slots for each MCPC system, the preferred embodiment hardwires the zeroth slot  103  as a convenient location for such slot allocation information. Hence, upon demodulating any carrier signal as configured above, the user can demultiplex the slot data and get a “map” of all services within that particular carrier by looking at the zeroth slot data. With this “map” then all the services on that carrier can be digitally reconstructed and retrieved.  
     67. Referring now to FIG. 16, in order for any particular service to use more than one slot (albeit sequential or nonsequential), a secondary set of multiplexors is used to partition the signal down to the data rate for each of the particular slots. In this example embodiment, the MCPC system  120  has four slots, each with a 8 KBS data rate. The zeroth slot  123 ,  143  ?is served for slot allocation data. The input base ba signal  121  (or service) has a 16 KBS data rate and use nonsequential slots  127  and  128  on the primary multiplexor  130 . The secondary multiplexor  132  is used to tition the 16 KBS signal down into two bitstreams c KBS as applied to slots  124 ,  126 .  
     68. In essence, the secondary multiplexor acts like a comparative switch  134 . By switching back and forth between the two slots  124 ,  126 , the 16 KBS bitstream is headed into two 8 KBS bitstreams by alternatingly dividing the incoming bits into two different directions. Larger systems (not shown) might have an even larger multiple of input lines into the multiplexor and demultiplexor devices. Hence, the commutative s hing must occur between a large number of input l and be programmably alterable as the allocations or e services are altered or updated. Such selective, co tative switching between the multiple input lines could easily be achieved by a device such as a Field Programmable Gate Array (FPGA) or Programmable Logic Array (PLA) that has been configured for such a task.  
     69. The primary multiplexor  130  also acts like a c mutative switch  136 . Multiplexor  130  switches down across each of the slots  123 ,  124 ,  125 , and  126 , and thus combines the four 8 KBS bitstreams into a 32 KBS bitstream  138 . Bitstream  138  is modulated, transmitted as an RF signal, and then demodulated (not shown) back into a 32 KBS signal  139 . The resulting demodulated 32 KBS signal  139  is fed into the primary demultiplexor  140  which similarly acts as a commutative switch  147  to divide the 32 KBS signal into four slots  143 ,  144 ,  145 , and  146  of 8 KBS each. The secondary demultiplexor  150  is connected across slots  144  and  146 . Demultiplexor  150  also acts as a commutative switch  152  to alternate between the 8 KBS bitstreams of slots  144 ,  146  and combine them into a resulting 16 KBS signal  154 .  
     70.FIG. 17 demonstrates, in tabular form, the commutative switching effect of the primary and second multiplexors and demultiplexors. Referring also to FIG. 16, the demodulated 32 KBS signal  139  is comprised of a sequence of bits as indicated by row  161 . This sequence  161  is repeatedly divided across the four slots (numbered 0 through 3), by the commutative action of the demultiplexor  140 , as indicated by row  163 . The bitstreams are ultimately comprised of service bits which are labeled as S b   s , as shown by  160 . According to this notation, the superscript b represents the ongoing number of times the series of slots (0 through 3) is sampled on the primary multiplexor. Hence b also represents the ongoing bit number emerging from each slot. The subscript s represents the particular slot number.  
     71. Using this notation the assignment of the bits of the transmitted bitstream  139  to each slot  0  through  3  (elements  143 - 146 ) is shown by row  165 . As the commutative action of the multiplexor  140  progresses, each bit of the incoming bitstream  139  is sequentially, and repeatedly, assigned to each slot. Slot  1  (element  144 ), for example, will have the bitstream S 0   1 , S 1   1 , S 2   1  . . . and so on. (see element  156 ). Accordingly, the bits of available data emerging across the four available slots would be S 0   0 , S 0   1 , S 0   2 , S 0   3 , S 1   0 , S 1   1 , S 1   2 , S 1   3 , S 2   0 , S 2   1 , S 2   2 , S 2   3 , . . . and so on. By adding the secondary demultiplexor  150  across slots  1  and  3  (elements  144 ,  146 ), the two 8 KBS bitstreams can be combined into the 16 KBS service bitstream  154  by the commutative action  152  of the demultiplexor  150 . As shown by row  167 , this resulting bitstream would include S 0   1 , S 0   3 , S 1   1 , S 1   3 , S 2   1 , S 2   3 , . . . and so on.  
     72. Using the principles described above, a multi-channel, multi-carrier (MCMC) transmission system is even more efficient at utilizing available bandwidth. With such an MCMC system, a plurality of services could be allocated across a plurality of MCPC systems. Referring now to FIG. 19, an example MCMC system is shown. In this example, three MCPC systems  170 ,  172 ,  174  are shown which generate RF carrier frequencies  171 ,  173 ,  175 . Each MCPC system has, for purposes of example, four slots per multiplexor/demultiplexor.  
     73. Service 1  (Sv 1 ) utilizes slots  1  and  2  (elements  191  and  192 ) of the primary multiplexor  220  of MCPC system  170 . Hence a secondary multiplexor  222  is used to divide Sv 1  between the two slots. Sv 2  utilizes slot  3  (element  193 ) of the primary multiplexor  220  of MCPC system  170 . Sv 3  utilizes slot  1  (element  195 ) of the primary multiplexor  230  of MCPC system  172 . Sv 4  utilizes slots  2  and  3  (elements  196  and  197 ) of the primary multiplexor  230  of MCPC system  172 . Hence a secondary multiplexor  232  is used to divide Sv 4  between the two slots. Sv 5  utilizes slots  1 ,  2 , and  3  (elements  199 ,  200 , and  201 ) of the primary multiplexor  240  of the MCPC system  174 . Hence a secondary multiplexor  242  is used to divide Sv 5  between the three slots.  
     74. Referring also to FIG. 18, the outputs of the primary multiplexors  220 ,  230 , and  240  are modulated into three separate carrier signals  171 ,  173 , and  175 . In FIG. 18, two areas of unusable (or already used) bandwidth  300  and  302  are shown. As a result, carrier signal  171  has been tuned to have a center frequency f 1  (element  191 ) and a bandwidth bw 1  (element  192 ) so that signal  171  fits on the transmission spectrum before signal portion  300 . Carrier signal  173  has been tuned to have a center frequency f 2  (element  193 ) and a bandwidth bw 2  (element  194 ) so that signal  173  fits on the transmission spectrum between signals  300  and  302 . Carrier signal  175  has been tuned to have a center frequency f 3  (element  195 ) and a bandwidth bw 3  (element  196 ) so that signal  175  fits on the transmission spectrum after signal  302 .  
     75. By tuning each carrier frequency used by the MCMC system to fit within the available transmission bandwidth on the frequency spectrum, usage of the spectrum is maximized. The Carrier signals  171 ,  173 , and  175  are then demodulated by their respective demodulators  226 ,  236 , and  246 . The demodulated base band signals are then fed into their respective primary demultiplexors  228 ,  238 , and  248 . As described above, the service bits on the output slots  250  through  261  are multiplexed by secondary multiplexors  229 ,  239 , and  249  to reconstruct the bitstreams for services  1  through  5  (Sv 1  through Sv 5 — 180 ,  182 ,  184 ,  186 , and  188 ).  
     76. The preferred embodiment also utilizes one complete service—exemplified here as service 1 —for a variety of administrative or “housekeeping” tasks. The number of slots allocated for this administrative service could vary depending upon the needs of the particular MCMC system in question. The bits in this service might be used, among other things, to perform the following functions: downloading (or uploading) software to (or from) a particular customer as needed; alphanumeric identification of services or carriers within the MCMC system or community; turning on or off various services within the MCMC system as required; and/or providing a revision number for the slot allocation table as contained in zeroth slot data.  
     77. As for transferring software, the MCMC network host might provide its service subscribers with periodic upgrades of software used to interact with the MCMC system. By allocating separate bits for this task, the service subscribers would be minimally affected by such upgrades. This would promote continual development of related software by the host and would likely result in more optimal system performance and bandwidth savings.  
     78. Similarly, the service 1  data might provide alphanumeric names for the various services within the MCMC network. Often this is much more useful to a user or service subscriber than a service number or other minimal identification means.  
     79. Occasionally, entire services might need to be turned on or off for maintenance and/or billing purposes. The service 1  data might provide such individualized control over the various services within the MCMC network.  
     80. As for the slot allocation table revision number, the zeroth slot—with its slot allocation table—will always be found in the same place on any particular demodulated and demultiplexed carrier signal, thereby acting as a “beacon” for the user to learn about that particular carrier signal. However, the remaining slots which comprise the various MCMC services can be dynamically altered and reallocated as the needs of the many users change. As a result, the slot allocation table will be revised and carry with it a new revision number. As indicated above, the administrative service (e.g. service 1 ) will show the most recent revision number. If a user is operating with an outdated version of the slot allocation table, the zeroth slot can be decoded to provide updated slot allocation information on an as needed basis.  
     81. As detailed above, the zeroth slots (input slots  190 ,  194 ,  198  and output slots  250 ,  254 ,  258 ) are used for slot allocation data information which will allow the user to locate, demodulate and reconstruct the various services within each particular carrier. As combined with the Service 1  data, a full “map” of the MCMC system can be quickly derived by the user. In operation, the disclosed device will internally switch back and forth between slot zero and Service 1  data as needed and carry the data on am In-Band carrier channel (See FIGS. 21 and 22) for processing.  
     82. For instance, upon startup of the system, a designated carrier is acquired and the slot zero data is processed via the In-Band Carrier channel. Once the Slot Allocation Table for the carrier is acquired, the system automatically switches over to process Service 1  data. Service 1  data can provide a system-wide “map” of the MCMC system, and/or it can provide the other aforementioned Service 1  functions. However, if the revision number of the slot allocation table changes, the system will automatically switch back to read slot zero data until a new and updated slot allocation table is acquired. As a result, Service 1  is the “steady state” condition for the data on the In-Band Carrier Channel. Only when a new carrier is acquired or when the slot allocation table changes does the In-Band Carrier Channel carry slot zero again data for processing.  
     83. Referring to FIG. 20, an example table is shown with the type of slot zero data and/or Service 1  data necessary to locate and reconstruct all service data on all the MCMC carrier signals for this particular system. The zeroth slot will carry the slot allocation data for each particular carrier. The Service 1  data will provide such system-wide data as the center carrier frequencies and the carrier bandwidths for all carriers in the MCMC system. By internally switching, as necessary, between these two data sources, a complete set of system-wide information (as shown in FIG. 20) can be collected and maintained more efficiently than placing all such data on only one data path. By providing this full “map” to the system, any service can be dynamically allocated and reallocated without affecting a users ability to find all of the services within a particular MCMC transmission system.  
     84. Accordingly, the MCMC transmission system of the present invention provides an efficient and versatile way to transmit data across available bandwidth on the transmission spectrum. The present invention utilizes the benefits of multiplexing multiple channels of information before modulating and transmitting the information as a carrier signal. Additionally, the present invention allows for users of all sizes to utilize only the particular amount of data transfer capability that they need. Hence, individual services can range in size from the basic rate of one slot (e.g. 8 KBS) on up to the entire capability of the entire MCMC transmission system. Moreover, the present MCMC system utilizes multiple carrier signals to transmit the allocated data services. A slot of header data is reserved in each carrier signal which provides the location of all services within that carrier. A separate service (e.g. one or many slots) might also be allocated for system administration and/or system-wide mapping.  
     85. Referring now to FIG. 21, a block diagram of the multiplexor configuration is shown as used in the preferred embodiment of the disclosed MCMC system. A microprocessor  300  is used to control the flow of the incoming service data. Accompanying hardware to the microprocessor  300  includes a flash memory  318  for program storage, a ram  320  for storage of variables and processor operation, and NV memory  322  for parameter storage. While any microprocessor might adequately perform such control, the preferred embodiment uses a Motorola 68302 and was chosen because of its preferred instruction set, data handling capabilities, reasonable cost and development toolset available.  
     86. The microprocessor  300  writes information relating to the aforementioned slot allocation table into a dual port RAM  318 . As detailed above, the slot allocation table contains information regarding the various carrier center frequencies, the carrier bandwidths, and the slots used for each service (e.g. “format information”). Such format information might enter the microprocessor from a variety of sources. The preferred embodiment uses a separate computer system, known as a Network Management System (NMS)  316 , to solicit and manage this format information. The NMS  316  uses a Windows application program to query and accept format information from an operator. The format information is then fed into the microprocessor  300  via a serial RS232 data link  317 .  
     87. As shown in this embodiment, Ports A through XX (elements  301  through  306 ) represent input ports for individual services (henceforth service ports) which are composed of one or more data slots (e.g. 8 KBS slots as discussed above). Since each service port might consist of one or more data slots, each service port has its own clock rate based upon the number of data slots designated for that particular service on that particular service port. For instance, a service port using five 8 KBS slots would have a higher clock rate (e.g. 40 kilohertz) than a service port using only one 8 KBS slot. As with other synchronous systems, this embodiment utilizes one clock cycle per bit. Such control data is maintained and transmitted via an In-Band Control Channel  324  which carries information gleaned from the zeroth slot and the administrative service (previously exemplified as Service 1 ).  
     88. The service ports  301 - 306  are queued into a multiplexor control device  308  via a series of FIFO (first in, first out) buffers  307 - 312 . The FIFO outputs enter the multiplexor control device  308  through a bus  313  in the order requested by the multiplexor control. The multiplexor request sequence is a function of the information format for the MCMC system. As mentioned above, such multiplexor control and processing is achieved through a programmable device such as an FPGA. The FIFO&#39;ed service port data is then multiplexed via multiplexor control  308  into an aggregate data stream  314  which is output to a modulator (not shown) for modulation and transmission to a respective receiver.  
     89. Referring now to FIG. 22, a block diagram of the receiver configuration is shown as used in the preferred embodiment of the disclosed MCMC system. In this configuration, a demodulator  350  converts the transmitted carrier signal (not shown) into an aggregate data stream  352  which enters a demultiplexor control block  354 . As with the multiplexor before, demultiplexor control is also achieved via an FPGA device.  
     90. The demodulator  350  is controlled via a microprocessor  356 . As with the multiplexor configuration, accompanying hardware to this separate microprocessor  356  includes a flash memory  358  for program storage, a ram  360  for storage of variables and processor operation, and NV memory  362  for parameter storage. Again, a Motorola 68302 was used for similar reasons and advantages as stated above.  
     91. The microprocessor  356  gleans format information data (e.g. slot zero and administrative Service 1  information) from an In-Band Control Channel  364  as fed from demultiplexor control  354 . Such format information is written into a Dual Port RAM  366  in the form of a Slot Allocation Table. The demultiplexor control  354  then reads this Slot Allocation Table data from the Dual Port RAM  366  and uses this data in order to properly demultiplex the demodulated bitstream  352  into the various services. Once properly demultiplexed, the services are output as the various service Ports A-F (elements  368 - 373 ). As comparable to the multiplexor configuration, each service port might consist of one or more data slots, with each service port having its own clock rate based upon the number of data slots designated for that particular service on that particular service port. Having now been received and decoded, the MCMC services of this particular system can now accessed via the service ports  368 - 373 .  
     92.FIG. 24 illustrates an alternative embodiment of the present invention. In the embodiment of FIG. 24, a system  500  is provided for digitally encoding and transmitting multiple audio and video signals related to one another. The system  500  includes a plurality of encoders  502 - 508  which receive corresponding input signals along lines  510 - 516 . The input signals at lines  510 - 516  may be analog or digital. If the input signals represent digital signals, the encoders  502 - 580  may include A/D converters to provide digital input signals. The input signals at lines  510 - 516  may represent any combination of audio and video signals.  
     93. By way of example, the input signal at line  510  may represent a video signal, while the remaining input signals at lines  512 - 516  represent audio signals. Optionally, the audio signals at lines  512 - 516  may relate to the video signal at line  510 . For instance, each of lines  512 - 516  may carry the speech portion of a television show, sports event and the like in separate languages. Hence, line  510  may carry the video signal for a movie, while line  512  carries the audio signal for the movie in English, line  514  carries the audio signal for the movie in French and line  516  carries the audio signal for the movie in German.  
     94. Optionally, the input lines  510 - 516  may carry any desired combination of audio and video signals, such as one audio signal with three video signals, one video signal with four audio signals, two video signals with six audio signals and the like.  
     95. For purposes of explanation, the alternative embodiment contemplates using a single video signal at line  510  with multiple related audio signals at lines  512 - 516  carrying audio signals of different languages.  
     96. The encoders  502 - 508  output encoded audio and video signals along lines  518 - 524  as packetized bit streams which are formatted, as explained above. The individual streams of packetized data are supplied to a multiplexor  526  which combines the input signals to form an aggregate bitstream output along line  532 . The multiplexor  526  combines the data packets from lines  518 - 524  in a time division multiplexed manner to form the aggregate bit stream  550  (FIG. 27). The aggregate bitstream is supplied to a modulator  528  which outputs same via link  530 . Optionally, the encoders, multiplexor and modulator may include internal memory and buffers to temporarily store data. Data is transmitted to and read from this temporary storage in a first-in-first-out manner.  
     97. Control lines  534 - 542  are provided as feedback to control the transmission rate at which packets of data are transmitted from the encoders  502 - 508  to the multiplexor  526  and from the multiplexor  526  to the modulator  528 . Optionally, the transmission rates and timing of the encoders, multiplexor and modulator may be controlled from a remote processor (not shown).  
     98. Next, the discussion turns to FIG. 27 which illustrates an exemplary aggregate bitstream  550  generated by the multiplexor  526  based on a time division multiplexing technique. The aggregate bitstream  550  includes a plurality of data sets  555 , each of which includes a single slot or channel  554  assigned to each encoder  502 - 508 .  
     99. During operation, the multiplexor  526  accesses the multiplexer&#39;s internal memory/buffers for each of lines  518 - 524  to obtain a set of data packets containing a single data packet associated with each input line  518 - 524 . The multiplexor  526  combines this set of data packets as illustrated in FIG. 27 in a time division multiplexed manner. Consecutive slots  554  receive a corresponding data packet from the assigned input line  518 - 524 . Thus, each slot  554  of a data set  555  includes a single data packet  556 - 562  for each encoder  502 - 508 . Optionally, each of packets  556 - 562  includes a presentation time stamp  564 - 570 . The presentation time stamps  564 - 570  represent offsets with respect to internal reference timers of corresponding encoders  502 - 508  as explained.  
     100. Once the data set  555  is formed in the multiplexor  526 , the set  556  is transmitted to the modulator  528 . Thereafter, the multiplexor  526  generates a next data set  572  of packets  574 - 580 . This process may be continually repeated throughout operation.  
     101. While the preferred embodiment of FIG. 24 illustrates far encoders, it is understood that any number of encoders may be utilized. Each data set  555 ,  572  of data slots  554  will be modified to include one slot per encoder.  
     102.FIG. 28 generally illustrates a decoding system  600  according to the present invention. The decoding system  600  includes a demultiplexor  602  which receives the aggregate bitstream  604  as its input. The demultiplexor  602  separates each data set  555  (FIG. 27) of data packets  556 - 562 . The demultiplexor  602  and transmits a data packet from a single slot  554  in the set  555  along a corresponding output line  606  and  608 .  
     103. More specifically, decoder demultiplexor  602  includes one output port  610 - 616  for each slot  554  of an incoming data set  555 . For a given data set  555 , the demultiplexor  602  delivers the data packet from slot #1 to the first port (e.g.,  610 ), the data packet from slot #2 to the second port (e.g., port  612 ), and the like. The decoding system  600  may connect decoders  618  and  620  to predetermined output ports of the demultiplexor  602  through switches  609  and  611 . The connected output ports correspond to slots  554  in the aggregate bitstream which contain desired data.  
     104. In the example of FIG. 28, it is desirable to decode the data streams from the first and third encoders ( 502  and  506  in FIG. 24). Hence, decoders  618  and  620  are connected at switches  609  and  611  along lines  606  and  608  to output ports  610  and  614 , respectively.  
     105. With reference to FIG. 27, decoder  618  decodes all packets  556  within the first slot of each data set  555 . Decoder  620  decodes all packets  560  received within the third slot  553 . The decoders  618  and  620  may output analog signals corresponding to the decoded bitstreams along lines  622  and  624 , respectively. The analog signals are supplied to a display  626  which presents corresponding audio and video information to a viewer.  
     106. By way of example, when the aggregate bitstream  604  includes a single video signal (such as corresponding to a movie) and a plurality of audio signals (such as corresponding to the soundtrack for the movie recorded in multiple languages), decoder  618  may decode the video signal, while decoder  620  decodes an associated audio signal for a desired language (e.g., English, French, German and the like). Thus, the display  626  may play a movie with a French soundtrack. Alternatively, by connecting the decoder  620  to one of ports  612  and  616 , the display  626  may output the audio track in a different language.  
     107. According to the example explained above, the preferred embodiment of the present invention enables multiple audio signals to be transmitted in different languages with a single related video signal. Hence, the need is avoided for transmitting separate video signals for each audio signal.  
     108. While several alternative embodiments, of the invention have been described hereinabove, those of ordinary skill in the art will recognize that the embodiments may be modified and altered without departing from the central spirit and scope of the invention. Thus, the embodiments described hereinabove are to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than by the foregoing descriptions, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced herein.