Abstract:
A method, apparatus for uplinking data is disclosed. The apparatus comprises a plurality of receive antennae, independently directable to a plurality of ground stations, each disposed in one of a plurality of cells; a time domain concentrator, communicatively coupled to the plurality of receive antennae, the time domain concentrator for selectably directing each of the plurality of receive antennae to one or more of the plurality of cells, and for concatenating each of the uplink transmissions in a time domain; and a frequency domain concentrator, communicatively coupled to the time domain concentrator, for concatenating the uplink transmissions in a frequency domain.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional Patent Application No. 60/376,382, entitled “HYBRID TDM/FDM UPLINK FOR SPOT-BEAM COMMUNICATION SYSTEM,” by Keith Jarett, filed Apr. 29, 2002, which application is hereby incorporated by reference herein. 
     This application is related to the following co-pending and commonly assigned patent application(s), all of which applications are incorporated by reference herein: 
     U.S. Provisional Application Ser. No. 60/376,105, entitled “SECURE DATA CONTENT DELIVERY SYSTEM FOR MULTIMEDIA APPLICATIONS UTILIZING BANDWIDTH EFFICIENT MODULATION”, by Charles F. Stirling, Bernard M. Gudaitis, William G. Connelly, and Catherine C. Girardey, filed Apr. 29, 2002; and 
     U.S. Provisional Application Ser. No. 60/376,244, entitled “METHOD TO SECURELY DISTRIBUTE LARGE DIGITAL VIDEO/DATA FILES WITH OPTIMUM SECURITY,” by Ismael Rodriguez and James C. Campanella, filed Apr. 29, 2002; 
     U.S. Utility patent application Ser. No. 10/213,396, filed Aug. 6, 2002, by inventor Joseph S. Ng, entitled “BANDWIDTH-EFFICIENT AND SECURE METHOD TO COMBINE MULTIPLE LIVE EVENTS TO MULTIPLE EXHIBITORS,” (now abandoned) which itself claims the benefit of U.S. Provisional Patent Application Ser. No. 60/376,333, filed Apr. 29, 2002, by inventor Joseph S. Ng, entitled “BANDWIDTH EFFICIENT AND SECURE METHOD TO COMBINE MULTIPLE LIVE EVENTS TO MULTIPLE EXHIBITORS”; 
     U.S. Utility patent application Ser. No. 10/178,602, filed Jun. 24, 2002, by inventor Michael A. Enright, entitled “METHOD AND APPARATUS FOR DECOMPRESSING AND MULTIPLEXING MULTIPLE VIDEO STREAMS IN REAL-TIME”, (now abandoned) which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/376,254, filed Apr. 29, 2002, by inventor Michael A. Enright, entitled “METHOD TO DECOMPRESS AND MULTIPLEX MULTIPLE VIDEO STREAMS IN REAL-TIME”; 
     U.S. Provisional Patent Application Ser. No. 60/376,087, filed Apr. 29, 2002, by inventor Mary A. Spio, entitled “METHODOLOGY FOR DISPLAY AND DISTRIBUTION OF LIVE CINEMA GRADE CONTENT IN REAL TIME”; 
     U.S. Utility patent application Ser. No. 10/360,019, filed Feb. 7, 2003, by inventors Joseph S. Ng and Robyn M. Akers, entitled “COMBINING MULTIPLE SIMULTANEOUS SOURCE CINEMA TO MULTIPLE EXHIBITOR RECEIVERS”, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/376,240, filed Apr. 29, 2002, by inventors Joseph S. Ng and Robyn M. Akers, entitled “COMBINING MULTIPLE SIMULTANEOUS SOURCE CINEMA TO MULTIPLE EXHIBITOR RECEIVERS”; 
     U.S. Utility patent application Ser. No. 10/172,214, entitled “COMPACT HIGH-POWER BEAM HOPPING SWITCH NETWORK” by Keith Jarett and Andrew H. Kwon, filed Jun. 13, 2002, which application is hereby incorporated by reference herein 
     U.S. Provisional Patent Application Ser. No. 60/376,243, filed Apr. 29, 2002, by inventors Bernard Mark Gudaitis and William G. Connelly, entitled “ARCHITECTURE CONTAINING EMBEDDED COMPRESSION AND ENCRYPTION ALGORITHMS WITHIN THE DATA FILE.” 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to systems and methods for communicating data, and in particular to a system and method for uplinking data using a hybrid multiplexing scheme. 
     2. Description of the Related Art 
     Modern satellites often employ a large number of narrow spot beams, often in a beam laydown that forms a cellular coverage of a wide geographic area. In addition to providing better performance, the narrow beams allow spatial re-use of the same frequency or time slot, so that the total throughput bandwidth of the satellite can be several times the allocated frequency band. Because the traffic demand is not equal for all the cells, it would be wasteful to allocate the same amount of bandwidth to each cell. Therefore, satellite systems typically use either Time Division Multiplexing (TDM) or frequency division multiplexing (FDM). 
     In TDM, each cell is allocated a slice of a “frame” of time, with the allocation repeating once per frame. The TDM approach is best illustrated by the large-terminal TDMA trunking systems such as those operated by INTELSAT. But these systems use regional beams or isolated spot beams, and these beams have much smaller traffic ratios than 100 to 1. 
     In FDM, each cell is allocated a slice of the total bandwidth. In either TDM or FDM, the allocation is intended to match the communication needs (throughput, etc.) of the traffic in that cell. 
     The FDM approach can be illustrated by the BEAMLINK system available from COMDEV. The system includes a static switch that directs each incoming cell to one or more of a bank of surface acoustic wave (SAW) filters. Each SAW filter passes a specific band of frequencies. SAW filters are grouped into banks, each of which in aggregate covers the full operating band. Within each bank, the outputs of the SAW filters are combined to obtain a composite signal that spans the full operating band. This signal can then be fed to a digital processor or transmitted to a large Gateway Earth station for demodulation of the individual signals. 
     The SPACEWAY system provides another illustration of the FDM approach to uplink capacity allocation. The SPACEWAY satellite has a static switch that directs each uplink cell to one or more A/D converters. Each A/D converter accepts a slice of frequencies. For SPACEWAY, the analog-to-digital (A/D) converter output is demodulated and processed on-board the satellite. 
     In a satellite or stratospheric platform system that covers a wide geographic area with a laydown of overlapping cells, the average traffic in each cell is roughly proportional to the user population within that cell. Cells which cover remote, unpopulated areas generally have far less traffic than cells that cover urban areas. The ratio between highest and lowest traffic cells can exceed 100 to 1. Handling rural cells requires A/D conversion of largely empty uplink bands. Further, because very narrow filters are difficult to implement, satellite systems using FDM have difficulty matching their allocations to such disparate requirements. In contrast, TDM systems can easily allocate very small fractions of time to those (typically rural) cells with light traffic. 
     This is not a problem for transmissions from the satellite to the ground (downlink transmissions), since the satellite can allocate power among all the cells it is serving, and can use its transmission power for other cells during the rest of the TDM frame. However, the ground station transmitter must be sized according to the instantaneous, or burst, data rate, even though this capability is used only a small fraction of the time. For example, the ground system might require a 100-watt transmitter operating during the 1% of the time that the satellite is “looking at” the cell. If the satellite were “looking at” the rural cell 100% of the time, a 1-watt transmitter could do the same job at much lower cost. However, while the satellite is “looking at” this cell and receiving the low power, lower data rate signal, the satellite cannot use the same assets to receive higher data rate signals from higher power transmitters in other cells. Hence, “looking at” or dwelling on cells with few ground stations transmitting low power signals for extended period of time results in a substantial waste in satellite communication throughput capacity. 
     Neither BEAMLINK nor the SPACEWAY systems are capable of efficiently handling anything approaching a 100 to 1 ratio of traffic between urban and rural cells. These systems can at best accommodate ratios up to 10 to 1 before they begin wasting capacity on rural cells. 
     What is needed is a system and method to reduce ground terminal transmitter power requirements, while efficiently utilizing the satellite resource. The present invention satisfies that need. 
     SUMMARY OF THE INVENTION 
     To address the requirements described above, the present invention discloses a method and apparatus for uplinking data. The method comprises the steps of: selecting a communications channel bandwidth and a communications channel dwell time for receiving the data from a first plurality of ground stations disposed in a first cell; directing one or more of a plurality of receive antennae to the first cell and dwelling the one or more of the plurality of receive antennae on the first cell for the selected dwell time, to receive a first uplink transmission comprising the data from at least one ground station of the first plurality of ground stations disposed in the first cell; and bandfiltering the first uplink transmission by the selected communications channel bandwidth. 
     The apparatus comprises a plurality of receive antennae, independently directable to a plurality of ground stations, each disposed in one of a plurality of cells; a time domain concentrator, communicatively coupled to the plurality of receive antennae, the time domain concentrator for selectably directing each of the plurality of receive antennae to one or more of the plurality of cells, and for concatenating each of the uplink transmissions in a time domain; and a frequency domain concentrator, communicatively coupled to the time domain concentrator, for concatenating the uplink transmissions in a frequency domain. 
     The present invention reduces ground terminal transmitter power requirements by using a satellite uplink payload configuration that blends FDM and TDM techniques. Urban beams are assigned both wider time slices and wider frequency bands than rural beams. The present invention allows frequency bandwidth allocated two urban cells to be 10 or more times that of the rural cells, while also allowing the time allocated to urban cells to be 10 or more times that of the rural. This allows the satellite to serve cells which differ in traffic capacity by a factor of 100 or more, which is not practical for either pure FDM or pure TDM systems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now to the drawings in which like reference numbers represent corresponding parts throughout: 
         FIG. 1  is a diagram showing an exemplary embodiment of the communication architecture; 
         FIGS. 2A-2C  are flow chart presenting exemplary process steps that can be used to practice one embodiment of the present invention; and 
         FIG. 3  is a diagram showing one embodiment of the time domain concentrator. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     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. 
       FIG. 1  is a diagram showing an exemplary embodiment of the communication system  100  architecture. The communication system  100  comprises an uplink segment  102  that includes a plurality of cells  104 A- 104 C (hereinafter alternatively referred to as cell(s)  104 ). Each cell  104  includes one or more ground stations  106 . The ground stations  106  uplink transmissions, which include uplink data, to a satellite  126 . 
     The satellite  126  receives the uplink transmissions, and transponds the received uplink transmissions to a second ground station  120 , such as a Gateway. The Gateway  120  is communicatively coupled to a backbone  118 , which provides the Gateway access to other information services, such as the Internet, local area network (LAN), wide area network (WAN). 
     The satellite  126  comprises a receive antenna array  108 , which includes a plurality of receive antennae  110 A- 110 C (hereinafter alternatively referred to as receive antennae  110 ). 
     The satellite  126  also comprises a time domain concentrator  112 . In one embodiment, the antenna array  108  provides one output from each uplink cell  104  to the time domain concentrator  112 . The time domain concentrator  112  combines the signals provided by each of the receive antennae  110  in the antenna array  108  by switching among the signals provided at the output of each receive antenna  110 . In one embodiment, the time domain concentrator  112  comprises a beam hopping switch network, which is further illustrated in  FIG. 3 , and described in the related text. 
     The foregoing switching operations, as well as many of the other operations performed in the following description can be performed by a communication processor  124  on board the satellite  126 . Or, these operations can be commanded and controlled from a ground control station and uplink to the satellite  126 . 
     Information regarding the selected communications channel beamwidth and a communications channel dwell time can be communicated to ground stations  106 , the satellite  126 , and any other entities requiring this information via an auxiliary channel. The information on the auxiliary channel can be transmitted at pre-selected time slots and frequencies, or time slots and frequencies that change as a function of time. The desired communications channel beamwidth and communications channel dwell time can be determined by balancing service capacity among all users, or by giving priority to certain users as required. 
     In an alternative embodiment, the beam hopping function is performed by a beam-forming uplink antenna. In this embodiment, the time domain concentrator  112 , under the direction and control of the communications processor  124 , provides one or more commands to each receive antenna  110 A- 110 C, to orient the boresight of the sensitive axis of the receive antenna at each of the cells  104  as desired. In doing so, the time domain concentrator  112  implement a beam-hopping or beam-agile network. 
     The time domain concentrator  112  provides the time-division multiplexed signals from the receive array  108  to a frequency domain concentrator  114 . The frequency domain concentrator  114  includes a filter bank  122 , which has a plurality of bandpass filters  128 A- 128 G. In one embodiment, the bandpass filters comprise one or more contiguous surface acoustic wave (SAW) filters of bandwidths that vary over a factor of approximately 10. Each of the bandpass filters  128 A- 128 G admits signals within its passband and rejects out-of-band signals as noise. 
     One or more of the time division multiplexed signals from the time domain concentrator  112  are provided to one or more of the filters  128 , thus frequency division multiplexing the time division multiplexed signals from the time domain concentrator. As shown in  FIG. 1 , the filters  128  of the filter bank  122  comprise filters  128  of differing bandwidths. For example, filter  128 A has a bandwidth greater than the bandwidth of filters  128 B- 128 H each succeeding filter has a bandwidth less than the filter preceding it. By using different combinations of filters  128 , a plurality of possible filter bandwidths can be implemented. The bandpass filters  128 B- 128 H can be implemented as analog filters, or as digital filters as the need requires. 
     Alternatively, the frequency domain concentrator  114  can comprise a digital channelizer. The digital channelizer comprises a plurality of analog-to-digital (A/D) converters, which convert the signals from the time domain concentrator  112  into digital form, and a processor to digitally excise empty frequency bands and concatenate occupied bands. 
     The frequency domain concentrator  114  also combines (for example, by concatention), the uplink transmissions provided by the time domain concentrator  112 . The resulting output is one or more groups of multiple carriers at close to 100% duty factor. This output is forwarded to a transmitter  116 , which transmits the information to the Gateway  120 , where the information is processed and routed to the appropriate destination. 
     In one embodiment, the information is demodulated on board the satellite  126  and demodulated before transmission to the Gateway  120 . Another embodiment, the information is transmitted directly to the Gateway  120  where it is demodulated. 
       FIGS. 2A-2C  are diagrams showing exemplary process steps that can be used to practice one embodiment of the present invention. 
     Referring first to  FIG. 2A , a communication channel beamwidth and a communication channel dwell time is selected, as shown in block  202 . The communication channel beamwidth and the communication channel dwell time are selected to receive an uplink transmissions comprising data from a first plurality of ground stations  106 A disposed in a first cell  104 A. In block  204 , one or more of the plurality of receive antenna  110  are directed to the first cell  104 A and dwelled in that position for the selected dwell time, thus allowing the uplink signal from the ground stations  106 A to be received. In block  206 , the uplink transmissions from the cells  106 A are bandfiltered to the selected communications channel bandwidth by the frequency domain concentrator  114 . In one embodiment, the processes performed in block  206  are performed by providing the uplink transmissions to one or more of the filters  122 A- 122 H of the filter bank  122 , wherein the filter(s)  122 A- 122 H are selected to implement the selected communications channel bandwidth. 
     Referring now to  FIG. 2B , blocks  210  through  214  illustrate analogous steps to those shown in blocks  204  through  206  above. However, blocks  210  through  214  show exemplary operations in receiving a second uplink transmission from a second plurality ground stations  106 B in a second cell  104 B. In block  210 , a second communications channel beamwidth and dwell time is selected. In block  212  one or more of the plurality of receive antennae  110  are directed to the second cell  104 D for the selected dwell time to receive the second uplink signal. Finally, in block  214 , the second uplink transmission is bandfiltered by the selected communications channel second bandwidth. 
     Typically, the operations shown in blocks  202  through  206  in blocks  210  through  214  occur concurrently, allowing signals to be received from several of the cells  104  to be received at the same time. 
     Referring now to  FIG. 2C , the bandfiltered uplink transmission(s) are combined together, or concatenated, as shown in block  218 . In block  220 , the concatenated and filtered uplink transmission(s) are forwarded to a second ground stations such as the Gateway  120 . 
       FIG. 3  is a diagram showing one embodiment of the time domain concentrator  114  or uplink beam hopping switch network. In this illustrative example, the array of receive antennae  110  can receive  192  distinct beams. Each beam is split by an array of first fan-out splitters  304 , producing, in this example 384 signals. These 384 signals are provided to 96 4:1 fan-in combiners  308 , those producing 96 signals. 
     The output of the fan-in combiners  308  is provided to an array of second fan-out splitters  310 , thus producing 192 signals  312 . These 192 signals  312  are provided to an array of 4:1 fan-in combiners, thus providing 48 outputs. Next, the output of the second fan-in combiners  314  are provided to a plurality (12) of 4×4 crossbars  316 . The plurality of crossbar as  316  permit any of the crossbar  316  inputs to be provided to any of the crossbar  316  output. 
     By appropriate selection of the first fan-in combiners  308  and a second fan-in combiners  314 , the 198 beams  302  can be provided to the output of the switch network  114 , as deemed appropriate in order to implement time division multiplexing of the received uplink transmissions. 
     The beam-hopping switch network first splits each of the inputs into two, both to allow for failures in the first stage of switch junctions and to mitigate blocking. Blocking refers to the fact that setting of the switch junctions to route one signal may interfere with the desired routing of another signal. In the preferred embodiment, each cell belongs to two groups of 8. If the load is heavy in one of these two groups, the cell can be served through its membership in the other group. 
     It can be seen that the foregoing switch network architecture does not assure that such blocking can never occur. Instead, the foregoing architecture reduces the probability of such blocking to acceptable levels. 
     The ability to select anytime slot to receive uplink data can also be used to reduce blocking. If a given cell needs service at a 10% duty factor, that 10% can be placed anywhere within a cyclic TDM frame, and the data will still get through to a Gateway  120  (or equivalently, to a buffering on-board processor). 
     Finally, the beam hopping switch network  112  need not connect any given uplink cell  104  to a particular bandpass filter  128 . Rather, it needs only to connect a given uplink cell  104  to any of several filters in the frequency domain concentrator  114  that have the same bandwidth and center frequency. This relaxed requirement allows a smaller network to do the job of a much larger matrix switch. 
     Group memberships are arranged orthogonally and pseudo-randomly. This has the benefit of minimizing the extent to which a heavy traffic load in a particular group “folds back” into the original group. For example, if the group memberships were arranged in rows and columns, sets of 64 cells would be isolated membership-wise from the other cells. If one group of 64 cells had a high traffic load and the other groups had lower loads, the switch network would not be able to help balance them by sharing loads. In the preferred embodiment, each cell is connected to each other cell through a maximum of 3 steps through group members. (i.e., given W and Z∃X and Y such that cell W is a co-member with cell X, which is a co-member with cell Y, which is a co-member with cell Z.) This “connectedness” of the groupings allows heavy loads to be separated and groups of cells that have similar loads to be gathered together. 
     An exemplary switch network  114  is disclosed in application Ser. No. 10/172,214, entitled “COMPACT HIGH-POWERBEAM HOPPING SWITCH NETWORK” by Keith Jarett and Andrew H. Kwon, filed Jun. 13, 2002, which application is hereby incorporated by reference herein. While the switch network of this related application is used for downlink beams rather than uplink beams as is the case in the instant invention, the same connectivity principles can be applied for application to an uplink antenna switch network. 
     The communication system  100  thus employs a combination of time division (beam hopping) and allocation of different bandwidths to each cell  104  in order to provide uplink capacities that can differ by large factors (up to roughly a factor of 100) from cell to cell. 
     CONCLUSION 
     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. 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.