System and satellite payload architecture for interactive data distribution services

[0002] This invention relates to satellite communications and more particularly to a satellite-based communications network and a satellite payload architecture for use in the extremely-high-frequency (EHF) bands.

[0003] In the emerging EHF bands of 20-60 GHz for use in satellite communications, use of traditional bent-pipe repeaters and single-uplink/downlink beams is no longer a viable architecture for systems that need to support the emerging information distribution and interactive broadcasting services targeted to mass markets. For widespread appeal, such systems must allow easy and low-cost access to the satellites by all information content providers, scattered throughout the coverage area, on a bandwidth-on-demand, as-needed basis.

[0004] With traditional payload designs, a satellite with a single uplink beam over a relatively large service area has a much lower gain/temperature figure of merit than that of a spot-beam design. For example, a single beam covering the 48 contiguous U.S. states has an edge-of-coverage gain/temperature value of about 0 dB/K. The same area can easily be covered by 100 0.5-degree spot beams each with an edge-of-beam gain/temperature of about 17 dB/K. This means that for uplinking the same information rate to the satellite one requires approximately 17 dB (a factor of 50 times) more radiated power with the single-beam design than with spot-beam designs. Provision of this additional amount of radiated power in the 20-60 GHz frequency bands, coupled with the much higher link margins needed for rain attenuation compared to those required for the lower frequency bands, makes the cost of uplinking too expensive, and operationally not desirable, to many would-be service providers.

[0005] A further requirement is the need to downlink wide-band, high-data-rate time-division-multiplexed (TDM) carriers. This allows for use of lowest-cost receive terminals, as well as, dynamic multiplexing of data packets from multiple services at the highest transmission efficiencies. To achieve these benefits with conventional bent-pipe satellite payloads, one has to back-haul the service/program contents from hundreds or thousands of distribution sites to a few designated central uplink sites. This is operationally inconvenient and expensive, and it is not conducive to the development of low-cost information distribution and broadcasting service markets.

[0006] The present invention overcomes the drawbacks of prior art systems through the provision of a new system and satellite payload architecture in support of the emerging interactive information distribution and broadcasting services in the new extremely-high-frequency bands (20-60 GHz). The system allows multiple service-program providers to access the system on a bandwidth-on-demand and on an as-needed basis. Furthermore, the service-program providers can directly transmit to the satellite from their premises through small, low-power, low-cost terminals, to provide a plurality of one-way and interactive information distribution services, including video, to small low-cost user/subscriber terminals on a controlled basis.

[0007] The present invention has many advantages over bent-pipe or back-hauled payload designs. The present invention includes such features as: (1) low-cost, individual or “personal” broadcasting terminals, (2) concurrent access to multiple program.(information) channels by a single end-user terminal, (3) return transmission capability for interactive applications, (4) direct transmissions to the satellite by all service-program providers on a bandwidth-on-demand and as-needed basis, (5) elimination of terrestrial backhaul transmission and very expensive uplink facilities at centralized hubs, (6) maximizing satellite transmission efficiency and system throughput, (7) providing maximum flexibility in allocation of uplink access capacity to all parts of the service area, and (8) support of single-hop mesh connectivity for special supplementary services among user terminals.

[0008] The new payload employs high-gain spot beams for low-cost uplinking, on-board signal regeneration and processing for transmission efficiency and multiplexing, and full-area broadcast downlink beams essential for wide-area coverage. User/subscriber terminals equipped with transmit capability can directly interact with the service-program providers in support of the emerging interactive Internet and multimedia applications and services. Multiplexing of large amounts of information onto wide-band downlink broadcast TDM carriers enables receive terminals to have concurrent access to multiple information service programs or channels.

[0009] Use of on-board data regeneration, processing and multiplexing allows every service-content provider to transmit at its own individual data-rate needs, which usually is much lower than the required TDM rates used for downlinking. The multiplexing function of the payload groups the received information data-packets into one or more TDM streams. The TDM streams are transmitted via a single broadcast beam to achieve optimum networking features, service delivery, and bandwidth utilization efficiency. Use of on-board signal processing further provides for maximum flexibility in access to the broadcast capacity from any location in the service area, thus achieving a substantial improvement in system utilization over the bent-pipe payloads. Use of high-gain uplink spot beams also provides for low-cost return transmissions by the small user terminals throughout the satellite coverage area. Such return transmission capability allows the system to support all types of emerging interactive multimedia and broadcasting services that otherwise would require the use of separate terrestrial return communication channels.

[0010] While the proposed system can be implemented with many different transmission technologies, one embodiment, particularly suited for downlink transmissions, is to make the system.as compatible with the emerging MPEG-DVB broadcast standards as possible. This is due to the fact that the MPEG-DVB standards are being adopted worldwide by most of the current generation of direct broadcast satellite systems for video and data distribution services.

[0011] Conventional ground-based systems employ the MPEG-2 standard for source encoding and multiplexing, whereby constituent digitized/compressed components of each program or service, such as video, audio and any associated data, are either combined into individual program transport streams or multiplexed with components of several other programs into one composite high-rate TDM transport stream, one per satellite transponder, for final distribution to subscriber terminals. As part of the transport-multiplexing stage, additional program specific information is also added to the transport stream in order for the subscriber terminals to properly access each transport stream and recover the authorized program-data streams. These systems, however, use traditional bent-pipe satellites which require the service-programs to be backhauled to a few ground-based uplink sites for MPEG-DVB processing and multiplexing. The proposed compatibility with MPEG-DVB broadcast standards under this invention should reduce the overall system development cost and result in a much lower cost for the end-user subscriber terminals.

[0012] In addition to its general use as an interactive information distribution network, the proposed system architecture can easily be adapted and employed for local-TV program distribution. In such an embodiment, each broadcaster can uplink its programming directly from its premises, through a low-cost terminal, instead of back-hauling the information to a centralized broadcast center as in present systems. When used for such services, because of the local nature of distribution, the satellite payload can be equipped with multiple “local” or “regional” downlink beams for maximum power efficiencies.

[0013] The disclosed system architecture also supports direct single-hop connections among low-cost subscriber terminals for low-volume point-to-point communications in support of supplementary services associated with the primary services.

[0014] Other advantages of the invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.

[0015] For a more complete understanding of the invention, reference should be made to the embodiments illustrated in greater detail in the accompanying drawings described below by way of example of the invention:

[0016] FIG. 1 is a block diagram of the overall satellite communication system according to the present invention;

[0017] FIG. 2 is a block diagram of the system function architecture and communication pathways of a satellite system according to the present invention;

[0018] FIG. 3 is a functional architecture and block diagram of the payload and the on-board digital regenerative signal processor of a satellite system of the present invention;

[0019] FIG. 4 is a functional, block diagram of a broadcast satellite terminal of a satellite system of the present invention;

[0020] FIG. 5 is a functional block diagram of an end-user satellite terminal of a satellite system of the present invention; and

[0021] FIG. 6 is an exploded view of the frequency and channelization plan of a satellite system of the present system.

[0022] FIG. 1 illustrates the general make-up and configuration of an interactive broadcast satellite system in accordance with the present invention. The major system elements are: the satellite 10; the satellite operations center (SOC) 50; the satellite access and broadcast control center (SABCC) 40; a plurality of broadcast satellite terminals (BST) 20 and a plurality of end-user satellite terminals (EST) 30. The payload architecture fo satellite 10, including processor 60 will be discussed in greater detail later with reference FIG. 3.

[0023] SOC 50 communicates with the satellite 10 for the traditional on-orbit station keeping and satellite telemetry, tracking and control (TT&C) functions.

[0024] Every service or program distribution center is equipped with one BST 20 through which individual service-program providers feed their contribution programs to a common broadcast platform in the satellite 10. The satellite payload recovers and multiplexes all individual service-program transmissions into a number of wide-band broadcast data streams 70 for transmission to all terminals in the system. All functions related to (1) network access by service-content distribution centers, (2) reception of and access to individual broadcast service-programs by authorized subscribers, and (3) control and management of system traffic-loading and operations are performed by SABCC 40.

[0025] FIG. 2 illustrates the architecture and functional block diagram of the present system, detailing the logical relationships and interfaces among the various elements. Every service-program distribution center is equipped with a small broadcast terminal (BST) 20 installed directly on its premises.

[0026] Program or application content-data residing on server system 80 at the distribution center is delivered to the BST 20, which, after appropriate formatting, uplinks them to satellite 10 under the control of SABCC 40. All such transmissions 72 are recovered by the satellite payload 10 and, after proper processing, the received individual service-program data streams are multiplexed into one of several downlink broadcast streams or channels 70. As part of the multiplexing process, all necessary program-specific information received from SABCC 40 is inserted into each downlink broadcast stream 70. These data carry information about configuration of the network in general, and specific information about how an end-user satellite terminal (EST) 30 may recover every service-program being broadcast. Control-data related to implementation of a conditional-access scheme to authorize access to each broadcast service-program is also included. End-user satellite terminals (ESTs) 30 receive the downlink broadcast channels 70, and, based on the proper authorization, extract the data streams related to all of the service-programs or applications they have subscribed to. As part of their operations, and for network control and management functions, all service-program distribution centers 75 provide their service-specific information to SABCC 40.

[0027] In support of interactive broadcast services and network management and control functions, the system relies upon a two-way out-of-band signaling and communications (S&C) capability available to all system elements of interactive multi-media applications.

[0028] From a communications point of view, the S&C networking among all the system entities is implemented through the use of connection-less, packet-based Internet-Protocol (IP) networking technologies, with the satellite 10 providing the functions of a network switch/router connecting all system elements together. As such, every system element delivers its S&C IP packets to the payload S&C packet processor-router 67, which in turn forwards each packet to its final destination.

[0029] In the uplink direction, EST 30 and BST 20 terminals are equipped with a low-cost CDMA transmit function to uplink their S&C IP packets over any of the pre-designated S&C channels 71. As shown in FIG. 3, these packets are recovered by dedicated S&C demodulators 65 in the payload and given to the S&C packet processor-router 67. Because of its relatively high volume of S&C traffic, SABCC 40 utilizes a dedicated transmission channel 73 to the satellite and the S-x/SCPC Demodulator 66.

[0030] In the other direction of traffic flow, the S&C packets are downlinked from the satellite in two ways. All S&C IP packets addressed to ESTs 30 and BSTs 20 are multiplexed onto the downlink broadcast channels 70, along with the primary service-program contents. Through this technique, 20 ESTs 30 can use the same single receiver, for the lowest cost, to extract the S&C packets. Again, because of the relatively high volume of traffic to SABCC 40, and the BSTs 20, a dedicated logical-channel on one of the downlink broadcast carriers 70 is used for sending the S&C packets that are addressed to them.

[0031] Known transmission technologies are employed by BSTs 20 and ESTs 30 for their uplink transmissions to the satellite. For uplink broadcast transmissions by BST terminals 20, frequency-division-multiple-access with single-channel-per-carrier (FDMA/SCPC) is used as a preferred technique to achieve optimum bandwidth efficiency and satellite payload implementation. For S&C transmissions by ESTs, because of the strong desire to keep their costs as low as possible, and the fact that such terminals need only transmit relatively short S&C messages, use of code-division-multiple-access (CDMA) is the preferred technique. In addition to being a simpler and more efficient random-access technique, CDMA flexibly supports simultaneous transmissions by different EST 30 terminals at different rates, all within a chosen operating range.

[0032] FIG. 3 illustrates the satellite 10 payload architecture of an interactive broadcast satellite system according to the present invention. In the uplink direction, the total target service area is covered by a relatively large (n) number of foot-prints or spots 74. Each spot 74 is served by one high-gain communication spot-beam 11 per frequency-polarization, for a total of 2n spot beams per satellite. In the downlink direction, two broadcast beams 12, one per frequency-polarization, provide downlink coverage to the same total service area 75. The high-gain uplink spot beams 11 are needed to support small low-power, low-cost broadcast earth station terminals (BSTs) 20 as explained earlier.

[0033] The satellite payload principally comprises: (1) a receive spot-beam antenna and RF-electronics subsystem 13 for with 2n spot-beams and 2n receive strings; (2) one uplink-frequency-subband filter-switch-matrix (UFSM) 15 with 2n input ports, each handling one spot-beam receive intermediate-frequency (Rx-IF) signal 14; (3) one digital regenerative signal processor (DRSP) 60, with 2n S-type input ports 16 (labeled S-1, . . . S-2n), m B-type input ports 17 (labeled B-1, . . . B-m) and one S-x-type input port 18 (labeled S-x); and (4) a transmit RF-electronics and antenna subsystem 19 for downlink broadcast transmissions.

[0034] In every spot or foot-print 74, every broadcast terminal (BST) 20 directly transmits its service-program data-streams via certain FDMA/SCPC channels 72 in designated uplink frequency sub-bands to the satellite. After reception by a spot-beam receiver, UFSM 15 selects the active sub-bands from each received IF signal and passes them to one of m B-type input-ports 17 (for broadcast-traffic) of DRSP 60 for further processing. DRSP 60 demodulates the incoming carriers, recovers the individual service data-streams and multiplexes them into N downlink broadcast channels 70 (BC#I-N).

[0035] All transmissions by BST 20 and EST 30 terminals in support of interactivity-communications and network signaling/control functions (S&C) are made via special access CDMA channels 71 in each spot-beam 74. To provide total service-area coverage for S&C transmissions in the uplink direction, the UFSM 15 separates the sub-band allocated for such S&C traffic from each beam's IF signal and delivers them to the S-type input-ports 16 of DRSP 60. After recovery by CDMA demodulators 65, S&C packets are given to the S&C packet processor-router 67 for routing to appropriate destinations. These include the payload configuration control processor 69, the broadcast-channel control processor 68 and the multi-service MPEG-2 transport multiplexers 63. S&C packets from SABCC 40 are transmitted via dedicated channels 73, recovered by S-x/SCPC demodulator 66, and are given to S&C packet processor-router 67. All S&C traffic destined for ESTs and BSTs are multiplexed onto the downlink broadcast channels 70 along with the main service-program traffic. End-user satellite terminals (EST) 30 can receive any one of the broadcast channels 70 (BC #I to BC #N) and recover the service-program contents they are authorized for.

[0036] Other key subsystems of the DRSP 60 are: one stream-switch-matrix (SSM) 62, a plurality of muti-service MPEG-2 transport multiplexers 63, a plurality of DVB modulators 64, a payload-configuration-control-processor (PCCP) 69, and a broadcast-channel control-processor (BCCP) 68. SSM 62, under control of SABCC 40, connects the individual broadcast MPEG service streams received from the DVB demodulators 61 to the appropriate multi-service MPEG-2 transport multiplexers 63. The primary function of the PCCP 69 is the reception and execution of configuration commands, from SABCC 40, for UFSM 38 and the SSM 62. Function of BCCP 68 is the reception of service-program specific information generated by the broadcast-channel management center 42 of SABCC 40. The required specific information is defined by the MPEG-2 standard and includes program association, program map, conditional access, and network information tables. The BCCP 68 delivers this specific information to the appropriate multi-service. MPEG-2 transport multiplexer 63.

[0037] Satellite Access and Broadcast Control Center (SABCC) As described earlier, SABCC 40 is the system entity that manages and controls the overall functioning of the proposed system. The key functional areas of SABCC 40 are shown in FIG. 2 and include the following: a satellite access-control center (SACC) 42, a broadcast-channel management center (BCMC) 41, and an operations support system (OSS) 43.

[0038] SACC 42 is responsible for the usage and management of all of the uplink transmission channels transmitted by each broadcast satellite terminal (BST) 20. Each BST 20 contacts SACC 42 to receive an uplink channel assignment for a given duration. A. BST 20 sends a request message to SACC 42, over an S&C channel 71, for an uplink access for a certain bandwidth and duration. SACC 42, after authentication of the BST, assigns a FDMA/SCPC channel, from the pool of frequencies for the spot beam in which the BST 20 is located, to handle the requested transmission rate/bandwidth. After completion of its broadcast transmissions, the BST informs SACC 42 and stops its transmissions. SACC 42 returns the freed channel to its pool of frequencies for assignment to the next requester.

[0039] BCMC 41 is responsible for the control and management of all the functions called for and identified by the MPEG-2 transport protocols that will help the system users access and retrieve the program contents they subscribe to. These include: creation of the network information tables, the program association tables, the conditional access tables, etc. These information will be transmitted to the satellite broadcast-channel control processor 68 for final multiplexing and inclusion in the MPEG transport streams 70 by multiplexers 63. Most of these service-program specific information is collected from the service-program providers prior to their uplink transmission activities. EST 30 owners, after registering into the system, and who wish to receive any of the broadcast service-programs will make their selections from an electronic service-program guide in the same manner as that of the pay-per-view systems of the video broadcast industry.

[0040] Depending on the business model existing between the satellite system operator and each individual service-program provider, the identity of each subscriber/end-user, its geographic location, service privilege profile, and the I.D. of its EST need to be provided, by the responsible party, to BCMC 41 for incorporation into the appropriate functions. The contractual “service provider” also operates its own subscriber management system in terms of billing, marketing, etc. In this manner, the satellite system operator can act as either the service provider or the provider of distribution/transmission services to many independent primary service-content providers as best suitable for each.

[0041] OSS 43 is the collection of all functions required to operate and manage the overall system. As a minimum, these functions cover both the technical, administrative and customer care areas for the satellite operator. Distribution of EST 30 and BST 20 terminals, and their installation and commissioning into the system, are in general arranged by the satellite system operator.

[0042] With FIG. 2 as the reference diagram, FIG. 4 illustrates the functional architecture of a broadcast satellite terminal (BST) 20 for use in the proposed system. BST terminals 20 are colocated with server system 80 at the service-program distribution centers 75 for direct transmission of the service-program material to satellite 10. In addition, BSTs 20 are equipped with a transmit and receive capability, and, consequenlty are able to communicate with end-user terminals (EST 30) and the system access and broadcast control center (SABCC 40) for interactivity-communications and for signaling/control (S&C) functionalities. The major functional entities of a BST 20 are described below.

[0043] An inter-working-function and MPEG-2 service-program adaptation unit 22 accepts the primary service-program from the service-program server 80 at a distribution center, converts and formats the data into an MPEG-compatible service stream 22A, and delivers this stream to a DVB modulator unit 23. This interface unit 22 also provides the necessary inter-working functions for S&C related functions as well.

[0044] A DVB-modulator 23 formats the data stream received from unit 22 into DVB-packets and performs the basic channel coding and modulation selected for the uplink transmissions.

[0045] An S&C packet processor 26 handles the S&C IP packet transmission and reception functions. In the transmit direction this unit encapsulates the relevant S&C messages, received from the service-program server system 80, or from the terminal controller 28, into IP data packets. These IP packets are then passed to a CDMA modulator unit 24 for onward transmission to satellite 10.

[0046] A DVB-demodulator 25, in tandem with an MPEG-2 Transport-stream demultiplexer 27 receives and recovers the downlink S&C channel 73 carried over a pre-designated broadcast TDM channel. These S&C data packets are given to packet processor 27 for further processing. Availability of this DVB demodulator unit enables the BST 20 operators to receive and monitor their own transmissions.

[0047] An intermediate-frequency interface unit (IFL) 29, in conjunction with a two-way RF electronics and antenna unit 22, perform the other key functions of the BST 20. A terminal controller unit 28 performs the overall management and control of the various functions of BST 20.

[0048] With FIG. 2 as the reference diagram, FIG. 5 shows the functional architecture of an end-user satellite terminal (EST) 30 for use in the proposed system. ESTs 30 are located at the end-user sites for direct reception of the service-program material from the satellite 10. In addition, ESTs 30 are equipped with a reverse-channel transmit capability and, consequently are able to communicate with broadcast terminals (BST 20) and the system access and broadcast control center (SABCC 40) for interactivity-communications and signaling/control functionalities. The major functional entities of an EST 30 are described below.

[0049] In the receive direction from satellite 10, an RF electronics and antenna out-door unit 32 receives the satellite broadcast transmissions 70 and converts them to corresponding IF signals. The received IF signals are then passed over an inter-facility link (IFL) to an IFL interface unit 33.

[0050] A DVB TDM demodulator 34 recovers the broadcast MPEG-2 service transport stream from each of the received IF signals. An MPEG-2 transport stream demultiplexer 35 extracts the selected service-program stream, selected by the end-user, from the associated transport stream. This demultiplexer 35 also separates the incoming S&C data packets for delivery to the S&C packet processor unit 36.

[0051] An inter-working-function and MPEG-2 service-program adaptation unit 39 performs the final conversion and formatting of the selected service-program content for delivery to the end-user application system 90.

[0052] An S&C packet processor 36 receives and distributes the incoming S&C IP packets to their appropriate recipients. A terminal controller unit 38 performs the overall management and control of the various functions of the EST 30.

[0053] Implementation of the present system and payload architecture follows general system design and engineering principles applicable to all satellite communication systems. The architecture is such that specific details of system design and configuration can be customized to meet the overall business, services and operations requirements of different markets. As usual, the state of satellite and related communications technologies at the time of system implementation will influence the actual design details and configurations. Accordingly, the following implementations provide an embodiment of the present invention which is an exemplary satellite payload design representative of the first generation of bandwidth-on-demand, interactive broadcast satellite systems in the EHF frequency bands.

[0054] With FIG. 3 as the system reference diagram, FIG. 6 illustrates a baseline frequency and channelization plan for the present system. The total system service area is divided into n uplink foot-prints or spots. Every spot can be served by two uplink beams, one on each polarization, for a total of 2n beams. As shown in FIG. 6(a), in the uplink direction, the primary frequency spectrum (PFS) of each polarization is divided into a number of K, preferably equal, segments called uplink frequency sub-bands (UFS). The size of the UFS is generally dictated by the input port capacity of the satellite's on-board digital regenerative signal processor (DRSP) 60 and is chosen as a compromise between complexity-size considerations for the payload DRSP 60 and the UFS filter-switch-matrix (UFSM) 38 assemblies on one hand and the system bandwidth-utilization efficiency on the other.

[0055] As shown in FIG. 6(b), two types of UFS bands are defined. S-UFS band is used for uplink S&C transmissions. B-UFS bands are used for uplink broadcast transmissions. As mentioned earlier, as a preferred embodiment, CDMA and SCPC are chosen for uplink S&C and broadcast transmissions, respectively. As shown in FIG. 6(c), a single S-UFS band is assigned to all uplink spot beams for S&C transmissions. As shown in FIGS. 3 and 6(d), the receive IF signal (Rx1-IF, . . . Rx2n-IF) from each uplink spot-beam is connected to an input-port of UFSM 15. On the output side, UFSM 15 needs to have 2n ports, each supporting one S-UFS, and m ports each supporting one B-UFS subband. Thus, there is a one-to-one correspondence between the number of UFSM 15 output-ports and the number of DRSP 60 input-ports. For example, assuming a value of 500 MHz for the primary spectrum PFS, and 25 MHz for each uplink frequency subband, a total of 20 unique uplink frequency subbands are available for each polarization.

[0056] Referring again to FIG. 6(a), each uplink frequency sub-band (UFS), numbered 1 through K, can be assigned to any given uplink spot-beam according to a frequency-assignment plan chosen for the system. Employing a typical 4-beam per frequency-reuse cluster design easily achievable by most EHF satellite antenna systems, every UFS band can be reused in each polarization once in every beam-cluster for a total of n/2 per system. Assignment of UFS bands to spot beams is managed and controlled by the SABCC 40 in support of the total system traffic loading demands at any time. When required, each spot-beam can be assigned up to the maximum number of B-UFS bands as long as the frequency-reuse constraints and rules for all beams are observed. Each B-UFS band is also divided into a number of FDMA/SCPC carriers, each assigned by SABCC 40 to a broadcast terminal on a demand-assigned basis.

[0057] In the uplink direction a minimum of one S-UFS band is assigned to every spot beam. Because of the characteristics of CDMA, the same single S-UFS band can be reused in all beams. At the satellite, the UFSM 15 selects the S-UFS band from every spot beam receive IF signal (Rx-IF) and passes each to a corresponding DRSP 60 S-type input-port. (See FIGS. 6(d) and 6(e)).

[0058] To support service-program uplink transmissions, the available B-UFS bands are assigned to each spot beam on an as-needed basis depending on the activity of all broadcast terminals in each beam. This is done under the SABCC 40 control and subject to the system frequency-assignment rules and restrictions as described earlier.

[0059] As shown in FIG. 6(e), in the downlink direction, the primary frequency spectrum of the system will be divided into a number of broadcast channels (BC#I . . . BC #N) according to the system design requirements. Each broadcast channel carries a single TDM transport stream. To provide the maximum capacity per satellite, both frequency-polarizations are used for the downlink transmissions. As an example, 20 27-MHz broadcast channels can be supported in a 500-MHz portion of the spectrum of a given satellite system on each polarization, for a total of 32 TDM channels per satellite. The exact transmission capacity of each TDM channel depends on the selected parameters for the DVB modulators 64 and the downlink availability performance requirements.

[0060] Recovery of all data-packets transmitted to the satellite, both service and S&C related, and grouping of them into downlink broadcast TDM channels is performed by the combination of the payload uplink-frequency-subband filter switch matrix (UFSM) 15 and on-board digital regenerative signal processor (DRSP) 60. All service-program uplink transmissions are carried via SCPC channels. Preferably three rates, one each for low-medium-, and high-data rate applications, are employed. Peak rates of 0.5 Mbps and 10 Mbps are good candidates to meet the low-cost objectives for the BSTs. At such rates, every B-UFS band can accomodate several of these carriers in a mixed mode.

[0061] Since the system is a bandwidth-on-demand service network, it is expected that many uplink frequency subbands (UFS) assigned to uplink beams will not be filled with carriers at all times. Thus, it is desirable to ensure that the downlink broadcast capacity, which is the key revenue-bearing resource of the system, is not under-utilized because of partially-filled uplink B-UFSs.

[0062] To maximize downlink broadcast capacity, several factors must be considered. First, uplink spectrum bandwidth is assigned to each spot beam in multiples of whole-UFS bands. For CDMA transmissions in support lo of network signaling and interactivity-communication (S&C) functions, one primary UFS band is assigned to, and reused in, all spot beams. For broadcast transmissions, a whole UFS band should be allocated to a beam for the duration of a BST's transmissions, even if only one terminal in a spot beam is to be active. Further, the size and complexity of the on-board digital regenerative signal processor (DRSP) 60 is heavily influenced by the bandwidth and number of the input ports which it must support.

[0063] A UFS band connected to one input port of the DRSP 60 requires a certain amount of DRSP processing resources regardless of the number of carriers active in that UFS. Thus, if the aggregate amount of service-program data-packets recovered from all of the carriers processed by the input ports do not completely fill the available plurality of downlink broadcast TDM streams for which the DRSP is sized, then, the satellite and its broadcast throughput will not be fully utilized. Since the downlink frequency spectrum is the limiting factor in determination of maximum capacity of a system, the proper sizing of the UFS filter-switch-matrix (UFSM) 15 and the DRSP 60 ports, in terms of quantity and bandwidth, is a critical consideration.

[0064] Accordingly, the number and bandwidth of UFSM 15 output ports and DRSP 60 input ports should be chosen such that the payload can handle a much larger number of B-UFS bands than the number needed to fill the downlink broadcast capacity purely on a bandwidth basis. This provides flexibility in meeting the varying and unpredictable traffic loadings from various spot beams during the life of the system while maximizing the utilization of the system. Of course, the actual sizing of UFSM-DRSP combination must be determined with regard to these parameters in the context of specific system implementation.

[0065] The choice of the exact number of service-programs per TDM transport stream and the final modulation rate is made based upon the specific satellite downlink transmit channel characteristics and coverage beams for each implementation.

[0066] The choice of uplink and downlink transmission rates and channel coding details are made for each implementation on a case by case basis, and per business and quality-of-service performance requirements. Additionally, if compatibility with an existing video-DBS system is a requirement, then, the downlink TDM channels of the new system will have to be fully compatible with the target DBS air-interface specifications.

[0067] Benefits of an MPEG-DVB-compatible architecture for the proposed interactive data distribution and broadcasting satellite system, in accordance to this invention, are many. Compatibility with a worldwide standard used in millions of consumer terminals will preferably result in the lowest-cost implementation for the system and end-user/subscriber terminals, resulting in wide-acceptance of the services offered. Additionally, use of embedded and field-proven conditional-access systems, network and electronic program guides, and subscriber management systems, already developed for the existing ground-based, MPEG-DVB compatible, direct broadcast satellite systems, will substantially lower the implementation and operational costs such systems.

[0068] While this invention has been described in connection with one embodiment, it is understood that the invention is not limited to that particular embodiment. On the contrary, the invention includes all alternatives, modifications, and equivalents as may be included within the spirit and scope of the appended claims.