WO2000042718A1

WO2000042718A1 - Gateway-switched satellite communication system

Info

Publication number: WO2000042718A1
Application number: PCT/US2000/000037
Authority: WO
Inventors: Mark A. Thompson; William L. Snell
Original assignee: Spacecode Llc
Priority date: 1999-01-14
Filing date: 2000-01-03
Publication date: 2000-07-20
Also published as: AU2598000A

Abstract

A switched communication satellite system (10) includes a satellite that is in geosynchronous earth orbit and receives a communication signal uplink from a transmitting user station directed to one or more recipient stations. A terrestrial switched gateway receives the communication signal in a downlink from the satellite and includes a routing switch that routes the communication signal as a routed communication signal to the one or more recipient stations. A transmitter system uplinks the routed communication signal from the switched gateway to the satellite to be transmitted to the one or more recipient stations.

Description

Gateway-Switched Satellite Communication System

Technical Field The present invention relates to satellite communication systems and, in particular, to a satellite communication system employing switching at a terrestrial gateway to direct communications.

Background Summary of the Invention

Communication systems employ switching to direct communications between points. In satellite communication systems, the communications may be point-to-point, as in telephonic communications or some on-demand broadcast or internet applications, or point-to-multipoint, as in specialized broadcast applications. For both types of communication, satellite communication systems typically employ communication switches that are carried on-board satellites. A disadvantage of carrying communication switches on-board satellites is that communication switches are typically complex, heavy, and capacity limiting, thereby increasing the cost and launch size of satellites and establishing a fixed limit on their communication capacity.

Another aspect of satellite communications are the delays or latencies that can arise when a satellite in geosynchronous Earth orbit (GEO) are employed. Transmission to and from a GEO satellite causes a delay of at least 0.25 second. A communication transmission that includes two transmissions to a GEO satellite causes a delay of at least 0.5 second. For many communication applications, such as voice communication, such a delay or latency can be unacceptable for most users. To avoid such latencies, some current satellite communication systems, such as Iridium and GlobalStar, are utilizing large constellations of satellites in low Earth orbit (LEO) or medium Earth orbit (MEO) to benefit from reduced latency due to the relatively close proximity to the Earth. The cost and complexity of providing communication through such large numbers of satellites are staggering. Current switched satellite communication systems suffer, therefore, from several disadvantages. Satellites typically carry complex, heavy, and capacity limiting components, such as communication switches. In addition, constellations of LEO satellites are commonly being utilized to provide low latency communications at significant costs and complexities.

An aspect of the present invention, therefore, is a determination that for significant volumes of communication bandwidth latencies of 0.5 second are generally acceptable. Examples of this type of communication are video transmissions including on-demand video, Internet, fax and data connections. For these latency-insensitive applications, the delay associated with a single GEO satellite is acceptable and can be achieved at costs and complexities that are significantly less than the costs and complexities of a constellation of MEO or LEO satellites. Moreover, many of these types of latency-insensitive communication are data-intensive and employ communication signals carrying information at rates on the order of at least a megabit-per-second.

In one implementation of the present invention, a switched communication satellite system includes a switchless satellite in geosynchronous earth orbit. The system receives a latency-insensitive communication signal for transmission to one or more recipient stations. The communication signal may be uplinked to the satellite from a transmitting user stationto be downlinked to a terrestrial switched gateway or the communication signal may be transmitted directly to the terrestrial switched gateway via a terrestrial route such as cable (e.g., fiber optics or coaxial), microwave relay, etc. The terrestrial switched gateway includes a routing switch that routes the communication signal as a routed communication signal. A transmitter at the terrestrially switched gateway uplinks the routed communication signal to the satellite to be transmitted to the one or more recipient stations. In an implementation employing frequency division multiple access (FDMA) techniques, for example, the signal is transmitted by the terrestrial gateway at a selected frequency such that the satellite automatically forwards the signal to the desired recipient or recipients. Incorporating the system routing switch into the terrestrial switched gateway allows the GEO satellite toto be switchless. Moreover, having the routing switch at the switched gateway allows the switch to be improved, expanded, and modified even after the satellite has been launched such as, for example, by coupling together multiple terrestrial switched gateways to provide ever expanding bandwidth capacities. In contrast, routing switches carried onboard satellites are limited to capabilities and capacities that are on-board at the time of launch. Over the 5-15 year operating life of many communication satellites, such inflexibility can greatly limit the capacity or capability of the communication system.

Additional objects and advantages of the present invention will be apparent from the detailed description of the preferred embodiment thereof, which proceeds with reference to the accompanying drawings.

Brief Description of Drawings Fig. 1 is a block diagram illustrating a satellite communication system with a satellite in communication with exemplary ground-based stations, including a ground-based switching gateway.

Fig. 2 is a flow diagram of a ground-switched satellite communication process. Fig. 3 is an illustration of a satellite telecommunications region having multiple separate downlink cells.

Fig. 4 is a block diagram illustrating a first ground-based switched gateway in the satellite communication system of Fig. 1.

Fig. 5 is a block diagram illustrating a satellite in the satellite communication system of Fig. 1.

Fig. 6 is a block diagram illustrating a satellite communication system with a satellite in communication with exemplary ground-based stations, including multiple ground-based switching gateways. Best Modes for Carrying Out the Invention

Fig. 1 is a block diagram illustrating a switched satellite communication system 10 with a geosynchronous Earth orbit (GEO) satellite 12 in communication with exemplary ground-based or terrestrial stations 14-18. A transmitting user station 14 transmits or uplinks a communication signal (e.g., Ku- or Ka-band) to satellite 12 to be eventually broadcast or downlinked to a recipient station 16. Recipient station 16 is referred to in the singular for purposes of simplicity, but may correspond to more than one and possibly many separate recipient stations. Moreover, it will be appreciated that satellite communication system 10 would typically include multiple or many transmitting stations and multiple or many recipient stations and that stations 14 and 16 are specified merely to illustrate communication over one of multiple channels carried by communication system 10.

The communication signal received at satellite 12 from transmitting user station 14 is downlinked to a terrestrial switched gateway 18 at an alternative frequency band (e.g., V-band) that is typically of a greater bandwidth than the frequency bands employed for transmissions between satellite 12 and stations 14 and 16. Terrestrial switched gateway 18 switches or routes the communication signal and directs it to recipient station 16, either via satellite 12 (e.g., V-band uplink and Ku- or Ka-band downlink) or via another (e.g., terrestrial) communication link to another communication network or gateway. For communications that terrestrial switched gateway 18 directs to recipient station 16 via satellite 12, for example, terrestrial switched gateway 18 employs a routing or switching technique such as frequency division multiple access (FDMA), or FDMA in combination with code division multiple access (CDMA).

In one implementation, for example, terrestrial switched gateway 18 employs FDMA techniques to route the communication signal to recipient station 16. In this implementation, satellite 12 directs the communication signal to recipient station 16 automatically according to the frequency at which the communication signal is transmitted to satellite 12 from terrestrial switched gateway 18, as described below in greater detail. Accordingly, terrestrial switched gateway 18 converts the communication signal received from transmitting user station 14 to a frequency corresponding to recipient station 16. Terrestrial switched gateway 18 transmits the frequency-converted communication signal to satellite 12, which automatically forwards the signal to recipient station 16. This transmission from transmitting user station 14 to recipient station 16 via switched gateway 18 and two uplinks to satellite 12 may be referred to as a "double hop" transmission.

As an alternative communication signal path, switched gateway 18 can receive a communication signal directly from a terrestrial transmitting user 20 via a separate communication channel 22 (including a channel local to gateway 18 or a terrestrial channel) rather than via satellite 12. Switched gateway 18 switches or routes such a directly received communication signal as described above so the signal can be directed to recipient station 16. Switched gateway 18 then uplinks the directly-received switched communication signal to satellite 12, which directs the signal to recipient station 16. This transmission from switched gateway 18 to recipient station 16 via one uplink to satellite 12 may be referred to as a "single hop" transmission.

Communication system 10 includes a network operations center 24, sometimes referred to as a NOC, which controls and coordinates the transmission of communication over system 10. Network operations center 24 is in communication with switched gateway 18 via a separate communication channel 26 and may communicate with transmitting user station 14 and recipient station 16 via satellite 12 or other communication channels. Operations center 24 obtains and maintains information about the communication traffic and the resource configuration of satellite 12, as described below in greater detail.

Communication system 10 also includes a satellite control center 28 that transmits and receives tracking, telemetry, and control signals for controlling satellite 12 and its operation. Control center 28 is in communication with switched gateway 18 and network operations center 24 via a separate communication channel (not shown). Network operations center 24 and control center 28 may be separate or a single integrated control center, and one or both of network operations center 24 and control center 28 may be in close proximity to or included in switched gateway 18.

The double hop transmission with GEO satellite 12 and switched gateway 18 introduces a delay or latency of at least about 0.5 second in the transmission of the communication signal from transmitting user station 14 to recipient station 16. Each "hop" to a GEO satellite requires about 0.25 second. For many communication applications, such as voice communication, such a delay or latency can be unacceptable for most users. To avoid such latencies, current satellite communication systems, such as Iridium (www.iridium.com) and GlobalStar (www.globalstar.com), are utilizing constellations of up to 66 satellites in low Earth orbit (LEO). The cost and complexity of providing communication through such large numbers of satellites are staggering.

One aspect of the present invention, however, is the determination that for significant volumes of communication bandwidth latencies of 0.5 second are generally acceptable. Examples of this type of communication are video transmissions including on-demand video, Internet, fax and data connections. For these latency-insensitive applications, the performance of a single GEO satellite 12 utilizing either single or double hop transmission is acceptable and can be achieved at costs and complexities that are significantly less than the costs and complexities of a constellation of LEO satellites. Moreover, many of these types of latency-insensitive communication are data-intensive and employ communication signals carrying information at rates on the order of at least a megabit-per-second.

With regard to the switching functionality, some conventional communication satellites employ satellite-based switching to direct communications signals from a transmitting user to a recipient. Signal switching typically requires extensive processor and memory capabilities, but the processor and memory capabilities on-board satellites are fixed. Satellites in orbit are inaccessible for upgrade or expansion. As a consequence, satellite-based switching is inflexible and typically cannot be improved once the satellite is in orbit. Relatedly, such satellites must have the maximum switching capacities of the communication system built-in before launch. This forces maximum component expenditure before even minimal capacity is required. Utilizing terrestrial switched gateway 18 for switching maximizes the flexibility, performance, and expandability of the communication system while minimizing the complexity, weight, and expense of satellite 10.

Fig. 2 is a flow diagram of a ground-switched satellite communication process 50 as used, for example, with GEO satellite 12. Communication process 50 allows communication system 10 to transmit intensive, latency-insensitive data with maximum efficiency and thereby to maximize the data bandwidth or capacity that can be carried by satellite 12. For purposes of illustration, communication process 50 is described with reference to an exemplary implementation in accordance with FDMA techniques.

Process block 52 indicates that a user of communication system 10 transmits to network operations center 24 a system access request for the transmission of a communication signal from a transmitting user station 14 to a recipient station 16. The system access request may originate from a user associated with transmitting user station 14 or recipient station 16 as, for example, a request for a communication channel for a transmission or a request for a service to be transmitted over communication system 10, respectively. Such a system access request would typically identify transmitting station 14 and recipient station 16 and would typically entail relatively little communication bandwidth. Moreover, the request may be transmitted via a control channel of communication system 10, or over another communication channel, and may be in the form of a low bandwidth CDMA transmission. As an illustrating example, network operations center 24 may provide a user associated with recipient station 16 with access to a computer network (e.g., Internet) over communication system 10. A request by the user for a selected site or page on the computer network may be transmitted as a CDMA transmission from recipient station 16 over a control channel to network operations center 24. This request amounts to a request for a transmission of the selected site or page over communication system 10. Process block 54 indicates that network operations center 24 assigns a channel for the requested transmission and sends corresponding channel assignment information to transmitting user station 14 and terrestrial switching gateway 18. In the illustrated FDMA-based implementation, the channel assignment corresponds to a frequency bandwidth assignment over which transmitting user station 14 is to transmit the communication signal. Network operations center 24 also sends to terrestrial switching gateway 18 routing information for routing the communication signal to recipient station 16. In the illustrated FDMA-based implementation, the routing information corresponds to a frequency bandwidth assignment for directing the communication signal to recipient station 16.

Process block 56 indicates that transmitting user station 14 transmits the communication signal to terrestrial switched gateway 18. In this illustration, the communication signal is transmitted as an uplink to satellite 12, which relays the communication signal to gateway 18. In one implementation, the communication signal uplinked from transmitting user station 14 has a carrier frequency (e.g., K- band) that is lower than the carrier frequency (e.g., V-band) at which the communication signal is downlinked to terrestrial switched gateway 18. Satellite 12 performs predetermined conversions between predetermined frequencies in the uplink frequency band and predetermined frequency sub-bands in the broader gateway downlink frequency band.

As an alternative to receiving the communication signal from transmitting user station 14 via a downlink from satellite 12, switched gateway 18 may receive the communication signal via a separate communication channel 22 other than satellite 12. The communication signal could alternatively be obtained or retrieved locally at switched gateway 18 such as, for example, from a cache or data store holding data that are transmitted frequently, or from a terrestrial connection.

Process block 58 indicates that terrestrial switched gateway 18 identifies recipient station 16 to which the communication signal is being transmitted. In the FDMA-based illustration, terrestrial switched gateway 18 may identify recipient station 16 based upon the carrier frequency of the downlinked communication signal and the channel assignment information received from network operations center 24 for the communication transmission and, optionally, the time at which the downlinked signal is received. The channel assignment information in combination with the predetermined conversion between uplinked and downlinked signal frequencies on satellite 12 allows terrestrial switched gateway 18 to correlate a given downlinked signal frequency with the communication signal transmitted from transmitting user station 14. This correlation may optionally be made within a preselected threshold time duration after gateway 18 receives the channel assignment information, thereby to improve the reliability of the correlation. In this illustrated implementation, terrestrial switched gateway 18 is capable of distinguishing or identifying the communication signal destined for recipient station 16 without demodulating the downlinked communication signal. Process block 60 indicates that terrestrial switched gateway 18 routes the communication signal to recipient station 16 to which the communication signal is directed. Fig. 3 is an illustration of a satellite telecommunications region 70 having multiple cells 72 (represented by circles) to which one implementation of satellite 12 directs narrow zone communication signals. Cells 72 correspond to different geographic areas within region 70. Different groups of cells 72 receive downlink signals carried on different channels of system 10. In some applications, the downlink signal carried on a single channel could be directed to a single cell 72.

Recipient station 16 is located within one of cells 72. Moreover, transmitting user station 14, switched gateway 18, and network operations center 24, and the satellite control center (not shown) could be located in different or the same cells 72, or completely outside satellite telecommunications region 70. It will be appreciated that the geographic region shown in Fig. 3 is merely illustrative and that operation of the present invention is applicable to other geographic regions. With routing based upon frequency division multiple access (FDMA) techniques, for example, the cell 72 within which recipient station 16 is located is associated with a selected channel or FDMA sub-band (e.g., nominal 167 MHz bandwidth channel) of a nominal 3.5 GHz bandwidth V-band uplink channel between terrestrial switched gateway 18 and satellite 12. Routing of the communication signal to recipient station 16 includes modulating and upconverting the communication signal to the selected sub-band. Alternatively, if recipient station 16 represents multiple separate recipient stations in multiple different cells 72, multiple selected channels or sub-bands associated with the cells 72 are identified and the communication signal is modulated and upconverted to the corresponding sub-bands. The routing of the communication signal may further include application of code division multiple access (CDMA) techniques in which a selected code or identifier associated with the recipient station 16 is associated with the FDMA sub-band signal to direct the communication signal specifically to the recipient station 16 within its cell 72.

Process block 62 indicates that the routed (e.g., FDMA) communication signal is uplinked from terrestrial switched gateway 18 to satellite 12.

Process block 64 indicates that satellite 12 downlinks the communication signal to the cell 72 where recipient station 16 is located according to the routing (e.g., FDMA sub-band) provided by terrestrial switched gateway 18.

In one implementation of satellite 12, satellite 12 performs predetermined conversions between predetermined frequency sub-bands in the gateway uplink frequency band and predetermined frequency sub-bands in the recipient downlink frequency band. In operation, satellite 12 directs predetermined sub- bands in the recipient downlink frequency band to predetermined transmission or downlink horns, as described below in greater detail. The transmission or downlink horns are correlated with predetermined cells 72 in telecommunications region 70.

In the FDMA routing or switching of the illustrated implementation, therefore, terrestrial switched gateway 18 upconverts the communication signal to the selected carrier frequency that corresponds to recipient station 16 and uplinks the signal to satellite 12. Satellite 12 performs a predetermined frequency conversion to convert the uplinked communication signal to a predetermined frequency sub-band in the recipient downlink frequency band. The predetermined sub-band in the recipient downlink frequency band is automatically directed to a predetermined transmission or downlink horn corresponding to the cell 72 where recipient station 16 is located, thereby transmitting or downlinking the signal to recipient station 16.

The FDMA routing or switching of the illustrated implementation is desirable in part because it requires minimal signal processing on-board satellite 12. Routing is achieved on satellite 12 by communication signals being directed to particular cells 72 according to the carrier frequencies of the communication signals without need to demodulate or otherwise read the communication signals. In contrast, code division multiple access (CDMA) techniques require a communication to be at least partly downconverted to read the routing code, thereby require additional processing on-board a satellite.

Fig. 4 is a block diagram illustrating terrestrial switched gateway 18 for use in an implementation utilizing FDMA in the routing of communication signals. Terrestrial switched gateway 18 includes a receiver system 80, a receiver antenna or horn 82, a transmitter system 84, and a transmitter antenna or horn 86 for, respectively, receiving and transmitting communication signals from and to satellite 12.

A routing system 88 is coupled between receiver system 80 and transmitter system 84 and receives communication signals from receiver system 80 and modifies them for transmission to recipient station 16. In this implementation, routing system 88 employs frequency division multiple access (FDMA) techniques to route the communication signals. The following description of switched gateway 18 is made primarily with reference to a double hop transmission of a communication signal from transmitting user station 14 to recipient station 16. It will be appreciated, however, that gateway 18 may be utilized in single hop transmissions as well. Receiver system 80 receives a downlink communication signal from satellite 12 at receiving antenna or horn 82, and the signal is passed to a a low noise amplifier (LNA) and downconverter system 92 that includes switching arrays and multiple individual receivers for receiving multiple separate signals or channels on the downlink communication signal. The switching arrays route each channel of the downlink signal to a corresponding amplifier/converter that provides pre-amplification of the downlink communication signals and downconverts them to an intermediate frequency (IF).

Routing system 88 receives the IF communication signals and correlates them with the corresponding recipient station according to the channel assignment information provided by network operations center 24. Routing system 88 also determines the carrier frequency associated with the recipient station to which the communication signals are directed and passes the IF communication signals and carrier frequency information to transmitter system 84. Transmitter system 84 includes an upconverter system 102 that receives the IF modulated signals and modulates them at the carrier frequencies associated with the recipient stations to which the communication signals are directed. The FDMA upconverted communication signal is passed to a high-power amplifier 104 that amplifies the signal and delivers it to transmitter antenna or horn 86 for transmission to satellite 12 as for example a V-band signal.

Routing system 88 may be implemented with a general purpose computer 120 having standard computer hardware components, including one or more data processors (e.g., microprocessors), a memory system that generally includes high-speed main memory in the form of a medium such as random access memory (RAM) and read only memory (ROM) semiconductor devices, and secondary storage in the form of long term storage mediums such as floppy disks, hard disks, tape, CD-ROM, flash memory, etc. and other devices that store data and software instructions using electrical, magnetic, optical or other recording media, and input and output data busses coupled to receiver system 80 and transmitter system 84. The computer would include switching or routing software for routing communication signals, such as with FDMA techniques as described above, as is known in the art.As a result, satellite 12 may be "switchless" in that it routes communication signals according to predetermined frequency assignments made at and transmitted from switched gateway 18.

Fig. 5 is a block diagram of an exemplary implementation of communication satellite 12. Satellite 12 includes a satellite receiving antenna or horn 143 that receives communication uplink signals and passes them an input 142 of an appropriate satellite low noise amplifier (LNA) and downconverter system 146having multiple individual receivers for receiving one or more signals within one or more uplink communication signals. For example, uplink signals from transmitting user stations 14 may be Ku-band signals (i.e., about 14 GHz ) while uplink signals from terrestrial switched gateway 18 may be V-band signals (i.e. about 38 GHz). Low noise amplifier (LNA) and downconverter system 146, as well as other systems within satellite 12 that are described below, would typically include more individual receivers than the number of signals or channels to be handled by satellite 12. The additional receivers, or other components, provide redundancy and may be utilized upon the failure of any individual component. Such redundancy is typically utilized in satellite design.

Accordingly, low noise amplifier (LNA) and downconverter system 146includes switching arrays to route each channel of the uplink signal to the corresponding active receivers that provide pre-amplification of the uplink communication signals and convert them to lower Ku-band frequency (e.g., 11-12 GHz).

An input multiplexer system 148 receives the low noise amplified and frequency converted uplink signals and channelizes and routes the signals to appropriate ones of redundant high power amplifiers in a high power amplifier system 152. In an implementation utilizing FDMA routing techniques, multiplexer 148 channelizes and routes the signals according to their carrier frequencies, which are assigned and applied at switched gateway 18. As a result, this channelizing and routing of the signals by satellite 12 is achieved automatically by multiplexer system 148 and without satellite 12 separately determining or identifying recipient station 16 from the communication signal. In this regard, therefore, satellite 12 is "switchless" and instead utilizes switching or routing determinations made at switched gateway 18.

Amplifier system 152 may employ, for example, driver amplifiers 151 with associated traveling wave tube amplifiers 153. Driver amplifiers 151 have two modes of operation: automatic gain and ground commandable gain. Traveling wave tube amplifiers 153 provide high reliability, high power output amplification. The outputs of high power amplifier system 148 are connected through an output filter system 154 to one or more transmit horns 160 for transmission as a downlink signal. A control unit 162 is bus connected to various ones of these components to control their operation and interaction. The satellite includes power sources, orientation and position control systems, communication control systems, etc. as are known in the art.

Fig. 6 is a block diagram illustrating an alternative switched satellite communication system 210 with a geosynchronous Earth orbit (GEO) satellite 212 that provides communication between a transmitting user station 214 and a recipient station 216. Transmitting user station 214 directs a communication signal to a recipient station 216 via GEO satellite 212 and one or more terrestrial switched gateways 218. Satellite 212 is generally the same as satellite 12 described above. In one implementation, transmitting user station 214 may uplink the communication signal to satellite 212 (e.g., Ku- or Ka-band), which would then downlink the signal (e.g., V-band) to one of terrestrial switched gateways 218 for routing to recipient station 216 via another uplink to satellite 212. In another implementation, transmitting user station 214 may deliver the communication signal directly to one of terrestrial switched gateways 218 via a terrestrial link, such as by microwave transmission, fiber optic or coaxial cable connection, or by originating locally at the gateway. The one of terrestrial switched gateways 218 would then route the signal to recipient station 216 via an uplink to satellite 212 or via a terrestrial (e.g., fiber optic) connection to another terrestrial switched gateway 218 from which the signal would be uplinked to satellite 212. Frequency division multiple access (FDMA) techniques may be employed to route or switch the signal similar to the manner described above with reference to gateway 18.

Terrestrial switched gateways 218 are spatially isolated from each other by distances of at least about 50-100 km, for example, but can be located in a common vicinity or region for ease of communication between them and common maintenance. Each of the terrestrial switched gateways 218 is assigned a unique V-band downlink channel (e.g., a nominal 3.5 GHz bandwidth) for receiving communication signals from transmitting user stations 214 in multiple selected cells 72, and a unique V-band uplink channel (e.g., a nominal 3.5 GHz bandwidth) for directing communication signals to recipient stations 216 in the multiple selected cells 72. Each of terrestrial switched gateways 218 typically serves different selected cells 72 and in this illustration is associated with nominal 167 MHz sub-bands of the V-band uplink and downlink channels.

In a transmission from transmitting user station 214 to one of terrestrial switched gateways 218 via an uplink to satellite 212 (e.g., Ku- or Ka-band), satellite 212 performs predetermined conversions between predetermined frequency sub-bands in the transmitting user uplink frequency band and predetermined frequency sub-bands in the gateway downlink V-band frequency. In operation, satellite 212 directs predetermined sub-bands in the gateway downlink frequency band to predetermined transmission or downlink horns that are correlated with predetermined ones of gateways 218.

Communication system 210 includes a network operations center 224, sometimes referred to as a NOC, which controls and coordinates the transmission of communication over system 210. Network operations center 224 is in communication with switched gateways 218 via a separate communication channel 226 and may communicate with transmitting user station 214 and recipient station 216 via satellite 212 or other communication channels. Operations center 224 obtains and maintains information about the communication traffic and the resource configuration of satellite 212, as described above with reference to operations center 24. Communication system 210 also includes a satellite control center 228 that transmits and receives tracking, telemetry, and control signals for controlling satellite 212 and its operation. Control center 228 is in communication with switched gateways 218 and network operations center 224 via a separate communication channel (not shown). Network operations center 224 and control center 228 may be separate or a single integrated control center, and one or both of network operations center 224 and control center 228 may be in close proximity to or included in one or different ones of switched gateways 218.

The operation of communication system 210 is illustrated with reference to a double hop transmission between transmitting user station 214 and a recipient station 216 that are in cells 72 associated with different terrestrial switched gateways 218A and 218B, respectively. Transmitting user station 214 uplinks a communication signal to satellite 212 on a Ka- or Ku-band assigned by network operations center 224 and associated with the cell 72 where station 214 is located (referred to as the transmitting cell). Satellite 212 converts the uplinked signal to a predetermined V-band channel to downlink the signal to the terrestrial switched gateway 218A with which the transmitting cell is associated.

The V-band link between satellite 212 and terrestrial switched gateways 218 is of a greater bandwidth than the frequency bands employed for transmissions between satellite 212 and stations 214 and 216 to accommodate communications between large numbers of stations located in many cells 72. In the present illustration, for example, the nominal 3.5 GHz bandwidth available in the V-band of each gateway 218 provides an overall capacity of up to about twenty cells 72 at a nominal bandwidth of 167 MHz each. The six gateways 218 illustrated in Fig. 6 could therefore accommodate about 120 cells 72, although more or fewer gateways 218 could be used together in the manner described herein. Accordingly, the V-band communications between satellite 212 and terrestrial switched gateways 218 are of a significantly wider bandwidth than communications between satellite 212 and any given cell 72, thereby providing an expansively expandable switching capacity for communication system 210. Terrestrial switched gateway 218A switches or routes the communication signal to recipient station 216. In the circumstances of this illustration, terrestrial switched gateway 218A determines that recipient station 216 is associated with a different terrestrial switched gateway 218B. Accordingly, the routing of the communication signal to recipient station 216 by terrestrial switched gateway 218A includes first directing the signal to terrestrial switched gateway 218B via a direct (e.g., fiber optic) communication link 230 between gateways 218. Terrestrial switched gateway 218B then directs to recipient station 16 via a V- band uplink to satellite 12. Terrestrial switched gateway 218B employs a routing or switching technique such as frequency division multiple access (FDMA), or FDMA in combination with code division multiple access (CDMA). In the illustrated FDMA- based implementation, the routing information corresponds to a frequency bandwidth assignment for directing the communication signal to recipient station 16. The V-band bandwidth assignment applied to the communication signal at gateway 218B is selected to be converted automatically at satellite 212 to a Ku- or Ka-band sub-band corresponding to the cell 72 in which recipient station 216 is located (called the receiving cell). Additional CDMA encoding applied to the communication signal can assure that the signal is received by recipient station 216, rather than other stations in the receiving cell.

In view of the many possible embodiments to which the principles of our invention may be applied, it should be recognized that the detailed embodiments are illustrative only and should not be taken as limiting the scope of our invention. For example, while the embodiments described are directed primarily to degradation in downlink communication signals, the present invention is similarly applicable to other types of downlink signals (e.g., control signals). Accordingly, the invention includes all such embodiments as may come within the scope and spirit of the following claims and equivalents thereto.

Claims

1. A communication satellite system, comprising: a switchless satellite in geosynchronous earth orbit and receiving a latency insensitive communication signal from a transmitting user station directed to one or more recipient stations; a terrestrial switched gateway that receives the communication signal in a downlink from the satellite and includes a routing system that routes the communication signal as a routed communication signal directed toward the one or more recipient stations and a transmitter system that uplinks the routed communication signal to the satellite to be transmitted to one or more recipient stations.

2. The system of claim 1 in which the latency insensitive communication signal is data intensive.

3. The system of claim 1 in which the routing system modulates the communication signal at one or more carrier frequencies corresponding to the one or more recipient stations.

4. The system of claim 3 in which the one or more carrier frequencies at which the communication signal is modulated are converted automatically to other carrier frequencies at the satellite for transmission to the one or more recipient stations.

5. The system of claim 1 in which the one or more recipient stations are located within one or more geographic cells and the routing system modulates the communication signal at one or more carrier frequencies corresponding to the one or more geographic cells.

6. The system of claim 1 in which the routing system employs frequency division multiple access (FDMA) techniques to route the communication signal.

7. The system of claim 6 in which the one or more recipient stations are located within one or more geographic cells and the frequency division multiple access (FDMA) techniques route the communication signal the one or more cells.

8. The system of claim 1 further comprising a network operations center that provides channel assignment information to the transmitting user station and the terrestrial switched gateway for identifying a communication channel for carrying the communication signal.

9. The system of claim 1 in which the terrestrial switched gateway further includes an input channel to receive a second communication signal directed to a selected recipient station, the second communication signal being received at the input channel from a terrestrial communication channel and being delivered to the routing system and the transmitter system to be transmitted to the selected recipient station.

10. The system of claim 1 further comprising plural terrestrial switched gateways in communication with each other via a communication link other than the switchless satellite.

11. The system of claim 10 in which the one or more recipient stations are located within one or more geographic cells and each of the plural terrestrial switched gateways provides routing of signals to different selected ones of the geographic cells.

12. A communication satellite process, comprising: uplinking a latency insensitive communication signal from the transmitting user station to a switchless satellite in geosynchronous orbit; and transmitting the communication signal to a terrestrial switched gateway that receives the communication signal in a downlink from the satellite in geosynchronous earth orbit, routing the communication signal at the terrestrial switched gateway as a routed communication signal to the one or more recipient stations, and uplinking the routed communication signal to the satellite in geosynchronous earth orbit for transmission to the one or more recipient stations.

13. The method of claim 12 in which the latency insensitive communication signal is data-intensive.

14. The method of claim 12 in which routing the communication signal includes modulating it at one or more carrier frequencies corresponding to the one or more recipient stations.

15. The system of claim 14 in which the one or more carrier frequencies at which the communication signal is modulated are converted automatically to other carrier frequencies at the satellite for transmission to the one or more recipient stations.

16. The method of claim 12 in which routing the communication signal employs frequency division multiple access (FDMA) techniques.

17. The method of claim 16 in which the one or more recipient stations are located within one or more geographic cells and the frequency division multiple access (FDMA) techniques route the communication signal the one or more cells.

18. The method of claim 12 further comprising generating channel assignment information for identifying a communication channel for carrying the communication signal and providing the channel assignment information to the transmitting user station and the terrestrial switched gateway.

19. The method of claim 12 further comprising receiving from a terrestrial communication channel a second communication signal directed to a selected recipient station and routing the second communication signal at the terrestrial switched gateway to the selected recipient station via the switchless satellite.

20. A communication satellite system, comprising: a switchless satellite in geosynchronous earth orbit and receiving a latency insensitive communication signal from a transmitting user station directed to one or more recipient stations; a terrestrial switched gateway system having plural spatially isolated and interconnected terrestrial switched gateways, at least one of the terrestrial switched gateways receiving the communication signal in a downlink from the satellite and at least one of the terrestrial switched gateways providing routing that routes the communication signal as a routed communication signal directed toward the one or more recipient stations via the satellite.

21. The system of claim 20 in which the one or more recipient stations are located within one or more geographic cells and each of the plural terrestrial switched gateways provides routing of signals to different selected ones of the geographic cells.

22. The system of claim 21 in which the communication signal is received at a first of the terrestrial switched gateways in a downlink from the satellite, transmitted to a second of the terrestrial switched gateways via an interconnection between them for routing to at least one of the recipient stations.

23. The system of claim 20 in which routing the communication signal includes modulating it at one or more carrier frequencies corresponding to the one or more recipient stations.

24. The system of claim 20 in which the one or more recipient stations are located within one or more geographic cells and routing the communication signal includes modulating it at one or more carrier frequencies corresponding to the one or more geographic cells.

25. The system of claim 20 in which frequency division multiple access (FDMA) techniques route the communication signal.

26. A communication satellite system, comprising: a switchless satellite in geosynchronous earth orbit; and a terrestrial switched gateway that receives a latency insensitive communication signal that originates from a transmitting user station and is directed to one or more recipient stations, the gateway including a routing system that routes the communication signal as a routed communication signal directed toward the one or more recipient stations and a transmitter system that uplinks the routed communication signal to the satellite to be transmitted to one or more recipient stations.

27. The system of claim 26 in which the latency insensitive communication signal is data intensive.

28. The system of claim 26 in which the routing system modulates the communication signal at one or more carrier frequencies corresponding to the one or more recipient stations.

29. The system of claim 28 in which the one or more carrier frequencies at which the communication signal is modulated are converted automatically to other carrier frequencies at the satellite for transmission to the one or more recipient stations.

30. The system of claim 26 in which the one or more recipient stations are located within one or more geographic cells and the routing system modulates the communication signal at one or more carrier frequencies corresponding to the one or more geographic cells.

31. The system of claim 26 in which the routing system employs frequency division multiple access (FDMA) techniques to route the communication signal.

32. The system of claim 26 in which the one or more recipient stations are located within one or more geographic cells and the frequency division multiple access (FDMA) techniques route the communication signal the one or more cells.

33. The system of claim 26 further comprising a network operations center that provides channel assignment information to the transmitting user station and the terrestrial switched gateway for identifying a communication channel for carrying the communication signal.

34. The system of claim 26 further comprising plural terrestrial switched gateways in communication with each other via a communication link other than the switchless satellite.

35. The system of claim 34 in which the one or more recipient stations are located within one or more geographic cells and each of the plural terrestrial switched gateways provides routing of signals to different selected ones of the geographic cells.