US20130336203A1 - Satellite architecture - Google Patents

Abstract

A method is presented for transmitting data in a satellite system having multiple spot beams comprising (1) sending a broadband signal in a forward direction from a gateway terminal to a communications satellite for relay to at least one subscriber terminal, (2) receiving the broadband signal at the communications satellite, wherein the communications satellite comprises a bent pipe repeater having a plurality of satellite-based transmission amplifiers, (3) using one of the plurality of satellite-based transmission amplifiers to amplify the broadband signal and no other broadband signal from the gateway terminal, to produce an amplified broadband signal, (4) sending the amplified broadband signal as one of a plurality of service spot beams to the at least one subscriber terminal, and (5) receiving and retrieving data from the amplified broadband signal at the at least one subscriber terminal.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a continuation of and claims priority to U.S. patent application Ser. No. 12/406,880, filed Mar. 18, 2009, which is a continuation application of International Application No. PCT/US2007/079567, filed Sep. 26, 2007. This application incorporates by reference U.S. patent application Ser. No. 12/406,880 in its entirety for all purposes.
• This application also claims the benefit of, and incorporates by reference through the foregoing International Application, the following applications:
• U.S. Provisional Application No. 60/827,959 (Attorney Docket No. 017018-008500US), filed Oct. 3, 2006,
• U.S. Provisional Application No. 60/827,924 (Attorney Docket No. 017018-008000US), filed Oct. 3, 2006,
• U.S. Provisional Application No. 60/827,927 (Attorney Docket No. 017018-008300US), filed Oct. 3, 2006,
• U.S. Provisional Application No. 60/827,960 (Attorney Docket No. 017018-008600US), filed Oct. 3, 2006,
• U.S. Provisional Application No. 60/827,964 (Attorney Docket No. 017018-008800US), filed Oct. 3, 2006.
  • This application also claims the benefit of U.S. Provisional Application No. 60/827,038 (Attorney Docket No. 017018-010400US), filed Sep. 26, 2006, through the foregoing International Application.
FIELD OF THE INVENTION
• The present invention relates to wireless communications in general and, in particular, to a satellite communications network.
BACKGROUND OF THE INVENTION
• Consumer broadband satellite services are gaining traction in North America with the start up of star network services using Ka band satellites. While such first generation satellite systems may provide multi-gigabit per second (Gbps) per satellite overall capacity, the design of such systems inherently limits the number of customers that may be adequately served. Moreover, the fact that the capacity is split across numerous coverage areas further limits the bandwidth to each subscriber.
• While existing designs have a number of capacity limitations, the demand for such broadband services continues to grow. The past few years have seen strong advances in communications and processing technology. This technology, in conjunction with selected innovative system and component design, may be harnessed to produce a novel satellite communications system to address this demand.
SUMMARY OF THE INVENTION
• The present invention relates to a method for transmitting data in a satellite system having multiple spot beams. The method comprises sending a broadband signal in a forward direction from a gateway terminal to a communications satellite for relay to at least one subscriber terminal. The method further comprises receiving the broadband signal at the communications satellite, wherein the communications satellite comprises a bent pipe repeater having a plurality of satellite-based transmission amplifiers, each satellite-based transmission amplifier capable of performing amplification to generate a service spot beam. The method further comprises amplifying the broadband signal using one of the plurality of satellite-based transmission amplifiers to produce an amplified broadband signal, wherein the one of the plurality of satellite-based transmission amplifiers is employed to amplify only the broadband signal and no other broadband signal from the gateway terminal. The method further comprises sending the amplified broadband signal to the at least one subscriber terminal, the amplified broadband signal being sent as one of a plurality of service spot beams, the one of the plurality of service spot beams having an earth surface coverage area including the at least one subscriber terminal, wherein the amplified broadband signal alone occupies the one of the plurality of service spot beams. The method further comprises receiving and retrieving data from the amplified broadband signal at the at least one subscriber terminal.
• In one embodiment, the amplified broadband signal is a single-carrier signal. The amplified broadband signal may support a data rate of at least 1 Gigabits per second (Gbps). The amplified broadband signal may have a bandwidth of at least 500 MHz.
• Each of the plurality of satellite-based transmission amplifiers may comprise a traveling wave tube amplifier (TWTA). In one embodiment, the plurality of service spot beams comprises 60 service spot beams. The broadband signal sent from the gateway terminal to the communications satellite may be contained in one of a plurality of feeder beams sent from gateway terminals to the communications satellite. In one embodiment, the plurality of feeder beams comprises 15 feeder beams. Each of the plurality of feeder beams may contain 4 carriers each representing a separate signal sent in the forward direction from a gateway terminal to the communications satellite.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1A is a block diagram of an exemplary satellite communications system configured according to various embodiments of the invention.
• FIG. 1B is a block diagram illustrating an alternative embodiment of a satellite communication system.
• FIG. 2A is an example of a multi-beam system configured according to various embodiments of the invention are shown.
• FIG. 2B is another example of a multi-beam system configured according to various embodiments of the invention are shown.
• FIG. 3 presents an embodiment of a ground system of gateways shown in block diagram form.
• FIG. 4 presents an embodiment of a SMTS shown in block diagram form.
• FIG. 5 presents an embodiment of a satellite shown in block diagram form.
• FIG. 6A presents an embodiment of an upstream translator shown in block diagram form.
• FIG. 6B presents an embodiment of a downstream translator shown as a block diagram.
• FIG. 7 is a block diagram illustrating a set of subscriber equipment which may be located at a subscriber location for the reception and transmission of communication signals.
• FIG. 8 shows an embodiment of a downstream channel.
• FIG. 9 shows an embodiment of an upstream channel.
• FIG. 10 shows an embodiment of a gateway transmitter.
• FIG. 11 shows an embodiment of gateway receiver.
• FIG. 12A illustrates an embodiment of a forward link distribution system.
• FIG. 12B illustrate an embodiment of a return link distribution system.
• FIG. 13 shows an embodiment of a channel diagram.
• FIG. 14 presents an illustrative frequency re-use plan that may be adopted in accordance with one embodiment of the invention.
• FIG. 15 presents an illustrative system employing adaptive use of satellite uplink bands in accordance with one embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
• Various embodiments of the present invention comprise systems, methods, devices, and software for a novel broadband satellite network. This description provides exemplary embodiments only, and is not intended to limit the scope, applicability or configuration of the invention. Rather, the ensuing description of the embodiments will provide those skilled in the art with an enabling description for implementing embodiments of the invention. Various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the invention.
• Thus, various embodiments may omit, substitute, or add various procedures or components as appropriate. For instance, it should be appreciated that in alternative embodiments, the methods may be performed in an order different than that described, and that various steps may be added, omitted or combined. Also, features described with respect to certain embodiments may be combined in various other embodiments. Different aspects and elements of the embodiments may be combined in a similar manner. Also, a number of steps may be required before, after, or concurrently with the following embodiments.
• It should also be appreciated that the following systems, methods, devices, and software may be a component of a larger system, wherein other procedures may take precedence over or otherwise modify their application.
• FIG. 1A is a block diagram of an exemplarysatellite communications system100 configured according to various embodiments of the invention. Thesatellite communications system100 includes anetwork120, such as the Internet, interfaced with agateway115 that is configured to communicate with one ormore subscriber terminals130, via asatellite105. Agateway115 is sometimes referred to as a hub or ground station.Subscriber terminals130 are sometimes called modems, satellite modems or user terminals. As noted above, although thecommunications system100 is illustrated as ageostationary satellite105 based communication system, it should be noted that various embodiments described herein are not limited to use in geostationary satellite based systems, for example some embodiments could be low earth orbit (LEO) satellite based systems.
• Thenetwork120 may be any type of network and can include, for example, the Internet, an IP network, an intranet, a wide-area network (“WAN”), a local-area network (“LAN”), a virtual private network, the Public Switched Telephone Network (“PSTN”), and/or any other type of network supporting data communication between devices described herein, in different embodiments. Anetwork120 may include both wired and wireless connections, including optical links. Many other examples are possible and apparent to those skilled in the art in light of this disclosure. As illustrated in a number of embodiments, the network may connect thegateway115 with other gateways (not pictured), which are also in communication with thesatellite105.
• Thegateway115 provides an interface between thenetwork120 and thesatellite105. Thegateway115 may be configured to receive data and information directed to one ormore subscriber terminals130, and can format the data and information for delivery to the respective destination device via thesatellite105. Similarly, thegateway115 may be configured to receive signals from the satellite105 (e.g., from one or more subscriber terminals) directed to a destination in thenetwork120, and can format the received signals for transmission along thenetwork120.
• A device (not shown) connected to thenetwork120 may communicate with one or more subscriber terminals, and through thegateway115. Data and information, for example IP datagrams, may be sent from a device in thenetwork120 to thegateway115. Thegateway115 may format a Medium Access Control (MAC) frame in accordance with a physical layer definition for transmission to thesatellite130. A variety of physical layer transmission modulation and coding techniques may be used with certain embodiments of the invention, including those defined with the DVB-S2 and WiMAX standards. Thelink135 from thegateway115 to thesatellite105 may be referred to hereinafter as thedownstream uplink135.
• Thegateway115 may use anantenna110 to transmit the signal to thesatellite105. In one embodiment, theantenna110 comprises a parabolic reflector with high directivity in the direction of the satellite and low directivity in other directions. Theantenna110 may comprise a variety of alternative configurations and include operating features such as high isolation between orthogonal polarizations, high efficiency in the operational frequency bands, and low noise.
• In one embodiment, ageostationary satellite105 is configured to receive the signals from the location ofantenna110 and within the frequency band and specific polarization transmitted. Thesatellite105 may, for example, use a reflector antenna, lens antenna, array antenna, active antenna, or other mechanism known in the art for reception of such signals. Thesatellite105 may process the signals received from thegateway115 and forward the signal from thegateway115 containing the MAC frame to one ormore subscriber terminals130. In one embodiment, thesatellite105 operates in a multi-beam mode, transmitting a number of narrow beams each directed at a different region of the earth, allowing for frequency re-use. With such amultibeam satellite105, there may be any number of different signal switching configurations on the satellite, allowing signals from asingle gateway115 to be switched between different spot beams. In one embodiment, thesatellite105 may be configured as a “bent pipe” satellite, wherein the satellite may frequency convert the received carrier signals before retransmitting these signals to their destination, but otherwise perform little or no other processing on the contents of the signals. A variety of physical layer transmission modulation and coding techniques may be used by thesatellite105 in accordance with certain embodiments of the invention, including those defined with the DVB-S2 and WiMAX standards. For other embodiments a number of configurations are possible (e.g., using LEO satellites, or using a mesh network instead of a star network), as evident to those skilled in the art.
• The service signals transmitted from thesatellite105 may be received by one ormore subscriber terminals130, via therespective subscriber antenna125. In one embodiment, theantenna125 and terminal130 together comprise a very small aperture terminal (VSAT), with theantenna125 measuring approximately 0.6 meters in diameter and having approximately 2 watts of power. In other embodiments, a variety of other types ofantennas125 may be used at thesubscriber terminal130 to receive the signal from thesatellite105. Thelink150 from thesatellite105 to thesubscriber terminals130 may be referred to hereinafter as thedownstream downlink150. Each of thesubscriber terminals130 may comprise a single user terminal or, alternatively, comprise a hub or router (not pictured) that is coupled to multiple user terminals. Eachsubscriber terminal130 may be connected to consumer premises equipment (CPE)160 comprising, for example computers, local area networks, Internet appliances, wireless networks, etc.
• In one embodiment, a Multi-Frequency Time-Division Multiple Access (MF-TDMA) scheme is used forupstream links140,145, allowing efficient streaming of traffic while maintaining flexibility in allocating capacity among each of thesubscriber terminals130. In this embodiment, a number of frequency channels are allocated which may be fixed, or which may be allocated in a more dynamic fashion. A Time Division Multiple Access (TDMA) scheme is also employed in each frequency channel. In this scheme, each frequency channel may be divided into several timeslots that can be assigned to a connection (i.e., a subscriber terminal130). In other embodiments, one or more of theupstream links140,145 may be configured with other schemes, such as Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Code Division Multiple Access (CDMA), or any number of hybrid or other schemes known in the art.
• A subscriber terminal, for example130-a, may transmit data and information to anetwork120 destination via thesatellite105. Thesubscriber terminal130 transmits the signals via the upstream uplink145-ato thesatellite105 using the antenna125-a. Asubscriber terminal130 may transmit the signals according to a variety of physical layer transmission modulation and coding techniques, including those defined with the DVB-S2 and WiMAX standards. In various embodiments, the physical layer techniques may be the same for each of thelinks135,140,145,150, or may be different. The link from thesatellite105 to thegateway115 may be referred to hereinafter as theupstream downlink140.
• Turning toFIG. 1B, a block diagram is shown illustrating an alternative embodiment of asatellite communication system100. Thiscommunication system100 may, for example, comprise thesystem100 ofFIG. 1A, but is in this instance described with greater particularity. In this embodiment, thegateway115 includes a Satellite Modem Termination System (SMTS), which is based at least in part on the Data-Over-Cable Service Interface Standard (DOCSIS). The SMTS in this embodiment includes a bank of modulators and demodulators for transmitting signals to and receiving signals fromsubscriber terminals130. The SMTS in thegateway115 performs the real-time scheduling of the signal traffic through thesatellite105, and provides the interfaces for the connection to thenetwork120.
• In this embodiment, thesubscriber terminals135 use portions of DOCSIS-based modem circuitry, as well. Therefore, DOCSIS-based resource management, protocols, and schedulers may be used by the SMTS for efficient provisioning of messages. DOCSIS-based components may be modified, in various embodiments, to be adapted for use therein. Thus, certain embodiments may utilize certain parts of the DOCSIS specifications, while customizing others.
• While asatellite communications system100 applicable to various embodiments of the invention is broadly set forth above, a particular embodiment of such asystem100 will now be described. In this particular example, approximately 2 gigahertz (GHz) of bandwidth is to be used, comprising four 500 megahertz (MHz) bands of contiguous spectrum. Employment of dual-circular polarization results in usable frequency comprising eight 500 MHz non-overlapping bands with 4 GHz of total usable bandwidth. This particular embodiment employs amulti-beam satellite105 with physical separation between thegateways115 and subscriber spot beams, and configured to permit reuse of the frequency on thevarious links135,140,145,150. A single Traveling Wave Tube Amplifier (TWTA) is used for each service link spot beam on the downstream downlink, and each TWTA is operated at full saturation for maximum efficiency. A single wideband carrier signal, for example using one of the 500 MHz bands of frequency in its entirety, fills the entire bandwidth of the TWTA, thus allowing a minimum number of space hardware elements. Spotbeam size and TWTA power may be optimized to achieve maximum flux density on the earth's surface of −118 decibel-watts per meter squared per megahertz (dbW/m²/MHz). Thus, using approximately 2 bits per second per hertz (bits/s/Hz), there is approximately 1 Gbps of available bandwidth per spot beam.
• With reference toFIG. 12A, an embodiment of a forwardlink distribution system1200 is shown. Thegateway115 is shown coupled to anantenna110, which generates four downstream signals. A single carrier with 500 MHz of spectrum is used for each of the fourdownstream uplinks135. In this embodiment, a total of two-frequencies and two polarizations allow four separatedownstream uplinks135 while using only 1 GHz of the spectrum. For example, link A135-A could be Freq 1U (27.5-28.0 GHz) with left-hand polarization, link B135-B could be Freq 1U (27.5-28.0) GHz with right-hand polarization, link C could be Freq 2U (29.5-30 GHz) with left-hand polarization, and link D could be Freq 2U (29.5-30 GHz) with left-hand polarization.
• Thesatellite105 is functionally depicted as four “bent pipe” connections between a feeder and service link. Carrier signals can be changed through thesatellite105 “bent pipe” connections along with the orientation of polarization. Thesatellite105 converts eachdownstream uplink135 signal into adownstream downlink signal150.
• In this embodiment, there are fourdownstream downlinks150 that each provides a service link for four spot beams205. Thedownstream downlink150 may change frequency in the bent pipe as is the case in this embodiment. For example, downstream uplink A135-A changes from a first frequency (i.e., Freq 1U) to a second frequency (i.e., Freq 1D) through thesatellite105. Other embodiments may also change polarization between the uplink and downlink for a given downstream channel. Some embodiments may use the same polarization and/or frequency for both the uplink and downlink for a given downstream channel.
• Referring next toFIG. 12B, an embodiment of a return link distribution system is shown. This embodiment shows fourupstream uplinks145 from four sets ofsubscriber terminals125. A “bent pipe”satellite105 takes theupstream uplinks145, optionally changes carrier frequency and/or polarization (not shown), and then redirects them asupstream downlinks140 to a spot beam for agateway115. In this embodiment, the carrier frequency changes between theuplink145 and thedownlink140, but the polarization remains the same. Because the feeder spot beams to thegateway115 is not in the coverage area of the service beams, the same frequency pairs may be reused for both service links and feeder links.
• Turning toFIGS. 2A and 2B, examples of amulti-beam system200 configured according to various embodiments of the invention are shown. Themulti-beam system200 may, for example, be implemented in thenetwork100 described inFIGS. 1A and 1B. Shown are the coverage of a number of feeder and servicespot beam regions225,205. In this embodiment, asatellite215 reuses frequency bands by isolating antenna directivity to certain regions of a country (e.g., United States, Canada or Brazil). As shown inFIG. 2A, there is complete geographic exclusivity between the feeder and service spot beams205,225. But that is not the case forFIG. 2B where there may in some instances be service spot beam overlap (e.g.,205-c,205-d,205-e), while there is no overlap in other areas. However, with overlap, there are certain interference issues that may inhibit frequency band re-use in the overlapping regions. A four color pattern allows avoiding interference even where there is some overlap between neighboring service beams205.
• In this embodiment, thegateway terminals210 are also shown along with their feeder beams225. As shown inFIG. 2B, thegateway terminals210 may be located in a region covered by a service spotbeam (e.g., the first, second and fourth gateways210-1,210-2,210-4). However, a gateway may also be located outside of a region covered by a service spotbeam (e.g., the third gateway210-3). By locatinggateway terminals210 outside of the service spotbeam regions (e.g., the third gateway210-3), geographic separation is achieved to allow for re-use of the allocated frequencies.
• There are oftenspare gateway terminals210 in a givenfeeder spot beam225. The spare gateway terminal210-5 can substitute for the primary gateway terminal210-4 should the primary gateway terminal210-4 fail to function properly. Additionally, the spare can be used when the primary is impaired by weather.
• Referring next toFIG. 8, an embodiment of adownstream channel800 is shown. Thedownstream channel800 includes a series ofsuperframes804 in succession, where eachsuperframe804 may have the same size or may vary in size. This embodiment divides asuperframe804 into a number of virtual channels808(1-n). The virtual channels808(1-n) in eachsuperframe804 can be the same size or different sizes. The size of the virtual channels808(1-n) can change betweendifferent superframes804. Different coding can be optionally used for the various virtual channels808 (1-n). In some embodiments, the virtual channels are as short as one symbol in duration.
• With reference toFIG. 9, an embodiment of anupstream channel900 is shown. This embodiment uses MF-TDMA, but other embodiments can use CDMA, OFDM, or other access schemes. Theupstream channel900 has 500 MHz of total bandwidth in one embodiment. The total bandwidth is divided into m frequency sub-channels, which may differ in bandwidth, modulation, coding, etc. and may also vary in time based on system needs.
• In this embodiment, eachsubscriber terminal130 is given a two-dimensional (2D) map to use for its upstream traffic. The 2D map has a number of entries where each indicates afrequency sub-channel912 and time segment908(1-5). For example, onesubscriber terminal130 is allocated sub-channel m912-m, time segment one908-1; sub-channel two912-2, time segment two908-2; sub-channel two912-2, time segment three908-3; etc. The 2D map is dynamically adjusted for eachsubscriber terminal130 according to anticipated need by a scheduler in the SMTS.
• Referring toFIG. 13, an embodiment of a channel diagram is shown. Only the channels for a singlefeeder spot beam225 and a singleservice spot beam205 are shown, but embodiments include many of eachspot beam225,205 (e.g., various embodiments could have 60, 80, 100, 120, etc. of each type ofspot beam225,205). Theforward channel800 includes nvirtual channels808 traveling from thegateway antenna110 to theservice spot beam205. Eachsubscriber terminal130 may be allocated one or more of thevirtual channels808. m MF-TDMA channels912 make up thereturn channel900 between the subscriber terminal (ST)antennas125 and thefeeder spot beam225.
• Referring next toFIG. 3, an embodiment of aground system300 ofgateways115 is shown in block diagram form. One embodiment could have fifteen active gateways115 (and possibly spares) to generate sixty service spot beams, for example. Theground system300 includes a number ofgateways115 respectively coupled toantennas110. All thegateways115 are coupled to anetwork120 such as the Internet. The network is used to gather information for the subscriber terminals. Additionally, each SMTS communicates with other SMTS and the Internet using thenetwork120 or other means not shown.
• Eachgateway115 includes atransceiver305, aSMTS310 and arouter325. Thetransceiver305 includes both a transmitter and a receiver. In this embodiment, the transmitter takes a baseband signal and upconverts and amplifies the baseband signal for transmission of thedownstream uplinks135 with theantenna110. The receiver downconverts and tunes theupstream downlinks140 along with other processing as explained below. TheSMTS310 processes signals to allow the subscriber terminals to request and receive information and schedules bandwidth for the forward and returnchannels800,900. Additionally, theSMTS310 provides configuration information and receives status from thesubscriber terminals130. Any requested or returned information is forwarded via therouter325.
• With reference toFIG. 11, an embodiment ofgateway receiver1100 is shown. This embodiment of thereceiver1100 processes fourreturn channels900 from four different service spot beams205. Thereturn channels900 may be divided among four pathways using antenna polarization and/orfiltering1104. Each return channel is coupled to a low-noise amplifier (LNA)1108. Downconversion1112 mixes down the signal into its intermediate frequency. Each of theupstream sub-channels912 is separated from the signal by a number oftuners1116. Further processing is performed in theSMTS310.
• Referring next toFIG. 10, an embodiment of agateway transmitter1000 is shown. Thedownstream channels800 are received at their intermediate frequencies from theSMTS310. With separate pathways, eachdownstream channel800 is up-converted1004 using two different carrier frequencies. Apower amplifier1008 increases the amplitude of theforward channel900 before coupling to theantenna110. Theantenna110 polarizes the separate signals to keep the fourforward channels800 distinct as they are passed to thesatellite105.
• With reference toFIG. 4, an embodiment of aSMTS310 is shown in block diagram form. Baseband processing is done for the inbound andoutbound links135,140 by a number of geographically separatedgateways115. EachSMTS310 is generally divided into two sections, specifically, thedownstream portion305 to send information to thesatellite105 and theupstream portion315 to receive information from thesatellite105.
• Thedownstream portion305 takes information from the switchingfabric416 through a number of downstream (DS)blades412. TheDS blades412 are divided among a number ofdownstream generators408. This embodiment includes fourdownstream generators408, with one for each of thedownstream channels800. For example, this embodiment uses four separate 500 MHz spectrum ranges having different frequencies and/or polarizations. A four-color modulator436 has a modulator for eachrespective DS generator408. The modulated signals are coupled to thetransmitter portion1000 of thetransceiver305 at an intermediate frequency. Each of the fourdownstream generators408 in this embodiment has Jvirtual DS blades412.
• Theupstream portion315 of theSMTS310 receives and processes information from thesatellite105 in the baseband intermediate frequency. After thereceiver portion1100 of thetransceiver305 produces all the sub-channels912 for the four separate baseband upstream signals, each sub-channel912 is coupled to adifferent demodulator428. Some embodiments could include a switch before thedemodulators428 to allow anyreturn link sub-channel912 to go to anydemodulator428 to allow dynamic reassignment between the four return channels908. A number of demodulators are dedicated to an upstream (US)blade424.
• TheUS blades424 serve to recover the information received from thesatellite105 before providing it to the switchingfabric416. TheUS scheduler430 on eachUS blade424 serves to schedule use of thereturn channel900 for eachsubscriber terminal130. Future needs for thesubscriber terminals130 of aparticular return channel900 can be assessed and bandwidth/latency adjusted accordingly in cooperation with the Resource Manager and Load Balancer (RM/LB) block420.
• The RM/LB block420 assigns traffic among the US and DS blades. By communication with other RM/LB blocks420 inother SMTSes310, each RM/LB block420 can reassignsubscriber terminals130 andchannels800,900 toother gateways115. This reassignment can take place for any number of reasons, for example, lack of resources and/or loading concerns. In this embodiment, the decisions are done in a distributed fashion among the RM/LB blocks420, but other embodiments could have decisions made by one master MR/LB block or at some other central decision-making authority. Reassignment ofsubscriber terminals130 could use overlapping service spot beams205, for example.
• Referring next toFIG. 5, an embodiment of asatellite105 is shown in block diagram form. Thesatellite105 in this embodiment communicates with fifteengateways115 and allSTs130 using sixty feeder and service spot beams225,205. Other embodiments could use more or less gateways/spot beams.Buss power512 is supplied using a power source such as chemical fuel, nuclear fuel and/or solar energy. A satellite controller516 is used to maintain attitude and otherwise control thesatellite105. Software updates to thesatellite105 can be uploaded from thegateway115 and performed by the satellite controller516.
• Information passes in two directions through thesatellite105. Adownstream translator508 receives information from the fifteengateways115 for relay tosubscriber terminals130 using sixty service spot beams205. Anupstream translator504 receives information from thesubscriber terminals130 occupying the sixty spot beam areas and relays that information to the fifteengateways115. This embodiment of the satellite can switch carrier frequencies in the downstream orupstream processors508,504 in a “bent-pipe” configuration, but other embodiments could do baseband switching between the various forward and returnchannels800,900. The frequencies and polarization for eachspot beam225,205 could be programmable or preconfigured.
• With reference toFIG. 6A, an embodiment of anupstream translator504 is shown in block diagram form. A Receiver and Downconverter (Rx/DC) block616 receives all the return link information for the area defined by aspot beam205 as an analog signal before conversion to an intermediate frequency (IF). There is a Rx/DC block616 for each servicespot beam area205. An IFswitch612 routes a particular baseband signal from a Rx/DC block616 to a particular upstream downlink channel. The upstream downlink channel is filled using an Upconverter and Traveling Wave Tube Amplifier (UC/TWTA) block620. The frequency and/or polarization can be changed through this process such that each upstream channel passes through thesatellite105 in a bent pipe fashion.
• Eachgateway115 has four dedicated UC/TWTA blocks620 in theupstream translator504. Two of the four dedicated UC/TWTA blocks620 operate at a first frequency range and two operate at a second frequency range in this embodiment. Additionally, two use right-hand polarization and two use left-hand polarization. Between the two polarizations and two frequencies, thesatellite105 can communicate with eachgateway115 with four separate upstream downlink channels.
• Referring next toFIG. 6B, an embodiment of adownstream translator508 is shown as a block diagram. Eachgateway115 has four downstream uplink channels to thesatellite105 by use of two frequency ranges and two polarizations. A Rx/DC block636 takes the analog signal and converts the signal to an intermediate frequency. There is a Rx/DC block636 for all sixty downstream uplink channels from the fifteengateways115. TheIF switch612 connects aparticular channel800 from agateway115 to a particularservice spot beam205. Each IF signal from the switch628 is modulated and amplified with a UC/TWTA block632. An antenna broadcasts the signal using a spot beam tosubscriber terminals130 that occupy the area of the spot beam. Just as with theupstream translator504, thedownstream translator508 can change carrier frequency and polarization of a particular downstream channel in a bent-pipe fashion.
• FIG. 7 comprises a block diagram illustrating a set ofsubscriber equipment700 which may be located at a subscriber location for the reception and transmission of communication signals. Components of this set ofsubscriber equipment700 may, for example, comprise theantenna125, associatedsubscriber terminal130 and any consumer premises equipment (CPE)160, which may be a computer, a network, etc.
• Anantenna125 may receive signals from asatellite105. Theantenna125 may comprise a VSAT antenna, or any of a variety other antenna types (e.g., other parabolic antennas, microstrip antennas, or helical antennas). In some embodiments, theantenna125 may be configured to dynamically modify its configuration to better receive signals at certain frequency ranges or from certain locations. From theantenna125, the signals are forwarded (perhaps after some form of processing) to thesubscriber terminal130. Thesubscriber terminal130 may include a radio frequency (RF)frontend705, a controller715, avirtual channel filter702, amodulator725, ademodulator710, afilter706, adownstream protocol converter718, anupstream protocol converter722, a receive (Rx)buffer712, and a transmit (Tx)buffer716.
• In this embodiment, theRF frontend705 has both transmit and receive functions. The receive function includes amplification of the received signals (e.g., with a low noise amplifier (LNA)). This amplified signal is then downconverted (e.g., using a mixer to combine it with a signal from a local oscillator (LO)). This downconverted signal may be amplified again with theRF frontend705, before processing of thesuperframe804 with thevirtual channel filter702. A subset of eachsuperframe804 is culled from thedownstream channel800 by thevirtual channel filter702, for example, one or morevirtual channels808 are filtered off for further processing.
• A variety of modulation and coding techniques may be used at thesubscriber terminal130 for signals received from and transmitted to a satellite. In this embodiment, modulation techniques include BPSK, QPSK, 8PSK, 16APSK, 32PSK. In other embodiments, additional modulation techniques may include ASK, FSK, MFSK, and QAM, as well as a variety of analog techniques. Thedemodulator710 may demodulate the down-converted signals, forwarding the demodulatedvirtual channel808 to afilter706 to strip out the data intended for theparticular subscriber terminal130 from other information in thevirtual channel808.
• Once the information destined for theparticular subscriber terminal130 is isolated, adownstream protocol converter718 translates the protocol used for the satellite link into one that the DOCSIS MAC block726 uses. Alternative embodiments could use a WiMAX MAC block or a combination DOCSIS/WiMAX block. ARx buffer712 is used to convert the high-speed received burst into a lower-speed stream that the DOCSIS MAC block726 can process. The DOCSIS MAC block726 is a circuit that receives a DOCSIS stream and manages it for theCPE160. Tasks such as provisioning, bandwidth management, access control, quality of service, etc. are managed by theDOCSIS MAC block726. The CPE can often interface with the DOCSIS MAC block726 using Ethernet, WiFi, USB and/or other standard interfaces. In some embodiments, aWiMax block726 could be used instead of a DOCSIS MAC block726 to allow use of the WiMax protocol.
• It is also worth noting that while adownstream protocol converter718 andupstream protocol converter722 may be used to convert received packets to DOCSIS or WiMax compatible frames for processing by aMAC block726, these converters will not be necessary in many embodiments. For example, in embodiments where DOCSIS or WiMax based components are not used, the protocol used for the satellite link may also be compatible with the MAC block726 without such conversions, and theconverters718,722 may therefore be excluded.
• Various functions of thesubscriber terminal130 are managed by the controller715. The controller715 may oversee a variety of decoding, interleaving, decryption, and unscrambling techniques, as known in the art. The controller may also manage the functions applicable to the signals and exchange of processed data with one ormore CPEs160. TheCPE160 may comprise one or more user terminals, such as personal computers, laptops, or any other computing devices as known in the art.
• The controller715, along with the other components of thesubscriber terminal130, may be implemented in one or more Application Specific Integrated Circuits (ASICs), or a general purpose processor adapted to perform the applicable functions. Alternatively, the functions of thesubscriber terminal130 may be performed by one or more other processing units (or cores), on one or more integrated circuits. In other embodiments, other types of integrated circuits may be used (e.g., Structured/Platform ASICs, Field Programmable Gate Arrays (FPGAs) and other Semi-Custom ICs), which may be programmed in any manner known in the art. The controller may be programmed to access memory unit (not shown). It may fetch instructions and other data from the memory unit, or write data to the memory-unit.
• As noted above, data may also be transmitted from theCPE160 through thesubscriber terminal130 and up to asatellite105 in various communication signals. TheCPE160, therefore, may transmit data to DOCSIS MAC block726 for conversion to the DOCSIS protocol before that protocol is translated with anupstream protocol converter722. The slow-rate data waits in theTx buffer716 until it is burst over the satellite link.
• The processed data is then transmitted from theTx buffer716 to themodulator725, where it is modulated using one of the techniques described above. In some embodiments, adaptive or variable coding and modulation techniques may be used in these transmissions. Specifically, different modulation and coding combinations, or “modcodes,” may be used for different packets, depending on the signal quality metrics from theantenna125 to thesatellite105. Other factors, such as network and satellite congestion issues, may be factored into the determination, as well. Signal quality information may be received from the satellite or other sources, and various decisions regarding modcode applicability may be made locally at the controller, or remotely. The RF frontend705 may then amplify and upconvert the modulated signals for transmission through theantenna125 to the satellite.
Satellite Architecture
• According to an embodiment of the invention, a novel architecture is presented for establishing a multi-beam satellite communication system having both forward links and return links connecting gateways and subscriber terminals. Such a multi-beam satellite communication system is illustrated in the figures. For example, referring toFIGS. 1A and 1B, agateway115 sends a forward link signal to one or more subscriber terminals130-athrough130-nviasatellite105. Here, a forward link refers to signals sent from a gateway to one or more subscriber terminals. Such gateway-to-subscriber signals are also sometimes referred to as downstream signals. In the reverse direction, the one or more subscriber terminals130-athrough130-nsend one or more return link signals togateway115. Such subscriber-to-gateway signals are also sometimes referred to as upstream signals.
• One of the many uses of the systems such as that shown inFIGS. 1A and 1B may be to provide network access (e.g., Internet access) to the subscriber terminals. For example, a subscriber terminal130-amay request a web page on the Internet by sending a network request using a return link (upstream) signal (145-a,140) togateway115 viasatellite105.Gateway115 responds by retrieving the requested web page fromnetwork120, which may directly or indirectly connected to the Internet.Gateway115 then sends the requested web page using a forward link (downstream) signal (135,150) to subscriber terminal130-aviasatellite105, thus completing the web page request and response. Different layers of networking protocol operations may be implemented in the process, as is known to one of ordinary skill in the art.
• According to the present embodiment of the invention,satellite105 comprises a bent pipe repeater that is capable of receiving one or more signals from Earth and transmitting the signals back toward Earth, possibly after frequency translation and polarization modification. For example, each signal received atsatellite105 at a particular frequency and polarization may be transmitted out ofsatellite105 at a different frequency and/or polarization. The bent pipe repeater may also provide switching operations, such that different “feeder signals” (i.e., signals sent to and from gateways) may be switched to be connected to different “service signals” (i.e., signals sent to and from subscriber terminals). The bent pipe repeater does not demodulate signals received at the satellite into data such as bits and re-modulate the data for transmission. This is in contrast to processing repeaters, which are capable of performing such demodulation and re-modulation to achieve gains in error correction performance. Even though processing repeaters are commercially available, a bent pipe repeater is adopted to achieve optimal efficiency in forward link and return link communications in accordance with the present embodiment of the invention.
• Referring toFIG. 6B, satellite components for handling forward links in the downstream direction from gateways to subscriber terminals may be implemented as shown in accordance with one embodiment of the invention. Here, 15 gateways together send 60 forward link signals to the satellite. Specifically, each gateway sends an uplink feeder beam comprising 4 different forward link signals utilizing an antenna. Each of the 4 forward link signals is transmitted using a different combination of frequency band and polarization. Each unique combination is referred to as a specific “color,” as discussed previously. Each forward link signal is received at the satellite at a particular receiver module636. Each receiver module636 may include a receiver such as a low noise amplifier (LNA) followed by a downconverter (DC) that converts the forward link signal to a convenient frequency, such as an intermediate frequency (IF).
• According to an embodiment of the invention, each forward link signal is a broadband signal. Here, the term “broadband” is used in the context of satellite communications and specifically refers to a signal having a bandwidth of at least 250 MHz. For example, in the present embodiment, each forward link signal is a broadband signal and has a bandwidth of 500 MHz.
• Each forward link signal is then connected through a switch628 to an appropriate transmit module632. Transmit module may include an upconverter (UC) that up-converts the IF forward link signal to a frequency suitable for transmission, followed by a satellite-based transmission amplifier. According to an embodiment of the invention, the satellite-based transmission amplifier may be a traveling wave tube amplifier (TWTA), which efficiently amplifies the signal as a single-carrier signal. Here, each satellite-based transmission amplifier is employed to amplify only one single-carrier signal, which allows the amplifier to be operated more efficiently. This design allows highly efficient use of the satellite-based transmission amplifiers.
• Thus, each satellite-based transmission amplifier produces an amplified single-carrier signal that may then be transmitted out using an antenna to form a spot beam that reaches Earth. The spot beam thus has an earth surface coverage area. Subscriber terminals that are within this particular earth surface coverage area would be able to receive the forward link signal. Here, each spot beam is formed by the output of a single satellite-based transmission amplifier. In other words, there is no need to combined the outputs of multiple transmission amplifiers to form each spot beam. This precludes power losses and allows the satellite-based transmission amplifiers to be operated even more efficiently.
• The novel use of a single carrier signal per satellite-based transmission amplifier and a single satellite-based transmission amplifier per spot beam aboard a bent-pipe repeater optimizes the ratio of data capacity to power consumption at the satellite, to obtain significant improvements in performance from satellite equipment.
Frequency Re-Use for Service and Gateway Beams
• According to an embodiment of the invention, a satellite system is presented that adopts multiple levels of frequency re-use to maximize usage of available frequency bandwidth. In addition to employing frequency re-use amongst multiple service beams such that different service beams may occupy a common frequency channel, the system further employs frequency re-use between service beams and feeder beams by locating gateways in regions separated from coverage areas of service beams. In addition, frequency re-use may also be employed amongst multiple feeder beams to allow further gains in spectral efficiency. Such multiple levels of frequency re-use is explained in more detail in an illustrative system as discussed below.
• Referring to the example systems depicted inFIGS. 6A and 6B, a star network includes 15 independent feeder beams to support 60 service beams. Thus, each feeder beam corresponds to four service beams. Here, this ratio is maintained in both the uplink and downlink direction. In the forward direction, every uplink feeder beam is relayed by the satellite to generate four downlink service beams. In the return direction, every four uplink service beams are relayed by the satellite to generate one downlink feeder beam. Thus, the star network can be viewed as having 15 groups of signals, each group containing one uplink feeder beam, one downlink feeder beam, four uplink service beams, and four downlink service beams.
• FIG. 14 presents an illustrative frequencyre-use plan400 that may be adopted in accordance with one embodiment of the invention.FIG. 14 shows the re-use of frequencies for just 1 of the 15 groups of signals discussed above. However, according to a preferred embodiment of the invention, the samefrequency re-use plan400 can be applied to each of the groups of signals. The particular values shown inFIG. 14, such as the specific frequency channels, are chosen as illustrative examples. Other values may be used within the scope of the present invention.
• First, anuplink feeder beam4002 comprising 4 carriers is shown as being sent from a gateway terminal to the satellite, by utilizing 4 different combinations of frequency and polarization (4 “colors”) as described previously. Here, these 4 colors are formed using two different 500 MHz uplink frequency channels, 27.5 GHz-28 GHz and 29.5 GHz-30 GHz, along with two different polarizations, right hand circular polarization (RHCP) and left hand circular polarization (LHCP).
• Next, fourdownlink service beams4004 are shown as being sent from the satellite to subscriber terminals. There are 4 colors shown, formed using two different 500 MHz downlink frequency channels, 17.7 GHz-18.2 GHz and 19.7 GHz-20.2 GHz, along with two different polarizations RHCP and LHCP. Here, because the four downlink service beams possess spatial diversity amongst themselves, which facilitates frequency re-use, different options exist for how the 4 colors may be used. In one implementation, all four colors are used, each for a different downlink service beam. In another implementation, only two of the colors are used for the four downlink service beams. For example, the two colors representing (1) 17.7 GHz-18.2 GHz with LHCP and (2) 17.7 GHz-18.2 GHz with RHCP may be used to transmit all four downlink service beams. Thus, the downlink service beams may be transmitted using the same 500 MHz bandwidth, but with alternating polarizations (LHCP and RHCP) assigned to physically adjacent downlink service beams, to allow closely spaced beams to be distinguished from one another. Other variations are possible and are within the scope of the present invention.
• Next, fouruplink service beams4006 are shown as being sent from subscriber terminals to the satellite. Here, the same 4 colors used to transmituplink feeder beam4002 may be re-used to transmit the four uplink service beams4008. Specifically, these 4 colors are formed using two different 500 MHz uplink frequency channels, 27.5 GHz-28 GHz and 29.5 GHz-30 GHz, along with two different polarizations, RHCP and LHCP. This is possible because the gateway sendinguplink feeder beam4002 is positioned at a different location on Earth than the subscriber terminals sending uplink service beams4006. Directional antennas on the satellite are therefore able to separately receiveuplink feeder beam4002 anduplink service beam4008, even though they may be transmitted using the same uplink frequencies and polarizations. In addition, because the four uplink service beams possess spatial diversity amongst themselves, which facilitates frequency re-use, different options exist for how these 4 colors may be used to transmit uplink service beams4006. For example, all 4 colors may be used, or just 2 colors may be used, or some variation may be adopted. The situation is similar to that discussed above with respect to the four downlink service beams4004.
• Finally, adownlink feeder beam4008 comprising 4 carriers is shown as being sent from the satellite to the gateway terminal. Here, the same 4 colors used to transmitdownlink service beams4004 may be re-used to transmit thedownlink feeder beam4008. Specifically, these 4 colors are formed using two different 500 MHz downlink frequency channels, 17.7 GHz-18.2 GHz and 19.7 GHz-20.2 GHz, along with two different polarizations RHCP and LHCP. This is possible because the gateway receivingdownlink feeder beam4008 is positioned at a different location on Earth than the subscriber terminals receiving downlink service beams4004. That is, the gateway is located in the feeder beam coverage area wheredownlink feeder beam4008 can be received. Separately, the subscriber terminals are located the service beam coverage areas wheredownlink service beams4004 can be received. As such,downlink feeder beam4008 anddownlink service beams4004 can re-use the same downlink frequencies and polarizations, yet still be separately received by the intended recipients.
• As mentioned previously, the samefrequency re-use plan400 may be applied to each of the 15 groups of signals. That is, the entire system comprising 15 uplink feeder beams, 60 downlink service beams, 60 uplink service beams, and 15 downlink feeder beams may simultaneously adopt the samefrequency re-use plan400. This is achieved by capitalizing on spatial diversity that may exist amongst the 60 service beam coverage areas, positioning the 15 feeder beam coverage areas sufficiently far away from the 60 service beam coverage areas, and positioning the 15 feeder beam coverage areas sufficiently far apart from one another. Accordingly, three different levels of frequency re-use are realized. First, frequency re-use is achieved amongst service beams. Second, frequency re-use is achieved between service beams and feeder beams. Third, frequency re-use is achieved amongst feeder beams.
Placement of Gateways Away From Service Beams
• According to an embodiment of the invention, a satellite system is presented having efficient placement of gateway terminals. As discussed previously, spatial diversity between gateways and subscriber terminals facilitates frequency re-use of between service beams and feeder beams. Also, spatial diversity amongst gateways facilitates frequency re-use amongst feeder beams. Placement of the gateways may take into account these and other considerations.
• In one embodiment, the plurality of different service beam coverage areas (e.g., 60 service beam coverage areas) may be designed to only provide strategically chosen partial coverage over a coverage region. Generally speaking, typical satellite systems that provide communications over a geographic region attempt to achieve full coverage such that service is available over the entire region. However, in accordance with the present embodiment of the invention, a satellite system may be designed to only provide strategically chosen partial coverage over a particular region. For example, the coverage region may comprise a region including the western, eastern, and southern portions of the United States. The specific coverage areas supported by the service beams may be chosen in different ways. For example, the coverage areas may correspond to “underserved” locations, where there may exist significant populations but where high bandwidth network access is not yet readily available.
• According to an embodiment of the present invention, the one or more gateways are placed away from the coverage areas of the service beams, to facilitate frequency re-use between service beams and feeder beams. In the example system discussed earlier, suppose the 60 uplink and downlink service beams have coverage areas in a region that spans the western, eastern, and southern portions of the United States. Then the 15 gateways may be located in a region, such as the middle portion of the United States, away from the coverage region of the service beams.
• In addition, a plurality of gateways (e.g., 15 gateways) may need to be located sufficiently far apart from each other such that frequency re-use may be further adopted amongst different feeder beams. For instance, each gateway may need to be placed such that has a minimum distance of 400 kilometers from any neighboring gateway. Thus, neighboring gateways may use the same frequency channels without interfering with one another.
• A further possible constraint on the placement of the gateways relates to physical proximity to higher bandwidth network access. For example, gateways may be located near optical fiber network connections. This allows the gateways to have fast and robust network access such that data communications requiring access to networks is not hindered. According to one embodiment of the invention, in addition to other requirements, each gateway is placed within a distance of 50 kilometers from an optical fiber network connection.
• Yet another possible constraint on the placement of the gateways relates to area weather patterns. Gateways may need to be located in areas that experience minimal rain fade. Just as an example, each gateway may be required to be placed at a location where overall rain fade at the uplink frequency is less 10 dB of fading for 99.99% of the time. This further constrains the selection of possible locations for gateway terminals.
• Thus, in accordance with an embodiment of the present invention, the placement of the gateways may take into account multiple factors such as those described above. While meeting such multiple constraints can make the placement of gateways significantly more challenging, a system that adopts these constraints is likely to achieve superior overall performance.
Piggy-Back Satellite Payload
• According to one embodiment, a portion of the total bus power aboard a communications satellite is used to support a version of the satellite communication system of the present invention. Referred to as a “piggy back” mode, this technique allows either an entire satellite communication system as described above, or a portion thereof, to be supported by a satellite that also carries other communications payload. For example, if a particular satellite has an available total bus power of 15 kilowatts (KW), and the satellite already has an existing payload that consumes 13 KW of bus power, there may remain 2 KW of excess bus power aboard the satellite. According to one embodiment of the invention, a satellite system as describe above, or a portion thereof, may be implemented by using the remaining 2 KW of bus power. Thus, an example system of 8 service beams and 2 corresponding feeder beams in the forward and return link directions may be deployed using theexcess 2 KW of bus power aboard the communication satellite described above.
• The added payload may constitute an independent satellite communication system. Alternatively, the added payload may constitute a fraction of a satellite system. For example, a full satellite system may employ 60 service beams and 15 corresponding feeder beams in the forward link and the return link direction, as discussed previously. A fraction of such a system may correspond to the 8 service beams and 2 corresponding feeder beams in the forward and return link directions discussed above. The features of the full satellite system may be substantially represented in the fractional system.
• The added payload may adopt a structure similar to that of an independent satellite architecture as described in embodiments discussed previously. For example, in the forward link direction, each feeder beam sent from a gateway to the satellite may comprise 4 signals (represented by four “colors,” for instance) that produce 4 separate single-carrier signals sent from the satellite as separate service spot beams to reach subscriber terminals. Other satellite architecture features may similarly be adopted for use in a system implemented as an added payload.
• Different implementations are possible. One implementation is briefly described below for illustrative purposes. Here, the added payload comprises a Ka package that can be added to an existing satellite procurement. Such a system may at a very high level enable trade-offs in design that minimize the impact of the package on the physical design and layout, weight, and power on the overall satellite design. An example market for this added payload may be the consumer broadband market. The package may be capable of 10 spot beams each of which is approximately 0.35 degrees Half Power Beam Width (HPBW) on transmit and receive. TWTA redundancy should be consistent with orbital life. The system may have four color re-use with 2 of the 10 spot beams for feeder links. The Effective Isotropic Radiated Power (EIRP) of the package may be 70 dBW per spot beam and the G/T may be 27 dB/° K per spot beam. The individual transponders may be wide band on the order of 500 MHz. Polarization may be circular and alternate spots may use alternately Left and Right Hand polarization. The input SFD may be settable from −105 to −85 dB in one dB steps.
• According to the invention, differently sized payloads may be thus added through use of “piggy back” mode to allow efficient use of excess bus power aboard satellites. Specific parameters such as the number of spot beams implemented may be varied according to the needs of the system.
Adaptive Use of Satellite Uplink Bands
• According to an embodiment of the invention, adaptive use of satellite uplink bands is employed. One example implementation of such a technique allows flexible use of frequency channels by a subscriber terminal that is a secondary spectrum license holder. The right of a secondary spectrum license holder to transmit on a specified frequency band is secondary to that of a primary spectrum license holder. That is, the primary spectrum license holder may be able to transmit signals on the frequency band whenever it chooses, without regard for other users. By contrast, a secondary spectrum license holder may only be allowed to transmit on the specified frequency band if the primary spectrum license hold is not transmitting on the specified band. Adaptive use of satellite uplink bands as described in various embodiments of the present invention may be utilized by a subscriber terminal which is a secondary spectrum holder, to ensure that when another signal, e.g., the primary license holder's signal, is detected, re-assignment of the transmit frequency channel can be performed to move satellite uplink transmission to a different frequency as to not interfere with the primary spectrum license holder.
• FIG. 15 presents an illustrative system employing adaptive use of satellite uplink bands in accordance with one embodiment of the invention. Here, acentral unit121 controls the assignment of transmit frequency channels and receive frequency channels used by subscriber terminals such as130-a-1 and130-a-2.Central unit121 may be coupled to agateway115 throughnetwork120.Central unit121 may thus be connected to other gateways as well, in order to control a larger satellite system. In an alternative embodiment,central unit121 may be contained in a gateway such asgateway115.
• Central unit121 assigns to subscriber terminal130-a-1 a transmit frequency channel in which to transmit satellite uplink signals145-a-1, as well a receive frequency channel in which to receive satellite downlink signals150. Similarly,central unit121 assigns to subscriber terminal130-a-2 a transmit frequency channel in which to transmit satellite uplink signals145-a-2, as well as a receive frequency channel in which to receive satellite downlink signals150. According to an embodiment of the invention,central unit121 may employ an adoptive scheme to assign transmit frequency channels to one or more subscriber terminals, based on local observations of the transmit frequency spectrum made by the subscriber terminals and reported back to thecentral unit121, as discussed below.
• Subscriber terminal130-a-1's transmission of satellite uplink signals145-a-1 in the assigned transmit frequency channel may be intermittent in nature. For example, the uplink signals may carry web page requests that only require short bursts of data. Thus, the satellite uplink signals may be sent during time-separated periods of transmission. That is, each period of transmission may be limited in duration. The periods of transmission may be separated by time in which no transmission is sent from subscriber terminal130-a-1.
• Subscriber terminal130-a-1 may monitor the assigned transmit frequency channel between these time-separated periods of transmission of satellite uplink signals. That is, when subscriber terminal130-a-1 is not transmitting, it can monitor the assigned transmit frequency channel for possible presence of other signals from outside sources. There may be different types of such outside sources, such as a Land Mobile Data Services (LMDS)user127. One context in which such a scenario could arise is whencentral unit121 assigns a transmit frequency channel that utilizes bandwidth in which theLMDS user127 is the primary spectrum license holder, and subscriber terminal130-a-1 is a secondary spectrum license holder. As such, subscriber terminal130-a-1 may not use the assigned transmit frequency channel if theLMDS user127 is using the channel.
• In addition to monitoring the assigned transmit frequency channel, subscriber terminal130-a-1 may also monitor at least one out-of-band frequency channel different from the assigned transmit frequency channel. For example, subscriber terminal130-a-1 may also monitor one or more neighboring frequency channels. The neighboring frequency channels may include a number of channels in the vicinity of the assigned transmit frequency channel. These may include channels that are immediately adjacent to the currently assigned transmit frequency channel, as well as other channels. Monitoring of out-of-band frequency channels facilitates detection of other signals, such assignal128, over a wider range of frequencies. This information allows a more complete picture to be formed regarding the spectrum that can potentially be used by subscriber terminal130-a-1 for signal transmission.
• In one embodiment, subscriber terminal130-a-1 transmits and receives satellite signals using a first antenna125-a-1, and performs monitoring of frequency channels using a second antenna126-a-1. Here, this dual antenna arrangement allows for easier implementation. The first antenna125-a-1 may be a parabolic reflective antenna pointed towardsatellite150. Thus, the first antenna is suited for transmitting and receiving satellite signals. The second antenna126-a-2 may be a dipole antenna designed for terrestrial signals. The second antenna may be well suited for detecting terrestrial signals that travel in the direction along the horizon, such as asignal128 sent fromLMDS user127. This is merely one example arrangement. Variations may be implemented within the scope of the invention.
• When a signal such assignal128 from theLMDS user127 is detected, subscriber terminal130-a-1 notifiescentral unit121. This may be done using an observation result reported back tocentral unit121. The observation result may be generated in different ways. As one example, subscriber terminal130-a-1 may generate observation result automatically on a periodic basis. As another example,central unit121 may request observation results from subscriber terminal130-a-1 at appropriate times. Also, an observation result may be reported in different formats, depending on implementation. The format may a Boolean value, a numeric value, etc. In one implementation, an observation result is sent regardless of whether presence of another signal is detected. In an alternative implementation, an observation result is only sent if presence of another signal is detected.
• In response,central unit121 may re-assign subscriber terminal130-a-1 to a different transmit frequency channel, in order to avoid interfering with the source of the detected signal. In this case, the frequency re-assignment serves to prevent interference withsignal128 sent byLMDS user127, which may be the primary spectrum license holder.Central unit121 may determine the new transmit frequency channel for subscriber terminal130-a-1 in different ways. In certain embodiments, the determination is a simple one that does not take into consideration monitoring performed at other subscriber terminals. For example, there may be a default frequency channel that is assigned.
• In other embodiments, the determination does take into account monitoring performed at other subscriber terminals. Some or all of the subscriber terminals may perform frequency channel monitoring and report observation results back tocentral unit121.Central unit121 may then decide on an overall frequency assignment that considers the needs of a plurality of subscriber terminals. Thus, the determination of a newly assigned transmit frequency channel for each subscriber terminal may be made as part of the overall frequency assignment. A simple example is described below for illustrative purposes.
• Suppose subscriber terminal130-a-1 is currently assigned to transmit satellite uplink signals on frequency channel X and reports that it observes that frequency channel X and most other frequency channels are being used by other signals (such assignal128 from an LMDS user), and that only one particular frequency channel Y appears to be unused by other signals. Further suppose that subscriber terminal130-a-2 is currently assigned to transmit satellite uplink signals on frequency channel Y and reports that it observes that frequency channel Y and most other frequency channels are not being used by other signals. In response,central unit121 may determine that the best overall frequency assignment would involve re-assigning subscriber terminal130-a-2 to a transmit frequency channel other than Y, so that channel Y can be assigned to subscriber terminals130-a-1. For instance, subscriber terminal130-a-2 may be re-assigned to frequency channel X, and subscriber terminal130-a-1 may be re-assigned to frequency channel Y. This allows both subscriber terminals to operate without interfering with other signals that may represent primary spectrum license holders, by taking into account the observations made at both subscriber terminals to arrive at a joint frequency plan for the subscriber terminals. Of course, this is only a simple example involving two subscriber terminals. Frequency assignments involving more subscriber terminals are within the scope of the present invention.
• It should be noted that the systems, methods, and software discussed above are intended merely to be exemplary in nature. It must be stressed that various embodiments may omit, substitute, or add various procedures or components as appropriate. For instance, it should be appreciated that in alternative embodiments, the methods may be performed in an order different than that described, and that various steps may be added, omitted or combined. Also, features described with respect to certain embodiments may be combined in various other embodiments. Different aspects and elements of the embodiments may be combined in a similar manner. Also, it should be emphasized that technology evolves and, thus, many of the elements are exemplary in nature and should not be interpreted to limit the scope of the invention.
• Specific details are given in the description to provide a thorough understanding of the embodiments. However, it will be understood by one of ordinary skill in the art that the embodiments may be practiced without these specific details. For example, well-known circuits, processes, algorithms, structures, and techniques have been shown without unnecessary detail in order to avoid obscuring the embodiments.
• Also, it is noted that the embodiments may be described as a process which is depicted as a flow chart, a structure diagram, or a block diagram. Although they may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be re-arranged. A process is terminated when its operations are completed, but could have additional steps not included in the figure.
• Moreover, as disclosed herein, the terms “storage medium” or “storage device” may represent one or more devices for storing data, including read only memory (ROM), random access memory (RAM), magnetic RAM, core memory, magnetic disk storage mediums, optical storage mediums, flash memory devices or other computer readable mediums for storing information. The term “computer-readable medium” includes, but is not limited to, portable or fixed storage devices, optical storage devices, wireless channels, a sim card, other smart cards, and various other mediums capable of storing, containing or carrying instructions or data.
• Furthermore, embodiments may be implemented by hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. When implemented in software, firmware, middleware or microcode, the program code or code segments to perform the necessary tasks may be stored in a machine readable medium such as a storage medium. Processors may perform the necessary tasks.
• Having described several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. For example, the above elements may merely be a component of a larger system, wherein other rules may take precedence over or otherwise modify the application of the invention. Also, a number of steps may be required before the above elements are considered. Accordingly, the above description should not be taken as limiting the scope of the invention, which is defined in the following claims.

Claims (2)

1. A method for transmitting data in a satellite system having multiple spot beams, the method comprising:

sending a broadband signal in a forward direction from a gateway terminal to a communications satellite for relay to at least one subscriber terminal;

receiving the broadband signal at the communications satellite, wherein the communications satellite comprises a bent pipe repeater having a plurality of satellite-based transmission amplifiers, each satellite-based transmission amplifier capable of performing amplification to generate a service spot beam;

amplifying the broadband signal using one of the plurality of satellite-based transmission amplifiers to produce an amplified broadband signal, wherein the one of the plurality of satellite-based transmission amplifiers is employed to amplify only the broadband signal and no other broadband signal from the gateway terminal;

sending the amplified broadband signal to the at least one subscriber terminal, the amplified broadband signal being sent as one of a plurality of service spot beams, the one of the plurality of service spot beams having an earth surface coverage area including the at least one subscriber terminal, wherein the amplified broadband signal alone occupies the one of the plurality of service spot beams; and

receiving and retrieving data from the amplified broadband signal at the at least one subscriber terminal.

2-19. (canceled)

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