Patent Application
20130069820
The present invention relates in general to communication systems and in particular to systems and methods for satellite-based communication.
Satellite communication systems provide various benefits to consumers of communication services such as for telephony, internet communications, television communications among others. Various satellite systems are currently available, which are discussed below.
Satellites employing a geostationary (GEO) orbit provide the convenience of having one or more satellites in such a system remain fixed in relation to the earth as the earth rotates. However, at the GEO orbit altitude, which is about 36,000 kilometers (km), communication latency is about 600 milliseconds (ms). Such latency leads to very slow communication throughput and is particularly ineffective for Internet communication. For example, the main page at “www.cnn.com”® might take up to 24 seconds to load with this latency period in effect.
For this reason, and others, satellites employing non-geostationary orbits (NGSOs), such as medium earth orbit (MEO), (between 2000 and 36000 km) and low earth orbit (LEO) (below 2000 km), have in certain cases, been used instead. The existing LEO and MEO satellite systems typically employ inclined orbits to enable such systems to reach high concentrations of customers located in the northern and southern hemispheres. In such orbits, the satellites move continuously with respect to various ground stations with which satellites communicate. Moreover, successive satellites in such constellations commonly move along different orbital planes. Thus, many such systems employ omni-directional antennas at earth-based user terminals to enable ongoing communication to take place as the various satellites in a constellation move through their respective orbits. However, such omni-directional antennas tend to have very low gain, thereby limiting the communication throughput (communication bandwidth) achievable using this approach. One way to compensate for the low gain level of the antennas at the user terminal is to significantly increase the power used for satellite antenna transmission. However, such increased satellite transmission power levels may exceed the power available using current satellite power generation technology, and are therefore impractical.
Additionally, satellites traveling in NGSO orbits may cause interference between one or more entities within a GEO satellite communication system. Accordingly, transmission activity by NGSO satellites is commonly interrupted when NGSO satellites get too close to a communication path between a GEO satellite and a ground station in communication with the GEO satellite. Such interruptions may impose significant inconvenience and expense on the operation of NGSO satellite systems.
Accordingly, there is a need in the art for satellite communication systems providing effective communication service at a reduced cost and which avoid interfering with existing satellite systems.
According to one aspect, the present invention is directed to a communications system that may include a constellation of satellites operating in a substantially equatorial, non-geostationary orbit around the earth, wherein at least one satellite includes a first antenna controllable to direct a first concentrated spot beam to at least one ground station; and a second antenna controllable to direct a second concentrated spot beam to at least one gateway ground station. Preferably, the at least one satellite is operable to establish a communication path between the ground station and the gateway station along the first and second spot beams. Preferably, at least one of the first antenna and the second antenna is mechanically steerable. Preferably, at least one of the first antenna and the second antenna is an electronically steerable antenna, such as a phased array antenna. Preferably, the at least one satellite is operable to avoid interference with GEO satellite communication with a GEO sub-satellite point on the earth, by communicating with ground stations on the earth having a minimum latitudinal angular separation from the GEO sub-satellite point. Preferably, the minimum latitudinal angular separation is about 5 degrees.
Preferably, the system is operable to avoid interference with GEO satellite communication with a GEO sub-satellite point on the earth, by using a satellite within the constellation of satellites having a sub-satellite point having a minimum longitudinal angular separation from the GEO sub-satellite point. Preferably, the minimum longitudinal angular separation is about 5 degrees. Preferably, a plurality of the satellites in the constellation are within a communication range of the ground station at any given time, thereby providing redundant satellite communication options for the ground station. Preferably, the ground station is operable to hand off communication from a first satellite to a second satellite in the event of a failure of the first satellite. Preferably, the constellation includes at least 16 satellites and wherein at least 3 satellites are within a communication range of the ground station at any given time. Preferably, the at least one ground station lacks a wired connection to any global communications network, and wherein the at least one gateway station has a wired connection to a global communications network.
Preferably, the global communications network includes the Internet. Preferably, the at least one satellite is operable to route data packet signals to a destination within the communications system based on a transmission frequency of the data packet signal. Preferably, the constellation of satellites operates in an orbit having an altitude between about 2,000 kilometers (km) and about 25,000 km. Preferably, the constellation of satellites operates in an orbit having an altitude between about 8,000 kilometers (km) and about 20,000 km.
According to another aspect, the invention is directed to a method that may include causing a constellation of satellites to travel along a substantially equatorial, non-geostationary orbit; controlling a first antenna aboard at least one satellite to direct a first concentrated spot beam to at least one ground station; and controlling a second antenna on the at least one satellite to direct a second concentrated spot beam to at least one gateway station. Preferably, the method further includes establishing a communication path between the ground station and the gateway station along the first and second spot beams. Preferably, the step of controlling the first antenna comprises at least one of: a) mechanically steering the first antenna to direct the first concentrated spot beam to the at least one ground station; and b) electronically steering the first concentrated spot beam.
Preferably, the step of controlling the second antenna comprises at least one of: a) mechanically steering the second antenna to direct the second concentrated spot beam to the at least one ground station; and b) electronically steering the second concentrated spot beam. Preferably, at least one of the first antenna and the second antenna is a phased array antenna. Preferably, the method further includes avoiding interference with communication between a GEO satellite and its GEO sub-satellite point on the earth, by having at least one satellite communicate only with ground stations on the earth having a minimum latitudinal angular separation from the GEO sub-satellite point.
Preferably, the minimum latitudinal angular separation is about 5 degrees. Preferably, the method further includes avoiding interference with communication between a GEO satellite and a sub-satellite point of the GEO satellite by using a satellite within the constellation of satellites, for communication with the ground station, having a sub-satellite point having a minimum longitudinal angular separation from the GEO sub-satellite point. Preferably, the minimum longitudinal angular separation is about 5 degrees.
According to another aspect, the invention is directed to a communications system that may include a constellation of satellites operating in a substantially equatorial, non-geostationary orbit; a plurality of ground stations configured to communicate with the satellites, at least one given ground station of the ground stations lacking a wired connection to any global communications network; and at least one gateway station coupled to a global communications network and to at least one satellite, wherein each satellite includes at least one antenna with a steerable beam controllable to continuously direct a first concentrated spot beam toward the given ground station. Preferably, the at least one antenna includes a mechanically steerable antenna. Preferably, the at least one antenna includes a phased array antenna. Preferably, each satellite is operable to communicate simultaneously with the given ground station, and the at least one gateway station to enable connectivity between the given ground station and the global communications network.
Preferably, the global communications network includes the Internet. Preferably, the given ground station is configured to transfer communication connectivity from a first satellite of the constellation to a succession of satellites entering a communication range of the given ground station, thereby providing substantially continuous communication connectivity of the given ground station to the global communications network. Preferably, the orbit of the satellite constellation has an altitude of between about 2,000 km and about 25,000 km. Preferably, the orbit of the satellite constellation has an altitude of between about 6,000 km and about 20,000 km. Preferably, the orbit of the satellite constellation has an altitude of between about 7,000 km and about 12,000 km.
Other aspects, features, advantages, etc. will become apparent to one skilled in the art when the description of the preferred embodiments of the invention herein is taken in conjunction with the accompanying drawings.
For the purposes of illustrating the various aspects of the invention, there are shown in the drawings forms that are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
In the following description, for purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one having ordinary skill in the art that the invention may be practiced without these specific details. In some instances, well-known features may be omitted or simplified so as not to obscure the present invention. Furthermore, reference in the specification to phrases such as “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of phrases such as “in one embodiment” or “in an embodiment” in various places in the specification do not necessarily all refer to the same embodiment.
Those skilled in the art will appreciate the fact that antennas, which may include beamformers, and/or may include equipment for communicating over optical links which communicate either with other satellites or with ground stations, are reciprocal transducers which exhibit similar properties in both transmission and reception modes. For example, the antenna patterns for both transmission and reception are generally identical and may exhibit approximately the same gain. For convenience of explanation, descriptions are often made in terms of either transmission or reception of signals, on the understanding that the pertinent description applies to the other of the two possible operations. Thus, it is to be understood that the antennas of the different embodiments described herein may pertain to either a transmission or reception mode of operation. Those of skill in the art will also appreciate the fact that the frequencies received and/or transmitted may be varied up or down in accordance with the intended application of the system.
One or more embodiments of the present invention address the various limitations of existing systems by providing a constellation of satellites traveling in a substantially equatorial LEO or MEO orbit that is operable to serve as a communication intermediary between ground stations that are not connected to any wired network, and gateway stations that provide a link to essentially an entirety of the wired, global communication network. The communication concerned may be used for Internet service, mobile phone service, locally wired telephone service, and/or satellite television, among others.
In an embodiment, the concentration and distribution of satellites within the constellation is preferably established so as to allow the constellation to effectively serve as an airborne equatorial communications trunk line providing continuous bandwidth availability to all regions within its service range. Notably, many of the areas most effectively served by embodiments of the present invention are located in developing, tropical (including equatorial), parts of the world that currently do not have fiber or other wired connectivity to the Internet or other wired global communications system. Thus, for such currently unwired regions, various embodiments of the present invention present the only available solution with which to address the current lack of high-speed communication. For less isolated regions, having substantially saturated wired connectivity, embodiments of the present invention still present a beneficial second source of high-speed data connectivity.
Embodiments of the present invention provide much reduced communication latency in comparison with GEO satellite systems. For earth stations at the equator, the distance to a GEO satellite is 36,000 km, thus 3.6×107 m (meters). In one embodiment, the distance from the earth station on the equator to a satellite in an equatorial medium earth orbit (at an altitude of 8,000 km) is clearly 8000 km (8×106 m). The latency due to data transmission for the GEO satellite, for one round trip (one trip from earth to satellite, and one trip from satellite to ground) is therefore 3.6×107 m /3.0×108m/s)×2=0.240 seconds, or 240 milliseconds (msec). A satellite round trip time (RTT) from a hub-based system requires two hops (up and down from the remote terminal to the hub and then up and down from the hub back to the remote terminal), and would thus incur a transmission time of 480 msec. With a MEO satellite in an 8000 km orbit, the one hop latency for earth terminals at the equator, the latency would be (8×106 /3×108)×2=0.053 sec or 53 msec. A full round trip (a trip from earth to the satellite and back again) time would thus be 106 msec. The latency reduction for MEO satellites vs. GEO satellites is thus considerable.
For earth stations at latitudes other than the equator, the same relationship holds. For example, the distance from an for an earth station at approximately 40° N latitude to a GEO satellite is about 38,600 km, and the distance from this same earth station to a satellite in an equatorial MEO orbit is about 10,500 km. Applying the formula above, the RTT latency to the GEO satellite from an earth station at 40° N latitude would be about 515 msec., and the RTT latency to a satellite in an equatorial MEO orbit from an earth station at 40° N latitude would be 140 msec. Other factors may contribute to communication latency such as processing time in computers (either at earth stations or in satellites) or routers. However, the dominant factor is the distance to and from the satellite. From the above, it may be seen that the orbit altitudes of various embodiments of the present invention are operable to substantially reduce communication latency.
Moreover, the at least substantially equatorial orbit contemplated by various embodiments herein operates to simplify the process of ensuring that satellites and ground stations orient their respective satellite dishes toward one another during periods of communication with one another. Further, suitable selection of the number of satellites in each constellation (one or more constellations may be employed), of the geocentric angle separating successive satellites within a constellation enable avoiding interference communication paths between GEO satellites and ground stations communicating with the GEO satellites.
Communication network 400 may be a ground-based network that may include the Internet. However, communication network 108 may refer to any communications network or system, or combination of such networks, capable of employing a satellite communications system to enable communication between one or more ground stations 106 with a network 400 and/or with each other. Such systems may include, either in place of or in addition to the Internet, telephone systems (landline and/or wireless), radio communications (one-way broadcast and/or two-way radio), television broadcasting, international warning system broadcast (such as for weather emergencies or other event), and/or other communication systems.
Gateway stations 700 may serve as communication intermediaries between one or more satellites and one or more ground-based communication networks, which may be wired or wireless. Herein, gateways 700 may serve as interfaces between communication network 400 and satellite system 150. Gateway stations 700 may include one or more gateway stations or gateway terminals for receiving/transmitting data for retransmission to satellite system 150 and/or communication network 108. Gateway stations 700 could be land-based and may provide any needed data communication routing and/or data format conversion needed to enable communication between communication network 150 and satellite system 700. For instance, gateway stations 700 may include controllers and/or other control means for controlling the location of a data communication path, such as by selecting one or more satellites from among a plurality of satellites to conduct data communication with and/or selecting one or more transponders on one satellite or distributed over a plurality of satellites for conducting data communication. In some respects, a gateway station 700 may be considered to be a special-purpose ground station. However, in other embodiments, one or more gateway stations 700 may be satellites serving as intermediary transceiving stations a) between a satellite and a ground station; b) between two satellites; and/or c) between two ground stations.
Herein, the terms “satellite system 150” and “satellites 150” are used interchangeably and generally refer to the totality of satellites employed as communication intermediaries in between gateway stations 700 and ground stations 100, and/or stand-alone subscribers 500. Satellite system 150 may include one or more satellite constellations, and each constellation may include one or more satellites. Thus, satellite system 150 may include any number of satellites 200 from one up to any desired number. Each satellite 200 of satellite system 150 may receive data from gateway 700 and retransmit such data either directly or via another satellite to one or more specified ground stations 100, any other satellite 200, any stand-alone subscriber 500, within satellite system 150. Conversely, satellite system 150 may receive data from one or more ground stations 106 and/or one or more stand-alone subscribers 500 and retransmit the received data to one or more gateway stations 700.
Ground stations 100 may be established in substantially permanently fixed locations and serve as communications hubs for networks of respective groups of local subscribers 120, as shown in
Each ground station 100 may be connected to one or more local subscribers 120, which may also be referred to as customer sites. Each subscriber may include one or more user terminals. The nature and communication bandwidth needs of the subscribers may vary widely. For instance, each subscriber may include one or more telephone companies, one or more Internet service providers, one or more Internet cafés, one or more individual communications customers, and/or other form of communication provider such as a cable television provider, or any combination of the foregoing.
Stand-alone subscribers 500 may be subscribers that communicate directly with a satellite 200 of satellite system 150 without employing a ground station 100 as an intermediary. This approach may be suitable where only a subscriber 500 is substantially isolated from other subscribers (such as subscribers 120), and establishment of a local network coupled to a ground station 100 is not cost effective. Herein, the term user station may refer to either a ground station, or a stand-alone subscriber (customer) on the earth.
Alternatively, two satellites may serve as successive intermediaries between two ground stations, where no single satellite has a line-of-sight connection with both of the ground stations at the same time. Thus, for example, with reference to
In an embodiment, at ground station 100-1 (and/or at other comparably configured ground stations within communication system 10), computing system 110 may read the destination IP address of each digital data packet 120, access table 116 within memory 214, and retrieve the transmission frequency corresponding to the IP address read from the digital data packet 120. Thereafter, ground station 106-a may convert digital data packet 120 into analog data packet signal 130 and transmit the data packet signal 130 using the transmission frequency retrieved from data table 216. Herein, the terms “packet” or “data packet” may refer to either digital data packet 120 or analog data packet signal 130. Herein, analog data packet signal 130 is preferably an analog waveform or signal that contains the digital packet information of data packet 120 and that is used to transmit the digital packet information over an analog communications channel.
Data table 116 shows exemplary permissible frequency ranges that may be used for the respective IP addresses. Ground station 100-1 may transmit each packet signal 130 using a transmission frequency anywhere within the transmission frequency range retrieved from data table 116 for a particular IP address. In some embodiments, the transmission frequency ranges of table 216 may be sub-divided into still smaller segments such that each segment of each range corresponds to a specific point of origin of each digital data packet 120.
The association of a frequency range, instead of merely a single frequency, with a given IP address, may be helpful in establishing frequency division thresholds aboard satellite 200 to enable routing data packet signals 130 based on the transmission frequencies of the signals 130. This approach may beneficially avoid having to demodulate the signals 130 (onboard satellite 200), and employ expensive equipment on satellite 200 to route the signals 130 based on digital routing data embedded in the signals.
Routing mechanisms, such as frequency dividers, may be deployed within satellite 200 for routing analog packet signals 130 through the satellite 200. The transmission frequency ranges, such as those shown in table 116, corresponding to the respective IP addresses, may be employed to set thresholds in the frequency dividers in order to implement routing decisions aboard satellite 200 that are consistent with the data in table 116 and that are consistent with the manner in which transmission frequencies were selected for each packet signal 130 prior to being transmitted from ground station 100-1 to satellite 200. Thus, for instance, in accordance with this embodiment, a packet signal 130 received at satellite 200 having a transmission frequency of 19.05 GHz (see
Considering another example, satellite 200 may serve as an intermediary for communication between ground station 100-1 and 100-2 of
Satellite 200 preferably receives the data packet signal 130 and preferably determines the transmission frequency of the received signal (data table establishing this correspondence is not shown). Satellite 200 then preferably routes the data packet signal 130 to an output transponder (satellite dish) on satellite 200 that is selected based on the transmission frequency of the received data packet signal 130. Satellite 200 then preferably retransmits the data packet signal 130 out of the transponder along the intended path, which in this case leads to ground station 100-2. It is assumed for this example that the destination IP address identifies customer site 120-2-a as its final destination. Thus, once the data packet signal 130 is received at ground station 100-2, modem 104-2 preferably demodulates the signal back into digital data packet 120, and identifies the destination IP address. Ground station 100-2 then preferably transmits the digital data packet 120 to customer site 120-2-a.
In the above example, satellite 200 serves as an intermediary between ground stations 100-1 and 100-2, each of which may be coupled to multiple local subscribers. However, satellite 200 may also be in communication with two or more ground-based communication stations of any suitable type. For instance, in other embodiments, satellite 200 may be an intermediary between a ground station and a gateway station, or between two gateway stations. Moreover, each satellite 200 may communicate with one or more satellites and/or with one or more ground stations.
Though one constellation of sixteen satellites is shown in
In an embodiment, each satellite 200 may include twelve customer dishes and two gateway dishes, each such dish being capable of pointing a steerable spot beam toward a communication destination on the surface of the earth 600 or on another satellite 600. It is noted that in other embodiments, satellites 200 may have fewer or more than two gateway dishes, and fewer or more than twelve customer dishes.
In this manner, each satellite 200 is preferably able to continuously communicate with at least one user station on the earth 600 and one gateway station 700 on the earth 600, as the satellite 200 travels along a given segment of its orbit 650 about the earth 600. In this manner, the satellite 200 serves as a link between a ground station 100 (
Steering of the dishes one or more of the satellites, the ground stations, and the gateway stations may be implemented by mechanical means, electronically (using phased array antennas or other mechanisms), and/or using a combination of the foregoing. In embodiments using a substantially equatorial orbit for satellites 200, the steering mechanism may be simplified and made more economical by imposing a need for only one axis of adjustment. More specifically, when a satellite 200 travels along an equatorial orbit 650, it may be sufficient to adjust the pitch angle of a steerable beam on the satellite 200 for the satellite 200 maintain a line-of-sight communication link with a selected ground station 100 on the earth 600. Where a satellite 200 travels along an inclined orbit, adjustment of the orientation of a beam on satellite may involve adjusting two orientation axes of the steerable beam to maintain line-of-sight communication with a given ground station 100.
In an embodiment, mechanically steerable dishes may be employed to continuously orient communication beams between satellite 200 and a corresponding ground station 100. In one embodiment, one-dimensional mechanically steerable beams may be employed to control dish orientations on a satellite 200 so as to maintain communication with a ground station 100. In this manner, communication between a given ground station 100 and a given satellite 200 may be maintained with a minimum of machine complexity, and at a minimum cost. Moreover, mechanically steerable spot beams are preferably able to orient beams with a high level of precision and thus effectively concentrate radio frequency (RF) energy within a small, precisely located footprint on the surface of the earth 600.
Similarly ground stations 100 and/or gateway stations 700 may also employ mechanical steering and/or electronic (such as phased array) steering to continuously track satellites and to thus maintain communication connectivity therewith. For ground stations 100 located on the equator, the option of deploying only one dimension of adjustment may exist. However, for ground stations 100 and/or gateway stations 700 at locations other than on the equator, more than one dimension of adjustment may be implemented to ensure sufficient adjustment capability is present to track satellites 200.
Moreover, in a system 10 where satellites 200 are expected to travel in a substantially equatorial orbit 650, communication dish orientation control at ground stations 100 and/or at stand-alone subscribers 500 may also employ mechanically steerable dishes for many of the same reasons discussed above for the dishes on satellites 200. Specifically, RF communication energy may be concentrated within a small and precisely located footprint so as to achieve a high level of communication bandwidth per unit of energy consumed.
However, in alternative embodiments, electronic steering, using phased array antennas, or other means may be employed in place of the mechanical steering mechanisms discussed above. Such electronic steering may be used on satellites 200, ground stations 100, and/or stand-alone subscribers 500.
Satellite system 150 (which includes one constellation of sixteen satellites in the embodiment of
In this embodiment, satellite 200-4, at the stage of its orbit shown in
Another self-healing scenario is shown for satellites 200-1 and 200-2. Normally, S3 could communicate with S4 through satellite 200-2 (or another satellite 200 positioned where 200-2 is shown in
One benefit of the system disclosed herein is that even if satellite system 150 is initially deployed with six satellites which may be substantially equally distributed over a substantially equatorial orbit (as shown in
One ongoing concern for satellite systems in general is avoidance of RF interference with other satellite systems. Since various embodiments disclosed herein concern satellites 200 traveling in equatorial orbits, there is a need to address avoidance of interference with GEO satellites. This is because GEO satellites, though in geostationary orbit, and thus stationary with respect to the ground stations the GEO satellites communicate with, lie within an equatorial plane. Thus, at various points of the travel of a satellite 200 along a LEO or MEO equatorial orbit, there is a risk of interference between the communication between satellite 200 and its associated ground station and communication between a GEO satellite and a ground station associated with the GEO satellite. In various embodiments of the present invention, selection of bounds of latitude and/or longitude of the ground stations 100 and gateway stations 700 that a given satellite 200 communicates with at any given point along the orbit 650 of the satellite 700 are operable to avoid undesired interference with the GEO satellite RF reception and transmissions energy. Various standards have been employed in the telecommunications industry to prevent unacceptable levels of interference. In one embodiment herein, an angular separation between separate communication beams of two degrees or more is considered sufficient to avoid unacceptable levels of interference. However, those of skill in the art will recognize that the principles discussed herein may be readily extended to accommodate minimum beam separation angles that are greater than or less than two degrees.
However, by establishing bounds for the latitudes of ground stations that satellite 200 may communicate with, interference may be beneficially avoided. A set of exemplary values are provided to illustrate this point. Using an earth 600 radius of 6,400 km, a satellite 200 altitude of 8,000 km, ground station 100 would have to be at a latitude of 3.2 degrees or greater (either North or South) for the discrimination angle α1 to meet or exceed two degrees. Clearly, the larger the required discrimination angle is, the greater the latitude angle ground station 100 will have to be at to avoid interference between satellite 200 and satellite 800.
In the example shown in
Various beam separation angles (α1, α2, and α3,) are shown in
In the embodiment of
Preferably, the above-discussed beam separation angles operate to prevent interference between beams directed toward a common point even if the two beams employ the same frequency. While detailed formulas are not provided herein, it may be seen that the separation angle between the GEO satellite 800 to M beam and the satellite 200 to M beam may be kept above the minimum separation angle by selecting ground stations 100 for communication with satellite 200 that are greater than a certain minimum angular distance (as measured in degrees of latitude) from the equator 630 in either a northern or southern direction.
The above addresses bounds for the latitude of ground stations 100 that a satellite 200 may communicate with when satellite 200 is in line with a GEO satellite 800 within an equatorial plane. However, where satellite 200 is not in proximity to a GEO satellite communication beam, it should be noted that the above-discussed constraints on the permissible latitudes for ground stations that can communicate with satellite 200 are not present. Thus, where no risk of interference with GEO satellite communications exists, satellites 200 may communicate with ground stations at any latitude within the latitudinal communication range of the satellite 200, which may be between 40 degrees latitude north and 40 degrees latitude south.
Having discussed restrictions on latitude, we turn next to methods for avoiding interference between satellites 200 within satellite system 150 and GEO satellites 800 when both the GEO and non-GEO satellites are communicating with ground stations located at or very near the equator.
In this embodiment, when satellite system 150 seeks communication with a ground station 100 at location E on the equator 630 in a region in which other stations receive and transmit RF energy along path 802 to GEO satellite 800, interference between satellites 200 of satellite system 150 and the GEO satellite 800 communication may be avoided by employing satellites 200 within satellite system 150 that are outside a specified forbidden angular range 640 within which a risk of interference exists. The deployment of steerable beams on satellites 200 preferably operates to enable satellites 200 to communicate with ground station at point E on the equator 630 of the earth 600 without incurring interference with communication between GEO satellite 800 and its associated ground station(s) at or near point E.
In the embodiment of
More specifically, non-interfering communication between ground station 100 at point E may occur over all of communication range 660 other than the segment of orbit 650 within forbidden range 640. A more specific example of the orbit/constellation configuration discussed above is considered in connection with
In the embodiment of
In the following, one particular approach for interference avoidance is described. It will be appreciated that the invention is not limited to this approach, as many communication arrangements are possible that provide continuous connectivity for satellite system 150 with ground station 100 while avoiding interference with GEO satellite 800.
By way of overview, various aspects of the satellite orbit, the satellite constellation design, and the nature of RF communication generate various resulting circumstances within which various communication options or schemes become available. More specifically, design aspects such as the orbit 650 altitude above the earth 600, the number and spacing of satellites 200 within satellite system 150 (in this case a single constellation 150) determine the following resulting circumstances:
the minimum topocentric elevation angle for satellite 200 above the horizon (which has a topocentric angle of zero degrees) to enable communication with ground station 100;
(b) the communication range 660 which corresponds to a portion of orbit 650 within which a given ground station has line-of-sight communication access with satellites 200 of satellite system 150;
(c) the range of longitude w within which a ground station can be located and still communicate with a given satellite 200 at a given point along its orbit 650; and
(d) the total number of satellites of satellite system 150 having line-of-sight communication ability with a given ground station 100 at any given moment.
Separately, the sensitivity to interference of GEO satellite 800 and its associated ground station may determine the angular value of the forbidden range 640.
Some specific values are now described for an exemplary embodiment. In this example, we employ an orbit 650 altitude of about 6,400 km (about equal to the radius of the earth) and sixteen satellites equally spaced within orbit 650, a negligible elevation angle, a communication range 660 of about 110 degrees, a communication longitude range ω for a given satellite 200, (at a given moment) of about 120 degrees (
The above conditions, including the recited negligible elevation angle, yielded a communication longitude range ω of about 120 degrees. The requirement for a minimum topocentric elevation angle at ground stations 100 will reduce the communication longitude range ω. Moreover, for a given satellite at a given altitude, the communication longitude range ω will decrease with increasing minimum topocentric elevation angle. For example, at an altitude of 6,000 km, with a minimum elevation angle of 5 degrees, it has been determined that each satellite 200 will have a communication longitude range ω of about 108 degrees. At this same altitude (6,000 km), in a system using sixteen equally angularly spaced satellites, and thus located at 22.5 geocentric degree intervals about orbit 650, a satellite at ground station 100 at point E (
A forbidden range 640 value of 2 degrees is considered to apply in this example. However, this value may vary depending on the circumstances. It will be understood to those of ordinary skill in the art that changing the design aspects of the orbit 650 and the constellation 150 will cause the above-listed resulting circumstances to change as well. Moreover, it will be understood that the present invention is not limited to the above-stated design aspects or the above-listed resulting circumstances.
The flexibility and redundancy enabled by the embodiment of
An example is considered in which ground station 100 at point E communicates with satellites 200-1 and 200-2 over a 22.5 degree geocentric angular segment of orbit 650, at an altitude of 6,000 km.
In this example, communication between each satellite 200 and ground station 100 may begin when satellite 200 is 5 (topocentric) degrees above the horizon. This situation is shown in
When the satellite 200 completes its progress through the 22.5 degree orbit segment, discussed above, it reaches the point that satellite 200-1 is shown at in
As satellite 200 moves along orbit segment 222, the change in topographic angle of satellite 200 as seen by ground station 100 at point E, indicated by angle 224, may be substantially more than the 22.5 degree value of angle 222. However, angle 224 is relevant mostly to the adjustment of the orientation of communication dishes and/or other tracking equipment at ground station 100 and/or on satellite 200. It may be seen that the topographic angle 224 that tracking equipment will rotate through as satellite 200 moves through a given angular orbit segment 222 increases with decreasing altitude of orbit 650. By way of illustration, for a very low altitude orbit 650, angle 224 would have to rapidly rotate from the western horizon to the eastern horizon to follow satellite 200 along a relatively small orbit angular segment 222.
From the above, it is clear that when communication range 660 is much larger than the orbit segment 222 needed for each satellite, a connectivity “session” of ground station 100 with each satellite may be conducted at a safe angular distance from forbidden range 640. As discussed earlier herein, this beneficially avoids interference with the reception/transmission RF energy for GEO satellite 800. While one such interference avoidance scheme is presented above, the geometry of orbit 650 and of satellite constellation 150 make many other such schemes possible. For instance, it may be readily seen from
Having provided an overview of the geometry of the orbit 650 and of the arrangement of ground stations 100 and gateway stations 700, we now provide some more detailed examples of the operation of an embodiment of the present invention over a portion of the earth 600.
The following examples discuss embodiments including an equatorial orbit 650 for the sake of illustration. However, the present invention is not limited to having satellites follow a purely equatorial orbit. Satellites within satellite system 150 may follow inclined orbits, if desired. Such inclined orbits may depart from the equator to any desired extent, such as, for instance, 1 degree of latitude or less, 5 degrees of latitude or less, or 10 degrees of latitude or less. In other embodiments, orbit 650 may depart from the equator by 10 degrees of latitude or more.
Various figures herein illustrate some earth stations as being ground stations 100 and others as gateway stations 700. In some embodiments, ground stations 100 are earth stations that do not have wired connections to global network 400, and gateway stations 700 are earth stations that do have such wired connections to global network 400. However, the present invention is not limited to the above-described arrangement. Some earth stations may function as both ground stations 100 and as gateway stations 700. Some ground stations 100 may have wired connections to a global network but still communicate through satellite system 150 for certain purposes. Moreover, some gateway stations 700 having connections to global network 400 may still communicate with one or more other gateway stations 700 in the event that satellite system 150 offers more convenient and/or more rapid communication over a particular segment of the earth 600. Otherwise stated, one or more ground stations 100 and one or more gateway stations 700 may have functions that are interchangeable. In any case, the communication connections available to a given earth station may change over time.
Thus, a ground station 100 that is located in tropical area that currently does not have a wired connection to global network 400 and thus depends exclusively on satellite communication for global connectivity, could eventually acquire such a wired connection to global network 400. Even upon the deployment of such a wired connection, satellite system 150 of the present invention could still provide valuable additional bandwidth for the now-wired ground station 100.
For the sake of discussion in
In this embodiment, satellite 200-3 preferably communicates with ground stations 100-1 and 100-2, and gateway station 700-1. Under circumstances where gateway station 700-1 (near Buenos Aires) has a wired connection to global network 400, satellite 200-3 is preferably able to extend this global connectivity to ground stations 100-1 (near Caracas) and 100-2 (near Brasilia), which for the sake of this example are treated as not having wired connections to global network 400. Thus, in this case, satellite system 150 may provide the only low-latency communication solution for ground stations 100-1 and 100-2.
In this embodiment, a similar situation may exist for satellite 200-2 which is shown located proximate to the African continent. In this embodiment, ground station 100-3 located near Kinshasa, Zaire is treated as lacking a wired connection to global network 400. Meanwhile, gateway stations 700-2 near Johannesburg and 700-3 near Tel Aviv are treated as having wired connections to global network 400. Thus, at a minimum, in this embodiment, satellite system 150, represented at the point in time shown in
However, the invention is not limited to providing only the above-listed function. Where desirable, satellite 200-2 also provides a useful communication link directly between gateway stations 700-2 and 700-3. In some cases, the wired connections to global network 400 available to gateway stations 700-2 and 700-3 may make the use of satellite system 150 unnecessary for direct communication between stations 700-2 and 700-3. However, in other instances, satellite system 150 may still serve as a useful additional link offering low-latency, high-bandwidth communication services between gateway stations 700-2 and 700-3. Moreover, in special circumstances, such as when a wired link fails, satellite system 150 could serve as a valuable backup communications option between gateway stations 700-2 and 700-3.
Similar to the above, satellite 200-1 may have communication links to gateway station 700-4, ground station 100-4, and/or ground station 100-5. For the sake of this discussion, ground stations 100-4 and 100-5 are treated as not having wired links to global network 400. Thus, in this situation, satellite 200-1 may be operable to provide backhaul communication service to gateway station 700-4 from ground station 100-4 (near Kuala Lumpur) and/or ground station 100-5 (near Bangkok).
A selection of particular cities at certain selected latitudes and longitudes was used to illustrate certain aspects of one or more embodiments of the present invention. However, it will be apparent to those having ordinary skill in the art that the principles discussed herein may be readily extended to any earth station in or near any city, at any longitude on the earth 600. Moreover, an embodiment of the present invention is capable of delivering the above described services within a north-to-south range from 40 degrees latitude north to 40 degrees latitude south.
In
A still further stage of advancement is shown in
Preferably, as the constellation of satellites 200 continues to travel along orbit 650, an infinite succession of satellites 200 forming part of satellite system 150 continues to enter the communication range, shown in
Processor 302 may be a general purpose processor having access to volatile and/or non-volatile memory. Processor 302 may be operable to coordinate the flow of data among the gateway dishes 316 and customer dishes 318. Data path control 304 is preferably operable to control the flow of data from various transponder inputs, along waveguides, and to various transponder outputs within satellite 200. Data path control 304 may be implemented using one or more MUX frequency splitters, by processor 302, by other devices, or using a combination of one or more of the foregoing.
Gateway dish tracking system 306 is preferably operable to enable gateway dishes 316 to maintain a communication path with a counterpart dish it is communicating with, where the counterpart dish may be on the surface of the earth 600 or on another satellite. The operation of tracking system 306 depends on the type of dish and beam used with dishes 316. The above discussion also applies to customer dish tracking system 308 and customer dishes 318, respectively. Below, two types of antenna are discussed along with tracking systems corresponding to each antenna type.
In one embodiment gateway dishes 316 and/or customer dishes may include a feed and one or more reflectors suitable for directing a spot beam in a desired direction. In this embodiment, the beam direction established may be mechanically steering the antenna assembly so as to control the orientation of the dish along one or more angular dimensions. The tracking system suitable for interacting with a mechanically steerable antenna is discussed next.
When gateway dishes 316 or customer dishes 318 employ mechanically steered antennas (such as those discussed in connection with
When gateway or customer dishes 316, 318 employ phased array antennas (such as those discussed in connection with
Customer dishes 318 and gateway dishes 316 may include any one of several types of satellite communication dishes capable of bi-directional communication with one or more ground stations, one or more other satellites, and/or a combination of ground stations and other satellites. Satellite 200 may include any number of customer dishes 318 and any number of gateway dishes 316.
Satellite 200 may receive customer beams 406 and gateway beam 408. The received beams may proceed through respective Low-Noise Amplifiers (LNAs) 402. The received gateway beam 408 may proceed to demux 410 and be directed out of satellite 200 along one or more of customer beams 416 and/or along gateway beam 418 under the control of data path control 304 and processor 302. In either of the above paths, the outbound beam is amplified in one or more TWTAs 412 prior to transmission out of satellite 200.
The received customer beams 406, after amplification, may proceed toward multiplexer 404, after which beams 406 may be directed toward along gateway beam 418 and/or toward demux 410 toward outbound customer beams 416 for transmission out of satellite 200. In either case, the outbound beams pass through TWTAs 412 prior to being transmitted out of satellite 200.
The number of gateway beams and customer beams in
For the purpose of illustration, customer receive beams 406 and customer transmit beams 416 are shown separately, as are the reception beams 408 and transmission beams 418 for the gateways. However, in one or more embodiments, individual antennas may be employed for both reception and transmission of data. In other embodiments, the data transmission task and the data reception task may performed by separate antennas for one or more of the customer and/or gateway communication paths.
Satellite 200 may include gateway transponders GW1 and GW2 for communication with two respective gateway stations on the earth. In other embodiments, satellite 200 could include fewer or more than two gateway transponders. Satellite 200 may further include twelve dishes (each with an associated transponder, as needed or desired) for communication with ground stations that are in communication with customers, including transponders C11, C12, C13, C14, C21, C22, C23, C24, C31, C32, C33, and C34. While twelve communication dishes directed to customer communication are shown in
In one embodiment, data received at an input of any of the transponders of satellite 200 shown in
It will be appreciated that rotation about axes 252-a/254-a and 256 does not necessarily correspond only to adjustment for longitude and latitude, respectively. In other words, in some embodiments, rotation about axis 256 by antenna 252 may change both the latitude and longitude of the location on the earth 600 with which antenna 252 communicates. Likewise, in some embodiments, rotation of antenna 252 about axis 252-a may change both the latitude and the longitude of the location on the earth 600 with which antenna 252 communicates.
In one embodiment, antenna 252 may communicate with a ground station 100, and antenna 254 may communicate with a gateway station 700, thereby connecting ground station 100 to a global communication network. However, in other embodiments, this arrangement may be varied. Although only two steerable antennas 252, 254 are shown in
When operating in conjunction with a suitable tracking system (discussed in connection with
In one or more embodiments, central processing unit (CPU) 1902 may be coupled to bus 1904. In addition, bus 1904 may be coupled to random access memory (RAM) 1906, read only memory (ROM) 1908, input/output (I/O) adapter 1910, communications adapter 1922, user interface adapter 1906, and display adapter 1918.
In one or more embodiments, RAM 1906 and/or ROM 1908 may hold user data, system data, and/or programs. I/O adapter 1910 may connect storage devices, such as hard drive 1912, a CD-ROM (not shown), or other mass storage device to computing system 1900. Communications adapter 1922 may couple computing system 1900 to a local, wide-area, or global network 1924. User interface adapter 1916 may couple user input devices, such as keyboard 1926 and/or pointing device 1914, to computing system 1900. Moreover, display adapter 1918 may be driven by CPU 1902 to control the display on display device 1920. CPU 1902 may be any general purpose CPU.
It is noted that the methods and apparatus described thus far and/or described later in this document may be achieved utilizing any of the known technologies, such as standard digital circuitry, analog circuitry, any of the known processors that are operable to execute software and/or firmware programs, programmable digital devices or systems, programmable array logic devices, or any combination of the above. One or more embodiments of the invention may also be embodied in a software program for storage in a suitable storage medium and execution by a processing unit.
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.
This application is a Continuation of PCT Application Serial No. PCT/US08/75372, filed Sep. 5, 2008, entitled “APPARATUS AND METHODS FOR SATELLITE COMMUNICATION” [Attorney Docket 790-5-PCT], published as Pub. No. WO 2009/051907 on Apr. 23, 2009, and this application is a Continuation-In-Part of PCT Application Serial No. PCT/US07/81763, filed Oct. 18, 2007, entitled “SYSTEM AND METHOD FOR SATELLITE COMMUNICATION” [Attorney Docket 790-2-PCT], published as Pub. No. WO 2009/51592 on Apr. 23, 2009; and this application is a Continuation-In-Part of PCT Application Serial No. PCT/US08/63853, filed May 16, 2008, entitled “SYSTEMS AND METHODS FOR SATELLITE COMMUNICATION” [Attorney Docket 790-4-PCT], published as Pub No. 2009/139778 on Nov. 19, 2009, all of which applications are hereby incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12761902 | Apr 2010 | US |
| Child | 13528613 | US | |
| Parent | PCT/US08/75372 | Sep 2008 | US |
| Child | 12761902 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US07/81763 | Oct 2007 | US |
| Child | PCT/US08/75372 | US | |
| Parent | PCT/US08/63853 | May 2008 | US |
| Child | PCT/US07/81763 | US |
