WO2021008349A1 - 基于波束常值偏置可共享无线电频谱的方法及低轨通信卫星系统 - Google Patents

基于波束常值偏置可共享无线电频谱的方法及低轨通信卫星系统 Download PDF

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WO2021008349A1
WO2021008349A1 PCT/CN2020/099137 CN2020099137W WO2021008349A1 WO 2021008349 A1 WO2021008349 A1 WO 2021008349A1 CN 2020099137 W CN2020099137 W CN 2020099137W WO 2021008349 A1 WO2021008349 A1 WO 2021008349A1
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orbit
offset
satellite
communication satellite
communication
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PCT/CN2020/099137
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English (en)
French (fr)
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李峰
侯凤龙
齐彧
林骁雄
裴胜伟
陈东
李新刚
包泽宇
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中国空间技术研究院
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Priority to US17/626,737 priority Critical patent/US20220294525A1/en
Priority to GB2200995.5A priority patent/GB2600591A/en
Priority to CA3146978A priority patent/CA3146978C/en
Publication of WO2021008349A1 publication Critical patent/WO2021008349A1/zh

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/185—Space-based or airborne stations; Stations for satellite systems
    • H04B7/1851—Systems using a satellite or space-based relay
    • H04B7/18513—Transmission in a satellite or space-based system
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H04B7/0617—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal for beam forming
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/185—Space-based or airborne stations; Stations for satellite systems
    • H04B7/1851—Systems using a satellite or space-based relay
    • H04B7/18519—Operations control, administration or maintenance
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/185—Space-based or airborne stations; Stations for satellite systems
    • H04B7/19—Earth-synchronous stations
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/185—Space-based or airborne stations; Stations for satellite systems
    • H04B7/195—Non-synchronous stations
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
    • H04W16/14—Spectrum sharing arrangements between different networks

Definitions

  • the invention relates to a method for sharing radio frequency spectrum based on beam constant offset and a low-orbit communication satellite system (that is, a method for sharing radio frequency spectrum with beam constant offset and a low-orbit communication satellite system), belonging to the technical field of earth orbit communication satellites .
  • Communication satellites have been one of the important applications of space technology. Communication satellites receive and send radio signals from the surface of the earth. With the advancement of satellite communication technology and the explosion of demand, radio frequency spectrum has become a very valuable commodity. A certain range of specific radio frequency spectrum can be auctioned for tens of billions of dollars.
  • a geostationary satellite is a typical communication satellite that orbits the earth in a plane intersecting the earth's equator ("equatorial plane"), and is about 36,000 kilometers away from the earth (about six times the radius of the earth). The orbital period is exactly A sidereal day.
  • Geosynchronous satellites orbit the earth at exactly the same angular velocity as the earth rotates around its axis. Geosynchronous satellites are relatively stationary with respect to the observer on the ground.
  • the huge distance between the geosynchronous (usually abbreviated as "GEO") satellite and the earth's surface can achieve coverage of a wide area, while requiring higher transmission signal power and greater communication delay, and the capacity of a single satellite is limited and cost It is also very expensive.
  • GEO geosynchronous
  • a satellite constellation system operating close to the surface of the earth may be more suitable.
  • the low-orbit satellite constellation system has the advantages of large system capacity and low latency. At the same time, the cost of a single satellite can be reduced through batch production.
  • Figure 1 shows a communication satellite system in low earth orbit (usually abbreviated as "LEO"), which operates in a polar orbit; its beam is not offset to form continuous coverage of the earth, but it cannot share the radio spectrum with GEO communication satellites.
  • the LEO orbit is generally considered to be a satellite orbit that does not exceed approximately 2,000 kilometers from the earth's surface. As shown in Figure 1, the orbital height of the satellite is small compared to the radius of the earth; in the scale diagram, it corresponds to approximately 1200 kilometers.
  • 1-110 is the earth; 1-120 is the north pole; 1-130 is the south pole; 1-140 is the LEO satellite; 1-150 is the LEO polar orbit; 1-160 is the Equator; 1-170 is the direction of satellite movement; 1-180 is the unbiased beam.
  • Figure 2 shows the same LEO satellite and GEO satellite orbits near the equator shown in Figure 1, assuming that the GEO satellite orbital plane completely coincides with the equatorial plane. In order to facilitate text labeling, Figure 2 does not show the orbital heights of LEO and GEO satellites in strict accordance with the scale, but only shows the schematic relationship.
  • the beam isolation angle between the GEO satellite and the LEO satellite received from the ground position from point C to A in beam 2-610 is less than the critical interference avoidance Angle ⁇ , LEO satellites and GEO satellites cannot share wireless spectrum in this area.
  • the beam separation angle between GEO satellites and LEO satellites received at any position in the entire arc CD within the beam range is greater than or equal to the critical interference avoidance angle ⁇ .
  • the LEO satellite offset is greater than a certain critical angle ⁇ 1 , any position in the entire beam coverage area supports LEO satellites and GEO satellites to share wireless spectrum.
  • Critical offset angle ⁇ 1 and critical interference avoidance angle ⁇ the latitude argument ⁇ where the LEO satellite is located, the half cone angle of the beam And the LEO satellite's orbital height H LEO and other parameters related.
  • H LEO the LEO satellite's orbital height
  • Figure 3 is a schematic diagram of the minimum offset angle requirement for adjacent LEO satellites on both sides of the ascending node to form double coverage under the condition of symmetrical beam offset.
  • the latitude angle of the two LEO satellites is exactly equal to the phase of the two adjacent LEO satellites.
  • Half of the angle which is ⁇ 1/2 ⁇ .
  • Figure 3 does not show the orbital heights of LEO and GEO satellites in strict accordance with the scale, but only shows the schematic relationship.
  • Figure 4 is a scheme for sharing radio frequency spectrum between a low-orbit communication satellite system and a geostationary satellite given in the patent "Communication satellite system CN107210805A with reduced interference", where the LEO polar orbit and the equatorial plane intersect at an ascending node and a descending node .
  • each satellite in the same orbit must implement a progressive beam offset around the pitch axis (perpendicular to the orbital plane) in the process of approaching the equator according to a unified law, and gradually after leaving the equator Restore the normal ground beam coverage; reserve a certain coverage area overlap overlap margin to ensure that each satellite in each orbit maintains an overall continuous coverage of the ground during the progressive offset process, and on this basis, ensure that the entire constellation is grounded Continuous coverage.
  • FIG. 5-1 shows the typical elevation angle variation curves of LEO satellites at different latitudes based on the progressive beam offset strategy.
  • Option 1 adopts the method of constant pitch angular velocity
  • Option 2 adopts the method of variable pitch angular velocity.
  • Figure 5-2 shows the rule of overlapping overlap widths of adjacent LEO satellites in the same orbit obtained by using schemes 1 and 2 in Figure 5-1.
  • the minimum overlap coverage area width obtained based on the beam progressive offset strategy is only 40%-60% of the overlap coverage area width of adjacent LEO satellites without beam offset.
  • the orbit correction in the tangential direction of the orbit surface can only be implemented during the non-progressive bias period, and there are certain restrictions on the arc range of the orbit correction.
  • the technical problem solved by the present invention is to overcome the shortcomings of the prior art, and provide a method for sharing radio frequency spectrum based on beam constant offset and a low-orbit communication satellite system.
  • the beam constant offset strategy proposed by the present invention can achieve overlapping overlaps between adjacent low-orbit communication satellites with a minimum coverage area of equal strength Design, and no longer need high-precision progressive beam offset control device.
  • the low-orbit communication satellite system that can share the radio spectrum based on the beam constant offset strategy has significant advantages in satellite design, manufacturing and operating costs.
  • the technical solution solved by the present invention is: a method for sharing radio frequency spectrum between a first communication satellite operating in low orbit and a second communication satellite operating near the equator (that is, a method for sharing radio frequency spectrum based on beam constant offset ), (low orbit is preferably a satellite orbit that does not exceed about 2000 kilometers on the earth's surface; the present invention does not strictly limit the orbital height of LEO satellites (ie, low-orbit satellites), generally as long as it is lower than the nearby shared radio spectrum
  • the orbit height of the high-orbit communication satellite operating in the equatorial orbit can support the formation of the LEO satellite system that meets the set requirements), characterized in that the first orbit where the first communication satellite is located is lower than the second orbit where the second communication satellite is located Orbit, the first orbit intersects the equatorial plane at an ascending node and a descending node, and the second orbit is a near-equator orbit.
  • the method includes:
  • the first communication satellite transmits a radio signal aimed at the surface of the earth to form a beam
  • the first communication satellite completes the conversion of the normal offset state of the transmitting beam near the ascending node, descending node, and the Arctic and Antarctic regions;
  • the degree of beam offset (that is, the magnitude of the constant offset) is based on the two beams corresponding to the shared frequency of the first communication satellite and the second communication satellite to complete the space isolation without mutual interference.
  • the minimum angle (that is, the minimum isolation angle) requirements and the first communication Satellite beam size, orbit height, phase angle of adjacent first communication satellite in the same orbit plane, orbital inclination of second communication satellite in near-equator orbit is determined; it has nothing to do with the specific latitude of the first communication satellite; beam offset degree Is a fixed constant value;
  • Beam offset for the ascending node, the first communication satellites near the equator are all biased towards the equator; for the descending node, the first communication satellites near the equator are all biased towards the equator;
  • the conversion of the beam constant offset state is carried out every four times when the first communication satellite moves to the vicinity of the ascending node, the descending node, the Arctic region and the Antarctic region during each orbital period;
  • the direction is opposite, and the degree of offset is the same;
  • the current beam that is, the beam of the satellite that undergoes the beam offset state transition
  • the current beam that is, the beam of the satellite that undergoes the beam offset state transition
  • the beam power is reduced, and interference to the second communication satellite will not occur.
  • the beam offset is realized by offsetting the entire first communication satellite attitude.
  • the device for implementing the satellite attitude bias includes a reaction wheel (that is, a momentum wheel) or a control moment gyroscope.
  • the attitude offset is implemented around the pitch axis of the first communication satellite.
  • the orbital thruster is pre-biased in the opposite direction of the pitch axis, and the center of mass can still be obtained during the pitch offset. And generate thrust along the tangential direction of the orbit.
  • This orbit-controlled thruster layout supports the orbit correction in the tangential direction of the orbit during the constant attitude offset period.
  • the constant value attitude offset refers to: realizing the constant value beam offset by offsetting the entire first communication satellite attitude by a constant value.
  • the beam is pre-biased in the direction of the pitch axis and then rotated by 180° around the yaw axis to realize the beam offset direction conversion.
  • the beam is pre-biased in the direction of the pitch axis, because the bias state is relatively fixed, optimization of the curvature of the earth is supported for the projection of the beam on the spherical surface.
  • the beam offset is realized by rotating one or more radio antennas of the first communication satellite.
  • the beam bias is completed by electronic control.
  • control method adopts phased array antenna technology for beam offset.
  • the vicinity of the Arctic region refers to the double or above coverage area formed by the low-orbit communication satellite system in the Arctic region.
  • the vicinity of the Antarctic region refers to the double or above coverage area formed by the low-orbit communication satellite system in the Antarctic region.
  • the first communication satellite near the equator refers to: for the ascending node, after the beam offset state reversal is completed near the south pole, the first communication satellite that has not implemented the beam offset state reversal near the north pole; At the intersection point, the first communication satellite that has not implemented the beam offset state reversal near the south pole after the beam offset state reversal is completed near the north pole.
  • the vicinity of the ascending node refers to the area between the plus and minus 1/2 phase angle of the ascending node, and includes the area corresponding to the plus and minus 1/2 phase angle of the ascending node, and the phase angle refers to the area adjacent to the same orbital plane.
  • the phase angle of the first communication satellite is not limited to the phase angle of the first communication satellite.
  • the vicinity of the descending node refers to the area between the plus and minus 1/2 phase angle of the descending node, and includes the area corresponding to the plus and minus 1/2 phase angle of the descending node.
  • the phase angle refers to the adjacent area in the same orbital plane.
  • the phase angle of the first communication satellite is not limited to the phase angle of the first communication satellite.
  • a communication satellite system comprising: a plurality of first communication satellites, the plurality of first communication satellites running in a plurality of first orbits;
  • the multiple first communication satellites in the first orbit are distributed according to a set phase rule
  • the first orbit intersects the equatorial plane at an ascending node and a descending node;
  • the ascending and descending intersection points of each first orbit and the equatorial plane are distributed at regular intervals, and the parameters of each first orbit other than the ascending and descending intersection points remain the same;
  • the second communication satellite is operating in a second orbit
  • the second orbit is near the equator and higher than the first orbit
  • the beam of the first communication satellite in the satellite system can coordinate to complete the continuous coverage of a certain ground area or global surface and its (ie a certain ground area or global surface) corresponding space within the set altitude, in the north and south poles. Form double and above coverage;
  • the first communication satellite moves to the vicinity of the ascending node, the descending node, the arctic area, and the antarctic area in each orbital period of each operation, and the beam offset state is converted once before and after each implementation.
  • the degree of bias is the same;
  • the degree of beam offset is based on the minimum angle requirement for the two beams corresponding to the shared frequencies of the first communication satellite and the second communication satellite to complete spatial isolation without mutual interference, and the beam size, orbit height, and the same orbital plane of the first communication satellite
  • the phase angle of the adjacent first communication satellite is determined; at the same time, it is related to the orbital inclination of the second communication satellite in the near-equator orbit; it has nothing to do with the specific latitude of the first communication satellite; the beam offset is a fixed constant value;
  • the first communication satellites near the equator are all biased toward the equator; for the descending node, the first communication satellites near the equator are all biased toward the equator.
  • the beam of the current first communication satellite is turned off and out of service, and the other two adjacent first orbits on both sides of the current first orbit
  • the beam of the first communication satellite provides service.
  • the first communication satellites in adjacent orbits respectively select to enter or leave a certain position in the dual coverage area to implement beam offset conversion to obtain the maximum conversion treatment between adjacent first communication satellites in different orbits time interval.
  • the current beam of the first communication satellite is closed and out of service, and the beams of adjacent satellites located in the same first orbit on the other side of the ascending node provide coverage services ;
  • the beam of the current first satellite is closed and out of service, and the adjacent satellite on the other side of the descending node in the same first orbit provides beam coverage service.
  • the beams of the first communication satellite near the ascending node and descending node are offset from the other side of the adjacent first communication satellite in the opposite direction before the beam is closed to form a double coverage of the ground service area.
  • At most one first communication satellite beam is closed and out of service at the same time near the ascending node and descending node, and the other adjacent first communication satellite beams are all turned on.
  • the beam constant offset mode supports uniform overlap and overlap of beam coverage areas between adjacent first communication satellites in the same orbital plane, and uses the least beam coverage margin to achieve continuous beam coverage.
  • the strategy of turning off and turning on the beam of the first communication satellite as a whole is supported.
  • the angular velocity of the beam of the first communication satellite rotating relative to the earth is the same as the angular velocity of the first communication satellite rotating relative to the earth.
  • the first communication satellite includes: an orbit-controlled thruster and a reaction wheel (ie momentum wheel) or a control moment gyroscope;
  • a reaction wheel ie momentum wheel
  • a control moment gyroscope ie momentum wheel
  • the orbit control thruster can provide the thrust required to generate the orbit control
  • the reaction wheel and the control moment gyro can be used to control the attitude of the satellite and provide a moment for the attitude change.
  • the first communication satellite further includes one or more radio antennas to implement beam transmission and reception.
  • the first communication satellite transmits radio signals aimed at the surface of the earth to form a beam.
  • the current beam is turned off and out of service, and the beam is turned on and the service is provided after the beam offset conversion ends.
  • setting the regular phase distribution means that the first communication satellites in the first orbit are evenly distributed at equal intervals.
  • the beam constant offset strategy proposed by the present invention maintains a fixed beam offset state when the LEO satellite moves along the orbit, and naturally supports the optimal coverage area between adjacent LEO satellites to overlap and overlap, which can significantly reduce The coverage overlap margin requirements of the satellites; only need to implement a beam constant offset conversion at the ascending node, descending node, and near the Arctic and Antarctic regions; the control accuracy of the dynamic process of beam offset conversion is not restricted.
  • the control accuracy of the beam bias device is low; the overall beam closing strategy can be adopted during the beam bias conversion; the angular velocity of the beam relative to the earth is the same as the angular velocity of the LEO satellite relative to the earth.
  • the orbit-controlled thruster can be pre-biased in the opposite direction of the pitch axis, and the center of mass and the center of mass can still be obtained during the pitch offset. Generate thrust along the tangential direction of the orbit.
  • This orbit-controlled thruster layout supports the orbit correction in the tangential direction of the orbit during the constant attitude offset. If a progressive offset pitch attitude is used to achieve beam progressive offset, LEO satellites cannot implement orbit corrections in the tangential direction of the orbit during the progressive offset around the pitch axis, and the LEO orbit correction ignition arc is subject to certain restrictions.
  • Figure 1 is a schematic diagram of the LEO satellite system of the current technology, which forms a continuous coverage of the earth without beam offset, but it cannot share the radio frequency spectrum with GEO communication satellites.
  • Figure 2 is a schematic diagram showing the minimum offset angle requirements of LEO satellite beams at different latitudes in order to realize the sharing of radio frequency spectrum with GEO communication satellites.
  • Fig. 3 is a schematic diagram of the minimum offset angle requirement of the adjacent LEO satellites on both sides of the ascending node in the current technology to form double coverage under the condition of symmetric beam offset.
  • Figure 4 is a schematic diagram of the LEO satellite system based on the current technology that can share the radio spectrum with the near-equator satellite communication satellite based on the progressive beam bias strategy.
  • Figure 5-1 is a schematic diagram of the typical elevation angle change curve of LEO satellites at different latitudes during the current technology's progressive beam offset process.
  • Figure 5-2 is a schematic diagram of the variation curve of typical continuous coverage band margin with latitude in the current technology's progressive beam offset process.
  • Figure 6 shows the LEO communication satellite system that can share the radio spectrum with GEO satellites based on the beam constant offset strategy.
  • the scenes of adjacent LEO satellites on both sides of the ascending node and descending node are selected.
  • Figure 7 shows the LEO communication satellite system that can share radio spectrum with GEO satellites based on the beam constant offset strategy.
  • the LEO satellite in a single orbit is selected when passing the ascending node and descending node positions.
  • Figure 8 shows the LEO communication satellite system that can share the radio spectrum with GEO satellites based on the beam constant offset strategy.
  • the LEO satellites in multiple adjacent orbits are selected when they enter and leave the Arctic dual coverage area. The scene of the bias state transition.
  • Figure 9 is a schematic diagram of the orbital thruster layout scheme when a constant beam offset is achieved by offsetting the LEO satellite pitch axis attitude.
  • Fig. 10 is a schematic diagram of a scheme for implementing beam offset direction conversion by rotating 180° around the yaw axis (pointing to the center of the earth).
  • the present invention is a method for sharing radio frequency spectrum with high-orbit communication satellites operating near the equator including geostationary satellites and a low-orbit communication satellite system based on beam constant offset.
  • the method includes: low-orbit communication satellites In the north and south poles and near the equator, complete the conversion of the transmission beam bias state.
  • the beam bias direction is opposite before and after each implementation, and the beam bias degree is a fixed constant value; for low-orbit communication satellites near the equator, they are biased toward the equator. ;
  • services are provided by the beams of other low-orbit communication satellites in the other two adjacent orbits on both sides of the current orbit.
  • adjacent low-orbit communication satellites located on the other side of the ascending node or descending node in the same orbit provide beam coverage services.
  • the low-orbit satellite communication system to which the present invention is applied includes a plurality of LEO satellites, and these LEO satellites travel around the earth in a plurality of orbits with a large inclination angle with respect to the equatorial plane. In each orbit, multiple LEO satellites travel at equal phase intervals; the ascending and descending nodes of each orbit and the equatorial plane are distributed at regular intervals; for each first orbit, the orbits other than ascending and descending nodes The parameters remain the same.
  • the low-orbit satellite communication system provides good coverage without gaps on the earth's surface below the orbit and within a certain altitude. For a low-orbit satellite system dedicated to global coverage, it is inevitable to adopt a high-inclination near-polar orbit. This is a general approach adopted to enable the low-orbit satellite communication system to complete the coverage of the Arctic and Antarctic regions. At the same time, this will inevitably lead to double or more coverage effects in the Arctic and Antarctic regions.
  • the invention enables the low-orbit satellite communication system to share radio frequency spectrum with near-equator high-orbit communication satellites including geostationary satellites, thereby saving extremely expensive radio frequency spectrum resources.
  • the constant beam offset strategy enables the LEO satellite beam coverage of the low-orbit satellite system to be selected according to the overlap design of the minimum coverage area.
  • the constant beam bias strategy can reduce the accuracy requirements of the beam bias control device.
  • the LEO satellite follows a circular polar orbit, where the LEO satellite polar orbit intersects the equatorial plane at an ascending node and a descending node.
  • the first communication satellites near the equator are all biased towards the equator; for the descending node, the first communication satellites near the equator are all biased towards the equator.
  • the LEO satellite implements a beam constant offset conversion near the ascending node, descending node, and near the Arctic and Antarctic regions. The beam offsets are the same before and after each implementation, but in opposite directions.
  • the LEO satellite maintains a constant beam offset state as shown in Figure 6-10. Except for LEO satellites that are crossing the equator, they need to close their beams to avoid mutual interference with the radio spectrum with GEO satellites.
  • the radio signals of LEO satellites and GEO satellites in other locations have sufficient beam offsets to maintain good beam offsets. Angular spacing interval, it is not necessary to turn off the transmission of any beam of the remaining LEO satellites.
  • the LEO satellites on the odd and even orbits are selected to enter or leave a certain position in the dual coverage area to perform the beam offset conversion.
  • the maximum conversion processing time interval between adjacent LEO satellites in different orbits can be obtained. This can ensure to the greatest extent that when the LEO satellite in the current orbit implements beam deflection, the beams of other LEO satellites in the other two adjacent orbits on both sides of the current orbit do not implement beam offset conversion and provide continuous beam coverage services, thereby ensuring any The coverage continuity of the LEO satellite system in the Arctic and Antarctic regions at all times.
  • LEO satellites in odd orbits perform beam offset conversion after entering the complete dual coverage area of the polar region
  • LEO satellites in even orbits perform beam offset conversion before leaving the complete dual coverage area of the polar region.
  • the beam of the current LEO satellite is closed and out of service, and the adjacent LEO satellite on the other side of the ascending node or descending node in the same orbit provides beam coverage service.
  • the adjacent LEO satellite on the other side of the ascending node or descending node in the same orbit provides beam coverage service.
  • Near the ascending node and descending node at most only one satellite beam is turned off at the same time, and the other adjacent satellite beams are all turned on.
  • the beams of adjacent satellites that are offset in the opposite direction from the other side before the beam is closed form a double coverage of the ground service area.
  • the beam offset conversion process near the ascending node or descending node it is required to complete beam closing, beam offset conversion, and beam opening within an adjacent LEO satellite phase interval period. This is to ensure that when the current LEO satellite is closed and out of service, the beams of the adjacent LEO satellites in front of it have been turned on and provide services, so that the beam coverage continuity of the low-orbit satellite system near the ascending node or descending node can be strictly guaranteed.
  • a uniform beam offset conversion period can generally be selected.
  • the cycles of beam closing, beam offset conversion, and beam opening are uniformly taken as the minimum requirements at the ascending node and descending node, that is, an adjacent LEO satellite phase interval period.
  • the orbit-controlled thruster can be pre-biased along the opposite direction of the pitch axis. After adopting this method, the thrust that passes the center of mass and along the tangential direction of the orbit can still be obtained when the pitch offset is performed. It supports the orbit correction in the tangential direction of the orbit during the constant attitude offset on both sides of the equator, and the ignition limited arc segment The range is smaller.
  • the beam can be used to implement a pre-bias scheme in the direction of the pitch axis.
  • the curvature of the earth can be optimized for the projection of the beam on the spherical surface.
  • the orbit control thruster can adopt the normal layout mode, and the LEO orbit correction ignition arc will not be restricted.
  • Figure 6 shows the LEO communication satellite system that can share the radio spectrum with GEO satellites based on the beam constant offset strategy.
  • the scenes of adjacent LEO satellites on both sides of the ascending node and descending node are selected.
  • 6-110 is the earth; 6-120 is the north pole; 6-130 is the south pole; 6-140 is the LEO satellite; 6-150 is the LEO polar orbit; 6-160 is the pole Equator; 6-170 is the direction of movement; 6-180 is the beam with constant offset; 6-210 is the satellite beams on both sides of the ascending node.
  • the offset directions are opposite, both Pointing to the equator; 6-220 represents the satellite beams on both sides of the descending node.
  • 6-230 represents the conversion of beam constant offset when entering the north pole The maximum potential crack range in the coverage area (assuming that the beam offset conversion is completed within a phase interval and the beam is turned on again);
  • 6-240 represents the maximum potential crack range in the coverage area caused by the beam constant offset conversion when entering the South Pole ( Assuming that the beam offset conversion is completed within a phase interval and the beam is turned on again);
  • 6-310-1 represents the LEO satellite near the ascending node that will close the beam at the next moment, and the current LEO satellite is located at -1 /2 ⁇ , where ⁇ is the phase angle of the two adjacent LEO satellites;
  • 6-310-2 represents the LEO satellite near the descending node, the beam will be closed at the next moment, the current LEO satellite is located at -1/2 ⁇ +180°;
  • 6-310-3 represents the LEO satellite near the North Pole waiting to close the beam for offset conversion (after the beam enters the Arctic dual coverage area provided by other satellites in the adjacent orbit as
  • the offset angles of the satellites on both sides of the ascending node and descending node need to meet two conditions at the same time. On the one hand, it needs to be greater than the critical offset angle ⁇ 1 so that the beam separation angle between the GEO satellite and LEO satellite received at any position is greater than or equal to Critical interference avoidance angle ⁇ ; on the other hand, it needs to be greater than the critical offset angle ⁇ 2 corresponding to the symmetrical offset of adjacent LEO satellites on both sides of the ascending node or descending node to form a double coverage.
  • the final offset angle takes the maximum of the two max ( ⁇ 1 , ⁇ 2 ). Among them, the specific definitions of the critical offset angles ⁇ 1 and ⁇ 2 are shown in Figure 2 and Figure 3.
  • the snapshot given in Figure 6 is the scene where the latitude of the adjacent LEO satellites on both sides of the ascending node and descending node is exactly equal to half of the phase angle of the adjacent LEO satellites.
  • the LEO satellite beams on both sides of the ascending node and descending node are both turned on. A good double coverage is formed near the node.
  • the LEO satellite 6-310-1 immediately behind the ascending node will be closed, and the LEO satellite 6-310-2 immediately behind the descending node will be closed.
  • Figure 6 also shows the process of covering cracks due to beam offset conversion near the North Pole.
  • the beam offset direction of the LEO satellite 6-310-3 is opposite to that of the adjacent satellite in front, and the beam of the LEO satellite is in the on state at the current moment.
  • the beam is closed, and the beam offset state is switched, and the beam direction is adjusted to the other side.
  • the offset size is unchanged.
  • the LEO satellite 6-310-3 completes the beam offset conversion within the phase interval of an adjacent LEO satellite and turns on the beam again, the maximum potential crack range generated by the LEO satellite in the current orbit is shown in 6-230.
  • the beam offset conversion process of the LEO satellite 6-310-4 near the South Pole is similar.
  • Fig. 7 shows the beam coverage of the LEO satellite moving forward by half the phase angle of the adjacent satellite based on Fig. 6, that is, the scene when the LEO satellite in the current orbit is passing the ascending node and descending node.
  • 7-110 is the earth
  • 7-120 is the north pole
  • 7-130 is the south pole
  • 7-140 is the LEO satellite
  • 7-150 is the LEO polar orbit
  • 7-160 is the equator
  • 7-170 is the direction of LEO movement
  • 7-230 is the maximum coverage area caused by the beam constant offset conversion when entering the north pole
  • 7-240 is the coverage area caused by the beam constant offset conversion when entering the south pole Maximum crack range
  • 7-310-1 represents the LEO satellite that closes the beam as a whole at the ascending node (when entering a position near the south latitude of the equator, it starts to close the beam as a whole, and the corresponding latitude argument is -1/2 ⁇ , ⁇ is The phase angles of two adjacent LEO
  • Figures 6 and 7 show the beam offsets of a series of LEO satellites in a single orbit and the beam offset switching moments and the corresponding overall beam closing moments.
  • the beam offset angle of the LEO satellite as the larger of the critical offset angles ⁇ 1 and ⁇ 2 , on the one hand, it ensures the continuous coverage of the LEO satellite near the equator, and on the other hand, it ensures the reception at any position near the equator.
  • the beam separation angles between the GEO satellites and LEO satellites obtained are all greater than or equal to the critical interference avoidance angle ⁇ .
  • Figure 8 is a scene where LEO satellites in multiple adjacent orbits enter and leave the Arctic dual coverage area and perform offset state transitions.
  • the LEO satellites in orbit i implement beam offsets near the North Pole.
  • the largest crack in the coverage area caused by the conversion can be covered by other LEO satellite beams in adjacent orbits i-1 and i+1.
  • 8-110 is represented as the i-th orbit
  • 8-120 is represented as the i-1th orbit
  • 8-130 is represented as the i+1th orbit
  • 8-210 is represented by the LEO satellite entering the North Pole in the i-th orbit.
  • the maximum potential coverage area crack range generated during beam offset conversion is composed of cracks caused by the reverse bias beam in orbit i and the beam to be closed.
  • LEO satellites in i-1 After entering the north pole double coverage area, it can be composed of adjacent orbit i+1 , LEO satellites in i-1 provide continuous coverage services; 8-220 represents the maximum potential coverage area crack size when the LEO satellite in the i-1 orbit leaves the North Pole to perform beam offset conversion, which is determined by the orbit i-1 The crack range caused by the reverse bias beam and the beam range to be closed; 8-230 represents the maximum potential coverage area crack range generated when the LEO satellite in the i+1 orbit leaves the North Pole to perform beam offset conversion.
  • the crack range caused by the reverse-biased beam in i+1 and the beam range to be closed; 8-310 represents the beam of the LEO satellite to be closed in the i-th orbit, when the beam enters the entire adjacent orbit and is provided by other LEO satellites The north pole double coverage area and leave a proper margin, and then close and start beam offset conversion; 8-320 indicates the beam of the LEO satellite that will be closed in orbit i-1; 8-330 indicates that the beam is about to be closed in orbit i+1 Closed LEO satellite beam; 8-410 represents the critical latitude of the LEO satellite sub-satellite point corresponding to the North Pole double coverage area. For beam 8-320 and 8-330, the beam offset conversion will be implemented after the beam is closed.
  • LEO satellites in adjacent odd-numbered and even-numbered orbits respectively select beam offset conversion when entering or leaving a certain position in the dual coverage area to obtain the maximum conversion processing time.
  • This method can ensure to the greatest extent that LEO satellites in orbit i can provide beams when they enter the Arctic dual coverage area to perform beam offset conversion and stop beam services.
  • LEO satellites in adjacent orbits i-1 and i+1 can provide beams. service.
  • the beam offset conversion near the South Pole is similar, and the same method can be used.
  • Fig. 9 is a schematic diagram of the orbit control thruster scheme when the constant beam offset is realized by offsetting the LEO satellite pitch axis attitude.
  • 9-110 is the earth
  • 9-120 is the north pole
  • 9-130 is the south pole
  • 9-140 is the LEO satellite
  • 9-150 is the orbital thruster
  • 9-160 is Is the equator
  • 9-170 indicates the direction of satellite movement
  • 9-180-1 indicates that the beam offset conversion is performed around the pitch axis + Y direction near the ascending node
  • 9-180-2 indicates that the pitch axis is used near the north pole- Y-direction rotation for beam offset conversion
  • 9-180-3 indicates that the pitch axis + Y direction rotation is used for beam offset conversion near the descending node
  • 9-180-4 indicates that the pitch axis-Y direction rotation is used near the South Pole Perform beam offset conversion.
  • Figure 9 adopts the layout of the orbit-controlled thruster reversed and pre-biased along the pitch axis.
  • the center of mass can still be obtained and the thrust along the tangential direction of the orbit can be generated, supporting the constant attitude Track correction in the tangential direction of the track during the offset period.
  • T1, T2, T3, and T4 show where the orbital thrusters can be arranged.
  • Figure 10 is a schematic diagram of a beam offset direction conversion scheme that uses a method of rotating 180° around the yaw axis (pointing to the center of the earth).
  • the beam pre-offset layout method is used to support orbit tangent during the constant beam offset period. Orbital correction of direction.
  • the layout of the orbit-controlled thruster can adopt the normal layout, and T1 and T2 show the positions of the orbit-controlled thrusters.
  • T1 and T2 show the positions of the orbit-controlled thrusters.
  • the polar orbit of the LEO satellite and the equatorial orbit of the GEO satellite have been described, but after reading the content of this disclosure, those skilled in the art will know how to make and use the embodiment of the present invention, such as other
  • the high-inclination LEO satellite system and the near-equator orbit high-orbit satellites with a certain orbital inclination can share radio frequency spectrum.
  • the inclination ⁇ i of a high-orbit satellite needs to be less than 1/2 ⁇
  • ⁇ is the phase angle of two adjacent LEO satellites
  • the orbital height of the high-orbit satellite is higher than that of the low-orbit satellite.
  • LEO satellite system can form a double or more coverage effect on the north and south poles.
  • the critical interference avoidance angle ⁇ 7°; the starting position of the progressive offset is selected as the north-south latitude 55°; At the intersection, the LEO satellite requires a maximum offset angle of 25° when the latitude argument is -3.6°, and the offset direction points to the equator; the LEO satellite requires a maximum offset angle of 25° when the latitude argument is 3.6°, and the offset The orientation points to the equator.
  • the LEO satellite For the descending node, the LEO satellite requires a maximum offset angle of 25° when the latitude argument is 176.4°, and the offset direction points to the equator; the LEO satellite requires a maximum offset angle of 25° when the latitude argument is 183.6°.
  • the bias direction points to the equator.
  • the half-width angle of the beam coverage area of a single LEO satellite is ⁇ 18° from north to south and ⁇ 26.5° from east to west, which can meet the requirements.
  • the corresponding constant beam offset angle is 21°.
  • the minimum separation angle between LEO satellite and GEO satellite can be guaranteed to be greater than 7°.
  • the overlap width of the coverage area between adjacent LEO satellites in the north-south direction is 159km, which is better than the 88km overlap width of the minimum coverage area in the north-south direction under the progressive beam offset strategy.
  • the beam offset state conversion starts when the sub-satellite point of the LEO satellite enters 65° north latitude, and for even-numbered orbits, the beam offset state conversion starts when the sub-satellite point of the LEO satellite leaves 65° north latitude. All beam offset conversions are completed within an adjacent LEO phase period. Among them, the beam offset conversion near the descending node and the south pole is similar to the method near the ascending node and the north pole, and can be treated symmetrically.
  • the width of the coverage area corresponding to the beam with a half-width angle of ⁇ 22° in the north-south direction is 1421km; in the constant beam offset strategy, the offset angle is 21° , The coverage area width of the beam with a half-width angle of ⁇ 18° in the north-south direction is 982km.
  • the ratio of the beam width of the constant offset strategy to that of the progressive offset strategy is 82%.
  • the ratio of the coverage area of the constant beam offset strategy to the coverage area of the progressive beam offset strategy is 69%.
  • the offset angle of the constant beam offset strategy is smaller than the offset angle of the progressive beam offset strategy, so the path loss of the constant offset strategy is smaller than the path loss under the progressive offset strategy.
  • the total load power of the LEO satellite under the constant beam offset strategy is only 69% of the total load power of the LEO satellite under the progressive offset strategy.

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Abstract

本发明提供一种基于波束常值偏置可与包括地球同步卫星在内的近赤道轨道运行的高轨通信卫星之间共享无线电频谱的方法及低轨通信卫星系统，方法包括：低轨通信卫星在南北极区、赤道附近完成发射波束常值偏置状态的转换，每次实施前后波束偏置方向相反，波束偏置程度为固定的常值；对于临近赤道附近的低轨通信卫星均偏向赤道方向；在北极、南极附近实施波束偏置转换期间，由当前轨道两侧相邻的另外两条轨道内其他低轨通信卫星的波束提供服务。在升交点、降交点附近实施波束偏置转换期间，由位于相同轨道内升交点或降交点另外一侧的相邻低轨通信卫星提供波束覆盖服务。

Description

基于波束常值偏置可共享无线电频谱的方法及低轨通信卫星系统
本申请要求于2019年7月12日提交中国专利局、申请号为201910630504.4、发明名称为“基于波束常值偏置可共享无线电频谱的方法及低轨通信卫星系统”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本发明涉及一种基于波束常值偏置可共享无线电频谱的方法及低轨通信卫星系统(即波束常值偏置共享无线电频谱的方法及低轨通信卫星系统)，属于地球轨道通信卫星技术领域。
背景技术
通信卫星已经是空间技术的重要应用之一，通信卫星从地球表面接收和发送无线电信号。随着卫星通信技术的进步和需求的爆发，无线电频谱已成为非常有价值的商品。某一范围的特定无线电频谱可以拍卖至几百亿美元的价格。
地球同步卫星是一种典型的通信卫星，其在与地球赤道(“赤道平面”)相交的平面内围绕地球运行，距离地球约36000千米(大约是地球半径的六倍)，轨道周期恰好是一个恒星日。地球同步卫星以与地球围绕其轴线旋转的完全相同的角速度绕地球运行，地球同步卫星相对于地面的观察者来说是相对静止的。
地球同步(通常缩写为“GEO”)卫星与地球表面之间的巨大距离可以实现广阔区域的覆盖，同时需要更高的发射信号功率，以及较大通信延迟，同时单颗星的容量有限并且成本也非常高昂。对于某些应用，例如互联网服务，靠近地球表面运行的卫星星座系统可能更适合。低轨卫星星座系统具有系统容量大、低延时优点，同时通过批生产可以降低单颗卫星成本。
图1为近地轨道(通常缩写为“LEO”)的通信卫星系统，其在极地轨道运行；其波束不偏置情况下对地球形成了连续覆盖，但不能与GEO通信卫星共享无线电频谱。LEO轨道通常被认为是不超过地球表面约2000千米的卫星轨道。如图1所示，与地球的半径相比，所述卫星轨道高度是小的；在比例图中，它对应于大约1200千米。在图1中，1-110表示为地球；1-120表示为北极点；1-130表示为南极点；1-140表示为LEO卫星；1-150表示为LEO极地轨道；1-160表示为赤道；1-170表示为卫星运动方向；1-180表示为未偏置的波束。
图2为与图1所示的赤道附近相同LEO卫星和GEO卫星轨道，假设GEO卫星轨道平面与赤道平面完全重合。为了便于文字标注，图2并未严格按照比例画出LEO、GEO卫星轨道高度，仅给出示意关系。2-110表示为地球表面；2-120表示为LEO卫星轨道；2-130表示为GEO卫星轨道；2-210表示为LEO卫星；2-220表示为GEO卫星；2-310表示为未偏置的波束；2-320表示为偏置后的波束；2-410表示为地球半径R E；2-420表示为LEO卫星轨道高度H LEO；2-430表示为GEO轨道高度H GEO；2-510表示为波束半锥角φ；2-520表示为临界偏置角θ 1；2-530表示为临界干扰规避角β；2-540表示为LEO卫星纬度幅角ω；2-610表示为未偏置的波束覆盖范围；2-620表示为偏置后的波束覆盖范围；2-710表示为LEO卫星的运动方向；2-810表示为GEO卫星轨道平面，其与赤道平面重合；2-820表示为LEO卫星轨道与赤道平面的升交点。
在图2中，LEO卫星的波束未进行偏置前，波束2-610内C点至A的某一范围内地面位置所接收到的GEO卫星与LEO卫星间的波束隔离角均小于临界干扰规避角β，在该区域内LEO卫星与GEO卫星无法共享无线频谱。向赤道方向偏置θ 1后，在波束范围内的整个弧段CD中的任意位置所接收到的GEO卫星与LEO卫星间的波束隔离角均大于等于临界干扰规避角β。LEO卫星偏置大于某一临界角度θ 1后，整个波束覆盖区域内的任意位置均支持 LEO卫星与GEO卫星可以共享无线频谱。临界偏置角度θ 1与临界干扰规避角β、LEO卫星所处的纬度幅角ω、波束的半锥角
Figure PCTCN2020099137-appb-000001
以及LEO卫星的轨道高度H LEO等参数相关。在其他参数固定的情况下，LEO卫星运动过程中越接近GEO卫星，为了通过偏置波束来实现与GEO卫星共享无线频谱所需要的临界偏置角度θ 1越大。
由图2分析可知，在与GEO卫星共享无线频谱情况下，为了避免LEO卫星对弧段AC范围内的GEO卫星用户带来干扰，除了关闭LEO卫星对应的部分波束外，将LEO卫星波束偏置一定角度是缓解与GEO卫星之间相互干扰的有效方法。
图3为升交点两侧相邻LEO卫星在对称波束偏置情况下形成二重覆盖的最低偏置角度要求示意图，其中两个LEO卫星所在的纬度幅角刚好等于相邻两颗LEO卫星的相位角的一半，即±1/2γ。为了便于文字标注，图3并未严格按照比例画出LEO、GEO卫星轨道高度，仅给出示意关系。在图3中，3-110表示为地球表面；3-120表示为LEO卫星轨道；3-130表示为GEO卫星轨道；3-210-1表示为LEO卫星k；3-210-2表示为LEO卫星k-1；3-220表示为GEO卫星；3-310-1表示为LEO卫星k偏置的波束，3-310-2表示为LEO卫星k-1偏置的波束；3-410表示为相邻两颗LEO卫星的相位角γ；3-420表示为了使升交点两侧相邻LEO波束形成二重覆盖的临界偏置角度θ 2；3-510表示升交点两侧相邻LEO的波束形成二重覆盖区域；3-610表示GEO卫星轨道平面，假设其与赤道平面重合；3-620表示为LEO卫星的运动方向；3-630表示为LEO卫星轨道与赤道平面相交的升交点；3-640表示为波束中心线。
在图3中，在升交点附近，LEO卫星k、LEO卫星k-1分别向赤道方向偏置θ 2后，其各自波束的前、后沿覆盖区域完全重合，其中LEO卫星k的纬度幅角为1/2γ，LEO卫星k-1的纬度幅角为-1/2γ，γ为相邻两颗LEO卫星的相位角。在形成二重覆盖的情况下，才可以保证在其中的一个LEO卫星 波束整体关闭情况下，其余相邻LEO卫星形成的覆盖区域仍为连续。
图4为专利“使干扰减少的通信卫星系统CN107210805A”给出的一种低轨道通信卫星系统与地球同步卫星共享无线电频谱的方案，其中LEO极地轨道与赤道平面相交于一升交点和一降交点。在图4中，4-110表示为地球；4-120表示为北极点；4-130表示为南极点；4-140表示为LEO卫星；4-150表示为LEO卫星极地轨道；4-160表示为赤道，其中赤道上空附近运行着一系列GEO卫星；4-170表示为运动方向；4-180表示为根据接近赤道的程度渐进向赤道偏置的波束；4-210表示升交点附近整体关闭波束的LEO卫星；4-220表示降交点附近整体关闭波束的LEO卫星。当低轨卫星沿其轨道行进时，LEO卫星波束逐渐偏置。作为逐渐偏置波束的结果，当LEO卫星接近赤道平面，其传输波束越来越朝向赤道平面瞄准。在所有卫星位置，LEO卫星的无线电信号和GEO无线电信号之间保持良好的角间距。在该轨道上沿着轨道均匀间隔地前进的LEO卫星向位于轨道下方的地球表面区域提供不间断的覆盖。被关闭的LEO卫星是最接近赤道平面的卫星。当LEO卫星穿过赤道平面时，被关闭的LEO卫星也会同时完成波束向另外一侧偏置方向的转换。当再开启的LEO卫星沿轨道行进时，它们恢复逐渐向前的倾斜，所述倾斜逐渐地将其覆盖区域提前于轨道。在沿轨道行进一半后，当它们再次到达另外一侧的赤道平面时，重复这个过程。
图4中所示的核心思想为：同轨道内的每颗卫星必须按照一个统一规律先后地在接近赤道的过程中实施绕俯仰轴(垂直于轨道平面)的渐进波束偏置，离开赤道后逐渐恢复正常对地波束覆盖状态；通过预留一定的覆盖区域重叠搭接余量来保证每条轨道内各个卫星在渐进偏置过程中对地面保持整体连续覆盖，在此基础上保证整个星座对地连续覆盖。
对于采取渐进波束偏置策略的LEO卫星，其单星波束整体覆盖区域一般会预留较大的余量用于相邻卫星覆盖区域重叠搭接设计。图5-1给出了基于渐进波束偏置策略的LEO卫星在不同纬度下的典型俯仰角变化曲线，方 案1采取了常值俯仰角速度的方法，方案2采取了变俯仰角速度方法。图5-2给出了采用图5-1中的方案1、2所得到的同轨道内相邻LEO卫星的覆盖区域重叠搭接宽度的规律。一般情况下，基于波束渐进偏置策略获得最小重叠覆盖区域宽度仅为波束不偏置情况下相邻LEO卫星重叠覆盖区域宽度的40％-60％。
对于LEO卫星系统的设计来说，等强度的最小覆盖区域重叠搭接设计才是最优的。渐进波束偏置设计必然要求同轨道内的相邻卫星预留出较大的波束覆盖余量。并且该方法需要在动态波束偏置过程中保持相对较高的控制精度，对LEO卫星的波束偏置装置要求也非常高。上述问题是基于渐进偏置方案的专利“使干扰减少的通信卫星系统CN107210805A”内在的不足之处。
此外，在采用通过姿态偏置实现波束渐进偏置情况下，仅能在非渐进偏置期间实施轨道面切向方向的轨道修正，对实施轨道修正的弧段范围有一定限制条件。
发明内容
本发明解决的技术问题为：克服现有技术不足，提供了一种基于波束常值偏置可共享无线电频谱的方法及低轨通信卫星系统。相对于专利“使干扰减少的通信卫星系统CN107210805A”中的波束渐进偏置策略，本发明提出的波束常值偏置策略可以实现相邻低轨通信卫星之间等强度的最小覆盖区域重叠搭接设计，同时不再需要高精度的渐进波束偏置控制装置。基于波束常值偏置策略可共享无线电频谱的低轨通信卫星系统在卫星的设计、制造及运营成本方面存在显著优势。
本发明解决的技术方案为：一种低轨道运行的第一通信卫星与近赤道轨道运行的第二通信卫星之间共享无线电频谱的方法(即为基于波束常值偏置可共享无线电频谱的方法)，(低轨优选为不超过地球表面约2000千米的卫星轨道；本发明并不严格对LEO卫星(即低轨卫星)的轨道高度做限制， 一般来说只要低于共享无线电频谱的近赤道轨道运行的高轨通信卫星轨道高度，支持构成满足设定需求的LEO卫星系统的轨道即可)，其特征在于：第一通信卫星所在的第一轨道低于第二通信卫星所在的第二轨道，第一轨道与赤道平面相交于一升交点和一降交点，第二轨道为近赤道轨道，所述方法包括：
(i)由第一通信卫星发射对准地球表面的无线电信号，形成一个波束；
(ii)第一通信卫星在升交点、降交点以及北极地区、南极地区附近完成发射波束常值偏置状态的转换；
波束偏置程度(即常值偏置大小)根据第一通信卫星和第二通信卫星共享频率对应的两个波束完成空间隔离而不互相干扰的最小角度(即最小隔离角)要求以及第一通信卫星的波束大小、轨道高度、同一轨道面内相邻第一通信卫星的相位角度大小、近赤道轨道第二通信卫星的轨道倾角确定；与第一通信卫星所处具体纬度无关；波束偏置程度为固定常值；
波束偏置，对于升交点，临近赤道附近的第一通信卫星均偏向赤道方向；对于降交点，临近赤道附近的第一通信卫星均偏向赤道方向；
波束常值偏置状态的转换，在每运行轨道周期内第一通信卫星运动至升交点附近、降交点附近以及北极地区附近、南极地区附近各实施一次，共四次；每次实施前后波束偏置方向相反，偏置程度相同；
波束偏置状态转换期间，当前波束(即发生波束偏置状态转换的卫星的波束)关闭并停止服务(即波束功率降低，不会发生对第二通信卫星的干扰)。
优选的，通过偏置整个第一通信卫星姿态来实现所述波束偏置。
优选的，实施卫星姿态偏置的装置包括反作用轮(即动量轮)或控制力矩陀螺。
优选的，采用绕第一通信卫星俯仰轴，进行姿态偏置实现。
优选的，通过偏置第一通信卫星俯仰轴姿态来实现常值波束偏置时，采用轨控推力器沿俯仰轴反方向预先偏置的布局方式，在进行俯仰偏置时仍可 获得过质心且产生沿轨道切向的推力，此轨控推力器布局方式支持在常值姿态偏置期间进行轨道切向方向的轨道修正。
优选的，常值姿态偏置，是指：通过常值偏置整个第一通信卫星姿态来实现所述常值波束偏置。
优选的，采用波束在俯仰轴方向实施预先偏置，然后绕偏航轴旋转180°的方法实现波束偏置方向转换。
优选的，波束在俯仰轴方向实施预先偏置时，因为偏置状态相对固定，支持针对波束在球面的投影进行关于地球曲率的优化。
优选的，其中通过转动第一通信卫星的一个或多个无线电天线来实现所述波束偏置。
优选的，其中所述波束偏置采用电子控制方式完成。
优选的，控制方式，采用相控阵天线技术进行波束偏置。
优选的，北极地区附近，是指：低轨通信卫星系统在北极地区形成的二重及以上覆盖区域。
优选的，南极地区附近，是指：低轨通信卫星系统在南极地区形成的二重及以上覆盖区域。
优选的，临近赤道附近的第一通信卫星，是指：对于升交点，在南极附近完成波束偏置状态反转后，还未实施北极附近波束偏置状态反转的第一通信卫星；对于降交点，在北极附近完成波束偏置状态反转后，还未实施南极附近波束偏置状态反转的第一通信卫星。
优选的，升交点附近，是指：升交点正负1/2相位角之间的区域，且包括升交点正负1/2相位角所对应的区域，相位角是指同一轨道面内相邻第一通信卫星的相位角度。
优选的，降交点附近，是指：降交点正负1/2相位角之间的区域，且包括降交点正负1/2相位角所对应的区域，相位角是指同一轨道面内相邻第一通信卫星的相位角度。
一种通信卫星系统，包括：多个第一通信卫星，多个第一通信卫星运行在多条第一轨道内；
所述第一轨道内的多个第一通信卫星按照设定相位规律分布；
所述第一轨道与赤道平面相交于一升交点和一降交点；
每条第一轨道与赤道平面的升、降交点按照设定规律间隔分布，各条第一轨道除升、降交点以外的参数保持相同；
所述第一通信卫星与包括地球同步卫星在内的近赤道轨道第二通信卫星之间共享无线电频谱；
所述第二通信卫星在第二轨道内运行；
所述第二轨道是近赤道轨道并且高于第一轨道；
所述卫星系统中第一通信卫星的波束能够协同完成对某一地面区域或全球表面以及其(即某一地面区域或全球表面)对应的设定海拔高度内空间的连续覆盖，在南北极区形成二重及以上覆盖；
所述第一通信卫星在每运行轨道周期内运动至升交点附近、降交点附近以及北极地区附近、南极地区附近各实施一次波束常值偏置状态的转换，每次实施前后波束偏置方向相反，偏置程度相同；
所述波束偏置程度根据第一通信卫星和第二通信卫星共享频率对应的两个波束完成空间隔离而不互相干扰的最小角度要求以及第一通信卫星的波束大小、轨道高度、同一轨道面内相邻第一通信卫星的相位角度大小确定；同时与近赤道轨道第二通信卫星的轨道倾角有关；与第一通信卫星所处具体纬度无关；波束偏置程度为固定常值；
所述波束偏置，对于升交点，临近赤道附近的第一通信卫星均偏向赤道方向；对于降交点，临近赤道附近的第一通信卫星均偏向赤道方向。
优选的，第一通信卫星在北极、南极附近实施波束偏置转换期间，当前第一通信卫星的波束关闭并停止服务，由当前第一轨道两侧相邻的另外两条第一轨道内的其他第一通信卫星的波束提供服务。
优选的，在北极或南极附近，相邻轨道的第一通信卫星分别选取进入或者离开二重覆盖区域某一位置时实施波束偏置转换以获取不同轨道相邻第一通信卫星之间最大转换处置时间间隔。
优选的，第一通信卫星在升交点附近实施波束偏置转换期间，当前第一通信卫星的波束关闭并停止服务，由升交点另外一侧位于相同第一轨道内相邻卫星的波束提供覆盖服务；
第一通信卫星在降交点附近实施波束偏置转换期间，当前第一位卫星的波束关闭并停止服务，由降交点另外一侧位于相同第一轨道内的相邻卫星提供波束覆盖服务。
优选的，升交点、降交点附近第一通信卫星在波束关闭前与另外一侧反方向偏置的相邻第一通信卫星的波束形成对地面服务区域的二重覆盖。
优选的，升交点、降交点附近同一时刻最多存在一颗第一通信卫星波束关闭并停止服务，其余相邻的第一通信卫星波束均开启。
优选的，波束常值偏置的方式支持同一轨道面内相邻第一通信卫星之间的波束覆盖区域均匀重叠搭接，利用最少的波束覆盖余量实现波束连续覆盖。
优选的，支持第一通信卫星整体关闭与开启波束策略。
优选的，第一通信卫星的波束相对于地球转动的角速度大小与第一通信卫星相对于地球转动的角速度相同。
优选的，第一通信卫星，包括：轨控推力器和反作用轮(即动量轮)或控制力矩陀螺；
轨控推力器能够提供产生轨控所需的推力；
反作用轮与控制力矩陀螺能用于卫星姿态的控制，并为姿态变化提供力矩。
优选的，第一通信卫星，还包括一个或多个无线电天线，来实现波束发射和接收。
优选的，第一通信卫星发射对准地球表面的无线电信号，形成一个波束。
优选的，波束偏置状态转换期间，当前波束关闭并停止服务，波束偏置转换结束后开启波束并提供服务。
优选的，设定相位规律分布是指第一轨道内的第一通信卫星等间隔均匀分布。
本发明与现有技术相比的优点在于：
(1)本发明提出的波束常值偏置策略在LEO卫星沿轨道前进时保持固定波束偏置状态，天然地支持最优的相邻LEO卫星间覆盖区域均匀重叠搭接设计，可以显著降低单颗卫星的覆盖搭接余量要求；仅需要在升交点、降交点以及北极地区、南极地区附近各实施一次波束常值偏置转换；对波束偏置转换动态过程的控制精度不做约束，对波束偏置装置的控制精度要求低；波束偏置转换期间可以采用整体波束关闭策略；波束相对于地球转动的角速度与LEO卫星相对于地球转动的角速度相同。
(2)通过偏置LEO卫星俯仰轴姿态来实现常值波束偏置时，可以采用轨控推力器沿俯仰轴反方向预先偏置的布局方式，在进行俯仰偏置时仍可获得过质心且产生沿轨道切向的推力，这种轨控推力器布局方式支持在常值姿态偏置期间进行轨道切向方向的轨道修正。如果是采用渐进偏置俯仰姿态实现波束渐进偏置的话，在绕俯仰轴姿态渐进偏置期间LEO卫星无法实施轨道切向方向的轨道修正，LEO轨道修正点火弧段受到一定限制。
(2)支持采用波束在俯仰轴方向实施预先偏置，然后绕偏航轴旋转180°的方法实现波束偏置方向转换方式。这种情况下，可以针对波束在球面的投影进行地球曲率优化；同时轨控推力器可以采取正常布局方式，LEO轨道修正点火弧段不会受到限制。
(3)采用电子控制方式完成波束偏置状态切换时，因为只存在两个波束偏置状态，可以降低波束偏置切换难度与成本。
附图说明
图1为现在技术的LEO卫星系统示意图，其波束不偏置情况下对地球形成了连续覆盖，但不能与GEO通信卫星共享无线电频谱。
图2为现在技术的为了实现与GEO通信卫星共享无线电频谱，LEO卫星波束在不同纬度下对应的最低偏置角度要求示意图。
图3为现在技术的升交点两侧相邻LEO卫星在对称波束偏置情况下形成二重覆盖的最低偏置角度要求示意图。
图4为现在技术的基于渐进波束偏置策略可以与近赤道卫星通信卫星共享无线电频谱LEO卫星系统示意图。
图5-1为现在技术的渐进波束偏置过程中LEO卫星在不同纬度幅角下的典型俯仰角变化曲线示意图。
图5-2为现在技术的渐进波束偏置过程中典型连续覆盖带余量随纬度幅角变化曲线示意图。
图6为基于波束常值偏置策略的可与GEO卫星共享无线电频谱的LEO通信卫星系统，选取了升交点、降交点两侧均有毗邻LEO卫星时刻场景。
图7为基于波束常值偏置策略的可与GEO卫星共享无线电频谱的LEO通信卫星系统，选取了单条轨道内的LEO卫星正经过升交点、降交点位置时的场景。
图8为基于波束常值偏置策略的可与GEO卫星共享无线电频谱的LEO通信卫星系统，选取了多条相邻轨道内的LEO卫星在进入北极二重覆盖区域、离开北极二重覆盖区域时刻进行偏置状态转换的场景。
图9为通过偏置LEO卫星俯仰轴姿态来实现常值波束偏置时的轨控推力器布局方案示意图。
图10为采用绕偏航轴(指向地球球心)旋转180°的方法实现波束偏置方向转换方案示意图。
具体实施方式
下面结合附图和具体实施例对本发明进行详细说明。
本发明一种基于波束常值偏置可与包括地球同步卫星在内的近赤道轨道运行的高轨通信卫星之间共享无线电频谱的方法及低轨通信卫星系统，方法包括：低轨通信卫星在南北极区、赤道附近完成发射波束常值偏置状态的转换，每次实施前后波束偏置方向相反，波束偏置程度为固定的常值；对于临近赤道附近的低轨通信卫星均偏向赤道方向；在北极、南极附近实施波束偏置转换期间，由当前轨道两侧相邻的另外两条轨道内其他低轨通信卫星的波束提供服务。在升交点、降交点附近实施波束偏置转换期间，由位于相同轨道内升交点或降交点另外一侧的相邻低轨通信卫星提供波束覆盖服务。
本发明所适用的低轨卫星通信系统包含多个LEO卫星，这些LEO卫星在相对于赤道平面有较大倾角的多个轨道上绕地球行进。在每个轨道中，多个LEO卫星以相等的相位间隔行进；每条轨道与赤道平面的升、降交点按照设定规律间隔分布；对于各条第一轨道，除升、降交点以外的轨道参数均保持相同。低轨卫星通信系统向轨道下方的地球表面上及其一定海拔高度内空间提供无间隙的良好覆盖。对于致力于全球覆盖的低轨卫星系统来说，采用大倾角近极地轨道是必然的。这是为了使低轨卫星通信系统完成对北极、南极地区覆盖而采用的一种通用做法，同时这也会必然导致北极、南极区域产生二重及以上覆盖效果。
本发明使得低轨卫星通信系统能够与包括地球同步卫星在内的近赤道高轨通信卫星之间共享无线电频谱，从而可以节省极为昂贵的无线电频谱资源。相对于渐进波束偏置策略，常值波束偏置策略可以使低轨卫星系统的LEO卫星波束覆盖范围可以按照最小覆盖区域重叠搭接设计进行选取。此外，相对于渐进波束偏置策略，常值波束偏置策略可以降低波束偏置控制装置的精度要求。这些特性使得基于波束常值偏置策略可共享无线电频谱的低轨通信卫星系统在卫星的设计、制造及运营成本方面存在显著优势。
根据本发明的实施例的LEO卫星沿着圆形极地轨道，其中LEO卫星极地轨道与赤道平面相交于一升交点和一降交点。对于升交点，临近赤道附近 的第一通信卫星均偏向赤道方向；对于降交点，临近赤道附近的第一通信卫星均偏向赤道方向。LEO卫星在升交点附近、降交点附近以及北极地区附近、南极地区附近各实施一次波束常值偏置转换，每次实施前后波束偏置大小相同，方向相反。
LEO卫星保持常值波束偏置状态如图6-10所示。除了正在穿越赤道的LEO卫星需要关闭波束来规避与GEO卫星之间的无线电频谱相互干扰外，其余位置LEO卫星的无线电信号和GEO卫星无线电信号之间因为进行了足够的波束偏置而保持良好的角间距间隔，没有必要关闭其余的LEO卫星任意波束的传输。
如果仅考虑单个轨道，近赤道两侧波束对称常值偏置策略必然会在北极、南极附近区域因波束偏置方向相反导致覆盖区域的裂缝。但是，对于致力于全球覆盖的低轨卫星系统来说，在与赤道保持较大倾角的多条相邻轨道上运行的低轨卫星系统必然会在北极、南极区域产生二重及以上覆盖效果。可以充分利用这一特性来解决基于近赤道两侧波束对称常值偏置策略导致单一轨道的北极、南极附近的覆盖区域裂缝问题。
在进入北极或南极二重覆盖区域后才开始实施波束偏置转换的情况下，使奇数、偶数不同轨道上的LEO卫星分别选取进入或者离开二重覆盖区域某一位置时实施波束偏置转换，可以获取不同轨道相邻LEO卫星之间最大转换处置时间间隔。这样可以最大程度地保证当前轨道的LEO卫星实施波束偏转时，当前轨道两侧相邻的另外两条轨道内的其他LEO卫星的波束不实施波束偏置转换并提供连续波束覆盖服务，从而保证任意时刻LEO卫星系统在北极、南极区域的覆盖连续性。例如，奇数轨道内的LEO卫星在进入极区的完整二重覆盖区域后进行波束偏置转换，偶数轨道内的LEO卫星在离开极区的完整二重覆盖区域前进行波束偏置转换。
当LEO卫星在升交点或降交点附近实施波束偏置转换期间，当前LEO卫星的波束关闭并停止服务，由位于相同轨道内升交点或降交点另外一侧相 邻LEO卫星提供波束覆盖服务。在升交点、降交点附近，同一时刻最多仅一颗卫星波束关闭，其余相邻的卫星波束均开启。在波束关闭前与另外一侧反方向偏置的相邻卫星的波束形成对地面服务区域的二重覆盖。
对于升交点或降交点附近的波束偏置转换过程，要求在一个相邻LEO卫星相位间隔周期内完成波束关闭、波束偏置转换、波束开启等工作。这是确保当前LEO卫星关闭并停止服务时，其前方相邻的LEO卫星的波束已经开启并提供服务，从而可以严格保证升交点或降交点附近低轨卫星系统的波束覆盖连续性。
对于北极地区、南极地区附近的波束偏置转换，理论上并不严格限制在一个相邻LEO卫星相位间隔周期内完成波束关闭、波束偏置转换、波束开启等工作，但是所用时间越长，该过程中单条轨道内产生的覆盖区域裂缝越大，对于不同轨道间LEO卫星协同实施波束偏置转换的具体位置与时机要求越苛刻。
结合LEO卫星硬件配置的能力，一般可以选取一个统一的波束偏置转换周期。在图6-10中，将波束关闭、波束偏置转换、波束开启的周期统一取为升交点、降交点处的要求最低要求，即一个相邻LEO卫星相位间隔周期。
如果是采用通过偏置俯仰轴姿态实现常值波束偏置的话，可以采用轨控推力器沿着俯仰轴反方向预先偏置的布局方式。采取该方法后，在进行俯仰偏置时仍可获得过质心且沿轨道切向方向的推力，支持在赤道两侧常值姿态偏置期间进行轨道切向方向的轨道修正，点火受限弧段范围更小。
如果是采用绕偏航轴(指向地球球心)旋转180°的方法实现波束偏置转换的话，可以采用波束在俯仰轴方向实施预先偏置方案。这种情况下，可以针对波束在球面的投影进行关于地球曲率的优化。同时轨控推力器可以采取正常布局方式，LEO轨道修正点火弧段不会受到限制。
如果是采用电子控制方式完成波束偏置状态切换时，因为只存在两个波 束偏置状态，可以降低波束偏置切换难度与成本。
图6为基于波束常值偏置策略的可与GEO卫星共享无线电频谱的LEO通信卫星系统，选取了升交点、降交点两侧均有毗邻LEO卫星时刻场景。在图6中，6-110表示为地球；6-120表示为北极点；6-130表示为南极点；6-140表示为LEO卫星；6-150表示为LEO极地轨道；6-160表示为赤道；6-170表示为运动方向；6-180表示为常值偏置的波束；6-210表示为升交点附近两侧卫星波束，基于常值波束偏置方案，其偏置方向相反，均指向赤道；6-220表示为降交点附近两侧卫星波束，基于常值波束偏置方案，其偏置方向相反，均指向赤道；6-230表示为进入北极时波束常值偏置转换导致的覆盖区域最大潜在裂缝范围大小(假设在一个相位间隔时间内完成波束偏置转换并再次开启波束)；6-240表示为进入南极时波束常值偏置转换导致的覆盖区域最大潜在裂缝范围大小(假设在一个相位间隔时间内完成波束偏置转换并再次开启波束)；6-310-1表示为升交点附近、下一时刻即将关闭波束的LEO卫星，当前LEO卫星所处纬度幅角为-1/2γ，其中γ为相邻两颗LEO卫星的相位角；6-310-2表示为降交点附近、下一时刻即将关闭波束的LEO卫星，当前LEO卫星所处纬度幅角为-1/2γ+180°；6-310-3表示为北极附近等待关闭波束进行偏置转换的LEO卫星(待该波束整体进入相邻轨道其他卫星提供的北极二重覆盖区域并留出适当余量后关闭)；6-310-4表示为南极附近等待关闭波束进行偏置转换的LEO卫星(待该波束整体进入相邻轨道其他卫星提供的南极二重覆盖区域并留出适当余量后关闭)。
升交点、降交点两侧卫星的偏置角度需要同时满足两个条件，一方面需要大于临界偏置角θ 1，使任意位置所接收到的GEO卫星与LEO卫星间的波束隔离角均大于等于临界干扰规避角β；另一方面还需要大于升交点或降交点两侧相邻LEO卫星相互对称偏置形成二重覆盖所对应的临界偏置角度θ 2。最终的偏置角度取两者中的最大值max(θ 1，θ 2)。其中，临界偏置角θ 1、θ 2的具体定义情况见图2、图3。
对于轨道倾角为0°的GEO卫星(轨道平面与赤道平面重合)，为了使处于纬度幅角为ω(本发明取为同一轨道内相邻LEO卫星相位角γ的一半，具体定义见图3)且波束半锥角为
Figure PCTCN2020099137-appb-000002
的LEO卫星与GEO卫星的最小波束隔离角大于临界干扰规避角β时，所对应的临界偏置角θ 1计算方法如下：
Figure PCTCN2020099137-appb-000003
Figure PCTCN2020099137-appb-000004
其中，地球半径R E、LEO卫星轨道高度H LEO、GEO轨道高度H GEO、波束半锥角
Figure PCTCN2020099137-appb-000005
临界偏置角θ 1、临界干扰规避角β、LEO卫星纬度幅角ω的定义见图2；ω大小等于1/2γ，γ为相邻两颗LEO卫星的相位角，具体定义见图3；α、η为角度变量。该公式为采用了一定工程简化的解析方法，因为GEO卫星相对于LEO轨道足够高，该简化计算结果精度足够工程上使用；也可以用数值迭代的方法进行求解。
如果需要与具有小倾角△i(△i不能大于1/2γ，γ为相邻两颗LEO卫星的相位角)的近赤道GEO卫星共享无线电频谱，则需要偏置相对更大的倾角来实现无线电频率干扰规避。这种情况下等价于在纬度幅角ω为1/2γ-△i位置处通过偏置临界偏置角θ 1来实现与轨道倾角为0的GEO卫星共享无线电频谱所对应的临界干扰规避角β。
对于临界偏置角度θ 2的具体数值，在给定几何参数下可以用数值迭代方法求解，具体定义情况见图3。
需要指出的是，上述计算均是获取LEO卫星在纬度幅角等于±1/2γ时所必须的最小临界偏置角；如果需要与多颗位于不同位置、具有不同倾角的GEO卫星同时共享无线电频率，只要在这一系列最小偏置角中选取最大值即可。
图6中给出的快照为升交点、降交点处两侧相邻LEO卫星所在的纬度 正好等于相邻LEO卫星相位角的一半场景，升交点、降交点各自两侧的LEO卫星波束均开启，在节点附近形成良好的二重覆盖。下一时刻，对于升交点后方的紧邻LEO卫星6-310-1即将关闭，降交点后方的紧邻LEO卫星6-310-2即将关闭。
图6同时也给出了在北极附近由于需要进行波束偏置转换产生覆盖裂缝的过程。LEO卫星6-310-3与其前方相邻卫星的波束偏置方向相反，当前时刻该LEO卫星波束为开启状态。当该LEO卫星波束继续向前运动至可以由相邻轨道LEO卫星提供二重覆盖区域并留出适当余量后关闭波束，并进行波束偏置状态转换，将波束方向调整至另一侧，波束偏置大小不变。假设LEO卫星6-310-3在一个相邻LEO卫星相位间隔时间内完成波束偏置转换并再次开启波束，则当前轨道内的LEO卫星产生的最大潜在裂缝范围大小如6-230所示。南极附近LEO卫星6-310-4波束偏置转换过程与之类似。
图7为在图6基础上LEO卫星向前运动半个相邻卫星相位角的波束覆盖情况，即当前轨道内的LEO卫星正经过升交点、降交点时刻的场景。在图7中，7-110表示为地球；7-120表示为北极点；7-130表示为南极点；7-140表示为LEO卫星；7-150表示为LEO极地轨道；7-160表示赤道；7-170表示为LEO运动方向；7-230表示为进入北极时波束常值偏置转换导致的覆盖区域最大裂缝范围；7-240表示为进入南极时波束常值偏置转换导致的覆盖区域最大裂缝范围；7-310-1表示为升交点处整体关闭波束的LEO卫星(当进入接近赤道南纬附近某一位置后开始整体关闭波束，对应的纬度幅角为-1/2γ，γ为相邻两颗LEO卫星的相位角；关闭期间实施波束偏置转换)；7-310-2表示为降交点处整体关闭波束的LEO卫星(当进入接近赤道北纬附近某一位置后开始整体关闭波束，对应的纬度幅角为-1/2γ+180°，γ为相邻两颗LEO卫星的相位角；关闭期间实施波束偏置转换)；7-310-3表示为北极附近已经整体关闭波束的LEO卫星(关闭期间实施波束偏置转换)；7-310-4表示为南极附近已经整体关闭波束的LEO卫星(关闭期间实施波束 偏置转换)。
图6、图7给出了单个轨道内的一系列LEO卫星的波束偏置情况以及波束偏置转换时刻以及与之对应的整体波束关闭时刻。将LEO卫星的波束偏置角度大小取为临界偏置角θ 1、θ 2中的较大值，一方面保证了LEO卫星在赤道附近的连续覆盖性，一方面保证了赤道附近任意位置处接收到的GEO卫星与LEO卫星间的波束隔离角均大于等于临界干扰规避角β。
图8为多条相邻轨道内的LEO卫星在进入北极二重覆盖区域、离开北极二重覆盖区域时刻进行偏置状态转换的场景，其中轨道i内的LEO卫星在进入北极附近实施波束偏置转换导致的覆盖区域最大裂缝可以由相邻轨道i-1、i+1内其他LEO卫星波束进行覆盖。在图8中，8-110表示为第i轨道；8-120表示为第i-1轨道；8-130表示为第i+1轨道；8-210表示为第i轨道内LEO卫星进入北极实施波束偏置转换时产生的最大潜在覆盖区域裂缝范围大小，由轨道i内反向偏置波束导致的裂缝以及待关闭的波束构成，在进入北极二重覆盖区域后可以由相邻轨道i+1、i-1内的LEO卫星提供连续覆盖服务；8-220表示为第i-1轨道内LEO卫星离开北极实施波束偏置转换时产生的最大潜在覆盖区域裂缝范围大小，由轨道i-1内反向偏置波束导致的裂缝范围以及待关闭的波束范围构成；8-230表示为第i+1轨道内LEO卫星离开北极实施波束偏置转换时产生的最大潜在覆盖区域裂缝范围大小，由轨道i+1内反向偏置波束导致的裂缝范围以及待关闭的波束范围构成；8-310表示为第i轨道内待关闭的LEO卫星波束，当该波束整体进入由相邻轨道其他LEO卫星提供的北极二重覆盖区域并留出适当余量后关闭并开始实施波束偏置转换；8-320表示为轨道i-1中即将关闭的LEO卫星波束；8-330表示为轨道i+1中即将关闭的LEO卫星波束；8-410表示为北极二重覆盖区域对应的LEO卫星星下点临界纬度。对于波束8-320、8-330，波束关闭后开始实施波束偏置转换，其最晚的实施时刻要求为完成当前波束偏置转换并开启波束后其同轨道前方相邻LEO卫星的波束后沿仍在北极二重覆 盖区域之内并留出适当余量。在该过程中，相邻奇数、偶数轨道的LEO卫星分别选取进入或者离开二重覆盖区域某一位置时施波束偏置转换以获取最大转换处置时间。采取这种方法可以最大程度地保证轨道i内的LEO卫星在进入北极二重覆盖区域实施波束偏置转换停止波束服务时，其相邻轨道i-1、i+1内的LEO卫星能够提供波束服务。在南极附近的波束偏置转换是类似的，采取同样的方法即可。
图9为通过偏置LEO卫星俯仰轴姿态来实现常值波束偏置时的轨控推力器方案示意图。在图9中，9-110表示为地球；9-120表示为北极点；9-130表示为南极点；9-140表示为LEO卫星；9-150表示为轨控推力器；9-160表示为赤道；9-170表示为卫星运动方向；9-180-1表示在升交点附近采用绕俯仰轴+Y方向旋转进行波束偏置转换；9-180-2表示在北极附近采用绕俯仰轴-Y方向旋转进行波束偏置转换；9-180-3表示在降交点附近采用绕俯仰轴+Y方向旋转进行波束偏置转换；9-180-4表示在南极附近采用绕俯仰轴-Y方向旋转进行波束偏置转换。图9采用了轨控推力器沿着俯仰轴反向预先偏置的布局方式，在沿着俯仰轴偏置情况下仍可获得过质心且产生沿轨道切向方向的推力，支持在常值姿态偏置期间进行轨道切向方向的轨道修正。T1、T2、T3、T4给出了轨控推力器可以布局的位置示意。
图10为采用绕偏航轴(指向地球球心)旋转180°的方法实现波束偏置方向转换方案示意图，采用了波束预先偏置布局的方法，支持在常值波束偏置期间进行轨道切向方向的轨道修正。在图10中，10-110表示为地球；10-120表示为北极点；10-130表示为南极点；10-140表示为LEO卫星；10-150表示为轨控推力器；10-160表示为赤道；10-170表示为卫星运动方向；10-180-1表示为升交点附近绕偏航轴旋转180°进行波束偏置转换；10-180-2表示为北极附近绕偏航轴旋转180°进行波束偏置转换；10-180-3表示为降交点附近绕偏航轴旋转180°进行波束偏置转换；10-180-4表示为南极附近绕偏航轴旋转180°进行波束偏置转换。轨控推力器布局可以采用正常布局方式，T1、T2 给出了轨控推力器可以布局的位置示意。这种情况下，因为偏置状态相对固定，支持针对波束在球面的投影进行关于地球曲率的优化。
由图6-10的介绍可知，波束在提供服务期间均为常值波束偏置状态，波束相对于地球转动的角速度与LEO卫星相对于地球转动的角速度相同。
本发明的实施例中已经针对LEO卫星的极地轨道和GEO卫星的赤道轨道进行了说明，但是在阅读本公开的内容之后，本领域技术人员将清楚如何制作和使用本发明的实施例，例如其他大倾角LEO卫星系统与具有一定轨道倾角的近赤道轨道高轨卫星之间实现无线电频谱共享。一般来说，-轨道高轨卫星的倾角△i需要小于1/2γ，γ为相邻两颗LEO卫星的相位角，且高轨卫星轨道高度高于低轨卫星的轨道。
为了便于直观地反映常值偏置策略的成本优势，下面以具体一低轨卫星系统为例做详细说明。
假设LEO卫星系统基本参数如下：轨道高度1200km，轨道倾角87.9°，一共18条轨道，每轨道内等间隔分布LEO卫星，每轨道内的LEO卫星数量为50个，在波束不偏置情况下每颗LEO卫星的波束覆盖区域的半宽角为南北±22°、东西±26.5°(整个覆盖区域为南北方向986km、东西方向1228km)，不偏置时相邻LEO卫星覆盖区域南北方向交叠163km。当LEO卫星星下点进入南、北纬度63°时，LEO卫星系统能够对北极、南极形成二重及以上覆盖效果。
基于渐进波束偏置策略，LEO卫星为了与某一轨道倾角为0°的GEO卫星共享无线电频谱，取临界干扰规避角β＝7°；选取渐进偏置起始位置为南北纬55°；对升交点，LEO卫星在纬度幅角为-3.6°时所需要最大偏置角为25°，偏置方向指向赤道；LEO卫星在纬度幅角为3.6°时所需要最大偏置角为25°，偏置方向指向赤道。对于降交点，LEO卫星在纬度幅角为176.4°时所需要最大偏置角为25°，偏置方向指向赤道；LEO卫星在纬度幅角为183.6°时所需要最大偏置角为25°，偏置方向指向赤道。对渐进波束偏 置规律进行优化，得到各个相邻LEO卫星间南北方向最小覆盖区域重叠搭接宽度为88km。
如果采用本发明的常值波束偏置策略，对于同样的星座构型参数，单颗LEO卫星的波束覆盖区域的半宽角为南北±18°、东西±26.5°时就可以满足要求，此时对应的常值波束偏置角大小为21°。对于升交点，纬度幅角为±3.6°时，波束偏置角度为21°时可以保证LEO卫星与GEO卫星之间最小隔离角大于7°。常值波束偏置策略下，南北方向相邻LEO卫星间覆盖区域重叠搭接宽度均为159km，优于渐进波束偏置策略下南北方向最小覆盖区域重叠搭接宽度88km。对于奇数轨道，当LEO卫星的星下点进入北纬65°时开始进行波束偏置状态转换，对于偶数轨道，当LEO卫星星下点离开北纬65°时开始进行波束偏置状态转换。所有的波束偏置转换在一个相邻LEO相位周期内完成。其中，降交点、南极附近的波束偏置转换与升交点、北极附近的做法类似，对称处理即可。
在渐进波束偏置策略中，偏置角度为25°时，南北方向半宽角为±22°的波束对应的覆盖区域宽度为1421km；常值波束偏置策略中，偏置角度为21°时，南北方向半宽角为±18°的波束对应的覆盖区域宽度为982km。
常值偏置策略的波束宽度与渐进偏置策略的波束宽度比为82％。对于最大偏置情况，常值波束偏置策略的覆盖区域面积与渐进波束偏置策略下的覆盖区域面积比为69％。
常值波束偏置策略的偏置角度小于渐进波束偏置策略的偏置角度，因此常值偏置策略路径损耗小于渐进偏置策略下的路径损耗。
进一步假设通量密度相等，则在最大偏置情况下，常值波束偏置策略下LEO卫星的载荷总功率仅为渐进偏置策略下LEO卫星载荷总功率的69％。
以上基本参数的对比表明，采用常值波束偏置策略的LEO卫星的研制成本可以大幅降低。

Claims (30)

  1. 一种低轨道运行的第一通信卫星与近赤道轨道运行的第二通信卫星之间共享无线电频谱的方法，其特征在于：第一通信卫星所在的第一轨道低于第二通信卫星所在的第二轨道，第一轨道与赤道平面相交于一升交点和一降交点，第二轨道为近赤道轨道，所述方法包括：
    (i)由第一通信卫星发射对准地球表面的无线电信号，形成一个波束；
    (ii)第一通信卫星在升交点、降交点以及北极地区、南极地区附近完成发射波束常值偏置状态的转换；
    波束偏置程度根据第一通信卫星和第二通信卫星共享频率对应的两个波束完成空间隔离而不互相干扰的最小角度要求以及第一通信卫星的波束大小、轨道高度、同一轨道面内相邻第一通信卫星的相位角度大小、近赤道轨道第二通信卫星的轨道倾角确定；与第一通信卫星所处具体纬度无关；波束偏置程度为固定常值；
    波束偏置，对于升交点，临近赤道附近的第一通信卫星均偏向赤道方向；对于降交点，临近赤道附近的第一通信卫星均偏向赤道方向；
    波束常值偏置状态的转换，在每运行轨道周期内第一通信卫星运动至升交点附近、降交点附近以及北极地区附近、南极地区附近各实施一次，共四次；每次实施前后波束偏置方向相反，偏置程度相同；
    波束偏置状态转换期间，当前波束关闭并停止服务。
  2. 根据权利要求1所述的方法，其特征在于：通过偏置整个第一通信卫星姿态来实现所述波束偏置。
  3. 根据权利要求2所述的方法，其特征在于：实施卫星姿态偏置的装置包括反作用轮或控制力矩陀螺。
  4. 根据权利要求2所述的方法，其特征在于：采用绕第一通信卫星俯仰轴，进行姿态偏置实现。
  5. 根据权利要求4所述的方法，其特征在于：通过偏置第一通信卫星俯仰轴姿态来实现常值波束偏置时，采用轨控推力器沿俯仰轴反方向预先偏置的布局方式，在进行俯仰偏置时仍可获得过质心且产生沿轨道切向的推力，此轨控推力器布局方式支持在常值姿态偏置期间进行轨道切向方向的轨道修正。
  6. 根据权利要求5所述的方法，其特征在于：常值姿态偏置，是指：通过常值偏置整个第一通信卫星姿态来实现所述常值波束偏置。
  7. 根据权利要求2所述的方法，其特征在于：采用波束在俯仰轴方向实施预先偏置，然后绕偏航轴旋转180°的方法实现波束偏置方向转换。
  8. 根据权利要求7所述的方法，波束在俯仰轴方向实施预先偏置时，因为偏置状态相对固定，支持针对波束在球面的投影进行关于地球曲率的优化。
  9. 根据权利要求1所述的方法，其特征在于：其中通过转动第一通信卫星的一个或多个无线电天线来实现所述波束偏置。
  10. 根据权利要求1所述的方法，其特征在于：其中所述波束偏置采用电子控制方式完成。
  11. 根据权利要求10所述的方法，其特征在于：控制方式，采用相控阵天线技术进行波束偏置。
  12. 根据权利要求1所述的方法，其特征在于：北极地区附近，是指：低轨通信卫星系统在北极地区形成的二重及以上覆盖区域。
  13. 根据权利要求1所述的方法，其特征在于：南极地区附近，是指：低轨通信卫星系统在南极地区形成的二重及以上覆盖区域。
  14. 根据权利要求1所述的方法，其特征在于：临近赤道附近的第一通信卫星，是指：对于升交点，在南极附近完成波束偏置状态反转后，还未实施北极附近波束偏置状态反转的第一通信卫星；对于降交点，在北极附近完成波束偏置状态反转后，还未实施南极附近波束偏置状态反转的第一通信卫 星。
  15. 根据权利要求1所述的方法，其特征在于：升交点附近，是指：升交点正负1/2相位角之间的区域，且包括升交点正负1/2相位角所对应的区域，相位角是指同一轨道面内相邻第一通信卫星的相位角度。
  16. 根据权利要求1所述的方法，其特征在于：降交点附近，是指：降交点正负1/2相位角之间的区域，且包括降交点正负1/2相位角所对应的区域，相位角是指同一轨道面内相邻第一通信卫星的相位角度。
  17. 一种通信卫星系统，其特征在于包括：多个第一通信卫星，多个第一通信卫星运行在多条第一轨道内；
    其中所述第一轨道内的多个第一通信卫星按照设定相位规律分布；
    其中所述第一轨道与赤道平面相交于一升交点和一降交点；
    每条第一轨道与赤道平面的升、降交点按照设定规律间隔分布，各条第一轨道除升、降交点以外的参数保持相同；
    所述第一通信卫星与包括地球同步卫星在内的近赤道轨道第二通信卫星之间共享无线电频谱；
    所述第二通信卫星在第二轨道内运行；
    所述第二轨道是近赤道轨道并且高于第一轨道；
    所述卫星系统中第一通信卫星的波束能够协同完成对某一地面区域或全球表面以及其对应的设定海拔高度内空间的连续覆盖，在南北极区形成二重及以上覆盖；
    其中所述第一通信卫星在每运行轨道周期内运动至升交点附近、降交点附近以及北极地区附近、南极地区附近各实施一次波束常值偏置状态的转换，每次实施前后波束偏置方向相反，偏置程度相同；
    其中所述波束偏置程度根据第一通信卫星和第二通信卫星共享频率对应的两个波束完成空间隔离而不互相干扰的最小角度要求以及第一通信卫星的波束大小、轨道高度、同一轨道面内相邻第一通信卫星的相位角度大小、 近赤道轨道第二通信卫星的轨道倾角确定；与第一通信卫星所处具体纬度无关；波束偏置程度为固定常值；
    其中所述波束偏置，对于升交点，临近赤道附近的第一通信卫星均偏向赤道方向；对于降交点，临近赤道附近的第一通信卫星均偏向赤道方向。
  18. 根据权利要求17所述系统，其特征在于：第一通信卫星在北极、南极附近实施波束偏置转换期间，当前第一通信卫星的波束关闭并停止服务，由当前第一轨道两侧相邻的另外两条第一轨道内的其他第一通信卫星的波束提供服务。
  19. 根据权利要求17所述系统，其特征在于：在北极或南极附近，相邻轨道的第一通信卫星分别选取进入或者离开二重覆盖区域某一位置时实施波束偏置转换以获取不同轨道相邻第一通信卫星之间最大转换处置时间间隔。
  20. 根据权利要求17所述系统，其特征在于：第一通信卫星在升交点附近实施波束偏置转换期间，当前第一通信卫星的波束关闭并停止服务，由升交点另外一侧位于相同第一轨道内相邻卫星的波束提供覆盖服务；
    第一通信卫星在降交点附近实施波束偏置转换期间，当前第一位卫星的波束关闭并停止服务，由降交点另外一侧位于相同第一轨道内的相邻卫星提供波束覆盖服务。
  21. 根据权利要求17所述的系统，其特征在于：升交点、降交点附近第一通信卫星在波束关闭前与另外一侧反方向偏置的相邻第一通信卫星的波束形成对地面服务区域的二重覆盖。
  22. 根据权利要求17所述的系统，其特征在于：升交点、降交点附近同一时刻最多存在一颗第一通信卫星波束关闭并停止服务，其余相邻的第一通信卫星波束均开启。
  23. 根据权利要求17所述的系统，其特征在于：波束常值偏置的方式支持同一轨道面内相邻第一通信卫星之间的波束覆盖区域均匀重叠搭接，利用 最少的波束覆盖余量实现波束连续覆盖。
  24. 根据权利要求17所述的系统，其特征在于：支持第一通信卫星整体关闭与开启波束策略。
  25. 根据权利要求17所述的系统，其特征在于：第一通信卫星的波束相对于地球转动的角速度大小与第一通信卫星相对于地球转动的角速度相同。
  26. 根据权利要求17所述的系统，其特征在于：第一通信卫星，包括：轨控推力器和反作用轮或控制力矩陀螺；
    轨控推力器能够提供产生轨控所需的推力；
    反作用轮与控制力矩陀螺能用于卫星姿态的控制，并为姿态变化提供力矩。
  27. 根据权利要求17所述的系统，其特征在于：第一通信卫星，还包括一个或多个无线电天线，来实现波束发射和接收。
  28. 根据权利要求17所述的系统，其特征在于：第一通信卫星发射对准地球表面的无线电信号，形成一个波束。
  29. 根据权利要求17所述的系统，其特征在于：波束偏置状态转换期间，当前波束关闭并停止服务，波束偏置转换结束后开启波束并提供服务。
  30. 根据权利要求17所述的系统，其特征在于：设定相位规律分布是指第一轨道内的第一通信卫星等间隔均匀分布。
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