EP0951760A1 - Procede pour commander la transmission d'un faisceau d'energie rayonnee dans un systeme par satellite cellulaire - Google Patents

Procede pour commander la transmission d'un faisceau d'energie rayonnee dans un systeme par satellite cellulaire

Info

Publication number
EP0951760A1
EP0951760A1 EP97923397A EP97923397A EP0951760A1 EP 0951760 A1 EP0951760 A1 EP 0951760A1 EP 97923397 A EP97923397 A EP 97923397A EP 97923397 A EP97923397 A EP 97923397A EP 0951760 A1 EP0951760 A1 EP 0951760A1
Authority
EP
European Patent Office
Prior art keywords
satellite
earth
spanning cell
elongate
longitudinal axis
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP97923397A
Other languages
German (de)
English (en)
Inventor
Edward F. Tuck
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Individual
Original Assignee
Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Individual filed Critical Individual
Publication of EP0951760A1 publication Critical patent/EP0951760A1/fr
Ceased legal-status Critical Current

Links

Classifications

    • 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
    • H04B7/204—Multiple access
    • H04B7/2041—Spot beam multiple access

Definitions

  • the present invention relates to the field of satellites. More particularly, this invention provides methods of conveying and controlling a beam of radiated energy to or from a satellite orbiting the Earth in an orbit which is not an Equatorial orbit at geosynchronous altitude.
  • the present invention offers optimized frequency utilization and enhanced availability, capacity and reliability of remote sensing and communication services.
  • central transmitting and receiving antennas are stationary, and subscribers may communicate with one another while moving from cell to cell.
  • a low Earth orbit network also allows subscribers to move, but the transmitting and receiving antennas aboard each satellite in the network are constantly in motion. Unlike some earlier communications systems which employed satellites in geosynchronous orbits, the spacecraft in low Earth orbit will move rapidly across the sky over any given place on the ground. Since the position of a low Earth orbit
  • LEO 15 (LEO) satellite is not fixed with respect to a location on the ground, some LEO networks require complicated schemes for steering radio beams to users on the ground. Since each LEO satellite is only visible for a few minutes from the user's point of view, any communication through the network that lasts more than a few minutes must be handled by more than one satellite. The complex switching that is required to "hand-off continuous communications service from one satellite to another imposes severe processing and power burdens on the LEO 0 satellites.
  • United States Patent No. 5,268,694 by Jan et al. discloses a communication system employing low Earth orbiting satellites which project footprints on the Earth by means of antennas radiating and receiving energy. Each footprint is divided into cells. The cell shape is shown as hexagonal and described as being more circular or elliptical dependent upon the beam control.
  • Hirshfield et al. describe a communications satellite payload providing for communication between user devices, such as hand-held cellular telephones and terrestrial gateways. The payload supports a plurality of independent antenna beams.
  • Jan et al. 5 show many discrete cells of small diameter which are organized in the footprint according to the best fit. In this manner they are not aligned with the satellite's track.
  • Hirshfield et al. show somewhat larger and more elliptical cells than Jan et al. Hirshfield cells are organized into a best-fit pattern and are not maintained in any particular reference to the changing relative velocity of the satellite over the Earth as it travels through its orbit.
  • Rouffet et al. teach a system for communication with
  • Rouffet et al. specifically call for beams aligned with the direction of a satellites travel in orbit (direction
  • Rouffet et al. do not suggest that the antenna beams be continuously maintained aligned with a vector which is the satellite's track on the Earth's surface.
  • the system described by Rouffet et al. is also constrained by the use of a single frequency band for communication. It is therefore necessary for the system to operate the beams alternatively to prevent interference.
  • Rouffet et al. disclose sub-division of the beams to implement a time division multiple access technique for preventing interference between signals and for no 0 other purpose. However, their elongated cell is not disclosed as being divided into a plurality of linear segments.
  • an "Earth-fixed cell” is a stationary region mapped to an "Earth- fixed grid” that has permanent fixed boundaries, just like a city or a state. Although the rapidly moving satellites still shine their radio beams over the ground in rapidly moving footprints, the locations of the footprints at any
  • This assignment process takes time and consumes processing capacity at both the terminal and the satellite. It is also subject to blocking, call interruption, and call dropping if there is not an idle communication channel in the next serving beam or satellite.
  • the Earth-fixed cell method avoids these problems by allocating communication channels (frequency, code and or time slot) on an Earth-fixed cell basis rather than on a satellite- fixed cell basis. Regardless of which satellite/beam is currently serving a particular cell, the terminal maintains the same channel assignment, thus substantially eliminating the "hand-off problem.
  • the Earth-fixed cell method uses software that provides position and attitude information about each satellite in the constellation. Position data from this software enables each satellite to map or bound the surface into areas representing an unchanging "Earth-fixed grid.” Each satellite is capable of steering, transmitting and receiving beams conveying packets of information to the Earth-fixed grid. The beams are continually adjusted to compensate the effects of satellite motion, attitude changes, and the rotation of the Earth. These goals are accomplished by partitioning satellite footprints into elongate, preferably linear, spanning cells and optionally also into multiple elongate, preferably linear, segments. Unfortunately, many satellite communication and remote sensing systems that will be launched in the near future will rely on the more conventional method of utilizing satellite-fixed cells. Without the great benefits of an Earth-fixed cell method, a large portion of the microprocessor capabilities and power capacities of these systems will be diverted to internal switching tasks.
  • the preferred embodiment of the Cellular Satellite System pertains to the management and allocation of radio beams which are generated by a satellite which moves with respect to the Earth's surface.
  • the invention pertains to any satellite which is not in an Equatorial orbit at geosynchronous altitude.
  • the present invention reduces hand-off overhead in systems that utilize satellite-fixed cells, augments frequency re-use, and enhances the communications and sensing capacity of the satellite. These goals are accomplished by partitioning satellite footprints into elongate spanning cells and multiple elongate segments.
  • the elongate spanning cells are areas that contain the satellite's track along the ground. They resemble long strips that extend along the entire footprint. Multiple elongate segments are smaller contiguous areas that lie within the elongate spanning cells.
  • the longitudinal axis of the elongate spanning cells is actually slightly offset from the projection of apparent direction of travel of the satellite by a correction angle ⁇ . This correction angle compensates for the changing relative motion of the Earth's surface at various latitudes.
  • terminals in the satellite's track remain within the spanning cells for approximately the entire time the satellite footprint passes over the terminal. This feature reduces the number of hand-offs as the satellite-fixed cells sweep over the terminal, augments frequency re-use and enhances the communications and sensing capacity of the satellite.
  • Figures 1 and 2 are schematic illustrations of the Earth and of satellites operating in orbits which are not Equatorial orbits at geosynchronous altitude.
  • Figure 3 reveals satellites in Earth orbit and the footprints they produce on the Earth's surface.
  • Figure 4 is a schematic diagram that shows a single footprint and a single elongate spanning cell. The alignment of the elongate spanning cell has been corrected by an angle ⁇ which compensates for the changing relative motion of the Earth's surface at various latitudes.
  • Figure 5 is a schematic diagram that reveals a single footprint and several elongate spanning cells.
  • Figure 6 presents another schematic diagram showing a single footprint, several elongate spanning cells and a number of multiple elongate segments within each elongate spanning cell.
  • Figures 7, 8 and 9 supply graphs which illustrate the functional relationships of the correction angle versus argument of perigee for a near-polar orbit, surface velocity versus latitude and latitude of nadir versus argument of perigee for an inclined orbit.
  • Figure 10 is a schematic illustration of a satellite in Earth orbit. This figure also portrays the satellite's track on the Earth, which resembles a spiral.
  • Figure 11 is a perspective view of a satellite which is designed for use with the preferred embodiment of the invention.
  • FIGs 12, 13, 14, 15 and 16 are schematic block diagrams of components aboard the satellite shown in Figure 1 1 which are employed to practice the present invention.
  • Figures 1 and 2 show a constellation 10 of satellites 12 circling the Earth E as they travel along polar, equatorial, or inclined orbits 11. Figures 1 and 2 also depict the Equator and several Great Circles.
  • the present invention may be practiced using only one or many satellites 12.
  • the present invention pertains only to satellites that use satellite-fixed cells, i.e., satellites that are constantly in motion with respect to the Earth.
  • the orbits 1 1 shown in Figures 1 and 2 may be any orbit which is not an Equatorial orbit or an orbit at geosynchronous altitude.
  • the term "orbit" refers to any trajectory of movement above the atmosphere of a celestial body, including circular and elliptical trajectories.
  • Figure 3 exhibits three satellites 12 moving along an orbital pathway 11 above the Earth E in a direction of travel T.
  • a continuous line is formed on the surface at the satellite's nadir N. This line is called the satellite's track T.
  • Each satellite 12 includes a radiation interface 14 which is capable of transmitting and/or receiving radiated energy 15a, 15b and 15c.
  • the term "radiated energy” pertains to any form of energy, including a signal, which is transported from one position to another. Radiated energy includes all forms of waves and particles irrespective of wavelength, including electromagnetic and optical radiation.
  • the radiation interface 14 comprises transmit and receive antennas. If the satellite employed to practice the present invention performs remote sensing tasks, the radiation interface 14 comprises sensors or detectors.
  • the spacecraft may also be used to direct some beneficial transmission toward the Earth E. Examples of such transmissions may include messages from a store-and-forward telecommunication system, compressed musical works for transfer to compact disks or illuminating radiation for a resource-mapping radar.
  • the satellites 12 communicate with personal, mobile and fixed terminals P, M, F and gateways G on or near the surface.
  • the word "terminal" is intended to encompass any device capable of sending or receiving radiated energy. Terminals include gateways. While most terminals are located on the Earth, they may be near the Earth, e.g., they may reside on an aircraft.
  • the area on the surface of the Earth that is illuminated by the radiated energy 15 emitted by a communications satellite 12 is known as the satellite's footprint 16.
  • the interface 14 collects some form of radiation from an elliptical region on the surface of the Earth known as a "reception zone.”
  • a reception zone 17 defines the area at a given time which is "viewed" by a sensor aboard a satellite 12.
  • a reception zone is substantially the same as a footprint 16, but a footprint 16 is defined by radiated energy 15 directed toward and impinging upon the Earth, while a reception zone 17 is defined by a surface on the Earth from which energy is radiated that may also be detected by a satellite at a particular instant.
  • the footprint and reception zone boundaries are set by the radiation pattern of the radiation interface 14.
  • the boundaries are selected by a selected roll-off of signal from a maximum value at or near the center of the footprint 16 or zone 17.
  • the three elliptical regions depicted in Figure 3 may be either footprints 16a, 16b and 16c or reception zones 17a, 17b and 17c.
  • Figure 4 exhibits a single footprint 16 containing a single elongate spanning cell 18.
  • the spatial points in each footprint 16 or reception zone 17 are mapped into long strips referred to as linear spanning cells 18 by electronic transformation of the spatial points by the radiation interface.
  • the elongate spanning cells extend across along an entire footprint 16 or reception zone 17.
  • Each cell 18 has two parallel sides along its longest dimension and a longitudinal axis 20 halfway between its two longest sides and parallel to them.
  • the two relatively short sides of the cell 18 are collinear with an ellipse, because the boundary of the footprint 16 or the reception zone 17 which each cell 18 spans is always an ellipse itself.
  • the edges of the elongate spanning cells are shaped by beam shaping and steering electronics aboard the satellite 12.
  • a footprint 16 and any elongate spanning cells 18 within it are constantly moving across the Earth's surface as the satellite 12 which creates the footprint 16 flies across the sky overhead.
  • the instantaneous position of an elongate spanning cell 18 relative to its footprint 16 is determined by the track T' of the satellite 12 over the ground and by a correction angle ⁇ .
  • the correction angle is chosen to align the satellite radiation interface 14 longitudinal axis 20 with the satellite's motion over the Earth's surface. If the Earth were not turning, no correction would be needed.
  • Figure 4 shows the instantaneous positions of both an uncorrected and a corrected elongate spanning cell extending along a footprint 16.
  • the uncorrected elongate spanning cell 18 is lightly shaded, and is centered along the projected line of the satellite's direction in orbit marked by reference character T.
  • the elongate spanning cell which has been aligned by altering its position by correction angle ⁇ is heavily shaded, and is centered along the line T, marked by reference character 24.
  • the correction angle ⁇ is measured at the intersection I of the satellite's track T and the line T, the projection of the satellite's direction in orbit. For the sake of clarity, the magnitude of the correction angle ⁇ has been exaggerated in Figure 4.
  • Figure 5 portrays a footprint 16 containing a number of linear spanning cells 18, while Figure 6 portrays both linear spanning cells 18 and multiple linear segments 22 within a footprint 16 (or reception zone 17).
  • the multiple linear segments 22 are provided by dividing the cell 16 with additional shaped and steered beams 15.
  • Multiple linear segments 22 add additional "space division multiple access" to the communication system. This provides more reuse of allocated frequencies, hence a larger number of users can be accommodated simultaneously.
  • the following discussion concerns the derivation of the appropriate correction angle ⁇ based on the satellite's latitude.
  • the derivation applies to the special case of a near-polar orbit.
  • the terminal will seem to move about 3/4 of the way across the cell 18 in the cell's three minute dwell time at the Equator, decreasing toward the poles.
  • the dwell time is the period of time the satellite footprint spends on a given point on the Earth's surface.
  • This phenomenon will increase handoff activity, since about half of the terminals will have to change cells from this cause in their three minute dwell time. As described above, this problem can be substantially eliminated by swinging the cell pattern a few degrees in each direction during the satellite's orbit. This compensation may be accomplished using a slow mechanical movement of the antenna or an electrical means, depending on the antenna design, and is described in complete detail below.
  • the frame of reference is the "fixed stars", i.e., a reference frame based on inertial space.
  • the Earth is turning on its axis and satellites are moving in their orbits with respect to this frame of reference. Since the orbits of satellites of Earth move through space with the Earth's center of mass, we have assumed for convenience that the frame of reference moves with the Earth in its orbit.
  • the surface of the Earth E as seen from this frame of reference moves from West to East.
  • the velocity is highest at the Equator, and decreases in proportion to the cosine of the latitude to zero at the poles. Because one nautical mile (about 6076.1 feet) is defined as one minute of longitude at the Equator, it is very convenient in the following analysis to work in nautical miles and in nautical miles per hour (knots).
  • the surface velocity of the Earth at a latitude L, V S (L), in knots, as seen by a distant observer in the reference frame is always from West to East, and is given by Equation One:
  • V (L) cos( ) (Equation One) s 24
  • L is the latitude in degrees of the point on the Earth's surface at which the velocity is being measured.
  • Equation Two In the simple case of a circular polar orbit, an orbit of constant altitude which passes over both the North Pole and the South Pole, the motion of the satellite is always at right angles to the motion of the Earth's surface, and, assuming a spherical Earth, the orbital period is the time it takes for the satellite to travel completely around the Earth, may be found using Equation Two:
  • Equation Two Equation Two
  • ⁇ is the period of orbit
  • r e is the radius of the Earth, i.e., 6378.165 km
  • h is the orbital altitude in km
  • Equation Three The orbital velocity of a satellite in a circular orbit is given by Equation Three:
  • the motion of the satellite's nadir across the surface of the Earth is the vector sum of the satellite's velocity and the Earth's surface velocity.
  • the angle at which the Earth's surface is moving with respect to the direction of the satellite's motion in the inertial reference frame is the angle portion of that vector sum. If the satellite 12 is moving Northward in its orbit, and the orbit is at a small angle to the Earth's axis, the Earth's surface will move from left to right below the satellite, and to fit that motion, the satellite's radiation pattern must be aligned in a Northwest-Southeast direction. As the satellite approaches the North Pole, the necessary angle of the correction decreases, and is zero when.directly over the North Pole NP.
  • the correction angle As the satellite proceeds Southward, the correction angle must swing to the satellite's right, to a Southwest-Northeast alignment, since West is now on the satellite's right. The correction angle reaches a maximum as the satellite crosses the Equator. The angle then decreases to zero as the satellite crosses the South Pole SP, reversing to a Northwest- Southeast alignment after the South Pole SP is crossed.
  • the discussion presented below utilizes the navigator's convention that True North is zero degrees, with the direction angle increasing as direction changes toward the East. In other words, the angle of direction changes from zero degrees through 360 degrees as the compass needle moves clockwise from the starting point of True North.
  • the correction angle, ⁇ (L) which is the angle of the motion of the Earth's surface with respect to the satellite at latitude L, may be determined using Equation Four:
  • V 0 is the orbital velocity of the satellite
  • i is the orbital inclination, /. e. , the angle measured between the plane containing the satellite's orbit and the plane containing the Earth's Equator
  • ⁇ is the argument of perigee, i.e., the satellite's orbital position as given by the number of degrees of a 360-degree orbit it has traveled since crossing the Equator in a Northbound direction
  • L( ⁇ ) is the latitude of the satellite at argument of perigee ⁇ .
  • L( ⁇ ) is equal to ⁇ for satellites in polar orbits, for a value of ⁇ of ninety degrees or less.
  • the graph 200 presented in Figure 7 was generated using a value of i of ninety degrees, which corresponds to a "pure" polar orbit.
  • i ninety degrees
  • the correction angle varies as the satellite 12 makes one complete orbit as shown in Figure 7.
  • Negative angles indicate motion to the left of the satellite as it proceeds in its orbit, while positive angles indicate motion to the right.
  • the satellite's nadir never reaches the pole, so that the maximum latitude is less than ninety degrees.
  • the latitude of the nadir can be found at any moment from Equation Five:
  • L is the latitude of the nadir
  • i is the inclination of the orbit
  • f is a very small anomaly which may be ignored for the purposes of this calculation
  • ⁇ is the argument of perigee of the satellite.
  • the graph 208 depicted in Figure 9 is based on Equation Five and plots the latitude of nadir 210 versus the argument of perigee 212 for a satellite in an inclined orbit.
  • the correct angle of the radiation interface 14, which may be an antenna 34, with respect to the body of the satellite 12 must be ascertained.
  • Other information that is required includes the relative speed and direction of the satellite, and the direction of the Earth's surface at the nadir.
  • the preferred method of acquiring the needed information employs a navigation receiver on the satellite
  • GPS Global Positioning System
  • Such receivers are readily available from a number of manufacturers. Thousands of personal versions of GPS receivers are produced each month by companies such as MagellanTM and GarminTM. Space-qualified versions are produced by companies such as Interstate ElectronicsTM, MotorolaTM and Rockwell InternationalTM. These receivers provide continuous information on their position with respect to the Earth's surface, already corrected for the Earth's motion, and all
  • Such receivers either provide, or can readily be adapted to provide, an output signal which gives a continuous value of the receiver's speed and direction with respect to the Earth's surface.
  • the satellite 12 which is used to implement the present invention will include attitude sensing and stabilization mechanisms that supply an output signal which give a continuous value of the receiver's speed and direction with respect to the Earth's surface.
  • Other systems on board the satellite 12 will contain attitude sensing and stabilization mechanisms which furnish 0 an output signal proportional to the orientation of the satellite's structure with respect to its direction of motion. These two signals can be added or subtracted to give a signal directly proportional to the relative angle of the satellite's body to the satellite's direction of motion over the Earth's surface T'.
  • the antenna can then easily be rotated by a conventional servo-mechanism to place its long axis in line with that direction of motion.
  • Figure 10 is a schematic depiction of a satellite 12 in a ten day polar orbit. The track of the satellite on 5 the ground appears as a spiral T'.
  • Figure 1 1 reveals one of many satellite designs that may be utilized to realize the benefits of the present invention.
  • the satellite 12 comprises a body 30, a solar array 32 and an antenna 34 which includes a narrow reflector with a parabolic cross-section.
  • the internal components of the satellite 12 include an inertia wheel 36, an antenna positioning servo 38 and a radio-frequency feed to antenna 39.
  • Figures 12 and 13 are schematic block diagrams 39 and 45 depicting generalized groups of electronic circuits aboard the satellite 12.
  • Figure 12 shows a GPS receiver 100 which produces an output that includes an altitude and latitude signal 40. This signal is fed to a converter 42 which, in turn, produces a control signal 44 that governs the action of an antenna positioning servo 38.
  • the GPS receiver 100 is described in great detail in the text which follows and in Figure 16.
  • 5 Figure 13 shows an alternative circuit that includes a radio receiver 46 which produces a synchronizing pulse 48 that is fed to timers 50.
  • the timers 50 generate an elapsed time code 52 which is supplied to a converter 54.
  • the converter emits a control signal 56 which directs the action of an antenna positioning servo 38.
  • Figure 14 is a schematic block diagram 57 that portrays the GPS receiver 100 and accompanying electronic components in greater detail.
  • the GPS receiver 100 generates two digital signals.
  • the first signal comprises a number which is the speed of the satellite over the Earth's surface, and an angle which is the angle between the satellite's velocity and the underlying meridian of longitude. These quantities are components of the satellite's velocity vector, represented as box 62 in Figure 14.
  • the second digital signal is the latitude of the satellite's nadir, shown as box 64 in Figure 14.
  • a microprocessor 66 receives these two signals 62 and 64 from receiver 100, in addition to the angle of the satellite's longitudinal axis with respect to the Earth's axis 60 which is supplied by an attitude sensor 58.
  • the microprocessor 66 multiplies the vector constant equal to the surface velocity of the Earth's Equator by the cosine of the latitude. This product yields the vector of the surface velocity at the satellite's nadir, V afford.
  • the microprocessor 66 also calculates the resultant of the satellite velocity vector and the surface vector V n .
  • the angle portion of this resultant, corrected by the angle of the satellite's longitudinal axis with the Earth's axis, is the beam offset angle 68.
  • FIG. 15 offers another schematic block diagram 71 that is specifically designed for use with satellites
  • a radio receiver 46, a star tracker 72 or a GPS receiver 100 may be utilized to generate an Equator-crossing pulse 74 which resets a timer 76.
  • the timer 76 sends a "time since crossing" ( ⁇ c ) signal 78 to a function generator 80.
  • the ⁇ c signal 78 is proportional to the time that has elapsed since the satellite 12 crossed the Equator.
  • the function generator 80 includes a memory which stores a quantity ⁇ , ⁇ , which is the time it takes the satellite to complete one half of its orbit around the globe, and also stores the satellite's velocity vector.
  • the function generator output is equal to the angle of the satellite's apparent motion over the Earth's surface, taking into account the surface velocity of the Earth at the satellite's nadir.
  • the surface velocity, V is the velocity at the Equator, V, in Equation Six:
  • V' VcosL (Equation Six)
  • L is the latitude at the satellite's nadir.
  • the latitude in this case can be set equal to:
  • An adder 84 algebraically sums the correction angle from the function generator's output with the actual offset of the satellite's longitudinal axis with respect to the Earth's axis 82 and its direction of motion with respect to the Earth's axis. The result is the beam offset angle 86, which is used to a control servo-mechanism 38 that points the satellite antenna 34.
  • FIG 16 is a schematic block diagram 100 of the internal components and functions of a GPS receiver.
  • the GPS receiver is a superheterodyne with a voltage-controlled local oscillator.
  • the existing 5 constellation of GPS satellites use a code-division modulation scheme (like CDMA), which allows all of the GPS satellites to use the same bandwidth segment. Signals from different GPS satellites are detected by matching them with a code that is peculiar to each satellite.
  • This function is performed by an active detector 1 12, which receives an input from an antenna 102 through a low-noise amplifier 104, a mixer 106, a band-pass filter 108 and an intermediate frequency amplifier 110.
  • a satellite selector 118 uses an algorithm to pick a set of GPS satellites, usually four, which are in view and whose positions are widely-enough spaced to provide a good navigation solution.
  • the satellites chosen by the selector 118 are indicated by arrow 120 in Figure 16.
  • the satellite selector 118 bases its selection on satellite position information from the almanac memory 132 and a present-time signal 126 from the local clock 124.
  • the local clock 124 is connected to a temperature-compensated crystal oscillator ("TXCO”) 125. All the internal
  • timing signals used in the GPS satellite are derived from the TXCO 125.
  • the selector 1 18 then passes the satellite's identity to the code generator 122, which generates the appropriate code for the desired satellite. This code is shifted in phase with respect to the local clock 124 until it matches the received signal code as determined by the active detector 112. This condition is maintained by a code tracking control loop 123.
  • the satellite selector 118 Since the GPS satellites are moving rapidly, the satellite selector 118 also calculates the frequency offset
  • the detected signal from the satellite is a bitstream which contains a fragment of the almanac 132, the satellite's ephemerides 134, a health bit 128 and another administrative information, and very precise time marks.
  • This bitstream is separated into its components by a signal decoder 130.
  • a GPS satellite orbit calculator 136 uses the almanac 132 and ephemeride 134 information and Kepler's equations to calculate the position 138 of each chosen GPS satellite in its orbit with a precision of a few meters. This information is transmitted to the satellite selector 118 and to the navigation microprocessor 140.
  • the navigation microprocessor 140 receives a timing signal from the local clock 124 and a timing signal from each satellite for each chosen satellite. Since the speed of radio signals is a known constant, the navigation
  • the navigation computer 140 has four pseudo-ranges. If, however, the ranges were accurate, three would be sufficient to find an exact position. To find an exact
  • the computer solves a system of four equations in four unknowns: latitude 142, longitude 146, altitude 144 and the local clock error. The result is a position 142, 144 & 146 and precise time 148 output.
  • the algorithms used in these calculations make allowance for the Earth's rotation, so that the position found is a point on the Earth's surface.
  • positions are generated frequently, usually at intervals of a second or less.
  • the receiver utilizes the most recent two or three positions and their associated times to calculate speed and direction of motion with respect to the Earth's surface. This task is accomplished in the speed and course computer 150.
  • the speed and course output 152 can be combined with knowledge of the orientation of the body of the satellite to its direction of motion, which is derived from an attitude computer 154, to determine the appropriate pointing angle 156 of the antenna 34.
  • two GPS receivers 100 and 158 can be employed, separated by several feet on the satellite's structure. The satellite's attitude and any rotation of its structure can be then be determined by comparing the positions of the two receivers 100 and 158.
  • the satellite 12 is furnished with information describing its velocity with respect to the Earth's surface from an Earth-based radar system. This information can be combined with information from the satellite's attitude-sensing equipment to generate an antenna pointing signal.
  • Another alternative utilizes circuits aboard the satellite 12 that generate a continuous relative- velocity signal.
  • An on-board computer is used to continuously solve Kepler's equations for the satellite's orbit and adds the Earth's motion, derived from the latitude of the nadir as calculated above. The computer is updated periodically by an Earth-based signal which provides the ephemerides of the satellite's orbit from radar or visual observations.
  • Yet another alternative inco ⁇ orates a method that is useful for a satellite in a stabilized circular orbit.
  • a device onboard the satellite is programmed with the equation of its fixed orbit.
  • the output signal of the device is the relative velocity and angle of the satellite's course over the Earth's surface.
  • the device receives synchronizing pulses periodically (as a practical matter, as infrequently as monthly for some orbits) from radar or visual sightings.
  • the resulting information which for such an orbit repeats itself each orbit and which in principle can be generated by a mechanism as simple as a cam, can be used to point the satellite antenna.
  • the dwell time of a terminal in an elongate spanning cell is on the order of two to eight times longer for the present invention than the time a terminal would reside in a cell of Jan et al. as shown in U.S. Patent No. 5,268,694.
  • the cells of the present invention when divided into four elongate segments, have a dwell time of 10/4 2.5 minutes.
  • a comparison of time of dwell with the cell of the present invention and Rouffet is not meaningful, since Rouffet's beams are made to hop around within the footprint to prevent interference between user terminals operating on the same frequency.
  • the Cellular Satellite System described above will enhance the ability of satellite communication systems, particularly those availing satellite fixed cell techniques, to carry higher message traffic volumes from a greater number of users. It can be seen that by pointing the satellite radiation interface 14 to maintain the elongate spanning cells 18 in alignment with the satellite's track T' over the Earth's surface, a terminal P,M,G in the satellite's track T' remains (dwells) within an elongate spanning cell 18 for approximately the entire time the satellite footprint 16 passes over the terminal P,M,G.
  • the dwell time of a terminal P,M,G within the track-aligned, elongate spanning cell 18 is many times longer than the dwell time of a terminal P,M,G in a hexagonal, circular or elliptical shaped satellite-fixed cell created by known satellites in comparable orbits. Even when the elongate spanning cell 18 is subdivided into multiple linear segments 22, a terminal P,M,G dwells for more than two times longer than in a satellite-fixed cell created by known satellites in comparable orbits. This feature saves time to access a satellite by reducing the number of hand-offs as the satellite-fixed cells 16 sweep over a terminal P,M,G. Saving time augments frequency re-use, and thereby enhances the communications and sensing capacity of the satellite 12 resulting in economic benefit to the users and proprietors of the system.
  • Reception zone Elongate spanning cells Longitudinal axis of elongate spanning cell Multiple elongate segments Corrected position of longitudinal axis Satellite body Solar array Parabolic reflector Inertia wheel Antenna positioning servo Radio-frequency feed to antenna Altitude and latitude signal Converter Control signal Radio receiver Synchronizing pulse Timers Elapsed time code Converter Control signal Attitude sensor Angle of satellite longitudinal axis with Earth's axis Satellite velocity vector Latitude Microprocessor Beam offset angle Star tracker Equator-crossing pulse Timer 78 Time since crossing

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Radio Relay Systems (AREA)

Abstract

Des empreintes de satellite (16a, 16b, 16c) sont divisées en cellules allongées (18) et en multiples segments allongés (22). Les cellules allongées (18) se présentent sous la forme de bandes allongées s'étendant le long d'une empreinte complète (16a, 16b, 16c). L'alignement des cellules allongées (18) le long d'une empreinte (16a, 16b, 16c) est déterminé par un angle de correction Ζ qui compense les variations du mouvement relatif de la surface de la terre à différentes latitudes.
EP97923397A 1997-01-17 1997-01-17 Procede pour commander la transmission d'un faisceau d'energie rayonnee dans un systeme par satellite cellulaire Ceased EP0951760A1 (fr)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/US1997/000204 WO1998032245A1 (fr) 1997-01-17 1997-01-17 Procede pour commander la transmission d'un faisceau d'energie rayonnee dans un systeme par satellite cellulaire

Publications (1)

Publication Number Publication Date
EP0951760A1 true EP0951760A1 (fr) 1999-10-27

Family

ID=22260195

Family Applications (1)

Application Number Title Priority Date Filing Date
EP97923397A Ceased EP0951760A1 (fr) 1997-01-17 1997-01-17 Procede pour commander la transmission d'un faisceau d'energie rayonnee dans un systeme par satellite cellulaire

Country Status (3)

Country Link
EP (1) EP0951760A1 (fr)
AU (1) AU2921097A (fr)
WO (1) WO1998032245A1 (fr)

Families Citing this family (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20080055151A1 (en) 2006-08-29 2008-03-06 Wildblue Communications, Inc. Network-Access Satellite Communication System
US9184829B2 (en) 2010-05-02 2015-11-10 Viasat Inc. Flexible capacity satellite communications system
US8218476B2 (en) 2010-05-02 2012-07-10 Viasat, Inc. Flexible capacity satellite communications system with dynamic distribution and coverage areas
US10511379B2 (en) 2010-05-02 2019-12-17 Viasat, Inc. Flexible beamforming for satellite communications
WO2013019673A1 (fr) 2011-07-29 2013-02-07 Viasat, Inc. Déploiement incrémental de passerelles dans un système de communication satellite du type « hub and spoke » utilisant des faisceaux très étroits fixes
EP2789109B1 (fr) 2011-12-08 2016-03-23 ViaSat, Inc. Gestion d'interference dans un système étoilé de communication par satellite à faisceaux d'antenne multiple.
US8509144B2 (en) 2011-12-08 2013-08-13 Viasat, Inc. Bent pipe beam switching for virtual utility gateways
US9275690B2 (en) 2012-05-30 2016-03-01 Tahoe Rf Semiconductor, Inc. Power management in an electronic system through reducing energy usage of a battery and/or controlling an output power of an amplifier thereof
US8805275B2 (en) 2012-06-11 2014-08-12 Viasat Inc. Robust beam switch scheduling
US9509351B2 (en) 2012-07-27 2016-11-29 Tahoe Rf Semiconductor, Inc. Simultaneous accommodation of a low power signal and an interfering signal in a radio frequency (RF) receiver
US9666942B2 (en) 2013-03-15 2017-05-30 Gigpeak, Inc. Adaptive transmit array for beam-steering
US9531070B2 (en) 2013-03-15 2016-12-27 Christopher T. Schiller Extending beamforming capability of a coupled voltage controlled oscillator (VCO) array during local oscillator (LO) signal generation through accommodating differential coupling between VCOs thereof
US9722310B2 (en) 2013-03-15 2017-08-01 Gigpeak, Inc. Extending beamforming capability of a coupled voltage controlled oscillator (VCO) array during local oscillator (LO) signal generation through frequency multiplication
US9837714B2 (en) 2013-03-15 2017-12-05 Integrated Device Technology, Inc. Extending beamforming capability of a coupled voltage controlled oscillator (VCO) array during local oscillator (LO) signal generation through a circular configuration thereof
US9716315B2 (en) 2013-03-15 2017-07-25 Gigpeak, Inc. Automatic high-resolution adaptive beam-steering
US9184498B2 (en) 2013-03-15 2015-11-10 Gigoptix, Inc. Extending beamforming capability of a coupled voltage controlled oscillator (VCO) array during local oscillator (LO) signal generation through fine control of a tunable frequency of a tank circuit of a VCO thereof
US9780449B2 (en) 2013-03-15 2017-10-03 Integrated Device Technology, Inc. Phase shift based improved reference input frequency signal injection into a coupled voltage controlled oscillator (VCO) array during local oscillator (LO) signal generation to reduce a phase-steering requirement during beamforming
US11146328B2 (en) * 2015-04-03 2021-10-12 Qualcomm Incorporated Method and apparatus for avoiding exceeding interference limits for a non-geostationary satellite system
WO2018190794A1 (fr) 2017-04-10 2018-10-18 Viasat, Inc. Réglage de zone de rayonnement afin d'adapter des communications par satellite

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2677197B1 (fr) * 1991-05-31 1994-09-16 Alcatel Espace Systeme de communications par satellites en orbite basse a destination de terminaux mobiles.
US5548294A (en) * 1994-08-17 1996-08-20 Teledesic Corporation Dielectric lens focused scanning beam antenna for satellite communication system
US5227802A (en) * 1991-12-23 1993-07-13 Motorola, Inc. Satellite system cell management

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9832245A1 *

Also Published As

Publication number Publication date
WO1998032245A1 (fr) 1998-07-23
AU2921097A (en) 1998-08-07

Similar Documents

Publication Publication Date Title
US5621415A (en) Linear cell satellite system
WO1998032245A1 (fr) Procede pour commander la transmission d'un faisceau d'energie rayonnee dans un systeme par satellite cellulaire
US6333924B1 (en) High latitude geostationary satellite system
US5957409A (en) Ellipitical satellite system which emulates the characteristics of geosychronous satellites
US5619211A (en) Position locating and communication system using multiple satellite constellations
RU2278472C2 (ru) Усовершенствованные система и способ организации системы негеостационарных спутников, не создающих помех в работе спутников, находящихся на геостационарном кольце
US20020136191A1 (en) System and method for satellite communications
US20060276128A1 (en) System and method for implementing a constellation of non-geostationary satellites that does not interfere with the geostationary satellite ring
US7065373B2 (en) Method of steering smart antennas
WO1998020634A2 (fr) Partage des frequences pour systeme de telecommunications par satellite
US6081227A (en) Method and apparatus for beam management in a satellite communication system
US6678519B2 (en) Elliptical satellite system which emulates the characteristics of geosynchronous satellites
US6990314B1 (en) Multi-node point-to-point satellite communication system employing multiple geo satellites
US11735818B2 (en) One-dimensional phased array antenna and methods of steering same
JPH10336111A (ja) Ｌｅｏネットワークにおける衛星間通信リンクの中断防止操作のための方法及び装置
US6611683B1 (en) Elliptical satellite system which emulates the characteristics of geosynchronous satellites
KR100589473B1 (ko) 시간 신호 송수신 방법
US20040211864A1 (en) Efficient communications utilizing highly inclined, highly elliptic orbits
US5574660A (en) Communication method and apparatus
EP1208660A2 (fr) Systeme de communication par satellite point-a-point multinodal utilisant plusieurs satellites geostationnaires
US6695262B2 (en) Spacecraft methods and structures for enhanced service-attitude accuracy
Seumahu Exploration of the equatorial LEO orbit for communication and other applications
WO2002039616A2 (fr) Constellation de satellites geostationnaires virtuels et procede de telecommunications par satellite
JP2004088563A (ja) 通信衛星システム
Ali et al. Little LEO Satellites

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

17P Request for examination filed

Effective date: 19990719

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): DE FR GB IT

GRAG Despatch of communication of intention to grant

Free format text: ORIGINAL CODE: EPIDOS AGRA

17Q First examination report despatched

Effective date: 20001108

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION HAS BEEN REFUSED

18R Application refused

Effective date: 20010527