US20020061730A1 - Multi-beam TDMA satellite mobile communications system - Google Patents

Multi-beam TDMA satellite mobile communications system Download PDF

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US20020061730A1
US20020061730A1 US09985597 US98559701A US2002061730A1 US 20020061730 A1 US20020061730 A1 US 20020061730A1 US 09985597 US09985597 US 09985597 US 98559701 A US98559701 A US 98559701A US 2002061730 A1 US2002061730 A1 US 2002061730A1
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satellite
earth station
information
beams
beam
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Nicholas Hart
Gunnar Bjornstrom
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Nicholas Hart
Gunnar Bjornstrom
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/14Relay systems
    • H04B7/15Active relay systems
    • H04B7/204Multiple access
    • H04B7/2041Spot beam multiple access
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/14Relay systems
    • H04B7/15Active relay systems
    • H04B7/185Space-based or airborne stations; Stations for satellite systems
    • H04B7/1853Satellite systems for providing telephony service to a mobile station, i.e. mobile satellite service
    • H04B7/18532Arrangements for managing transmission, i.e. for transporting data or a signalling message
    • H04B7/18534Arrangements for managing transmission, i.e. for transporting data or a signalling message for enhancing link reliablility, e.g. satellites diversity
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/14Relay systems
    • H04B7/15Active relay systems
    • H04B7/185Space-based or airborne stations; Stations for satellite systems
    • H04B7/1853Satellite systems for providing telephony service to a mobile station, i.e. mobile satellite service
    • H04B7/18539Arrangements for managing radio, resources, i.e. for establishing or releasing a connection
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/14Relay systems
    • H04B7/15Active relay systems
    • H04B7/185Space-based or airborne stations; Stations for satellite systems
    • H04B7/1853Satellite systems for providing telephony service to a mobile station, i.e. mobile satellite service
    • H04B7/18545Arrangements for managing station mobility, i.e. for station registration or localisation
    • H04B7/18547Arrangements for managing station mobility, i.e. for station registration or localisation for geolocalisation of a station
    • H04B7/1855Arrangements for managing station mobility, i.e. for station registration or localisation for geolocalisation of a station using a telephonic control signal, e.g. propagation delay variation, Doppler frequency variation, power variation, beam identification

Abstract

An earth station (8) receives a return signal (3) via more than one satellite link (4 a , 4 b) from a mobile terminal (2) using TDMA. The earth station (8) selects one or more of the satellite links (4 a) for transmitting a forward signal (15) on the basis of the quality of signal (3; 15) received via each link. The earth section (8) allocates frequency channels to the mobile terminals (2) according to their location on the surface of the earth, so that the propagation time to and from those mobile terminals (2) which share the same frequency channel is approximately the same. The satellite (4 a; 4 b) includes an antenna which generates an array of beams which are individually pointed to fixed regions of the earth, until the elevation of the satellite (4 a ; 4 b) relative to a fixed region falls below a minimum value, in which case the corresponding beam is redirected to a new area, while the other beams remain pointed at the corresponding fixed areas. In this way, beam-to-beam handover is reduced, while maintaining the boresight of the antenna pointing at the nadir.

Description

    TECHNICAL FIELD
  • The present invention relates to a method and apparatus for communication via satellite, and in particular but not exclusively for voice or data communication using non-geostationary satellites and/or mobile terminals. [0001]
  • BACKGROUND ART
  • In communication systems which use non-geostationary satellites, the number and orientation of satellites in view of a ground-based terminal varies during a call. Thus, the communication link between the terminal and any one satellite may become weaker as the elevation angle of the satellite decreases and ultimately the link may become inoperable as the satellite moves out of sight of the terminal. It is therefore desirable to select another satellite for communication with the terminal, in a procedure known as “handover”. The document U.S. Pat. No. 3,349,398 describes one such method. However, handover between satellites may result in loss of part of the signal, or sudden variations in signal quality, which are unacceptable in voice or data communications. [0002]
  • Furthermore, the line of sight between the terminal and a particular satellite may become obstructed by buildings, trees or other obstacles as the terminal or the satellite moves during a call. This effect is known as “blockage”, and leads to fading in the received signal. [0003]
  • Signal fading may also occur when a signal transmitted by a satellite is reflected off the ground or buildings and the reflected signal is received at the terminal together with the direct signal. The phase difference between the direct and reflected signals may lead to destructive interference at the terminal, so that the received signal strength is reduced. This is known as “multipath” fading. [0004]
  • The document WO-A-93 09578 discloses a satellite communication system in which the satellites monitor the quality of signal received from a terminal and determine which one is best suited to handle the call to the terminal. One of the satellites re-transmits the signal received from the terminal to other satellites or gateways. [0005]
  • The conference paper “The Globalstar Mobile Satellite System for Worldwide Personal Communications” by Wiedeman and Viterbi, 3[0006] rd International Mobile Satellite Conference, Jun. 16-18, 1993, Pasadena, Calif. discloses a communication system in which return link signals are received by two or three satellites; gateway stations measure the signal level of each of these alternate paths and control which signal paths are used. This system is exclusively designed for use with code-divided multiple access (CDMA).
  • However, CDMA suffers from a number of drawbacks when used for mobile communications. The mobile terminals are complex, since they require a separate decoder for each satellite path. Moreover, CDMA is inefficient in frequency re-use unless the users are evenly distributed, and power levels cannot be freely varied for each user without causing interference for other users. Furthermore significant interference takes place at peak levels of use. [0007]
  • STATEMENT OF THE INVENTION
  • According to one aspect of the present invention, there is provided a method of communication between a terrestrial station and a plurality of terminals using TDMA to address each of the terminals from the terrestrial station, in which diversity is provided in the link between the terrestrial station and each terminal, by sending the same information through two or more satellites. [0008]
  • The information may be sent in the same TDMA time slot through the two or more satellites, or may be sent in different time slots. [0009]
  • In this way, blockage may be reduced without the inherent disadvantages of CDMA. [0010]
  • The terrestrial station may either decode the best received signal from each terminal or may combine all of the received signals to reduce error in the received signal. The terrestrial station may then select a forward link to each terminal through one or more of the satellites according to the quality of signal received from the terminal through the satellites. [0011]
  • Thus, a smooth handover may be achieved and blockage and fading may be reduced. [0012]
  • In order that the selection of satellite for the forward link may be transparent to the terminal, the terrestrial station may calculate the delay in the transmission via the selected satellite and adjust the timing of its transmission accordingly so that the transmitted signal is received by the terminal in the same time slot throughout the call. The calculation may take into account both the variation in delay as the selected satellite moves relative to the earth, and the difference in delay when handing over from one satellite to another, so that the quality of communication is not impaired by handover and complex circuitry is not required in the terminal. [0013]
  • In addition, the terrestrial station may compensate for the Doppler shift in the signal received from the terminal and adjust the frequency of the transmitted signal accordingly so that the terminal receives a signal at a constant frequency throughout a call. The Doppler shift may be partially compensated for by the satellites. [0014]
  • According to another aspect of the present invention, in order to facilitate simultaneous communication with multiple users through one satellite, areas of the earth are divided into a number of fixed regions, with a frequency being assigned to a terminal both for transmission and reception of signals according to the region in which the terminal is located. The locations of the regions are determined according to their positions on the earth, rather than their positions relative to the satellite. Simultaneous communication between different terminals in the same region and at the same frequencies may be achieved by allocating different time slots within a repeating time frame to each of the terminals. Since the different terminals using the same frequencies are contained within a fixed region and the variation in propagation delays is therefore limited, interference between the adjacent time slots is avoided. [0015]
  • According to another aspect of the present invention, there is provided a method of controlling a non-geostationary satellite which generates a plurality of individually steerable beams to provide communications links, in which each beam is directed towards a fixed region of the earth's surface until the beam is no longer suitable for communication with that fixed region as a result of the progress of the satellite relative to the earth's surface. The beam is then redirected to a new fixed region with which satisfactory communication is possible. Calls to the previous fixed region may be routed through another satellite. [0016]
  • In this way, the frequency of beam-to-beam handover may be reduced, without affecting the frequency of satellite-to-satellite handover. [0017]
  • The present invention extends to a terrestrial station having means for performing the functions of one or more of the earth stations or terminals described above.[0018]
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • Specific embodiments of the present invention will now be described with reference to the accompanying drawings, in which: [0019]
  • FIG. 1 is a schematic block diagram of the forward and return links between an earth station and a mobile terminal; [0020]
  • FIG. 2 is a schematic elevation showing alternative paths between the earth station and the mobile terminal; [0021]
  • FIG. 3 is a schematic diagram of the earth station; [0022]
  • FIG. 4 is a schematic diagram of the mobile terminal; [0023]
  • FIG. 5 is a schematic diagram of one of the satellites; [0024]
  • FIG. 6 is a diagram of the format of forward and return packets within a frame according to a first embodiment; [0025]
  • FIG. 7 shows the arrangement of spot beam footprints on the earth's surface; [0026]
  • FIG. 8 shows the arrangement of cells on the earth's surface in the first embodiment; [0027]
  • FIG. 9 shows how the beams of a satellite are directed in the first embodiment as the satellite progresses in its orbit; [0028]
  • FIG. 10 is a diagram of the format of forward and return packets within a frame according to a second embodiment; and [0029]
  • FIG. 11 is a diagram of an alternative format to that shown in FIG. 10. [0030]
  • MODES FOR CARRYING OUT THE INVENTION
  • First Embodiment [0031]
  • A first embodiment of the present invention will now be described with reference to FIGS. [0032] 1 to 8.
  • In FIG. 1, a transmitter [0033] 2 of a mobile terminal transmits a signal 3. The mobile terminal has a substantially omni-directional antenna, so that the transmitted signal 3 is received by a first satellite 4 a and a second satellite 4 b in view of the mobile terminal. The signal 3 is retransmitted from each satellite 4 a, 4 b as separate signals 3 a and 3 b. These signals 3 a and 3 b are received by an earth station 8 having first and second receivers 8 a and 8 b for receiving signals from the first and second satellites 4 a and 4 b respectively. In this embodiment, the earth station 8 has first and second directional antennas directed towards the first and second satellites 4 a, 4 b respectively. Thus, the same information is received twice by the earth station 8 in the separate signals 3 a and 3 b. The earth station 8 may therefore select the better of the two signals 3 a and 3 b, e.g. the one with the lowest error rate, for conversion to an analog signal for transmission over a public service telephone network (PSTN) 9. Alternatively, if both signals contain errors, data may be derived from both signals to provide a combined signal with fewer or no errors. The combined signal is then analog converted and sent to the PSTN 9.
  • The earth station [0034] 8 also analyses the received signals 3 a and 3 b to determine which is of better quality. Since there is a strong correlation between the strength of a return link from one of the satellites 4 a, 4 b and the strength of a forward link to the portable transmitter 2 through the same satellite 6 a, 6 b, the earth station 8 selects one of the satellites 6 a, 6 b for the forward link to the portable transmitter 2 and generates a selection signal 10.
  • When a signal is received from the PSTN [0035] 9 for transmission to the portable terminal 2, the signal is passed to a transmitter 12 in the earth station. The transmitter 12 selects one of the satellites 4 a, 4 b, as shown schematically in FIG. 1 by a switch 14, in response to the selection signal 10. In this case, the first satellite 4 a is selected as the most suitable for the forward link. The transmitter 12 then transmits a signal 15 to the first satellite 4 a, which retransmits the signal as a signal 15 a to a receiver 16 of the mobile terminal. The transmitter 2 and the receiver 16 may be connected to the same antenna on the mobile terminal, or to separate antennas. In both cases, the receiving antenna is omni-directional and therefore may receive signals from either of the satellites 4 a, 4 b. Thus, the receiver 16 receives a signal 15 through the stronger link.
  • A situation in which blockage occurs will now be described with reference to FIG. 2. This figure shows a section of the earth's surface on which the earth station [0036] 8 and a mobile terminal 18 are located. The first and second satellites 4 a, 4 b are within the line of sight of both the earth station 8 and the mobile terminal 18. The angle of elevation εb of the second satellite 4 b relative to the mobile terminal 18 is greater than the angle of elevation εa of the first satellite 4 a and the path distances between the earth station 8 and the second satellite 4 b, and between the second satellite 4 b and the mobile terminal 18 are shorter than those between the first satellite 4 a and the mobile terminal 18 and earth station 8.
  • However, in this case the mobile terminal [0037] 18 is positioned close to a tall obstacle 20 such as a tree, which obscures the line of sight 1 b between the mobile terminal 18 and the second satellite 4 b. Thus, when the mobile terminal 18 transmits a signal 3, this signal 3 is only weakly received by the second satellite 4 b and thus the retransmitted signal 6 b is more likely to contain errors. The earth station selects the first satellite 4 a as providing a better forward link and transmits the response signal 15 only to the first satellite 4 a. This response signal is retransmitted as signal 15 a to the mobile terminal 18. Since the line of sight 1 a between the first satellite 4 a and the mobile terminal 18 is not obscured, the response signal is received strongly by the mobile terminal 18. The mobile terminal 18 does not need to select from which satellite 4 a, 4 b it is to receive the response signal 15 a, since this is decided at the earth station 8. Selection of the satellites 4 a, 4 b is therefore transparent to the mobile terminal.
  • If, on the other hand, the mobile terminal [0038] 18 were to move such that the obstacle 20 no longer obstructs the line of sight 1 b, then the earth station 8 may receive a better signal from the second satellite 4 b and will therefore select the second satellite 4 b for the forward link.
  • When different frequencies are used for the forward and return links, and the fading is due to multipath interference, there may not be a strong correlation between the quality of forward and return links. In this case, the mobile terminal [0039] 18 transmits information to the earth station 8 relating to the strength of the signal received by the terminal 18 from the earth station 8. If the earth station 8 receives a good return link signal from the first satellite 4 a but information transmitted by the mobile terminal 18 indicates that fading is occurring on the forward link, the earth station 8 may then select the satellite from which the next best signal is received for the forward link. In a case where each satellite generates several overlapping beams for communication with mobile terminals at different frequencies, the earth station 8 selects instead a different beam generated by the first satellite.
  • The operation of the mobile terminal [0040] 18 and the earth station 8 will now be explained with reference to FIGS. 3, 4, and 5.
  • Earth Station [0041]
  • In this example, analog speech signals are received at the earth station [0042] 8 from the PSTN 9 for transmission to the mobile terminals 18. As shown in FIG. 3, the analogue speech signals are digitized and encoded by a codec 81 and the encoded speech is converted into a series of discrete packets at a multiplexer/demultiplexer 82.
  • The transmission of the packets is controlled by a controller [0043] 88 which selects which satellite 4 is to be used for the forward link on the basis of the quality of signal received from each satellite 4. The controller 88 controls a selector 83 to send each packet to one of a plurality of buffers 85 a, 85 b, 85 c. The timing of the output of each buffer 85 is controlled by the controller 88. The packets output from the buffer 85 a, 85 b, 85 c are radio frequency modulated by corresponding RF modulators/modulators 86 a, 86 b, 86 c, the frequency of modulation being controlled by the controller 88. The RF signals are modulated in different frequency bands selected by the controller 88 according to a selected bean of the satellite 4 in which the signals are to be retransmitted to the mobile terminal 18. The RF signals are transmitted by directional antennas 87 a, 87 b, 87 c which are each steered towards a corresponding satellite 4 a, 4 b, 4 c.
  • Each directional antenna [0044] 87 also receives signals transmitted from mobile terminals on the return link from the corresponding satellite 4, which are radio frequency demodulated by the RF modulators/demodulators 86 to form received packets. The received packets are buffered by the buffers 85 and selected by the selector 83. The series of packets is separated in channels by the multiplexer/demultiplexer 82 and decoded by the codec 81 which may also perform error checking by comparing packets received from the same mobile terminal 18 via different satellites 4. The resultant analog signals are sent to the PSTN 9 on different lines.
  • The earth station [0045] 8 need not be connected directly to the PSTN 9. Instead, earth stations are preferably connected to PSTNs and other fixed and mobile networks through a ground network, as described in British Patent application no. 94 23950.6 and the corresponding International (PCT) application filed on May 12, 1995, both incorporated herein by reference.
  • Mobile Terminal [0046]
  • As shown in FIG. 4, each mobile terminal [0047] 18 includes a microphone 60 in which speech is converted into analog signals. The analog signals are converted to digital signals by an A/D converter 62 and the digital signals are encoded to form the packets by a coder 64. The coded packets are RP modulated by an RP modulator 66 for transmission from an omnidirectional aerial 68.
  • Signals received through the aerial [0048] 68 are RF demodulated by a demodulator 70 as received packets. The received packets are then decoded by a packet decoder 72 to form digital speech signals which are converted to analog speech signals by a D/A converter 74. The analog signals are output to a loudspeaker 76 to produce audible speech. The operation of the mobile terminal 18 is controlled by a control unit 59, such as a microprocessor and/or DSP device, which is connected to additional conventional handset components such as a key pad (not shown).
  • Satellite [0049]
  • Referring to FIG. 5, each satellite [0050] 4 includes an antenna 90 and a beam-forming device 92, which may be a radiating array antenna and a large Butler matrix as described in British Patent application No. 9407669.2 (incorporated herein by reference). The beam-forming device 92 converts signals from each element of the array into signals from a plurality of beams and vice versa. Signals received by the antenna 90 from the mobile terminals 18 are fed via a control unit 94 to an antenna 96 which retransmits the signals towards the base station in a frequency band corresponding to the beam in which the signals were received. The antenna 96 may be steered towards the earth station 8. Likewise, signals received from the antenna 96 from the earth station 8 are redirected to one of the beams of the antenna 90 according to the frequency band in which the signals are transmitted from the earth station 8.
  • For the sake of clarity, a single antenna [0051] 90 and beam-forming device 92 are shown. However, since different carrier frequencies are used for the forward and return links, separate receiving and transmitting antennas 90 and beam-forming devices 92 will preferably be used.
  • Signalling Format [0052]
  • As shown in FIG. 6, the earth station [0053] 8 can communicate with a number of mobile terminals 18 at the same time by sending packets R1 to Rn sequentially in a repeating time frame F, the beginning of which is marked by a frame header signal. Each frame F is divided into a number of time slots t1 to tn corresponding to different channels, each channel being assigned to one of the mobile terminals 18 by the earth station 8 when a call is set up.
  • For example, if the mobile terminal [0054] 18 has been assigned to the first channel, it will decode only the packet R1 in the first slot t1 in each frame F to generate a voice signal. The method of multiplexed communication is known as Time Divided Multiple Access, or TDMA.
  • A channel is assigned to each mobile terminal [0055] 18 during call setup by transmitting an instruction signal to the mobile terminal 18 from the earth station 8.
  • Each mobile terminal [0056] 18 is assigned a return channel having a predetermined time slot t, different from that of the forward channel, in the frame F, for transmission of a return packet T1 to Tn. For example, the mobile terminal 18 to which the first slot t1 is assigned for reception of the packet R1 may be assigned the third slot t3 for the transmission of a return packet T1. Different frequencies ff and fr are used for the forward and return channels so that the mobile terminals 18 communicate in full duplex mode.
  • Alternatively, a half duplex mode could be used, in which the return packets T would be transmitted at the same frequency as the forward packets R, with the forward packets R alternating with the return packets T in the frame F. [0057]
  • Each forward and return packet consists of a header portion [0058] 24 containing control information, speech data 26 and a check portion 28 such as a CRC for correcting errors in the speech data 26.
  • In order to ensure that the correct signal is received by each mobile terminal [0059] 18, in the same time slot t in every frame F, the earth station 8 delays the timing of transmission from the buffers 85 to a particular satellite to compensate for the variations in propagation delay via another satellite, and for the change in delay in handing over from one satellite to another. In order to determine the correct timing, the controller 88 of the earth station 8 may include a store unit storing ephemerides of the positions of the different satellites so that their position and range may be calculated at any instant. In addition, the position of each mobile terminal 18 is determined. This may be achieved by comparing the delays in the signals 3 a, 3 b transmitted from-the mobile terminal 18 by different satellites 4 a, 4 b. However, this method requires that the signals 3 are received from more than one satellite if an unambiguous measurement is to be achieved. Because of blockage, this may not be possible. Hence, additional position determining methods should be used.
  • As each satellite [0060] 4 a, 4 b generates an array of beams at different angles, the angular position of the mobile terminal 18 relative to a satellite is determined by identifying the beam in which the return signal 3 is detected. In addition, the Doppler shift of the signal 3 is measured to determine the angle of the mobile terminal 18 relative to the direction of motion of the satellite. The position of each mobile terminal 18 is calculated by some or all of the above techniques.
  • The earth station [0061] 8 may store the last known position of each mobile terminal 18, so that position calculation need only be carried out if the mobile terminal 18 is not found in its previous area.
  • Alternatively, each mobile terminal [0062] 18 may include Global Positioning System (GPS) hardware for determining the position of the mobile terminal 18, which information may be incorporated in signals transmitted to the earth station 8.
  • The timing of transmission of the return packets T is synchronized by the mobile terminal [0063] 18 with the timing of the reception of the forward packets R. Since the earth station 8 controls the timing at which the forward packets 12 are received, the timing of the mobile terminal 18 is controlled by the earth station 8. To allow some margin for timing error, the time slots are separated by short intervals, called “guard bands”.
  • Furthermore, the controller [0064] 88 of the earth station 8 measures the Doppler shift of the signal 3 received from each mobile terminal and controls the modulation frequency of the RF modulators 86 to compensate for the Doppler shift, so that the signal 15 a is always received by the mobile terminal 18 at the assigned frequency. By the above compensatory techniques, which are carried out at the earth station 8, the processing burden on the mobile terminals 18 is reduced so that their reliability may be increased, their construction may be substantially simplified and they may be manufactured at low cost.
  • More than one satellite may be selected for the forward link, the signal [0065] 15 from the earth station 8 being transmitted to each selected satellite with a timing calculated so that the signals 15 a, 15 b from the satellites 4 a,4 b arrive simultaneously at the mobile terminal 18.
  • Beam Arrangement [0066]
  • Each satellite [0067] 4 a, 4 b has an array antenna 90, for communication with the mobile terminal 18, which synthesizes a number of overlapping spot beams each having a projected area 50 on the earth's surface of between 1000 km and 300 km in diameter, as shown in FIG. 7. In FIG. 7, the nadir of the satellite 4 a on the earth's surface is shown at point A and the nadir of the satellite 4 b is shown at point B, with the great circle distance between these points being represented by the horizontal axis. The vertical axis represents distance along a great circle orthogonal to the great circle connecting the nadirs of the two satellites 4 a, 4 b. The mobile terminal 18 is located within the footprint 50 of one spot beam of the satellite 4 a and within the footprint 51 of a spot beam of the satellite 4 b, so that communication is possible via either satellite.
  • Each array antenna [0068] 90 may project 121 beams collectively covering substantially the entire field of view of the satellite 4 a, 4 b.
  • Fixed Regions [0069]
  • As shown in FIG. 8, the area of the earth's surface is divided by the controller [0070] 88 into regions 52 and a sub-carrier transmission and reception frequency pair is assigned to each region 52. Thus, the transmit and receive frequency for each mobile terminal 18 are determined according to the region 52 in which it is located, the regions 52 being fixed relative to the earth's surface. A sample spot beam footprint 50 is shown overlapping a group of regions 52, which are hexagonal in this example.
  • When a call is set up, the position of the mobile terminal [0071] 18 is determined by the controller 88 of the earth station 8 according to the techniques described above and a control signal is transmitted to the mobile terminal 18 to assign a particular pair of frequencies. These frequencies remain unchanged throughout the call unless the mobile terminal 18 itself moves into another cell 52. Each cell 52 has a radius of approximately 200-300 km, so the mobile terminal 18 is unlikely to move frequently between cells 52 during a call. It should be noted that the size and position of each cell is defined with reference to the earth's surface and not to a satellite beam.
  • In another alternative, the assignment of frequencies to regions may change in a predetermined sequence (so-called “frequency hopping”). [0072]
  • All of the mobile terminals [0073] 18 within the same cell 52 transmit and receive at the same pairs of frequencies ff and fr, and the signals from the different mobile terminals 18 are separated using TDMA, as shown in FIG. 6. Since the different mobile terminals 18 are contained within the relatively small, fixed area of the cell and are all at approximately the same distance from any one satellite, the variation in the uplink propagation delay between different mobile terminals and any one satellite is limited. In this way, the problem of interference between signals in adjacent time slots is greatly reduced.
  • Handover [0074]
  • The assignment of regions [0075] 52 to spot beams is determined at the satellite 4 or at the earth station 8 so that handover of regions 52 between spot beam areas 50 is transparent to the mobile terminal 18.
  • FIG. 9 shows the allocation of a row of spot beams [0076] 51 in the beam pattern of a satellite 4 a to groups of regions 52 at time To and at a later time T1. At time To, overlapping spot beams 51 a to 51 l are directed at centres Ca to C1 of groups of regions 52 on the surface of the earth. As the satellite progresses in its orbit, the spot beams 51 are individually steered so as to remain pointing at their respective centres C.
  • After T[0077] o, the elevation angle of the satellite 4 a with respect to the centre Ca becomes undesirably low for reliable communication. The earth station 8 detects the position of the centre Ca with respect to the satellite 4 a and controls the satellite 4 a by sending control signals to redeploy the beam 51 a to a new centre Cn. By this time, another satellite 4 b (not shown in FIG. 9) is already covering the regions 52 around the centre Ca with one of its spot beams, so that satellite-to-satellite handover is achieved without any interruption of the communication service. At time T1, all of the spot beams 51 have been redeployed except for the beam 51 m.
  • Thus, the coverage area of the antenna as a whole moves progressively forward, and the antenna boresight or focal direction remains pointing downwards directly below the satellite. [0078]
  • The coverage area of the spot beams [0079] 51 of the satellite 4 a progresses in a fashion which may be likened to the progress of a caterpillar or tank track, with the spot beams corresponding to the elements of the track. Each spot beam 51 is individually and continually steered to remain fixed on a centre until it reaches the outermost rearward position of the beam pattern, when it is redeployed to the outermost forward position. However, the overall beam pattern projected by the antenna of the satellite 4 a progresses on a continuous track over the earth's surface with the progression of the satellite. This method provides reduced frequency of beam-to-beam handover, although it does not reduce the frequency of satellite-to-satellite handover.
  • Preferably, the earth station [0080] 8 continuously determines the correct direction for each of the beams 51 and sends control signals to the satellite 4 a to control the direction of the beams 51. However, the means for determining the beam directions may alternatively be incorporated in the satellite, or in a separate ground-based satellite control station.
  • Second Embodiment [0081]
  • A second embodiment will now be described with reference to FIGS. [0082] 1 to 5, 10 and 11. The second embodiment differs from the first embodiment in the operation of the earth station 8, mobile terminal 18 and satellites 4, and in that the mobile terminal 18 receives signals from different satellites 4 in different time slots.
  • Signalling Format [0083]
  • As shown in FIG. 10, the mobile terminal [0084] 18 communicates with the earth station 8 during allocated time slots t within a repeating time frame T, via the first and second satellites 4 a, 4 b, or via first and second beams of one satellite, at pairs of frequencies f1, f1′ and f2, f2′ respectively.
  • In the example shown, the earth station [0085] 8 transmits a packet Rx1 in time slot t1 via the first satellite 4 a, which packet is received at frequency f1 by the mobile terminal 18. The mobile terminal 18 then transmits a packet Tx1 in time slot t3 at the frequency f1′ via a beam generated by the satellite 4 a. The earth station 8 transmits a packet Rx2, containing the same information as the packet Rx1, via the second satellite 4 b, or via a further beam generated by the satellite 4 a, which retransmits the packet Rx2 to the mobile terminal 18 at frequency f2 in time slot to. The mobile terminal 18 then transmits a packet Tx2, containing the same information as the packet Tx1, in time slot to at the frequency f2′. The packet Tx2 is retransmitted to the earth station 8 by the second satellite 4 b. In this way, the controller 59 has sufficient time to retune the RF modulator 66 or demodulator 70 during the intervening time slots.
  • Alternatively, two RF demodulators and two RF modulators may be provided in the mobile terminal, tuned to the frequencies f[0086] 1 and f2 and f1′ and f2′ respectively.
  • When the mobile terminal has received both the packets Rx[0087] 1 and Rx2, the packet decoder 72 combines the two, or selects the better packet, for conversion to speech, as in the first embodiment. Similarly, the earth station 8 combines the two transmitted packets Tx1 and Tx2 or selects the better packet, to improve the quality of the signal transmitted to the PSTN 9.
  • In this example, each time frame T comprises eight time slots t, so that eight mobile terminals [0088] 18 can communicate with the earth station 8 at the frequencies f1, f1′, f2 and f2′ using TDMA. However, the allocation of time slots is flexible, to optimize the number of users and quality of communication, as described below.
  • During call set-up, the mobile terminal [0089] 18 monitors pilot signals transmitted by the satellites 4 to determine which satellites are in view and whether any satellite links are blocked. This information is transmitted to the earth station 8. If only one satellite is in view, the earth station 8 allocates only one time slot for transmission and one for reception at the pair of frequencies corresponding to that satellite. The mobile terminal 18 monitors the pilot signals during the calls so that, if another satellite comes into view, the mobile terminal 18 communicates this information to the earth station and further transmit and receive time slots are allocated at the pair of frequencies corresponding to the other satellite. Although in the above example two time slots are allocated for transmission by the mobile terminal 18, only one of the time slots may be used if the return link is satisfactory in order to conserve power and reduce electromagnetic emissions, which is particularly important for hand-held mobile terminals.
  • The controller [0090] 59 of the mobile terminal 18 monitors the quality of signal received from both satellites 4 a and 4 b and normally transmits only during the time slot and at the frequency corresponding to the satellite from which the stronger signal is received. However, if the selected return link provides only a weak signal, as in the case of multipath fading, the earth station 8 communicates this information to the mobile terminal 18 and the alternative return link is selected.
  • Furthermore, if a greater number of users is to be accommodated at any time, only one time slot for each of transmission and reception may be allocated to each mobile terminal [0091] 18.
  • If none of the satellites provides a link of satisfactory quality, a lower baud rate is selected by the earth station [0092] 8 and the voice data is divided into two different packets in each time frame. As shown in FIG. 11, the frequencies f1, f1′ are used for communication via only the first satellite 4 a. The voice data encoded in a single packet Rx1 or Rx2 in the embodiment shown in FIG. 10 is divided between two packets Rxa and Rxb which are transmitted at the frequency f1′ by the earth station 8 at half the normal baud rate in time slots t3 and t5 respectively. Likewise, the voice data transmitted by the mobile terminal 18 is divided between two packets Txa and Txb in each time frame T and transmitted in time slots t and t6 at half the normal baud rate. The reduction of baud rate reduces the probability of bit errors. Alternatively, two satellite beams may be used for transmission and reception, and the packets Rxa, Rxb and Txa, Txb may be divided between the two beams.
  • The above technique of selecting a lower baud rate and dividing the transmitted signal into two or more packets may also be employed in the first embodiment. [0093]
  • Handover [0094]
  • In the second embodiment, the satellite beams are not steered but sweep across the earth's surface at a constant rate as the satellite [0095] 4 progresses in its orbit. As in FIG. 7, the beams overlap so that the mobile terminal 18 is able to communicate via more than one beam at least some of the time. Furthermore, beams from different satellites 4 a, 4 b may overlap so that the mobile terminal 18 is able to communicate via more than one satellite 4 a, 4 b. Transmission or reception frequencies are allocated according to the spot beam in which the mobile terminal 18 falls and not according to the position of the mobile terminal 18 on the earth's surface. As the beams of each satellite 4 sweep over the earth's surface, the mobile terminal 18 will pass from one beam to the next and a call will therefore need to be handed over from beam to beam to reach the mobile terminal 18. This is achieved by determining at the earth station 8 which beam the mobile terminal 18 falls within and allocating a call with the mobile terminal 18 in the appropriate beam. When the mobile terminal 18 is handed over to a new beam, a command signal is sent to the mobile terminal 18 including information on the time slots t and the transmit and receive frequencies to be used by the mobile terminal in the new beam, and the mobile terminal thereafter uses the new frequencies and time slots indicated in the command signal for communication via that satellite 4.
  • The earth station [0096] 8 may use any of a number of well-known techniques to determine to which new beam the mobile terminal is to be handed over and when handover is to take place. For example, since the positions of the satellites 4 and of the mobile terminal 18 are known, the passage of the mobile terminal through the beams projected by any of the satellites 4 is entirely predictable and this information may obviously therefore be used to determine when handover is to take place, and to which beam.
  • Alternatively, the strength or quality of signals received from the mobile terminal [0097] 18 through the current beam may be monitored and handover performed when the signal through the current beam is unacceptable. Diversity may be provided through two beams of the same satellite, providing a soft beam-to-beam handover.
  • The timing of forward link transmissions is controlled by the earth station [0098] 8 and the return link transmissions are synchronized with the reception of forward link signals, as in the first embodiment. However, in the second embodiment the mobile terminals 18 adjust the frequency of transmission on the return link to compensate for Doppler shift detected in the received signals, as well as the earth station 8 compensating for Doppler shift on the forward link.
  • Since the mobile terminals [0099] 18 using the same transmission frequency are no longer confined to a fixed region, the guardbands between time slots at the mobile terminal transmission frequencies are larger in the second embodiment than in the first embodiment, to avoid interference between adjacent time slots on the return link.
  • Although the above embodiments have been described with reference to a mobile or portable (e.g. hand-held) terminal, transportable or even fixed terminals may be used in the same communications system. [0100]
  • The system is not restricted to any particular constellation of satellites, but may advantageously be applied to satellites in low earth orbits of less than 2000 km altitude or medium earth orbits of between 10,000 and 20,000 km altitude. [0101]
  • Preferably, a subsynchronous orbit of approximately 6 hours' period may be used, corresponding to an altitude of 10355 km. [0102]
  • In both embodiments, the number of time-slots in each time frame may be chosen according to the likely density of users. Although different frequencies are used by the mobile terminals for transmission and reception in the preferred embodiments, a single frequency may be used, with alternate time slots assigned for transmission and reception. [0103]
  • The embodiments are described above for illustrative purposes only and the present invention is not limited in scope thereto. [0104]

Claims (41)

  1. 1. A method of satellite communication between a first earth station (18) and a second earth station (8) comprising:
    receiving at the second earth station (8) information transmitted from the first earth station (18) within one or more time-division multiplexed time slots (t) and relayed via a plurality of beams (51) generated by one or more satellites (4);
    said method being characterised by the steps of:
    selecting ore or more of said satellite beams (51) according to a property of the information received via said satellite beams (51); and
    transmitting further information (15) from said second earth station (8) to the first earth station (18) such that the further information (15) is relayed via said selected one or more satellite beams (51).
  2. 2. A method as claimed in claim 1, further comprising:
    calculating variations in the delay in the transmission link between the first earth station (18) and the second earth station (8) via said selected one or more satellite beams (51), and transmitting the further information from the second earth station (8) to the one or more satellites (4) which generate the or each selected satellite beam (51) with a timing determined so as to compensate for said variations.
  3. 3. A method as claimed in claim 2, wherein the further information is transmitted from the second earth station (8) to the first earth station (18) via two or more said selected beams (51), and the timings of the transmissions are determined so that the information is received substantially simultaneously at the first earth station (18) via the selected beams (51).
  4. 4. A method as claimed in any preceding claim, further comprising measuring the Doppler shift from a predetermined frequency of the frequency of a signal (3 a; 3 b) containing the information received at the second earth station (8), and selecting the frequency of a signal (15) containing the further information so as to compensate for the measured Doppler shift.
  5. 5. A method as claimed in any preceding claim, further comprising determining the position of the first earth station (18); wherein the further information is transmitted from the second earth station (8) with a frequency (ff) determined according to the derived position of the first earth station (16).
  6. 6. A method as claimed in claim 5, further comprising transmitting to the first earth station (18) a control signal for controlling the transmission and reception frequencies (fr,ff) of the first earth station (18), the control signal being generated according to the derived position of the first earth station (18).
  7. 7. A method as claimed in claim 1 or 2, wherein the second earth station (8) receives the information more than once in different time slots (t3,t7) via a corresponding number of said satellite beans (51).
  8. 8. A method as claimed in claim 7, wherein the second earth station (8) receives the information transmitted by the first earth station (18) within a first time slot (t3) in a first frequency channel (f1′) of a first satellite beam (51), and
    receives the information which is transmitted again by the first earth station (18) during a second time slot (t7) in a second frequency channel (f2′) of a second satellite beam (51).
  9. 9. A method as claimed in claim 8, further comprising:
    comparing respective properties of the received information transmitted by the first earth station (18) during the first and second time slots (t3, t7) and
    transmitting the further information at a selected frequency corresponding to one of the first and second satellite beams (51) according to the result of the comparison.
  10. 10. A method as claimed in any preceding claim, wherein if a property of the received information fails to satisfy a predetermined criterion, the second earth station (8) transmits the further information at a lower rate, and if the property of the received information satisfies said predetermined criterion, the second earth station (8) transmits the further information at a higher rate.
  11. 11. A method as claimed in claim, 10, wherein the information is transmitted by the steps of:
    dividing the further information into first and second portions (Rxa, Rxb);
    transmitting the first portion (Rxa) to the first earth station (18) within a third time slot (t3); and
    transmitting the second portion (Rxb) to the first earth station (18) within a fourth time slot (t7).
  12. 12. A method as claimed in any preceding claim, wherein said property relates to the quality of previous information previously received by the first earth station (18) from the second earth station (8).
  13. 13. A method as claimed in any one of claims 1 to 11, wherein the property relates to the quality of said information received by the second earth station (8).
  14. 14. A method of satellite communication using TDMA channels, comprising:
    transmitting the same information from a first earth station (18) within each of a plurality of time slots (t) to a second earth station (8), at respective, different frequencies (f1′, f2′) so that the information is received in respective, different beams generated by one or more satellites (4).
  15. 15. Apparatus for use in a satellite communications earth station (18) using TDMA channels, comprising:
    a receiver (8 a, 8 b) arranged to receive information relayed by one or more satellites (6) from a remote earth station (18) within one or more time slots (t), the information being relayed via a plurality of beams (51) generated by said one or more satellites (6);
    beam selecting means (34) for selecting one or more of said satellite beams (51) according to a property of the information received therein, and a transmitter (12) arranged to transmit further information to the remote earth station (18) such that the information is relayed to the remote earth station (18) via the selected one or more satellite beams (51).
  16. 16. Apparatus as claimed in claim 15, further comprising:
    means (88) for calculating variations in the transmission delay to the remote earth station (18) via the selected one or more satellite beams (51), and control means (85,88) for controlling the timing of the transmitter (12) to compensate for the variations.
  17. 17. Apparatus as claimed in claim 16, wherein the beam selecting means (14) is arranged to select two or more of said satellite beams (51), and the control means (85,88) is arranged to control the timing of the transmitter (12) so that the transmitted information is received substantially simultaneously at the remote earth station (18) via each of the selected beams (51).
  18. 18. Apparatus as claimed in any one of claims 15 to 17, further comprising means (88) for measuring the Doppler shift in a received signal containing the information, and means (86,88) for adjusting the frequency of the transmitter (12) to compensate for the measured Doppler shift.
  19. 19. Apparatus as claimed in any one of claims 15 to 18, further comprising means (88) for deriving the position of the remote earth station (18); and frequency selecting means (86, 88) for selecting the frequency of the transmitter (12) according to the derived position of the remote earth station (18).
  20. 20. Apparatus as claimed in claim 19, including means (88) for generating a control signal for controlling the transmission and reception frequency of the remote earth station (18) according to the derived position thereof, the transmitter (12) being arranged to transmit the control signal to the remote earth station (18).
  21. 21. Apparatus as claimed in claim 15 or 16, wherein the receiver (8 a, 8 b) is arranged to receive the information more than once sequentially via a corresponding number of said beams (51).
  22. 22. Apparatus as claimed in claim 21, wherein the receiver (8 a, 8 b) is arranged to receive the information transmitted by the remote earth station (18) within a first time slat (t3) in a first frequency channel (f1′) of a first satellite beam (51), and to receive the information which is repeated by the remote earth station (18) during a second time slot (t7) in a second frequency channel (f2′) of a second satellite beam (51).
  23. 23. Apparatus as claimed in claim 21 or 22, further comprising:
    comparing means (88) for comparing a property of the information transmitted by the remote earth station (18) during the first and second time slots (t3,t7); wherein
    the transmitter (12) is arranged to transmit a signal (15) in a frequency channel corresponding to one of the first and second beams (51) selected by the comparing means (88).
  24. 24. Apparatus as claimed in any one of claims 15 to 23, wherein the transmitter (12) is arranged to transmit at a lower rate if the received information fails to satisfy a predetermined criterion and to transmit at a higher rate if the predetermined criterion is satisfied.
  25. 25. Apparatus as claimed in claim 24, wherein the transmitter (12) is arranged to divide the information to be transmitted into first and second portions (Rxa, Rxb), to transmit the first portion (Rxa) to the remote earth station (18) within a third time slot (t3) and to transmit the second portion (Rxb) to the remote earth station (18) within a fourth time slot (t7).
  26. 26. Apparatus as claimed in any one of claims 15 to 25, wherein said property relates to the quality of previous information previously received by the remote earth station (18) from the satellite communications earth station (8).
  27. 27. Apparatus as claimed in any one of claims 15 to 25, wherein the property relates to the quality of the received information.
  28. 28. A user station (18) for satellite communications, comprising a transmitter (2) arranged to transmit the same information within each of a plurality of time slots (t) to a base station (8) at respective different frequencies (f1′,f2′) so as to be receivable in respective different beams (51) generated by one or more satellites (4).
  29. 29. A method of communication between a base station (8) and a plurality of user stations (18) each of which are located within the coverage area (50) of a beam (51) generated by a satellite (4), said beam (51) carrying a plurality of frequency channels,
    characterised by allocating each of said frequency channels to a group of said user stations (18) which fall within one of a plurality of predetermined regions (52) within the beam (51) such that the variation in propagation delay to said satellite (4) among said group of said user stations (18) is limited, and communicating between the base station (8) and said user stations (18) within said beam (51) in said allocated frequency channels.
  30. 30. A method as claimed in claim 29, wherein said group comprises ones of said user stations (18) which are approximately equidistant from said satellite (4).
  31. 31. A method as claimed in claim 30, further comprising determining the positions of the user stations (18) relative to the earth's surface and allocating each of said frequency channels according to the determined positions of the user stations (18).
  32. 32. Apparatus for communication with a plurality of user stations (18) which are located within the coverage area (50) of a beam (51) generated by a satellite (4), said beam (51) carrying a plurality of frequency channels,
    characterised by frequency channel allocating means (88) for allocating each of said frequency channels to a group of said user stations (18) which fall within one of a plurality of predetermined regions (52) within the beam (51) such that the variation in propagation delay to said satellite (4) among said group of said user stations (18) is limited, and means (85, 86, 87) arranged to communicate with said user stations (18) within said beam in said allocated frequency channels.
  33. 33. Apparatus as claimed in claim 32, including grouping means (88) for determining said groups of said user stations (18) such that each group comprises ones of said user stations (18) which are approximately equidistant from said satellite (4).
  34. 34. Apparatus as claimed in claim 33, including position determining means (88) arranged to determine the positions of the user stations (18) relative to the earth's surface, the grouping means (88) being arranged to determine said predetermined regions (52) relative to the earth's surface.
  35. 35. A method of satellite communication, comprising:
    directing a plurality of beams (51 a-51 m) from a ion-geostationary satellite (4 a) to a corresponding plurality of regions (52) which are fixed relative to the surface of the earth; and
    determining when one of said beams (51 a-51 m) fails to satisfy a predetermined criterion, and redirecting said one of said beams (51 a-51 m) from the corresponding one of the fixed regions (52) to another fixed region (52) such that said one of said beams (51 a-51 m) satisfies said predetermined criterion; characterised in that the directions of other ones of said plurality of beams (51 a-51 m) which satisfy said predetermined criterion are maintained at the corresponding ones of the fixed regions (52) while said one of said plurality of beams (51 a-51 m) is redirected.
  36. 36. A method as claimed in claim 35, wherein said directing and redirecting steps comprise sending a command signal to said satellite (4 a) from an earth-based station (8), so as to control the direction of the beams (51 a-51 m) of said satellite (4 a).
  37. 37. A method as claimed in claim 35 or 35, wherein said predetermined criterion comprises a range of desirable beam directions whereat the satellite (4 a) has an elevation angle greater than a predetermined minimum elevation angle with respect to the fixed region (52).
  38. 38. Apparatus for satellite communication, comprising means operable to determine a plurality of beam directions, for a plurality of beams (51 a-51 m) projected by a non-geostationary satellite (4 a), to corresponding fixed regions (52) of the earth's surface;
    means operable to detect whether one or more of said beams (51 a-51 m) fail to satisfy a predetermined criterion; and
    means operable to determine a new beam direction to a new fixed region (52) for each of said one or more of said beams (51 a-51 m), such that the predetermined criterion is satisfied by the beam in the new beam direction; characterised by control means operable to control said non-geostationary satellite (4 a) so as to direct the beams (51 a-51 m) in the corresponding beam directions such that the directions of other ones of said beams (51 a-51 m) for which a new beam direction is not determined are maintained at the corresponding fixed regions (52).
  39. 39. Apparatus as claimed in claim 38, wherein said control means includes means for sending a control signal to said satellite (4 a).
  40. 40. Apparatus as claimed in claim 38 or 39, wherein said predetermined criterion comprises a range of desirable beam directions to points (Ca-Cm) on the earth's surface whereat the satellite (4 a) has an elevation angle greater than a predetermined minimum elevation angle.
  41. 41. A terrestrial station including apparatus as claimed in any one of claims 15 to 27, 32 to 34 and 38 to 40.
US09985597 1994-07-22 2001-11-05 Multi-beam TDMA satellite mobile communications system Abandoned US20020061730A1 (en)

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GB9414829A GB2293725B (en) 1994-07-22 1994-07-22 Satellite communication method and apparatus
GBGB9414829.3 1994-07-22
GBPCT/GB95/01103 1995-05-16
PCT/GB1995/001103 WO1996003814A1 (en) 1994-07-22 1995-05-16 Multi-beam tdma satellite mobile communications system
US08750915 US6314269B1 (en) 1994-07-22 1995-05-16 Multi-beam TDMA satellite mobile communications system
US09985597 US20020061730A1 (en) 1994-07-22 2001-11-05 Multi-beam TDMA satellite mobile communications system

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US09985597 US20020061730A1 (en) 1994-07-22 2001-11-05 Multi-beam TDMA satellite mobile communications system

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US08750915 Continuation US6314269B1 (en) 1994-07-22 1995-05-16 Multi-beam TDMA satellite mobile communications system

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US20020061730A1 true true US20020061730A1 (en) 2002-05-23

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US09778839 Abandoned US20010046841A1 (en) 1994-07-22 2001-02-08 Multi-beam TDMA satellite mobile communications system
US09985597 Abandoned US20020061730A1 (en) 1994-07-22 2001-11-05 Multi-beam TDMA satellite mobile communications system

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US09778839 Abandoned US20010046841A1 (en) 1994-07-22 2001-02-08 Multi-beam TDMA satellite mobile communications system

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Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20040147222A1 (en) * 2000-09-19 2004-07-29 Hughes Electronics Corporation Method and system of efficient spectrum utilization by communications satellites
US20050068230A1 (en) * 2003-09-29 2005-03-31 Munoz Michael S. Reducing co-channel interference in satellite communications systems by antenna re-pointing
US20060291409A1 (en) * 2005-04-05 2006-12-28 Rich Battista Multiple return link
US20080143589A1 (en) * 2006-08-22 2008-06-19 Viasat, Inc. Downstream Broad Beam Diversity With Interference Cancellation
US20100085908A1 (en) * 2008-10-06 2010-04-08 Viasat, Inc. Terminal measurement based synchronization for mesh satellite communications
US20110080898A1 (en) * 2009-10-06 2011-04-07 Carlos Cordeiro Millimeter-wave communication station and method for multiple-access beamforming in a millimeter-wave communication network
WO2014026228A1 (en) * 2012-08-14 2014-02-20 University Of South Australia Channel allocation in a communication system
WO2015123623A1 (en) * 2014-02-17 2015-08-20 Ubiqomm Broadband access system via drone/uav platforms
US9479964B2 (en) 2014-04-17 2016-10-25 Ubiqomm Llc Methods and apparatus for mitigating fading in a broadband access system using drone/UAV platforms
US9571180B2 (en) 2014-10-16 2017-02-14 Ubiqomm Llc Unmanned aerial vehicle (UAV) beam forming and pointing toward ground coverage area cells for broadband access
US9590720B2 (en) 2015-05-13 2017-03-07 Ubiqomm Llc Ground terminal and gateway beam pointing toward an unmanned aerial vehicle (UAV) for network access
US9614608B2 (en) 2014-07-14 2017-04-04 Ubiqomm Llc Antenna beam management and gateway design for broadband access using unmanned aerial vehicle (UAV) platforms
US9660718B2 (en) 2015-05-13 2017-05-23 Ubiqomm, LLC Ground terminal and UAV beam pointing in an unmanned aerial vehicle (UAV) for network access
US9712228B2 (en) 2014-11-06 2017-07-18 Ubiqomm Llc Beam forming and pointing in a network of unmanned aerial vehicles (UAVs) for broadband access
US9853713B2 (en) 2016-05-06 2017-12-26 Ubiqomm Llc Unmanned aerial vehicle (UAV) beam pointing and data rate optimization for high throughput broadband access
US9853712B2 (en) 2014-02-17 2017-12-26 Ubiqomm Llc Broadband access system via drone/UAV platforms
US9859972B2 (en) 2014-02-17 2018-01-02 Ubiqomm Llc Broadband access to mobile platforms using drone/UAV background

Families Citing this family (66)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19618142B4 (en) * 1996-05-06 2005-03-17 Süddeutscher Rundfunk -Anstalt des öffentlichen Rechts- A method for transmitting COFDM-modulated broadcasting signals via a satellite system and satellite transponders for implementing the method
GB9713722D0 (en) * 1996-07-18 1997-09-03 Motorola Inc Geosynchronous communications satellite system with reconfigurable service area
GB2316832B (en) * 1996-08-24 2001-05-16 Ico Services Ltd Signal assessed user terminal system access in satellite communication systems
GB2318482B (en) * 1996-10-16 2001-06-13 Ico Services Ltd Communication system
GB2319696B (en) 1996-11-20 2001-08-01 Inmarsat Ltd Communication method and apparatus
EP0851628A1 (en) 1996-12-23 1998-07-01 ICO Services Ltd. Key distribution for mobile network
JPH10190543A (en) * 1996-12-28 1998-07-21 Casio Comput Co Ltd Communication terminal equipment
EP0869628A1 (en) 1997-04-01 1998-10-07 ICO Services Ltd. Interworking between telecommunications networks
JP3153496B2 (en) * 1997-05-21 2001-04-09 株式会社日立製作所 Communication service providing method using a long artificial satellites staying time in the zenith direction
EP0890907B1 (en) 1997-07-11 2000-06-14 ICO Services Ltd. Providing web access to users in a vehicle
EP0954117A1 (en) 1998-04-30 1999-11-03 ICO Services Ltd. Transmission quality reporting
EP0967739A1 (en) 1998-06-24 1999-12-29 ICO Services Ltd. Measurement of cellular environment in idle mode and transmission to central at beginning of call
JP3974712B2 (en) * 1998-08-31 2007-09-12 富士通株式会社 Digital broadcasting transmission and reception reproducing method and a digital broadcast transmission and receiving and reproducing system as well as digital broadcasting transmitting apparatus and a digital broadcasting receiving and reproducing device
US6865166B1 (en) 1998-11-06 2005-03-08 Northrop Grumman Corporation Interference management of a processing communications satellite
US6785553B2 (en) 1998-12-10 2004-08-31 The Directv Group, Inc. Position location of multiple transponding platforms and users using two-way ranging as a calibration reference for GPS
EP1011210A1 (en) * 1998-12-15 2000-06-21 ICO Services Ltd. Allocation of radio frequency spectrum
US6337980B1 (en) 1999-03-18 2002-01-08 Hughes Electronics Corporation Multiple satellite mobile communications method and apparatus for hand-held terminals
US6990314B1 (en) 1999-03-18 2006-01-24 The Directv Group, Inc. Multi-node point-to-point satellite communication system employing multiple geo satellites
US7215954B1 (en) * 1999-03-18 2007-05-08 The Directv Group, Inc. Resource allocation method for multi-platform communication system
US6920309B1 (en) 1999-03-18 2005-07-19 The Directv Group, Inc. User positioning technique for multi-platform communication system
US6501941B1 (en) 1999-03-23 2002-12-31 Hughes Electronics Corporation Method for identifying growth limits of handheld services for mobile satellite communications
US6606307B1 (en) * 1999-03-23 2003-08-12 Hughes Electronics Corporation Techniques for utilization of bandwidth space assets
FR2793631B1 (en) * 1999-05-10 2001-07-27 Centre Nat Etd Spatiales Bidirectional communication terminal multmedia
EP1056222A1 (en) 1999-05-24 2000-11-29 ICO Services Ltd. Data multiplexing for diversity operation
US6662011B1 (en) * 1999-09-20 2003-12-09 Motorola, Inc. Method for performing rapid handoffs in a wireless communication system using virtual connections
DE60037872T2 (en) * 1999-10-26 2009-02-26 Nxp B.V. Controlling a multi-directional antenna structure in a mobile station for use in a radio communication network
US6788917B1 (en) * 2000-01-19 2004-09-07 Ericsson Inc. Timing systems and methods for forward link diversity in satellite radiotelephone systems
US7339520B2 (en) * 2000-02-04 2008-03-04 The Directv Group, Inc. Phased array terminal for equatorial satellite constellations
WO2001097409A1 (en) * 2000-06-15 2001-12-20 Ico Services Ltd. Allocation of radio frequency spectrum
US7257418B1 (en) 2000-08-31 2007-08-14 The Directv Group, Inc. Rapid user acquisition by a ground-based beamformer
US6763242B1 (en) 2000-09-14 2004-07-13 The Directv Group, Inc. Resource assignment system and method for determining the same
US8396513B2 (en) 2001-01-19 2013-03-12 The Directv Group, Inc. Communication system for mobile users using adaptive antenna
US7187949B2 (en) 2001-01-19 2007-03-06 The Directv Group, Inc. Multiple basestation communication system having adaptive antennas
US7809403B2 (en) 2001-01-19 2010-10-05 The Directv Group, Inc. Stratospheric platforms communication system using adaptive antennas
FR2821516B1 (en) * 2001-02-26 2005-09-09 Cit Alcatel Method and telecommunication system satellites and base station for such a system
US7142809B1 (en) * 2001-02-27 2006-11-28 The Directv Group, Inc. Device and method to locally fill gaps in spotbeam satellite systems with frequency re-use
US7006789B2 (en) * 2001-09-14 2006-02-28 Atc Technologies, Llc Space-based network architectures for satellite radiotelephone systems
US6771608B2 (en) 2001-11-05 2004-08-03 The Boeing Company Link tracking with a phased array antenna in a TDMA network
US6947740B2 (en) * 2002-06-13 2005-09-20 Spacecode Llc Communication satellite in a satellite communication system with high aspect ratio cell arrangement and shared and allocable bandwidth
US7697477B2 (en) * 2002-11-07 2010-04-13 Northrop Grumman Corporation Communications protocol to facilitate handover in a wireless communications network
JP2005167460A (en) * 2003-12-01 2005-06-23 Matsushita Electric Ind Co Ltd Electronic apparatus connectable to radio network, and radio network system
US7639646B2 (en) * 2004-03-17 2009-12-29 Qualcomm Incorporated Satellite diversity system, apparatus and method
US7933552B2 (en) * 2004-03-22 2011-04-26 Atc Technologies, Llc Multi-band satellite and/or ancillary terrestrial component radioterminal communications systems and methods with combining operation
CA2581601C (en) 2004-11-16 2013-03-19 Atc Technologies, Llc Satellite communications systems, components and methods for operating shared satellite gateways
US20070264929A1 (en) * 2004-12-18 2007-11-15 Chao-Chun Chen Satellite communication system architecture
US20060135153A1 (en) * 2004-12-18 2006-06-22 Chao-Chun Chen Satellite communication system architecture
US7697886B2 (en) * 2005-05-19 2010-04-13 Delphi Technologies, Inc. Method and system to increase available bandwidth in a time division multiplexing system
US20070123252A1 (en) * 2005-10-12 2007-05-31 Atc Technologies, Llc Systems, methods and computer program products for mobility management in hybrid satellite/terrestrial wireless communications systems
US8090041B2 (en) * 2006-01-20 2012-01-03 Atc Technologies Llc Systems and methods for forward link closed loop beamforming
FR2903828B1 (en) * 2006-07-13 2009-03-27 Thales Sa Method for time synchronization of a waveform orthogonal frequency evasion and satellite radio communication system has management decentralized transit time.
EP2067278B1 (en) 2006-08-22 2016-06-15 Koninklijke Philips N.V. Method for transmitting data in a mobile system and radio stations therefor
US8538323B2 (en) 2006-09-26 2013-09-17 Viasat, Inc. Satellite architecture
EP2645596B1 (en) 2006-09-26 2016-12-21 ViaSat, Inc. Improved spot beam satellite systems
US7742738B2 (en) * 2006-12-27 2010-06-22 Nortel Networks Limited Method and system for diversity using orthogonal frequency/division multiplexing
US20080311844A1 (en) * 2007-03-19 2008-12-18 Viasat, Inc. Multiple Input Receiver In Satellite Communication System
US7792070B1 (en) * 2007-04-13 2010-09-07 Douglas Burr Multi-beam satellite network to maximize bandwidth utilization
US20090161797A1 (en) * 2007-06-08 2009-06-25 Cowles Philip R Satellite detection of automatic identification system signals
US7876865B2 (en) * 2007-06-08 2011-01-25 COM DEV International Ltd System and method for decoding automatic identification system signals
US7969923B2 (en) 2008-11-14 2011-06-28 Dbsd Satellite Services G.P. Asymmetric TDD in flexible use spectrum
US8780788B2 (en) 2009-09-25 2014-07-15 Com Dev International Ltd. Systems and methods for decoding automatic identification system signals
US9236934B1 (en) 2009-10-16 2016-01-12 Viasat, Inc. Satellite system architecture for coverage areas of disparate demand
US9331774B2 (en) 2010-06-09 2016-05-03 Exactearth Ltd. Systems and methods for segmenting a satellite field of view for detecting radio frequency signals
US8800932B2 (en) 2010-07-26 2014-08-12 Lockheed Martin Corporation Medium earth orbit constellation with simple satellite network topology
US9015567B2 (en) 2012-04-12 2015-04-21 Com Dev International Ltd. Methods and systems for consistency checking and anomaly detection in automatic identification system signal data
CN103796319B (en) * 2014-01-16 2017-04-19 北京大学 Multibeam satellite mobile communications downlink frequency multiplexing method
US20150341109A1 (en) * 2014-05-20 2015-11-26 Delphi Technologies, Inc. Satellite communication system with time-multiplexed communication from spot beam defined sub-regions

Citations (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3262116A (en) * 1964-01-16 1966-07-19 Satellite And Space Comm Syste Satellite and space communications systems
US3651406A (en) * 1969-10-03 1972-03-21 Magnavox Co System for plural channel signal reception and readout and method of operation
US3858007A (en) * 1972-01-26 1974-12-31 Licentia Gmbh Circuit arrangement for synchronizing pulse bursts
US3896382A (en) * 1972-11-17 1975-07-22 Communications Satellite Corp Precipitation attenuation detection system
US4041397A (en) * 1976-04-28 1977-08-09 The United States Of America As Represented By The Secretary Of The Navy Satellite up link diversity switch
US4105973A (en) * 1976-10-15 1978-08-08 Bell Telephone Laboratories, Incorporated Multibeam, digitally modulated, time division, switched satellite communications system
US4189675A (en) * 1978-05-30 1980-02-19 Nasa Satellite personal communications system
US4218654A (en) * 1978-04-28 1980-08-19 Kokusai Denshin Denwa Kabushiki Kaisha Space diversity system in TDMA communication system
US4715048A (en) * 1986-05-02 1987-12-22 Canadian Patents And Development Limited Frequency offset diversity receiving system
US4744083A (en) * 1984-09-14 1988-05-10 Geostar Corporation Satellite-based position determining and message transfer system with monitoring of link quality
US4975707A (en) * 1989-07-13 1990-12-04 Energetics Satellite Corporation Multiple satellite locating system
US5008679A (en) * 1990-01-31 1991-04-16 Interferometrics Incorporated Method and system for locating an unknown transmitter
US5233636A (en) * 1990-05-11 1993-08-03 Electronics And Telecommunications Research Institute Analog and digital phase detector for bit synchronism
US5265694A (en) * 1992-02-17 1993-11-30 Mazda Motor Corporation Slip control system for vehicle
US5408237A (en) * 1991-11-08 1995-04-18 Teledesic Corporation Earth-fixed cell beam management for satellite communication system
US5841766A (en) * 1994-12-12 1998-11-24 Ericsson Inc. Diversity-oriented channel allocation in a mobile communications system

Family Cites Families (24)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3495175A (en) * 1967-07-19 1970-02-10 Moore Associates Inc Automatic channel selection system for a multichannel communication system
US3906166A (en) * 1973-10-17 1975-09-16 Motorola Inc Radio telephone system
JPS5551370B2 (en) * 1976-01-19 1980-12-24
US4700374A (en) * 1984-07-06 1987-10-13 Alcatel N.V. Mobile telephone location system
US4972151A (en) * 1985-10-01 1990-11-20 Hughes Aircraft Company Steered-beam satellite communication system
US4813036A (en) * 1985-11-27 1989-03-14 National Exchange, Inc. Fully interconnected spot beam satellite communication system
GB8612561D0 (en) * 1986-05-22 1986-07-02 Signal Processors Ltd Radio location & apparatus
US4819227A (en) * 1986-08-14 1989-04-04 Hughes Aircraft Company Satellite communications system employing frequency reuse
US4872015A (en) * 1986-12-01 1989-10-03 Hughes Aircraft Company Satellite communications system for mobile users
EP0337267B1 (en) 1988-04-14 1993-12-29 ANT Nachrichtentechnik GmbH Method and arrangement for reducing frequency-deviations in a mobile satellite communication
ES2109973T3 (en) * 1988-06-14 1998-02-01 Ericsson Telefon Ab L M Mobile radio cell change without notice.
CA1338020C (en) 1988-10-28 1996-01-30 Bary Robert Bertiger Satellite cellular telephone and data communication system
US5187805A (en) * 1989-10-02 1993-02-16 Motorola, Inc. Telemetry, tracking and control for satellite cellular communication systems
US5287541A (en) * 1989-11-03 1994-02-15 Motorola, Inc. Global satellite communication system with geographic protocol conversion
FR2664449B1 (en) * 1990-07-03 1994-03-25 Alcatel Espace space telecommunications system.
US5230082A (en) * 1990-08-16 1993-07-20 Telefonaktiebolaget L M Ericsson Method and apparatus for enhancing signalling reliability in a cellular mobile radio telephone system
CA2052466C (en) * 1990-10-02 2001-05-08 Masayuki Sakamoto Method of handover and route diversity in mobile radio communication
FR2682238B1 (en) 1991-10-02 1994-10-07 Alcatel Espace communications system by satellites in low orbit destination terminals.
US5261118A (en) * 1991-10-04 1993-11-09 Motorola, Inc. Simulcast synchronization and equalization system and method therefor
DE69229678D1 (en) * 1991-10-28 1999-09-02 Teledesic Llc Satellite communication system
US5233626A (en) * 1992-05-11 1993-08-03 Space Systems/Loral Inc. Repeater diversity spread spectrum communication system
JP2706600B2 (en) * 1992-05-28 1998-01-28 ティアールダブリュー インコーポレイテッド Cellular telecommunications system to a medium earth altitude satellite based
US5268694A (en) * 1992-07-06 1993-12-07 Motorola, Inc. Communication system employing spectrum reuse on a spherical surface
CA2105710A1 (en) * 1992-11-12 1994-05-13 Raymond Joseph Leopold Network of hierarchical communication systems and method therefor

Patent Citations (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3262116A (en) * 1964-01-16 1966-07-19 Satellite And Space Comm Syste Satellite and space communications systems
US3651406A (en) * 1969-10-03 1972-03-21 Magnavox Co System for plural channel signal reception and readout and method of operation
US3858007A (en) * 1972-01-26 1974-12-31 Licentia Gmbh Circuit arrangement for synchronizing pulse bursts
US3896382A (en) * 1972-11-17 1975-07-22 Communications Satellite Corp Precipitation attenuation detection system
US4041397A (en) * 1976-04-28 1977-08-09 The United States Of America As Represented By The Secretary Of The Navy Satellite up link diversity switch
US4105973A (en) * 1976-10-15 1978-08-08 Bell Telephone Laboratories, Incorporated Multibeam, digitally modulated, time division, switched satellite communications system
US4218654A (en) * 1978-04-28 1980-08-19 Kokusai Denshin Denwa Kabushiki Kaisha Space diversity system in TDMA communication system
US4189675A (en) * 1978-05-30 1980-02-19 Nasa Satellite personal communications system
US4744083A (en) * 1984-09-14 1988-05-10 Geostar Corporation Satellite-based position determining and message transfer system with monitoring of link quality
US4715048A (en) * 1986-05-02 1987-12-22 Canadian Patents And Development Limited Frequency offset diversity receiving system
US4975707A (en) * 1989-07-13 1990-12-04 Energetics Satellite Corporation Multiple satellite locating system
US5008679A (en) * 1990-01-31 1991-04-16 Interferometrics Incorporated Method and system for locating an unknown transmitter
US5233636A (en) * 1990-05-11 1993-08-03 Electronics And Telecommunications Research Institute Analog and digital phase detector for bit synchronism
US5408237A (en) * 1991-11-08 1995-04-18 Teledesic Corporation Earth-fixed cell beam management for satellite communication system
US5265694A (en) * 1992-02-17 1993-11-30 Mazda Motor Corporation Slip control system for vehicle
US5841766A (en) * 1994-12-12 1998-11-24 Ericsson Inc. Diversity-oriented channel allocation in a mobile communications system

Cited By (42)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7376417B2 (en) * 2000-09-19 2008-05-20 The Directv Group, Inc. Method and system of efficient spectrum utilization by communications satellites
US20040147222A1 (en) * 2000-09-19 2004-07-29 Hughes Electronics Corporation Method and system of efficient spectrum utilization by communications satellites
US20050068230A1 (en) * 2003-09-29 2005-03-31 Munoz Michael S. Reducing co-channel interference in satellite communications systems by antenna re-pointing
US6940452B2 (en) * 2003-09-29 2005-09-06 Northrop Grumman Corporation Reducing co-channel interference in satellite communications systems by antenna re-pointing
US8428000B2 (en) 2005-04-05 2013-04-23 Skybitz, Inc. Multiple return link
US20060291409A1 (en) * 2005-04-05 2006-12-28 Rich Battista Multiple return link
US9496946B2 (en) 2005-04-05 2016-11-15 Skybitz, Inc. Multiple return link
US20100284324A1 (en) * 2005-04-05 2010-11-11 Rich Battista Multiple Return Link
US7782811B2 (en) * 2005-04-05 2010-08-24 Skybitz, Inc. Multiple return link
US7944993B2 (en) 2006-08-22 2011-05-17 Viasat, Inc. Downstream broad beam diversity
US20080143589A1 (en) * 2006-08-22 2008-06-19 Viasat, Inc. Downstream Broad Beam Diversity With Interference Cancellation
US20080214107A1 (en) * 2006-08-22 2008-09-04 Viasat, Inc. Upstream Broad Beam Diversity
US20080144596A1 (en) * 2006-08-22 2008-06-19 Viasat, Inc. Cooperative Orthogonal Multi-Satellite Communication System
US7881246B2 (en) 2006-08-22 2011-02-01 Viasat, Inc. Cooperative orthogonal multi-satellite communication system
US7904020B2 (en) * 2006-08-22 2011-03-08 Viasat, Inc. Downstream broad beam diversity with interference cancellation
US20080144734A1 (en) * 2006-08-22 2008-06-19 Viasat, Inc. Downstream Broad Beam Diversity
US7929909B2 (en) 2006-08-22 2011-04-19 Viasat, Inc. Upstream broad beam diversity with interference cancellation
US20100085909A1 (en) * 2008-10-06 2010-04-08 Viasat, Inc. Terminal self-synchronization for mesh satellite communications
US20100085908A1 (en) * 2008-10-06 2010-04-08 Viasat, Inc. Terminal measurement based synchronization for mesh satellite communications
US8675635B2 (en) 2008-10-06 2014-03-18 Viasat, Inc. Master terminal synchronization for mesh satellite communications
US8675634B2 (en) * 2008-10-06 2014-03-18 Viasat, Inc. Terminal measurement based synchronization for mesh satellite communications
US8625565B2 (en) * 2009-10-06 2014-01-07 Intel Corporation Millimeter-wave communication station and method for multiple-access beamforming in a millimeter-wave communication network
US20140161105A1 (en) * 2009-10-06 2014-06-12 Carlos Cordeiro Millimeter-wave communication station and method for multiple-access beamforming in a millimeter-wave communication network
US9414380B2 (en) * 2009-10-06 2016-08-09 Intel Corporation Millimeter-wave communication station and method for multiple-access beamforming in a millimeter-wave communication network
US20110080898A1 (en) * 2009-10-06 2011-04-07 Carlos Cordeiro Millimeter-wave communication station and method for multiple-access beamforming in a millimeter-wave communication network
US9763253B2 (en) 2012-08-14 2017-09-12 University Of South Australia Channel allocation in a communication system
CN104584457A (en) * 2012-08-14 2015-04-29 南澳大利亚大学 Channel allocation in a communication system
WO2014026228A1 (en) * 2012-08-14 2014-02-20 University Of South Australia Channel allocation in a communication system
US9859972B2 (en) 2014-02-17 2018-01-02 Ubiqomm Llc Broadband access to mobile platforms using drone/UAV background
US9853712B2 (en) 2014-02-17 2017-12-26 Ubiqomm Llc Broadband access system via drone/UAV platforms
WO2015123623A1 (en) * 2014-02-17 2015-08-20 Ubiqomm Broadband access system via drone/uav platforms
US9853715B2 (en) 2014-02-17 2017-12-26 Ubiqomm Llc Broadband access system via drone/UAV platforms
US9479964B2 (en) 2014-04-17 2016-10-25 Ubiqomm Llc Methods and apparatus for mitigating fading in a broadband access system using drone/UAV platforms
US9614608B2 (en) 2014-07-14 2017-04-04 Ubiqomm Llc Antenna beam management and gateway design for broadband access using unmanned aerial vehicle (UAV) platforms
US9571180B2 (en) 2014-10-16 2017-02-14 Ubiqomm Llc Unmanned aerial vehicle (UAV) beam forming and pointing toward ground coverage area cells for broadband access
US9712228B2 (en) 2014-11-06 2017-07-18 Ubiqomm Llc Beam forming and pointing in a network of unmanned aerial vehicles (UAVs) for broadband access
US9800320B2 (en) 2014-11-06 2017-10-24 Ubiqomm Llc Beam forming and pointing in a network of unmanned aerial vehicles (UAVs) for broadband access
US9866312B2 (en) 2014-11-06 2018-01-09 Ubiqomm Llc Beam forming and pointing in a network of unmanned aerial vehicles (UAVs) for broadband access
US9660718B2 (en) 2015-05-13 2017-05-23 Ubiqomm, LLC Ground terminal and UAV beam pointing in an unmanned aerial vehicle (UAV) for network access
US9590720B2 (en) 2015-05-13 2017-03-07 Ubiqomm Llc Ground terminal and gateway beam pointing toward an unmanned aerial vehicle (UAV) for network access
US9853713B2 (en) 2016-05-06 2017-12-26 Ubiqomm Llc Unmanned aerial vehicle (UAV) beam pointing and data rate optimization for high throughput broadband access
US9980267B2 (en) 2016-05-06 2018-05-22 Bridgewest Finance Llc Unmanned aerial vehicle (UAV) beam pointing and data rate optimization for high throughput broadband access

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