Multi-beam TDMA satellite mobile communications system
First Claim
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;
selected one 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).
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Accused Products
Abstract
An earth station receives a return signal via more than one satellite link from a mobile terminal using TDMA. The earth station selects one or more of the satellite links for transmitting a forward signal on the basis of the quality of signal received via each link. The earth section allocates frequency channels to the mobile terminals according to their location on the surface of the earth, so that the propagation time to and from those mobile terminals which share the same frequency channel is approximately the same. The satellite 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 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.
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Citations
41 Claims
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1. A method of satellite communication between a first earth station (18) and a second earth station (8) comprising:
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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;
selected one 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). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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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).
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15. Apparatus for use in a satellite communications earth station (18) using TDMA channels, comprising:
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a receiver (8a, 8b) 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 (14) 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). - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 41)
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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).
- ,f2′
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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.
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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.
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35. A method of satellite communication, comprising:
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directing a plurality of beams (51a-51m) from a non-geostationary satellite (4a) to a corresponding plurality of regions (52) which are fixed relative to the surface of the earth; and
determining where one of said beams (51a-51m) fails to satisfy a predetermined criterion, and redirecting said one of said beams (51a-51m) from the corresponding one of the fixed regions (52) to another fixed region (52) such that said one of said beams (51a-51m) satisfies said predetermined criterion;
characterised in that the directions of other ones of said plurality of beams (51a-51m) which satisfy said predetermined criterion are maintained at the corresponding ones of the fixed regions (52) while said one of said plurality of beams (51a-51m) is redirected. - View Dependent Claims (36, 37)
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38. Apparatus for satellite communication, comprising means operable to determine a plurality of beam directions, for a plurality of beams (51a-51m) projected by a non-geostationary satellite (4a), to corresponding fixed regions (52) of the earth'"'"'s surface;
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means operable to detect whether one or more of said beams (51a-51m) 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 (51a-51m), 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 (4a) so as to direct the beams (51a-51m) in the corresponding beam directions such that the directions of other ones of said beams (51a-51m) for which a new beam direction is not determined are maintained at the corresponding fixed regions (52). - View Dependent Claims (39, 40)
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Specification