Methods for effecting seamless handover and enhancing capacity in elliptical orbit satellite communications systems
First Claim
1. A method for effecting a seamless handover of a communications signal from a first satellite to a second satellite when the first and second satellites are at orbital positions which coincide, the method comprising:
- determining a time at which a first signal path length from a transmitting earth station to a receiving earth station through the first satellite is equal to a second signal path length from the transmitting earth station to the receiving earth station through the second satellite; and
effecting the communications signal handover from the first satellite to the second satellite at the time so determined.
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Abstract
Seamless handover of a communications signal from a first satellite to a second satellite is provided when the satellites are at orbital positions which coincide. Timing marks are inserted simultaneously in signals transmitted through the satellites, and signals received from the satellites compared to determine the difference in path length. Handover occurs when the path length difference is zero and the two signals are perfectly synchronized. Interference between the signals transmitted through the two satellites is avoided by using different transmission modes, such as different carrier frequencies, orthogonal senses of polarization, or digital signals with uncorrelated spreading codes. Using these different transmission modes in the right- and left-leaning orbits of a Cobra Teardrop system also permits overlaying multiple teardrop patterns, at longitudinal spacings comparable to the Basic Cobra system, as well as closer in-track spacing of satellites. The result is over an order of magnitude increase in global system capacity.
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Citations
19 Claims
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1. A method for effecting a seamless handover of a communications signal from a first satellite to a second satellite when the first and second satellites are at orbital positions which coincide, the method comprising:
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determining a time at which a first signal path length from a transmitting earth station to a receiving earth station through the first satellite is equal to a second signal path length from the transmitting earth station to the receiving earth station through the second satellite; and
effecting the communications signal handover from the first satellite to the second satellite at the time so determined. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method for effecting handover of a communications signal from a first satellite which is in a first elliptical orbit and descending in altitude, to a second satellite which is in a second elliptical orbit and ascending in altitude, when the first and second satellites are at orbital positions which coincide, the method comprising:
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determining a time at which the first satellite and the second satellite are at the same altitude; and
simultaneously turning the first satellite off and turning the second satellite on at the time so determined. - View Dependent Claims (14)
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15. A method of enhancing the communications capacity of a Cobra Teardrop satellite constellation having a first plurality of satellites in a left-leaning ground track and a right-leaning ground track which form a first set of teardrop patterns, and a second plurality of satellites in a left-leaning ground track and a right-leaning ground track which form a second set of teardrop patterns, the method comprising:
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communicating with the satellites in the left-leaning ground tracks using signals in a first mode;
communicating with the satellites in the right-leaning ground tracks using signals in a second mode, such that the signals in the second mode do not interfere with the signals in the first mode; and
arranging the orbits of the first and second pluralities of satellites such that the first and second sets of teardrop patterns are displaced from each other in longitude but are overlapping. - View Dependent Claims (16, 17, 18, 19)
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Specification