Method and apparatus for increasing the capacity of a satellite transponder by reuse of bandwidth
First Claim
1. A method of communicating between correspondent pairs of earth stations through an earth orbiting satellite and comprising,transmitting signals from the earth stations simultaneously in channels that have at least a partial overlap in bandwidth,retransmitting from the satellite to the earth stations a composite signal which is a composite of the signals transmitted by the two earth stations,storing at each receiving earth station information constituting a base band representation of the signal transmitted by the receiving earth station,delaying the stored information by an amount of time equal to the satellite round trip delay,preparing an estimate of the portion of the composite signal that is transmitted by the receiving earth station by processing the composite signal using the stored information,subtracting from the composite signal received at each earth station the portion of the composite signal transmitted by that earth station to provide a desired signal corresponding to the signal transmitted by the other earth station of the correspondent pair, anddemodulating the desired signal.
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Accused Products
Abstract
A method and apparatus for increasing the capacity of present and future satellite communication systems transmits signals from correspondent pairs of earth stations simultaneously in channels that have at least a partial overlap in bandwidth. Each receiver at each earth station subtracts from the received composite signal the portion of the composite signal which was transmitted by the receiving earth station. This leaves a desired signal which corresponds to the signal transmitted by the other earth station of the correspondent pair and which is then demodulated. Each receiver at each earth station thus reconstructs an estimated target signal which has the amplitude, delay, frequency and phase of the signal as transmitted from the earth station and retransmitted by the satellite. The reconstructed target signal provides a very precise estimate of the portion of the composite signal transmitted by the earth station. The reconstructed target signal estimate is provided by repeated correlations of known signals against signals which are only partially known in order to produce an output which can be filtered to eliminate further parameters. The further parameters are put back into the estimation process, and said portion of the composite signal is regenerated in this manner of iteration.
33 Citations
17 Claims
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1. A method of communicating between correspondent pairs of earth stations through an earth orbiting satellite and comprising,
transmitting signals from the earth stations simultaneously in channels that have at least a partial overlap in bandwidth, retransmitting from the satellite to the earth stations a composite signal which is a composite of the signals transmitted by the two earth stations, storing at each receiving earth station information constituting a base band representation of the signal transmitted by the receiving earth station, delaying the stored information by an amount of time equal to the satellite round trip delay, preparing an estimate of the portion of the composite signal that is transmitted by the receiving earth station by processing the composite signal using the stored information, subtracting from the composite signal received at each earth station the portion of the composite signal transmitted by that earth station to provide a desired signal corresponding to the signal transmitted by the other earth station of the correspondent pair, and demodulating the desired signal.
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4. Apparatus for increasing the capacity of an earth orbiting satellite by communicating between correspondent pairs of earth stations in channnels that have at least a partial overlap in bandwidth, said apparatus comprising,
first transmitting means at a first earth station of the correspondent pair for transmitting a first signal to the satellite in a first frequency band for retransmission by the satellite to a second earth station of the correspondent pair, second transmitting means at a second earth station of the correspondent pair for transmitting a second signal to the satellite in a second frequency band for retransmission by the satellite to the first earth station of the correspondent pair, said first frequency band having at least partial overlap with the second frequency band so that each earth station receives a composite signal which is a composite of the first and second signals transmitted from the earth stations, receiver means at each earth station for subtracting from the received composite signal the portion of the composite signal transmitted by that earth station to provide a desired signal corresponding to the signal transmitted by the other earth station of the correspondent pair, said receiver means including transmitted storage means for storing information constituting a baseband representation of the signal transmitted by that earth station and for delaying the information by an amount of time equal to the satellite round trip delay, said receiver means also including means for preparing an estimate of the portion of the composite signal that is transmitted by that earth station by processing the composite signal using the stored information, and demodulation means for demodulating the desired signal at each earth station.
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11. A receiver for an earth station of the kind which receives a composite signal from an earth orbiting satellite and the composite signal includes both a first signal transmitted from the earth station to the satellite on a first channel and a second signal transmitted from another earth station to the satellite on a second channel and wherein there is at least partial overlap of the first and second channels so that the first signal must be subtracted from the composite signal at the receiving earth station before the second signal can be demodulated, said receiver comprising,
estimated target signal means for reconstructing an estimated target signal which has the amplitude, delay, frequency and phase of the first signal as retransmitted from the satellite and received at the earth station, the estimate target signal means include transmitted signal storage means for delaying a baseband representation of the signal transmitted by the earth station by an amount of time equal to the satellite round trip delay, and subtraction means for subtracting the estimated target signal from the composite signal to produce a desired signal which corresponds to the second signal and which can be demodulated at the earth station.
Specification