Orthogonal code division multiple access on a return link
First Claim
1. A method of providing orthogonal CDMA communication in a return link, comprising:
- receiving a first pilot signal at a plurality of terminals;
deriving at least one transmit timing characteristic from the received first pilot signal, wherein deriving is performed within each of the plurality of terminals;
transmitting, at an assigned time, a pilot signal from each of the plurality of terminals in accordance with the derived at least one transmit timing characteristic;
receiving a control signal, the content of the control signal providing instructions to adjust the at least one transmit timing characteristic; and
adjusting, responsive to the control signal, the at least one transmit timing characteristic.
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Accused Products
Abstract
A technique for realizing code synchronism to enable the application of modulation codes needed for implementing orthogonal CDMA modulation for reverse link communications. In a satellite communications system using orthogonal CDMA in the reverse link, a ground station transmits a first pilot signal in the forward link direction, which is acquired and tracked by a terminal or remote station, and used in recovering carrier phase and modulation chip clock timing. The terminal then derives a transmission carrier frequency and chip clock timing to be used, from the recovered forward pilot carrier frequency and chip clock timing. The terminal transmits a second pilot signal in the reverse link direction which, after being received and retransmitted by a satellite, is detected at the ground station. Terminals have the ability to advance or retard the timing of their signals for transmission relative to the timing derived from the forward link pilot signal. The ground station tracks timing, and in some embodiments also tracks frequency, of the terminal pilot signal, and compares these parameters to a reverse link reference signal. Based at least in part on the results of the comparison, the ground station transmits a control signal on the forward link to each terminal, thereby commanding the terminal to advance or retard its respective transmission timing. Each terminal then adjusts its transmission timing and/or frequency in small increments to maintain a desired level of time alignment with the ground station.
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Citations
35 Claims
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1. A method of providing orthogonal CDMA communication in a return link, comprising:
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receiving a first pilot signal at a plurality of terminals;
deriving at least one transmit timing characteristic from the received first pilot signal, wherein deriving is performed within each of the plurality of terminals;
transmitting, at an assigned time, a pilot signal from each of the plurality of terminals in accordance with the derived at least one transmit timing characteristic;
receiving a control signal, the content of the control signal providing instructions to adjust the at least one transmit timing characteristic; and
adjusting, responsive to the control signal, the at least one transmit timing characteristic. - View Dependent Claims (2)
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3. A method of operating a communications system having a forward link and a reverse link, to provide orthogonal CDMA communication in the reverse link, comprising:
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transmitting a first pilot signal from a ground station in the forward link direction;
receiving the first pilot signal at a terminal, and recovering carrier phase and modulation chip clock timing therein;
transmitting a second pilot signal from the terminal in the reverse link direction;
comparing, at the ground station, the second pilot signal to a reverse link reference signal;
transmitting, in the forward link direction, a control signal, the content of the control signal based at least in part on the comparison between the second pilot signal and the reverse link reference signal; and
adjusting, responsive to the control signal, at least one operational parameter of the terminal. - View Dependent Claims (4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A terminal, comprising:
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means for receiving a first pilot signal;
means for recovering carrier phase and modulation chip clock timing from the first pilot signal;
means for transmitting a second pilot signal from the terminal;
means for receiving a control signal;
means for transmitting an orthogonal CDMA traffic signal, the orthogonal CDMA traffic signal having a first timing characteristic; and
means for adjusting the first timing characteristic in response to said control signal. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28)
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29. A ground station operating in a communications system having a forward link and a reverse link, to provide orthogonal CDMA communication in the reverse link, comprising:
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means for transmitting a first pilot signal in the forward link direction;
means for receiving a second pilot signal from at least one terminal in the reverse link direction, and for recovering carrier phase and modulation chip clock timing therein;
means for comparing the second pilot signal to a reverse link reference signal; and
means for transmitting, in the forward link direction, a control signal to control at least one operational parameter of the terminal, the content being based at least in part on the comparison between the second pilot signal and the reverse link reference signal.
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30. A terminal device, comprising:
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a processor;
a memory of stored CDMA signal transmit timing characteristic control information coupled to the processor; and
a machine accessible medium, coupled to the processor, having instructions encoded therein, the instructions, when executed by the processor, cause the terminal device to;
receive a first pilot signal;
recover carrier phase and modulation chip clock timing from the first pilot signal;
transmit a second pilot signal;
receive a control signal;
transmit an orthogonal CDMA traffic signal having a first timing characteristic; and
adjusting the first timing characteristic in response to said control signal. - View Dependent Claims (31, 32, 33, 34, 35)
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Specification