Importance

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Abstract

A satellite communication system between a hub terminal and remote terminals simultaneously uses two or more satellites for communication. Rapid signal acquisition for mobile terminals is achieved by incorporation of a Global Positioning System receiver to establish initial frequency and time references. High resolution time distribution is provided by use of spread spectrum coded signals. A combined Time Division Multiple Access/Code Multiplex architecture receives simultaneous signals of widely varying signal strengths. Rapid and numerous changes to the polling sequence is possible. The hub terminal incorporates two high directivity antennas each illuminating a separate geostationary satellite transponder with a spread spectrum coded signal, each orthogonal to the other. The remote terminals employ an antenna of sufficiently small aperture to enable simultaneous reception of both orthogonal transponder signals. Each remote terminal transmits one signal that illuminates both satellite transponders and is received separately by each hub terminal antenna. All transmissions are synchronized to a precision time frame and are spread spectrum encoded. Multiple remote terminals may transmit simultaneously using orthogonal codes. Block addressing reduces the data bandwidth of the hub terminal. The network architecture allows numerous blocks to be established, each block containing any number of remote terminals and each remote terminal may be assigned to be a member numerous blocks. A single command issued by the hub terminal to a particular block, thereby addresses the multiple remote terminals which are members of that block. In order to demodulate the data received from multiple remote terminals, the hub terminal generates a numerical database that fully represents the composite received signal. Iterative digital signal processing is performed in real-time to establish the code phase of each remote terminal. Initial processing of the database demodulates only strong signals. In an iterative manner, the successfully demodulated signals are subtracted from the database and processing is reperformed to extract the weaker signals.

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First Claim