Multiplex communications – Communication over free space – Repeater
Reexamination Certificate
1998-06-02
2001-10-09
Hsu, Alpus H. (Department: 2662)
Multiplex communications
Communication over free space
Repeater
C370S349000, C370S474000, C342S352000, C455S013100, C714S776000
Reexamination Certificate
active
06301231
ABSTRACT:
TECHNICAL FIELD
The present invention is related generally to telecommunications systems and, in particular, to satellite communications with satellite link diversity.
BACKGROUND OF THE INVENTION
Geosynchronous satellites are relied upon as part of larger communication networks by businesses, universities and individuals to provide a wide variety of communication services. Because a single satellite in geosynchronous orbit may transmit to a large portion of the Earth's surface, satellites are ideal for providing communication services to remote or thinly populated areas where cabling (e.g., land line, fiber optics, etc.) would not be economically feasible, or where rights-of-way would not easily be established. Satellites therefore allow advanced communication services to be made available around the world. For example, satellite systems are well suited for providing geographically distributed media services, such as video broadcasting.
Recently, it has been proposed to use a constellation of low-Earth orbit (LEO) satellites to provide telecommunications services to the entire world. In a LEO system, signals are transmitted from a first Earth-based terminal to a satellite on an up-link, routed through the constellation, and then transmitted from the satellite to a second Earth-based terminal on a down-link. The satellites therefore act as nodes in a network through which the signals are routed. The information carried in the signals may be generically referred to herein as “data,” and may include audio, video, or other types of data.
Many LEO systems have proposed routing data through the constellation in the form of “data packets.” At the first Earth-based terminal, the data to be transmitted is divided into multiple data packets that are routed through the satellite constellation and then reassembled at the destination Earth-based terminal to reconstitute the original data. In systems that packetize data for transmission, each data packet may take an independent route through the constellation from the source Earth-based terminal to the destination Earth-based terminal. If network traffic is light, data packets are quickly routed through the communication system. Sometimes, however, the satellite communication network may become congested due to equipment failures or particularly heavy data packet traffic, for example. Congestion could slow delivery of data packet traffic, and impact the timeliness of traffic required for near real-time applications, such as videoconferencing. It can be appreciated, therefore, that there is a significant need for techniques that reduce congestion within a LEO satellite communication system. The present invention provides this and other advantages as will be illustrated by the following description and accompanying figures.
SUMMARY OF THE INVENTION
The present invention is directed to a constellation-based satellite communication system and, in an exemplary embodiment, provides a technique for transmitting data from a first Earth-based terminal to a first and second satellite in non-geosynchronous Earth orbits. The first Earth-based terminal includes an antenna system to communicate with the first and second satellites and a transmitter coupled to the antenna to transmit to the first and second satellites. The transmitter transmits a request for a communication link with the first satellite at a first data rate. A receiver in the first Earth-based terminal is coupled to the antenna system to receive from the first and second satellites. The receiver receives a reply from the first satellite in response to the request for a communication link. If the reply indicates that a communication link is available at the first data rate, a connection is established and transmission initiated. If, however, the reply indicates that the first data rate is not available and only a second data rate (less than the first data rate) is available, then a request for a communication link is transmitted to the second satellite. If a reply from the second satellite indicates that a communication link is available, then a communication link is established with both the first and second satellites.
The system also includes a communication controller which, in response to the reply from the first satellite, apportions the data into first and second data portions. The transmitter establishes a first communication link with the first satellite to transmit the first data portion to the first satellite at the second data rate and, while maintaining the first communication link, establishes a second communication link with the second satellite to transmit the second data portion to the second satellite at a third data rate (which, when summed with the second data rate equals the first data rate).
The first satellite typically has a current maximum data rate. In some instances, the current maximum data rate is less than the first data rate. In this case, the transmitter transmits at the second data rate, wherein the second data rate is less than the current maximum data rate. In other instances, the current maximum data rate is greater than the first data rate. In that case, the transmitter transmits at the second data rate, wherein the second data rate is less than the current maximum data rate by a predetermined amount.
The system may also include a second Earth-based terminal designated as a recipient of the data transmitted from the first Earth-based terminal. Because the first and second data portions are independently routed through the satellite constellation, the portions may arrive at the second Earth-based terminal at different times and in a different order than initially sent. The second Earth-based terminal therefore includes a communication controller to process the first and second data portions and recover the data in the order that it was sent.
In an exemplary embodiment, the system also includes an error correction encoder in the first Earth-based terminal to process the data and thereby generate encoded data. In this embodiment, the first and second data portions comprise encoded data. The second Earth-based terminal includes an error correction decoder to process at least a portion of the first and second encoded data portions and thereby recover the data.
The system may further include a third satellite in Earth orbit wherein the communication controller apportions the data into first, second and third different data portions and the transmitter, while maintaining the first and second communication links, establishes a third communication link with the third satellite to transmit the third data portion to the third satellite at a fourth data rate less than the first data rate.
In yet another embodiment, the system may further comprise a relay satellite in Earth orbit to receive data portions sent to different satellites. The relay satellite can process the received data portions and thereby recover the data. In this embodiment, the relay satellite either directly transmits the recovered data to the second Earth-based terminal or forwards the recovered data through the satellite constellation for delivery to the second Earth-based terminal.
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Hassan Amer A.
Lundstrom Mark E.
Zukoski John A.
Donohue Michael J.
Hsu Alpus H.
Seed IP Law Group PLLC
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