Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
1998-12-17
2001-03-13
Chung, Phung M. (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S790000
Reexamination Certificate
active
06202189
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to data communications systems and, more particularly, to digital data communications systems.
BACKGROUND OF THE INVENTION
In recent years the need for global data networking capability has rapidly expanded. In order to meet this need, broadband satellite communication systems have been proposed as an alternative to land-based communication systems. One type of satellite data communication system is described in a variety of U.S. patents assigned to the assignee of this patent application, including U.S. Pat. Nos. 5,386,953; 5,408,237; 5,527,001; 5,548,294; 5,641,135; 5,642,122; and 5,650,788. These patents and other pending applications assigned to the assignee of this patent application describe a satellite communication system that includes a constellation of low-Earth-orbit (LEO) satellites for transmitting data from one location on the Earth's surface to another location. More specifically, each LEO satellite has a communication “footprint” that covers a portion of the Earth's surface as a satellite passes over the Earth. The communication footprint defines the area of the Earth within which ground terminals can communicate with the satellite. Located within each footprint are a large number of cells. During the period of time a cell remains within the borders of a satellite footprint, ground terminals located in the cell transmit data to and receive data from the “servicing” satellite. When a satellite reaches the end of its servicing arc, another satellite in orbit is positioned to “service” the Earth-fixed cells previously covered by the satellite reaching the end of its servicing arc.
Data to be sent from one location on the Earth to another location is transmitted from a ground terminal located within a cell to the satellite serving the cell via an uplink data channel. The data is routed through the constellation of LEO satellites via an intersatellite link data channel to the satellite serving the cell within which the ground terminal of the designated receiver is located. The latter satellite transmits the data to the receiver ground terminal via a downlink data channel. Thus, the constellation of LEO satellites and the ground terminals form a satellite data communication network wherein each ground terminal and satellite forms a node of the network.
Typically, data transmissions sent via uplink, intersatellite link or downlink data channels are broken into digital data packets, each of which include a header and a payload. The header data packets contain address and control information designed to direct the data packets through the satellite constellation to a desired ground terminal. The payload contains the information being transmitted, which is intended for the satellite or the ground terminal or both.
In order for a LEO satellite data communication system to be competitive, it must allow broadband transmission at a relatively low cost. Low cost requires that the satellites be light in weight and relatively inexpensive to manufacture. One way of keeping satellite weight and cost low is to minimize the complexity of electronic signal processing hardware, and keep transmission and reception power requirements low. Unfortunately, low transmission and reception power conflicts with the need for a highly reliable data communication system having a low bit error rate and packet loss rate as it is relatively easy to lose data contained in low-power signals.
One way of improving the reliability of low-power data communication signals that is well-known in the satellite communication field is to forward error correction (FEC) code the data to be transmitted. See U.S. Pat. Nos. 5,117,427; 5,446,747; and 5,473,601 for examples of FEC coding of digital data signals. Other systems and methods which use FEC coding in novel ways to mininize power requirements and maximize reliability are described in U.S. patent application Ser. No. 09/035,645 entitled “Coding System and Method For Low-Earth-Orbit Satellite Data Communication” and U.S. patent application Ser. No. 08/949,412 also entitled “Coding System and Method For Low-Earth-Orbit Satellite Data Communication”, both assigned to the assignee of this patent application and both incorporated herein by reference.
The present invention is directed to a coding system for a LEO satellite data communication network that uses FEC coding in a novel way not only to minimize power requirements and maximize reliability but also to minimize the bandwidth used for coding.
SUMMARY OF THE INVENTION
In accordance with this invention, a coding system ideally suited for use in a low-Earth-orbit (LEO) satellite data communication network is provided. Data to be transmitted from one location on the earth to another location is assembled into digital data packets containing a header and a payload which collectively contain input data bits of information. Prior to transmission, the input data bits of information are forward error correction (FEC) coded by a punctured serial concatenated convolutional encoder. The punctured serial concatenated convolutional encoder employs an outer encoder that outer convolutionally encodes the input data bits to produce outer encoded data bits and outer encoded parity bits. The outer encoded parity bits are punctured, and the remaining outer encoded parity bits and the outer encoded data bits are bit interleaved. The resulting bit interleaved, outer encoded data and remaining parity bits are inner convolutionally encoded by an inner encoder to produce concatenated coded, bit interleaved inner data bits and concatenated coded, bit interleaved inner parity bits. The concatenated coded, bit interleaved inner parity bits are punctured, and the remaining concatenated coded, bit interleaved inner parity bits and the concatenated coded, bit interleaved inner data bits are combined to produce serially concatenated convolutional coded data and parity bits. Preferably, the inner and outer convolutional coders are both systematic and recursive.
In accordance with other aspects of this invention, the serially concatenated convolutional coded data and parity bits are decoded by a serial concatenated convolutional decoder. First, the serially concatenated convolutional data and parity bits are decombined to separate data bits from parity bits, producing a data stream and a parity stream. Inner convolutional encoded erasures are inserted into the parity stream to replace the parity bits eliminated by puncturing during encoding. The resulting supplemented parity stream and the data stream are inner decoded by a soft-input soft-output (SISO) inner module to obtain updated bit probabilities of the inner encoder input and output. The updated bit probabilities of the inner encoder input are de-interleaved and decombined to separate data bits from parity bits. Outer convolutional encoded erasures are then inserted into the parity stream to replace the parity bits eliminated by puncturing during encoding. The resulting supplemented parity stream and the data stream are outer decoded by a SISO outer module to obtain updated bit probabilities of the outer encoder input and output. The updated bit probabilities of the outer encoder output are decombined to separate data bits from parity bits, and the parity stream is thereafter punctured. The punctured parity stream and the data stream are bit interleaved and then applied to the SISO inner module where the decoding process described above is repeated. The decoding process is repeated for a predetermined number of cycles, i.e., iterations, until the SISO outer module accurately reproduces the original input data bits of information.
In accordance with alternate aspects of this invention, rather than the parity bits resulting from both the outer convolutional encoder and the inner convolutional encoder being punctured, the parity bits of either the outer convolutional encoder or the inner convolutional encoder can be punctured.
In accordance with fuither aspects of this invention, prior to serially concatenated convolutional encodin
Griep Karl R.
Hinedi Sami M.
Million Samson
Christensen O'Connor Johnson & Kindness PLLC
Chung Phung M.
Teledesic LLC
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