Abstract: A method of data transmission in a data communication network includes negotiating a connection between a source terminal and a destination terminal in the data communication network. During the connection negotiation process, optimal field lengths are determined for recording a source identifier and a sequence number in data packets transmitted in the connection. The source identifier identifies a connection from the source end to the destination end of the data transmission, while the sequence number identifies the relative position of a data packet in a series of data packets transmitted in the connection. The length of the source identifier and sequence number fields may either be calculated or selected from a set of predetermined field length values.

Abstract: A method of data transmission in a data communication network includes negotiating a connection between a source terminal and a destination terminal in the data communication network. During the connection negotiation process, optimal field lengths are determined for recording a source identifier and a sequence number in data packets transmitted in the connection. The source identifier identifies a connection from the source end to the destination end of the data transmission, while the sequence number identifies the relative position of a data packet in a series of data packets transmitted in the connection. The length of the source identifier and sequence number fields may either be calculated or selected from a set of predetermined field length values.

Abstract: A scalable satellite data communication system that provides incremental global broadband services using Earth-fixed cells may begin with a limited satellite deployment that initially serves a limited number of Earth-fixed cells. The system has the flexibility to incrementally increase the number of Earth-fixed cells that are served, with minimal constraints on the relative locations of the cells on the Earth, by adding satellites of potentially greater complexity to the system. Backward compatibility with existing user terminals is achieved by maintaining the same satellite communication interface as with the already-deployed satellite constellation. Continuous and/or non-continuous service may be provided to selected Earth-fixed cells. Scheduled non-continuous service is particularly advantageous for bulk data transport services. Satellites may use simple mechanically-steered antennas.

Abstract: A method of data transmission in a data communication network includes negotiating a connection between a source terminal and a destination terminal in the data communication network. During the connection negotiation process, optimal field lengths are determined for recording a source identifier and a sequence number in data packets transmitted in the connection. The source identifier identifies a connection from the source end to the destination end of the data transmission, while the sequence number identifies the relative position of a data packet in a series of data packets transmitted in the connection. The length of the source identifier and sequence number fields may either be calculated or selected from a set of predetermined field length values.

Abstract: A data communication system and method that allocates an amount of bandwidth to a ground terminal for uplink transmission of one or more data packets in a low-Earth-orbit (LEO) satellite data communication network. A bandwidth request message is generated and transmitted to a bandwidth allocation processing unit in the LEO satellite data communication network. The bandwidth request message requests allocation of an amount of bandwidth to a ground terminal for uplink transmission of one or more data packets and identifies a priority status of the data packets for which bandwidth is sought. The bandwidth allocation processing unit allocates bandwidth to the ground terminal in accordance with the priority status identified in the bandwidth request message. Allocated bandwidth is reported to the ground terminal in a bandwidth allocation response.

Abstract: A modem includes a high speed parallel processing transmitter, receiver and decoder. Each of the transmitting and receiving portions of the modem include a plurality of parallel processing channels that process data in a sub-band. Each of the processing channels can operate at a rate which is less than the overall rate at which data is processed. In each channel is a unique word sub-band filter and a data sub-band filter that are selectively enabled to filter data in the channel. The unique word filters in the transmitting portion of the modem are specifically tuned to make the unique word that precedes the data portion of a data burst easy to detect. In the receiving portion of the modem, the unique word sub-band filters are tuned to quickly detect the unique word. Once a unique word has been received, the data sub-band filters in the receiving portion of the modem are enabled in each of the channels to filter the data portion of a burst.

Abstract: A data communication system for a constellation of satellites (13a, 13b, . . . ) that employ Earth-fixed cellular beam management technology is disclosed. The data to be communicated is formed into data packets by a transmitting ground terminal (60). Each data packet includes a header (41) with control information and a payload (43) of data to be communicated. The information contained in the header is used to route the data packets through the satellite constellation to the appropriate intended satellite or to a downlink satellite (104). The header and payload databits are outer forward error correction (FEC) encoded (64, 70), optionally interleaved separately (66, 72), and inner error correction encoded by inner FEC encoders (68, 74). After receipt by an uplink satellite (62), processing of the header is accomplished to recover the header of the original signal.

Abstract: A low-cost, low maintenance earth-based station is disclosed which includes a fixed aperture antenna directed to a fixed location. The system operates with a plurality of non-geosynchronous satellites that will periodically pass through a beam coverage region of the antenna. When one of the satellites comes within range of the earth-based station, the earth-based station detects the presence of the satellite and synchronizes the earth-based station with the satellite. When synchronization is complete, the earth-based station transmits stored data to the satellite. The data to be transmitted is stored within a data storage device that may be present at the earth-based station or remotely located and transmitted to the earth-based station using conventional techniques.

Abstract: A serial concatenated convolutional coding system for a constellation of low-Earth-orbit (LEO) satellites for transmitting input data bits of information is disclosed. The input data bits are systematically outer convolutional encoded (30), producing outer encoded data bits and outer encoded parity bits. Some of the bits of the outer encoded parity bits are remove by a puncturer (32), and the remaining outer encoded parity bits and the outer encoded data bits are bit interleaved (34). The bit interleaved, outer encoded data and remaining parity bits are systematically inner convolutional encoded (36) producing concatenated coded, bit interleaved inner data bits and concatenated coded, bit interleaved inner parity bits. Some of the bits of the concatenated coded, bit interleaved inner parity bits are removed by a puncturer (38), and the remaining concatenated coded, bit interleaved inner parity bits and the concatenated coded, bit interleaved inner data bits are combined (40).

Abstract: A data communication system for a constellation of low-Earth orbit (LEO) satellites (13a, 13b, . . . ) that employ Earth-fixed cellular beam management technology is disclosed. The data to be communicated is formed into data packets by a transmitting ground terminal (41). Each data packet includes a header (41) and a payload (43). The header (41) contains address and other control information and the payload (43) contains the data to be communicated. The header and payload databits are separated (71) and outer forward error correction (FEC) encoded (72, 73) with an outer error correction code. The symbols of the outer encoded header and payload codewords are interleaved, first separately (74, 75) and then together (76). The outer encoded, interleaved header and payload codewords are inner encoded by an inner FEC encoder (77). Upon receipt by an uplink satellite (63), the inner error correction code is removed (87) and the resulting codeword symbols are de-interleaved (88, 89, 90).

Abstract: The Satellite Communication System disclosed in the specification is a dynamic constellation (C) of satellites (S). The present invention is capable of offering continuous voice, data and video service to customers across the globe on the land, on the sea, or in the air. The preferred embodiment of the invention comprises a low Earth orbit satellite system that includes 40 spacecraft (S) traveling in each of 21 orbital planes at an altitude of 700 km (435 miles). This relatively large number of satellites employed by the preferred embodiment was selected to provide continuous coverage of the Earth's surface at a high minimum mask angle (1230a) of forty degrees. Each of the individual 840 spacecraft (S) functions as an independent sovereign switch of equal rank which knows the position of its neighbors, and independently handles traffic without ground control.

Abstract: A system for acquiring the beacon of a satellite and synchronizing data transmission between the satellite and a ground terminal is disclosed. The ground terminal conducts a search for a satellite to be acquired. The search may be based on previously developed information from which the location of the satellite can be predicted and, thus, limited to a small area of the sky, or cover a large area of the sky in accordance with a search routine. After the beacon of a satellite is acquired, the geographic area served by the satellite is determined. If the satellite does not serve the cell within which the ground terminal is located, a further satellite search is conducted, which may be based in part on information contained in the beacon of the acquired satellite. After the satellite serving the cell containing the ground terminal is acquired, a test is made to determine how long the satellite will continue to cover the cell.

Abstract: A method for reducing co-channel or cross-channel interference between cells of a cell network in a frequency division multiple access (FDMA) communications system is disclosed. The method comprises the steps of: dividing the cells of the cell network into a first subset of cells and a second subset of cells; dividing the available bandwidth for the system into a first set of sub-bands, each of which has a sub-band bandwidth and a second set of sub-bands, each of which has a sub-band bandwidth, the second set of sub-bands being offset in frequency from the first set of sub-bands; assigning the first set of sub-bands to the first subset of cells and the second set of sub-bands to the second subset of cells.

Abstract: Methods and apparatus which route, control and manage traffic throughout a Satellite Communication System operating in low Earth orbit are disclosed. Voice, video and data traffic from terrestrial gateways (G) and from portable (P), mobile (M) or fixed (F) terminals are directed up through the constellation of satellites (S) and back down to destinations on Earth. The satellites provide continuous worldwide communication services while insuring uniform end-to-end transmission delays. The satellite network is highly adaptive to the constantly changing network topology, and will offer a synchronous circuit switched communication service that provides sequential delivery of user data, regardless of the type of the data transmitted. The network employs datagram switching, as opposed to conventional virtual circuit switching techniques.

Abstract: A technique for sharing radio frequency spectrum between multiple satellite communication systems. A first and a second satellite communication system each contain a plurality of satellites in a plurality of non-geostationary (non-GSO) Earth orbits. Each of the plurality of non-GSOs has a predefined orbital plane. Within each orbital plane, satellites of the first and second satellite communication systems are alternating, such that each orbital plane contains satellites from each of the satellite systems. In this manner, it is possible to achieve satisfactory discrimination between satellites and Earth-based stations. The Earth-based station of each communication system will communicate with the closest satellite of its respective communication system.

Abstract: A technique for sharing radio frequency spectrum in a multiple communication satellite system with a plurality of satellites in each of a plurality of non-geostationary (non-GSO) Earth orbits. A first satellite communication system uses a plurality of predefined non-GSO Earth orbits and a second satellite communication system uses a plurality of predefined orbits that are interleaved with the orbital planes of the first satellite communication system. In this manner, it is possible to achieve satisfactory discrimination between satellites and Earth-based stations. With near polar orbits, the topocentric separation between satellites decreases as the latitude of the Earth-based stations increases due to the convergence of orbital planes near the poles. To compensate for the decreased topocentric separation, the system utilizes one or more mitigation techniques to select one of a plurality of possible satellites to communicate with the Earth-based station in order to effectively increase topocentric separation.

Abstract: A system for acquiring the beacon of a satellite and synchronizing data transmission between the satellite and a ground terminal is disclosed. The ground terminal conducts a search for a satellite to be acquired. The search may be based on previously developed information from which the location of the satellite can be predicted and, thus, limited to a small area of the sky, or cover a large area of the sky in accordance with a search routine. After the beacon of a satellite is acquired, the geographic area served by the satellite is determined. If the satellite does not serve the cell within which the ground terminal is located, a further satellite search is conducted, which may be based in part on information contained in the beacon of the acquired satellite. After the satellite serving the cell containing the ground terminal is acquired, a test is made to determine how long the satellite will continue to cover the cell.

Abstract: An antenna having multiple antenna elements that are selectively activated performs an initial acquisition of a satellite signal by activating only a few of the antenna elements. This results in a broad beam width and increases the likelihood of detecting the signal from the satellite. When the satellite signal is initially detected, the system increases the number of active elements to narrow the beam width. The system incrementally increases the number of active antenna elements until the detected signal from the satellite exceeds a predetermined threshold. At that point, the location of the satellite may be precisely determined and all antenna elements activated to lock onto the satellite signal. If the antenna loses acquisition of the satellite signal, the reverse process may be implemented whereby some elements are selectively deactivated to broaden the beam width of the antenna in an effort to reacquire the satellite signal.

Abstract: The present invention overcomes the limitations encountered by conventional packet switching using virtual circuits. The present invention utilizes a "datagram" approach that routes every packet (22) conveyed by the system independently at every node in the network. The packets (22) are directed along an optimized pathway through the network by a fast packet switch (38) that directs traffic based on instructions from an adaptive routing processor (12A) that continuously runs an adaptive routing software (12B). This adaptive routing processor (14) supplies an output (12C) to a routing cache memory (20) which stores fast packet switch routing port output tags (30). An input packet processor (28) extracts a supercell address from the header (24) of each packet (22) and uses the supercell address (21A) as an index to retrieve a fast packet switch output port tag (30) stored in the routing cache memory (20).