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 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: 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 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: A symbol lock detector for an incoming coherent digital communication signal which utilizes a subcarrier modulated with binary symbol data, d.sub.k, and known symbol interval T by integrating binary values of the signal over nonoverlapping first and second intervals selected to be T/2, delaying the first integral an interval T/2, and either summing or multiplying the second integral with the first one that preceded it to form a value X.sub.k. That value is then averaged over a number M of symbol intervals to produce a static value Y. A symbol lock decision can then be made when the static value Y exceeds a threshold level .delta..