Location method for a elective call receiver operating in a satellite communication system
First Claim
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1. In a communication system in which orbiting satellites illuminate portions of the earth with beams of RF energy, each beam being activated during an assigned frame and transmitting information identifying its frame number and a reference delivery area, a method for a selective call receiver to estimate its home position, comprising:
- a) receiving and storing information received from multiple beams, including information identifying each beam'"'"'s frame number and reference delivery area wherein the step of receiving is turned off after receiving data of interest included in a received frame and then turned on again at a turn-on time preceding the expected receipt of a next frame, and wherein the time of arrival of a given beam is measured by measuring a time difference between the turn-on time and receipt of the given beam;
b) determining a home region in which the selective call receiver is likely located, based at least in part on the information stored in step a);
c) determining a travel time to the selective call receiver of at least one beam from each of multiple satellites and measuring the times of arrival at the selective call receiver of beams received from at least one pair of satellites (beam pairs) and, for each beam pair, calculating a real DTOA (Differential Time of Arrival) that corresponds to a difference between measured times of arrival of beams in the beam pair; and
d) selecting, from within the home region, an estimated home position that is consistent with the travel times determined in step c).
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Accused Products
Abstract
A selective call receiver (24) that receives signals transmitted by orbiting satellites (A, B) uses certain information transmitted by the satellites to calculate an estimate of its position. Using that estimate and other information, the selective call receiver (24) is able to save power by disregarding certain information contained in transmitted signals that are not intended for it.
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Citations
16 Claims
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1. In a communication system in which orbiting satellites illuminate portions of the earth with beams of RF energy, each beam being activated during an assigned frame and transmitting information identifying its frame number and a reference delivery area, a method for a selective call receiver to estimate its home position, comprising:
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a) receiving and storing information received from multiple beams, including information identifying each beam'"'"'s frame number and reference delivery area wherein the step of receiving is turned off after receiving data of interest included in a received frame and then turned on again at a turn-on time preceding the expected receipt of a next frame, and wherein the time of arrival of a given beam is measured by measuring a time difference between the turn-on time and receipt of the given beam; b) determining a home region in which the selective call receiver is likely located, based at least in part on the information stored in step a); c) determining a travel time to the selective call receiver of at least one beam from each of multiple satellites and measuring the times of arrival at the selective call receiver of beams received from at least one pair of satellites (beam pairs) and, for each beam pair, calculating a real DTOA (Differential Time of Arrival) that corresponds to a difference between measured times of arrival of beams in the beam pair; and d) selecting, from within the home region, an estimated home position that is consistent with the travel times determined in step c). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. In a satellite communication system in which a region has been identified as a probable location of a particular selective call receiver, and wherein the region contains rows of areas which could each contain the selective call receiver, a method of choosing one area as the selective call receiver'"'"'s most likely location, comprising:
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for each of multiple rows in the region; a) selecting an area, and calculating for the selected area a metric value that is indicative of the likelihood that the selective call receiver is located in the selected area; b) repeating step a) with other areas in the same row until a predetermined number of areas exhibit metric values that indicate a decreasing likelihood that the selective call receiver is located in the predetermined number of areas, and then terminating the calculation of metric values for other areas in the same row; and c) choosing, as the selective call receiver'"'"'s most likely position in the region, the area whose metric value is most indicative of the selective call receiver being located therein.
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13. In a communication system in which orbiting satellites illuminate logical delivery areas (LDA'"'"'s) on the earth with beams of RF energy, each beam being activated during an assigned frame and transmitting information identifying its frame number and a reference delivery area, a method for a selective call receiver to estimate its home position, comprising:
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a) receiving and storing information received from multiple beams, including information identifying each beam'"'"'s frame number and reference delivery area; b) calculating a preliminary home region in which the selective call receiver is likely located, based at least in part on the information stored in step a); c) comparing the preliminary home region to a previously determined home region that is stored in the selective call receiver, thereby to determine whether an overlap area exists between the previously determined home region and the preliminary home region, and using the overlap area, if any, as a home region; d) measuring times of arrival at the selective call receiver of pairs of beams (beam pairs) received from a corresponding pair of satellites and, for each beam pair, calculating a real differential time of arrival that corresponds to a difference between measured times of arrival of beams in the beam pair; e) for each beam pair measured in step d);
calculating a theoretical differential time of arrival at each LDA within the home region, and calculating a difference between the theoretical differential time of arrival and the real differential time of arrival; andf) selecting from within the home region, as an estimated home LDA, an LDA at which differences between the theoretical and the real differential times of arrival are minimal. - View Dependent Claims (14, 15)
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16. In a communication system in which orbiting satellites illuminate logical delivery areas (LDA'"'"'s) on the earth with beams of RF energy, each beam being activated during an assigned frame and transmitting information identifying its frame number and a reference delivery area, a method for a selective call receiver to estimate its home position, comprising:
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a) receiving and storing information received from multiple beams; b) calculating a preliminary home region in which the selective call receiver is likely located, including measuring a signal strength for each received beam, calculating a beam center location for a received beam that has the greatest signal strength, and wherein the preliminary home region is selected such that it contains the beam center location; c) comparing the preliminary home region to a previously determined home region that is stored in the selective call receiver, thereby to determine whether an overlap area exists between the previously determined home region and the preliminary home region; d) if no overlap area exists between the previously determined home region and the preliminary home region, the preliminary home region is used as a home region, and, if an overlap area does exist, the overlap area is used as a home region; e) measuring times of arrival at the selective call receiver of pairs of beams (beam pairs) received from a corresponding pair of satellites and, for each beam pair, calculating a real differential time of arrival that corresponds to a difference between measured times of arrival of beams in the beam pair; f) for each beam pair measured in step d);
calculating a theoretical differential time of arrival at each LDA within the home region, and calculating a difference between the theoretical differential time of arrival and the real differential time of arrival; andg) selecting from within the home region, as an estimated home position, an LDA at which differences between the theoretical and the real differential times of arrival are minimal.
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Specification