Multipath tolerant location system and method therefor
First Claim
1. A multipath tolerant method for determining a location of a locatable unit comprising steps of:
- a) determining a maximum propagation duration, said maximum propagation duration being determined in response to a distance between first and second known-position locators;
b) determining a time difference, said time difference being approximately equal to a difference between a propagation duration for at least one location signal traveling between said locatable unit and said first known-position locator and a propagation duration for said at least one location signal traveling between said locatable unit and said second known-position locator;
c) verifying that said time difference is less than or equal to said maximum propagation duration; and
d) calculating a current location for said locatable unit in response to said step c), wherein said step d) is responsive to said at least one location signal when said time difference is less than or equal to said maximum propagation duration; and
said step d) is substantially unresponsive to said at least one location signal when said time difference is greater than said maximum propagation duration.
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Abstract
A multilateration location system (12) includes a locatable unit (16) and any number of known-position locators (14). A time of arrival detector (22) determines instants in time when a location signal (20) transmitted by the locatable unit (16) arrives at various known-position locators (14). For each combination of two known-position locators (14) that receive the location signal (20), a pre-estimation process (32) determines whether the difference in arrival times is less than or equal to a maximum propagation duration for the locator pair. The maximum propagation duration is based upon the distance between the locators (14) in the locator pair. If the difference is greater than the maximum propagation duration, the difference is omitted from the data set processed by a multilateration calculation process (34). A post estimation filtering process (36) screens out location estimates that are too distant from a predicted position.
88 Citations
23 Claims
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1. A multipath tolerant method for determining a location of a locatable unit comprising steps of:
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a) determining a maximum propagation duration, said maximum propagation duration being determined in response to a distance between first and second known-position locators; b) determining a time difference, said time difference being approximately equal to a difference between a propagation duration for at least one location signal traveling between said locatable unit and said first known-position locator and a propagation duration for said at least one location signal traveling between said locatable unit and said second known-position locator; c) verifying that said time difference is less than or equal to said maximum propagation duration; and d) calculating a current location for said locatable unit in response to said step c), wherein said step d) is responsive to said at least one location signal when said time difference is less than or equal to said maximum propagation duration; and
said step d) is substantially unresponsive to said at least one location signal when said time difference is greater than said maximum propagation duration. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A multipath tolerant multilateration method for determining a location of a locatable unit comprising the steps of:
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a) arranging a set of at least three known-position locators within a monitored area; b) communicating at least one location signal which propagates between each known-position locator in said set and a locatable unit located in said monitored area; c) for each combination of two known-position locaters in said set, determining a maximum propagation duration, said maximum propagation duration being determined in response to the distance between the two known-position locaters, wherein said step of determining determines said maximum propagation duration for each combination of two known-position locaters in said set to be in a range of 50% to 150% of the time required for an electromagnetic signal to propagate between the two known-position locaters; d) for each combination of two known-position locaters in said set, determining a time of arrival difference, said time of arrival difference being a duration approximately equal to the difference between propagation durations for said at least one location signal traveling between said locatable unit and each of the two known-position locators; e) for each combination of two known-position locaters in said set, comparing said maximum propagation duration determined in said step c) with said time of arrival difference determined in said step d); and f) calculating a current location for said locatable unit in response to said step - View Dependent Claims (15, 16, 17, 18)
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19. A location determination system that tolerates multipath transmissions of location signals, said system comprising:
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a locatable unit positioned in a monitored area; first and second known-position locators arranged to transmit at least one location signal to or receive said at least one location signal from said monitored area; means for identifying a maximum propagation duration, said maximum propagation duration being determined in response to a distance between said first and second known-position locators; means for forming a time difference, said timed difference being approximately equal to the difference between a first duration during which said at least one location signal propagates between said locatable unit and said first known-position locator and a second duration during which said at least one location signal propagates between said locatable unit and said second known-position locator; means, coupled to said identifying means and to said forming means, for verifying that said time difference is less than or equal to said maximum propagation duration; and means, coupled to said verifying means, for calculating a current location for said locatable unit, wherein said calculating means is configured to be responsive to said at least one location signal when said time difference is less than or equal to said maximum propagation duration and said calculating means is configured to be substantially unresponsive to said at least one location signal when said time difference is greater than said maximum propagation duration. - View Dependent Claims (20, 21, 22, 23)
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Specification