Anonymous tracking using a set of wireless devices
First Claim
1. A method for estimating the cardinality of a set of one or more tags in a system that comprises the set of one or more tags and one or more readers, wherein:
- the one or more readers are adapted to transmit a command requesting that each tag that receives the command determine whether to transmit a reply;
each receiving tag is adapted to determine whether to transmit a reply based on a specified probability level; and
each receiving tag that determines to transmit a reply (i) selects a timeslot of a frame in which to transmit the reply based on (1) a specified total number of timeslots in the frame and (2) a specified random-number seed and (ii) transmits the reply in the selected timeslot;
the method comprising;
(a) during each of a plurality of time intervals;
(a1) transmitting a command requesting that each tag that receives the command determine whether to transmit a reply; and
(a2) receiving, in one or more timeslots of a frame corresponding to the time interval, replies from one or more tags; and
(b) providing an estimate of the cardinality of the set of one or more tags in the system based on (i) timeslots in each of the plurality of time intervals that are zero timeslots, wherein a zero timeslot is a timeslot having no received reply, and (ii) the total number of timeslots in each frame'"'"',wherein the estimate t0 of the cardinality of the set of one or more tags in the system in step (b) is calculated using at least;
(i) the total number f of timeslots in each frame, (ii) the probability p that a tag will reply in a timeslot, (iii) a load factor ρ
0 defined as a ratio of a number of tags to frame size, and (iv) the number zi of zero timeslots for time interval i,wherein the estimate t0 of the cardinality of the set of one or more tags in the system in step (b) is derived using the equations
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Accused Products
Abstract
In one embodiment, a method for estimating the number of tags in a set of tags in a system of tags and readers. The method includes, during each of a plurality of time intervals: (i) transmitting a command requesting that each tag that receives the command determine whether to transmit a reply; and (ii) receiving, in one or more timeslots of a frame corresponding to the time interval, replies from one or more tags. The method further includes providing an estimate of the number of tags in the set of one or more tags based on (i) timeslots in each of the plurality of time intervals that are zero timeslots, i.e., timeslots having no received reply, and (ii) the total number of timeslots in each frame.
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Citations
15 Claims
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1. A method for estimating the cardinality of a set of one or more tags in a system that comprises the set of one or more tags and one or more readers, wherein:
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the one or more readers are adapted to transmit a command requesting that each tag that receives the command determine whether to transmit a reply; each receiving tag is adapted to determine whether to transmit a reply based on a specified probability level; and each receiving tag that determines to transmit a reply (i) selects a timeslot of a frame in which to transmit the reply based on (1) a specified total number of timeslots in the frame and (2) a specified random-number seed and (ii) transmits the reply in the selected timeslot; the method comprising; (a) during each of a plurality of time intervals; (a1) transmitting a command requesting that each tag that receives the command determine whether to transmit a reply; and (a2) receiving, in one or more timeslots of a frame corresponding to the time interval, replies from one or more tags; and (b) providing an estimate of the cardinality of the set of one or more tags in the system based on (i) timeslots in each of the plurality of time intervals that are zero timeslots, wherein a zero timeslot is a timeslot having no received reply, and (ii) the total number of timeslots in each frame'"'"', wherein the estimate t0 of the cardinality of the set of one or more tags in the system in step (b) is calculated using at least;
(i) the total number f of timeslots in each frame, (ii) the probability p that a tag will reply in a timeslot, (iii) a load factor ρ
0 defined as a ratio of a number of tags to frame size, and (iv) the number zi of zero timeslots for time interval i,wherein the estimate t0 of the cardinality of the set of one or more tags in the system in step (b) is derived using the equations - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A system for estimating the cardinality of a set of one or more tags in a system that comprises the set of one or more tags and one or more readers, wherein:
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the one or more readers are adapted to issue a command requesting that the tags issue a reply to identify themselves, the command including (i) timing information defining a total number of timeslots for the reply, (ii) a probability that a tag will reply in a given timeslot, and (iii) a random-number seed; and in response to the command, one or more of the tags is adapted to (i) select a timeslot in which to reply to the command and (ii) issue the reply in the selected timeslot; the system adapted to; (a) during each of a plurality of time intervals; (a1) issue a command; (a2) receive, in one or more timeslots, replies from the one or more tags; and (a3) determine the number of zero timeslots corresponding to the time interval, wherein a zero timeslot is a timeslot identified as having no tags transmitting therein during the time interval in reply to the command; and (b) provide an estimate of the cardinality of the set of one or more tags in the system based on (i) a sum of the number of zero timeslots across the plurality of time intervals and (ii) the total number of timeslots, wherein the estimate t0 of the cardinality of the set of one or more tags in the system in step (b) is calculated using at least;
(i) the total number f of timeslots in each frame, (ii) the probability p that a tag will reply in a timeslot, (iii) a load factor ρ
0 defined as a ratio of a number of tags to frame size, and (iv) the number zi of zero timeslots for time interval i,wherein the estimate t0 of the cardinality of the set of one or more tags in the system in step (b) is derived using the equations
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13. A non-transitory machine-readable medium, having encoded thereon program code, wherein, when the program code is executed by a machine, the machine implements a method for estimating the cardinality of a set of one or more tags in a system that comprises the set of one or more tags and one or more readers, wherein:
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the one or more readers are adapted to issue a command requesting that the tags issue a reply to identify themselves, the command including (i) timing information defining a total number of timeslots for the reply, (ii) a probability that a tag will reply in a given timeslot, and (iii) a random-number seed; and in response to the command, one or more of the tags is adapted to (i) select a timeslot in which to reply to the command and (ii) issue the reply in the selected timeslot; the method comprising; (a) during each of a plurality of time intervals; (a1) issuing a command; (a2) receiving, in one or more timeslots, replies from the one or more tags; and (a3) determining the number of zero timeslots corresponding to the time interval, wherein a zero timeslot is a timeslot identified as having no tags transmitting therein during the time interval in reply to the command; and (b) providing an estimate of the cardinality of the set of one or more tags in the system based on (i) a sum of the number of zero timeslots across the plurality of time intervals and (ii) the total number of timeslots, wherein the estimate t0 of the cardinality of the set of one or more tags in the system in step (b) is calculated using at least;
(i) the total number f of timeslots in each frame, (ii) the probability p that a tag will reply in a timeslot, (iii) a load factor ρ
0 defined as a ratio of a number of tags to frame size, and (iv) the number zi of zero timeslots for time interval i,wherein the estimate t0 of the cardinality of the set of one or more tags in the system in step (b) is derived using the equations
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14. A method for estimating the cardinality of a set of one or more tags in a system that comprises the set of one or more tags and one or more readers, wherein:
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the one or more readers are adapted to transmit a command requesting that each tag that receives the command determine whether to transmit a reply; each receiving tag is adapted to determine whether to transmit a reply based on a specified probability level; and each receiving tag that determines to transmit a reply (i) selects a timeslot of a frame in which to transmit the reply based on (1) a specified total number of timeslots in the frame and (2) a specified random-number seed and (ii) transmits the reply in the selected timeslot; the method comprising; (a) during each of a plurality of time intervals; (a1) transmitting a command requesting that each tag that receives the command determine whether to transmit a reply; and (a2) receiving, in one or more timeslots of a frame corresponding to the time interval, replies from one or more tags; and (b) providing an estimate of the cardinality of the set of one or more tags in the system based on (i) timeslots in each of the plurality of time intervals that are zero timeslots, wherein a zero timeslot is a timeslot having no received reply, and (ii) the total number of timeslots in each frame, wherein; the estimate t0 of the cardinality of the set of one or more tags in the system in step (b) is calculated using at least;
(i) the total number f of timeslots in each frame, (ii) the probability p that a tag will reply in a timeslot, (iii) a load factor ρ
0 defined as a ratio of a number of tags to frame size, and (iv) the number zi of zero timeslots for time interval i; andan optimal number n of time intervals in the plurality of time intervals is selected using the equation
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15. A method for estimating the cardinality of a set of one or more tags in a system that comprises the set of one or more tags and one or more readers, wherein:
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the one or more readers are adapted to transmit a command requesting that each tag that receives the command determine whether to transmit a reply; each receiving tag is adapted to determine whether to transmit a reply based on a specified probability level; and each receiving tag that determines to transmit a reply (i) selects a timeslot of a frame in which to transmit the reply based on (1) a specified total number of timeslots in the frame and (2) a specified random-number seed and (ii) transmits the reply in the selected timeslot; the method comprising; (a) during each of a plurality of time intervals; (a1) transmitting a command requesting that each tag that receives the command determine whether to transmit a reply; and (a2) receiving;
in one or more timeslots of a frame corresponding to the time interval, replies from one or more tags; and(b) providing an estimate of the cardinality of the set of one or more tags in the system based on (i) timeslots in each of the plurality of time intervals that are zero timeslots, wherein a zero timeslot is a timeslot having no received reply, and (ii) the total number of timeslots in each frame, wherein; the estimate t0 of the cardinality of the set of one or more tags in the system in step (b) is calculated using at least;
(i) the total number f of timeslots in each frame, (ii) the probability p that a tag will reply in a timeslot, (iii) a load factor ρ
0 defined as a ratio of a number of tags to frame size, and (iv) the number zi of zero timeslots for time interval i; andan optimal number of timeslots f is selected using the equations
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Specification