Location Estimation of Wireless Terminals Based on Combinations of Signal-Strength Measurements and Geometry-of-Arrival Measurements
A method and apparatus for estimating the location of a wireless terminal are disclosed. The location of the wireless terminal is estimated based on one or more signal strength measurements in conjunction with: (i) one or more angle-of-arrival measurements, (ii) one or more time-of-arrival measurements, or (iii) a combination of (i) and (ii). At each measurement time, the illustrative embodiment (a) determines the candidate locations for the wireless terminal, (b) computes a measurement likelihood function for any signal strength measurements that are available at that time, (c) computes a measurement likelihood function for any geometry-of-arrival measurements that are available at that time, (d) computes a joint likelihood function for all measurements available at that time, and (e) updates the location probability distribution for the wireless terminal with the joint measurement likelihood function. Estimates of the location of the wireless terminal are obtained from the location probability distribution.
1 . A method comprising:
receiving
(i) a first signal measurement for a first signal as received by a wireless terminal, and
(ii) a second signal measurement for a second signal as transmitted by said wireless terminal;
generating a first multi-dimensional probability distribution for the location of said wireless terminal based on said first signal measurement;
generating a second multi-dimensional probability distribution for the location of said wireless terminal based on a comparison of said second signal measurement to a predicted value of said second signal measurement; and
estimating the location of said wireless terminal based on
(i) said first multi-dimensional probability distribution, and
(ii) said second multi-dimensional probability distribution.
2 . The method of claim 1 wherein said first signal measurement and said second signal measurement are made at substantially the same time.
3 . The method of claim 1 wherein said first signal measurement is a signal strength measurement.
4 . The method of claim 1 wherein said second signal measurement is an angle-of-arrival measurement.
5 . The method of claim 1 wherein said second signal measurement is a time-of-arrival measurement.
6 . The method of claim 1 wherein said second signal measurement is a time-difference of arrival measurement.
7 . The method of claim 1 wherein estimating the location of said wireless terminal comprises:
pruning a first list of candidate locations for said wireless terminal to a second list of candidate locations of said wireless terminal based on said first signal measurement; and
choosing an estimated location for said wireless terminal based on said second list of locations and said second signal measurement.
8 . The method of claim 1 wherein estimating the location of said wireless terminal comprises:
pruning a first list of candidate locations for said wireless terminal to a second list of candidate locations of said wireless terminal based on said second signal measurement; and
choosing an estimated location for said wireless terminal based on said second list of locations and said first signal measurement.
9 . The method of claim 1 wherein said first probability distribution and said second probability distribution are defined for a surface.
10 . The method of claim 1 wherein a unique location for said wireless terminal is mathematically indeterminate from only said first signal measurement.
11 . The method of claim 1 wherein a unique location for said wireless terminal is mathematically indeterminate from only said second signal measurement.
12 . A method comprising:
(a) receiving
(i) a first signal strength measurement for a first signal as received by a wireless terminal at a first time,
(ii) a second signal strength measurement for said first signal as received by said wireless terminal at a second time, wherein said first time is different than said second time, and
(iii) a time-of-arrival measurement for a second signal as received by said wireless terminal; and
(b) estimating the location of said wireless terminal at said first time based on
(i) said first signal strength measurement for said first signal,
(ii) said second signal strength measurement for said first signal,
(iii) said time-of-arrival measurement for said second signal.
13 . The method of claim 12 wherein (a) receiving further comprises (iv) a second time-of-arrival measurement for a third signal as received by said wireless terminal; and
wherein estimating the location of said wireless terminal is also based on (iv) said second time-of-arrival measurement for said third signal.
14 . The method of claim 12 wherein (a) receiving further comprises (iv) an angle-of-arrival measurement for a third signal as transmitted by said wireless terminal; and
wherein estimating the location of said wireless terminal is also based on (iv) said angle-of-arrival measurement for said third signal.
15 . The method of claim 12 wherein said first signal strength measurement and said time-of-arrival measurement are made at substantially the same time.
16 . The method of claim 12 wherein said first signal and said second signal are transmitted from different locations.
17 . The method of claim 12 wherein said second signal is transmitted by an Earth satellite.
18 . The method of claim 12 wherein a unique location for said wireless terminal is mathematically indeterminate from only said first signal strength measurement.
19 . The method of claim 18 wherein a unique location for said wireless terminal is also mathematically indeterminate from said first signal strength measurement and said second signal strength measurement.
20 . The method of claim 12 wherein a unique location for said wireless terminal is mathematically indeterminate from only said time-of-arrival measurement.
21 . A method comprising:
receiving
(i) a signal strength measurement for a first signal as received by a wireless terminal,
(ii) a first time-of-arrival measurement for a second signal as received by said wireless terminal, wherein said second signal is transmitted by a first Earth satellite, and
(iii) a second time-of-arrival measurement for a third signal as received by said wireless terminal, wherein said third signal is transmitted by a second Earth satellite,
matching said signal strength measurement against a database that associates locations with signal measurements to generate a first multi-dimensional probability distribution for the location of said wireless terminal;
generating a second probability distribution for the location of said wireless terminal based on said first time-of-arrival measurement and said second time-of-arrival measurement; and
estimating the location of said wireless terminal based on:
(i) said first multi-dimensional probability distribution, and
(ii) said second multi-dimensional probability distribution.
22 . The method of claim 21 wherein generating said second probability distribution comprises generating a time-difference-of-arrival measurement from said first time-of-arrival measurement and said second time-of-arrival measurement.
23 . The method of claim 21 further comprising receiving an indication that a fourth signal that is transmitted by a first base station is not received by said wireless terminal; and
wherein estimating the location of said wireless terminal is also based on the fact that said fourth signal is not received by said wireless terminal.
24 . The method of claim 21 wherein said signal strength measurement, said first time-of-arrival measurement, and said second time-of-arrival measurement are made at substantially the same time.
25 . The method of claim 21 wherein estimating the location of said wireless terminal comprises:
pruning a first list of candidate locations of said wireless terminal to a second list of candidate locations of said wireless terminal based on said first time-of-arrival measurement and said second time-of-arrival measurement; and
choosing an estimated location of said wireless terminal based on said second list of locations and said signal strength measurement.
26 . The method of claim 21 wherein estimating the location of said wireless terminal comprises:
pruning a first list of candidate locations of said wireless terminal to a second list of candidate locations of said wireless terminal based on said signal strength measurement; and
choosing an estimated location of said wireless terminal based on said second list of locations, said first time-of-arrival measurement, and said second time-of-arrival measurement.
27 . The method of claim 26 wherein said first probability distribution and said second probability distribution are defined for a surface.
28 . The method of claim 21 wherein a unique location for said wireless terminal is mathematically indeterminate from only said signal strength measurement.
29 . The method of claim 28 wherein a unique location for said wireless terminal is also mathematically indeterminate from said signal strength measurement in combination with any other signal strength measurements received by said wireless terminal.
30 . The method of claim 21 wherein a unique location for said wireless terminal is mathematically indeterminate from only said first time-of-arrival measurement and said second time-of-arrival measurement.
31 . The method of claim 30 wherein a unique location for said wireless terminal is also mathematically indeterminate from said first time-of-arrival measurement and said second time-of-arrival measurement in combination with any other time-of-arrival measurements received by said wireless terminal.