Method for tracking location of a mobile unit
Location of a mobile unit is determined by a combined probability, derived from a first probability for possible locations based on a current sample of radio signal characteristics and a second probability that a unit has moved from a prior location or probable location to each possible location.
1. A system for locating within an area a mobile unit arranged for a wireless radio communications with fixed devices, wherein location is determined by comparing radio signal characteristics between the mobile unit and the fixed devices to a database relating the radio signal characteristics to location within the area, wherein at least one portion of the area includes a barrier, comprising;
means for assigning the at least one portion including the barrier with a probability of zero;
means for taking sequential samples of the radio signal characteristics;
for each sample of the radio signal characteristics, means for determining two or more possible initial locations for the mobile unit and assigning a location probability that the mobile unit is at each of the possible locations, each location probability modified to account for the barrier;
for each possible location determined using a sample after an initial sample, means for determining a movement probability that the mobile unit has moved from each possible location for one or more prior samples to the possible location, the movement probability being derived from proximity of the possible location for the one or more prior samples and the possible locations for the current sample, wherein the movement probability is modified by factors including at least the probability of zero for the at least one portion including the barrier of the mobile unit between the possible location for the one or more prior samples and the possible location for a current sample; and
means for selecting a location for the mobile unit as the most probable location for the current sample based on a combination of the location and movement probabilities.
2. The system as specified in claim 1 wherein the location probability is assigned according to a comparison of the sampled radio signal to radio signal characteristics for the location in the database.
3. The system as specified in claim 1 wherein the database includes data characterizing quality of radio signal characteristics for locations within the area and wherein the location probability is assigned according to the quality characterizing data.
4. The system as specified in claim 1 wherein the movement probability is determined by comparing distance between the locations to expected distance for movement of the mobile unit in a time period between the samples.
5. A system for locating within an area a mobile unit arranged for a wireless radio communications with fixed devices, wherein location is determined by comparing radio signal characteristics between the mobile unit and the fixed devices to a database relating the radio signal characteristics to location within the area, wherein at least one portion the area includes a barrier, comprising;
means for assigning the at least one portion including the barrier with a probability of zero;
means for taking sequential samples of the radio signal characteristics;
for each sample of the radio signal characteristics, means for determining two or more possible initial locations for the mobile unit and assigning a location probability that the mobile unit is at each of the possible locations, each location probability modified to account for the barrier;
for each possible location determined using a sample after an initial sample, means for determining a movement probability that the mobile unit has moved from a selected location determined for one or more prior samples to the possible location, the movement probability being derived from proximity of the possible location for the one or more prior samples and the possible locations for the current sample, wherein the movement probability is modified by factors including at least the probability of zero for the at least one portion including the barrier of the mobile unit between the possible location for the one or more prior samples and the possible location for a current sample; and
means for selecting a location for the mobile unit as the most probable location for the current sample based on a combination of the location and movement probabilities.
6. The system as specified in claim 5 wherein the location probability is assigned according to a comparison of the sampled radio signal to radio signal characteristics for the location in the database.
7. The system as specified in claim 5 wherein the database includes data characterizing quality of radio signal characteristics for locations within the area and wherein the location probability is assigned according to the quality characterizing data.
8. The system as specified in claim 5 wherein the movement probability is determined by comparing distance between the locations to expected distance for movement of the mobile unit in a time period between the samples.
9. A system, comprising:
means for receiving a first sample signal from a mobile unit, the first sample signal including first signal characteristics;
means for comparing the first signal characteristics to a database, the database including characterizing data of a plurality of locations, wherein at least one portion of the locations includes a barrier;
means for assigning the at least one portion including the barrier with a probability of zero;
means for assigning a first set of initial locations of the mobile unit and determining first location probabilities for each initial location of the first set based on the comparison of the first signal characteristics to the database, the first location probabilities being modified to account for the barrier;
means for receiving a further sample signal from the mobile unit, the further sample including further signal characteristics;
means for comparing the further signal characteristics to the database characterizing the plurality of locations;
means for assigning a further set of locations of the mobile unit and determining further location probabilities for each location of the further set based on the comparison of the further signal characteristics to the database, the further location probabilities modified to account for the barrier;
means for determining movement probabilities for each location of the first and the further sets, the movement probabilities being based on a proximity between each of the locations within the first and further sets and the ability of the mobile unit to move between the locations, the movement probabilities being modified to account for the barrier for the mobile unit between locations; and
means for combining the first and further location probabilities with the movement probabilities for each of the locations and selecting a location having the highest combined location and movement probabilities as the location of the mobile unit.
10. The system as specified in claim 9 wherein the database includes data characterizing a quality of radio signal characteristics for locations and wherein the location probability is assigned according to the quality characterizing data.
11. The system as specified in claim 9 wherein the movement probability is determined by comparing a distance between the plurality of locations to an expected distance for movement of the mobile unit in a time period between the first and the further samples.
12. A system for locating a mobile unit, comprising:
a computer; and
a database, in communication with the computer, relating radio signal characteristics for signals between the mobile unit and a plurality of access points to a plurality of locations of an area in which the mobile unit operates, the computer being programmed to perform the following:
assigning at least one portion of the area that includes a barrier with a probability of zero;
taking sequential samples of the radio signal characteristics;
for each sample of the radio signal characteristics, determining two or more possible initial locations for the mobile unit and assigning a location probability that the mobile unit is at each of the possible locations, each location probability modified to account for the barrier;
for each possible location determined using a sample after an initial sample, determining a movement probability that the mobile unit has moved from each possible location for one or more prior samples to the possible location, the movement probability being derived from proximity of the possible location for the one or more prior samples and the possible locations for the current sample, wherein the movement probability is modified by factors including at least the probability of zero for the at least one portion including the barrier of the mobile unit between the possible location for the one or more prior samples and the possible location for a current sample; and
selecting a location for the mobile unit as the most probable location for the current sample based on a combination of the location and movement probabilities.
13. The system as specified in claim 12 wherein the location probability is assigned according to a comparison of the sampled radio signal to radio signal characteristics for the location in the database.
14. The system as specified in claim 12 wherein the database includes data characterizing quality of radio signal characteristics for locations within the area and wherein the location probability is assigned according to the quality characterizing data.
15. The system as specified in claim 12 wherein the movement probability is determined by comparing distance between the locations to expected distance for movement of the mobile unit in a time period between the samples.
16. A system for locating a mobile unit, comprising:
a computer; and
a database, in communication with the computer, relating radio signal characteristics for signals between the mobile unit and a plurality of access points to a plurality of locations of an area in which the mobile unit operates, the computer being programmed to perform the following:
assigning at least one portion of the area that includes a barrier with a probability of zero;
taking sequential samples of the radio signal characteristics;
for each sample of the radio signal characteristics, determining two or more possible initial locations for the mobile unit and assigning a location probability that the mobile unit is at each of the possible locations, each location probability modified to account for the barrier;
for each possible location determined using a sample after an initial sample, determining a movement probability that the mobile unit has moved from a selected location determined for one or more prior samples to the possible location, the movement probability being derived from proximity of the possible location for the one or more prior samples and the possible locations for the current sample, wherein the movement probability is modified by factors including at least the probability of zero for the at least one portion including the barrier of the mobile unit between the possible location for the one or more prior samples and the possible location for a current sample; and
selecting a location for the mobile unit as the most probable location for the current sample based on a combination of the location and movement probabilities.
17. The system as specified in claim 16 wherein the location probability is assigned according to a comparison of the sampled radio signal to radio signal characteristics for the location in the database.
18. The system as specified in claim 16 wherein the database includes data characterizing quality of radio signal characteristics for locations within the area and wherein the location probability is assigned according to the quality characterizing data.
19. The system as specified in claim 16 wherein the movement probability is determined by comparing distance between the locations to expected distance for movement of the mobile unit in a time period between the samples.