Mobile-based positioning using measurements of received signal power and timing
A hybrid method of estimating position of a mobile device which utilizes both received signal power and timing measurements. Received signal power of signals received by the mobile device from a plurality of cells are measured and corresponding received signal power measurements are stored. The method further includes measuring, at the mobile device, times of arrival of signals received from the plurality of cells. A plurality of time difference of arrival (TDOA) measurements are determined from the times of arrival. A power-time hybrid Gaussian maximum likelihood estimator and positioning assistance data for the plurality of cells are used to generate a maximum likelihood estimate of the position of the mobile device by evaluating a joint conditional probability of the received signal power measurements and the plurality of TDOA measurements. Gaussian random variables may be used to represent the received signal power measurements and the TDOA measurements.
1. A method of estimating a position of a mobile device, the method comprising:
measuring, at the mobile device, received signal power of a first set of signals received from a plurality of cells and storing corresponding received signal power measurements;
measuring, at the mobile device, a plurality of times of arrival of a second set of signals received from the plurality of cells;
determining, at the mobile device, a plurality of time difference of arrival (TDOA) measurements from the plurality of times of arrival; and
generating, using a power-time hybrid Gaussian maximum likelihood estimator and positioning assistance data for the plurality of cells, a maximum likelihood estimate of the position of the mobile device by evaluating a joint conditional probability of the received signal power measurements and the plurality of TDOA measurements, where the received signal power measurements are represented by a first Gaussian random variable and the plurality of TDOA measurements are represented by a second Gaussian random variable.
2. The method of claim 1 , wherein the received signal power measurements are included in a vector r p , r p =h p (x)+n p , and wherein h p,m (x) is an average received signal power from an m th of the plurality of cells and n p,m =x m is a measured power error term for the m th of the plurality of cells, the method further comprising:
modeling x m as N(0, σ p,m 2 ) such that r p,m becomes the first Gaussian random variable with variance σ p,m 2 , mean h p,m (x), and a conditional probability density function
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3. The method of claim 2 , wherein the plurality of TDOA measurements are included in a vector r t , wherein r t =h t (x)+n t , and wherein h t (x) is a TDOA ground-truth vector and n t is a TDOA noise component, the method further comprising:
modeling n t,m as N(0σ t,m 2 ) such that r t,m becomes the second Gaussian random variable with variance of σ t,m 2 , mean h t,m (x) and a conditional probability density function
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4. The method of claim 1 , further comprising:
receiving, from a network server, first cell parameters for a first plurality of cells from a base station almanac (BSA) accessible to the network server, wherein the plurality of cells form a subset of the first plurality of cells;
storing, within a memory of the mobile device, the first cell parameters as a first micro-BSA; and
deriving the positioning assistance data from a subset of the first cell parameters associated with the plurality of cells.
5. The method of claim 4 , further comprising:
deriving initial positioning assistance data from an initial subset of the first cell parameters associated with an initial subset of the first plurality of cells, wherein one or more cells included within the subset of the first plurality of cells are not included within the initial subset of the first plurality of cells;
measuring, at the mobile device, received signal power of an initial plurality of signals received from an initial subset of the first plurality of cells and storing a corresponding initial plurality of received signal power measurements;
measuring, at the mobile device, an initial plurality of times of arrival of a plurality of signals received from the initial subset of the first plurality of cells;
determining, at the mobile device, an initial plurality of TDOA measurements from the initial plurality of times of arrival; and
generating, using the power-time hybrid Gaussian maximum likelihood estimator and the initial positioning assistance data, an initial maximum likelihood estimate of the position of the mobile device by evaluating a joint conditional probability of the initial plurality of received signal power measurements and the initial plurality of TDOA measurements, wherein the initial plurality of received signal power measurements are represented by a first initial Gaussian random variable and the plurality of TDOA measurements are represented by a second initial Gaussian random variable.
6. The method of claim 5 , wherein the initial positioning assistance data is generated by the first micro-BSA based on an initial seed estimate.
7. The method of claim 4 , further comprising:
predicting, by an artificial intelligence (AI) management module, an expected route to be traveled by the mobile device;
receiving, from the network server, second cell parameters for a second plurality of cells from the BSA wherein the second plurality of cells are determined by the AI management module to be proximate an expected route to be traveled by the mobile device and wherein the second plurality of cells include at least one cell not included within the first plurality of cells; and
storing, within the memory of the mobile device, the second cell parameters as a second micro-BSA.
8. The method of claim 7 , further comprising:
measuring, at the mobile device, received signal power of signals received from a subset of the second plurality of cells and storing corresponding second received signal power measurements;
measuring, at the mobile device, second times of arrival of signals received from the subset of the second plurality of cells;
determining, at the mobile device, a plurality of second TDOA measurements from the second times of arrival; and
generating, using the power-time hybrid Gaussian maximum likelihood estimator and second positioning assistance data for the subset of the second plurality of cells derived from the second cell parameters, a maximum likelihood estimate of a second position of the mobile device by evaluating a joint conditional probability of the second received signal power measurements and the plurality of second TDOA measurements.
9. The method of claim 7 , wherein the predicting includes detecting Doppler shifts in frequencies of signals received by the mobile device.
10. The method of claim 7 , wherein the predicting includes determining the mobile device is traveling on a roadway and extracting route information from a map including the roadway.
11. The method of claim 7 , further comprising:
selecting the second plurality of cells based on pattern recognition information generated by the AI management module, wherein the pattern recognition information includes information relating to cells proximate the expected route previously used by the mobile device for generating prior position estimates.
12. The method of claim 1 , wherein the plurality of TDOA measurements are included within a first TDOA measurement vector, the method further comprising:
determining a quality of the maximum likelihood estimate of the position of the mobile device by at least calculating a first TDOA residual error vector using the maximum likelihood estimate of the position of the mobile device;
detecting, based on the first TDOA residual error vector, a bad cell included within the plurality of cells;
constructing a second TDOA measurement vector by removing the TDOA measurements associated with the bad cell from the first TDOA measurement vector;
generating, using the power-time hybrid Gaussian maximum likelihood estimator and the second TDOA measurement vector, an updated maximum likelihood estimate of the position of the mobile device; and
determining a quality of the updated maximum likelihood estimate of the position of the mobile device based on the second TDOA measurement vector.
13. The method of claim 12 , wherein the determining the quality of the updated maximum likelihood estimate of the position of the mobile device includes calculating a second TDOA residual error vector using the updated maximum likelihood estimate of the position of the mobile device, the method further including:
detecting one or more additional bad cells based on evaluating the second TDOA residual error vector.
14. The method of claim 12 , wherein the determining the quality of the maximum likelihood estimate of the position of the mobile device includes determining whether at least a minimum number of cells are included within the first TDOA measurement vector.
15. The method of claim 12 , wherein the determining the quality of the maximum likelihood estimate of the position of the mobile device includes determining a first geometric dilution of precision (GDOP) between the and locations of the cells in the first TDOA measurement vector.
16. The method of claim 15 , further comprising:
determining the first GDOP exceeds a threshold and at least one of indicating an error condition or determining a position of the mobile device using an alternate positioning method.
17. The method of claim 4 , further comprising:
storing, within the memory of the mobile device, second cell parameters for a second plurality of cells from the BSA as a second micro-BSA, wherein the second plurality of cells includes at least one cell not included within the first plurality of cells.
18. The method of claim 4 , further comprising:
determining an improved estimate of the position of the mobile device based at least upon TDOA measurements associated with an additional subset of the first plurality of cells and improved positioning assistance data corresponding to the additional subset of the first plurality of cells, wherein the improved positioning assistance data is generated by the micro-BSA based on the maximum likelihood estimate of the position of the mobile device.
19. The method of claim 18 , further comprising:
determining additional position estimates for the mobile device based on further improved positioning assistance data generated by the micro-BSA based on a prior one of the additional position estimates.
20. The method of claim 19 , further comprising:
assessing a quality of the additional position estimates by at least one of evaluating contours in a position estimation cost function or calculating a time difference of arrival (TDOA) residual error vector.
21. The method of claim 20 , further comprising: requesting updated positioning assistance data from at least one of the micro-BSA and the network server when the quality is below a defined quality threshold.
22. A mobile device, comprising:
a processor;
a memory in communication with the processor, the memory storing program instructions which, when executed by the processor, cause the processor to:
measure received signal power of a first set of signals received from a first plurality of cells and store corresponding received signal power measurements;
measure a first plurality of times of arrival of a second set of signals received from the first plurality of cells;
determine a first plurality of time difference of arrival (TDOA) measurements from the first plurality of times of arrival; and
generate, using a power-time hybrid Gaussian maximum likelihood estimator and first positioning assistance data for the first plurality of cells, a maximum likelihood estimate of a position of the mobile device by evaluating a joint conditional probability of the received signal power measurements and the first plurality of TDOA measurements, the received signal power measurements are represented by a first Gaussian random variable and the first plurality of TDOA measurements are represented by a second Gaussian random variable.
23. The mobile device of claim 22 , wherein the instructions further include instructions which, when executed by the processor, cause the processor to:
measure a second plurality of times of arrival of a third set of signals received from a second plurality of cells;
determine a second plurality of TDOA measurements from the second plurality of times of arrival; and
generate, using second positioning assistance data for the second plurality of cells and the second plurality of TDOA measurements, an updated estimate of the position of the mobile device.
24. The mobile device of claim 22 , wherein the instructions further include instructions which, when executed by the processor, cause the processor to:
store, within a micro-BSA established within the memory, cell parameters for the first plurality of cells and the second plurality of cells; and
derive the first positioning assistance data and the second positioning assistance data from the cell parameters.
25. A method of estimating a position of a mobile device, the method comprising:
measuring, at the mobile device, received signal power of a first set of signals received from a plurality of cells and storing corresponding received signal power measurements;
measuring, at the mobile device, a plurality of times of arrival of a second set of signals received from the plurality of cells;
determining, at the mobile device, a plurality of time difference of arrival (TDOA) measurements from the plurality of times of arrival; and
generating, using a Gaussian maximum likelihood estimator, an estimate of the position of the mobile device based on the plurality of TDOA measurements, the received signal power measurements, and positioning assistance data for the plurality of cells.