Method and system for a self-calibrated multi-magnetometer platform

A multi-magnetometer device comprises at least two z-axis aligned and physically rotated magnetometer triads utilized for measuring corresponding earth's magnetic field. The magnetic field measurements are utilized to measure rotation measurements of a single orthogonal axis along the 360 degrees of the complete circle without user's assistance and/or magnetometer movement for magnetometer calibration. The multi-magnetometer device may compute its magnetic heading utilizing the magnetic field measurements if no magnetic perturbations are detected. When magnetic perturbations are detected, a perturbation mitigation process may be performed. The rotation measurements may be generated by selectively combining the magnetic field measurements. Hard-iron components are determined utilizing the rotation measurements, and are removed from the magnetic field measurements. Soft-iron components are determined utilizing the hard-iron free magnetic field measurements, and are removed from the hard-iron free magnetic field measurements. The resulting perturbation free magnetic field measurements are utilized to compute magnetic heading.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to communication systems. More specifically, certain embodiments of the invention relate to a method and system for a self-calibrated multi-magnetometer platform.

BACKGROUND OF THE INVENTION

Magnetometers are instruments used for measuring the strength and direction of various magnetic fields such as the earth's magnetic field. The earth's magnetic field may be utilized to determine, for example, heading of a moving vehicle or a pedestrian. The heading of a moving pedestrian, for example, is defined as the angle formed between the longitudinal axis of the pedestrian and magnetic north. Magnetometers come in many different forms. A magnetometer triad is a magnetometer that is able to measure all three orthogonal components of magnetic field. Readings of the Earth's magnetic field provided by magnetometer triads may be utilized to compute the heading of a vehicle or a pedestrian in motion. Magnetometers may work very well in clean magnetic environments like in the outdoors. However, they may be strongly influenced by magnetic perturbations produced by manmade infrastructure in the indoors, for example. These magnetic perturbations may affect headings derived from magnetic filed measurements of the magnetometers.

BRIEF SUMMARY OF THE INVENTION

A method and/or system for a self-calibrated multi-magnetometer platform, substantially as shown in and/or described in connection with at least one of the figures, as set forth more completely in the claims.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the invention may be found in a method and system for a self-calibrated multi-magnetometer platform. In various embodiments of the invention, a multi-magnetometer device or platform comprises at least two magnetometer triads that are aligned along z axis in a XYZ coordinate system, and physically incrementally rotated in a xy-plane of the XYZ coordinate system. At least two of the physically rotated magnetometer triads may be utilized to measure the corresponding earth's magnetic field. Rotation measurements of a single orthogonal axis along the 360 degrees of the complete circle may be taken utilizing the magnetic field measurements from the physically rotated magnetometers without user's assistance and/or magnetometer movement. The physically rotated magnetometers may be automatically calibrated utilizing the rotation measurements. The multi-magnetometer device may combine the magnetic field measurements from the physically rotated magnetometers for magnetic perturbation detection. The combined magnetic field measurements may be utilized to compute the magnetic heading for the multi-magnetometer device if no magnetic perturbations are detected. Upon detection of magnetic perturbations, the multi-magnetometer device may automatically initiate a perturbation mitigation process on the magnetic field measurements. The rotation measurements may be generated by selectively combining the magnetic field measurements from the physically rotated magnetometers. The perturbation mitigation process may determine hard-iron components of the detected magnetic perturbations utilizing the rotation measurements. The determined hard-iron components may be removed from the magnetic field measurements from the physically rotated magnetometers to form hard-iron free magnetic field measurements, which may be utilized to determine soft-iron components of the detected magnetic perturbations. The multi-magnetometer device may remove the determined soft-iron components from the hard-iron free magnetic field measurements to form perturbation free magnetic field measurements. The perturbation free magnetic field measurements may be utilized to compute the magnetic heading for the multi-magnetometer device.

FIG. 1is a diagram illustrating an exemplary multi-magnetometer device that is operable to self-calibrate magnetic field measurements without physically moving magnetometers of the multi-magnetometer device, in accordance with an embodiment of the invention. Referring toFIG. 1, there is shown a multi-magnetometer device100comprising a host processor110, a plurality of magnetometers122-126and a memory130. The multi-magnetometer device100may be located in, for example, a hand-held device such as a cellphone or other wireless communication device such as a media player.

A magnetometer such as the magnetometer112may comprise suitable logic, circuitry and/or code that may be operable to measure the magnitude of various magnetic fields such as the earth's magnetic field. The magnetic field measurements are scalar measurements while the magnetic field itself is a vector. Depending on implementation, the magnetometer112may be mounted externally on the multi-magnetometer device100, or may be integrated inside the multi-magnetometer device100. The magnetometer112may provide the magnetic field measurements to the processor120in order to compute magnetic heading (also called magnetic azimuth) of the multi-magnetometer device100. The magnetometer112may be implemented or configured in various ways. For example, the magnetometer112may utilize a tri-axis (triad) such as x, y, and z axis in a XYZ coordinate system to measure three orthogonal components of magnetic fields. The magnetometer112with a triad implementation is referred to a magnetometer triad. In an exemplary embodiment of the invention, the magnetometer triads112-116may be aligned along z-axis and may be physically rotated between one to another in a predetermined increment such as 30 degrees in xy-plane. In this regard, one magnetometer axis may be placed in the predetermined increment such as 30 degrees along the whole 360 degrees of azimuth. In an exemplary embodiment of the invention, the magnetic field measurements of the physically rotated magnetometer triads112-116may be utilized to simulate rotation measurements of a single magnetometer without assistance from user and/or without physically moving the single magnetometer.

The host processor120may comprise suitable logic, circuitry and/or code that may be operable to process signals received from the magnetometer triads112-116. The received signals may comprise various magnetic field measurements such as the earth's magnetic field measurements. In an exemplary embodiment of the invention, in instances where the magnetometer triads112-116are aligned along z-axis, and are physically rotated between one to another in an increment such as 30-degrees in xy-plane, the host processor120may combine the magnetic field measurements from the physically rotated magnetometer triads112-116to perform magnetic perturbation detection. In this regard, the host processor120may be operable to compare the magnitudes of the combined magnetic field measurements with a perturbation threshold value. In instances where none of the magnitudes of the combined magnetic field measurements is greater than the perturbation threshold value, the host processor may determine that there are no magnetic perturbations. In instances where one or more of the magnitudes of the combined magnetic field measurements are greater than the perturbation threshold value, the host processor120may declare the detection of magnetic perturbations. In an exemplary embodiment of the invention, the host processor120may automatically signal or trigger the calibration unit122to start a perturbation mitigation process on the magnetic field measurements from the physically rotated magnetometer triads112-116. Magnetic perturbation components of the detected magnetic perturbations may be removed from the magnetic field measurements through the perturbation mitigation process to provide perturbation-free magnetic field measurements. The host processor120may utilize the magnetic heading filter124to process the perturbation-free magnetic field measurements to compute or estimate magnetic heading (magnetic azimuth) for the multi-magnetometer device100.

The calibration unit122may comprise suitable logic, circuitry and/or code that may be operable to perform an automatic perturbation mitigation process on the magnetic field measurements from the magnetometer triads112-116. In various exemplary embodiments of the invention, the calibration unit122may utilize the magnetic field measurements from the physically rotated magnetometer triads112-116to simulate or form rotation measurements of a single orthogonal axis along the 360 degrees of the complete circle. In this regard, rotation measurements such as 30-degree rotation measurements of a single orthogonal axis along the 360 degrees of the complete circle may be simulated by selecting the magnetic field measurements taken, at different time instants, by the different physically rotated magnetometer triads112-116. For example, the magnetic field measurement taken at a current time instant, tcurrent, by the physically rotated magnetometer triad112, the magnetic field measurement taken at the time instant, tcurrent+Δt, Δt>0, by the physically rotated magnetometer triad114, and the magnetic field measurement taken at the time instant, tcurrent+2Δt, by the physically rotated magnetometer triad114, may be selected to simulate or form the rotation measurements at the time instants tcurrent, tcurrent+Δt, and tcurrent+2Δt of a single orthogonal axis along the 360 degrees of the complete circle. In an exemplary embodiment of the invention, the calibration unit122may utilize the simulated rotation measurements to determine or compute hard-iron components of the detected magnetic perturbations. The calibration unit122may remove the determined hard-iron components from the combined magnetic field measurements to form hard-iron free magnetic field measurements. The calibration unit122may utilize the hard-iron free magnetic field measurements to determine or compute soft-iron components of the detected magnetic perturbations. The calibration unit122may remove the determined soft-iron components from the hard-iron free magnetic field measurements to form perturbation free magnetic field measurements. The calibration unit122may provide the perturbation free magnetic field to the magnetic heading filter124.

The magnetic heading filter124may comprise suitable logic, circuitry and/or code that may be operable to compute or estimate the magnetic heading (magnetic azimuth) for the multi-magnetometer device100. In this regard, in instances where no magnetic perturbations are detected, the magnetic heading filter124may utilize the magnetic field measurements directly from the physically rotated magnetometer triads112-116to compute or estimate the magnetic heading for the multi-magnetometer device100. In instances where magnetic perturbations are detected, the magnetic heading filter124may utilize the perturbation free magnetic field measurements supplied from the calibration unit122to compute or estimate the magnetic heading for the multi-magnetometer device100. Various algorithms such as Kalman filtering may be utilized by the magnetic heading filter124to compute or estimate the magnetic heading.

The memory130may comprise suitable logic, circuitry, interfaces and/or code that may be operable to store information such as executable instructions and data that may be utilized by the processor120and/or other associated component units such as, for example, the calibration unit122and the magnetic heading filter124. The memory130may comprise RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage.

In an exemplary operation, the multi-magnetometer device100may be operable to collect various magnetic field measurements such as earth's magnetic field measurements utilizing the magnetometers112-116, which may be mounted on the multi-magnetometer device100or may be coupled inside the multi-magnetometer device100. With regard to a XYZ coordinate system, the magnetometer triads112-116may be aligned along z-axis and may be physically rotated in xy-plane between one to another in 30 degrees increments, for example. The magnetic field measurements from the physically rotated magnetometer triads112-116may be utilized by the host processor120to compute the magnetic heading for the multi-magnetometer device100. In this regard, the multi-magnetometer device100may be operable to combine the magnetic field measurements from the physically rotated magnetometers112-116to perform magnetic perturbation detection. The magnitudes of the combined magnetic field measurements may be utilized to detect magnetic perturbations. In instances where the magnetic perturbations are not detected, the magnetic field measurements from the physically rotated magnetometers112-116may be directly forwarded to the magnetic heading filter124so as to estimate or compute the magnetic heading for the multi-magnetometer device100. In instances where the magnetic perturbations are detected, the calibration unit122may be automatically triggered to start a perturbation mitigation process on the magnetic field measurements from the physically rotated magnetometers112-116. In this regard, the calibration unit122may select the magnetic field measurements from the physically rotated magnetometer triads112-116to simulate or form rotation measurements of a single orthogonal axis along the 360 degrees of the complete circle. The calibration unit122may utilize the simulated rotation measurements to determine hard-iron components of the detected magnetic perturbations. The calibration unit122may generate hard-iron free magnetic field measurements by removing the determined hard-iron components from the magnetic field measurements from the physically rotated magnetometers112-116. Soft-iron components of the detected magnetic perturbations may be determined utilizing the hard-iron free magnetic field measurements. The calibration unit122may remove the determined soft-iron components from the hard-iron free magnetic field measurements. The calibration unit122may provide the resulting perturbation-free magnetic field measurements to the magnetic heading filter124. The magnetic heading filter124may estimate the magnetic heading for the multi-magnetometer device100utilizing the perturbation-free magnetic field measurements.

FIG. 2is a diagram illustrating an exemplary signal flow implemented in a multi-magnetometer platform for self-calibrating magnetic field measurements without physically moving magnetometers of the multi-magnetometer device, in accordance with an embodiment of the invention. Referring toFIG. 2, there is shown a signal flow200in a self-calibrated multi-magnetometer platform such as the multi-magnetometer device100. The magnetometer triads112-116may be aligned along z-axis and may be physically rotated between one to another in a predetermined increment such as 30 degrees in xy-plane. The physically rotated magnetometer triads112-116may be utilized to measure the earth's magnetic field for the multi-magnetometer device100. At least two of the physically rotated magnetometer triads112-116may be enabled or utilized to take the earth's magnetic field measurements for the multi-magnetometer device100. A self-calibration process that may be utilized to calibrate the magnetic field measurements from the physically rotated magnetometer triads112-116may start in step210, where the physically rotated magnetometer triads112-116may be utilized to provide corresponding earth's magnetic field measurements to the host processor120. The host processor120may combine the received magnetic field measurements from the physically rotated magnetometer triads112-116to form combined magnetic field measurements for the multi-magnetometer device100. In step220, the host processor120may perform magnetic perturbation detection by comparing the magnitudes of the combined magnetic field measurements with a perturbation threshold value. Upon detection of magnetic perturbations, the host processor120may automatically trigger or signal the calibration unit122for a magnetic perturbation mitigation process. In step230, the calibration unit122may utilize or execute perturbation mitigation software or application, for example, to start the calibration of the magnetic field measurements from the physically rotated magnetometer triads112-116. In this regard, the calibration unit122may first generate the rotation measurements of a single orthogonal axis along the 360 degrees of the complete circle utilizing the magnetic field measurements from the physically rotated magnetometer triads112-116. The calibration unit122may select all possible orthogonal pairs of individual axis of the physically rotated magnetometer triads112-116in order to cover the whole 360 degrees of azimuth. In this regard, the calibration unit122may select the magnetic field measurements taken, at different time instants, by the different physically rotated magnetometer triads112-116in order to simulate the rotation measurements of a single orthogonal axis along the 360 degrees of the complete circle. The calibration unit122may determine hard-iron components of the detected magnetic perturbations utilizing the simulated rotation measurements. The determined hard-iron components may be removed from the combined magnetic field measurements for the physically rotated magnetometer triads112-116. The resulting hard-iron free magnetic field measurements may be utilized by the calibration unit122to determine soft-iron components of the detected magnetic perturbations. The calibration unit122may remove the determined soft-iron components from the hard-iron free magnetic, field measurements to form perturbation free or clean magnetic field measurements for the multi-magnetometer device100. The calibration unit122may provide the perturbation-free magnetic field measurements to the magnetic heading filter124. In step240, the magnetic heading filter124may utilize the perturbation-free magnetic field measurements to compute or estimate the magnetic heading for the multi-magnetometer device100.

In step220, in instances where no magnetic perturbations are detected, the exemplary process may proceed in step250, where the host processor120may directly forward the combined magnetic field measurements for the physically rotated magnetometer triads112-116to the magnetic heading filter124. The exemplary process may proceed in step240to compute the magnetic heading for the multi-magnetometer device100.

FIG. 3is a block diagram illustrating exemplary steps that may be implemented in a multi-magnetometer platform to generate rotation measurements without user's assistance and/or magnetometer movement, in accordance with an embodiment of the invention. Referring toFIG. 3, assuming that a plurality of magnetometer triads112-116are mounted on the single multi-magnetometer device100. The magnetometer triads112-116may be aligned along z-axis and physically rotated in xy-plane between one to another in a determined increment such as 30-degrees, for example. In step302, at least two of the plurality of physically rotated magnetometers112-116may be utilized to measure the earth's magnetic field. In step304, the host processor120may selectively combining the magnetic field measurements from the plurality of physically rotated magnetometer triads112-116by selecting all possible orthogonal pairs of individual axis of the rotated magnetometer triads, covering the whole 360 degrees. In step306, the host processor120may generate or simulate rotation measurements utilizing the selectively combining the magnetic field measurements. In step308, the host processor120may input or provide the rotation measurements to the perturbation mitigation algorithm implemented in the calibration unit122.

FIG. 4is a block diagram illustrating exemplary steps that may be implemented in a multi-magnetometer platform to detect magnetic perturbations utilizing rotation measurements that are determined without user's assistance and/or magnetometer movement, in accordance with an embodiment of the invention. Referring toFIG. 4, assuming that a plurality of magnetometer triads112-116are mounted on the single multi-magnetometer device100. The magnetometer triads112-116may be aligned along z-axis and physically rotated in xy-plane between one to another in a determined increment such as 30-degrees, for example. At least two of the plurality of physically rotated magnetometers112-116may be utilized to measure the earth's magnetic field. In step402, the host processor120may be operable to select or determine a perturbation threshold value for perturbation detection.

In step404, the host processor120may be operable to compare the magnitudes of rotation measurements with the selected perturbation threshold value. The rotation measurements may be derived utilizing the magnetic filed measurements supplied from the at least two of the plurality of physically rotated magnetometers112-116without user's assistance and/or magnetometer movement. In step406, in instances where one or more magnitudes of the rotation measurements are greater than the selected perturbation threshold value, then in step408, the host processor120may declare that magnetic perturbations are detected with respect to the selected perturbation threshold value. In step410, the host processor120may automatically trigger the calibration unit122to start a perturbation mitigation process to calibrate the magnetic field measurements from the at least two of the plurality of physically rotated magnetometers112-116. In step406, in instances where none of the magnitudes of the rotation measurements is greater than the selected perturbation threshold value, then in step412, the host processor120may declare that the magnetic field measurements from the at least two of the plurality of physically rotated magnetometers112-116are perturbation free.

FIG. 5is a block diagram illustrating exemplary steps that may be performed in a multi-magnetometer platform to automatically calibrate magnetic field measurements without user's assistance and/or magnetometer movement, in accordance with an embodiment of the invention. Referring toFIG. 5, assuming that a plurality of magnetometer triads112-116are mounted on the single multi-magnetometer device100. The magnetometer triads112-116may be aligned along z-axis and physically rotated in xy-plane between one to another in a determined increment such as 30-degrees, for example. At least two of the plurality of physically rotated magnetometers112-116may be utilized to measure the earth's magnetic field. In step502, upon detection of magnetic perturbations, the calibration unit122may receive a trigger or may be signaled for starting a perturbation mitigation process on the magnetic field measurements from the physically rotated magnetometers112-116. In step503, the calibration unit122may generate or simulate rotation measurements of a single orthogonal axis along the 360 degrees of the complete circle by selectively combining the magnetic field measurements from the plurality of physical rotated magnetometer triads. For example, the calibration unit122may combine the magnetic field measurement taken at a current time instant, tcurrent, by the physically rotated magnetometer triad112, the magnetic field measurement taken at the time instant, tcurrent+Δt, Δt>0, by the physically rotated magnetometer triad114, and the magnetic field measurement taken at the time instant, tcurrent+2Δt, by the physically rotated magnetometer triad114, may be selected to simulate or form the rotation measurements at the time instants tcurrent, tcurrent+Δt, and tcurrent+2Δt of a single orthogonal axis along the 360 degrees of the complete circle. In step504, the calibration unit122may be operable to determine hard-iron components of the detected magnetic perturbations utilizing rotation measurements. In step506, the calibration unit122may remove the determined hard-iron components from the magnetic field measurements from the physically rotated magnetometers112-116to form hard-iron free magnetic field measurements. In step508, the calibration unit122may be operable to determine soft-iron components of the detected magnetic perturbations utilizing the hard-iron free magnetic field measurements. In step510, the calibration unit122may be operable to remove the determined soft-iron components from the hard-iron free magnetic field measurements to form perturbation free magnetic field measurements for the multi-magnetometer device100. In step512, the magnetic heading filter124may utilize the perturbation free magnetic field measurements to determine or estimate the magnetic heading for the multi-magnetometer device100.

In various exemplary aspects of the method and system for a self-calibrated multi-magnetometer platform, a multi-magnetometer device such as the multi-magnetometer device100that comprises at least two magnetometers such as the magnetometer triads112-116. The magnetometer triads112-116may be aligned, in a XYZ coordinate system, along z axis and may be physically rotated in a predetermined or dynamically changed increment such as 30-degrees in xy-plane. At least two of the physically rotated magnetometer triads112-116may be utilized to measuring corresponding earth's magnetic field. The host processor120may be operable to measure or form rotation measurements of a single orthogonal axis along the 360 degrees of the complete circle utilizing the corresponding magnetic field measurements collected by the physically rotated magnetometers112-116without user's assistance and/or magnetometer movement. The host processor120may be operable to calibrate the physically rotated magnetometer triads112-116utilizing the rotation measurements. In an embodiment of the invention, the host processor120may be operable to combine the magnetic field measurements from the physically rotated magnetometer triads112-116to form combined measurements for the multi-magnetometer device100. Various algorithms such as, for example, a least-square combining, a maximal or maximum ratio combining (MRC) and/or an arithmetic average combining, may be utilized to combine the magnetic field measurements. The magnitudes of the combined measurements may be compared with a perturbation threshold so as to detect magnetic perturbations in the magnetic field measurements from the physically rotated magnetometer triads112-116. In instances where one or more magnitudes of the combined measurements are not greater than the perturbation threshold value, the host processor120may declare that the magnetic field measurements are free of perturbation. The host processor120may directly forward the combined magnetic field measurements from the physically rotated magnetometer triads112-116to the magnetic heading filter124so as to compute the magnetic heading for the multi-magnetometer device100. In instances where one or more magnitudes of the combined measurements are greater than the perturbation threshold value, the host processor120may declare the detection of the magnetic perturbations. In this regard, the host processor120may trigger or signal the calibration unit122to start a perturbation mitigation process on the magnetic field measurements from the physically rotated magnetometer triads112-116. The calibration unit122may start the perturbation mitigation process by selectively combining the magnetic field measurements from the physically rotated magnetometer triads112-116to generate or simulate the rotation measurements. In this regard, the magnetic field measurements taken, at different time instants, by the different physically rotated magnetometer triads112-116, may be selected to be combined to form the rotation measurements. For example, the magnetic field measurement taken at a current time instant, tcurrent, by the physically rotated magnetometer triad112, the magnetic field measurement taken at the time instant, tcurrent+Δt, Δt>0, by the physically rotated magnetometer triad114, and the magnetic field measurement taken at the time instant, tcurrent+2Δt, by the physically rotated magnetometer triad114, may be selected to simulate or form the rotation measurements at the time instants tcurrent, tcurrent+Δt, and tcurrent2Δt of a single orthogonal axis along the 360 degrees of the complete circle. The calibration unit122may determine hard-iron components of the detected magnetic perturbations utilizing the rotation measurements. The determined hard-iron components may be removed from the magnetic field measurements from the physically rotated magnetometer triads112-116to form hard-iron free magnetic field measurements. The host processor120may utilize the hard-iron free magnetic field measurements to determine soft-iron components of the detected magnetic perturbations. The determined soft-iron components may be removed from the hard-iron free magnetic field measurements to form perturbation free magnetic field measurements. The calibration unit122may provide the perturbation free magnetic field measurements to the magnetic heading filter124to compute the magnetic heading for the multi-magnetometer device100.