Indoor Heading Sensor Using Outlier Rejection for Magnetic Disturbance
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Solution Overview
Problem
Indoor navigation systems face challenges in accurately determining heading changes due to magnetic disturbances and sensor offset drifts, especially in environments with complex infrastructure and frequent orientation changes.
Innovation Solution
A method combining data from motion and direction sensors, using a filter to correct heading angle measurements by identifying and rejecting outliers from inertial and magnetic data, and employing a hypothesis testing algorithm to validate heading changes, thereby stabilizing the odometric model.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetometer readings are used to determine heading changes, then the system can directly detect compass heading changes, but magnetic disturbances cause false heading changes and reduce reliability
Solution Approach 1:
The patent introduces an intermediary filtering mechanism that processes magnetometer readings through a series of validation steps. The filter compares heading changes against expected physical constraints and sensor performance characteristics, accepting only those readings that pass consistency checks. This intermediary layer separates the raw magnetometer data from the final heading output, blocking magnetic disturbances while preserving valid heading changes.
Solution Approach 2:
The system implements feedback by continuously monitoring sensor readings and comparing them against expected behavior models. When magnetic disturbances cause anomalous readings, the feedback mechanism detects the inconsistency and adjusts the filtering parameters or rejects the problematic readings. This closed-loop approach allows the system to adapt to varying magnetic interference conditions and maintain reliable heading determination.
2Speed
If gyroscope angular rate data is integrated to determine heading, then the system can capture rapid orientation changes, but sensor offset drift causes large heading drift over time
Solution Approach 1:
The patent merges multiple sensor data sources (gyroscope angular rate, accelerometer direction, magnetometer heading) into a unified heading estimation process. Each sensor provides complementary information that compensates for the weaknesses of others. The gyroscope captures rapid changes, the accelerometer provides gravity reference, and the magnetometer offers absolute heading reference. By combining these sources through sensor fusion algorithms, the system achieves both rapid response and long-term accuracy.
Solution Approach 2:
The system uses feedback to continuously correct gyroscope drift by comparing integrated heading against absolute references from magnetometer and accelerometer data. When drift is detected, the feedback mechanism adjusts the heading estimate by applying correction terms derived from the other sensors. This ongoing correction prevents cumulative drift while preserving the gyroscope's advantage of capturing rapid orientation changes.
3Adaptability or versatility
If device orientation relative to user changes frequently, then the system can adapt to different carrying positions, but orientation changes are falsely interpreted as heading changes
Solution Approach 1:
The patent introduces an intermediary orientation detection and compensation mechanism that separates device orientation changes from actual heading changes. The system uses accelerometer and magnetometer data to detect when the device is reoriented by the user, and then compensates for this reorientation in the heading calculation. This intermediary layer identifies the difference between device rotation and world-frame heading change, preventing false heading measurements while maintaining adaptability to different carrying positions.
Solution Approach 2:
The system applies counter-weighting by introducing compensatory calculations that offset the effect of device reorientation. When the device is rotated by the user, the system calculates the opposing rotation needed to return to the original reference frame, and applies this counter-rotation to the heading data. This counteracts the false heading changes while preserving the ability to use the device in various orientations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces the impact of disturbances and sensor offsets, providing a more accurate and stable heading determination in indoor environments, even in the presence of magnetic interference and device orientation changes.
Implementation Method 1
Gyroscopes are normally used to measure angular rates, including heading changes which are the angular rate projected onto the horizontal plane
Implementation Method 2
The projection requires that 3 the downward direction is known. This can be computed from a vector accelerometer
Implementation Method 3
The most natural alternative is to start with the vector magnetometer, since its standard use is as a compass sensor, i.e., a heading sensor
Data Source
AI summary
A method and system are provided for determining a heading angle of a user of a portable electronic device in an indoor environment. In an embodiment, the device collects rotational movement information indicative of rotational movement of the device and determines a first heading angle of the device. The first heading angle is determined by using the downward direction of the device to determine the vertical angular rate in the horizontal plane, and integrating the vertical angular rate to form the first heading angle. The device collects first direction information from a first direction sensor and second direction information from a second direction sensor and uses it determine which of the first and second direction information is an outlier, e.g., inaccurate due to an occurrence of a disturbance. The device then corrects the heading angle by comparing the heading angle to the first and second direction information.