The basis is a dead reckoning navigation solution, which is obtained mainly from using patterns of the INS output for step-detection and magnetometer readings. Step detection uses a fuzzy logic approach to identify movement on the same floor or if the user is walking up- or downstairs. This height determination is aided by the barometer.
It is observed that a MEMS IMU is able over several seconds to provide a classical strapdown calculation with a relative positioning accuracy of a few centimeters: a so-called µ-trajectory segment is generated. The strapdown solution is constrained by the dead reckoning solution. As a consequence, the generated µ-trajectory allows the compensation of the satellite - user motion during the coherent correlation process, thus it enables long coherent integration intervals (maximally 2 seconds in a dynamic situation).
The processing is done in a strict sequence of repeating steps:
First, a µ-trajectory segment is generated using the dead reckoning navigation solution that incorporates correction terms for biases estimated by the IKF.
In a second step, the signal processing generates code phase and Doppler measurements using reference signals whose generation is controlled by the relative movement between a satellite and the user (ephemeris data and µ-trajectory!) and estimated clock drift. Due to the long coherent intervals, the real-time provision of data bits from a reference receiver is required.
Then based on these measurements, the IKF estimates the difference of the true trajectory to the dead-reckoning trajectory in order to derive corresponding dead-reckoning biases as well as receiver clock parameters. Then, a new processing cycle starts with the generation of the next µ-trajectory segment.
The signal processing measurements are accompanied with appropriate accuracy information in order to allow the IKF a weighting of the received measurements.
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