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Signal Processing Design for an Ultra Sensitive Indoor GNSS Navigation Receiver

A new GNSS/INS navigation system (DINGPOS = Demonstrator for Indoor GNSS Positioning), has been developed by a team led by IFEN GmbH under ESA contract. The objective has been to study satellite based navigation in harsh environments (e.g. indoor) characterized by low signal-to-noise ratios. AUDENS ACT was responsible for the design and development of the signal processing part (acquisition and tracking of satellite signals)

A key element of the receiver is the realization of very long coherent integration periods -in the order of seconds - to 1) collect enough energy to allow reliable code phase measurements in the range of C/N0 = 0....5 dBHz, and 2) mitigate the impact of multipath and cross-correlation.

The receiver uses as sensors a L1/L5 GNSS software receiver, a MEMS IMU including a magnetometer and a barometer, WLAN power readings as well as a ZigBee based radio navigation system. The NavX-NSR V2.0 software receiver (IFEN GmbH) acts as integration platform.

The PNS-based IKF controls the GNSS tracking channels with an ultra-tightly coupling (UTC) scheme: the integration scheme is called partially coherent as the input data to the IKF are code pseudo-ranges (or equivalently code discriminator values), which is a non-coherent observation. On the other hand, the feedback from the IKF to the software receiver is coherent and the IKF controls code phase, code rate, carrier phase and Doppler of the tracking channels via provision of the user motion, called '-trajectory'.

The user motion is determined by a MEMS-type IMU. Since analysis revealed that the strapdown-only accuracy of the -trajectory can not meet the required accuracy, a new approach combining dead-reckoning, an IKF and a modified strapdown INS has been designed and implemented.

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