Real-Time Low-Cost Multipath Mitigation Technique Calibrated Through Real Data Repeatable Testing

M-A. Fortin, J-C. Guay, R. Jr Landry

Abstract:	This paper proposes a new statistical multipath detector for antenna–array based GNSS receivers. After a brief review of the state–of–the–art in multipath detection, we depict how multipath produces biased estimations in a traditional single– antenna receiver and we extend the Maximum Likelihood synchronization approach to multiples antennas, considering both structured and unstructured arrays. The observation that the spatially colored Gaussian noise assumption captures the statistical behavior of multipath motivates the proposal of a detector based on the structure of the covariance matrix. This test does not require assumptions about the number of signals, their synchronization parameters, or the Directions of Arrival, and can be directly applied in the Intermediate Frequency stage, just after de Analog–to–Digital Converters. In addition, The detector comes almost for free, since the vast majority of beamforming strategies require the computation of the covariance matrix. Computer simulations assess the performance in coherent multipath detection. continuous scans still allowed detection and characterization of very short delayed multipath (i.e. 0.1±0.05 chip) in a real outdoors dynamic environment with low-profile obstructions. Also, a byproduct, a standard deviation study of the ACF peak’s position gives a further insight on multipath characterization. In order to maintain a representative progressive ACF scan, the Delay Lock Loop (DLL) feedback is kept as fast as possible (i.e. 1 ms). Another noncoherent smoothing parameter is made available to average out noise over time. Thus, different optimum “real-time” total scan time may be achieved according to the signal’s characteristics and user dynamics. This constraint allows for a snapshot of the multipath to be characterized and used to correct the Pseudo-Range (PR) measurement, thus improving the navigation solution’s accuracy. After a brief review of current receiver errors, including multipath and its existing mitigation techniques, the VSC approach is formally introduced and compared in terms of resources to other existing techniques. According to the further described methodology, recorded real-world multipath scenarios (after using simulators for initial calibration) are used to test the VSC performances on GPS L1 C/A. To speed up testing and to ensure fine-tuning through repeatability, the same real GNSS recordings were played back several times with Averna’s tunable RF Record&Playback equipment. The paper then sums up the current findings and opens up onto the upcoming multipath challenges.
Published in:	Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009) September 22 - 25, 2009 Savannah International Convention Center Savannah, GA
Pages:	2316 - 2328
Cite this article:	Fortin, M-A., Guay, J-C., Landry, R. Jr, "Real-Time Low-Cost Multipath Mitigation Technique Calibrated Through Real Data Repeatable Testing," Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009), Savannah, GA, September 2009, pp. 2316-2328.
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