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Sensors 2018, 18(12), 4249; https://doi.org/10.3390/s18124249

Accuracy Bounds for Array-Based Positioning in Dense Multipath Channels

1
Signal Processing and Speech Communication Laboratory, Graz University of Technology, 8010 Graz, Austria
2
Christian Doppler Laboratory for Location-aware Electronic Systems, Graz University of Technology, 8010 Graz, Austria
3
NXP Semiconductors, 8101 Gratkorn, Austria
This paper is an extended version of our paper published in the 8th International Conference on Localization and GNSS (ICL-GNSS) in 2018.
*
Author to whom correspondence should be addressed.
Received: 30 September 2018 / Revised: 23 November 2018 / Accepted: 26 November 2018 / Published: 3 December 2018
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Abstract

The accuracy of radio-based positioning systems will be limited by multipath interference in realistic application scenarios. This paper derives closed-form expressions for the Cramér–Rao lower bound (CRLB) on the achievable time-of-arrival (ToA) and angle-of-arrival (AoA) estimation-error variances, considering the presence of multipath radio channels, and extends these results to position estimation. The derivations are based on channel models comprising deterministic, specular multipath components as well as stochastic, diffuse/dense multipath. The derived CRLBs thus allow an evaluation of the influence of channel parameters, the geometric configuration of the environment, and system parameters such as signal bandwidth and array geometry. Our results quantify how the ToA and AoA accuracies decrease when the signal bandwidth is reduced, because more multipath will then interfere with the useful LoS component. Antenna arrays can (partly) compensate this performance loss, exploiting diversity among the multipath interference. For example, the AoA accuracy with a 16-element linear array at 1 MHz bandwidth is similar to a two-element array at 1 GHz , in the magnitude order of one degree. The ToA accuracy, on the other hand, still scales by a factor of 100 from the cm-regime to the m-regime because of the dominating influence of the signal bandwidth. The position error bound shows the relationship between the range and angle information under realistic indoor channel conditions and their different scaling behaviors as a function of the anchor–agent placement. Specular multipath components have a maximum detrimental influence near the walls. It is shown for an L-shaped room that a fairly even distribution of the position error bound can be achieved throughout the environment, using two anchors equipped with 2 × 2 -array antennas. The accuracy limit due to multipath increases from the 1–10-cm-range at 1 GHz bandwidth to the 0.5–1-m-range at 100 MHz . View Full-Text
Keywords: indoor positioning; wireless positioning; CRLB; AoA; ToA; antenna-array signal processing indoor positioning; wireless positioning; CRLB; AoA; ToA; antenna-array signal processing
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Wilding, T.; Grebien, S.; Mühlmann, U.; Witrisal, K. Accuracy Bounds for Array-Based Positioning in Dense Multipath Channels. Sensors 2018, 18, 4249.

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