Sippel E (2022)
Publication Language: English
Publication Type: Authored book, Monography
Publication year: 2022
DOI: 10.13140/RG.2.2.15657.47209
In the last twenty years, mobile communication systems have gone through a tremendous development, increasing the available consumer data rate by several orders of magnitude. Currently, the quickly emerging 5G and particularly the upcoming 6G technology renew the overall concept of communication networks by providing a universal standard, which is able to cover each part of the everyday life. In contrast, localization systems are mainly established within the global positioning system for outdoor navigation, while indoor localization systems are rare, particularly in the consumer sector. This is reasoned in the currently available implementations, which are either exact, but expensive using the broadband or ultra wide band technology or cheap, but very inexact via receive-signal-strength measurements. To deal with this problem, an alternative approach is studied in this thesis, which is based on the evaluation of spatially distributed phase measurements. Usually, spatially distributed phase measurements are recorded via antenna arrays. If the measurement process is incoherent, the phase-difference-of-arrival measurements are typically used to estimate the angle-of-arrival at each receiver, thereby assuming the impinging wave to be plane. Thereafter, the angular information of several receivers can be combined via multiangulation to calculate a beacon's position. This is done either individually for every measurement instances or recursively, for example using the extended Kalman filter. Though this broadly established method appears to be well suited at first glance, it restricts the achievable localization performance of indoor localization systems because of several reasons. First, the angle-of-arrival estimation depicts a non-linear mapping, whose result is only suitable for subsequent position estimation to a very limited extend because of noise shaping. Second, the impinging wave is assumed to be plane, which is only an approximation of the actually wave form, particularly indoors. Third, the localization accuracy mainly depends on the array's aperture size, which is strongly limited by the plane wave assumption. Hence, for highly accurate positioning an alternative approach is necessary, which does not rely on a plane wave assumption and does not perform any non-linear preprocessing, such as angle-of-arrival estimation. To avoid these limitations, holographic localization concepts estimate a beacon's position via brute-force searches, which quickly become computationally expensive in large areas, particularly for 3D positioning. To enable highly accurate, real-time 3D localization, the holographic extended Kalman filter approach is presented in this thesis, which directly evaluates phases or phase differences in a recursive extended Kalman filter based manner. Thus, the preprocessing is reduced to the phase extraction from complex valued signals, which implies minimal noise shaping, and the computation of phase differences, which is a linear mapping. Further, no assumptions about the received wave form are met and, therefore, the array apertures can be arbitrarily increased, strongly improving the achievable localization accuracy. Thereby, the reception of circular waves also reduces the influence of multipath propagation. In this thesis, the generally applicable holographic extended Kalman filter approach is implemented via the phase-difference holographic extended Kalman filter, which only evaluates phase differences and, hence, is applicable in many different applications, and via the quasi-coherent holographic extended Kalman filter, which involves the evaluation of absolute phases by assuming very stable frequency references, enabling extremely accurate tracking of changes of direction. To enable very accurate positioning via spatially distributed phase measurements, antenna arrays are necessary, which provide phase measurements on an equivalent level of accuracy. However, antenna arrays are impaired by channel phase mismatch, mutual coupling, and antenna position deviations. Usually, these are calibrated within anechoic chambers, which suppress the multipath propagation. Unfortunately, the antenna array impairments alter until the receivers are mounted into their final measurement environment. Therefore, an in-situ calibration method is proposed, which calibrates the receivers within the designated localization environment. Similar to the localization, the calibration measurements are performed within the arrays' near field to reduce the influence of the multipath propagation. Altogether, the proposed concepts enable indoor localization measurement with mm accuracy using a 24 GHz narrowband radar system.
APA:
Sippel, E. (2022). Holographic 3D Indoor Localization.
MLA:
Sippel, Erik. Holographic 3D Indoor Localization. 2022.
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