| 1. |
- Bartoletti, Stefania, et al.
(author)
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Positioning methods
- 2024
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In: Positioning and Location-based Analytics in 5G and Beyond. - 9781119911463 ; , s. 21-50
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Book chapter (other academic/artistic)abstract
- This chapter introduces the main positioning methods, starting from the state-of-the-art and following a statistical estimation perspective. This is followed by an in-depth treatment of radio positioning, first focusing on device-based positioning and then on device-free positioning. Finally, recent approaches based on artificial intelligence methods for positioning are detailed.
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| 2. |
- Cassioli, Dajana, et al.
(author)
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Low complexity Rake receivers in ultra-wideband channels
- 2007
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In: IEEE Transactions on Wireless Communications. - 1536-1276. ; 6:4, s. 1265-1275
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Journal article (peer-reviewed)abstract
- One of the major issues for the design of ultra-wideband (UWB) receivers is the need to recover the signal energy dispersed over many multipath components, while keeping the receiver complexity low. To this aim we consider two schemes for reduced-complexity UWB Rake receivers, both of which combine a subset of the available resolved multipath components. The first method, called partial Rake (PRake), combines the first arriving multipath components. The second is, known as selective Rake (SRake) and combines the instantaneously strongest multipath components. We evaluate and compare the link performance of these Rake receivers in different UWB channels, whose models are based on extensive propagation measurements. We quantify the effect of the channel characteristics on the receiver performance, analyzing in particular the influence of small-scale fading statistics. We find that for dense channels the performance of the simpler PRake receiver is almost as good as that of the SRake receiver, even for a small number of fingers. In sparse channels, however, the SRake outperforms the PRake significantly. We also show that for a fixed transmitted energy there is an optimum transmission bandwidth.
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| 3. |
- Gong, Zijun, et al.
(author)
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Data-Aided Doppler Compensation for High-Speed Railway Communications over mmWave Bands
- 2021
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In: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; 20:1, s. 520-534
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Journal article (peer-reviewed)abstract
- IEEE Millimeter wave communications show great potentials in many applications, one of which is the high-speed railway (HSR) communication system. However, a major challenge is the Doppler effect caused by the relative-movement between the train and the base station (BS), which leads to fast channel variation. To compensate for the Doppler shift, an accurate channel model is indispensable, and the far-field channel model is generally employed, which assumes that the dimensions of the antenna arrays are negligible compared to the distance between transmitter and receiver. This model is widely used in Cellular systems, but the underlining assumption is not always true for railway communication systems. In this paper, the modeling of the Doppler effect for millimeter wave in HSR communications is conducted, and data-aided Doppler estimation and compensation algorithms are designed based on the new model. We show that the conventional far-field channel model is based on the first-order Taylor expansion of the actually channel, and the second-order component cannot be ignored for HSR communications. Extensive simulations are conducted to verify the validity of the new model and the effectiveness of the proposed algorithms.
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| 4. |
- Leitinger, Erik, et al.
(author)
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A Belief Propagation Algorithm for Multipath-Based SLAM
- 2019
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In: IEEE Transactions on Wireless Communications. - 1536-1276. ; 18:12, s. 5613-5629
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Journal article (peer-reviewed)abstract
- We present a simultaneous localization and mapping (SLAM) algorithm that is based on radio signals and the association of specular multipath components (MPCs) with geometric features. Especially in indoor scenarios, robust localization from radio signals is challenging due to diffuse multipath propagation, unknown MPC-feature association, and limited visibility of features. In our approach, specular reflections at flat surfaces are described in terms of virtual anchors (VAs) that are mirror images of the physical anchors (PAs). The positions of these VAs and possibly also of the PAs are unknown. We develop a Bayesian model of the SLAM problem and represent it by a factor graph, which enables the use of belief propagation (BP) for efficient marginalization of the joint posterior distribution. The resulting BP-based SLAM algorithm detects the VAs associated with the PAs and estimates jointly the time-varying position of the mobile agent and the positions of the VAs and possibly also of the PAs, thereby leveraging the MPCs in the radio signal for improved accuracy and robustness of agent localization. The algorithm has a low computational complexity and scales well in all relevant system parameters. Experimental results using both synthetic measurements and real ultra-wideband radio signals demonstrate the excellent performance of the algorithm in challenging indoor environments.
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| 5. |
- Lien, J., et al.
(author)
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A Comparison of Parametric and Sample-Based Message Representation in Cooperative Localization
- 2012
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In: International Journal of Navigation and Observation. - : Hindawi Limited. - 1687-5990 .- 1687-6008. ; 2012, s. Art. ID. 281592-
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Journal article (peer-reviewed)abstract
- Location awareness is a key enabling feature and fundamental challenge in present and future wireless networks. Most existing localization methods rely on existing infrastructure and thus lack the flexibility and robustness necessary for large ad hoc networks. In this paper, we build upon SPAWN (sum-product algorithm over a wireless network), which determines node locations through iterative message passing, but does so at a high computational cost. We compare different message representations for SPAWN in terms of performance and complexity and investigate several types of cooperation based on censoring. Our results, based on experimental data with ultra-wideband (UWB) nodes, indicate that parametric message representation combined with simple censoring can give excellent performance at relatively low complexity.
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| 6. |
- Maranò, Stefano, et al.
(author)
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NLOS identification and mitigation for UWB localization based on experimental data
- 2010
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In: IEEE Journal on Selected Areas in Communications. - 0733-8716 .- 1558-0008. ; 28:7, s. 1026-1035
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Journal article (peer-reviewed)abstract
- Sensor networks can benefit greatly from location-awareness, since it allows information gathered by the sensors to be tied to their physical locations. Ultra-wide bandwidth (UWB) transmission is a promising technology for location-aware sensor networks, due to its power efficiency, fine delay resolution, and robust operation in harsh environments. However, the presence of walls and other obstacles presents a significant challenge in terms of localization, as they can result in positively biased distance estimates. We have performed an extensive indoor measurement campaign with FCC-compliant UWB radios to quantify the effect of non-line-of-sight (NLOS) propagation. From these channel pulse responses, we extract features that are representative of the propagation conditions. We then develop classification and regression algorithms based on machine learning techniques, which are capable of: (i) assessing whether a signal was transmitted in LOS or NLOS conditions; and (ii) reducing ranging error caused by NLOS conditions. We evaluate the resulting performance through Monte Carlo simulations and compare with existing techniques. In contrast to common probabilistic approaches that require statistical models of the features, the proposed optimization-based approach is more robust against modeling errors.
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| 7. |
- Maranò, Stefano, et al.
(author)
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Nonparametric obstruction detection for UWB localization
- 2009
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In: 2009 IEEE Global Telecommunications Conference, GLOBECOM 2009; Honolulu, HI; United States; 30 November 2009 through 4 December 2009. - 9781424441488
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Conference paper (peer-reviewed)abstract
- Ultra-wide bandwidth (UWB) transmission is a promising technology for indoor localization due to its fine delay resolution and obstacle-penetration capabilities. However, the presence of walls and other obstacles introduces a positive bias in distance estimates, severely degrading localization accuracy. We have performed an extensive indoor measurement campaign with FCC-compliant UWB radios to quantify the effect of non-line-of-sight (NLOS) propagation. Based on this campaign, we extract key features that allow us to distinguish between NLOS and LOS conditions. We then propose a nonparametric approach based on support vector machines for NLOS identification, and compare it with existing parametric (i.e., model-based) approaches. Finally, we evaluate the impact on localization through Monte Carlo simulation. Our results show that it is possible to improve positioning accuracy relying solely on the received UWB signal.
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| 8. |
- Molisch, Andreas, et al.
(author)
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A comprehensive standardized model for ultrawideband propagation channels
- 2006
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In: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 54:11, s. 3151-3166
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Journal article (peer-reviewed)abstract
- A comprehensive statistical model is described for ultrawideband (UWB) propagation channels that is valid for a frequency range from 3-10 GHz. It is based on measurements and simulations in the following environments: residential indoor, office indoor, builtup outdoor, industrial indoor, farm environments, and body area networks. The model is independent of the used antennas. It includes the frequency dependence of the path gain as well as several generalizations of the Saleh-Valenzuela model, like mixed Poisson times of arrival and delay-dependent cluster decay constants. A separate model is specified for the frequency range below 1 GHz. The model can thus be used for realistic performance assessment of UWB systems. It was accepted by the IEEE 802.15.4a Task Group as standard model for evaluation of UWB system proposals. This paper also presents a critical assessment of the applicability of the model and possible generalizations and improvements.
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| 9. |
- Reichert, Maximilian, et al.
(author)
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Quantum-enhanced Doppler lidar
- 2022
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In: npj Quantum Information. - : Springer Science and Business Media LLC. - 2056-6387. ; 8:1
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Journal article (peer-reviewed)abstract
- We propose a quantum-enhanced lidar system to estimate a target’s radial velocity, which employs squeezed and frequency-entangled signal and idler beams. We compare its performance against a classical protocol using a coherent state with the same pulse duration and energy, showing that quantum resources provide a precision enhancement in the estimation of the velocity of the object. We identify three distinct parameter regimes characterized by the amount of squeezing and frequency entanglement. In two of them, a quantum advantage exceeding the standard quantum limit is achieved assuming no photon losses. Additionally, we show that an optimal measurement to attain these results in the lossless case is frequency-resolved photon counting. Finally, we consider the effect of photon losses for the high-squeezing regime, which leads to a constant factor quantum advantage higher than 3 dB in the variance of the estimator, given a roundtrip lidar-to-target-to-lidar transmissivity larger than 50%.
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| 10. |
- Shen, Yuan, et al.
(author)
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Fundamental Limits of Wideband Localization— Part II: Cooperative Networks
- 2010
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In: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 56:10, s. 4981 - 5000
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Journal article (peer-reviewed)abstract
- The availability of position information is of great importance in many commercial, governmental, and military applications. Localization is commonly accomplished through the use of radio communication between mobile devices (agents) and fixed infrastructure (anchors). However, precise determination of agent positions is a challenging task, especially in harsh environments due to radio blockage or limited anchor deployment. In these situations, cooperation among agents can significantly improve localization accuracy and reduce localization outage probabilities. A general framework of analyzing the fundamental limits of wideband localization has been developed in Part I of the paper. Here, we build on this framework and establish the fundamental limits of wideband cooperative location-aware networks. Our analysis is based on the waveforms received at the nodes, in conjunction with Fisher information inequality. We provide a geometrical interpretation of equivalent Fisher information (EFI) for cooperative networks. This approach allows us to succinctly derive fundamental performance limits and their scaling behaviors, and to treat anchors and agents in a unified way from the perspective of localization accuracy. Our results yield important insights into how and when cooperation is beneficial.
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| 11. |
- Widmer, Joerg, et al.
(author)
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Enablers toward 6G positioning and sensing
- 2024
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In: Positioning and Location-based Analytics in 5G and Beyond. - 9781119911463 ; , s. 75-97
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Book chapter (other academic/artistic)abstract
- This chapter provides the reader with an overview of three major trends toward 6G, namely integrated sensing and communication, the ability to control radio wave propagation in the environment thanks to reconfigurable intelligent surfaces, and advances in model-based and model-free signal processing. This list of trends is by no means exhaustive, but only aims to highlight the tremendous potential for research and innovation toward 6G positioning.
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| 12. |
- Win, Moe Z., et al.
(author)
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History and Applications of UWB
- 2009
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In: Proceedings of the IEEE. - 0018-9219. ; 97:2, s. 198-204
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Journal article (other academic/artistic)
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| 13. |
- Witrisal, Klaus, et al.
(author)
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High-accuracy localization for assisted living : 5G systems will turn multipath channels from foe to friend
- 2016
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In: IEEE Signal Processing Magazine. - 1053-5888. ; 33:2, s. 59-70
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Journal article (peer-reviewed)abstract
- Asisted living (AL) technologies, enabled by technical advances such as the advent of the Internet of Things, are increasingly gaining importance in our aging society. This article discusses the potential of future high-accuracy localization systems as a key component of AL applications. Accurate location information can be tremendously useful to realize, e.g., behavioral monitoring, fall detection, and real-time assistance. Such services are expected to provide older adults and people with disabilities with more independence and thus to reduce the cost of caretaking. Total cost of ownership and ease of installation are paramount to make sensor systems for AL viable. In case of a radio-based indoor localization system, this implies that a conventional solution is unlikely to gain widespread adoption because of its requirement to install multiple fixed nodes (anchors) in each room. This article therefore places its focus on 1) discussing radiolocalization methods that reduce the required infrastructure by exploiting information from reflected multipath components (MPCs) and 2) showing that knowledge about the propagation environment enables localization with high accuracy and robustness. It is demonstrated that new millimeter-wave (mm-wave) technology, under investigation for 5G communications systems, will be able to provide centimeter (cm)-accuracy indoor localization in a robust manner, ideally suited for AL.
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| 14. |
- Wymeersch, Henk, 1976, et al.
(author)
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A Machine Learning Approach to Ranging Error Mitigation for UWB Localization
- 2012
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In: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 60:6, s. 1719 - 1728
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Journal article (peer-reviewed)abstract
- Location-awareness is becoming increasingly important in wireless networks. Indoor localization can be enabled through wideband or ultra-wide bandwidth (UWB) transmission, due to its fine delay resolution and obstacle-penetration capabilities. A major hurdle is the presence of obstacles that block the line-of-sight (LOS) path between devices, affecting ranging performance and, in turn, localization accuracy. Many techniques have been proposed to address this issue, most of which make modifications to the localization algorithm. Since many localization algorithms work with distance or angle estimates, rather than received waveforms, information inherent in the wideband waveform is lost, leading to sub-optimal ranging error mitigation. To avoid this information loss, we present a novel approach to mitigate ranging errors directly in the physical layer. In contrast to existing techniques, which detect the non-line-of-sight (NLOS) condition, our approach directly mitigates the bias incurred in both LOS and non-LOS conditions. In particular, we apply two classes of non-parametric regressors to form an estimate of the ranging error. Our work is based on, and validated by, an extensive indoor measurement campaign with FCC-compliant UWB radios. The results show that the proposed regressors provide significant performance improvements in various practical localization scenarios, compared to conventional approaches.
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