| 1. |
- Ballal, Tarig, et al.
(author)
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A Simple and Computationally Efficient Algorithm for Real-Time Blind Source Separation of Speech Mixtures
- 2006
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Conference paper (peer-reviewed)abstract
- In this paper we exploit the amplitude diversity provided by two sensors to achieve blind separation of two speech sources. We propose a simple and highly computationally efficient method for separating sources that are W-disjoint orthogonal (W-DO), that are sources whose time-frequency representations are disjoint sets. The Degenerate Unmixing and Estimation Technique (DUET), a powerful and efficient method that exploits the W-disjoint orthogonality property, requires extensive computations for maximum likehood parameter learning. Our proposed method avoids all the computations required for parameters estimation by assuming that the sources are "cross high-low diverse (CH-LD)", an assumption that is explained later and that can be satisfied exploiting the sensors settings/directions. With this assumption and the W-disjoint orthogonality property, two binary time-frequency masks that can extract the original sources from one of the two mixtures, can be constructed directly from the amplitude ratios of the time-frequency points of the two mixtures. The method works very well when tested with both artificial and real mixtures. Its performance is comparable to DUET, and it requires only 2% of the computations required by the DUET method. Moreover, it is free of convergence problems that lead to poor SIR ratios in the first parts of the signals. As with all binary masking approaches, the method suffers from artifacts that appear in the output signals.
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| 4. |
- Chen, Hui, 1992, et al.
(author)
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A Tutorial on Terahertz-Band Localization for 6G Communication Systems
- 2022
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In: IEEE Communications Surveys and Tutorials. - 1553-877X. ; 24:3, s. 1780-1815
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Journal article (peer-reviewed)abstract
- Terahertz (THz) communications are celebrated as key enablers for converged localization and sensing in future sixth-generation (6G) wireless communication systems and beyond. Instead of being a byproduct of the communication system, localization in 6G is indispensable for location-aware communications. Towards this end, we aim to identify the prospects, challenges, and requirements of THz localization techniques. We first review the history and trends of localization methods and discuss their objectives, constraints, and applications in contemporary communication systems. We then detail the latest advances in THz communications and introduce THz-specific channel and system models. Afterward, we formulate THz-band localization as a 3D position/orientation estimation problem, detailing geometry-based localization techniques and describing potential THz localization and sensing extensions. We further formulate the offline design and online optimization of THz localization systems, provide numerical simulation results, and conclude by providing lessons learned and future research directions. Preliminary results illustrate that under the same transmission power and array footprint, THz-based localization outperforms millimeter wave-based localization. In other words, the same level of localization performance can be achieved at THz-band with less transmission power or a smaller footprint.
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| 5. |
- Liu, Xing, et al.
(author)
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Constrained Wrapped Least Squares: A Tool for High Accuracy GNSS Attitude Determination
- 2022
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In: IEEE Transactions on Instrumentation and Measurement. - 1557-9662 .- 0018-9456. ; 71
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Journal article (peer-reviewed)abstract
- Attitude determination is a popular application of Global Navigation Satellite Systems (GNSS). Many methods have been developed to solve the attitude determination problem with different performance offerings. We develop a constrained wrapped least-squares (C-WLS) method for highaccuracy attitude determination. This approach is built on an optimization model that leverages prior information related to the antenna array and the integer nature of the carrier-phase ambiguities in an innovative way. The proposed approach adopts an efficient search strategy to estimate the vehicle’s attitude parameters using ambiguous carrier-phase observations directly, without requiring prior carrier-phase ambiguity fixing. The performance of the proposed method is evaluated via simulations and experimentally utilizing data collected using multiple GNSS receivers. The simulation and experimental results demonstrate excellent performance, with the proposed method outperforming the ambiguity function method, the constrained LAMBDA and multivariate constrained LAMBDA methods, three prominent attitude determination algorithms.
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| 7. |
- Zheng, Pinjun, et al.
(author)
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Coverage Analysis of Joint Localization and Communication in THz Systems with 3D Arrays
- 2024
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In: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; 23:5, s. 5232-5247
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Journal article (peer-reviewed)abstract
- As a key enabler of Terahertz (THz)-based wireless technologies, large-scale multiple-input-multiple-output systems are well known for their advantages in both communication and localization. Contrary to existing works that mostly focus on planar arrays, this paper first explores the potential of three-dimensional (3D) spatial array structures in joint localization and communication coverage enhancement. We consider a THz-band wireless system where a user is equipped with a 3D array receiving downlink far-field signals from multiple base stations with known positions and orientations over Rician fading channels. First, we derive the constrained Cramér-Rao bound (CCRB) for the localization (i.e., position and orientation estimation) performance, based on which we define the localization coverage metrics. Then, we derive the communication key performance indicators (KPIs) including instantaneous signal-to-noise ratio, outage probability, and ergodic capacity, and define the corresponding coverage metrics. To facilitate localization applications using 3D arrays, a maximum likelihood-based algorithm for joint user equipment (UE) position and orientation estimation is proposed, which is initialized by a least squares-based solution. Our numerical results show that the 3D array configuration offers overall higher coverage than the planar array w.r.t. both localization and communication KPIs, although with minor performance loss in certain UE positions and orientations. The proposed localization algorithm is also verified to be efficient in simulations as it attains the derived CCRB.
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| 8. |
- Zheng, Pinjun, et al.
(author)
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JrCUP: Joint RIS Calibration and User Positioning for 6G Wireless Systems
- 2024
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In: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; 23:6, s. 6683-6698
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Journal article (peer-reviewed)abstract
- Reconfigurable intelligent surface (RIS)-assisted localization has attracted extensive attention as it can enable and enhance localization services in extreme scenarios. However, most existing works treat RISs as anchors with known positions and orientations, which is not realistic in applications with mobile or uncalibrated RISs. This work considers the joint RIS calibration and user positioning (JrCUP) problem with an active RIS. We propose a novel two-stage method to solve the considered JrCUP problem. The first stage comprises a tensor-estimation of signal parameters via rotational invariance techniques (tensor-ESPRIT), followed by a channel parameters refinement using least-squares. In the second stage, a two-dimensional search algorithm is proposed to estimate the three-dimensional user and RIS positions, one-dimensional RIS orientation, and clock bias from the estimated channel parameters. The Cramér-Rao lower bounds of the channel parameters and localization parameters are derived to verify the effectiveness of the proposed tensor-ESPRIT-based algorithms. In addition, simulation results reveal that the active RIS can significantly improve the localization performance compared to the passive case under the same system power supply in practical regions. Moreover, we observe the presence of blind areas with limited JrCUP localization performance, which can be mitigated by either leveraging more prior information or deploying extra base stations.
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| 9. |
- Zheng, Pinjun, et al.
(author)
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Localization Coverage Analysis of THz Communication Systems with a 3D Array
- 2022
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In: GLOBECOM - IEEE Global Telecommunications Conference. ; , s. 5378-5383
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Conference paper (peer-reviewed)abstract
- This paper considers the problem of estimating the position and orientation of a user equipped with a threedimensional (3D) array receiving downlink far-field THz signals from multiple base stations with known positions and orientations. We derive the Cram´er–Rao Bound for the localization problem and define the coverage of the considered system. We compare the error lower bound distributions of the conventional planar array and the 3D array configurations at different user equipment (UE) positions and orientations. Our numerical results obtained for array configurations with an equal number of elements show very limited coverage of the planar-array configuration, especially across the UE orientation range. Conversely, a 3D array configuration offers an overall higher coverage with minor performance loss in certain UE positions and orientations.
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| 10. |
- Zheng, Pinjun, et al.
(author)
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Misspecified Cramér-Rao Bound of RIS-Aided Localization Under Geometry Mismatch
- 2023
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In: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings. - 1520-6149. ; 2023-June
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Conference paper (peer-reviewed)abstract
- In 5G/6G wireless systems, reconfigurable intelligent surfaces (RIS) can play a role as a passive anchor to enable and enhance localization in various scenarios. However, most existing RIS-aided localization works assume that the geometry of the RIS is perfectly known, which is not realistic in practice due to calibration errors. In this work, we derive the misspecified Cramér-Rao bound (MCRB) for a single-input-single-output RIS-aided localization system with RIS geometry mismatch. Specifically, unlike most existing works that use numerical methods, we propose a closed-form solution to the pseudo-true parameter determination problem for MCRB analysis. Simulation results demonstrate the validity of the derived pseudo-true parameters and MCRB, and show that the RIS geometry mismatch causes performance saturation in the high signal-to-noise ratio regions.
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