| 1. |
- Cosmas, John, et al.
(author)
-
Towards joint communication and sensing (Chapter 4)
- 2023
-
In: Towards Sustainable and Trustworthy 6G: Challenges, Enablers, and Architectural Design. - 9781638282396 ; , s. 121-158
-
Book chapter (other academic/artistic)abstract
- Localization of user equipment (UE) in mobile communication networks has been supported from the early stages of 3rd generation partnership project (3GPP). With 5th Generation (5G) and its target use cases, localization is increasingly gaining importance. Integrated sensing and localization in 6th Generation (6G) networks promise the introduction of more efficient networks and compelling applications to be developed.
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| 2. |
- Bartoletti, Stefania, et al.
(author)
-
Introduction and fundamentals
- 2024
-
In: Positioning and Location-based Analytics in 5G and Beyond. - 9781119911463 ; , s. 1-18
-
Book chapter (other academic/artistic)abstract
- This chapter introduces the book and presents the main principles and fundamentals for positioning and location-based analytics, thus effectively providing the basis for the following chapters. After a brief introduction and motivation for the book, we present the main use cases, verticals, and applications for positioning and location-based analytics. Then, we provide the technical fundamentals for understanding positioning and navigation algorithms, as well as location-based analytics. An introduction to the architectural principles is presented. Finally, an outline of the book chapters is provided.
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| 3. |
- Bartoletti, Stefania, et al.
(author)
-
Positioning methods
- 2024
-
In: Positioning and Location-based Analytics in 5G and Beyond. - 9781119911463 ; , s. 21-50
-
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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| 4. |
- Behravan, Ali, 1971, et al.
(author)
-
Positioning and Sensing in 6G: Gaps, Challenges, and Opportunities
- 2023
-
In: IEEE Vehicular Technology Magazine. - 1556-6080 .- 1556-6072. ; 18:1, s. 40-48
-
Journal article (peer-reviewed)abstract
- Among the key differentiators of 6G compared to 5G will be the increased emphasis on radio-based positioning and sensing. These will be utilized not only for conventional location-aware services and for enhancing communication performance but also to support new use case families with extreme performance requirements. This article presents a unified vision from stakeholders across the value chain in terms of both opportunities and challenges for 6G positioning and sensing as well as use cases, performance requirements, and gap analysis. Combined, this motivates the technical advances in 6G and guides system design.
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| 5. |
- Chen, Hui, 1992, et al.
(author)
-
6G Localization and Sensing in the Near Field: Features, Opportunities, and Challenges
- 2024
-
In: IEEE Wireless Communications. - 1536-1284 .- 1558-0687. ; In press
-
Journal article (peer-reviewed)abstract
- The far-field channel model has historically been used in wireless communications due to the simplicity of mathematical modeling and convenience for algorithm design. With the need for high data rates, low latency, and ubiquitous connectivity in the sixth generation (6G) of communication systems, new technology enablers such as extremely large antenna arrays (ELAAs), reconfigurable intelligent surfaces (RISs), and distributed multiple-input-multiple-output (D-MIMO) systems will be adopted. These enablers not only aim to improve communication services but also have an impact on localization and sensing (L&S), which are expected to be fundamentally built-in functionalities in future wireless systems. Despite appearing in different scenarios and supporting different frequency bands, such enablers share the so-called near-field (NF) features, which will provide extra geometric information conducive to L&S. In this work, we describe the NF features, namely, the spherical wave model, spatial non-stationarity, and beam squint effect. After discussing how L&S see NF differently from communication, the opportunities and open research challenges are provided.
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| 6. |
- Chen, Hui, 1992, et al.
(author)
-
A Tutorial on Terahertz-Band Localization for 6G Communication Systems
- 2022
-
In: IEEE Communications Surveys and Tutorials. - 1553-877X. ; 24:3, s. 1780-1815
-
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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| 7. |
- Chen, Hui, 1992, et al.
(author)
-
Channel Model Mismatch Analysis for XL-MIMO Systems from a Localization Perspective
- 2022
-
In: GLOBECOM - IEEE Global Telecommunications Conference. ; , s. 1588-1593
-
Conference paper (peer-reviewed)abstract
- Radio localization is applied in high-frequency (e.g., mmWave and THz) systems to support communication and to provide location-based services without extra infrastructure. For solving localization problems, a simplified, stationary, narrowband far-field channel model is widely used due to its compact formulation. However, with increased array size in extra-large MIMO systems and increased bandwidth at upper mmWave bands, the effect of channel spatial non-stationarity (SNS), spherical wave model (SWM), and beam squint effect (BSE) cannot be ignored. In this case, localization performance will be affected when an inaccurate channel model deviating from the true model is adopted. In this work, we employ the MCRB (misspecified Cram´er-Rao lower bound) to lower bound the localization error using a simplified mismatched model while the observed data is governed by a more complex true model. The simulation results show that among all the model impairments, the SNS has the least contribution, the SWM dominates when the distance is small compared to the array size, and the BSE has a more significant effect when the distance is much larger than the array size.
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| 8. |
- Chen, Hui, 1992, et al.
(author)
-
Doppler-Enabled Single-Antenna Localization and Mapping Without Synchronization
- 2022
-
In: GLOBECOM - IEEE Global Telecommunications Conference. ; , s. 6469-6474
-
Conference paper (peer-reviewed)abstract
- Radio localization is a key enabler for joint communication and sensing in the fifth/sixth generation (5G/6G) communication systems. With the help of multipath components (MPCs), localization and mapping tasks can be done with a single base station (BS) and single unsynchronized user equipment (UE) if both of them are equipped with an antenna array. However, the antenna array at the UE side increases the hardware and computational cost, preventing localization functionality. In this work, we show that with Doppler estimation and MPCs, localization and mapping tasks can be performed even with a singleantenna mobile UE. Furthermore, we show that the localization and mapping performance will improve and then saturate at a certain level with an increased UE speed. Both theoretical Cram´er-Rao bound analysis and simulation results show the potential of localization under mobility and the effectiveness of the proposed localization algorithm.
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| 9. |
- Chen, Hui, 1992, et al.
(author)
-
MCRB-based Performance Analysis of 6G Localization under Hardware Impairments
- 2022
-
In: 2022 IEEE International Conference on Communications Workshops, ICC Workshops 2022. ; , s. 115-120
-
Conference paper (peer-reviewed)abstract
- Location information is expected to be the key to meeting the needs of communication and context-aware services in 6G systems. User localization is achieved based on delay and/or angle estimation using uplink or downlink pilot signals. However, hardware impairments (HWIs) distort the signals at both the transmitter and receiver sides and thus affect the localization performance. While this impact can be ignored at lower frequencies where HWIs are less severe, modeling and analysis efforts are needed for 6G to evaluate the localization degradation due to HWIs. In this work, we model various types of impairments and conduct a misspecified Cramér-Rao bound analysis to evaluate the HWI-induced performance loss. Simulation results with different types of HWIs show that each HWI leads to a different level of degradation in angle and delay estimation performance.
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| 10. |
- Chen, Hui, 1992, et al.
(author)
-
Modeling and Analysis of OFDM-based 5G/6G Localization under Hardware Impairments
- 2024
-
In: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; 23:7, s. 7319-7333
-
Journal article (peer-reviewed)abstract
- Localization is envisioned as a key enabler to satisfy the requirements of communications and context-aware services in the fifth/sixth generation (5G/6G) communication systems. User localization can be achieved based on delay and angle estimation using uplink/downlink pilot signals. However, hardware impairments (HWIs) (such as phase noise and mutual coupling) distort the signals at both the transmitter and receiver sides and thus affect the localization performance. While this impact can be ignored at lower frequencies with less severe HWIs, and less stringent localization requirements, modeling and analysis efforts are needed for high-frequency bands to assess degradation in localization accuracy due to HWIs. In this work, we model various types of impairments for a mmWave multiple-input-multiple-output communication system and conduct a misspecified Cramér-Rao bound analysis to evaluate HWI-induced performance losses in terms of angle/delay estimation and the resulting 3D position/orientation estimation error. We also investigate the effect of individual and overall HWIs on communications in terms of symbol error rate (SER). Our extensive simulation results demonstrate that each type of HWI leads to a different level of degradation in angle and delay estimation performance, and the prominent impairment factors on delay estimation will have a dominant negative effect on SER.
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| 11. |
- Chen, Hui, 1992, et al.
(author)
-
Multi-RIS-Enabled 3D Sidelink Positioning
- 2024
-
In: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; In Press
-
Journal article (peer-reviewed)abstract
- Positioning is expected to support communication and location-based services in the fifth/sixth generation (5G/6G) networks. With the advent of reflective reconfigurable intelligent surfaces (RISs), radio propagation channels can be controlled, making high-accuracy positioning and extended service coverage possible. However, the passive nature of the RIS requires a signal source such as a base station (BS), which limits the positioning service in extreme situations, such as tunnels, dense urban areas, or complicated indoor scenarios where 5G/6G BSs are not accessible. In this work, we show that with the assistance of (at least) two RISs and sidelink communication between two user equipments (UEs), the absolute positions of these UEs can be estimated in the absence of BSs. A two-stage 3D sidelink positioning algorithm is proposed, benchmarked by the derived Cramér-Rao bounds. The effects of multipath and RIS profile designs on positioning performance are evaluated, and localization analyses are performed for various scenarios. Simulation results demonstrate the promising positioning accuracy of the proposed BS-free sidelink communication system. Additionally, we propose and evaluate several solutions to eliminate potential blind areas where positioning performance is poor, such as removing clock offset via round-trip communication, adding geometrical prior or constraints, as well as introducing more RISs.
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| 12. |
- Chen, Hui, 1992, et al.
(author)
-
Phone signals can help you find your way in cities even without GPS
- 2022
-
In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 611:7936, s. 454-455
-
Journal article (other academic/artistic)abstract
- Existing telecommunications infrastructure could operate as a miniaturized global positioning system, offering submetre resolution in urban areas and indoors, where location information from satellites is often inaccurate.
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| 13. |
- Chen, Hui, 1992, et al.
(author)
-
RISs and Sidelink Communications in Smart Cities: The Key to Seamless Localization and Sensing
- 2023
-
In: IEEE Communications Magazine. - 0163-6804 .- 1558-1896. ; 61:8, s. 140-146
-
Journal article (peer-reviewed)abstract
- A smart city involves, among other elements, intelligent transportation, crowd monitoring, and digital twins, each of which requires information exchange via wireless communication links and localization of connected devices and passive objects (including people). Although localization and sensing (L&S) are envisioned as core functions of future communication systems, they have inherently different demands in terms of infrastructure compared to communications. Wireless communications generally requires a connection to only a single access point (AP), while L&S demand simultaneous line-of-sight propagation paths to several APs, which serve as location and orientation anchors. Hence, a smart city deployment optimized for communication will be insufficient to meet stringent L&S requirements. In this article, we argue that the emerging technologies of reconfigurable intelligent surfaces (RISs) and sidelink communications constitute the key to providing ubiquitous coverage for L&S in smart cities with low-cost and energy-efficient technical solutions. To this end, we propose and evaluate AP-coordinated and self-coordinated RIS-enabled L&S architectures and detail three groups of application scenarios, relying on low-complexity beacons, cooperative localization, and full-duplex transceivers. A list of practical issues and consequent open research challenges of the proposed L&S systems is also provided.
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| 14. |
- Ge, Yu, 1995, et al.
(author)
-
Doppler Exploitation in Bistatic mmWave Radio SLAM
- 2022
-
In: GLOBECOM - IEEE Global Telecommunications Conference. ; , s. 6463-6468
-
Conference paper (peer-reviewed)abstract
- Networks in 5G and beyond utilize millimeter wave (mmWave) radio signals, large bandwidths, and large antenna arrays, which bring opportunities in jointly localizing the user equipment and mapping the propagation environment, termed as simultaneous localization and mapping (SLAM). Existing approaches mainly rely on delays and angles, and ignore the Doppler, although it contains geometric information. In this paper, we study the benefits of exploiting Doppler in SLAM through deriving the posterior Cram´er-Rao bounds (PCRBs) and formulating the extended Kalman-Poisson multi-Bernoulli sequential filtering solution with Doppler as one of the involved measurements. Both theoretical PCRB analysis and simulation results demonstrate the efficacy of utilizing Doppler.
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| 15. |
- Ge, Yu, 1995, et al.
(author)
-
Experimental Validation of Single Base Station 5G mm Wave Positioning: Initial Findings
- 2022
-
In: 2022 25th International Conference on Information Fusion, FUSION 2022. - Piscataway : IEEE.
-
Conference paper (peer-reviewed)abstract
- 5G cellular networks can utilize millimeter wave signals, and support large bandwidths and large antenna arrays, which provide more geometric-based signals and higher delay and angle resolutions. These merits bring new opportunities in positioning the user with limited infrastructure through the use of combined angle and delay information. However, there are many practical challenges to overcome, in order to have a functioning single base station 5G mmWave positioning system. In this paper, we describe a deployed single base station mmWave positioning system, and provide an example of the measurement data. Furthermore, we perform measurement validation on a limited measurement data set by performing base station localization. Additional evaluations performed on simulation model data provide guidelines on the required size of the data set and receiver antenna configuration, which will be implemented in upcoming measurements.
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| 16. |
- Ge, Yu, 1995, et al.
(author)
-
Experimental Validation of Single BS 5G mmWave Positioning and Mapping for Intelligent Transport
- 2024
-
In: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359. ; In Press
-
Journal article (peer-reviewed)abstract
- Positioning with 5G signals generally requires connection to several base stations (BSs), which makes positioning more demanding in terms of infrastructure than communications. To address this issue, there have been several theoretical studies on single BS positioning, leveraging high-resolution angle and delay estimation and multipath exploitation possibilities at mmWave frequencies. This paper presents the first realistic experimental validation of such studies, involving a commercial 5G mmWave BS with a customized beam sweep procedure and a user equipment (UE) development kit mounted on a test vehicle. We present the relevant signal models, and signal processing methods, and validate these based on data collected in an outdoor science park environment. Our results indicate that positioning is possible, but the performance is limited by the knowledge of the position and orientation of the infrastructure and the multipath visibility and diversity
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| 17. |
- Ghazalian, Reza, et al.
(author)
-
Bi-Static Sensing for Near-Field RIS Localization
- 2022
-
In: GLOBECOM - IEEE Global Telecommunications Conference. ; , s. 6457-6462
-
Conference paper (peer-reviewed)abstract
- We address the localization of a reconfigurable intelligent surface (RIS) for a single-input single-output multicarrier system using bi-static sensing between a fixed transmitter and a fixed receiver. Due to the deployment of RISs with a large dimension, near-field (NF) scenarios are likely to occur, especially for indoor applications, and are the focus of this work. We first derive the Cram´er-Rao bounds (CRBs) on the estimation error of the RIS position and orientation and the time of arrival (TOA) for the path transmitter-RIS-receiver. We propose a multi-stage low-complexity estimator for RIS localization purposes. In this proposed estimator, we first perform a line search to estimate the TOA. Then, we use the far-field approximation of the NF signal model to implicitly estimate the angle of arrival and the angle of departure at the RIS center. Finally, the RIS position and orientation estimate are refined via a quasi-Newton method. Simulation results reveal that the proposed estimator can attain the CRBs. We also investigate the effects of several influential factors on the accuracy of the proposed estimator like the RIS size, transmitted power, system bandwidth, and RIS position and orientation.
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| 18. |
- Ghazalian, Reza, et al.
(author)
-
Joint User Localization and Location Calibration of A Hybrid Reconfigurable Intelligent Surface
- 2024
-
In: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359. ; 73:1, s. 1435-1440
-
Journal article (peer-reviewed)abstract
- The recent research in the emerging technology of reconfigurable intelligent surfaces (RISs) has identified its high potential for localization and sensing. However, to accurately localize a user placed in the area of influence of an RIS, the RIS location needs to be known a priori and its phase profile is required to be optimized for localization. In this paper, we study the problem of the joint localization of a hybrid RIS (HRIS) and a user, considering that the former is equipped with a single reception radio-frequency (RF) chain enabling simultaneous tunable reflections and sensing via power splitting. Focusing on the downlink of a multi-antenna base station, we present a multi-stage approach for the estimation of the HRIS position and orientation as well as the user position. Our simulation results, including comparisons with the Cramér-Rao lower bounds, demonstrate the efficiency of the proposed localization approach, while showcasing that there exists an optimal HRIS power splitting ratio for the desired multi-parameter estimation problem.
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| 19. |
- Ghazalian, Reza, et al.
(author)
-
RIS Position and Orientation Estimation via Multi-Carrier Transmissions and Multiple Receivers
- 2023
-
In: IEEE International Conference on Communications. - 1550-3607. ; 2023-May, s. 2915-2920
-
Conference paper (peer-reviewed)abstract
- Reconfigurable intelligent surfaces (RISs) are considered as an enabling technology for the upcoming sixth generation of wireless systems, exhibiting significant potential for radio localization and sensing. An RIS is usually treated as an anchor point with known position and orientation when deployed to offer user localization. However, it can also be attached to a user to enable its localization in a semi-passive manner. In this paper, we consider a static user equipped with an RIS and study the RIS localization problem (i.e., joint three-dimensional position and orientation estimation), when operating in a system comprising a single-antenna transmitter and multiple synchronized single-antenna receivers with known locations. We present a multi-stage estimator using time-of-arrival and spatial frequency measurements, and derive the Cramér-Rao lower bounds for the estimated parameters to validate the estimator's performance. Our simulation results demonstrate the efficiency of the proposed RIS state estimation approach under various system operation parameters.
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| 20. |
- Kim, Hyowon, 1987, et al.
(author)
-
RIS-Aided Monostatic Sensing and Object Detection with Single and Double Bounce Multipath
- 2023
-
In: 2023 IEEE International Conference on Communications Workshops: Sustainable Communications for Renaissance, ICC Workshops 2023. ; , s. 1883-1889
-
Conference paper (peer-reviewed)abstract
- We propose a framework for monostatic sensing by a user equipment (UE), aided by a reconfigurable intelligent surface (RIS) in environments with single- and double-bounce signal propagation. We design appropriate UE-side precoding and combining, to facilitate signal separation. We derive the adaptive detection probabilities of the resolvable signals, based on the geometric channel parameters of the links. Then, we estimate the passive objects using both the double-bounce signals via passive RIS (i.e., RIS-sensing) and the single-bounce multipath direct to the objects (i.e., non-RIS-sensing), based on a mapping filter. Finally, we provide numerical results to demonstrate that effective sensing can be achieved through the proposed framework.
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| 21. |
- Kim, Hyowon, et al.
(author)
-
RIS-Enabled and Access-Point-Free Simultaneous Radio Localization and Mapping
- 2024
-
In: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; 23:4, s. 3344-3360
-
Journal article (peer-reviewed)abstract
- In the upcoming sixth generation (6G) of wireless communication systems, reconfigurable intelligent surfaces (RISs) are regarded as one of the promising technological enablers, which can provide programmable signal propagation. Therefore, simultaneous radio localization and mapping (SLAM) with RISs appears as an emerging research direction within the 6G ecosystem. In this paper, we propose a novel framework of RIS-enabled radio SLAM for wireless operation without the intervention of access points (APs). We first design the RIS phase profiles leveraging prior information for the user equipment (UE), such that they uniformly illuminate the angular sector where the UE is probabilistically located. Second, we modify the marginal Poisson multi-Bernoulli SLAM filter and estimate the UE state and landmarks, which enables efficient mapping of the radio propagation environment. Third, we derive the theoretical Cramér-Rao lower bounds on the estimators for the channel parameters and the UE state. We finally evaluate the performance of the proposed method under scenarios with a limited number of transmissions, taking into account the channel coherence time. Our results demonstrate that the RIS enables solving the radio SLAM problem with zero APs, and that the consideration of the Doppler shift contributes to improving the UE speed estimates.
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| 22. |
- Li, Kai, et al.
(author)
-
Self‐Densification of Highly Mesoporous Wood Structure into a Strong and Transparent Film
- 2020
-
In: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095.
-
Journal article (peer-reviewed)abstract
- In the native wood cell wall, cellulose microfibrils are highly aligned and organized in the secondary cell wall. A new preparation strategy is developed to achieve individualization of cellulose microfibrils within the wood cell wall structure without introducing mechanical disintegration. The resulting mesoporous wood structure has a high specific surface area of 197 m2 g−1 when prepared by freeze‐drying using liquid nitrogen, and 249 m2 g−1 by supercritical drying. These values are 5 to 7 times higher than conventional delignified wood (36 m2 g−1) dried by supercritical drying. Such highly mesoporous structure with individualized cellulose microfibrils maintaining their natural alignment and organization can be processed into aerogels with high porosity and high compressive strength. In addition, a strong film with a tensile strength of 449.1 ± 21.8 MPa and a Young's modulus of 51.1 ± 5.2 GPa along the fiber direction is obtained simply by air drying owing to the self‐densification of cellulose microfibrils driven by the elastocapillary forces upon water evaporation. The self‐densified film also shows high optical transmittance (80%) and high optical haze (70%) with interesting biaxial light scattering behavior owing to the natural alignment of cellulose microfibrils.
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| 23. |
- Liu, Xing, et al.
(author)
-
Constrained Wrapped Least Squares: A Tool for High Accuracy GNSS Attitude Determination
- 2022
-
In: IEEE Transactions on Instrumentation and Measurement. - 1557-9662 .- 0018-9456. ; 71
-
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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| 24. |
- Lu, Yi, et al.
(author)
-
Joint RIS Calibration and Multi-User Positioning
- 2022
-
In: IEEE Vehicular Technology Conference. - 1550-2252. ; 2022-September
-
Conference paper (peer-reviewed)abstract
- Reconfigurable intelligent surfaces (RISs) are expected to be a key component enabling the mobile network evolution towards a flexible and intelligent 6G wireless platform. In most of the research works so far, RIS has been treated as a passive base station (BS) with a known state, in terms of its location and orientation, to boost the communication and/or terminal positioning performance. However, such performance gains cannot be guaranteed anymore when the RIS state is not perfectly known. In this paper, by taking the RIS state uncertainty into account, we formulate and study the performance of a joint RIS calibration and user positioning (JrCUP) scheme. From the Fisher information perspective, we formulate the JrCUP problem in a network-centric single-input multiple-output (SIMO) scenario with a single BS, and derive the analytical lower bound for the states of both user and RIS. We also demonstrate the geometric impact of different user locations on the JrCUP performance while also characterizing the performance under different RIS sizes. Finally, the study is extended to a multiuser scenario, shown to further improve the state estimation performance.
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| 25. |
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| 26. |
- Wang, Shennan, Dr. 1992-, et al.
(author)
-
Strong, transparent, and thermochromic composite hydrogel from wood derived highly mesoporous cellulose network and PNIPAM
- 2022
-
In: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 154, s. 106757-
-
Journal article (peer-reviewed)abstract
- Composite polymer hydrogels are of significant interests for high optical transparency and mechanical performance. In this work, a strong and transparent composite hydrogel is developed from a highly mesoporous cellulose network prepared from wood via top-down delignification followed by TEMPO-mediated oxidation and in situ polymerization of PNIPAM. Individualization of cellulose microfibrils inside the wood cell wall is critical for the fabrication of free-standing composite hydrogel with high water content of 94.9 wt% and high optical transmittance of 85.8% with anisotropic light scattering behavior. The composite hydrogel also showed anisotropic mechanical properties with a tensile strength, Young's modulus and toughness of 317 kPa, 5.4 MPa, and 39.2 kJ m- 3 in axial direction, and 152 kPa, 0.31 MPa and 57.1 kJ m- 3 in the transverse direction, respectively. It also showed thermochromic behavior, i.e., reversibly changing between transparent and brightly white by a temperature change between 25 and 40 degrees C, demonstrating great potential for optical applications.
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| 27. |
- Widmer, Joerg, et al.
(author)
-
Enablers toward 6G positioning and sensing
- 2024
-
In: Positioning and Location-based Analytics in 5G and Beyond. - 9781119911463 ; , s. 75-97
-
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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| 28. |
- Wymeersch, Henk, 1976, et al.
(author)
-
6G Radio Requirements to Support Integrated Communication, Localization, and Sensing
- 2022
-
In: 2022 Joint European Conference on Networks and Communications and 6G Summit, EuCNC/6G Summit 2022. ; , s. 463-469
-
Conference paper (peer-reviewed)abstract
- 6G will be characterized by extreme use cases, not only for communication, but also for localization, and sensing. The use cases can be directly mapped to requirements in terms of standard key performance indicators (KPIs), such as data rate, latency, or localization accuracy. The goal of this paper is to go one step further and map these standard KPIs to requirements on signals, on hardware architectures, and on deployments. Based on this, system solutions can be identified that can support several use cases simultaneously. Since there are several ways to meet the KPIs, there is no unique solution and preferable configurations will be discussed.
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| 29. |
- Zhang, Xin, et al.
(author)
-
High-Performance All-Small-Molecule Organic Solar Cells Enabled by Regio-Isomerization of Noncovalently Conformational Locks
- 2022
-
In: Advanced Functional Materials. - : WILEY-V C H VERLAG GMBH. - 1616-301X .- 1616-3028. ; 32:19
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Journal article (peer-reviewed)abstract
- The power conversion efficiencies (PCEs) of organic solar cells (OSCs) have surpassed 19% thanks to the innovation of polymer donors and molecular acceptors. However, the batch-to-batch variations in polymer materials are detrimental to the reproducibility of the device performance. In comparison, small-molecule donors (SMDs) possess some unique advantages, such as well-defined molecular weights, easy purification, and excellent batch-to-batch repeatability. Herein, a pair of regioisomeric SMDs (BT-O1 and BT-O2) has been synthesized with alkoxy groups as S center dot center dot center dot O noncovalently conformational locks (NoCLs) at the inner and outer position, respectively. Theoretical and experimental results reveal that the regioisomeric effect has a significant influence on the light-harvest ability, energy levels, molecular geometries, internal reorganization energy, and packing behaviors for the two SMDs. As a result, BT-O2-based binary device shows an impressive PCE of 13.99%, much higher than that of BT-O1 based one (4.07%), due to the better-aligned energy level, more balanced charge transport, less charge recombination, lower energy loss, and more favorable phase separation. Furthermore, the fullerene derivative PC71BM is introduced into BT-O2:H3 as the third component to achieve a notable PCE of 15.34% (certified 14.6%). Overall, this work reveals that NoCLs is a promising strategy to achieve high-performance SMDs for all-small-molecule OSCs.
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| 30. |
- 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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| 31. |
- 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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| 32. |
- 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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| 33. |
- 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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| 34. |
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