A Tutorial on 5G NR V2X Communications Garcia, Mario H. Castaneda; Molina-Galan, Alejandro; Boban, Mate ...
IEEE Communications surveys and tutorials,
01/2021, Letnik:
23, Številka:
3
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The Third Generation Partnership Project (3GPP) has recently published its Release 16 that includes the first Vehicle-to-Everything (V2X) standard based on the 5G New Radio (NR) air interface. 5G NR ...V2X introduces advanced functionalities on top of the 5G NR air interface to support connected and automated driving use cases with stringent requirements. This article presents an in-depth tutorial of the 3GPP Release 16 5G NR V2X standard for V2X communications, with a particular focus on the sidelink, since it is the most significant part of 5G NR V2X. The main part of the paper is an in-depth treatment of the key aspects of 5G NR V2X: the physical layer, the resource allocation, the quality of service management, the enhancements introduced to the Uu interface and the mobility management for V2N (Vehicle to Network) communications, as well as the co-existence mechanisms between 5G NR V2X and LTE V2X. We also review the use cases, the system architecture, and describe the evaluation methodology and simulation assumptions for 5G NR V2X. Finally, we provide an outlook on possible 5G NR V2X enhancements, including those identified within Release 17.
We consider a single-anchor multiple-input multiple-output orthogonal frequency-division multiplexing system with imperfectly synchronized transmitter (Tx) and receiver (Rx) clocks, where the Rx ...estimates its position based on the received reference signals. The Tx, having (imperfect) prior knowledge about the Rx location and the surrounding geometry, transmits reference signals based on a set of fixed beams. We develop strategies for the power allocation among the beams aiming to minimize the expected Cramér-Rao lower bound for Rx positioning. Additional constraints on the design are included to make the optimized power allocation robust to uncertainty on the line-of-sight (LOS) path direction. Furthermore, the effect of clock asynchronism on the proposed allocation strategies is studied. Our evaluation results show that, for non-negligible synchronization error, it is optimal to allocate a large fraction of the available power for the illumination of the non-LOS (NLOS) paths, which help resolve the clock offset. In addition, the complexity reduction achieved by our proposed suboptimal approach incurs only a small performance degradation. We also propose an off-grid compressed sensing-based position estimation algorithm, which exploits the information on the clock offset provided by NLOS paths, and show that it is asymptotically efficient.
Performance Limits of Single-Anchor Millimeter-Wave Positioning Kakkavas, Anastasios; Castaneda Garcia, Mario H.; Stirling-Gallacher, Richard A. ...
IEEE transactions on wireless communications,
2019-Nov., 2019-11-00, 20191101, Letnik:
18, Številka:
11
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The fundamental limits of single-anchor multi-antenna positioning are investigated. Exploiting the structure of the multiple input-multiple output-orthogonal frequency division multiplexing ...(MIMO-OFDM) channel at millimeter-wave frequencies, we present geometrically intuitive asymptotic expressions for the Fisher information on position, orientation and velocity for large bandwidth and number of antennas. The effects of synchronization errors and mobility are studied and it is shown that non-line-of-sight (NLOS) paths can be used to estimate the synchronization error and drastically improve the positioning performance. We also show that, in the presence of line-of-sight (LOS), mobility has a small impact on the achievable positioning accuracy, but in the NLOS-only scenario it can significantly improve the achievable performance, depending on the variance of the synchronization error. Finally, considering a communication system with device-specific transmission and reception constraints, we compare the positioning accuracy between the downlink and the uplink and show that they are equivalent under the same received signal-to-noise ratio (SNR).
Tilting in UCA-based LoS MIMO systems Palaiologos, Michail; Garcia, Mario H. Casta neda; Stirling-Gallacher, Richard A. ...
IEEE wireless communications letters,
09/2023, Letnik:
12, Številka:
9
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We consider a 4×4 line-of-sight multiple-input multiple-output (LoS MIMO) system with uniform circular arrays (UCAs) at the transmitter (Tx) and receiver (Rx). First, we show that the optimum design ...of non-tilted UCAs of four antennas can be generalized to the design of optimum elliptical arrays (EAs). Afterwards, we investigate the effect of tilting the Tx or Rx UCA over different transmit distances. Although it is commonly considered that tilting a UCA at a fixed transmit distance is detrimental, we show that a tilted UCA can be optimum, in terms of capacity, at other transmit distances. We showcase that this can be explained based on the optimum design of EAs of four antennas. Specifically, we provide a valid approximation for the optimum transmit distance when a UCA is tilted by a given angle or, equivalently, for the optimum tilting angle of a UCA at a certain transmit distance. The use of the approximations is validated with simulations, also for the design of UCAs with more than 4 antennas.
The availability of abundant spectrum makes millimeter wave (mm-wave) a prominent candidate technology for the next generation of cellular networks. Highly directional transmission is essential for ...the exploitation of mm-wave bands to compensate for high propagation loss. The directional transmission, nevertheless, necessitates a specific design for mm-wave initial cell discovery, as conventional omni-directional broadcasting may fail in delivering cell discovery information. To address this issue, this paper provides an analytical framework for mm-wave beamformed cell discovery based on an information-theoretic approach. Design options are compared considering four fundamental and representative broadcasting schemes to evaluate discovery latency and overhead. The schemes are then simulated under realistic system parameters. Analytical and simulation results reveal four key findings: 1) analog/hybrid beamforming performs as well as digital beamforming in terms of cell discovery latency; 2) single-beam exhaustive scan optimizes the latency and, however, leads to the overhead penalty; 3) multi-beam simultaneous scan can significantly reduce the overhead and provide the flexibility to achieve tradeoff between the latency and the overhead; and 4) the latency and the overhead are relatively insensitive to extreme low block error rates.
Robust Non-uniform LoS MIMO Array Design Palaiologos, Michail; Castaneda Garcia, Mario H.; Kakkavas, Anastasios ...
IEEE transactions on wireless communications,
2024
Journal Article
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The array design of multiple-input multiple-output (MIMO) systems in a line-of-sight (LoS) environment is investigated. Properly designed uniform array configurations at the transmitter (Tx) and ...receiver (Rx) can extract maximum spatial multiplexing gain only for a fixed transmit distance between the Tx and Rx arrays and for a fixed orientation of the arrays. However, such designs suffer from significant capacity variations when the position and/or orientation of the arrays is modified. To alleviate this, we examine robust, joint design of non-uniform Tx and Rx arrays, where the minimum capacity over a range of varying array positions and orientations is maximized. First, we show that, by leveraging convex relaxation, the joint Tx and Rx array design problem can be solved with convex optimization techniques in an iterative manner. Moreover, an alternative design method based on dynamic programming (DP) is proposed, which is shown to outperform the convex optimization approach. As the DP algorithm is quite demanding in terms of computational complexity, a modified DP-based algorithm is also proposed, where the Tx and Rx arrays are designed to have the same configuration. It is shown that the resulting non-uniform array configurations with the proposed designs outperform both uniform and non-uniform array designs of the literature in terms of the system robustness.
Radio based positioning of a user equipment (UE) based on deep learning (DL) methods using channel state information (CSI) fingerprints have shown promising results. DL models are able to capture ...complex properties embedded in the CSI about a particular environment and map UE's CSI to the UE's position. However, the CSI fingerprints and the DL models trained on such fingerprints are highly dependent on a particular propagation environment, which generally limits the transfer of knowledge of the DL models from one environment to another. In this paper, we propose a DL model consisting of two parts: the first part aims to learn environment independent features while the second part combines those features depending on the particular environment. To improve transfer learning, we propose a meta learning scheme for training the first part over multiple environments. We show that for positioning in a new environment, initializing a DL model with the meta learned environment independent function achieves higher UE positioning accuracy compared to regular transfer learning from one environment to the new environment, or compared to training the DL model from scratch with only fingerprints from the new environment. Our proposed scheme is able to create an environment independent function which can embed knowledge from multiple environments and more effectively learn from a new environment.
Deep learning (DL) methods have been recently proposed for user equipment (UE) localization in wireless communication networks, based on the channel state information (CSI) between a UE and multiple ...base stations (BSs) in the uplink. With the CSI from the available BSs, UE localization can be performed in different ways. On the one hand, a single neural network (NN) can be trained for the UE localization by considering the CSI from all the available BSs as one overall fingerprint of the user's location. On the other hand, the CSI at each BS can be used to obtain an estimate of the UE's position with a separate NN at each BS, and then the position estimates of all BSs are combined to obtain an overall estimate of the UE position. In this work, we show that UE localization with the latter approach can achieve a higher positioning accuracy. We propose to consider the uncertainty in the UE localization at each BS, such that overall UE's position is determined by combining the position estimates of the different BSs based on the uncertainty at each BS. With this approach, a more reliable position estimate can be obtained in case of variations in the channel.
Design of Single User Limited Feedback Systems Castaneda Garcia, Mario H.; Mezghani, Amine; Nossek, Josef A.
IEEE transactions on wireless communications,
2014-Oct., 2014-10-00, 20141001, Letnik:
13, Številka:
10
Journal Article
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The available channel state information (CSI) in a limited feedback system like the frequency division duplex (FDD) downlink is not perfect since it is subject to estimation, quantization and ...feedback errors, and in addition, can be outdated. Despite the fact that the capacity of limited feedback systems is unknown in general, we derive a novel lower bound on the capacity of single user limited feedback systems with imperfect CSI. Based on this bound, we propose the design of an FDD system by finding the optimum training and number of feedback bits. To this end we also take the FDD uplink into account, since practical FDD systems represent two-way systems. We also provide closed-form approximations for the optimum downlink training, uplink training and number of feedback bits which basically maximize lower bounds on the FDD downlink and uplink capacity with imperfect CSI.
Position Information From Reflecting Surfaces Kakkavas, Anastasios; Castaneda Garcia, Mario H.; Seco-Granados, Gonzalo ...
IEEE wireless communications letters,
06/2021, Letnik:
10, Številka:
6
Journal Article
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In the context of positioning an agent with a single-anchor, this contribution focuses on the Fisher information about the position, orientation and clock offset of the agent provided by ...single-bounce reflections. The availability of prior knowledge of the agent's environment is taken into account via a prior distribution of the position of virtual anchors, and the rank, intensity and direction of provided information is studied. We show that when no prior knowledge is available, single-bounce reflections offer position information in the direction parallel to the reflecting surface, irrespective of the agent's and anchor's locations. We provide a geometrically intuitive explanation of the results and present numerical examples demonstrating their potential implications.
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