Multi-Array 5G V2V Relative Positioning: Performance Bounds

We study the performance bounds of vehicle-to-vehicle (V2V) relative positioning for vehicles with multiple antenna arrays. The Cram\'{e}r-Rao bound for the estimation of the relative position and the orientation of the Tx vehicle is derived, when angle of arrival (AOA) measurements with or without time-difference of arrival (TDOA) measurements are used. In addition, geometrically intuitive expressions for the corresponding Fisher information are provided. The derived bounds are numerically evaluated for different carrier frequencies, bandwidths and array configurations under different V2V scenarios, i.e. overtaking and platooning. The significance of the AOA and TDOA measurements for position estimation is investigated. The achievable positioning accuracy is then compared with the present requirements of the 3rd Generation Partnership Project (3GPP) 5G New Radio (NR) vehicle-to-everything (V2X) standardization

Non-uniform array design for robust LoS MIMO via convex optimization

The array design problem of multiple-input multiple-output (MIMO) systems in a line-of-sight (LoS) transmit environment is examined. As uniform array configurations at the transmitter (Tx) and receiver (Rx) are optimal at specific transmit distances only, they lead to reduced spectral efficiency over a range of transmit distances. To that end, the joint design of nonuniform Tx and Rx arrays towards maximizing the minimum capacity of a LoS MIMO system across a range of transmit distances is investigated in this paper. By introducing convex relaxation, the joint Tx and Rx array design is cast as a convex optimization problem, which is solved in a iterative manner. In addition, we also implement a local search to obtain a refined solution that achieves an improved performance. It is shown that the non-uniform configurations designed with our proposed approach outperform uniform and non-uniform array designs of the literature in terms of capacity and/or complexity.Comment: 6 pages, 5 figures, submitted for publication at IEEE PIMRC202

Cooperative localization with angular measurements and posterior linearization

The application of cooperative localization in vehicular networks is attractive to improve accuracy and coverage of the positioning. Conventional distance measurements between vehicles are limited by the need for synchronization and provide no heading information of the vehicle. To address this, we present a cooperative localization algorithm using posterior linearization belief propagation (PLBP) utilizing angle-of-arrival (AoA)-only measurements. Simulation results show that both directional and positional root mean squared error (RMSE) of vehicles can be decreased significantly and converge to a low value in a few iterations. Furthermore, the influence of parameters for the vehicular network, such as vehicle density, communication radius, prior uncertainty, and AoA measurements noise, is analyzed

5G Downlink Multi-Beam Signal Design for LOS Positioning

In this work, we study optimal transmit strategies for minimizing the positioning error bound in a line-of-sight scenario, under different levels of prior knowledge of the channel parameters. For the case of perfect prior knowledge, we prove that two beams are optimal, and determine their beam directions and optimal power allocation. For the imperfect prior knowledge case, we compute the optimal power allocation among the beams of a codebook for two different robustness-related objectives, namely average or maximum squared position error bound minimization. Our numerical results show that our low-complexity approach can outperform existing methods that entail higher signaling and computational overhead.Comment: accepted for publication at IEEE GLOBECOM 201

Power Allocation and Parameter Estimation for Multipath-based 5G Positioning

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 Cram\ue9r-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

Power Allocation and Parameter Estimation for Multipath-based 5G Positioning

We consider a single-anchor multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) 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 the reference signals based on a set of fixed beams. In this work, we develop strategies for the power allocation among the beams aiming to minimize the expected Cram\'er-Rao lower bound (CRLB) for Rx positioning. Additional constraints on the design are included to ensure that the line-of-sight (LOS) path is detected with high probability. Furthermore, the effect of clock asynchronism on the resulting allocation strategies is also studied. We also propose a gridless compressed sensing-based position estimation algorithm, which exploits the information on the clock offset provided by non-line-of-sight paths, and show that it is asymptotically efficient.Comment: 30 pages, 6 figures, submitted to IEEE Transactions on Wireless Communication

Cooperative Localization with Angular Measurements and Posterior Linearization

The application of cooperative localization in vehicular networks is attractive to improve accuracy and coverage. Conventional distance measurements between vehicles are limited by the need for synchronization and provide no heading information of the vehicle. To address this, we present a cooperative localization algorithm using posterior linearization belief propagation (PLBP) utilizing angle-of-arrival (AoA)-only measurements. Simulation results show that both directional and positional root mean squared error (RMSE) of vehicles can be decreased significantly and converge to a low value in a few iterations. Furthermore, the influence of parameters for the vehicular network, such as vehicle density, communication radius, prior uncertainty and AoA measurements noise, is analyzed.Comment: Submitted for possible publication to an IEEE conferenc

Radiation from a phased array of dielectric loaded parallel-plate waveguides

68 σ.Στην παρούσα εργασία μελετώνται τα χαρακτηριστικά ακτινοβολίας μιας φασικής στοιχειοκεραίας που αποτελείται από σχισμές σε ένα αγώγιμο επίπεδο, τροφοδοτούμενες από κυματοδηγούς παράλληλων πλακών με διηλεκτρικό φορτίο. Το πρόβλημα συνοριακών τιμών διατυπώνεται μέσω ενός συστήματος συζευγμένων ιδιόμορφων ολοκληρωτικών εξισώσεων, με αγνώστους τα μαγνητικά ρεύματα πάνω στις σχισμές. Για την επίλυση του συστήματος εφαρμόζεται μια εκθετικά συγκλίνουσα εκδοχή της μεθόδου Nyström. Η απομόνωση της ιδιομορφίας του πυρήνα, μέσω της έκφρασης του ως άθροισμα μιας αναλυτικής και μιας ιδιόμορφης συνάρτησης, καθώς και η επιτάχυνση της σύγκλισης της σειράς που εμφανίζεται στην ολοκληρωτική εξίσωση, είναι εξαιρετικής σημασίας για την επιτυχία της μεθόδου. Η εκθετική σύγκλιση του αλγορίθμου καθιστά εφικτή τη λήψη αποτελεσμάτων εξαιρετικής ακρίβειας με μικρή τάξη συστήματος. Σημαντικό πλεονέκτημα της μεθόδου είναι το χαμηλό υπολογιστικό της κόστος, λόγω της μικρής τάξης του συστήματος και της αποφυγής της ανάγκης αριθμητικών ολοκληρώσεων κατά τον υπολογισμό των στοιχείων της μήτρας του συστήματος, σε αντίθεση με ό,τι συμβαίνει σε διάφορες υλοποιήσεις της μεθόδου των ροπών. Το πλεονέκτημα αυτό έχει ιδιαίτερη σημασία για στοιχειοκεραίες πολλών στοιχείων. Η ορθότητα της μεθόδου επιβεβαιώνεται μέσω της αρχής διατήρησης της ισχύος, της ισότητας των διαγραμμάτων εκπομπής και λήψης και με πλήθος συγκρίσεων με άλλες εργασίες. Μέσα από διάφορα αριθμητικά παραδείγματα δείχνουμε ότι με κατάλληλη επιλογή των παραμέτρων της διάταξης μπορεί να επιτευχθεί πολύ υψηλή απόδοση προσαρμογής, ακόμα και για πολύ μικρό εύρος της σχισμής.The subject of this work is the investigation of the radiation characteristics of a finite phased array of slots, fed by dielectrically loaded parallel-plate waveguides, and radiating through a common ground plane. The boundary-value problem is formulated in terms of a system of coupled singular integral equations, with unknowns the magnetic currents on the slots. The system is solved in the framework of an exponentially converging Nystrӧm method taking full account both of the singularities of the kernels and the singularities at the edges (edge conditions). The isolation of the singularity of the kernel, by writing it as the sum of an analytic part and a singular part, is of paramount importance for the successful application of the method. The exponential convergence of the algorithm allows us to obtain highly accurate results with low matrix sizes. This is a very important advantage of the presented method (especially useful in studying large arrays) which, in conjunction with the obviation of the need for numerical integrations in evaluating the matrix elements, leads to low computational cost. This stands in contrast with many well-known implementations of conventional MoM, which require the evaluation of several inner product integrals. The correctness of the implementation is confirmed by testing the principle of power conservation, the equality of the transmission and reception patterns, and by comparing our results with those of previously published works. Numerical examples are presented which show how, by properly selecting the physical and geometrical parameters of the structure, a very high matching efficiency can be achieved even for very narrow slot width.Αναστάσιος Θ. Κακκαβά