In this paper, we describe a global distributed solution that enables the simultaneous performance of time synchronization and positioning in ultra-wideband (UWB) ad hoc networks. On the one hand, the proposed synchronization scheme basically relies on cooperative two-way-ranging/time-of-arrival transactions and a diffusion algorithm that ensures the convergence of clock parameters to average reference values in each node. Although the described solution is generic at first sight, its sensitivity to time-of-arrival accuracy imposes the choice of an impulse-radio ultra-wideband physical layer in the very context. On the other hand, a distributed algorithm coupled with this synchronization scheme mitigates the impact of non-line-of-sight ranging errors on positioning accuracy without any additional protocol hook. More particularly, the realistic UWB ranging error models we use take into account UWB channel effects, as well as detection noises and relative clock drifts. Then, it is demonstrated that a cooperative and distributed maximization of the log-likelihood of range estimates can reduce the uncertainty on estimated positions in comparison with classical distributed weighted least squares approaches. Finally, the proposed distributed maximum log-likelihood algorithm proves to preserve a reasonable level of complexity in each node by approximating asynchronously the positive gradient direction of the log-likelihood function. For both distributed synchronization and positioning algorithms, simulation results are provided to illustrate the relevance of such a solution.

Absolute positioning of vehicles is based on Global Navigation Satellite Systems (GNSSs) combined with on-board sensors and high-resolution maps. In cooperative intelligent transportation systems, the positioning performance can be augmented by means of vehicular networks that enable vehicles to share location-related information. This paper presents an implicit cooperative positioning (ICP) algorithm that exploits the Vehicle-to-Vehicle (V2V) connectivity in an innovative manner, avoiding the use of explicit V2V measurements such as ranging. In the ICP approach, vehicles jointly localize non-cooperative physical features (such as people, traffic lights, or inactive cars) in the surrounding areas, and use them as common noisy reference points to refine their location estimates. Information on sensed features are fused through V2V links by a consensus procedure, nested within a message passing algorithm, to enhance the vehicle localization accuracy. As positioning does not rely on explicit ranging information between vehicles, the proposed ICP method is amenable to implementation with off-the-shelf vehicular communication hardware. The localization algorithm is validated in different traffic scenarios, including a crossroad area with heterogeneous conditions in terms of feature density and V2V connectivity, and a real urban area by using Simulation of Urban MObility (SUMO) for traffic data generation. Performance results show that the proposed ICP method can significantly improve the vehicle location accuracy compared to the stand-alone GNSS, especially in harsh environments, such as in urban canyons, where the GNSS signal is highly degraded or denied.

, The Ultra WideBand (UWB) radiolocation functionality usually relies on the ability to perform a very precise estimation of the Time Of Flight (TOF). Unfortunately, in spite of the fine performances demonstrated by the UWB systems, indoor dense multipath channels may alter the precision of the range estimate from severe blockage situations. This paper addresses the general problem of Non Line Of Sight (NLOS) errors in the specific context of UWB range estimation. Typical ranging errors due to the NLOS propagation are exhibited by deriving experimental results from real indoor VNA measurements into realistic statistical error models. Index Terms, Ultra Wideband (UWB), Ranging, NLOS, Propagation Channel, Indoor environments

Reconfigurable intelligent surfaces (RISs) have tremendous potential for both communication and localization. While communication benefits are now well understood, the breakthrough nature of the technology may well lie in its capability to provide and support localization capabilities. We present an overview of RIS-enabled localization scenarios, considering various numbers of RISs, single- or multi-antenna base stations, narrowband or wideband transmissions, and near- and far-field operations. Based on this overview, we also highlight key research directions and open challenges specific to RIS-enabled localization and sensing.

This paper presents an analytical comparison of three modulation schemes applied to two low data rate (LDR) ultra wideband (UWB) non-coherent receivers, namely the quadratic detector and the differential detector. In order to evaluate properly the impact of UWB multipath channels on performance, new statistical models on energy collection are proposed, and then taken into account in the analytical expressions of the error probability. Finally, critical system parameters, such as the optimal integration time for energy collection or major synchronization tolerances (coarse synchronization granularity, clock constraints) are derived from the obtained results.