Joint Device Positioning and Clock Synchronization in 5G Ultra-Dense Networks

Abstract

In this article, we address the prospects and key enabling technologies for highly efficient and accurate device positioning and tracking in fifth generation (5G) radio access networks. Building on the premises of ultra-dense networks (UDNs) as well as on the adoption of multicarrier waveforms and antenna arrays in the access nodes (ANs), we first formulate extended Kalman filter (EKF)-based solutions for computationally efficient joint estimation and tracking of the time of arrival (ToA) and direction of arrival (DoA) of the user nodes (UNs) using uplink (UL) reference signals. Then, a second EKF stage is proposed in order to fuse the individual DoA/ToA estimates from one or several ANs into a UN position estimate. Since all the processing takes place at the network side, the computing complexity and energy consumption at the UN side are kept to a minimum. The cascaded EKFs proposed in this article also take into account the unavoidable relative clock offsets between UNs and ANs, such that reliable clock synchronization of the access-link is obtained as a valuable by-product. The proposed cascaded EKF scheme is then revised and extended to more general and challenging scenarios where not only the UNs have clock offsets against the network time, but also the ANs themselves are not mutually synchronized in time. Finally, comprehensive performance evaluations of the proposed solutions on a realistic 5G network setup, building on the METIS project based outdoor Madrid map model together with complete ray tracing based propagation modeling, are provided. The obtained results clearly demonstrate that by using the developed methods, sub-meter scale positioning and tracking accuracy of moving devices is indeed technically feasible in future 5G radio access networks operating at sub-6 GHz frequencies, despite the realistic assumptions related to clock offsets and potentially even under unsynchronized network elements.

How to make the propagation time through an optical fiber fully insensitive to temperature variations

“…), which is undesirable in a host of applications such as precise time and frequency transfer, or applications requiring highly accurate time synchronization of (data) signals. Further such applications are anticipated in the (near) future given for example the demanding timing requirements of autonomous manufacturing (e.g., synchronization of robots working together) and future 5G networks [3].…”

5G mmWave Positioning for Vehicular Networks

“…Preliminary studies have shown that errors on the order of a few centimeters can be achieved using a bandwidth of 100 MHz [2]. However, in order to achieve extreme ranging precision, other technological factors have to be considered, such as the imperfection of the internal clock-oscillator [3]. Not only the delay estimation accuracy increases with the bandwidth, but also the resolution improves.…”

“…In dense networks, devices can connect to a plurality of access nodes, which provides higher data rates with less energy consumption, under the condition that interference and mobility problems can be solved. If these challenges can be addressed and if access points can somehow announce their coordinates, ultra-dense networks can enable ultra-accurate positioning [3]. The reason is that positioning accuracy depends on not only the quality of the individual measurements (for which large bandwidths and many antennas are beneficial), but also the diversity and number of reference stations.…”

“…In fact, determination of the position and orientation using only one access point may be possible. In [3], tracking was performed using extended Kalman filters in two stages: a local tracker at each base station for the AOA and TOA, followed by a global tracker of the user position. The same work also accounted for time-varying clock parameters, and through high-fidelity simulation, demonstrated localization and tracking with uncertainties of less than 1 m in the 3.5 GHz band.…”

Distributed GNSS-based Time Synchronization and applications

“…As it is shown in [20], Root Mean Square Errors (RMSEs) of coordinates' estimates is considerably dependent on the synchronism of the access nodes. The time servers places in the direct proximity of small cell would reduce time offsets, hence, improving the precision of positioning.…”