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

Mike Koivisto*, Mário Costa, Janis Werner*, Kari Heiska, Jukka Talvitie*, Kari Leppänen, Visa Koivunen and Mikko Valkama*
* Department of Electronics and Communications Engineering, Tampere University of Technology, Finland
Huawei Technologies Oy (Finland) Co., Ltd
Department of Signal Processing and Acoustics, Aalto University, Finland

Abstract - In this article, we address the prospects and key enabling technologies for high-efficiency device localization and tracking in fifth generation (5G) radio access networks. Building on the premises of ultra-dense networks as well as on the adoption of multicarrier waveforms and antenna arrays in the access nodes (ANs), we first develop extended Kalman filter (EKF) based solutions for efficient joint estimation and tracking of the time of arrival (ToA) and direction of arrival (DoA) of the user nodes (UNs) using the uplink (UL) reference signals. Then, a second EKF stage is proposed in order to fuse the individual DoA/ToA estimates from multiple ANs into a UN location estimate. The cascaded EKFs proposed in this article also take into account the unavoidable 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 further generalized to yet more 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 in realistic 5G network setup, building on the METIS project based Madrid map model together with complete ray tracing based propagation modeling, are reported. 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, despite the realistic assumptions related to clock offsets and potentially even under unsynchronized network elements.

The article is currently under review in IEEE Transactions on Wireless Communications

Available in arXiv.org (Download PDF)

Media files:

Video 1: User node position and network clock offset tracking example of the proposed joint DoA/ToA Pos&Sync EKF in comparison to the classical DoA-only EKF. Furthermore, 99% confidence ellipses are used for both methods in the video above for the sake of clarity. The video also shows the accuracy of the obtained access node clock offset estimates relative to a reference access node.


Download: MP4.

Video 2: User node position and clock offset tracking example of the proposed joint DoA/ToA Pos&Sync EKF in comparison to the joint DoA/ToA Pos&Clock EKF when the measurement estimates from one LoS access node (AN) are used for positioning and clock offset estimation puposes. For the joint DoA/ToA Pos&Sync EKF, the ANs within the network are assumed to be mutually unsynchronized whereas the synchronized ANs are assumed in the case of the joint DoA/ToA Pos&Clock EKF. Note that the classical DoA-only EKF cannot be adopted in this case, since only the measurements of a single LoS-AN are processed at a time and the height of the user is unknown. This is one substantial benefit of the proposed joint DoA/ToA processing methods, compared to the earlier DoA-only method. Furthermore, 95% confidence ellipses are used for both methods in the video above. The video also shows the accuracy of the obtained access node clock offset estimates relative to a reference access node.


Download: MP4.