Joint Device Positioning and Clock Synchronization in 5G Ultra-Dense Networks (1604.03322v3)

Abstract: In this article, we address the prospects and key enabling technologies for highly efficient and accurate device positioning and tracking in 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 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 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-6GHz frequencies, despite the realistic assumptions related to clock offsets and potentially even under unsynchronized network elements.

• The paper proposes a cascaded Extended Kalman Filter (EKF) approach for jointly estimating device position and clock offset in 5G ultra-dense networks.
• This two-stage methodology first estimates Time of Arrival (ToA) and Direction of Arrival (DoA) at individual access nodes, then fuses them centrally for a unified position and clock estimate.
• The research demonstrates achieving sub-meter positioning accuracy and robust nanosecond-level clock synchronization, even in networks where access nodes lack mutual synchronization.

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

The analyzed paper explores advanced techniques for precise device positioning and clock synchronization within the framework of 5G ultra-dense networks (UDNs). The authors articulate a methodological approach leveraging extended Kalman filters (EKFs) to co-estimate device position and time synchronization from uplink (UL) reference signals, a crucial step toward achieving sub-meter positioning accuracy as envisioned for 5G deployments. Below, I provide a detailed exposition of the methodologies, results, and implications addressed in the research.

The research addresses key challenges in 5G UDNs, emphasizing the necessity of centimeter-level accuracy for emerging applications such as autonomous vehicles and dense Internet of Things (IoT) ecosystems. Building on the anticipated characteristics of 5G, like extensive use of multi-antenna base stations (BSs) and multicarrier waveforms, the paper proposes a novel cascaded EKF architecture. This approach decomposes the positioning and synchronization problem into two stages: local estimation of Time of Arrival (ToA) and Direction of Arrival (DoA) at individual access nodes (ANs), followed by centralized fusion into a unified position and clock offset estimate.

Significant advancements introduced include:

1. Efficient DoA/ToA Tracking: The paper devises computationally efficient EKF-based mechanisms to track ToA and DoA at the ANs using UL pilots. The adoption of a continuous white noise acceleration (CWNA) model is pivotal in achieving accurate angle and timing measurements across dynamic scenarios.
2. Position and Clock Synchronization: Utilizing the tracked measurements from multiple ANs, a secondary EKF phase aggregates the DoA/ToA data into a robust estimate of user equipment (UE) position and clock offset. This architecture not only enhances positional accuracy but also allows for synchronized network time dissemination, accommodating mutual temporal offsets among ANs.
3. Handling Unsynchronized Networks: The methodology extends to unsynchronized networks, addressing real-world situations where ANs lack mutual synchronization. By considering unsynchronized AN clocks as unscented parameters, the proposed EKF design remains applicable and effective even under such challenging conditions.

The paper underscores multiple numerical evaluations, implemented within a realistic simulation environment derived from the METIS Madrid grid model. Evaluations reveal substantial improvements compared to traditional methods, consistently achieving sub-meter accuracy under varied conditions, regardless of network synchronization levels. Key results indicate:

• Positioning accuracies consistently reaching below 0.5 meters with adequate pilot subcarrier allocation.
• Robust clock offset estimation on the order of nanoseconds, demonstrating the system's potential to support stringent synchronization requirements essential for 5G operation.

The implications of this research are twofold: Practically, it provides a feasible framework for high-accuracy localization in 5G networks, crucial for applications demanding precision such as augmented reality and vehicular communication systems. Theoretically, it advances comprehension of joint estimation systems, fostering avenues for further innovation in adaptive filtering and network synchronization techniques.

Future directions suggested by the research include extending the proposed approach to three-dimensional positioning and incorporating the results into mobility management and beamforming techniques within 5G networks, potentially leading to enhanced network operation efficiency and spectrum utilization.

This paper lays a solid foundation for understanding and implementing advanced joint positioning and synchronization systems in 5G technologies, clearly aligning with the emerging standards and application requirements defining next-generation communication systems.