Research on Mobile Network High-precision Absolute Time Synchronization based on TAP

TL;DR

This work tackles the challenge of sub-$1\,\mathrm{\mu s}$ absolute time synchronization in mobile networks by proposing TAP, a timing method that leverages air-interface PHY signals for precise downlink delay estimation and time signaling. It develops an end-to-end TAP clock model, decomposes sources of timing error into $e_{src}$, $e_{Gr}$, $e_{inGr}$, $e_{air}$, and $t_0$, and uses Allan variance-based optimization to guide design choices. The authors implement a TAP-based 5G prototype with a BS delivering SIB9 time information and UEs running a deterministic-latency timing module; field tests show timing accuracy better than $200\,\mathrm{ns}$ with high reliability and substantial improvement over NTP/PTP and original TAP. The work also discusses 5G-TSN compatibility, terminal coordination, and security considerations, while noting remaining challenges in defending against replay/forwarding attacks. Overall, TAP demonstrates strong potential for time-sensitive industrial applications in GNSS-denied environments, though security enhancements and multi-source coordination are needed for industrial deployment.

Abstract

With the development of mobile communication and industrial internet technologies, the demand for robust absolute time synchronization based on network for diverse scenarios is significantly growing. TAP is a novel network timing method that aims to achieve sub-microsecond synchronization over air interface. This paper investigates the improvement and end-to-end realization of TAP. This paper first analyzes the effectiveness and deficiencies of TAP by establishing an equivalent clock model which evaluates TAP from timing error composition and allan variance. Second, this paper proposes a detailed base station and terminal design and the corresponding improvement of TAP. Both hardware compensation and protocol software design are taken into account so as to minimize timing error and system cost while maximizing compatibility with 3GPP. Finally, this paper presents a TAP end-to-end 5G prototype system developed based on software defined radio base station and COTS baseband module. The field test results show that the proposed scheme effectively solves the problems of TAP in application and robustly achieves 200ns level timing accuracy in various situations. The average accuracy with long observations can reach 1 nanosecond. It is 2$\sim$3 orders of magnitude better than common network timing methods, including NTP, PTP and the original TAP.

Figures (9)

• Figure 1: The delay compensation of PTP.
• Figure 2: The principle and scenario of TAP compared with NTP and PTP.
• Figure 3: The proposed equivalent TAP-clock model.
• Figure 4: Design of TAP implementation for BS and UEs.
• Figure 5: Workflow of the state machine in timing module.