TAP: A High-Precision Network Timing Method over Air Interface Based on Physical-Layer Signals

Abstract

Absolute time synchronization (timing) is a constant demand in various fields. There are many timing techniques at present. They are mainly based on dedicated equipments such as GNSS or specific protocols such as NTP, PTP, SIB16, etc. Different timing methods are applied according to the scenario, cost and demands for timing accuracy. Recently, the timing demands for some wireless scenarios have become increasingly urgent, like power IoT and auto-driving. However, due to the instability and complexity of radio link, the current methods can hardly meet the demands of high-precision and low cost simultaneously in mobile network. Here we propose a timing method over air interface based on physical layer signals (TAP). Periodic physical layer signals in both downlink and uplink channel are considered to reduce the impact of radio link instability on timing. We implemented the proposed method on an open source LTE software defined radio platform named OpenAirInterface and conducted a series of tests. Our tests prove that TAP can provide microsecond-level timing over the air interface, and it is more stable and precise than PTP. Further simulation shows that using TAP in 5G NR can improve the timing accuracy.