Toward High Accuracy Positioning in 5G via Passive Synchronization of Base Stations Using Thermally-Insensitive Optical Fibers

Wenwu Zhu,Gregory T Jasion,Meng Ding,Radan Slavik,Seyed Reza Sandoghchi,David J Richardson,Thomas D Bradley,Francesco Poletti,Eric R Numkam Fokoua,Yong Chen,Marco N Petrovich,Mingshan Zhao

doi:10.1109/access.2019.2934982

Abstract

Positioning accuracy in 5G networks (achieved via techniques based on observed time difference of arrival (OTDoA)) is limited by the synchronization error between the cellular base stations. Here, we demonstrate that these base stations can be synchronized entirely passively through the use of emerging forms of hollow core fiber (HCF) as the data transmission medium in the 5G front-haul network. This is possible due to the excellent thermal stability of HCF which allows the synchronization error among cellular base stations to be reduced significantly as compared to systems based on standard single mode fibers. Reducing this synchronization error is necessary to meet the strict timing requirements envisaged for 5G networks. We analyze the polarization mode dispersion, chromatic dispersion, and thermal stability of the HCF and give suggestions on how to use the HCF to balance overall radio over fiber (RoF) link performance in 5G front-haul networks. In a proof of concept experiment we show that HCF links enable the positioning error (calculated with the OTDoA method) to be reduced down to the centimeter level even when subject to tens of degrees Celsius temperature variations. This represents a 20-fold improvement over standard single mode fiber systems which would require active compensation schemes to achieve similar levels of time synchronization accuracy.

Highlights

The fifth generation mobile networks (5G) will provide greater bandwidth, 10 times larger data rates per user, 100 times more connected users, ultra-low latency, and high accuracy geographical positioning as a new service [2]
hollow core fiber (HCF)-based radio over fiber (RoF) links allow for centimeter-level positioning accuracy using Observed Time Difference of Arrival (OTDoA), even when the temperature varies by as much as ±30 ◦C or when the polarization of the light propagating through the fiber changes
We evaluated the thermal delay at two wavelengths, 1553 and 1611 nm; 1553 nm is a wavelength near the center of the hollow core photonic bandgap fiber (HC-PBGF) transmission window, while 1611 nm is the wavelength at which our HC-PBGF is fully thermally insensitive [34]

Summary

INTRODUCTION

The fifth generation mobile networks (5G) will provide (as compared to 4G) greater bandwidth, 10 times larger data rates per user, 100 times more connected users, ultra-low latency, and high accuracy geographical positioning as a new service [2]. We investigate how the 5G synchronization and positioning accuracy can be achieved in a simple, passive, and efficient way using new emerging optical fibers These fibers, known as Hollow Core Fibers (HCF), offer excellent thermal stability of propagation delay [34], allowing for a drastic (∼20 times) reduction of the synchronization error between different RRHs. As we show here, HCF-based RoF links allow for centimeter-level positioning accuracy using OTDoA, even when the temperature varies by as much as ±30 ◦C or when the polarization of the light propagating through the fiber changes. This level of accuracy will allow for the synchronization of RRHs in an entirely passive way and meet the time error criterion proposed by the current standardization efforts and be even future-proof should stricter standards be adopted

THERMAL SENSITIVITY OF OPTICAL FIBERS

CONCLUSION