Abstract
Synchronization is a long-standing challenge in modern large-scale distributed systems, and newly deployed systems such as 5G and modern netted radars require more extensive synchronization. As the number of distributed stations increasing, new synchronization solution with much effort on extensibility is highly expected. In this paper we first analyze the requirements on extensibility of fiber-based sync systems, and then propose a phase-stabilized side-branch radio-over-fiber (RoF) link, which fully satisfies the extensibility requirements. The extensible side-branch link can be constructed at any intermediate point along the main link, without any reconfiguration at the central station, which is especially feasible when adding extra stations in system capacity expansion. The main link phase shift is first stabilized by tuning the optical carrier wavelength, while another phase-locked-loop constructed at the starting point of the branch link stabilizes the phase shift from the central station to the end of branch link, by phase locking two phase-varying signals. Moreover, the phase-stable side branch is inherently extensible to multiple frequency signals, which can be used in receivers requiring multiple local oscillators (LOs). Two frequency signals are simultaneously disseminated to the end of branch link in the experiment, with frequency stability optimization of two orders of magnitude on both LOs achieved. The proposed stable side-branch RoF link shows the potential of constructing a highly-extensible frequency dissemination network for the synchronization in modern distributed systems.
Highlights
F REQUENCY synchronization is the key enabling technology in modern large-scale distributed information systems and applications like time-sensitive networking for 5G fronthaul and backhaul [1]–[4], indoor/outdoor positioning [5], [6], carrierManuscript received July 27, 2021; revised September 13, 2021; accepted September 15, 2021
The crucial point is that when an extra remote station is added, the whole link structure of the bus or ring-form system has to be modified to be compatible with the extra sites (Fig. 1(b)), whereas one does not have to revise the structure of the already–constructed synchronization link when adopting the side-branch topology (Fig. 1(c))
We present a phase-stabilized side-branch radioover-fiber (RoF) link that simultaneously disseminates different frequencies to the end of the branch link, which satisfies both of the above requirements on synchronization extensibility
Summary
F REQUENCY synchronization is the key enabling technology in modern large-scale distributed information systems and applications like time-sensitive networking for 5G fronthaul and backhaul [1]–[4], indoor/outdoor positioning [5], [6], carrier. The crucial point is that when an extra remote station is added (which is common in system upgrading and capacity expansion), the whole link structure of the bus or ring-form system has to be modified to be compatible with the extra sites (Fig. 1(b)), whereas one does not have to revise the structure of the already–constructed synchronization link when adopting the side-branch topology (Fig. 1(c)). This feature makes the branch-link synchronization option especially convenient for dealing with the ever-increasing number of distributed stations. Two LOs at different frequencies are coherently transferred to the remote end of the branch link in the experiment, and the frequency stability of the recovered LOs can be optimized by two orders of magnitude
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