High Rate CV-QKD Secured Mobile WDM Fronthaul for Dense 5G Radio Networks

TL;DR

This paper demonstrates a high-rate, secure CV-QKD system integrated into 5G fronthaul links, achieving low excess noise, coexistence with classical signals, and secure key rates suitable for dense 5G networks.

Contribution

It introduces a novel coherent CV-QKD transmission method with spectral tailoring and pilot tone multiplexing for high-speed 5G fronthaul links, ensuring secure key rates under practical conditions.

Findings

Achieved secure key rates of 18 and 10 Mb/s under strict security assumptions.

Demonstrated coexistence with 11 classical signals in the C-band.

Maintained low excess noise of 0.1% to 0.5% over 13.2 km fiber link.

Abstract

A coherent transmission methodology for a continuous-variable quantum key distribution (CV-QKD) system based on quantum-heterodyne measurement through a coherent intradyne receiver is experimentally demonstrated in the framework of 5G mobile fronthaul links. Continuous optical carrier synchronization is obtained through training information, which is multiplexing to the quantum signal as pilot tone in both, frequency and polarization. Spectral tailoring by means of optical carrier suppression and single-sideband modulation is adopted to simultaneously mitigate crosstalk into the quantum channel and self-interference for the pilot tone, thus allowing for a high signal-to-noise ratio for this training signal. Frequency offset correction and optical phase estimation for the free-running local oscillator of the receiver is accurately performed and guarantees low-noise quantum signal reception at high symbol rates of 250 MHz and 500 MHz with additional Nyquist pulse shaping. A low excess noise in the order of 0.1% to 0.5% of shot-noise units is obtained for fiber-based transmission over a fronthaul link reach of 13.2 km. Moreover, co-existence with 11 carrier-grade classical signals is experimentally investigated. Joint signal transmission in the C-band of both, quantum signal and classical signals, is successfully demonstrated. Secure-key rates of 18 and 10 Mb/s are obtained under strict security assumptions, where Eve has control of the receiver noise, for a dark and a lit fiber link, respectively. Moreover, rates of 85 and 72 Mb/s are resulting for a trusted receiver scenario. These secure-key rates are well addressing the requirements for time-shared CV-QKD system in densified 5G radio access networks with cloud-based processing.