A research contribution focusing on the Quantum Key Distribution (QKD)-enabled solutions assisting in the security framework of an optical 5G fronthaul segment is presented. We thoroughly investigate the integration of a BB84-QKD link, operating at telecom band, delivering quantum keys for the Advanced Encryption Standard (AES)-256 encryption engines of a packetized fronthaul layer interconnecting multiple 5G terminal nodes. Secure Key Rate calculations are studied for both dedicated and shared fiber configurations to identify the attack surface of AES-encrypted data links in each deployment scenario. We also propose a converged fiber-wireless scenario, exploiting a mesh networking extension operated by mmWave wireless links. In addition to the quantum layer performance, emphasis is placed on the strict requirements of 5G-oriented optical edge segments, such as the latency and the availability of quantum keys. We find that for the dark fiber case, secret keys can be distilled at fiber lengths much longer than the maximum fiber fronthaul distance corresponding to the round-trip latency barrier, for both P2P and P2MP topologies. On the contrary, the inelastic Raman scattering makes the simultaneous transmission of quantum and classical signals much more challenging. To counteract the contamination of noise photons, a resilient classical/QKD coexistence scheme is adopted. Motivated by the recent advancements in quantum technology roadmap, our analysis aims to introduce the QKD blocks as a pillar of the quantum-safe security framework of the 5G/B5G-oriented fronthaul infrastructure.

Quantum key distribution (QKD) has gained a lot of attention over the past few years, but the implementation of quantum security applications is still challenging to accomplish with the current technology. Towards a global-scale quantum-secured network, satellite communications seem to be a promising candidate to successfully support the quantum communication infrastructure (QCI) by delivering quantum keys to optical ground terminals. In this research, we examined the feasibility of satellite-to-ground QKD under daylight and nighttime conditions using the decoy-state BB84 QKD protocol. We evaluated its performance on a hypothetical constellation with 10 satellites in sun-synchronous Low Earth Orbit (LEO) that are assumed to communicate over a period of one year with three optical ground stations (OGSs) located in Greece. By taking into account the atmospheric effects of turbulence as well as the background solar radiance, we showed that positive normalized secure key rates (SKRs) up to $3.9\times {10}^{-4}$ (bps/pulse) can be obtained, which implies that satellite-to-ground QKD can be feasible for various conditions, under realistic assumptions in an existing infrastructure.

We present a real-world Gigabit Passive Optical Network (GPON)-based Fiber to the Home (FTTH) network serving up to 32 users, installed in COSMOTE laboratories in Athens. The deployment relies on the use of fiber optics and GPON telecom equipment which are identical to those found in the currently deployed FTTH infrastructure. We describe real-life network designs that correspond to specific installations considered in Athens urban metropolitan area. We propose a practical upstream Quantum Access Network (QAN) over the installed FTTH network, relied on a centralized quantum receiver (Bob) station located at the operator's Central Office, which exploits the Time-Division Multiplexing (TDM) framing technique to receive single-photons from multiple independent quantum transmitters (Alice) located at users premises. This integration scheme is characterized by performing a series of noise measurements at single-photon level to evaluate the potential of the coexistence of classical/quantum links on the same fiber cores. The noise count rates are found to follow the Raman noise profile for specified values of effective Raman cross-sections of downstream and upstream GPON data channels. Subsequently, the experimental results are exploited to evaluate the performance of the widely-used Coherent One Way (COW) Quantum Key Distribution (QKD) protocol. The presented simulation results for the quantum layer suggest the feasibility of our integration scheme for short feeder fiber segments. Finally, the dependance of the Secure Key Rate (SKR) on the network capacity is also discussed.