# On the QKD Integration in Converged Fiber/Wireless Topologies for Secured, Low-Latency 5G/B5G Fronthaul

^{*}

## Abstract

**:**

## Featured Application

**The results of this paper provide a reference for the future design of a quantum-secured 5G/B5G optical edge layer, assisted by novel integration strategies of Quantum Key Distribution (QKD) technological blocks across the deployed fiber/wireless fronthaul topologies.**

## Abstract

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Dark Fiber Topology

^{−6}ns

^{−1}and a quantum efficiency of 10% were assumed. These values correspond to the typical performance of the widely used InGaAs modules photon counters for single-photon detection at telecom wavelengths [39]. The high DCR that these modules exhibit can significantly limit the transmission distance where no secure key can be distilled anymore. In order to overcome this limitation, we also considered the use of Silicon (Si) SPAD modules in Bob stations, offering significant advantages such as operation at room temperatures without the need of complex cooling mechanisms, higher values of quantum efficiency with very low timing jitter and much lower noise and dark current. To take advantage of the above benefits at telecom wavelengths where Si-based photon counters are virtually blind, an upconversion module is required to translate the wavelength of the incoming telecom single-photons into the visible range. In our study, we adopted at Bob stations an upconversion-assisted single-photon detection scheme based on an integrated periodically poled lithium niobite (ppLN) waveguide pumped by long wavelengths at 2 μm [40]. Based on the reported results in [40], a total efficiency of 10% and a dark count rate (DCR) of 6 × 10

^{−8}ns

^{−1}were assumed. Finally, the optical loss of the internal components at Bob station was fixed at 2.65 dB.

^{−60}. More specifically, in [44], the ASP for a confidentiality attack was compared to the maximum amount of data that can be processed. In order to keep the ASP as low as possible, i.e., at 2

^{−60}, the maximum data that can be transmitted is about 0.3887 terabytes [44]. By assuming a 10 Gbps packetized data flow over eCPRI transport layer, a key generation rate of at least

^{−60}, which corresponds to 256 bits/0.83 bps = 5.14 min refresh time.

#### 2.2. Shared Fiber Topology

#### 2.3. Fiber-Wireless Topology

## 3. Results

#### 3.1. Performance Evaluation of Dark Fiber Topology

#### 3.2. Performance Evaluation of Shared Fiber Topology

#### 3.3. Performance Evaluation of Fiber-Wireless Topology

## 4. Discussion

## 5. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## Appendix A. Maximum Fiber Fronthaul Distance Corresponding to Round-Trip Latency Barrier

## References

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**Figure 1.**Quantum-secured evolved Common Public Radio Interface (eCPRI) transport layer interconnecting the Baseband Unit (BBU) and the 5G terminal nodes. A dedicated fiber link is used for quantum key exchange between Alice and Bob stations.

**Figure 2.**Quantum-secured multi-user topology with a centralized Alice station and multiple Bob stations located at the 5G terminal nodes. A passive optical distribution network based on 1:N splitter stage implements the P2MP topology with dedicated fiber segments for classical and quantum layer respectively.

**Figure 3.**Quantum-secured eCPRI transport layer interconnecting the BBU and the 5G terminal nodes. One Standard Single-Mode Fiber (SSMF) link is used for both packetized classical data flow from the BBU node and the 5G Terminal Node (and vice versa) and for the photon transmission from Alice to Bob.

**Figure 4.**Quantum-secured multi-user topology with a centralized Alice station and multiple Bob stations located at the 5G terminal nodes. A passive optical distribution network based on 1:N splitter stage implements the P2MP topology with shared single-mode fiber segments for classical and quantum layer.

**Figure 5.**Fi-Wi topology supporting the secured P2MP distribution using mmWave nodes to interconnect several 5G terminal nodes which are physically connected with mmWave mesh clients.

**Figure 6.**Secure Key Rate (SKR) as a function of fiber length, for the P2P dark fiber link, for both InGaAs and upconverted CMOS-based Quantum Key Distribution (QKD) setups. The horizontal lines with different styles correspond to the Advanced Encryption Standard (AES) limits for key refresh times equal to 5.14 min (0.83 bps), 1 min (4.3 bps) and 1.4 s (183 bps), respectively.

**Figure 7.**SKR as a function of fiber length, for the P2MP dark fiber link serving N = 4, 16 or 64 users, for (

**a**) InGaAs; and (

**b**) upconverted CMOS-based QKD setups. The horizontal lines with different styles correspond to the AES limits for key refresh times equal to 5.14 min (0.83 bps), 1 min (4.3 bps) and 1.4 s (183 bps), respectively.

**Figure 8.**SKR as a function of fiber length, for the P2P shared fiber link, for both InGaAs and upconverted CMOS-based QKD setups, where: (

**a**) the quantum channel at 1550 nm is multiplexed with the classical signals at 1310 nm (downlink) and at 1490 nm (uplink); (

**b**) the quantum channel at 1550 nm is multiplexed with the classical signals at 1310 nm for both downlink and uplink. The horizontal lines with different styles correspond to the AES limits for key refresh times equal to 5.14 min (0.83 bps), 1 min (4.3 bps) and 1.4 s (183 bps), respectively.

**Figure 9.**SKR as a function of fiber length, for the P2P shared fiber link, for both InGaAs and upgraded (i.e., with total efficiency equal to 20%) upconverted CMOS-based QKD setups, where: (

**a**) the quantum channel at 1550 nm is multiplexed with the classical signals at 1310 nm (downlink) and at 1490 nm (uplink); (

**b**) the quantum channel at 1550 nm is multiplexed with the classical signals at 1310 nm for both downlink and uplink. The horizontal lines with different styles correspond to the AES limits for key refresh times equal to 5.14 min (0.83 bps), 1 min (4.3 bps) and 1.4 s (183 bps), respectively.

**Figure 10.**SKR as a function of fiber length, for the P2MP shared fiber link serving N = 4, 16 or 64 users, where the quantum channel at 1550 nm is multiplexed with the classical signals at 1310 nm for both downlink and uplink, for (

**a**) InGaAs; and (

**b**) upconverted CMOS-based QKD setups. The horizontal lines with different styles correspond to the AES limits for key refresh times equal to 5.14 min (0.83 bps), 1 min (4.3 bps) and 1.4 s (183 bps), respectively.

**Figure 11.**${\mathrm{QBER}}_{\mathrm{Raman}}$ and ${\mathrm{QBER}}_{\mathrm{dark}}$ for 1, 4, 16 and 64 terminal users, at the maximum propagation distance (i.e., at the point where SKR approaches zero) for each case, for the configuration where the quantum channel at 1550 nm is multiplexed with the classical signals at 1310 nm for both downlink and uplink, for (

**a**) InGaAs; and (

**b**) upconverted CMOS-based QKD setups.

**Figure 12.**SKR as a function of fiber length, for the Fi-Wi topology serving N = 16 or 64 users, where the quantum channel at 1550 nm is multiplexed with the classical signals at 1310 nm for both downlink and uplink, for (

**a**) InGaAs; and (

**b**) upconverted CMOS-based QKD setups. The horizontal lines with different styles correspond to the AES limits for key refresh times equal to 5.14 min (3.7 bps), 1 min (19.2 bps) and 1.4 s (823 bps), respectively.

**Figure 13.**SKR as a function of fiber length, for the P2MP shared fiber link (blue line) and for the Fi-Wi topology (orange line) serving N = 64, where the quantum channel at 1550 nm is multiplexed with the classical signals at 1310 nm for both downlink and uplink, for (

**a**) InGaAs; and (

**b**) upconverted CMOS-based QKD setups. The horizontal lines with different styles correspond to the AES limits for different key refresh times: 0.83 bps corresponds to 5.14 min refresh time for the data encryption for P2MP; 3.7 bps corresponds to 5.14 min refresh time for the data encryption and for the controlled functions for Fi-Wi; 183 bps corresponds to 1.4 s refresh time for the data encryption for P2MP; and 823 bps corresponds to 1.4 s refresh time for the data encryption and for the controlled functions for Fi-Wi.

**Figure 14.**SKR as a function of fiber length, for the P2MP shared fiber link (blue line) and for the Fi-Wi topology (orange line) serving N = 64, where the quantum channel at 1550 nm is multiplexed with the classical signals at 1310 nm for both downlink and uplink, for (

**a**) InGaAs; and (

**b**) upconverted CMOS-based QKD setups. The horizontal lines with different styles correspond to the AES limits for different key refresh times: 0.83 bps corresponds to 5.14 min refresh time for the data encryption for P2MP; 3.7 bps corresponds to 5.14 min refresh time for the data encryption and for the controlled functions for Fi-Wi; 183 bps corresponds to 1.4 s refresh time for the data encryption for P2MP; and 198 bps corresponds to 1.4 s and 1 min refresh times for the data encryption and the controlled functions, respectively, for Fi-Wi.

**Table A1.**Latency components considered for our study, based on the available parameters within [28].

Latency Components | |
---|---|

Round-Trip Delay Components | Typical Time |

Propagation fiber delay | 10 μs/km |

Radio Frequency (RF) overhead | 40 μs |

eCPRI overhead | 10 μs |

BBU | 2700 μs |

Fronthaul equipment processing delay | 4 μs |

One-way encryption/decryption | 34 μs |

QKD post-processing | 11 μs |

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Zavitsanos, D.; Ntanos, A.; Giannoulis, G.; Avramopoulos, H. On the QKD Integration in Converged Fiber/Wireless Topologies for Secured, Low-Latency 5G/B5G Fronthaul. *Appl. Sci.* **2020**, *10*, 5193.
https://doi.org/10.3390/app10155193

**AMA Style**

Zavitsanos D, Ntanos A, Giannoulis G, Avramopoulos H. On the QKD Integration in Converged Fiber/Wireless Topologies for Secured, Low-Latency 5G/B5G Fronthaul. *Applied Sciences*. 2020; 10(15):5193.
https://doi.org/10.3390/app10155193

**Chicago/Turabian Style**

Zavitsanos, Dimitris, Argiris Ntanos, Giannis Giannoulis, and Hercules Avramopoulos. 2020. "On the QKD Integration in Converged Fiber/Wireless Topologies for Secured, Low-Latency 5G/B5G Fronthaul" *Applied Sciences* 10, no. 15: 5193.
https://doi.org/10.3390/app10155193