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1.	Hong, Yuanyuan, et al. (author) A Multi-Floor Arrayed Waveguide Grating Based Architecture with Grid Topology for Datacenter Networks 2020 In: IEEE Access. - 2169-3536 .- 2169-3536. ; 8, s. 107134-107145 Journal article (peer-reviewed)abstract This paper proposes a grid topology based passive optical interconnect (POI) architecture that is composed of multiple floors of arrayed waveguide grating routers (AWGRs) to offer high connectivity and scalability for datacenter networks. In the proposed POI signal only needs to pass one AWGR, and thus can avoid the crosstalk accumulation and cascaded filtering effects, which exist in many existing POI architectures based on cascaded AWGRs. Meanwhile, due to high connectivity, the proposed grid topology based POI also has the potential advantage of high reliability. Simulation results validate the network performance. With a proper node degree, the proposed grid topology can achieve acceptable blocking probability. Besides, steady performance is kept when the number of floors increases, indicating good scalability of the proposed POI.
2.	Yaghoubi, Forough, 1988-, et al. (author) Techno-economic and business feasibility analysis of 5G transport networks 2019 In: Optical and Wireless Convergence for 5G Networks. - : Wiley. ; , s. 273-295 Book chapter (other academic/artistic)abstract This chapter introduces a techno-economic framework that provides a complete market analysis of the various business actors for any type of mobile access network deployments. It presents a case study where the proposed business feasibility framework is applied. The chapter presents a comprehensive techno-economic framework for estimating the total cost of ownership (TCO) of a backhaul network segment as well as for analyzing the business viability of a given wireless network deployment. It focuses on two backhaul technologies: microwave and fiber. The chapter addresses the framework proposed specifically only the backhaul segment, but it is general enough to also be applied to the other 5G transport solutions. It also presents the TCO module used in the proposed framework. The module covers both the Capital Expenditure and the Operational Expenditure aspects of the backhaul segment. The backhaul network is responsible for aggregating the users' traffic from the wireless access to the metro/backbone segment of the network.
3.	Ahmed, Jawwad, et al. (author) Efficient Inter-Thread Scheduling Scheme for Long-Reach Passive Optical Networks 2013 In: IEEE Communications Magazine. - 0163-6804 .- 1558-1896. ; 51:2, s. S35-S43 Journal article (peer-reviewed)abstract These days there is a clear trend toward extending the reach of passive optical networks to cover large geographical areas, which enables reduction of the number of central offices and hence has the potential of cost saving in network operation. On the other hand, this reach extension necessitates the design of efficient dynamic bandwidth allocation schemes in order to tackle performance degradation caused by the increased propagation delay in long reach PONs. Among many existing approaches, the multi-thread-based DBA scheme where several bandwidth allocation processes are performed in parallel is considered one of the most effective options to improve network performance in LRPONs. We have found that without proper intercommunication between the overlapped threads, multi-thread DBA may lose efficiency and even perform worse than the conventional single-thread algorithm. With this in mind, this article reviews different inter-thread scheduling schemes for LR-PONs, and proposes a novel approach of integrating the key ideas of the existing ones. Extensive simulation results confirm that our proposed scheme can significantly improve DBA performance for LR-PONs under a variety of scenarios with consideration of different values of network load and reach.
4.	Chen, Biao, et al. (author) Add/drop multiplexing and TDM signal transmission in an optical CDMA ring network 2007 In: Journal of Optical Networking. - 1536-5379. ; 6:8, s. 969-974 Journal article (peer-reviewed)
5.	Chen, Biao, et al. (author) Efficient and fine scheduling algorithm for bandwidth allocation in Ethernet passive optical networks 2006 In: IEEE Journal of Selected Topics in Quantum Electronics. - 1077-260X .- 1558-4542. ; 12:4, s. 653-660 Journal article (peer-reviewed)abstract A novel fine scheduling algorithm is introduced for upstream bandwidth allocation in an Ethernet-based passive optical network. This scheduling algorithm consists of an inter optical network unit (ONU) scheduler at the optical line terminal (OLT) and an intra-ONU scheduler at each ONU. In the inter-ONU scheduling, a novel GATE/REPORT approach is introduced to eliminate the unused remainders without transmission delay and maximize the utilization of bandwidth. Our novel intra-ONU scheduler gives fair bandwidth allocation to the queues of different priorities for each user in a hierarchical and decentralized way. Numerical results have shown that our overall scheduling algorithm can fulfill various requirements of delay and throughput for the transmission of multimedia traffic for each end user..
6.	Chen, Jiajia, et al. (author) A novel algorithm for intra-ONU bandwidth allocation in ethernet passive optical networks 2005 In: IEEE Communications Letters. - 1089-7798 .- 1558-2558. ; 9:9, s. 850-852 Journal article (peer-reviewed)abstract A novel decentralized algorithm is introduced for the intra-ONU bandwidth allocation in an Ethernet Passive Optical Network (EPON). The algorithm is of low computational complexity, and can guarantee both the priority and fairness of the differentiated services. Simulation results are presented and compared with those of two existing bandwidth allocation algorithms.
7.	Chen, Jiajia, et al. (author) A novel hierarchical algorithm for intra-ONU scheduling in an ethernet passive optical network 2005 In: Network Architectures, Management, and Applications III. - : SPIE. ; , s. W220-W220 Conference paper (peer-reviewed)abstract The quality of service (QoS) requirements of end users and services are totally different, and thus the multi-oriented (user-oriented and service-oriented) scheduling for access networks based on a remote scheduling system especially for EPONs is desired to replace the single-oriented (user-oriented or service-oriented) scheduling. In this paper we introduce a novel hierarchical algorithm of intra-ONU scheduling for multi-oriented QoS, which can guarantee both the priority of the differentiated services and the fairness of the different users. Numerical results have shown that our overall scheduling algorithm can fulfill various requirements of delay and throughput for the transmission of multimedia traffic for each end user.
8.	Chen, Jiajia, et al. (author) A Novel Joint Scheduling Algorithm for Multiple Services in 10G EPON 2008 In: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 7137 Journal article (other academic/artistic)abstract In this paper, we propose and evaluate a novel joint scheduling algorithm for multiple services which can support differentiated services and bandwidth allocation with global priority of different traffic such as Triple-play: voice, video and Internet services. Simulation results show that for the higher priority traffic better delay and jitter performance can be achieved compared with the lower priority traffic.
9.	Chen, Jiajia, et al. (author) Characterization of Longitudinal Thermal Conductivity of Graphene Film 2021 In: 2021 22nd International Conference on Electronic Packaging Technology, ICEPT 2021. Conference paper (peer-reviewed)abstract The chase of high performance by chip manufacturers has greatly increased the power consumption of integrated circuits, which brings great challenges to the heat dissipation of electronics systems. It has also slowed down following up of the Moore's Law, and it is expected to hit the wall soon [1]. Graphene film with high in-plane thermal conductivity is one of the key materials to make it possible for electronics industry to continue to follow the Moore's Law. However, there are few studies focusing on the longitudinal thermal conductivity of graphene films. The purpose of this study is to investigate the longitudinal thermal conductivity of graphene films according to ASTM D5470 [2]. The results show that the longitudinal thermal conductivity of the pressed graphene film is greater than that of the unpressurized graphene film. The longitudinal thermal conductivity is 10.6 W/m· K for the unpressurized graphene film and 20.6 W/m· K for the pressed graphene film.
10.	Chen, Jiajia, et al. (author) Joint Bandwidth Scheduling to Support Differentiated Services and Multiple Service Providers in 1G and 10G EPONs 2009 In: Journal of Optical Communications and Networking. - : The Optical Society. - 1943-0620 .- 1943-0639. ; 1:4, s. 343-351 Journal article (peer-reviewed)abstract Dynamic bandwidth allocation (DBA) is one of the key issues for the current (1G) and next-generation (10G) Ethernet-based passive optical network (EPON) systems. We present a novel bandwidth scheduling scheme that integrates specific scheduling implementations in the optical line terminal and optical network units. This scheduling enables multiservice access with scalable quality of service support for the triple-play (video, voice, and data) services and open access. Our simulation results show that the proposed scheduling algorithm performs very well in supporting service differentiation and fair allocation of bandwidth to different service providers. A performance comparison between 1G and 10G systems is also presented. To the best of our knowledge, no detailed study of DBA in a 10G EPON can be found in the literature so far.
11.	Chen, Jiajia, et al. (author) Self-protection scheme against failures of distributed fiber links in an Ethernet passive optical network 2006 In: Journal of Optical Networking. - 1536-5379. ; 5:9, s. 662-666 Journal article (peer-reviewed)abstract A novel self-protection scheme for an Ethernet passive optical network is introduced and studied at both the physical and the media access control layers. The scheme is simple and fast and can provide 1: 1 protection and automatic traffic restoration against the fiber link failure between a remote node ( RN) and any optical network unit (ONU). Simulation results show that fiber failure does not degrade the transmission performance, and the restoration time depends mainly on the switch time of the physical layer. Our protection scheme saves many long fibers, does not influence other normal ONUs, and requires no active device in the RN.
12.	Chen, Qiman, et al. (author) Flexible Service Chain Mapping in Server-Centric Optical Datacenter Networks 2018 In: 2018 ASIA COMMUNICATIONS AND PHOTONICS CONFERENCE (ACP). - : IEEE. - 9781538661581 Conference paper (peer-reviewed)abstract We investigate flexible service chain mapping in server-centric optical terconnects, handling virtual network function (VNF) dependency operly. Blocking probability decreases by a factor of 10 when signing multiple VNFs in the same server is allowed.
13.	Chen, XÍ, et al. (author) TDHQ Enabling Fine-granularity Adaptive Loading for SSB-DMT Systems 2018 In: IEEE Photonics Technology Letters. - : Institute of Electrical and Electronics Engineers Inc.. - 1041-1135 .- 1941-0174. ; 30:19, s. 1687-1690 Journal article (peer-reviewed)abstract In this letter, we introduce time domain hybrid quadrature amplitude modulation (TDHQ) for the single sideband (SSB) discrete multi-tone (DMT) systems. Experimental results reveal that with a single precoding set and the proposed adaptive loading algorithm, the TDHQ scheme can achieve finer granularity and therefore smoother continuous growth of data rate than that with the conventional quadrature amplitude modulation (QAM). Besides, thanks to the frame construction and the tailored mapping rule, the scheme with TDHQ has an obviously better peak to average power ratio (PAPR).
14.	Guo, Changjian, et al. (author) Experimental Demonstration of a Hybrid 1/2-dimentional En/Decoding Optical Code Division Multiple Access System 2008 In: Optical Transmission, Switching, and Subsystems VI. - : SPIE. ; , s. 713611- Conference paper (peer-reviewed)
15.	Guo, Sihua, et al. (author) Characterization of a Novel Cost-efficient and Environmentally Friendly Graphene-enhanced Thermal Interface Material 2023 In: 24th European Microelectronics and Packaging Conference, EMPC 2023. Conference paper (peer-reviewed)abstract With the continuous development of electronic devices, effective heat dissipation has become a major factor affecting service life. Thermal interface materials (TIM) play a key role in controlling heat dissipation of electronic devices and have thus attracted widespread attention. In this study, we used graphene flakes (GF) derived from graphene film that is wasted during the preparation of commercial large-scale graphene-enhanced TIMs as thermally conductive fillers to formulate a new TIM. The thermal conductivity of the developed TIM is 50% higher with GFs than without. Furthermore, the TIM has a tensile strength of 0.46 MPa with an elongation at break of 1225%, a maximum compression strength of 0.64 MPa at 50% compression, and high mechanical cycle stability. This report provides a cost-efficient and environmentally friendly approach to producing high-performance TIMs for electronic cooling applications.
16.	Li, Jun, 1988, et al. (author) Bandwidth Slicing to Boost Federated Learning over Passive Optical Networks 2020 In: IEEE Communications Letters. - : Institute of Electrical and Electronics Engineers Inc.. - 1089-7798 .- 1558-2558. ; 24:7, s. 1492-1495 Journal article (peer-reviewed)abstract During federated learning (FL) process, each client needs to periodically upload local model parameters and download global model parameters to/from the central server, thus requires efficient communications. Meanwhile, passive optical network (PON) is promising to support fog computing where FL tasks can be executed and the traffic generated by FL needs to be transmitted together with other types of traffic for broadband access. In this letter, a bandwidth slicing algorithm in PONs is introduced for efficient FL, in which bandwidth is reserved for the involved ONUs collaboratively and mapped into each polling cycle. Results reveal that the proposed bandwidth slicing significantly improves training efficiency while achieving good learning accuracy for the FL task running over the PON.
17.	Li, Jun, et al. (author) Delay-aware bandwidth slicing for service migration in mobile backhaul networks 2019 In: Journal of Optical Communications and Networking. - : Institute of Electrical and Electronics Engineers Inc.. - 1943-0620 .- 1943-0639. ; 11:4, s. B1-B9 Journal article (peer-reviewed)abstract Fog computing is expected to be integrated with communication infrastructure, giving rise to the concept of fog-enhanced radio access networks (FeRANs) to support various mission-critical applications. Such architecture brings computation capabilities closer to end users, thereby reducing the communication latency to access services. In the context of FeRAN, service migration is needed to tackle limited resources in a single fog node and to provide continuous service for mobile end users. To support service migration, high capacity and low latency are required in mobile backhaul networks. Passive optical networks can be a promising solution for such mobile back-haul, in which bandwidth is shared by both migration traffic and that which is not associated with service migration. In this paper, we propose a bandwidth slicing mechanism, in which the bandwidth can be provisioned to the migration traffic and non-migration traffic dynamically and effectively to meet their different delay requirements. Simulation results verify that the proposed delay-aware bandwidth slicing scheme can handle the migration traffic properly, i.e., sending it within a required time threshold, while limiting the impact of the migration traffic on the latency and jitter of the non-migration traffic, particularly that with high priority.
18.	Li, Jun, 1988, et al. (author) Enabling technologies for low-latency service migration in 5G transport networks [Invited] 2021 In: Journal of Optical Communications and Networking. - : Institute of Electrical and Electronics Engineers Inc.. - 1943-0620 .- 1943-0639. ; 13:2, s. A200-A210 Journal article (peer-reviewed)abstract The fifth generation (5G) mobile communications system is envisioned to serve various mission-critical services such as industrial automation, cloud robotics, and safety-critical vehicular communications. To satisfy the stringent end-to-end latency requirement of these services, fog computing has been regarded as a promising technology to be integrated into 5G networks, in which computing, storage, and network functions are provisioned close to end users, thus significantly reducing the latency caused in transport networks. However, in the context of fog-computing-enabled 5G networks, the high mobility feature of users brings critical challenges to satisfy the stringent quality of service requirements. To address this issue, service migration, which transmits the associated services from the current fog server to the target one to follow the users' travel trace and keep the service continuity, has been considered. However, service migration cannot always be completed immediately and may lead to a situation where users experience a loss of service access. In this regard, low-latency service migration plays a key role to reduce the negative effects on services being migrated. In this paper, the factors that affect the performance of service migration are analyzed. To enable low-latency service migration, three main enabling technologies are reviewed, including migration strategies, low-latency, and high-capacity mobile backhaul network design, and adaptive resource allocation. Based on a summary of the reviewed technologies, we conclude that dynamic resource allocation is the worthiest one to research. Therefore, we carry out a use case, where reinforcement learning (RL) is adopted for autonomous bandwidth allocation in support of low-latency service migration in a dynamic traffic environment and evaluate its performance compared to two benchmarks. The simulation demonstrates that the RL-based algorithm is able to self-adapt to a dynamic traffic environment and gets converged performance, which has an obviously smaller impact on non-migration traffic than the two benchmarks while keeping the migration success probability high. Meanwhile, unlike the benchmarks, the RL-based method shows performance fluctuations before getting converged, which may cause unstable system performance. It calls for future research on advanced smart policies that can get convergence quickly, particularly for handling the migration of latency-sensitive services in 5G transport networks.
19.	Li, Jun, et al. (author) Online Resource Management in Fog-enhanced Cellular Networks for Real-Time Vehicular Services Other publication (other academic/artistic)abstract Fog computing is expected to be integrated with existing communication infrastructures, giving rise to the concept of fog-enhanced cellular networks (FeCNs) to support real-time services. In such FeCNs, service migration is necessary to maintain the service continuity and satisfy stringent latency requirements of real-time vehicular services, where the service is migrated from a source fog node to a target fog node following the vehicle's moving trace. Fog servers, however, need to have sufficient computational resources available to support such a migration. Also, provisioning resource for the migrated real-time services needs to be completed as soon as possible to minimize the service interruption. This paper proposes a distributed online resource management (ORM) scheme, in which resources for real-time vehicular services are provisioned with high priority. Once resources are scarce in one fog node, services with low priority can be migrated to neighboring fog nodes and their resources can be released in a distributed fashion. We propose two algorithms tailored to reduce the negative effects on the affected services. As a case study, the Luxembourg traffic volume model has been considered to verify the performance of the proposed scheme. Simulation results show that the performance of the proposed scheme is dependent on the backhaul capacity. Compared with other schemes, the one-hop access probability for real-time vehicular services implying low delay performance can be effectively improved, while the performance of other services can also be well maintained by providing sufficient backhaul capacity.
20.	Li, Jun, 1988, et al. (author) Scalable Federated Learning over Passive Optical Networks 2021 In: 2021 Optical Fiber Communications Conference and Exhibition, OFC 2021 - Proceedings. - : Institute of Electrical and Electronics Engineers Inc.. - 9781943580866 Conference paper (peer-reviewed)abstract Two-step aggregation is introduced to facilitate scalable federated learning (SFL) over passive optical networks (PONs). Results reveal that the SFL keeps the required PON upstream bandwidth constant regardless of the number of involved clients, while bringing 10% learning accuracy improvement. © 2021 OSA.
21.	Li, Jun, et al. (author) Service Migration in Fog Computing Enabled Cellular Networks to Support Real-Time Vehicular Communications 2019 In: IEEE Access. - : Institute of Electrical and Electronics Engineers (IEEE). - 2169-3536. ; 7, s. 13704-13714 Journal article (peer-reviewed)abstract Driven by the increasing number of connected vehicles and related services, powerful communication and computation capabilities are needed for vehicular communications, especially for real-time and safety-related applications. A cellular network consists of radio access technologies, including the current long-term evolution (LTE), the LTE advanced, and the forthcoming 5th generation mobile communication systems. It covers large areas and has the ability to provide high data rate and low latency communication services to mobile users. It is considered the most promising access technology to support real-time vehicular communications. Meanwhile, fog is an emerging architecture for computing, storage, and networking, in which fog nodes can be deployed at base stations to deliver cloud services close to vehicular users. In fog computing-enabled cellular networks, mobility is one of the most critical challenges for vehicular communications to maintain the service continuity and to satisfy the stringent service requirements, especially when the computing and storage resources are limited at the fog nodes. Service migration, relocating services from one fog server to another in a dynamic manner, has been proposed as an effective solution to the mobility problem. To support service migration, both computation and communication techniques need to be considered. Given the importance of protocol design to support the mobility of the vehicles and maintain high network performance, in this paper, we investigate the service migration in the fog computing-enabled cellular networks. We propose a quality-of-service aware scheme based on the existing handover procedures to support the real-time vehicular services. A case study based on a realistic vehicle mobility pattern for Luxembourg scenario is carried out, where the proposed scheme, as well as the benchmarks, are compared by analyzing latency and reliability as well as migration cost.
22.	Lin, Rui, et al. (author) Integrating Quantum Key Distribution with the Spatial Division Multiplexing Enabled High Capacity Optical Networks 2018 In: 2018 Asia Communications and Photonics Conference (ACP). - : IEEE. - 9781538661581 Conference paper (peer-reviewed)abstract In this talk, we discuss integrating the quantum key distribution (QKD) with the spatial division multiplexing (SDM) enabled optical communication network for the cyber security.
23.	Shen, Xiaoman, et al. (author) Heterogeneous LTE/DSRC Approach to Support Real-time Vehicular Communications 2018 In: 2018 10TH INTERNATIONAL CONFERENCE ON ADVANCED INFOCOMM TECHNOLOGY (ICAIT). - : IEEE. ; , s. 122-127 Conference paper (peer-reviewed)abstract Vehicle-to-everything (V2X) communications have become a key enabler for future autonomous driving by providing sensing and cooperation abilities beyond traditional on-board sensors. The main candidate technologies for V2X communications are dedicated short range communication (DSRC)/IEEE 802.11p and long-term evolution (LTE), each of which has its own strengths and weaknesses. DSRC provides low-latency direct connectivity, but suffers from serious link degradation and reliability issues. On the other hand, LTE is able to provide high capacity data transmission, while its latency remains an issue due to the long transmission time interval. Integrating these two radio technologies as a heterogeneous solution is promising to complement each other and support V2X applications with differentiated service requirements. This paper proposes a service-aware radio access technology (RAT) selection algorithm that enables a heterogeneous LTE/DSRC solution, where LTE and/or DSRC are selected according to services. Each vehicle is assumed to be equipped with both LTE and DSRC interfaces. The heterogeneous solution selects RAT based on the services requirements with consideration of the networks performance. The solution is implemented with integration of the C-ITS standard and validated through the OMNet++ and SUMO based network simulator. A see-through scenario, where a fleet of vehicles require real-time video data sharing to assist efficient driving, is considered. The simulation results demonstrate that the proposed approach outperforms the purely DSRC approach significantly and is able to simultaneously support safety message transmission with low latency, video streaming with high bandwidth requirements, and other applications with different service requirements.
24.	Shen, Zhiyang, et al. (author) A Critical Assessment of graphene based heat pipes for electronics and power module cooling applications 2023 In: 2023 24th International Conference on Electronic Packaging Technology, ICEPT 2023. Conference paper (peer-reviewed)abstract As the most effective heat transfer device, heat pipes have received widespread attention, but traditional heat pipes may be difficult to meet heat dissipation requirements in the near future. Since graphene was discovered, its ultra-high thermal conductivity has been the focus of people's research and application. Therefore, the combination of graphene and heat pipes is a method to improve the performance of existing heat pipes. This paper is a critical assessment of recent advances in graphene-based heat pipes. In the paper, we conducted a simple theoretical analysis of the operation of the heat pipe, and also summarized the research status, enhancement mechanism, and enhancement method of graphene-enhanced heat pipes, and predicted the future development direction. The results show that depositing graphene-based materials on wicks, using graphene-based nanofluids, and application of graphene composites are effective ways to enhance the performance of heat pipes.
25.	Skubic, Björn, et al. (author) Dynamic Bandwidth Allocation for Long-Reach PON : Overcoming Performance Degradation 2010 In: IEEE Communications Magazine. - 0163-6804 .- 1558-1896. ; 48:11, s. 100-108 Journal article (peer-reviewed)abstract A passive optical network, with its inherent point to multi-point structure, allows for centralized placement of active equipment and possible extension of its boundary towards core networks. This property of the PON can be exploited for node consolidation where multiple central offices are replaced by a single one covering a larger service area. Such node consolidation is being particularly driven by the need for network operational cost saving, and is offering significant challenges to PONs. The degree of node consolidation that can be achieved is limited by the reach of conventional PON systems. In order to achieve a larger degree of node consolidation, an extension of the PON reach, beyond the conventional 20 km, is required. This article addresses the challenges of the dynamic bandwidth allocation, where increased reach results in a degradation of DBA performance and quality of service support. This degradation is a consequence of the increased propagation delay of the DBA messages exchanged between different PON elements. A potential solution to the performance degradation is the introduction of a multi-threaded DBA. In this article, we examine for both Gigabit PON and Ethernet PON, the extent to which DBA performance degradation can be reduced by exploiting multi-threading. It is found that for both standards, multi-threading, if done properly, can be used to mitigate the performance degradation due to the increased reach. To make bandwidth allocation efficient, new schemes for coordinating the multiple threads are required in long reach PON.
26.	Skubic, Björn, et al. (author) Dynamic bandwidth allocation in EPON and GPON 2010 In: Convergence of Mobile and Stationary Next-Generation Networks. - Hoboken, NJ, USA : John Wiley & Sons. - 9780470543566 - 9780470630976 Book chapter (peer-reviewed)
27.	Skubic, Björn, et al. (author) Improved scheme for estimating T-CONT bandwidth demand in status reporting DBA for NG-PON 2009 In: Network Architectures, Management, and Applications VII. - : SPIE - International Society for Optical Engineering. - 9780819480354 ; , s. 76330E- Conference paper (peer-reviewed)abstract A scheme for estimating T-CONT bandwidth demand within dynamic bandwidth allocation (DBA) for next-generation passive optical network (NG-PON) is proposed and evaluated. Estimating T-CONT bandwidth demand is considered as a main challenge in gigabit-capable passive optical network (GPON) DBA. The proposed minimum guaranteed T-CONT content (MGTC) scheme allows for a more conservative estimate of bandwidth demand. It is shown that at high load significant improvements in delay, jitter and bandwidth utilization can be achieved with the proposed scheme. For light loads the conventional scheme shows better delay performance. However, this may be overcome by controlled overgranting in the MGTC scheme.
28.	Yuan, Mingzhi, et al. (author) Fragmentation and structural transitions of few-layer graphene under high shear stress 2021 In: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 118:21 Journal article (peer-reviewed)abstract A key factor that determines the mechanical and electrical performance of graphene-based materials and devices is how graphene behaves under extreme conditions, yet the response of few-layer graphene to high shear stress has not been investigated experimentally. Here we applied high pressure and shear to graphene powder using a rotational diamond anvil cell and studied the recovered sample with multiple means of characterization. Sustaining high pressure and shear, graphene breaks into nanometer-long clusters with generation of large number of defects. At a certain stress level, it transforms to amorphous state and carbon onions. The reduction of infrared reflectivity in the severely sheared phase indicates the decrease in conductivity. Our results unveil the shear sensitive nature of graphene, point out the effects of shear on its physical properties, and provide a potential method to manipulate this promising material.
29.	Zeng, Weikang, et al. (author) Data-Efficient Artificial Neural Networks with Gaussian Process Regression for 3D Visible Light Positioning 2021 In: 2021 Optical Fiber Communications Conference and Exhibition, OFC 2021 - Proceedings. Conference paper (peer-reviewed)abstract A data-efficient artificial neural network based 3D VLP system using Gaussian process regression is proposed and experimentally demonstrated. Training data from the real environment can be reduced by >50% with negligible loss in positioning accuracy.
30.	Zhang, Lin, et al. (author) Cr-promoted formation of B2+L21 composite nanoprecipitates and enhanced mechanical properties in ferritic alloy 2023 In: Acta Materialia. - : Elsevier. - 1359-6454 .- 1873-2453. ; 243 Journal article (peer-reviewed)abstract The critical role of Cr on nanoprecipitates and the mechanical property of Fe-Ni-Al-Mn ferritic steel were systematically studied in this research. The two types of nanoprecipitates in the Cr added alloy were characterized through a combination of aberration-corrected scanning transmission electron microscopy and atom probe tomography techniques. The atomic-scale structure and chemistry analysis reveal that fine globular-shaped precipitates have a B2-structure, while coarse elongated precipitates have B2+L21 composite structures. The first-principles calculations reveal that the segregation of Cr at the L21/bcc interface reduces the interface and strain energy for the nucleation of the L21-type phase. With the increasing precipitate size, the B2 structure is gradually transformed to L21 to reduce elastic strain, thereby promoting the formation of B2+L21 composite nanoprecipitate. The addition of 10 wt% Cr results in an increase of ∼275 MPa in yield strength without obvious loss of ductility. The effect of Cr on the strength mechanisms were quantitatively analyzed, revealing that the strength of the ferritic alloy mainly improved by the formation of B2+L21 composite nanoprecipitate, which is more effective than solid solution strengthening.
31.	Zhang, Tiankai, et al. (author) Ion-modulated radical doping of spiro-OMeTAD for more efficient and stable perovskite solar cells 2022 In: Science. - : AMER ASSOC ADVANCEMENT SCIENCE. - 0036-8075 .- 1095-9203. ; 377:6605, s. 495-501 Journal article (peer-reviewed)abstract Record power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) have been obtained with the organic hole transporter 2,2,7,7-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9-spirobifluorene (spiro-OMeTAD). Conventional doping of spiro-OMeTAD with hygroscopic lithium salts and volatile 4-tert-butylpyridine is a time-consuming process and also leads to poor device stability. We developed a new doping strategy for spiro-OMeTAD that avoids post-oxidation by using stable organic radicals as the dopant and ionic salts as the doping modulator (referred to as ion-modulated radical doping). We achieved PCEs of >25% and much-improved device stability under harsh conditions. The radicals provide hole polarons that instantly increase the conductivity and work function (WF), and ionic salts further modulate the WF by affecting the energetics of the hole polarons. This organic semiconductor doping strategy, which decouples conductivity and WF tunability, could inspire further optimization in other optoelectronic devices.
32.	Zhang, Z., et al. (author) Accuracy enhancement of indoor visible light positioning using point-wise reinforcement learning 2019 In: Optics InfoBase Conference Papers. - Washington, D.C. : OSA - The Optical Society. - 9781943580538 Conference paper (peer-reviewed)abstract A point-wise reinforcement learning (PWRL) algorithm is proposed for a multi-detector based visible light positioning system. Experimental results demonstrate that the average positioning error is reduced up to 70% by employing the proposed PWRL.
33.	Zhang, Zhuo, et al. (author) Demonstration of three‐dimensional indoor visible light positioning with multiple photodiodes and reinforcement learning 2020 In: Sensors. - : MDPI AG. - 1424-8220. ; 20:22, s. 1-14 Journal article (peer-reviewed)abstract To provide high‐quality location‐based services in the era of the Internet of Things, visible light positioning (VLP) is considered a promising technology for indoor positioning. In this paper, we study a multi‐photodiodes (multi‐PDs) three‐dimensional (3D) indoor VLP system enhanced by reinforcement learning (RL), which can realize accurate positioning in the 3D space without any off-line training. The basic 3D positioning model is introduced, where without height information of the receiver, the initial height value is first estimated by exploring its relationship with the received signal strength (RSS), and then, the coordinates of the other two dimensions (i.e., X and Y in the horizontal plane) are calculated via trilateration based on the RSS. Two different RL processes, namely RL1 and RL2, are devised to form two methods that further improve horizontal and vertical positioning accuracy, respectively. A combination of RL1 and RL2 as the third proposed method enhances the overall 3D positioning accuracy. The positioning performance of the four presented 3D positioning methods, including the basic model without RL (i.e., Benchmark) and three RL based methods that run on top of the basic model, is evaluated experimentally. Experimental results verify that obviously higher 3D positioning accuracy is achieved by implementing any proposed RL based methods compared with the benchmark. The best performance is obtained when using the third RL based method that runs RL2 and RL1 sequentially. For the testbed that emulates a typical office environment with a height difference between the receiver and the transmitter ranging from 140 cm to 200 cm, an average 3D positioning error of 2.6 cm is reached by the best RL method, demonstrating at least 20% improvement compared to the basic model without performing RL.
34.	Zhang, Zhuo, et al. (author) Iterative point-wise reinforcement learning for highly accurate indoor visible light positioning 2019 In: Optics Express. - : OPTICAL SOC AMER. - 1094-4087 .- 1094-4087. ; 27:16, s. 22161-22172 Journal article (peer-reviewed)abstract Iterative point-wise reinforcement learning (IPWRL) is proposed for highly accurate indoor visible light positioning (VLP). By properly updating the height information in an iterative fashion, the IPWRL not only effectively mitigates the impact of non-deterministic noise but also exhibits excellent tolerance to deterministic errors caused by the inaccurate a priori height information. The principle of the IPWRL is explained, and the performance of the IPWRL is experimentally evaluated in a received signal strength (RSS) based VLP system and compared with other positioning algorithms, including the conventional RSS algorithm, the k-nearest neighbors (KNN) algorithm and the PWRL algorithm where iterations exclude. Unlike the supervised machine learning method, e.g., the KNN, whose performance is highly dependent on the training process, the proposed IPWRL does not require training and demonstrates robust positioning performance for the entire tested area. Experimental results also show that when a large height information mismatch occurs, the IPWRL is able to first correct the height information and then offers robust positioning results with a rather low positioning error, while the positioning errors caused by the other algorithms are significantly higher.
35.	Abtahi, Farzad, et al. (author) Optimal Design of Cost- and Energy-Efficient Scalable Passive Optical Backbone Networks 2012 In: 2012 Asia Communications And Photonics Conference (ACP). - Washington, D.C. : OSA. - 9781467362740 ; , s. AS3D.4- Conference paper (peer-reviewed)abstract We propose an optimization model minimizing number of wavelengths in passive optical backbone networks and obtaining the same resource usage as in networks based on active switching while reducing both cost and power consumption.
36.	Al-Awis, S. N., et al. (author) Phenomenological formula for modelling of physical layer impairments in elastic optical networks 2015 In: Asia Communications and Photonics Conference, ACPC 2015. - Washington, D.C. : OSA. - 9781943580064 Conference paper (peer-reviewed)abstract An empirical modelling technique is introduced to estimate impact of physical layer impairments in elastic optical networks, which can be used to evaluate transmission quality. The model has been verified experimentally with accuracy beyond (97.3%).
37.	Al-Awis, Suhail Najm, et al. (author) Phenomenological Formula for Modelling of Physical Layer Impairments in Elastic Optical Networks 2015 In: Asia Communications and Photonics Conference 2015. - 9781943580064 Conference paper (peer-reviewed)abstract An empirical modelling technique is introduced to estimate impact of physical layer impairments in elastic optical networks, which can be used to evaluate transmission quality. The model has been verified experimentally with accuracy beyond (97.3%).
38.	Archambault, Emile, et al. (author) Routing and spectrum assignment in elastic filterless optical networks 2016 In: IEEE/ACM Transactions on Networking. - : IEEE. - 1063-6692 .- 1558-2566. ; 24:6, s. 3578-3592 Journal article (peer-reviewed)abstract Elastic optical networking is considered a promising candidate to improve the spectral efficiency of optical networks. One of the most important planning challenges of elastic optical networks is the NP-hard routing and spectrum assignment (RSA) problem. In this paper, we investigate offline RSA in elastic filterless optical networks, which use a passive broadcast-and-select architecture to offer network agility. Here elastic optical network is referred to as the optical network that can adapt the channel bandwidth, data rate, and transmission format for each traffic demand in order to offer maximum throughput. In elastic filterless networks, the presence of unfiltered signals resulting from the drop-and-continue node architecture must be considered as an additional constraint in the RSA problem. In this paper, first the RSA problem in elastic filterless networks is formulated by using integer linear program (ILP) to obtain optimal solutions for small networks. Due to the problem complexity, two efficient RSA heuristics are also proposed to achieve suboptimal solutions for larger networks in reasonable time. Simulation results show that significant bandwidth savings in elastic filterless networks can be achieved compared to the fixed-grid filterless solutions. The proposed approach is further tested in multi-period traffic scenarios and combined with periodical spectrum defragmentation, leading to additional improvement in spectrum utilization of elastic filterless optical networks.
39.	Cao, Wei, et al. (author) Interaction With Social Robots : Improving Gaze Toward Face but Not Necessarily Joint Attention in Children With Autism Spectrum Disorder 2019 In: Frontiers in Psychology. - : FRONTIERS MEDIA SA. - 1664-1078. ; 10 Journal article (peer-reviewed)abstract It is widely recognized that robot-based interventions for autism spectrum disorders (ASD) hold promise, but the question remains as to whether social humanoid robots could facilitate joint attention performance in children with ASD. In this study, responsive joint attention was measured under two conditions in which different agents, a human and a robot, initiated joint attention via video. The participants were 15 children with ASD (mean age: 4.96 +/- 1.10 years) and 15 typically developing (TD) children (mean age: 4.53 +/- 0.90 years). In addition to analyses of fixation time and gaze transitions, a longest common subsequence approach (LCS) was employed to compare participants' eye movements to a predefined logical reference sequence. The fixation of TD toward agent's face was earlier and longer than children with ASD. Moreover, TD showed a greater number of gaze transitions between agent's face and target, and higher LCS scores than children with ASD. Both groups showed more interests in the robot's face, but the robot induced a lower proportion of fixation time on the target. Meanwhile participants showed similar gaze transitions and LCS results in both conditions, suggesting that they could follow the logic of the joint attention task induced by the robot as well as human. We have discussed the implications for the effects and applications of social humanoid robots in joint attention interventions.
40.	Cao, Yuan, et al. (author) Hybrid Trusted/Untrusted Relay Based Quantum Key Distribution over Optical Backbone Networks 2021 In: IEEE Journal on Selected Areas in Communications. - 0733-8716 .- 1558-0008. ; 39:9, s. 2701-2718 Journal article (peer-reviewed)abstract Quantum key distribution (QKD) has demonstrated a great potential to provide future-proofed security, especially for 5G and beyond communications. As the critical infrastructure for 5G and beyond communications, optical networks can offer a cost-effective solution to QKD deployment utilizing the existing fiber resources. In particular, measurement-device-independent QKD shows its ability to extend the secure distance with the aid of an untrusted relay. Compared to the trusted relay, the untrusted relay has obviously better security, since it does not rely on any assumption on measurement and even allows to be accessed by an eavesdropper. However, it cannot extend QKD to an arbitrary distance like the trusted relay, such that it is expected to be combined with the trusted relay for large-scale QKD deployment. In this work, we study the hybrid trusted/untrusted relay based QKD deployment over optical backbone networks and focus on cost optimization during the deployment phase. A new network architecture of hybrid trusted/untrusted relay based QKD over optical backbone networks is described, where the node structures of the trusted relay and untrusted relay are elaborated. The corresponding network, cost, and security models are formulated. To optimize the deployment cost, an integer linear programming model and a heuristic algorithm are designed. Numerical simulations verify that the cost-optimized design can significantly outperform the benchmark algorithm in terms of deployment cost and security level. Up to 25% cost saving can be achieved by deploying QKD with the hybrid trusted/untrusted relay scheme while keeping much higher security level relative to the conventional point-to-point QKD protocols that are only with the trusted relays.
41.	Cao, Yuan, et al. (author) Mixed Relay Placement for Quantum Key Distribution Chain Deployment over Optical Networks 2020 In: 2020 European Conference on Optical Communications, ECOC 2020. Conference paper (peer-reviewed)abstract Four mixed trusted/untrusted relay placement strategies for quantum key distribution chain deployment over optical networks are proposed, which can improve a security level up to 119% relative to the conventional purely trusted relay placement.
42.	Cao, Yuan, et al. (author) Multi-Tenant Provisioning for Quantum Key Distribution Networks With Heuristics and Reinforcement Learning : A Comparative Study 2020 In: IEEE Transactions on Network and Service Management. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-4537. ; 17:2, s. 946-957 Journal article (peer-reviewed)abstract Quantum key distribution (QKD) networks are potential to be widely deployed in the immediate future to provide long-term security for data communications. Given the high price and complexity, multi-tenancy has become a cost-effective pattern for QKD network operations. In this work, we concentrate on addressing the online multi-tenant provisioning (On-MTP) problem for QKD networks, where multiple tenant requests (TRs) arrive dynamically. On-MTP involves scheduling multiple TRs and assigning non-reusable secret keys derived from a QKD network to multiple TRs, where each TR can be regarded as a high-security-demand organization with the dedicated secret-key demand. The quantum key pools (QKPs) are constructed over QKD network infrastructure to improve management efficiency for secret keys. We model the secret-key resources for QKPs and the secret-key demands of TRs using distinct images. To realize efficient On-MTP, we perform a comparative study of heuristics and reinforcement learning (RL) based On-MTP solutions, where three heuristics (i.e., random, fit, and best-fit based On-MTP algorithms) are presented and a RL framework is introduced to realize automatic training of an On-MTP algorithm. The comparative results indicate that with sufficient training iterations the RL-based On-MTP algorithm significantly outperforms the presented heuristics in terms of tenant-request blocking probability and secret-key resource utilization.
43.	Cao, Yuan, et al. (author) Multi-tenant secret-key assignment over quantum key distribution networks 2019 In: Optics Express. - : OPTICAL SOC AMER. - 1094-4087. ; 27:3, s. 2544-2561 Journal article (peer-reviewed)abstract Quantum key distribution (QKD) networks are promising to progress towards widespread practical deployment over existing fiber infrastructures in the near future. Given the high cost and difficulty of deploying QKD networks, multi-tenancy becomes promising to improve cost efficiency for future QKD networks. In a multi-tenant QKD network, multiple QKD tenants can sham the same QKD network infrastructure to obtain secret keys for securing their data transfer. Since the secret-key resources are finite and precious in QKD networks, how to achieve efficient multi-tenant secret-key assignment (MTKA) to satisfy the secret-key demands of multiple QKD tenants over QKD networks becomes a significant problem. In this regard, this study addresses the MTKA problem over QKD networks. A new multi-tenant QKD network architecture is proposed based on software defined networking (SDN) and quantum key pool (QKP) techniques. A secret-key rate sharing scheme is presented and a heuristic algorithm is designed to implement efficient MTKA over QKD networks. A new performance metric, namely matching degree (MD) that reflects the balance between QKD network secret-key resources and QKD tenant requests, is defined and evaluated. Simulation studies indicate that high QKD tenant requests accommodation and efficient secret-key resource usage can be achieved via maximizing the value of MD.
44.	Cao, Yuan, et al. (author) Reinforcement learning based multi-tenant secret-key assignment for quantum key distribution networks 2019 In: Optics InfoBase Conference Papers. - Washington, D.C. : OSA - The Optical Society. Conference paper (peer-reviewed)abstract We propose a reinforcement learning based online multi-tenant secret-key assignment algorithm for quantum key distribution networks, capable of reducing tenant-request blocking probability more than half compared to the benchmark heuristics.
45.	Cen, Min, et al. (author) Advanced Fault-Monitoring Scheme for Ring-Based Long-Reach Optical Access Networks 2017 In: Journal of Lightwave Technology. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0733-8724 .- 1558-2213. ; 35:10, s. 1876-1886 Journal article (peer-reviewed)abstract This paper presents a novel fiber fault-monitoring system for long-reach optical access networks based on a transmission-reflection analysis approach. By launching an un-modulated continuous-wave optical signal into the feeder ring and measuring the transmitted and reflected/backscattered optical powers, the proposed monitoring scheme is able to detect, identify, and localize any major fault (covering both reflective and nonreflective events) with a good spatial accuracy (<= 10 m) and a high detection speed (3 s). Both experimental and simulation results have demonstrated that the proposed system provides fiber monitoring functionality better than that obtained by the conventional methods.
46.	Cen, M., et al. (author) Advanced Transmission-Reflection-Analysis (TRA) system for Long-Reach Passive Optical Network monitoring 2015 In: International Conference on Transparent Optical Networks. - : IEEE Computer Society. - 9781467378802 Conference paper (peer-reviewed)abstract Long-Reach Passive Optical Networks (LR-PONs) allows for extending the distance between the central office (CO) and end users from a few kilometers to several tens of kilometers and beyond. It in turn reduces the number of active equipment in the field, bringing potentially cost saving. However, due to its high capacity and large coverage, LR-PON becomes increasingly vulnerable to various failures. Therefore, network monitoring becomes extremely important to guarantee an appropriate level of network reliability and performance. In this paper, we report on an advanced LR-PON monitoring solution that can supervise the whole LR-PON ring section in a cost-effective manner. Instead of using the conventional optical time domain reflectometry (OTDR) approach, we implement multi wavelength Transmission-Reflection Analysis (nλ-TRA) as the monitoring technique. The TRA approach is based on the unique relationship between the optical powers transmitted and backscattered by the fiber for a given loss location. Since TRA only requires measuring the power levels of monitoring signals, it outperforms other conventional methods thanks to its superior detection speed and a simple system configuration. Both experimental results have demonstrated that the proposed system can reach high accuracy for fault localization.
47.	Cen, M., et al. (author) Efficient monitoring for ring-based long-reach passive optical networks 2015 In: Optical Fiber Communication Conference, OFC 2015. - Washington, D.C. : The Optical Society. - 9781557529374 Conference paper (peer-reviewed)abstract An efficient monitoring scheme based on transmission-reflection analysis is proposed for long-reach passive optical networks. Both experimental simulation results have demonstrated that the proposed scheme provides better localization functionality than the conventional methods.
48.	Cen, M., et al. (author) Fast and simple fault monitoring for long-reach passive optical networks 2014 In: 2014 European Conference on Optical Communication, (ECOC). - : IEEE. - 9782954944401 ; , s. 6964070- Conference paper (peer-reviewed)abstract We propose a fast and simple monitoring system based on multi-wavelength bi-directional transmission reflection analysis approach for long-reach passive optical networks. Both experimental and simulation results have demonstrated the proposed system can reach high accuracy for fault localization.
49.	Cen, Min, et al. (author) Full monitoring for long-reach TWDM passive optical networks 2016 In: Optics Express. - : Optical Society of America. - 1094-4087. ; 24:14, s. 15782-15797 Journal article (peer-reviewed)abstract This paper presents a novel and simple fiber monitoring system based on multi-wavelength transmission-reflection analysis for long-reach time and wavelength division multiplexing passive optical networks. For the first time, the full localization functionality of long-reach passive optical networks is possible with the proposed monitoring scheme, including supporting fault detection, identification, and localization in both feeder and distribution fiber segments. By measuring the transmitted and reflected/backscattered optical powers launched by an unmodulated continuous-wave optical source, the proposed solution is able to supervise the network with good spatial accuracy, a high detection speed and a low impact on data traffic. Both the theoretical analysis and experimental validation show that the proposed scheme is capable of providing an accurate fault monitoring functionality for long-reach time and wavelength division multiplexing passive optical networks.
50.	Cen, M., et al. (author) Full monitoring for Long-Reach TWDM Passive Optical Networks based on TRA technique 2016 In: International Conference on Transparent Optical Networks. - : IEEE Computer Society. - 9781509014675 Conference paper (peer-reviewed)abstract Long-Reach Passive Optical Networks (LR-PONs) consolidates of metropolitan and access networks by extending the distance between the Central Office (CO) and the end users, which in turn simplifies the network and potentially brings cost savings. With the explosively growing of data traffic, Time and Wavelength Division Multiplexing (TWDM) technology have also been employed in LR-PON to realize high capacity. However, due to high capacity and large coverage, the presence of a single failure may cause a huge loss of data and affect a large number of subscribers in LR-PON. Efficient network fault monitoring therefore becomes a key to improve the level of network reliability. In this paper, we report an advanced solution realizing fault detection, identification and localization in both feeder and distribution fiber segments of TWDM LR-PON. Instead of using the conventional optical time domain reflectometry (OTDR) approach, we implement multi wavelength Transmission-Reflection Analysis (nλ-TRA) as the monitoring technique, which is able to provide a good spatial accuracy and a high detection speed without interfering with the data traffic. Theoretical analysis and experimental validation demonstrate that the proposed scheme is capable of providing an accurate fault monitoring functionality.

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