# Photonic Network Communications

Online ISSN: 1572-8188
Recent publications
Article
The variation in refractive index of the atmosphere causes wavefront aberration of optical signal propagating through the random atmosphere. This leads to various effects such as beam spreading, wandering and scintillation (intensity fluctuation) which are responsible for severe signal degrading of the free space optical (FSO) communication system. Incorporation of adaptive optics (AO) technique mitigates the effect of wavefront aberration distortions and reducing the signal fading. Non-conventional adaptive optics is demonstrated using complex search algorithms which requires large number of iterations and computations to obtain the optimum value of the results. In this paper, Convolutional Neural Networks (CNN)-based novel wavefront aberration compensation technique is proposed. The aim of this work is to experience and validate the CNN-based wavefront sensorless adaptive optics (WFSLess AO) technique for 70 m realtime FSOC. The major issues such as time-consuming iterative processes and latency in complex search algorithms and similar algorithms are greatly avoided by detecting the wavefront distortion from the direct images of the optical beam used in the experimentation. LeNet CNN architecture is realized to compensate wavefront distortion for the acquired data sample under different weather condition. Experiments are conducted on Xilinx Spartan-6 FPGA using high level synthesis. The performance of the proposed scheme is compared to existing approaches (T Weyrauch and MA Verontsov in Appl. Opt. 44:6388–6401, 2005; MJ Booth in Opt. Express 14:1339–1352, 2006; H Linhai and R Changhui in Opt. Express 19:371–379, 2011) and it shows an effective Strehl Ratio, Root Mean Square and reduced computation time thereby resolves the latency issue while maintaining accuracy which is a serious problem in AO systems.

Article
In today’s environment, digital technology and digital computing are unavoidable components of the creation of electronic gadgets. Quantum-dot cellular automata, or QCA, is a new paradigm for realizing digital logic on the nanoscale. QCA technology is a type of nanotechnology that is used to construct computational circuits. Due to its low latency and area consumption, it can be a promising technique for overcoming CMOS limitations at the nanoscale. Also, fault-tolerant circuits ensure circuit resilience using dependable circuits in this technology. The multiplexer is one of the essential circuits in computer logic. In the most widely used circuits, the multiplexer is an important and primary component. Therefore, in this paper, using the micro-level polarization of QCA, we attempt to develop a fault-tolerant multiplexer architecture. The study employs fault-tolerant majority gates to create a fault-tolerant 2:1 multiplexer. QCADesigner develops and simulates the proposed multiplexer. The results indicate the efficiency of the proposed design in comparison with other designs.

Article
This paper describes a novel multi-dimensional OCDMA coding technique with the objective of enhancing capacity of the optical communication network. In order to overcome the drawbacks associated with the conventional coding methods, multiple modes, time slots and multicarrier are utilized to construct the code set using prime sequences. The general procedure for code construction using the proposed method is described in this paper and the performance of the proposed coding technique has been analyzed for 36 users using 3 frequency channels and 5 fiber modes. By properly assigning 12 time slots to orthogonal group of users, the encoded data transmitted simultaneously by all 36 users have been correctly decoded without interference. The obtained results confirm the ability of the proposed method to improve the network capacity by supporting maximum number of concurrent users. Due to mode and frequency spreading, the data security against interceptor is also ensured in the proposed method than the conventional mode division multiplexing.

Article
Recently, the distributed fiber optic sensing (DFOS) techniques have advanced rapidly. There emerges various types of DFOS sensors that can monitor physical parameters such as temperature, strain, and vibration. With these DFOS sensors deployed, the telecom networks are capable of offering additional services beyond communications, such as monitoring road traffic condition, monitoring utility pole health, monitoring city noise and accident, thus evolving to a new paradigm of Infrastructure-as-a-Sensor (IaaSr) or Network-as-a-Sensor (NaaSr). When telecom network carriers upgrade their infrastructures with DFOS sensors to provide such IaaSr/NaaSr services, there will arise a series of critical challenges: (1) where to place the DFOS sensors, and (2) how to provision the DFOS sensing fiber routes to cover the whole network infrastructures with the minimum number of DFOS sensors? We name this as the DFOS placement problem. In this paper, we prove that the DFOS placement problem is an NP-hard problem, and we analyze the upper bound of the number of DFOS sensors used. To facilitate the optimal solution, we formulate the DFOS placement problem with an Integer Linear Programming model that aims at minimizing the number of DFOS sensors used. Furthermore, we propose a cost-efficient heuristic solution, called Explore-and-Pick (EnP), which can achieve a close-to-optimal performance in a fast manner. We analyze the approximation ratio and the computational complexity of the proposed EnP algorithm. In addition, we conduct comprehensive simulations to evaluate the performance of the proposed solutions. Simulation results show that the EnP algorithm can outperform the baseline algorithm by 16% in average and 26% at best, and it achieves a performance that is close to the optimal result obtained by ILP.

Article
In the present work, a high-speed optical encoder is proposed based on two-dimensional photonic crystal ring resonator using coupled mode theory and resonance effect. Square-shaped ring resonator, couplings rods, and several waveguides have been utilized in the proposed structure. Silicon rods in air structure have been designed with rod radius of 0.1a and lattice constant ‘a’ as 540 nm. The photonic band gap is being calculated using plane wave expansion method and finite-difference-time-domain method to analyze the performance characteristics of optical encoder like transmission spectra, electric field view, contrast ratio, response time, etc. The operating wavelength of structure is 1550 nm, to perform encoder operation where only one input port is activated at a time while other input ports are inactivated, and accordingly equivalent binary encoded signal is produced at output ports. The proposed encoder is designed with fast response time 222.76 fs, high data rate of 4.48 Tbps, and ultra-compact size of 140.84 µm². Hence the proposed device is suitable for high-speed optical computation as photonic integrated circuit.

Article
Elastic Optical Networks (EON) have recently attracts researchers, as one of the most promising technologies for flexibly assign spectrum resources to link requests,and benefits from higher spectral efficiency and system capacity. The spectrum assignment problem is dividing the bandwidth into frequency slices and connecting requests with different capacities using different numbers of frequency slices to transfer data. On the other hand, one of the most important issues in cloud computing is to model the problem as a multilayer optimization problem, which is well-known as Multi-Protocol Label Switching (MPLS). In this paper, the network is considered as a two-layer network in which the physical layer is the optical fiber layer on elastic optical network layer. In elastic optical network (EON), the network spectrum is divided into smaller spectrum slots to improve the spectrum utilization, but the high-quality spectrum division also complicates the routing and spectrum allocation (RSA) problem. In previous researches, RSA has been considered independent from MPLS. In this paper, a new mathematical model for MPLS is introduced in which the optical fiber layer joints with RSA. The objective function is defined as minimizing the total allocation costs. To verify the model, the optimal objective functions of different values of the capacities of modules in both layers are compared. It is shown that the combination of these two problems reduces the total allocation costs for large values of optical slices and could increase it in cases where the number of optical slices is small while the number of modules is high.

Article
A novel architecture with point-to-multipoint direct communication (P2MPDC) between any two optical network units (ONUs) for data center is proposed in the paper. By designing transceiver module (TM) ingeniously, the architecture is finished to realize P2MPDC between ONUs in wavelength division multiplexing passive optical networks (WDM-PONs). By constructing wavelength routing module (WRM), backup fiber can be saved to reduce the capital expenditures (CapEx) of network. By utilizing interconnected optical fibers between ONUs, the network has achieved three-level protections (feeder optical fiber protection, distributed optical fiber protection and interconnected optical fiber protection). Finally, by the simulation and analysis, the effectiveness of the proposed architecture is demonstrated.

Article
In this paper, an all-optical miniaturized binary to gray code converter is designed and analyzed. The all-optical domain is now an alternative for electronic devices, where performance and speed are the key issues. Code converters are significantly used in digital data transmission in the areas of error detection and correction. Gray code is one of the cyclic codes, where the cyclic shift of each codeword is also a code word. An all-optical XOR gate, realized using a Y-shaped power combiner is used in this design to generate the desired gray code from the given binary code. The insertion loss and extinction ratio parameters are found to be 0.347 dB and 22.26 dB, respectively. The entire simulation is carried out using finite-difference time-domain method. The obtained practical results are verified mathematically using MATLAB.

Article
In this study, an optical switch based on two-dimensional photonic crystals is presented for the slow light regime. This regime enhances light–matter interaction and can be used to design low-power all-optical devices. Due to slow light properties in photonic crystals, the maximum flat band for the group index of 8 was obtained. The threshold light intensity was reduced to 16 mW/µm² in comparison with other works. The maximum rise and fall times were calculated about 1 ps, which means the switching frequency is about 1 THz. The total footprint of the proposed switch is 5.5 × 9 µm², which makes the possibility for optical integration.

Article
With the success of commercial spaceflights, space information infrastructure (SII) has received much attention in recent years. Blueprints such as the low earth orbit global communication network and the data center in space have been proposed. To these ends, a satellite backbone network (SBN) is an essential part of SII and can connect multiple heterogeneous space networks, provide high-throughput connections for other space information devices, and even provide space computing power. To obtain ultra-high bandwidth and resource flexibility over limited channels, we propose a timeslot-based optical switched SBN (OSBN). More specifically, we show the node structure, switching system and bandwidth-on-demand (BoD) mechanism of the proposed OSBN. By simulation, we analyze the OSBN’s performances under different designed parameters and suggest the best ones. In addition, the BoD mechanism is verified to enhance differentiated service-of-quality. Experimentally, we demonstrate the access and handover processing of OSBN. Additionally, we analyze the performance of space computing over an imitated OSBN platform.

Article
In this work, an all-optical half adder is proposed based on a two-dimensional photonic crystal with uniform structural parameters. The proposed structure is composed of a triangular lattice of dielectric rods in air. The structure has been designed based on interference of light in waveguides which are formed by removing a number of dielectric rods. The structure has been simulated by using the plane wave expansion and the finite difference time domain methods. The size of the proposed structure is small with dimensions of 17 μm × 12.2 μm. The structural parameters such as radius of dielectric rods and dielectric constant are uniform across the structure, which makes it easier to fabricate with less fabrication errors. The proposed structure does not need high input power, and it has a fast response time.

Article
In this study, a novel two-dimensional photonic crystal-based structure, including 70 and 90 rods along the x and z directions, has been proposed for multiplying two-bit numbers. The fundamental rods are made of silicon, and the lattice constant is equal to 608 nm. The structure consists of six cross-connection waveguides, and the nonlinear rods have been placed inside them. Dependence of the refractive index to the applied optical intensity for nonlinear rods helps to have the desired interferences and activate the correct output ports. The finite difference time domain and the plane-wave expansion methods are used to simulate the optical wave propagation throughout the structure and calculation of the band diagram. Time analysis of the structure shows the delay time is just around 6.5 ps that is proper to optical processing. Also, the contrast ratio is equal to 2.72 dB. The obtained results demonstrate the capability of the presented structure to be using for optical applications.

Article
This paper examines the implementation of multi-level amplitude modulation enforced by trellis coding in a downlink non-orthogonal multiple access channel for visible light communication (VLC). The non-orthogonal transmission is applied using superposition coding and successive interference cancellation with the support of a trellis decoder. The VLC is addressed by a channel model according to Lambert. Two levels of maximum likelihood signal detection are observed and compared, each for corresponding 4 and 8 trellis-coded modulation (TCM). The power ratio allotment is examined to investigate the system performance in the bit error rate. The simulation showed that a threshold of power ratio is needed to ensure good performance of signal detection. Further simulation with successive detection had shown effective results for up to three users.

Article
The current generation optical networks are evolving as transparent networks by implementing all optical components like OXCs, OADMs, etc., and hence, minimizing the network operational cost. The routing and wavelength assignment is the major issue of concern while planning these networks with the thrust on maximum resource utilization, minimum operational and capital expenses. The various factors like reduced O-E conversions taking place, dynamic routing, network state dependence and additive nature of impairments make the system more vulnerable to risk of high levels of accumulated impairments, thereby decreasing the quality of transmission (QoT). In some cases, QoT is so low that it becomes difficult to retrieve the signal at receiving end. Considering the huge data traffic being carried by the network, it becomes crucial to inculcate the impact of physical layer impairments (PLIs) in path selection and routing applications. In order to address the issue, impact of different PLIs on quality of signal is presented in the form of BER and Q-factor. The impact is then considered for routing applications with focus on range, intelligibility and scalability of the system. The network performance in terms of blocking rate is calculated. The regenerator placement is suggested as one of the methodologies of improvement in network performance. Further, network behavior is studied by making 0%, 50%, and 100% nodes regeneration capable.

Article
Visible light communication (VLC) network is an appropriate solution to meet the 5G and 6G. It can overcome the spectrum scarcity and capacity in the radio frequency (RF) networks. This network faces some challenges. Obstacles can break links and disconnect the network. Mobile nodes cannot receive data continuously because the transmitters have few fields of view. Using common MAC solutions in wireless networks does not solve VLC network problems. VLC MAC solutions should solve deafness, hidden node, full-duplex capability, channel utilization, and connectivity. This paper provided a survey in MAC layer solutions in VLC networks based on the systematic literature review (SLR). The methods have been recently published from 2011 to 2021. We analyzed analytically and statistically and the technical taxonomy presented with the SLR process according to the proposed solutions. Solutions were categorized into half-duplex, full-duplex, cooperative, and VLC/RF categories. Also, other proposed methods were described briefly. We explained the features, advantages, and disadvantages of each method. MAC layer design challenges in VLC networks were discussed to fill the gap in the previous literature. By classification and problem analysis, fewer attention topics that need more research were extracted. We found that fairness and reliability metrics received less attention and dynamic resource allocation was the main context in the VLC MAC solutions. Finally, future research challenges and open issues in VLC MAC solutions were proposed.

Article
The presented research deals with designing of a new ultra compact all-optical RS flip-flop on a two-dimensional (2-D) hexagonal photonic crystal platform. The flip-flop is designed by using two NOR gates, photonic crystal waveguides, four silicon ring resonators, four input ports and two output ports. The designed flip-flop structure has hexagonal silicon rods in the air host with a lattice constant a of 630 nm. Si rods have a radius of 0.2a and operating waveleangth of 1550 nm. The novel design provides proper distinction between logic 1 and logic 0 at the output by giving 8.7 dB and 4 dB contrast ratio at Q and Qbar output, respectively. Furthermore, uncomplicated structure resulting in small dimension of 28 μm * 28 μm makes it appropriate for optical integrated circuit in optical networks. FDTD method is used to model the proposed structure and simulated using RSoft FullWAVE simulator tool.

Article
Reflective semiconductor optical amplifier (RSOA) is an efficient gain medium and finds application in passive optical network. Due to its double-pass characteristics compared to ordinary semiconductor optical amplifier, gives better switching performance. RSOA based gain dynamics is utilized to design and analyze the NOR gate using soliton pulses for the first time in this communication. The simulation results using MATLAB show an efficient performance (Q value more than 80 dB) of this gate with less complexity in hardware. The NOR gate is characterized by calculating extinction ratio (ER ~ 14 dB), contrast ratio (CR ~ 15 dB), Q value (~ 90 dB), and the effect of amplified spontaneous emission noise is also investigated. This NOR gate uses a single RSOA and can be used to design any optical logic processors in future.

Article
This article explains the subject of IP Addressing and Subnetting in a very simplified way for network engineers, university students and anyone in the world of information technology, and my goal is to learn and benefit and our love for each other increases.

Article
This paper addresses the problem of minimizing total slot idle time in assigning spectrum to a 2-class traffic, considering both incremental and dynamic arrival and permanence rules. Deadlock avoidance under incremental traffic is first shown to be possible with the use of non-greedy spectrum assignment policies in some link states which are identified from knowledge of the connection request sizes, thus keeping total idleness finite and minimal. Then, the concept of deadlock avoidance is extended to dynamic traffic with the purpose of proposing an algorithm that mitigates fragmentation losses with appropriate greedy traffic-aware assignment policies. Since deadlock is not permanent under dynamic traffic, avoidance by assignment denial is not used. Instead, the proposed algorithm is only reluctant to assign dysfunctional, deadlock-prone voids in favour of functional voids if they are available. Other priorities may also apply if multiple searches are allowed.

Article
Resources of Passive Optical Networks (PONs) can be shared by a diverse spectrum of customers such as residential users, business subscribers, mobile network operators, and service providers. A PON customer can rent one or several Optical Network Units (ONUs) from an Infrastructure Service Provider. The ONUs of a customer (multi-ONU customer) can be subject to large spatiotemporal traffic variability, resulting in underutilization of particular ONUs and overutilization of others. The Interleaved Polling with Adaptive Cycle Time with Multi-ONU SLAs support (MOS-IPACT) algorithm has been recently proposed to promote the redistribution of unused bandwidth of underloaded ONUs of a multi-ONU customer. This paper introduces an analytical model to evaluate the duration of idle periods in bandwidth usage, as well as a performance evaluation of the MOS-IPACT algorithm in networks with traditional and multi-ONU customers. Numerical results show that the MOS-IPACT algorithm efficiently distributes the excess bandwidth among the ONUs of multi-ONU customers without compromising the bandwidth availability.

Article
Underground mining (UM) is an industry worldwide known for its hostile work environment; therefore, a proper communication system is essential to preserve the miners’ safety. However, the irregular features of UM tunnels as well as their environment prone to electromagnetic interference make it difficult to implement traditional wireless communication systems. Therefore, a viable solution is to complement the systems with a communication infrastructure based on visible light communication (VLC). Nevertheless, VLC systems for underground mines have not been widely developed, although there is extensive literature on VLC applications in indoor non-hostile environments. This article develops a study and characterization of the physical factors and external phenomena of the UM tunnels, as well as the orientation of optical components that affect the performance of VLC systems. In order to evaluate and verify the behavior of the UM-VLC channel, the channel impulse response (CIR) and the received optical power distribution in the UM scenario are presented. Furthermore, to analyze the performance of the UM-VLC system, the bit error rate (BER) curves are obtained based on the IEEE 802.15.7 standard considering perfect and imperfect channel state information (CSI), and by using the least square (LS), minimum mean square error (MMSE), and spectral temporal averaging (STA) channel estimation techniques. The metrics analyzed show and validate the adverse effects of the UM environment on the VLC system and its channel, which gives a solid baseline to find proper solutions and mitigate those effects.

Article
In this paper, we analyze and compare the use and benefits of several combining schemes to create diversity at the optical receiver in a multi-cell indoor Visible Light Communication (VLC) system. Furthermore, its implementation in a pyramidal Angle Diversity Receiver (ADR) to mitigate Inter-Cell Interference (ICI) in the system is analyzed. Thus, four combining schemes in the receiver side are studied and implemented: Select Best Combining (SBC), Equal Gain Combining (EGC), Generalized Selection Combining (GSC), and Maximum Ratio Combining (MRC). These techniques, in conjunction with the presented ADR, configure an optical receiver that enhances the performance of the VLC system by selecting or combining the received optical signals. The results indicate that the ADR implemented with the MRC scheme outperforms the SBC, EGC and GSC schemes in terms of Signal-to-Interference-to-Noise Ratio and User Data Rate. This is because MRC assigns weights to both the interference and the received signals, thus improving the quality of the combined signal in the ADR in the presence of ICI.

Article
Data-parallel computing applications (DPCAs) (e.g., MapReduce, web search, etc.) are driving the need of scalable, low-latency, high-speed, and energy-efficient datacenters, because a DPCA consists of a series of heavy-computation stages within a datacenter, and each stage contains multiple parallel flows that must be completed before next stage starts, referred to as “Coflow”. These parallel flows are grouped as a Coflow. Coflow is a networking abstraction to convey application-level communication requirements by exposing rich semantics of DPCAs to underlying networks, e.g., latency of data transmission between two computation stages, known as “Coflow Completion Time” (CCT). Packet-switched optical network (PSON) is a practical intra-datacenter interconnect solution for DPCAs, as it is designed as a low-complexity and scalable one-stage switching architecture, using advanced optical networking technologies, such as Arrayed Waveguide Grating Routers and wavelength-division multiplexing. In this work, we study how to minimize CCT in PSON-enabled datacenters by placing senders and receivers of Coflows to proper transceiver nodes and scheduling data transmission wisely, for which we propose a Coflow-aware placement and scheduling algorithm, consisting of Min-Priority placement algorithm and Priority-aware scheduling algorithm. They are designed to cooperate with each other to jointly minimize CCT. Numerical simulations demonstrate the benefits of joint design of Coflow placement and scheduling algorithm, compared to state-of-the-art scheduling and placement algorithms designed without correlation.

Article
Access Networks based on Passive Optical Network (PON) technology can offer transport services to broadband service providers, such as mobile backhauling/fronthauling for Mobile Network Operators and multi-ONU Service Level Agreements for Virtual Network Operators. Besides that, Infrastructure Service Provider (InP) also provides broadband access services to end-users, such as residential subscribers and single or multi-site enterprises. In such a scenario, the InPs support diverse customers in the same PON. This paper proposes a bandwidth slicing mechanism to assure bandwidth isolation for different PON customers who rent part of a PON infrastructure from the InP. We introduce a Dynamic Bandwidth Allocation algorithm for Ethernet PONs called MAB-IPACT, which assures bandwidth on different granularity: conventional customers with a single ONU, multi-ONU customers owning a group of ONUs and providing a single type of service, and multi-ONU customers having diverse types of services. The MAB-IPACT algorithm also prioritizes bandwidth distribution among subgroups of ONUs of the same multi-ONU customer. A subgroup of ONUs is a subset of ONUs that belongs to the same multi-ONU customer, which are employed for the same type of service (e.g., ONUs for business service.). Simulation results show that the proposed mechanism improves the network performance of multi-ONU customers with subgroups of ONUs serving different services.

Article
In this paper, we consider the problem of clustering nodes in a wireless visible light communication (VLC) network while simultaneously forming a spanning tree backbone. More precisely, let G=(V,E) be a complete Euclidean input graph instance with a set of wireless node devices V and connection links E representing the VLC network. We consider the problem of partitioning k≤|V| nodes into disjoint cliques of the size of at most ⌊kt⌋+1 nodes where t≤k(k,t∈Z+) in such a way that a unique vertex of each clique is used to form a spanning tree backbone. The underlying idea is to form clusters of nodes while simultaneously providing connectivity between them. Thus, we maximize the total power received and total residual energy of the k chosen nodes of the network for such a structure. We also consider the simplified version of the problem in which no backbone structure is required. Recall that clustering the nodes of a wireless network allows handling efficiently problems related to scalability and routing. In order to achieve the grouping task optimally, we propose mixed-integer linear and quadratic programming models based on classical combinatorial optimization problems. In order to compare our proposed models, we assume that every node in the network can communicate through a direct-line-of-sight VLC channel. Our numerical results indicate that the linearized quadratic models are preferable as they allow solving to optimality most of the tested instances and in less computational effort.

Article
Optical networks are currently the only technology capable of providing extremely high data transmission rates. Because of this, systems must be increasingly efficient and immune to failures. One way to improve network efficiency is to use dynamic approaches like Adaptive Control of Operating Point, which consists of autonomously choosing the best operating point for optical amplifiers on the link, thus providing the best configuration concerning Quality of transmission. Unlike the previous works that focused on optimizing Optical Signal-To-Noise Ratio, our proposal and analysis are focused on maximizing the transmission rate. In this paper, we compare the results obtained by five different and widely used evolutionary and swarm-based algorithms in the search for maximizing the transmission rate in optical links. We have observed that the differential evolution provided the best results in the analyzed scenarios.

Article
In this paper, we solve virtualized passive optical network (VPON) assignment and virtualized baseband unit (vBBU) placement using an integer linear programming formulation, an approximated heuristic using linear relaxation, and a proactive heuristic based on a specific kind of recurrent neural network. We also studied the application of multi-step forecasting in Cloud-Fog Radio Access Network (CF-RAN) traffic demands for joint use with integer linear programming once it allows the solver more time to generate solutions. Also, we examine if the error in batch prediction impacts the final solution in terms of blocking and correctness.

Article
A microring-embedded Mach–Zehnder interferometer (MZI) system is proposed to form the multiplexing (demultiplexing) for wireless and light fidelity (WiFi and LiFi) uplink and downlink transmission. The system consists of two center microrings at the transmitter and a center microring at the receiver with two small rings along the sides of the center microrings. The whispering-gallery mode (WGM) is formed by the nonlinearity effect induced by the two small rings with suitable parameters. The embedded gold gratings are excited by the WGM, where the plasmon oscillation and electron density are obtained. All possible multiplexing/demultiplexing (MUX/DEMUX) schemes based on space–time input can be applied. The transmission is performed using the tested node. The uplink and downlink input source wavelengths of 1.10 µm and 1.30 µm for LiFi and WiFi are manipulated. The manipulated tested node is employed with a maximum length of 1, 000 km away from the transmitted point via a fiber optic cable. The results obtained have shown that the optimum transmission bit rate of 2.52 Petabit s-1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${s}^{-1}$$\end{document} with the optimum bit error rate (BER) of 0.38 is obtained.

Article
The development of devices for communication networks to transmit information has become an active and growing field of research. Multiplexer/demultiplexer (M/D) is one of the basic devices in this field. In this paper, an M/D design is introduced based on the surface plasmon resonance in optical ring resonators. The number of inputs and outputs of M/D is 3 × 1 and 1 × 3, respectively. All parameters of the structure, including radius and width of ring resonators and waveguides, have been evaluated to obtain the optimal response. Also, we used the nonlinear gold property to expand the range of M/D performance and simulated the results for intensities less than 100 MW/cm². Selectivity in the number of inputs and outputs, controllability using several parameters, all optically, selectivity in operation frequency, nanoscale size, reconfigurability, and integrated capability are the features of this design. In our simulation, we consider transmission and reflection of light in each port based on the finite difference time domain for evaluation of results.

Article
Security in quantum dot cellular automata (SQCA) is an emerging trend in the arena of nanotechnology. Its features are high computing speed, smaller size and low power depletion in comparison to transistor oriented technology. This article proposes a nanoscale Crypto-Codec circuit which produces cipher texts in order to obtain security during nanocommunication. Single layer crossing is used to design the Crypto-Codec circuit to minimize the fabrication difficulty. In this article higher attention is given to obtain high level of security by providing two layers of security using two different keys at two levels. Cryptographic communication architecture is proposed employing Crypto-Codecs and 2 × 2 Crossbar switch for authentic information sharing. The result resembles with the theoretical values, which endorse the precision of the proposed circuit. Circuit density of the design is calculated to prove that QCA circuits possess higher devise density in comparison to CMOS circuit. Stuck-at-fault analysis is performed to obtain faultless design. The proposed circuit is designed using QCA designer tool.

Article
The inappropriate distribution of traffic in high workload areas leads to congestion, packet loss, and poor service quality provided by data center networks (DCNs). In this paper, we have proposed a new method for traffic engineering (TE) as a modular approach. Based on this algorithm, depending on the type of traffic, when enough resources are not available for routing, the best path for that flow would be chosen. In the proposed algorithm, the less loaded paths for conduction of current are selected with regard to the present conditions as soon as a current is generated between two hosts, their position is identified in the DCN, and the paths between the two are obtained. We have simulated our algorithm by Mininet emulator. The results demonstrated that the SEMTE method performed an average of 30% better in energy consumption and 70% better in increasing maximum link utilization (MLU) compared to the conventional equal cost multi-path (ECMP) algorithm; however, there was some overhead on the system in terms of time of reading information from OpenFlow switches.

Article
Software-defined network (SDN) is an architecture with a physical or conceptual central controller. This architecture separates data and control plane causing network flexibility, programmability, and manageability. A packet when is received by the forwarding element (FE) as the first packet of the flow is forwarded towards the controller in the packet-in message; then, the controller decides for all packets belonging to the flow. The controller imposes the rule for the flow to the FE; thus, the FE acts based on the matching rules with the ingress packet in the flow table. Routing can be done by considering performance metrics to improve entire network performance in SDN. Performance and cost metrics include utilization, delay, jitter, packet loss ratio (PLR), blocking probability (BP), and link cost, so an optimized path selection is a multi-objective optimization problem and NP-Hard that we will consider. In this paper, we try to provide a comprehensive algorithm for optimizing the entire network performance in SDN. We propose the novel algorithm for flow routing based on three steps: (1) a linear algorithm is developed to extract the path between each source and destination in the controller, (2) non-dominated ranking is used to categorize the extracted paths, and finally, (3) the crowd distance sorting algorithm is implemented to select the optimized route from all performance dimensions. To evaluate the proposed algorithm, the shortest path and greedy-based routing algorithms will be simulated by Java, and the simulation results show that the proposed optimization algorithm improves the all mentioned performance criteria, simultaneously.

Article
Some of the vital problems around the conventional CMOS technology are leakage-power consumption, physical-scalability limits, and short-channel effects. These deficiencies have led to many studies about nano-scale designs. Quantum dot cellular automata (QCA) is a potential answer in nanotechnology. Scholars have considered the four-dot squared cell as the main factor in the QCA. Also, a full-adder is a fundamental unit in every digital system. However, the importance of cell and area consumption limitation in circuit designing has been completely ignored in most of the related studies. Therefore, in this paper, we have offered a one-bit multi-layer full-adder cell. The practical accuracy of the proposed circuits has been assessed using QCADesigner. According to the obtained results and the design, the presented design has efficient cell usage against all the prior designs regarding cell counts and area occupation, leading to around 7% improvement in cell number than the common full-adder design. The simulation outcomes have also shown that the introduced design has excellent efficiency regarding cell and area aspects.

Article
Quantum-dot cellular automata (QCA) is one of the most prominent technologies in nanometer-scale with appreciable reduction of size and power consumption and high switching frequency to overcome the scaling limitations of complementary metal-oxide semiconductor. On the other hand, code converters play a key role in signal processing and efficient network designs. The researchers have focused on emerging nano-devices that can identify errors throughout information transfer. Therefore, in this research, a new QCA-based 4-bit binary to gray converter circuit employing the appropriate configuration of the XOR gate as a basic building block has been suggested. The layout has been generated using the QCADesigner simulation tool to test the functionality of the code converter. The performance results indicated that the proposed converter works properly and has optimum performance parameters such as latency, complexity, and consumed area as compared to the current schemes.

Article
This article reports a design and analysis of 8×8 dilated banyan network using 1×2 and 2×1 gated Mach−Zehnder interferometric (GMZI) crossbar photonic switches for crosstalk reduction. The GMZI crossbar switches are designed using proton exchanged channel waveguides with single-crystal lithium niobate on insulator. The features of the designed GMZI switches are its broadband operation, low insertion loss, and low crosstalk. These are verified by the numerical experiments using full-vectorial 2D finite-difference beam propagation method and using various figure-of-merits. The OFF-state feature in the proposed 1×2 and 2×1 GMZI switches provides a crosstalk reduction in the network since the idle switches are configured to be in OFF-state to avoid the crosstalk propagation. We performed a comparative study on 8×8 dilated banyan network based on 2×2 MZI switches and the proposed GMZI switches. The fully loaded 8×8 dilated banyan network with the proposed GMZI switches leads to crosstalk reduction of more than 25 dB, which provide broadband operation over a wavelength range of 1530–1570 nm and 50% reduced footprint against the 2×2 MZI-based implementation.

Article
The continuous increase of data traffic for present-day applications necessitates the development of Elastic Optical Networks (EONs). Significant advancements in efficient Routing and Spectrum Assignment (RSA) algorithms for EONs have been noticed in the recent past. These existing algorithms did not mention constraints on the number of transceivers per node in a network. However, for the planning of a realistic network, it is necessary to estimate the number of transceivers required at each node for the efficient operation of a network. Therefore, transceiver constraints should be taken into account while designing the RSA algorithms. In this paper, we present the impact of putting a limit to the number of transmitters and receivers available at each node of an EON. Moreover, the cost of a network heavily depends on the number of transceivers that each node in the network may offer. Hence, estimating the required number of transceivers per node in a network is vital to approximate the design cost of a network. Here, we present an Integer Linear Programming (ILP) formulation that includes the transceiver constraints and also develop a transceiver-aware heuristic algorithm for routing and spectrum assignment in EONs. Simulation results help us provide a proper design tool to estimate the number of transceivers per node in elastic optical networks.

Article
In recent years, cloud data centers have received increased attention by the research community, due to their key function of hosting a big number of cloud applications and services. At the same time, however, various and conflicting requirements have emerged, such as a mixture of different type of flows in shallow buffer switches, which are interconnected via fiber optics in many-to-one network topology. In this environment, the conventional transmission control protocol (TCP) exhibits severe performance degradation. In this paper, the issues affecting TCP performance in data center networks are studied and different congestion control schemes, such as CUBIC, DCTCP, HighSpeed, NewReno and Vegas, are presented and evaluated by means of computer simulations in realistic data center network scenarios. Our results show that DCTCP eliminates the performance problems of conventional TCP in data center networks and exhibits the performance and fairness properties required for efficient network deployment.

Article
Optical circuit switching networks have been recognized as a promising solution for inter-datacenter networks. However, for intra-datacenter networks, they may fall short in efficiently provisioning traffic requests due to their relatively coarse-grained channel assignment and special intra-datacenter traffic patterns. Optical time slice switching (OTSS) has been recently proposed as an optical-switching technique that can provide flexible and transparent optical circuits by extending the merit of flex-grid switching to the time domain, thus achieving much finer granularity. As OTSS requires nanosecond speed optical switches which are expensive, it might not be economically viable to make a one-time upgrade for the entire datacenter. Thus, we expect fine-grained OTSS-enabled and coarse-grained flex-grid-enabled optical switching techniques to co-exist in the foreseeable future. In this study, we investigate an OTSS-enabled flex-grid (OTSS-FG) architecture for intra-datacenter networks. For scenarios where traffic flows are given, we develop a Mixed Integer Linear Program to study the optimal bandwidth allocation scheme in an OTSS-FG architecture. When traffic flows are generated in real time, by leveraging machine-learning techniques to detect flow types, we propose a flow-aware bandwidth allocation (FABA) scheme and a dynamic version of FABA, called “D-FABA” scheme. Numerical simulations show that proposed bandwidth allocation scheme can outperform benchmark schemes in terms of average delay and blocking probability.

Article
In this paper, the spectral efficiency and quantum limit for transmission of a BPSK signal in a WDM system are computed after analyzing the error probability in the presence of component crosstalk. The analysis of bit error rate (BER) is derived from the non-Gaussian probability density function for finite (N) interferers obtained using a new mathematical formulation employing Maclaurin series expansion of the N﻿th power of zero-order Bessel function. The model is verified with the experimental data taken from the literature. The effects of number of interfering channels, SNR and data rate on BER are studied. Results show how spectral efficiency and quantum limit deviate from ideal values due to the presence of interferers. The spectral efficiency decreases with the appearance of interferers, thus escalating the transmission cost per bit. From the study of quantum limit, it is seen that the minimum number of photons per bit required for BPSK transmission is to be increased to maintain a fixed BER as the number of interferers increases.

Article
Lithium niobate nanophotonic structures have recently become a promising candidate for efficient nonlinear frequency-conversion processes. Here, the second harmonic generation in a graphene-based LN waveguide is theoretically proposed at the telecommunication band. The structure is able to gain high conversion efficiency due to the large nonlinear coefficient of LN and tight field confinement. The subwavelength mode confinement inside the LN layer is strongly influenced by the graphene conductivity. In the presented structure, the nonlinear interaction of propagating plasmons can be widely tuned by slightly change in the surface conductivity of graphene monolayer which is a promising feature for SHG applications in comparison to the conventional structures which rely on geometry variation. According to the results, SH intensity of ISH=0.09kW/cm2 is observed at the fundamental wavelength of 1550nm with a 7% of nonlinear conversion efficiency. To analyze the geometrical parameters and show the tunability of the configuration, the effect of input frequency and waveguide length on SH output power are demonstrated at PFF=1W and μc = 0.6 eV. The calculations reveal that the PSH becomes lower by lengthening the waveguide where the maximum output of PSH=72.5mW is obtained at 1 μm-long waveguide.

Article
This article reports a design and analysis of 8x8 dilated banyan network using 1x2 and 2x1 gated Mach-Zehnder interferometric (GMZI) crossbar photonic switches for crosstalk reduction. The GMZI crossbar switches are designed using proton exchanged (PE) channel waveguides with single-crystal lithium niobate on insulator (LNOI). The features of the designed GMZI switches are its broadband operation, low insertion loss, and low rosstalk. These are veri�fied by the numerical experiments using full-vectorial 2D �finite-difference beam propagation method (FD-BPM) and using various �figure-of-merits. The OFF-state feature in the proposed 1x2 and 2x1 GMZI switches provide a crosstalk reduction in the network since the idle switches are confi�gured to be in OFF-state to avoid the crosstalk propagation. We performed a comparative study on 8x8 dilated banyan network based on 2x2 MZI switches and the proposed GMZI switches. The fully loaded 8x8 dilated banyan network with the proposed GMZI switches leads to crosstalk reduction of more than 25 dB, provide broadband operation over a wavelength range of 1530 nm to 1570 nm and 50% reduced footprint against the 2x2 MZI based implementation.

Article
Sign detection has a wide application in digital fixed-point signal processing; however, it seems hard to conduct it in residue number systems (RNSs) based on complementary metal oxide semiconductor (CMOS). Also, quantum-dot cellular automata (QCA), as a useful substitution for CMOS technologies, provide many benefits such as low energy utilization and high velocity. However, up to now, there is not any paper that investigated the design of the QCA-based sign detection system. Therefore, here, we will introduce a method for RNS sign detection in the three-moduli set {2ⁿ⁺¹ − 1, 2ⁿ − 1, 2ⁿ}. In the suggested design, we offer a new QCA-based design in one layer for sign detection of three-moduli set {2ⁿ⁺¹ − 1, 2ⁿ − 1, 2ⁿ}. It is not only used for arithmetic units of RNS but also applied for cost and performance improvement of the total system. We simulate and analyze the proposed detection method using the QCADesigner simulator. We also compare the cell count, delay, and occupied area. Experimental results showed that the proposed architecture requires 5.60 µm² of the circuit area, and the delay is decreased.

Article
Passive optical networks (PONs) are a preferred technology for implementing fiber-to-the-home networks. Though PONs minimize power consumption compared to digital subscriber loops (DSL), they still constitute a significant portion of the power consumed in the telecommunication network. Several research efforts have thus focused on minimizing power consumption in a PON network, e.g., optimal PON dimensioning, sleep modes, and designing next-generation power efficient PON candidates, like bit-interleaved PON (Bi-PON), wavelength split time and wavelength division multiplexed PON (TWDM-PON) and wavelength-switched TWDM-PON. A natural question thus arise is what are the power savings of these various mechanisms and are there some synergy gains if these efforts can be combined? In this work, we propose analytical models for evaluating the power saving potentials of optimal PON dimensioning, sleep modes, and next-generation PON candidates like Bi-PON, wavelength split and wavelength switched TWDM-PON. For optimal PON dimensioning, we consider a promised grade of service to the users, while to explore the sleep mode functionality, we consider state-of-the-art dynamic bandwidth allocation (DBA) algorithms like sleep mode aware (SMA) and hybrid sleep mode aware (HSMA). We then propose the power models to assess the power efficiency of sleep modes in combination with the optimal dimensioning. In addition, we further extend these mechanisms to the next-generation PON candidates and evaluate the power saving potentials. Furthermore, in order to show the accuracy of the proposed models, we validate all these analytical models with the simulation results.

Article
Elastic optical networks allow for a division of the optical spectrum into frequency slots, which can be combined to create channels with bandwidth defined by demand. Their flexibility provides greater spectral efficiency when compared with traditional optical networks with fixed grids. Traffic grooming strategies allow for even more efficiency in the use of network resources, reducing the number of guard bands and the utilization of transmitters and receivers. This work proposes a mechanism that influences the RMLSA algorithms causing a controlled level of spacing between the lightpaths. This makes it possible to expand lightpaths in the future to fulfill new customer requests through traffic grooming. The proposed mechanism does not require the use of specific traffic grooming or RMLSA algorithms, and it can be used in conjunction with existing solutions or future solutions. The experiments carried out show that the proposed mechanism reduces the bandwidth blocking ratio and the number of necessary transceivers, and also increases the request–lightpath ratio and energy efficiency in the network.

Article
Recently, a number of projected successive interference cancellation (PSIC) and projected parallel interference cancellation (PPIC) structures, which make use of the non-negativity constraint in incoherent OCDMA systems to enhance their performance, have been proposed and studied in (Seleem et al. in IEEE Commun Lett 16:1721–1724, 2012). Although these structures showed improved performance, they still inherit the same shortcomings of the conventional SIC/PIC structures such as large detection delay for the SIC detector and slow convergence speed for the PIC detector. In this work, we propose a new projected block-wise SIC (PBSIC) structure that not only exploits the non-negativity constraint but also overcomes the drawbacks associated with the conventional SIC/PIC structures. In particular, it largely reduces the detection delay of the PSIC detector of (Seleem et al. in IEEE Commun Lett 16:1721–1724, 2012), while it enjoys the same fast convergence speed. Two approaches for decreasing the computational complexity of the proposed detector are investigated. Simulation results are in total agreement with our theoretical findings.

Article
In the wireless ultraviolet sensor network, interference causes data retransmission, which is not conducive to communication between sensor nodes. Aiming at the serious communication interference problem of three-dimensional k-connected wireless ultraviolet light sensor network, this paper proposes a novel low-interference wireless ultraviolet network fault-tolerant topology control algorithm. The number of vertices disjoint paths between nodes and base stations is used as a fault-tolerance index to reduce network interference and ensure two-way fault tolerance between nodes and base stations. At the same time, genetic algorithm crossover and mutation operators are used to construct a particle swarm optimization algorithm, which is used to solve a reasonable power distribution scheme from the fault-tolerant network constructed by the 3D k-YG algorithm. The performance of the proposed algorithm is verified through simulation experiments. The experimental results show that the proposed algorithm can not only construct fault-tolerant topology, but also effectively reduce network interference.

Article
This paper theoretically studies the design and performance analysis of the reliable satellite-based quantum key distribution (QKD) over free-space optics channel. The proposed QKD system is based on the optical quadrature phase-shift keying (QPSK) modulation and the dual-threshold/heterodyne detection (DT/HD) receiver that helps to reduce quantum bit error rate (QBER) and improve the receiver sensitivity. In addition, a key retransmission scheme is also designed to enhance the reliability of the proposed QKD system. Performance of the key transmission is analyzed in terms of QBER and the probability of sifted key, taking into account the impacts of free-space path loss, atmospheric attenuation, beam spreading loss, atmospheric turbulence, and receiver noise. In addition, we newly develop an analytical framework by using the 3-D Markov chain model that allows us to investigate the key loss rate (KLR) performance at the link layer. Numerical results quantitatively show that our proposed satellite-based QKD system can offer significant performance improvement over the conventional ones.

Article
In this paper, a novel energy-aware grooming-based algorithm, named energy minimization algorithm (EMA), is proposed that aims at providing the quality of service requirements in elastic optical networks in terms of network energy efficiency and requests blocking probability. To this end, EMA divides the incoming requests into high priority and low priority requests and applies fragmentation and squeezing mechanisms on the low priority traffic to alleviate the blocking probability of high priority requests. Moreover, EMA proposes a novel mechanism to select the optimal paths in the routing phase so that the network energy consumption is minimized. The simulation results reveal that the proposed EMA improves the network energy efficiency and mitigates the requests blocking probability.

Article
A compact microstrip patch antenna was designed using IE3D v.15 simulation tool and improves its performance by using PBG structure and also has to achieve the desired resonant frequency by using the PBG structure. The bandwidth of this compact MPA was increased from 11.32 to 55.44% in frequency range 2.62–4.63 GHz by use of PBG structure at ground plane of the substrate, and the antenna is resonating at frequency 2.74 GHz with maximum return loss − 29.29 dB. This antenna is suitable for S band operations, i.e. WiMAX and Wi-Fi applications.

Top-cited authors
• Shahid Chamran University of Ahvaz
• Scuola Superiore Sant'Anna
• Shahid Chamran University of Ahvaz
• Universitat Politècnica de Catalunya
• Shahid Chamran University of Ahvaz