Multiple Optical Network Units Research Articles

Positioning multiple optical network units in fiber-wireless networks: An efficient hybrid [formula omitted]-harmonic means clustering approach

Wireless-optical broadband access network (WOBAN) or fiber-wireless (FiWi) is a robust and cost-effective solution to provide high bandwidth network connectivity to mobile subscribers. Optical network unit (ONU) placement is a topological optimization problem that plays a vital role in effective deployment of FiWi network. Recently, some artificial intelligence-based approaches for positioning ONUs were proposed and generated promising results. However, the reported performance in the literature is far from the ideal state. This issue emphasizes the necessity of introducing new placement methods or improving the performance of existing methods. This paper presents a hybrid clustering algorithm for finding the optimal position of multiple ONUs. The proposed backtracking K-harmonic means (BKHM) is an integration of K-harmonic means (KHM) and a backtracking search algorithm (BSA). BKHM not only efficiently specifies the optimal positions of ONUs but also significantly decreases the implementation cost. To demonstrate the performance of the BKHM, we evaluate it on well-known placement benchmarks compared with BSA, KHM, whale optimization algorithm (WOA), enhanced backtracking search (EBS), harris hawks optimization (HHO), and chaotic local search-based levy flight distribution (CLF) algorithms. The experimental results and statistical analysis proved that the proposed BKHM algorithm outperformed its counterparts on most benchmarks in terms of cost optimization, convergence accuracy, and solution quality.

Comparative analysis of techniques in long reach passive optical networks: overview and design

Abstract Long reach PON is an attractive option for addressing the growing bandwidth needs of internet applications and also serving multiple ONUs. Due to newly augmented technologies such as 4K/8K television, video meetings/conferencing, and online gaming, end-user bandwidth demands are exponentially rising day by day. Wavelength division multiplexing–based passive optical network (WDM-PON), which can deliver high data rates over long distances, is the ultimate solution to the growing bandwidth demand. It is possible to reduce the number of active cabinets and central offices while increasing the number of optical network units (ONUs) with the use of passive optical networks (PONs). At higher bit rates, researchers faced lot of issues like increased pulse width due to increased distance, burst loss, fault detection, etc. In this paper, we have discussed few challenges faced in passive optical networks. Also, we have discussed about the methodology to overcome these issues.

Robust Key Update With Controllable Accuracy Using Support Vector Machine for Secure OFDMA-PON

In this paper, we first propose a novel secret key update scheme only with a single support vector machine (SVM). To achieve robust and efficient key management for secure orthogonal frequency division multiple access-based passive optical network (OFDMA-PON). The key sequences required to be shared between multiple optical network units (ONUs) and optical line terminal (OLT) are converted into partial quadrature amplitude modulation (QAM) symbol phases, and then masked into the whole upstream signal using two-dimensional chaos. The session keys can be distributed in real-time without consuming exclusive secure channels and resulting in data rate loss. A well-trained support vector machine (SVM) implemented at the receiver enables error-free key decision. Moreover, the numerous cross validations are conducted to verify the superior generalization performance under various parameters including key length and modulation format. The 16-QAM, 32-QAM, and 64-QAM OFDM signal transmissions are successfully demonstrated over 25 km standard single mode fiber (SSMF) by an experiment. The results show that the controllable restored accuracy of key can be realized by regulating the pivotal algorithm parameter to flexibly adapt to different system conditions, thus this scheme can be a promising efficient key update technology for future secure PON.

A novel fuzzy-based algorithm for ONU placement in FiWi broadband access network

Optical network unit (ONU) placement is an essential challenge in fiber-wireless (FiWi) access networks, which affects the development cost and quality of services. Recently, some intelligent methods for ONU placement were developed and achieved encouraging results; however, their performance is far from the ideal state. A hybrid ONU placement method (AOFCM) based on Fuzzy C-Means (FCM) and Arithmetic Optimization (AO) algorithm is presented in this work, which makes full use of the merits of both algorithms. The AOFCM is a population-based iterative algorithm that models the ONU placement as a multi-modal optimization problem. It starts the optimization process with a collection of individuals. An individual contains the coordinates of multiple ONUs. AOFCM sequentially applies the FCM and the AO algorithms to the population such that the fitness of each individual is improved. With a test on four placement benchmarks, the proposed AOFCM is proven to significantly improve counterpart algorithms in cost minimization and convergence speed.

400-Gbps/80-km Rate-Flexible PCS-64-QAM WDM-CPON With Pseudo-m-QAM Chaotic Physical Layer Encryption

For next-generation high-capacity, rate-flexible, and secure 400-G passive optical network (PON), a scheme joint wavelength division-multiplexed (WDM), entropy-regulated probabilistic constellation shaping-64-quadrature amplitude modulation (PCS-64-QAM) and chaotic encryption mapping, is proposed and demonstrated. For the first time, chaotic encryption is realized over the PCS-based PON with the architecture from one optical line terminal (OLT) to multiple optical network units (ONUs). Chaotic encryption with an initial-value-sensitive feature can generate a large amount of parallel encrypted sequences which provide a key pair corresponding with every possible entropy/rate. A novel mapping from PCS-64-QAM with various entropies to pseudo- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> -QAM is designed, which erases the entropy information of the link and encrypted the original information of the sequence. The encryption transmission is demonstrated over a real-time dual-polarized coherent optical platform with an 80-km link and typically one-to-many PON configuration, and a net 211.80∼348.12-Gb/s rate result within the hard-decision forward error correction (FEC) threshold is achieved for 6λ × 2 ONUs group. The rate of each polarization state can be tuned in a minimum 3.408-Gbps step in the demonstration. Expanding from the basis of the original WDM-CPON, this work prepares an adapted chaotic encryption scheme for large-scale access. Overall, our proposed scheme can provide an abundant system loss budget, a large rate tunable range, and basic physical layer security for next-generation rate-flexible coherent PON (FLCS-CPON).

Implementation of Marin Predators Algorithm for optimizing the position of multiple Optical Network Units in Fiber Wireless Access Networks

• The problem of the optimal placement of multiple ONUs in FiWi networks is solved using- Marin predators algorithm (MPA) • A cost function is defined in terms of the average distance among ONUs and users. • The optimized locations are used in a developed simulation model to analyze the performance of FiWi network in terms of throughput and average propagation delay of FiWi access network. • The results obtained through the MPA are benchmarked with respect to the Harris Hawks Optimization (HHO), Whale Optimization algorithm (WOA), Moth-Flame optimization (MFO) and Greedy algorithms. Fiber-Wireless (FiWi) access network is a hybrid network that offers huge bandwidth and ubiquity to the users and is expected to play a dominant role in the emerging next generation communication networks. In this manuscript, a novel Marine Predators algorithm (MPA) is used to optimally place multiple Optical Network Units (ONUs) in FiWi access network. The optimized locations are used in a developed simulation model to assess the performance of FiWi network in terms of throughput and average propagation delay considering peer-to-peer communication. Also, the optimizer’s performance was evaluated in terms of fitness value, exploration, exploitation, computational complexity and nature of convergence curve. The MPA's efficiency is benchmarked with respect to a heuristic, Greedy algorithm, as well as existing efficient metaheuristics – Moth-Flame Optimization (MFO), Whale Optimization algorithm (WOA) and Harris-Hawks Optimization (HHO). It was found that MPA outperforms Greedy, MFO, WOA and HHO algorithms in each of the cases.

Dynamic Subcarrier Assignment in OFDMA-PONs Based on Deep Reinforcement Learning

Orthogonal Frequency Division Multiplexing Access Passive Optical Networks (OFDMA-PONs), a solution for the next-generation optical access network, allows multiple optical network units (ONUs) to dynamically share subcarriers (SCs) to support efficient bandwidth allocation. In uplink transmission, multiple ONUs can share orthogonal low bit rate SCs to transmit data at different time slots (TSs) during the transmission cycle. In this paper, the dynamic subcarrier allocation (DSA) scheme based on deep reinforcement learning (DRL) is proposed for various ONU bandwidth requests. The novel scheme jointly allocates time slots, subcarriers, and modulation formats in a dynamic and flexible manner. The ONU can save transmit power by using a lower order modulation format while meeting the delay requirement. The simulation part demonstrates how the proposed DRL-based DSA scheme can be adapted to various situations, including 1) variation in the size of ONU bandwidth requests, and 2) variation in the weight of different indicators. The extensive simulation results show that, for the first time, the proposed DRL-based DSA algorithm achieves optimal traffic latency with substantial power saving, compared with the traditional two-dimensional DSA algorithms.

Optimizing multiple ONUs placement in Fiber-Wireless (FiWi) access network using Grasshopper and Harris Hawks Optimization Algorithms

FiWi network is a multi-domain network that integrates optical and wireless networks. Hybrid fiber-wireless (FiWi) access network endeavours at consolidating the huge amount of available bandwidth of optical networks and the ubiquity, mobility of wireless access networks with the motive of reducing cost and complexity. This manuscript entails investigations undertaken towards optimal placement of multiple Optical Network Units (ONUs) in FiWi network using two recent optimization algorithms named as Harris Hawks Optimization (HHO) and Grasshopper Optimization algorithms (GOA). The results of the investigations are then benchmarked with respect to the Whale Optimization algorithm (WOA). The outcomes demonstrate the superiority of the proposed HHO algorithm over GOA and WOA algorithms, and return the lowest value of cost function; WOA outperforms GOA in terms of improved convergence rate and time complexity. Additionally, the diversification and intensification features of HHO, GOA and WOA have been compared. In order to benchmark the performance of the HHO and GOA optimizers, a series of convergence curves corresponding to different values of controlling parameters are plotted, and their optimal values determined. The dependence of objective function value upon distribution of users and initial placement of ONUs is also studied; the random placement of users and deterministic placement of ONUs return the lowest value of objective function.

Software-Defined Time-Shifted IPTV architecture for locality-awareness TWDM-PON

IPTV brought great potential to give network providers the capacity to expand their market value and revenue generated by increasing the number of users. Time-shifted IPTV (TS-IPTV) is one way of accomplishment through IP multicasting. Amongst the access network solutions, Ethernet passive optical network (EPON) is regarded as one of the best solutions due to its high bandwidth provision, low operation and maintenance cost. Software-Defined Networking (SDN) separates the network control plane from the data-forwarding plane with the promise to dramatically improve the network resource utilization. Time and wavelength division multiplexed access passive optical network (TWDM-PON) is the ultimate solution for the next generation PON (NG-PON2), in which each wavelength is shared between multiple optical network units (ONUs) by employing the time division and multiplexing access mechanism. Local-awareness based TWDM-PON allows for the higher bandwidth and optimal flexibility, fiber management, service convergence and resources sharing. In this paper, the SDN is integrated into the TWDM-PON architecture to facilitate an orchestrated multicasting time shifted IPTV through the SDN controller to control and manage the traffic. The simulation results show that the proposed architecture and mechanism improves the quality of service (QoS) requirements in terms of the mean packet delay, jitter, throughput and packet loss.

Analysis of a hybrid Fixed-Elastic DBA with guaranteed fronthaul delay in XG(s)-PONs

Reusing the existing Optical Distribution Network (ODN) of Passive Optical Networks (PONs) to bring connectivity to residential households together with providing the so-called front-haul (FH) network in Cloud Radio Access Networks (C-RAN) is a promising converged fixed and mobile network architecture envisioned by network operators. This article overviews how to exploit Fixed Bandwidth Reservations allowed in ITU-T XG(S)-PONs and their suitability for the transmission of front-haul (FH) traffic, thus allowing one Remote Radio Unit (RRU) coexist with multiple residential Optical Network Units (ONUs) in the same PON. We explain how to configure such periodic reservations to improve access in the upstream channel of a PON, showing worst-case access delays below 100 μs for eCPRI’s functional split IU.

Optical network unit placement in Fiber-Wireless (FiWi) access network by Whale Optimization Algorithm

Abstract Fiber-Wireless (FiWi) Access Network is proposed as a dominant and advantageous next generation hybrid access network. FiWi integrates wireless access technology with the optical access networks to provide potential benefits of both the technologies. Optical Network Unit (ONU) placement problem in FiWi network plays a vital role as it permits efficient utilization of network resources and enhances the performance in terms of cost efficiency and throughput. In this paper, we consider ONUs placement problem. The present work outlines the deployment of FiWi network and proposes a novel nature-inspired, population based metaheuristic paradigm called as Whale Optimization Algorithm (WOA) for optimal placement of multiple ONUs based on different distribution of wireless routers and ONUs. The outcomes are compared with the existing strategies of Greedy and Moth Flame Optimization (MFO) algorithms. To the best of our knowledge, WOA has never been used in this domain previously. The results in this manuscript prove that the proposed WOA outperforms the Greedy (deterministic) and MFO algorithms, and returns the lowest value of cost function; it results in faster convergence rate and lower time complexity than these algorithms. Moreover, the exploration and exploitation capability of WOA is significantly better than MFO algorithm. The results show dependence of the objective function value on the distribution of wireless users and ONUs; it is reported that random placement of users and deterministic placement of ONUs return the lowest value of objective function.

Adaptive Hybrid Path Search MFO Algorithm for Optical Network Unit Placement in Fiber-Wireless Access Network

Fiber-Wireless (Fi-Wi) access network is an emerging solution for high bandwidth and wide coverage network which satisfy the demands of many applications. Research work is going on in this field on several issues and some are Optical Network Unit (ONU) placement, routing, survivability; energy consumption etc. ONU placement problem plays important role as it makes network economic and allows optimal use of resources. In this research work, Adaptive Hybrid Path Search (AHPS) - Moth-Flame Optimization algorithm has been proposed to position multiple ONUs, optimally in the network. The comparative study of different variants of MFO algorithm implementing logarithmic, Archimedes’, hyperbolic and AHPS are presented for ONU placement problem. The outcomes of the simulation are based on different configuration of users and ONUs. It has been reported that the proposed algorithm provides most optimal result among all the MFO variants.

Bandwidth Allocation and Control Message Scheduling Algorithms for Improving the QoSs of High Priority Traffic in PON

The passive optical network (PON) is the most promising candidate for supporting multiple service classes, i.e., high priority (HP) traffic and best-effort (BE) traffic, in the next-generation broadband access networks. Providing an efficient dynamic bandwidth allocation (DBA) algorithm is the most important issue for supporting multiple service classes of traffic simultaneously. This paper presents a new DBA algorithm, which is the modified version of the hybrid slot-size/rate (HSSR) scheme, and is called the modified HSSR (MHSSR) algorithm. We have also modified the control message scheduling algorithm to fit it to the proposed scheme. In the proposed MHSSR scheme, each cycle time, i.e., the length of a time cycle, is equally divided into two parts. In the 1st part of the cycle time, the bandwidth is dynamically allocated to the HP traffic of all the optical network units (ONUs). In contrast, in the 2nd part of the cycle time, the bandwidth is dynamically allocated to the BE traffic of one or multiple ONUs. Furthermore, to ensure guaranteed service for the HP traffic, the 1st part of the cycle time is extended while the 2nd part of the cycle time is compressed if the demand of the HP traffic is very high. However, the 1st part of the cycle time will never be compressed, even at the lightly loaded condition of the HP traffic. The modified control message-scheduling algorithm effectively coordinates the timing sequence between the two parts of the cycle time and ensures the synchronization between two Gate messages to each ONU. We have evaluated the performance of the proposed schemes through numerical simulations in terms of end-to-end packet delay, bandwidth wastage, remaining bytes per time cycle, jitter, and throughput for different offered loads. From the comparative analysis, it can be seen that the proposed scheme provides better performance than the existing HSSR and delay variation-guaranteed schemes.

Joint Resource Allocation and Software-Based Reconfiguration for Energy-Efficient OFDMA-PONs

The widely deployed passive optical network (PON) is a cost-effective way to create a front/backhaul carrier for ubiquitous wireless access connectivity. To hide the difference of frame formats and multiplexing methods, an orthogonal frequency division multiplexing access PON (OFDMA-PON) was proposed. In upstream transmission, multiple optical network units (ONUs) from the same segment or residential area can transmit data through a shared group of orthogonal low-bitrate subcarriers (SCs) during different time slots (TSs) within the entire transmitting period. In downstream transmission, the optical line terminal can send control signaling of reconfiguring ONUs’ parameters so that SCs can be reallocated among segments, thus sleeping segments with empty data load while ensuring service continuity. Though energy savings can be ensured for upstream data transmission by using existing solutions, only frequency and time domains are involved. It is meaningful for us to make the flexible and energy- efficient configuration of transmitting power and modulation level assigned for ONUs in terms of improving energy efficiency. In this paper, we investigate joint resource allocation for energy-efficient upstream data transmission in OFDMA-PONs, with the help of software-based ONU reconfiguration. We formulate the problem, and the upper bound of energy saving is also derived. To solve the problem in a short span of time, we propose a novel heuristic algorithm whose effectiveness has been demonstrated by extensive simulations.

Tunable Multiwavelength Optical Comb Enabled WDM-OFDM-PON With Source-Free ONUs

In this paper, we propose and experimentally demonstrate a multiuser wavelength-division-multiplexing passive optical network (WDM-PON) system combining with orthogonal frequency division multiple (OFDM) technique. A tunable multiwavelength optical comb (MOC) is designed to supply flat optical lines for assisting the configuration of the proposed multiple source-free optical network units enhanced WDM-OFDM-PON system. Schematized by cascading a phase modulator and an intensity modulator with a recirculation loop, the MOC can output 29 ideal channel optical comb lines with the flatness of 0.85 dB. For the MOC enabled WDM-OFDM-PON system, source-free and interference-free multiuser upstream transmission over a single fiber can be efficiently supported, while downstream transmission channels can convey the baseband data stream and radio frequency OFDM signals simultaneously so that the proposed system can be connected to wire-line users and wireless users simultaneously.

Modeling and Analysis of Watchful Sleep Mode With Different Sleep Period Variation Patterns in PON Power Management

Reducing power consumption in an access network has become an increasingly imperative design goal, due to the fact that information and telecommunication technologies contribute to an increasingly large proportion of greenhouse gas emissions. The passive optical network (PON) is considered as the most attractive and promising technology to provide low-cost services to end users in a power-efficient way due to the passive nature of remote nodes. However, it is necessary to further reduce the energy consumption of PONs, with the wide deployment of PONs and the rapid growth of data transfer rates in PONs. In this paper, we focus on the watchful sleep mode with different sleep period variation patterns for multiple optical network units (ONUs). This is because, in the traditional operational mode, ONUs have to continually listen to and inspect traffic from the OLT and hence always remain active even when there is no/light traffic, which contributes to the majority of energy wastage to the PON. We first modeled the watchful sleep mode based on the Markov chain model in order to analyze the effect of each key parameter on system performances in terms of the energy-saving efficiency and data packet delay. Due to the fact that the sleep state is the key to power-saving, we designed four different sleep period variation patterns (e.g., constant, linear_1, linear_2, and exponential patterns) to study the impact of these different patterns on the integrated performance in terms of the normalized cost value. Through extensive simulations, we found that, in the watchful sleep mode, the effect of the number (n) of (sleep, listen) state pairs would be insignificant, and the effects of other parameters on the performances are analyzed comprehensively. The minimum normalized cost value can be obtained under the four different sleep period variation patterns, which represent the optimal trade-off between the above two conflicting performances indexes.

OLT-centralized sampling frequency offset compensation scheme for OFDM-PON.

We propose an optical line terminal (OLT)-centralized sampling frequency offset (SFO) compensation scheme for adaptively-modulated OFDM-PON systems. By using the proposed SFO scheme, the phase rotation and inter-symbol interference (ISI) caused by SFOs between OLT and multiple optical network units (ONUs) can be centrally compensated in the OLT, which reduces the complexity of ONUs. Firstly, the optimal fast Fourier transform (FFT) size is identified in the intensity-modulated and direct-detection (IMDD) OFDM system in the presence of SFO. Then, the proposed SFO compensation scheme including phase rotation modulation (PRM) and length-adaptive OFDM frame has been experimentally demonstrated in the downlink transmission of an adaptively modulated optical OFDM with the optimal FFT size. The experimental results show that up to ± 300 ppm SFO can be successfully compensated without introducing any receiver performance penalties.

Optical network unit placement in Fiber-Wireless (FiWi) access network by Moth-Flame optimization algorithm

Abstract Hybrid wireless-optical broadband access network (WOBAN) or Fiber-Wireless (FiWi) is the integration of wireless access network and optical network. This hybrid multi-domain network adopts the advantages of wireless and optical domains and serves the demand of technology savvy users. FiWi exhibits the properties of cost effectiveness, robustness, flexibility, high capacity, reliability and is self organized. Optical Network Unit (ONU) placement problem in FiWi contributes in simplifying the network design and enhances the performance in terms of cost efficiency and increased throughput. Several individual-based algorithms, such as Simulated Annealing (SA), Tabu Search, etc. have been suggested for ONU placement, but these algorithms suffer from premature convergence (trapping in a local optima). The present research work undertakes the deployment of FiWi and proposes a novel nature-inspired heuristic paradigm called Moth-Flame optimization (MFO) algorithm for multiple optical network units’ placement. MFO is a population based algorithm. Population-based algorithms are better in handling local optima avoidance. The simulation results are compared with the existing Greedy and Simulated Annealing algorithms to optimize the position of ONUs. To the best of our knowledge, MFO algorithm has been used for the first time in this domain, moreover it has been able to provide very promising and competitive results. The performance of MFO algorithm has been analyzed by varying the ‘b’ parameter. MFO algorithm results in faster convergence than the existing strategies of Greedy and SA and returns a lower value of overall cost function. The results exhibit the dependence of the objective function on the distribution of wireless users also.

Novel elastic protection against DDF failures in an enhanced software-defined SIEPON

Abstract Ever-increasing bandwidth demands on passive optical networks (PONs) are pushing the utilization of every fiber strand to its limit. This is mandating comprehensive protection until the end of the distribution drop fiber (DDF). Hence, it is important to provide refined protection with an advanced fault-protection architecture and recovery mechanism that is able to cope with various DDF failures. We propose a novel elastic protection against DDF failures that incorporates a software-defined networking (SDN) capability and a bus protection line to enhance the resiliency of the existing Service Interoperability in Ethernet Passive Optical Networks (SIEPON) system. We propose the addition of an integrated SDN controller and flow tables to the optical line terminal and optical network units (ONUs) in order to deliver various DDF protection scenarios. The proposed architecture enables flexible assignment of backup ONU(s) in pre/post-fault conditions depending on the PON traffic load. A transient backup ONU and multiple backup ONUs can be deployed in the pre-fault and post-fault scenarios, respectively. Our extensively discussed simulation results show that our proposed architecture provides better overall throughput and drop probability compared to the architecture with a fixed DDF protection mechanism. It does so while still maintaining overall QoS performance in terms of packet delay, mean jitter, packet loss, and throughput under various fault conditions.

Dynamic Bandwidth and Wavelength Allocation Scheme for Next-Generation Wavelength-Agile EPON

Recently, the IEEE 802.3 Ethernet Working Group has classified three architectures for the next-generation Ethernet passive optical network (NG-EPON). They are called single-scheduling domain (SSD) PON, multi-scheduling domain (MSD) PON, and wavelength-agile (WA) PON, and they differ based on how a group of optical network units (ONUs) share a wavelength. Existing dynamic bandwidth and wavelength allocation (DBWA) schemes for conventional EPON can be applied to MSD-PON and SSD-PON, but not WA-PON. This is because WA-PON is a new architecture with full flexibility where a flexible number of wavelengths can be assigned to one ONU, and multiple ONUs can transmit at the same time. In this work, we develop a mathematical model and a novel DBWA scheme for transmission scheduling in WA-PON. However, as WA-PON incurs penalties in terms of delay and power consumption when an ONU activates its transmissions on new wavelengths, a trade-off between energy saving and data-transfer latency reduction needs to be carefully addressed when performing transmission scheduling. So, we develop a power-consumption model and modify the proposed DBWA scheme to enhance the energy efficiency of WA-PON. Finally, we conduct simulation experiments for performance evaluation of the three PON architectures in terms of latency and packet loss ratio. We quantitatively investigate the influence of various parameters, such as the number of ONU transceivers and ONU buffer size, on WA-PON latency and packet loss ratio, and we evaluate the energy efficiency gain of the modified DBWA scheme.