Number Of Optical Network Units Research Articles

Capacity Optimization of the Next-Generation Passive Optical Networks Based on Genetic Algorithm

This paper proposes an analytical and a numerical models for Next Generation Passive Optical Network (NGPON) by combining Gigabit-PON (GPON) and 10 Gigabit asymmetrical PON (XGPON) technologies. This allows for a larger number of subscribers to be accommodated on the network, up to 256. A capacity optimization procedure based on Genetic Algorithm (GA) techniques is then proposed and analyzed. The uplink and downlink capacities are maximized by optimizing various link parameters, such as the number of Optical Network Units (ONUs), the average optical transmitter power, the receiver sensitivity and the network operating margins. Simulation results shown that, among others, the Distributed-feedback laser (DBF) average power, the Positive-Intrinsic-Negative (PIN) sensitivity and the network margin are the key parameters entrusted to the GA technique in order to maximize the downlink capacity. In contrast, the Fabry Perot (FP) average power, the Avalanche Photodiode (APD) sensitivity and network margin are found to be the most influential parameters optimized by GA to maximize uplink capacity. Significantly, it is demonstrated that the GA technique, when used in optimizing NGPON capacity, enabling 256 subscribers and offering a data rates up to 71.02 Gb/s and 390.56 Gb/s in the upstream and downstream directions, respectively.

Dynamic ONU grouping algorithm based on combination partition for centralized flexible PON

The traditional optical access network architecture is fixed, and passive optical networking (PON) is only used as the transmission pipeline, which fails to make full use of the exchange capability of OLTs. In this paper, a dynamic optical network unit (ONU) grouping algorithm based on combination partition (DGACP) is proposed in the centralized flexible PON architecture. The algorithm transforms the global partitioning problem into a local partitioning problem, thereby reducing the number of algorithm iterations while obtaining the minimum cross-OLT traffic. Simulation results show that compared with the existing dynamic PON slice restructuring algorithm (DRA), the traffic gain of the DGACP is almost equal or slightly better, and the maximum running time is reduced from around 180 s to less than 0.5 s when the number of ONUs is 512.

Demonstration of an 800G CDM-SDM coherent PON utilizing weakly coupled multicore fibers with CDM tributary manipulation

In this Letter, we present an experimental demonstration of downstream signaling in a 16 × 50 Gbit/s coherent passive optical network (CPON) using the code and space division multiplexing (CDM-SDM) approach. We realize optical SDM through the utilization of a 4-core weakly coupled multicore fiber (WC-MCF), enhancing the total available optical launch power at the optical line terminal (OLT). This enhancement significantly improves the power budget for CPONs that connect with a large number of optical network units (ONUs). At the second stage of the CPON, four CDM-assigned ONUs are connected to individual cores of the WC-MCF, thereby supporting the connectivity of up to 16 ONUs. Through experiments, we have noted substantial disparities in the downstream signaling performance among individual CDM-assigned ONUs, particularly as the capacity is increased to 800 Gbit/s. To address this issue, we have employed an innovative approach by leveraging space–time coding techniques to manipulate the CDM tributaries, to achieve a balanced reception performance for all ONUs within the CPON. We believe that the proposed CDM-SDM CPON scheme, complemented by the advanced DSP flow chart, holds significant promise for future PON systems characterized by substantial capacity and extensive connectivity.

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.

A Comprehensive Framework For Itu Next Generation Pons

Due to the higher number of Optical Network Units (ONU), the power dissipation of Next Generation Passive Optical Network (PON) has gradually risen. Several energy energy-saving schemes have been proposed by the International Telecommunication Union (ITU) such as Cyclic Doze Mode (CDM) and Cyclic Sleep Mode (CSM). The performance of the small capacity devices (nodes) is relying on traffic advent or arrival rate and traffic threshold on which Local Wakeup Indication (LWI) ignited. Thus, an investigative model of ONU to review different CSM / CDM control schemes need extremely important and as well as becoming a hot topic among the scientific community. The state-of-the-art models do not use the sleep buffer parameter that yields lower performance assessment of the CSM process at limited traffic advent rates. They are incapable to acquire the CSM / CDM process at the above traffic rates. The proposed work boosts the current Discrete-Time Markov Chain (DTMC) established power exhibit taking into account a parameter i.e. sleep buffer at each ONU. Additionally, it governs the LWI events at the ONU and as well as Optical Line Terminal (OLT). Furthermore, the suggested exhibit precisely measures the ONU sojourn in every CSM / CDM state, energy savings, and power dissipation of ONU which depends on the advent rate of traffic. According to the recommended model, a CSM / CDM framework is also supplemented to configure all the parameters effectively under the given average delay constraints.

Entirely passive remote node design and system architecture for bus topology based 80Gbps symmetrical NG-PON2

The next generation passive optical network stage 2 (NG-PON2) is a broadcast network in which a large number of optical network units (ONUs) can be served using various network topologies. In this paper, a purely passive remote node (RN) design based on fiber bragg grating (FBG) is presented for the bus topology of a high split NG-PON2 system. The performance of the proposed node has been analysed for a symmetric 80 Gbps NG-PON2 system serving 1024 ONUs in terms of bit error rate (BER) and optical signal to noise ratio (OSNR). The working of the proposed node has been explained with the optical frequency spectrums for downstream and upstream signals. The observed OSNR levels for the ONUs operating at the 1st RN is 84.8743 dB which decreases to 75.7973 dB for the ONUs connected to the 8th RN. The BER level < 10–9 for both upstream and downstream confirms the correct working of the proposed node in the NG-PON2 system.

Traffic localization-based dynamic bandwidth allocation algorithm for improvement of QoS in peer-to-peer architecture of passive optical networks

Passive optical network (PON) is a popular technology, in recent days, which can be merged with peer-to-peer (P2P) network architecture. In P2P architecture, there is no need for a dedicated server and each peer can provide the data and receive the required data from other peers. With increasing traffic, there occurs aproblem in resource sharing and therefore, the users experience higher latency and lower overall quality of services (QoSs). There are several recent studies regarding the use of PON in P2P network architecture, and some of them are studied for localization of traffic. But in the case of localizing traffic, the use of multiple upstream wavelengths was not studied previously. In this paper, we have proposed a new PON architecture and a new dynamic bandwidth allocation (DBA) algorithm called localizing traffic-based DBA (LT-DBA) to improve the overall QoSs of the PON-based P2P network. By localizing the intra-PON traffic, this architecture separates the inter-PON and intra-PON traffic. Here, in addition to the conventional passive optical splitter, a wavelength reflector is used which can reflect the upstream wavelength used for intra-PON traffic. We also propose an efficient management scheme of the intra-PON traffic, where no report is needed to send to the optical line terminal (OLT). The OLT needs not to allocate time-slot for local packets, and there is a huge optimization of resources. The LT-DBA scheme was evaluated by formulating mathematical models and numerical simulations. The simulations were performed by varying the percentage of local data and by changing the number of optical network units in PON. The simulation results show that our proposed architecture and LT-DBA scheme outperform the existing REDIRECT DBA scheme in terms of end-to-end delay, jitter, and throughput.

Nonlinear Quantization for Power-Domain Non-Orthogonal Multiple Access Passive Optical Network

A passive optical network (PON) system is required to accommodate multi-services represented by fifth/sixth (5G/6G) mobile communication systems. While maintaining low cost, to meet these requirements (which are high capacity, low latency, and high reliability), the PON system must accommodate a large number of optical network units (ONUs). The use of power-domain non-orthogonal multiple access (PD-NOMA) for PON has been studied to increase the number of accommodatable ONUs. However, with an increase in the ratio of transmitted power between multiplexed ONUs, the effect of quantization noise in the analog-to-digital converter (ADC) is more significant. This study proposes to apply an optimal quantizer based on the Lloyd-Max algorithm (which is a nonlinear quantization algorithm) to PD-NOMA-PON. In general, the Lloyd-Max algorithm requires continuous probability density function when setting the partitions. We adopt a continuous function estimated from the discrete probability distribution extracted by the low-resolution ADC using an expectation maximization algorithm. We conduct experiments to verify the feasibility of the proposed quantizer for the downlink and confirm the improvement of the optical signal-to-noise ratio penalty for all power ratios.

Performance Analysis of the Limited Bandwidth Allocation Scheme With Excess Distribution

The limited scheme with excess distribution (LS-ED), being a superior grant-sizing protocol in terms of average delay minimization while providing fairness and quality of service (QoS) satisfaction in Ethernet passive optical networks (EPONs), has already been deployed in diverse technologies. An analysis of the protocol is of paramount importance for obtaining deeper insight into several network design and deployment aspects. Thus, the primary objective of this paper is to perform a rigorous mathematical analysis of LS-ED, for the first time to the best of our knowledge, with the help of a discrete time Markov chain (DTMC). Owing to the dependency of the grant size of a particular optical network unit (ONU) on the queue length of other ONUs, the exact queuing analysis of this scheme necessitates solving a Markov model of the same dimension as the number of ONUs, which makes the analysis complicated and mathematically intractable. A lower-dimensional valid approximation model may allow us to perform such an analysis. In this paper, for the first time to the best of our knowledge, we present an analysis of the scheme, wherein the system dynamics are captured from the perspective of the scheduler leading to an approximate model. The model aids in obtaining a closed-form expression for the average cycle time and throughput along with closed-form expressions for average buffer occupancy and average delay at low load. Finally, we provide useful design insights for EPONs employing LS-ED.

An ILP-based CapEx and OpEx efficient multi-stage TDM/TWDM PON design methodology

Abstract With reference to huge investment needed for greenfield passive optical network (PON) deployment, it is immensely important to define procedures and algorithms aimed towards optimal layout and network planning to reduce the overall expenditure due to capital expenditure and operational expenditure as much as possible. We propose an integer linear programming (ILP) based optimization model that explores optimal network dimensioning and placement of network equipment at appropriate locations so as to minimize the overall expenditure. Based on the number of users [optical network units (ONUs)], user’s bandwidth demand, power budget, maximum distance from optical line terminal (OLT) to users, available number of wavelengths and OLT ports, and geographical locations of ONUs, OLT and candidate locations of remote nodes (RNs), the model selects the number, type, splitting ratio and locations of passive devices. The RN device type is selected to be either power splitter or array waveguide grating. Optimal PON architecture is appropriately identified to be time division multiplexing or time-and wavelength division multiplexing (TWDM) depending on the requirement. It provides complete interconnection details among all devices, the overall expenditure, the number of OLT ports and the number and associated data rates of wavelengths to be used. We show exhaustive results for two deployment regions (viz. urban and rural) with different number of ONUs and bandwidth demands from users.We also show result with actual locations of OLT, ONUs and RNs selected from Google map. The proposed ILP model has low computational complexity and offers optimal solution within a reasonable time limit, without requiring a heuristic approach that provides a sub-optimal solution. The TWDM-PON conforms to next-generation PON stage 2 (NG-PON2) specifications and can be used as a useful tool for setting up NG-PON2.

Experimental demonstration of SCMA-OFDM for passive optical network

Abstract We introduces a novel architecture for next generation passive optical network (PON) based on the employment of sparse code multiple access (SCMA) combined with orthogonal frequency division multiplexing (OFDM) modulation, in which the binary data is directly encoded to multi-dimensional codewords and then spread over OFDM subcarriers. The feasibility of SCMA-OFDM-PON is verified with experimental demonstration. We show that the SCMA-OFDM offers 150% overloading gain in the number of optical network units compared with the orthogonal frequency division multiplexing access.

Effective Utilization of Unallocated Intervals in TDD-Based Fronthaul Employing TDM-PON

A time-division-multiplexing passive optical network (TDM-PON) accommodating a time-division duplex (TDD)-based mobile fronthaul (MFH) contributes to the realization of a low-cost network. However, there are two issues with the TDM-PON. The first is the limited number of optical network units (ONUs) that can be accommodated because the statistical multiplexing effect is weaker than with the accommodation of a conventional MFH. The other issue is the discovery process for registering new ONUs. While operating the discovery process, the signals of the registered ONUs cannot be forwarded in the optical link, and a huge latency is added to the registered ONUs. We have proposed a technique for the effective utilization of unallocated intervals, which certainly occur in optical links. Secondary service signals are forwarded in the unallocated intervals to increase the number of ONUs. The discovery process also operates in the unallocated intervals to avoid any latency increase. In this paper, we report evaluation results obtained using the numerical simulations.

Power budget of direct-detection ultra-dense WDM-Nyquist-SCM PON with low-complexity SSBI mitigation

Abstract The power budget (PB) of a direct-detection ultra-dense wavelength division/subcarrier multiplexing (SCM) passive optical network (PON) is assessed numerically for downstream, when a low-complexity iterative signal-to-signal beat interference (SSBI) mitigation technique is employed. Each SCM signal, inserted in a 12.5 GHz width optical channel, is comprised of two or three electrically generated and multiplexed 16-quadrature-amplitude-modulation (QAM) or 32-QAM Nyquist pulse-shaped subcarriers, each with a 7% forward error correction bit rate of 10.7 Gbit/s. The PB and maximum number of optical network units (ONUs) served by each optical line terminal (OLT) are compared with and without SSBI mitigation. When SSBI mitigation is realized, PB gains up to 4.5 dB are attained relative to the PB in the absence of SSBI mitigation. The PB gain enabled by the SSBI mitigation technique proposed in this work increases the number of ONUs served per OLT at least by a factor of 2, for the cases of higher spectral efficiency. In particular, for a SCM signal comprised of three subcarriers, the maximum number of ONUs served per OLT is between 2 and 32, and between 8 and 64, in the absence of SSBI mitigation, and when SSBI mitigation is employed, respectively, depending on the fiber length (up to 50 km) and order of QAM.

Energy Efficient Segmentation for Green FiWi network

Increasing number of internet users and variety of applications, demand more energy in the network to work. This requires efficient energy management in all kinds of networks. In this paper, we present an energy efficient segmentation (EES) scheme for FiWi network. The scheme works in two phases viz. segmentation phase and energy management phase. Based on traffic load conditions the EES scheme awakes minimal number of ONUs (Optical Network Units) and keeps remaining ONUs in sleep mode. This scheme maintains minimum quality of service (QoS) and saves network energy. Hence it is an efficient solution for green FiWi network.

Real-time monitoring in passive optical access networks using L-band ASE and varied bandwidth and reflectivity of fiber Bragg gratings

This paper presents a passive optical access network monitoring approach using an L-band amplified spontaneous emission source and varied bandwidths, reflectivity and Bragg wavelengths of fiber Bragg gratings (FBGs). In this technique, the reflection spectra of dedicated FBGs are used as the branch identifier to monitor the integrity of the distribution fiber in a point-to-multipoint network. FBGs with different bandwidths, reflectivity and Bragg wavelengths were used to monitor an increased number of optical network units within the limited bandwidth of the monitoring source. Simulations and experimental testing have been conducted to ensure the feasibility of this system. An experimental setup using four FBGs was conducted for different types of splitters. The signal processing to determine the faulty branches is presented. This system is capable of monitoring up to 32 distribution fibers using a limited monitoring source bandwidth of 10.8nm with a power margin of 2dB.

512-ONU Real-Time Dynamic Load Balancing With Few Wavelength Reallocations in 40 Gbps λ-Tunable WDM/TDM-PON [Invited

The wavelength (λ)-tunable wavelength-division multiplexing/time-division multiplexing passive optical network (WDM/TDM-PON) can distribute traffic loads fairly by dynamically reallocating a certain number of optical network units (ONUs) from highly loaded optical subscriber units (OSUs) to lightly loaded OSUs. This reallocation can be executed by hitless λ-tuning. However, hitless λ-tuning causes delays or fluctuations in traffic. To reduce these penalties, the number of wavelength reallocations should be suppressed. Thus, we proposed a dynamic-load-balancing (DLB) algorithm that can distribute traffic loads among OSUs with few wavelength reallocations. However, no demonstration of the proposed DLB algorithm had been conducted up to now, and the impact of the reallocation frequency on the average latency remained unevaluated. In this paper, we demonstrate the DLB algorithm in a 40-Gbps λ-tunable WDM/TDM-PON. The demonstrations confirm that our DLB algorithm can distribute 512-ONU traffic loads fairly among 4 OSUs in real time with fewer reallocation frequencies compared to the conventional round-robin algorithm, and little impact on average latency, with various input traffic rates.

Survivable deployment of cloud-integrated fiber-wireless networks against multi-fiber failure

Cloud-integrated fiber-wireless (FiWi) networks inheriting advantages of optical and wireless access networks have a broad prospect in the future. As various component failures may occur in cloud-integrated FiWi networks, survivability is becoming one of the key important issues. It is necessary to provide survivability strategies for cloud-integrated FiWi networks. Hence, this paper mainly focuses on the survivability of cloud-integrated FiWi networks against multiple fibers failure. Firstly, in this paper, a novel integer linear programming (ILP) solution is proposed to tolerate the failure of multiple distribution fibers with capacity and coverage constraints in the context of urban area. Then, considering the complexity of ILP models, an efficient heuristic scheme is proposed, in order to get the approximate solutions of ILP. Simulation results and analysis give the configurations of optical network units (ONUs) and wireless routers with different constraints and show the network coverage of clients for different number of ONUs and wireless routers with ILP solution and heuristic approach, respectively.

WDM‐OFDMA‐PON uplink optical transmission using bandwidth enhanced injection‐locked FP‐LD

ABSTRACTWe propose a scalable support WDM‐based orthogonal frequency division multiple access‐passive optical network uplink transmission system using an injection‐locked Fabry–Perot laser diode (IL‐FP‐LD). This system uses an injection‐locking technique to enhance the usable bandwidth by making stable channel states. By properly controlling the IL‐FP‐LD operation, the number of optical network units (ONU) within a wavelength can be increased, which improves the optical bandwidth efficiency for the uplink transmission. The experimental results show an enhanced modulation bandwidth of 3.5 GHz. Compared with a conventional RSOA which has a modulation bandwidth of 1.5 GHz, our scheme improves the number of ONUs that can be accommodated within a wavelength more than two times. The total discrete multitone signal received from the ONUs, with QPSK mapping on the subcarriers was 6.77 Gbps over a 23‐km standard single mode fiber transmission. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1727–1732, 2015

Analysis of Modulation Order to Guarantee Real-Time Service Throughputs in OFDMA-PON

In an orthogonal frequency-division multiple access passive optical network (OFDMA-PON), each optical network unit (ONU) chooses a modulation format based on the signal-to-noise ratio (SNR) at its receiver. An ONU with a high SNR can use a high-order modulation format to increase its transmission efficiency. When upstream resources are fully utilized, this increases an aggregated upstream throughput by ONUs, but the throughput is varied by ONUs' modulation orders. To guarantee upstream throughputs of real-time services, we first estimate the network throughout in a case that a total upstream resource is fully and fairly distributed to ONUs. By using the estimation, then, we present the lowest order of available modulation formats for the throughput guarantee. We investigate how the modulation order affects the number of ONUs that can be serviced in the OFDMA-PON.

Maximum covering planning of survivable Fiber-Wireless access network considering network connectivity

Fiber-Wireless (FiWi) access network is now becoming a promising architecture for access networks. Survivability is one of the key issues in the planning of FiWi access network because many high-rate traffic flows may be interrupted in case of a single fiber failure, which can cause a huge traffic loss. In addition, the users need ubiquitous broadband access that can be provided by FiWi access network. In this paper, we propose the protection approach called Maximum Covering Planning with Survivability (MCPS), including Integer Linear Programming (ILP) solution and heuristic solution, for the planning of survivable FiWi access network against single distribution fiber failure. The proposed approach aims at maximum coverage under the constraints of network connectivity. When a distribution fiber is broken, the interrupted Optical Network Unit (ONU) can transmit traffic to its backup ONU through the wireless paths between them. Simulation results show the network coverage of clients for different number of ONUs in different urban areas, and demonstrate the relationship between network coverage and the cost represented by the number of WiFi routers.