Long-reach Passive Optical Networks Research Articles

A Distance-Weighted Dynamic Bandwidth Allocation Algorithm for Improved Performance in Long-Reach Passive Optical Networks for Next Generation Networks

In recent years, there has been an increasing trend towards extending the coverage of passive optical networks (PONs) over large geographical areas. Long-reach PONs (LRPONs) are capable of extending the distance covered by PONs from 20 km to 100 km, leading to cost savings in the network operation by reducing the number of central offices. They have become widely deployed due to their ability to provide high-speed, long-distance data transmission over optical fibers. In addition, the next generation of optical access networks are expected to provide high-capacity mobile and wireless backhauling over a wide coverage area. However, this extended reach also requires the design of efficient dynamic bandwidth allocation (DBA) schemes to address the performance degradation caused by the increased propagation delay in LRPONs. The DBA schemes commonly used for upstream traffic transmission in traditional PONs are not well-suited for use in LRPONs due to their inefficiency in bandwidth utilization due to the increased round-trip time (RTT) between the optical line terminal (OLT) and the optical network unit (ONU). In this study, we present an efficient DBA algorithm, the Distance-Weighted Bandwidth Allocation DWDBA Algorithm, specifically enhanced for multi-wavelength LRPONs. Our DBA algorithm utilizes a scheduling policy that assigns weight vectors to Optical Network Units (ONUs) based on their distance from the Optical Line Terminal (OLT), sorting them accordingly without penalizing any ONU due to their distance. The DWDBA takes the laser tuning time into consideration. We conducted extensive simulations to evaluate the performance of the proposed algorithm under various scenarios and compared it to the IPACT algorithm. The results of the simulations show that the proposed algorithm outperformed the IPACT algorithm in terms of bandwidth utilization and queue delay.

Performance investigation of contention and monitoring in long-reach passive optical networks

Abstract Optical fibers are a key inventive discovery that contributed to the digital revolution, although cost becomes a major factor for long-distance communication. Whereas passive optical networks (PONs) offer reduced costs and cater to multiple users; hence, they are becoming more common in LANs, densely inhabited areas, and backbone networks. Numerous experiments on PON systems have been authored in the last couple of years, with results expressed in terms of BER, eye openings, quality of received bits factor, signal-to-noise ratio (SNR), and burst blocking, which demands a vast review of PONs based on these parameters. So, a comprehensive review of PONs is extensively researched to identify the methods’ limitations. Along with long-reach(LR)-PON systems, power conservation in PONs and burst contention are also addressed. To demonstrate the performance of PON architectures, the findings are provided in terms of delay, energy efficiency, and operations intensity.

Efficiency enhancement of long-reach passive optical network using the polarization coding

Abstract This paper, propose a new passive optical network (PON) system structure based on the two orthogonal polarization states of the same wavelength. This method is usually applied to increase the number of simultaneous users in the network, it can double the number of potential users. The proposed technique utilized to increase split ratio and consequently increase the reach and the split ratio. This can be achieved by implementing technologies such as power splitter. In terms of bit rate, the proposed PON offers a bit rate of 10 Gbps for downstream transmissions. The results obtained in this work are shown that the proposed system can accommodate more users simultaneously for the typical Q factor is greater than 6.

Real-Valued Neural Network Nonlinear Equalization for Long-Reach PONs Based on SSB Modulation

Real-valued neural network nonlinear equalization for complex-valued signals combined with single sideband (SSB) modulation is proposed to be a promising scheme for long-reach passive optical networks (LR-PONs). With the assist of neural network equalizer (NNE), fiber nonlinearity induced by large launch power can be mitigated. We experimentally demonstrate a transmission of 120 Gbps 16-QAM SSB signal in C-band over an 80-km single mode fiber (SMF) without optical inline amplifier and pre-amplifier.

Power budget- and SRLG-aware cost-efficient partial protection planning models and architectures for long-reach passive optical networks

In a long-reach passive optical network (LR-PON), protection for optical network units (ONUs) against their distribution fiber (DF) failures is highly desirable to ensure uninterrupted Internet access to the associated users. In the distribution section of the LR-PON, shared-risk link groups (SRLGs) are formed by DFs due to sharing fiber cables and conduits. Most of the existing SRLG-aware DF protection schemes require residual bandwidth with ONUs. Therefore, they fail to provide protection to all ONUs under high reliability requirements (RRs) and result to be very cost-inefficient as well. We first propose a SRLG-aware reliability framework to compute the connection reliability of every ONU and joint reliability of every ONU-ONU pair and ONU-node pair. Thereafter, we propose two different SRLG-aware nonresidual bandwidth based partial protection schemes and their compatible architectures to provide partial DF protection to ONUs against SRLG failures to satisfy the given RR. Following the proposed schemes, we formulate two different integer linear programming (ILP) based optimization problems to set up backup connections by using backup DFs and other backup optical resources with the minimum protection cost. The proposed ILP-based protection planning models restrict the backup DF lengths to bound the propagation delay to satisfy the strict delay requirement for real-time applications. Since the proposed ILP-based models turn out to be computationally intractable for large network problems, we also propose two heuristic schemes that provide comparable results to that of the ILP-based models. We evaluate the performance of the proposed partial protection schemes with reference to the protection cost and total length of backup DFs (TLBDF). The exhaustive simulation results show that the proposed partial protection schemes not only satisfy high RRs, but also require a much lower protection cost, TLBDF, and optical power margin in comparison to the existing SRLG-aware protection schemes.

Fast Feed-Forward Optical and Electrical Gain Control to Extend the Dynamic Range of the Burst-Mode Digital Coherent Receiver for High-Speed TDM-PON Systems

This paper introduces a new burst-mode coherent receiver configuration that drastically widens the receiver input dynamic range. Its key advance is a fast feed forward gain control scheme for both a semiconductor optical amplifier (SOA) used as a preamplifier and trans-impedance amplifiers (TIAs) set at the coherent receiver. The two-stage optical and electrical gain control greatly decreases the received burst signal's power variations and increases the receiver dynamic range which attenuates the quantization errors in analogue-to-digital conversion (ADC). To elucidate the receiver sensitivity characteristics, bit error rate (BER) calculations are conducted on 10 Gbit/s single polarization quadrature phase shift keying (SP-QPSK) signal coherent reception. The calculations focus on two significant parameters that greatly impact the quantization noise; ADC vertical resolution and received signal's state of polarization (SOP). The calculation results confirm that the proposed configuration achieves high sensitivity, better than −44 dBm, and wide dynamic range of 30 dB in the worst SOP condition, even when 5-bit ADC is used. Transmission experiments verify the calculated sensitivities and extremely high loss budget of 48.6 dB is achieved in 40-km single mode fiber (SMF) transmission. These results show that the proposal has the potential to realize 10 Gbit/s class long-reach and high splitting ratio PONs; the extremely wide dynamic range yields 40 km reach PON systems with 512- or 1024-way splits with no change in receiver configuration.

Modelling and simulation of optical transmitter for 5G passive optical networks

5G is altering the communications future. The 5G literature focuses on wireless and radio technology, but fiber optics play a crucial supporting role in signal transmission to and from the next generation of base stations (BSs) that will serve customers. With the increasing bandwidth requirements of 5G ultra-high-speed applications, passive optical networks (PONs) are the optimal solution. Targeting long-reach 5G PONs, an integrated, high-speed, and cost-effective optical transmitter circuit was constructed and tested. This engine can be combined into a 5G-compliant optical transceiver module. For the purpose of validating the engine performance, a theoretical analysis and an OptiSim<sup>TM</sup>-based design simulation model are carried out. Bit error rate (BER), phase-shifting, and eye diagram were all taken into account when analyzing the transmitter performance. The article findings validate the optical transmitter design. The design is cost-effective and requires no extra components, such as a filter.

Nonlinear Effect and MAI Impact on SAC-OCDMA System Based on 2D Multi-Diagonal Code and Laser Array

A new architecture for Spectral Amplitude Coding Optical Code Division Multiple Access (SAC-OCDMA) system based on two Dimensional Multi Diagonal (2D-MD) codes named 2D-MD SAC-OCDMA and utilizing a laser optical source is proposed for Long-Reach Passive Optical Network (LR-PON). In this work, a computer simulator tool is used, for the first time, as a SAC-OCDMA simulation set-up utilizing the unique combination of a coherent laser array and 2D-MD codes. In addition, the system performance is addressed numerically by taking into account Multiple Access Interference (MAI), optical coherent source noise, first, second and third order fiber dispersion, nonlinear effects and photo-detector noise. Simulation results indicate that for a single user (i.e., without considering MAI), the system can operate at a maximum bit rate of 55 Gb/s over 250 km of Single Mode Fiber (SMF), with a Bit Error Rate (BER) below 10−9 (Q-limit = 15.5 dB), when only first order fiber dispersion is considered. However, including the effects of second and third order fiber dispersion as frequency domain parameters, results in a reduction of the maximum bit rate to 40 Gb/s, while maintaining a Q-factor above the Q-limit under the same transmission distance. Furthermore, we demonstrate that the proposed architecture extends the SMF transmission reach up to 600 km and 480 km, when considering linear and nonlinear effects, respectively. Finally, we show that our proposed 2D-MD SAC-OCDMA system outperforms existing solutions presented in the literature for LR-PON configuration, in terms of both aggregate bit rate and transmission reach.

Advanced nonlinear equalizer for Filter Bank Multicarrier‐based Long Reach‐Passive Optical Network system

SummaryThe performance of the intensity‐modulated Filter Bank Multicarrier (FBMC) system using direct detection with advanced nonlinear equalizer in Long Reach‐Passive Optical Network (LR‐PON) is presented in this paper. First, the performance of the FBMC system and its nonlinearity in the channel are analyzed. We introduce two nonlinear equalizers, namely, Artificial Neural Networks–Nonlinear Feed‐Forward Equalizer (ANN‐NFFE) and Deep Neural Network–Nonlinear Equalizer (DNN‐NLE). Both the equalizers can mitigate the nonlinearities in the signal. Also, the impact of the system in downlink is analyzed using simulation by varying the data rates for various fiber lengths. The FBMC using SMT provides better spectral efficiency. The performance of both equalizers is compared. The addition of the DNN‐NLE equalizer provides a better OSNR, good accuracy, and better BER compared with ANN‐NFFE.

Optimal planning and design of SRLG-aware survivable LR-PON for wireless and FTTx networks

Protection to optical network units (ONUs) against failure of their distribution fibers (DFs) in a long-reach passive optical network (LR-PON) is highly desirable to provide uninterrupted internet services to the users. In practical network scenarios, DFs form shared-risk link groups (SRLGs). The existing SRLG-aware protection schemes depend on residual bandwidth of ONUs. Therefore, they are cost-inefficient and also fail to satisfy high reliability requirements (RRs). We for the first time propose a nonresidual bandwidth based partial protection scheme and related architecture to provide partial protection to ONUs against a single SRLG failure. Following the proposed scheme, we formulate an integer linear programming (ILP)-based optimization problem to provision backup DFs and network components for providing protection with the minimum protection cost. To meet the strict delay requirement for real-time applications, the proposed ILP model restricts the length of backup DFs to be employed to restore the traffic transmission. As the proposed ILP model becomes computationally intractable for large networks, we also propose a heuristic scheme that provides fairly close results to that of the ILP model. We assess the performance of the proposed partial protection scheme in terms of protection cost and total length of backup DFs (TLBDF). Through exhaustive simulation study we show that the proposed partial protection scheme not only satisfies high RRs but also requires much lower protection cost and TLBDF as compared to the existing SRLG-aware protection schemes.

Cost analysis of rural roll-out using a long-reach passive optical network: trading off the upfront cost under uncertainty of the user take-up rate

High deployment cost with respect to expected revenue is the main barrier to fiber-to-the-home (FTTH) roll-out in rural areas. This problem, as shown in this paper, is exacerbated by the uncertainty associated with the end-user take-up rate. The randomness associated with subscribers’ service take-up yields considerable fluctuation and escalation in the total cost of deployment. This adverse and varying environment makes it difficult to produce firm business cases and can increase the reluctance of potential investors and incumbent operators to deploy FTTH access networks. In this paper, we develop a holistic framework for examining real-world FTTH deployment scenarios, taking as a case study one of the most rural counties in Ireland. Further, we carry out an in-depth techno-economic analysis identifying the methods more applicable in the rural scenario. We analyze the cost effectiveness of FTTH deployment, also proposing solutions that provide different levels of upfront investment risk, relating it to uncertainty in customers’ take-up rates. For example, we show how a lower take-up rate can be made profitable by adopting a strategy that favors lower upfront costs at the expense of higher connectivity costs.

A modified convolutional neural network-based signal demodulation method for direct detection OFDM/OQAM-PON

Orthogonal frequency division multiplexing/offset quadrature amplitude modulation (OFDM/OQAM) is a promising modulation candidate for passive optical network (PON) due to its high flexibility, better time–frequency focusing characteristic, great resistance to the inter symbol and inter carrier interferences and higher spectrum efficiency compared to OFDM. However, the intrinsic imaginary interference together with linear and nonlinear distortions make it more difficult to recover the transmitted OFDM/OQAM signal at the receiver side. To mitigate the transmission impairments, a modified convolutional neural network (CNN) is utilized to learn the channel state information and the constellation demapping mechanism for OFDM/OQAM-PON. The distorted received signals are equalized implicitly to obtain the transmitted binary bits directly. The simulation results show that the CNN based receiver (Rx) can compensate the linear and nonlinear distortions more effectively compared to traditional pilot-based Rx, especially for the high order modulation long-reach PON.

High-power SOA-integrated EADFB laser for long-reach passive optical network systems

A high-power optical transmitter module based on an SOA-assisted extended-reach EADFB laser (AXEL) chip was developed at a wavelength of 1.49 µm to improve the loss budget of current passive optical access networks. The fiber-coupled output power of the modulated signal is 10 dBm owing to the post-amplification effect of the integrated SOA with an extinction ratio of 10 dB. Fiber transmission was demonstrated at data rates of 1.25 and 2.5 Gbit/s, assuming GE-PON and G-PON downstream signals, respectively. Error-free transmission over 100-km fiber was achieved with loss budgets of 46 and 43 dB at 1.25 and 2.5 Gbit/s, respectively.

Design for Long-Reach Coexisting PON Considering Subscriber Distribution with Wavelength Selective Asymmetrical Splitters

Design for Long-Reach Coexisting PON Considering Subscriber Distribution with Wavelength Selective Asymmetrical Splitters

High-speed and long-reach PON employing PM-DQPSK signal and coherent receiver

Abstract The development of communication technology requires a new type of passive optical network (PON) architecture. The architecture needs to be based on time division multiplexing (TDM) of 40 Gbit/s downstream and 10 Gbit/s upstream, and it can realize TDM PON prototype. The PON system achieved the system distance of 120 km supporting 128 ONU with power budget of 53.5 dB via polarization multiplexing differential quadrature phase shift keying format signal which employs the coherent receiver and the digital signal processing.

QoT-aware adaptive modulation format-based resource provisioning for clustered LR-PON

• This study presents a QoT-aware adaptive modulation format based on resource provisioning (QAMF-RP) algorithm for software-defined long-reach passive optical networks architecture. • The LR-PON architecture incorporates orthogonal frequency division multiplexing-based time-wavelength division multiplex PON (OFDM-based-TWDM-PON), thus high bandwidth utilisation and small bandwidth allocation granularity with limited network resources is possible to deal with this rapid traffic growth. • What’s more, the proposed QAMF-RP algorithm addresses the challenges associated with the higher upstream channel idle time owing to long round trip time and data-reliable transmission for all types of services. • We believe that our study makes a significant contribution to the literature because our results show a promising performance of the proposed system that significantly reduce average latency, improve throughput and network QoS, ensure optimal resource provisioning, and satisfy various service requirements. The range of conventional passive optical networks (PONs) is 20 km, which are difficult to satisfy the requirements of accommodating increasing number of users and coverage areas. Thus, a software-defined long-reach PON (LR-PON) architecture which extends the access network to hundreds of kilometres is proposed in this paper. Using the proposed LR-PON architecture, which incorporates orthogonal frequency division multiplexing-based time-wavelength division multiplex PON (OFDM-based-TWDM-PON), high bandwidth utilisation and small bandwidth allocation granularity with limited network resources is possible to deal with this rapid traffic growth. Further, to address major challenges such as higher upstream channel idle time owing to long round trip time and data-reliable transmission for all types of services, while considering energy consumption, we also propose a quality-of-transmission (QoT)-aware adaptive modulation format-based resource provisioning algorithm that considers the PHY and MAC layers. The results of simulations conducted to verify the performance of the proposed architecture and algorithm demonstrate that they can reduce average latency, significantly improve throughput and network QoS, ensure optimal resource provisioning, and satisfy various service requirements.

Artificial Neural-Network-Based Pre-Distortion for High Loss-Budget 60-km Long-Reach Passive Optical Network

High launch optical power can compensate for severe fading and power loss in long-reach passive optical networks (LR-PONs); however, it also aggravates nonlinear degradation, which necessitates the use of complex DSP-based nonlinear compensation techniques at optical network users (ONUs). DSP-related techniques also necessitate the use of additional hardware/software components by the receiver, which can greatly increase implementation costs and energy consumption, particularly when dealing with large-scale ONU deployment. This is the first study to propose artificial neural network (ANN)-based pre-distortion to eliminate the need for complex DSP at ONUs in a high-launch-power LR-PON, thereby permitting the use of a simplified architecture at the user end. In the first phase of the study, the proposed ANN-based pre-distortion scheme was implemented in a single-channel IMDD OFDM LR-PON, which achieved a data rate of >55 Gbps over 60-km transmission with a loss budget of 30 dB without the need for optical inline- or pre-amplification. In the second phase of experiments, the same scheme was applied to a 4-channel wavelength division multiplexing (WDM) OFDM LR-PON. Here, the proposed scheme achieved data rates of >200 Gbps using launch power of 18 dBm per lane, resulting in a loss budget of roughly 29 dB over 60-km single mode fiber transmission.

Histogram Based Clustering for Nonlinear Compensation in Long Reach Coherent Passive Optical Networks

In order to meet the increasing capacity requirements, network operators are extending their optical infrastructure closer to the end-user while making more efficient use of the resources. In this context, long reach passive optical networks (LR-PONs) are attracting increasing attention.Coherent LR-PONs based on high speed digital signal processors represent a high potential alternative because, alongside with the inherent mixing gain and the possibility of amplitude and phase diversity formats, they pave the way to compensate linear impairments in a more efficient way than in traditional direct detection systems. The performance of coherent LR-PONs is then limited by the combined effect of noise and nonlinear distortion. The noise is particularly critical in single channel systems where, in addition to the the elevated fibre loss, the splitting losses should be considered. In such systems, Kerr induced self-phase modulation emerges as the main limitation to the maximum capacity. In this work, we propose a novel clustering algorithm, denominated histogram based clustering (HBC), that employs the spatial density of the points of a 2D histogram to identify the borders of high density areas to classify nonlinearly distorted noisy constellations. Simulation results reveal that for a 100 km long LR-PON with a 1:64 splitting ratio, at optimum power levels, HBC presents a Q-factor 0.57 dB higher than maximum likelihood and 0.21 dB higher than k-means. In terms of nonlinear tolerance, at a BER of 2×10 − 3 , our method achieves a gain of ∼2.5 dB and ∼1.25 dB over maximum likelihood and k-means, respectively. Numerical results also show that the proposed method can operate over blocks as small as 2500 symbols.

Low-Complexity Adaptive Chromatic Dispersion Estimation Scheme Using Machine Learning for Coherent Long-Reach Passive Optical Networks

In the coherent long-reach passive optical networks (LRPON), it is crucial to propose cost-effective digital signal processing (DSP) technologies to reduce the overall complexity and power consumption. This paper has proposed a low-complexity chromatic dispersion (CD) estimation scheme based on deep neural networks (DNN) and the error vector magnitude (EVM). To add comparisons, the performances of CD estimation schemes using other two well-known machine learning algorithms including the k-nearest neighbor (KNN) and the decision tree (DT) have also been investigated. The simulation results show that the proposed CD estimation scheme is effective in the coherent LRPON with the quadrature phase shift keying (QPSK) and 16-ary quadrature amplitude modulation (QAM) systems at 14Gbaud rate, 28Gbaud rate and 56Gbaud rate. The comprehensive performances of the DNN outperform those of the KNN and the DT. The mean estimation error of the DNN is less than 20ps/nm within the 100 km access distance in the 28Gbaud QPSK/16QAM systems. What's more, compared with classical methods using the CD scanning and frequent domain equalizers (FDE), the computation complexity of the proposed CD estimation scheme based on the DNN-EVM has been respectively reduced by 72.3 times, 86.7 times and 2.8 times about the amount of multipliers, adders and comparators.

Decision-Feedback Frequency-Domain Volterra Nonlinear Equalizer for IM/DD OFDM Long-Reach PON

A low-complexity third-order decision-feedback frequency-domain Volterra nonlinear equalizer (DF-FD-VNLE) with superior nonlinearity-compensation performance is proposed and experimentally demonstrated for OFDM long-reach PONs. High optical launch power up to 18 dBm is implemented to mitigate the chromatic dispersion induced power fading and increase the power budget. By reconstructing and subtracting the nonlinear noise in frequency domain with the knowledge of the nonlinear channel, the proposed DF-FD-VNLE outperforms the conventional time-domain VNLE (TD-VNLE) and feed-forward FD-VNLE (FF-FD-VNLE), resulting in better received signal-to-noise ratio (SNR) performance. The nonlinearity-compensation performance of the DF-FD-VNLE can be further improved with the usage of a FF-FD-VNLE or more than one iteration. Complexity and experimental analyses show that similar complexity and higher SNR can be achieved by using the one-iteration DF-FD-VNLE with FD linear equalization (FD-LE), compared with that of the FF-FD-VNLE. Compared with conventional TD-VNLE, the required number of real-valued multiplication (RNRM) of the one-iteration DF-FD-VNLE with FF-FD-VNLE (FD-LE) is reduced by a factor of as much as 82.19% (89.61%) at a memory length of 14 and a truncation factor of 3. Based on the one-iteration DF-FD-VNLE with FF-FD-VNLE, around 53.79 Gb/s single wavelength OFDM IM-DD transmission over 60.8-km SSMF is successfully demonstrated at a BER of 3.8 × 10−3 and a received optical power (ROP) of −2 dBm, achieving 15% capacity improvement compared to the conventional TD-VNLE.