Long-reach Optical Access Networks Research Articles

Design of QoS-aware long-reach optical backhaul for wireless and FTTx networks with enhanced backup resource utilization

• Proposed a long-reach optical access network architecture (LCQ-LR-OAN) that utilizes backup resources for providing the protection and alleviating network congestion. The LCQ-LR-OAN can simultaneously support different types of users with different QoS requirements. • Proposed a partial protection strategy that provides protection to all shared optical resources while keeping the unshared optical resources unprotected. We also developed survivability and network congestion alleviating mechanisms using a single set of optical resources. • Considered user priority (e.g., FTTH, FTTC, FTTB and FTTO) with reference to providing the protection. • Proposed a novel DBA scheme (EBA) to allocate the bandwidth of the backup OLT to the LR-PONs during the network congestion periods. • The LCQ-LR-OAN requires lower cost compared to that of the other existing LR-OAN architectures. The LCQ-LR-OAN architecture does not depend on any specific PON standard, viz., EPON, GPON. Thus, it can be used with all the PON standards. In this paper, we explore a low-cost and quality-of-service (QoS)-aware long-reach optical backhaul for the wireless and fiber-to-the-x (FTTx) networks. We exploit the reserved and idle optical resources to provide protection against failures and offer extra bandwidth to the users in the network congestion hours. We use a single set of optical resources to both provide protection and reduce network congestion, thereby incurring the minimum total expenditure. For the practical network scenarios, the simulation outcomes reveal that the proposed architecture can reduce 11 - 79 % average packet delay in the network congestion hours. It offers higher connection availabilities, i.e., five-nine availability ( ∼ 0.99999 ) with full protection and four-nine availability ( ∼ 0.9999 ) with partial protection. Meantime, it requires ∼ 30 % less capital expenditure cost than the other existing benchmark and state-of-the-art long-reach optical backhaul architectures. The proposed architecture is validated by simulation studies and practical data.

Fibre optic parametric amplifier for high capacity burst-mode access networks.

We compare performance of a polarization insensitive fiber optic parametric amplifier (PI-FOPA), a commercial erbium doped fiber amplifier (EDFA) and a discrete Raman amplifier (DRA) in a 50 km long-reach optical access network transmitting bursts of 10 Gbps signal with traffic density ranged from 5% to 97%. We demonstrate that for the same power budget the PI-FOPA allows for transmission of bursty traffic with density up to 97% while DRA and EDFA are limited to 30% and 15%, respectively. Alternatively, we demonstrate PI-FOPA to allow for 3 dB and 5 dB higher power budget than the DRA and EDFA, respectively, for the worst case scenario of 75% traffic density.

Combining modified Manchester modulation with optical equalization for improved dispersion tolerance in IM/DD access networks

In this paper the intensity modulation and direct detection of an optical link utilizing a Modified Manchester (MM) signal at the bitrate of 10 Gb/s and 25 Gb/s are presented for long-reach optical access networks. First-order and second-order optical equalizer were utilized to compensate the distortion in MM signal waveform caused by the chromatic dispersion in standard single mode fiber (SSMF). The assessment of the system performance was centered on bit error rate (BER), power penalty, eye diagrams and chromatic dispersion tolerance. Based on the calculated results the use of second-order optical equalizer, can extend the transmission distance by 20 km (SSMF) and 3.5 km at 10 Gb/s and 25 Gb/s, respectively. Based on the calculated results, the use of second-order optical equalizer is therefore promising in the next generation of long-reach optical access networks.

Centralized vs. Decentralized Bandwidth Allocation for Supporting Green Fog Integration in Next-Generation Optical Access Networks

The surging numbers of wireless devices and the accompanying exponential growth of user traffic have led edge and fog computing to become essential components in future access networks. By bringing more processing toward the edge of the network, they enable the realization of various demanding applications while supporting numerous resource-constrained devices. Their integration with passive optical networks and their huge offered bandwidth has therefore attracted much research interest. In this article, we review these computing concepts and examine key considerations for their integration with long-reach optical access networks when the employed upstream bandwidth allocation is either centralized or decentralized.

Integrating Fog With Long-Reach PONs From a Dynamic Bandwidth Allocation Perspective

Integrating fog computing with optical access networks is believed to form a highly capable fronthaul that will live up to the various requirements and challenges of tomorrow's access networks. Such integration combines the high capacity of optical fiber with closer-to-the-edge computing and storage capabilities. However, because optical access networks were not originally designed to carry offloaded traffic nor support edge-to-edge communications, the network architecture and employed bandwidth allocation both need to be reconsidered in this new setting. In this paper, we study the offloading performance in a long-reach optical access network when the underlying bandwidth allocation is either centralized or decentralized. We investigate how offloading can be supported in each paradigm and develop an analytical framework that is tested against numerical results. The effect of offloading on regular upstream traffic is also examined as well as the effects of cloudlet placements and network extension on the offloading performance.

Adaptively loaded SP-offset-QAM OFDM for IM/DD communication systems.

In this paper, we propose adaptively loaded set-partitioned offset quadrature amplitude modulation (SP-offset-QAM) orthogonal frequency division multiplexing (OFDM) for low-cost intensity-modulation direct-detection (IM/DD) communication systems. We compare this scheme with multi-band carrier-less amplitude phase modulation (CAP) and conventional OFDM, and demonstrate >40 Gbit/s transmission over 50-km single-mode fiber. It is shown that the use of SP-QAM formats, together with the adaptive loading algorithm specifically designed to this group of formats, results in significant performance improvement for all these three schemes. SP-offset-QAM OFDM exhibits greatly reduced complexity compared to SP-QAM based multi-band CAP, via parallelized implementation and minimized memory length for spectral shaping. On the other hand, this scheme shows better performance than SP-QAM based conventional OFDM at both back-to-back and after transmission. We also characterize the proposed scheme in terms of enhanced tolerance to fiber intra-channel nonlinearity and the potential to increase the communication security. The studies show that adaptive SP-offset-QAM OFDM is a promising IM/DD solution for medium- and long-reach optical access networks and data center connections.

Advanced Fault-Monitoring Scheme for Ring-Based Long-Reach Optical Access Networks

This paper presents a novel fiber fault-monitoring system for long-reach optical access networks based on a transmission–reflection analysis approach. By launching an unmodulated continuous-wave optical signal into the feeder ring and measuring the transmitted and reflected/backscattered optical powers, the proposed monitoring scheme is able to detect, identify, and localize any major fault (covering both reflective and nonreflective events) with a good spatial accuracy (≤10 m) and a high detection speed (3 s). Both experimental and simulation results have demonstrated that the proposed system provides fiber monitoring functionality better than that obtained by the conventional methods.

Low-cost coherent receiver for long-reach optical access network using single-ended detection.

A low-cost coherent receiver using two 2×3 optical hybrids and single-ended detection is proposed for long-reach optical access network. This structure can detect the two polarization components of polarization division multiplexing (PDM) signals. Polarization de-multiplexing and signal-to-signal beat interference (SSBI) cancellation are realized by using only three photodiodes. Simulation results for 40 Gb/s PDM-OFDM transmissions indicate that the low-cost coherent receiver has 3.2 dB optical signal-to-noise ratio difference compared with the theoretical value.

LONG-REACH OPTICAL ACCESS NETWORKS (LR-OANS): A PROMISING CANDIDATE FOR FUTURE OPTICAL ACCESS

The ever-increasing demand for broader bandwidth per user, which results from the continuous development of new bandwidth-hungry services and applications, creates the motivation to upgrade the currently deployed Time-Division Multiplexing Passive Optical Networks (TDM-PONs) to Next-Generation Optical Access Networks (NG-OANs). Beside the need for more bandwidth per user, a further extension in the range and an increase in the split ratio are highly desirable in PONs. These additional requirements can be achieved by adopting so-called Long-Reach Optical Access Networks (LR-OANs). LR-OANs offer a promising solution that ensures a significant number of users can be supported over a longer range. Moreover, they introduce a cost-effective approach in which both the access and metro segments of the telecommunication network are combined into one backhaul segment, which results in the consolidation of many central offices into one trunk-exchange. This cost-effective approach gave us the motivation to provide a comprehensive survey on the LR-OANs. In this study, we first provide a brief review of different potential technologies, proposed for next-generation optical access. We then provide a review of different stat-of-the-art LR-OAN architectures including opportunities and challenges in each one. A comparison among them based on key network specification is also provided.

On-the-field performance of quintuple-play long-reach OFDM-based WDM-PON optical access networks

In this paper the on-the-field performance of a WDM-PON optical access providing quintuple-play services using orthogonal frequency division multiplexing (OFDM) modulation is evaluated in a real fiber-to-the-home (FTTH) network deployed by Towercom operator in Bratislava (Slovakia). A bundle of quintuple-play services comprising full-standard OFDM-based signals (LTE, WiMAX, UWB and DVB-T) and an ad-hoc OFDM-GbE signal is transmitted in coexistence per single user. Both downstream and upstream transmission performances are evaluated in different on-the-field long-reach optical link distance configurations. Four wavelength multi-user transmission of quintuple-play OFDM services is demonstrated exceeding 60.8 km reach in standard single mode fiber.

Highly Utilized Fiber Plant with Extended Reach and High Splitting Ratio Based on AWG and EDFA Characteristics

In this paper, we propose a hybrid time-division multiplexing and dense wavelength-division multiplexing scheme to implement a cost-effective and scalable long-reach optical access network (LR-OAN). Our main objectives are to increase fiber plant utilization, handle upstream and downstream flow through the same input/output port, extend the reach, and increase the splitting ratio. To this end, we propose the use of an arrayed waveguide grating (AWG) and an erbium-doped fiber amplifier (EDFA) in one configuration. AWG is employed to achieve the first and second objectives, while EDFA is used to achieve the third and fourth objectives. The performance of the proposed LR-OAN is verified using the Optisystem and Matlab software packages under bit error rate constraints and two different approaches (multifiber and single-fiber). Although the single-fiber approach offers a more cost-effective solution because service is provided to each zone via a common fiber, it imposes additional losses, which leads to a reduction in the length of the feeder fiber from 20 km to 10 km.

Demonstration of Long-Reach PON Using 10 Gb/s 3R Burst-Mode Wavelength Converter

Long-reach optical access networks promise significant cost savings. To merge existing metro and access networks to a single long-reach network, the long-reach technology has to address not only the power loss and fiber dispersion problems but also mismatch between two merged entities in terms of wavelengths and operational modes, especially during the transition period when support of legacy services is still required. In this letter, we demonstrate a long reach network employing a 10 Gb/s burst-mode O/E/O wavelength converter. The converter can simultaneously address the power loss, dispersion, and mismatch problems by a compact assembly. Two upstream wavelengths located in the 1310 nm and 1550 nm windows in the access section are converted to a DWDM wavelength of 1554.13 nm in the metro section. Error-free performance is achieved with a loud/soft ratio of 10 dB at a sensitivity of -27 dBm and the overhead for the burst-mode operation is as low as 0.512%.

Ultra-high capacity optical networks [Guest Editorial

Increasing the capacity of optical networks has always been an important aim of academic and industrial optical communications research. Bandwidth-hungry applications are challenging the communications network capacity more than ever before, and therefore, research and development aimed at increasing network capacity has become much more urgent over the past few years. Research into ultra-high capacity networks addresses areas such as ultra-high speed transmission, network convergence, dynamic routing, and long-reach optical access networks.

Digital Coherent Receivers for Long-Reach Optical Access Networks

The relative merits of coherent-enabled optical access network architectures are explored, with a focus on achievable capacity, reach and split ratio. We review the progress in implementing the particular case of the ultra dense wavelength division multiplexed (UDWDM) passive optical network (PON), and discuss some challenges and solutions encountered. The applicability of digital signal processing (DSP) to coherent receivers in PONs is shown through the design and implementation of parallelized, low-complexity application-specific digital filters. In this work, we focus on mitigating the impact of local oscillator laser (LO) relative intensity noise (RIN) on receiver sensitivity, and propose an algorithm which compensates for this impairment. This phenomenon is investigated theoretically and then experimentally by evaluating the sensitivity of a coherent receiver incorporating different tunable light sources; a low-RIN external cavity laser (ECL) and a monolithically integrated digital supermode distributed Bragg reflector (DS-DBR) laser. It is shown that the RIN of the signal laser does not significantly contribute to the degradation of the receiver sensitivity. Finally, a 10 Gbit/s coherent PON is demonstrated using a DS-DBR laser as the LO laser. It is found that a receiver sensitivity of -38.8 dBm is achievable assuming the use of hard-decision forward error correction.

Scalable and Spectrally Efficient Long-Reach Optical Access Networks Employing Frequency Interleaved Directly Detected Optical OFDM

Extending the reach of traditional passive optical networks (PONs) to 100 km and increasing the split ratio beyond 1:64 are promising solutions in future optical access networks. These systems can accommodate increased users at longer distances potentially at low cost. With the increasing demand for higher bandwidths, current networks may soon require that bit rates upgrade to 100 Gb/s and beyond. However, the traditional on-off-keyed PON cannot be scaled up to such bit rates, as very high-speed opto-electronic devices are required that are still maturing. Therefore, to provide a comprehensive solution to these scalability issues of existing PONs, we propose a spectrally efficient (4 bit/s/Hz) 100 Gb/s long-reach PON based on 64 quadrature amplitude modulation (QAM) and frequency interleaved directly detected optical orthogonal-frequency-division multiplexing. We show that the proposed system may operate effectively over 100 km of single mode fiber with a 1024-way split and a receiver bandwidth of 25 GHz. It is also shown that the system can be provisioned to support even higher numbers of users (e.g., 2048, 4096, etc.) simply by varying the order of QAM with little compromise in bit rates. Moreover, the effects of various link parameters such as laser linewidths, fiber dispersion, filter profiles, etc. are also investigated for proper link dimensioning.

Free-Running 1550 nm VCSEL for 107 Gb/s Transmission in 997 km PON

We present a cooler-less, free-running 1550 nm vertical cavity surface emitting laser (VCSEL) directly modulated at 10.7 Gb/s. We also report on error-free transmission through 40 km of standard single-mode optical fiber, achieved without the use of dispersion-mitigation or mid-span amplification. Inverse-dispersion fiber was utilized to realize a dispersion-matched 99.7 km optical access uplink supporting error-free transmission with 27 dB loss margin. These results indicate the feasibility of implementing cooler-less long-wavelength VCSEL devices in long-reach optical access networks.

Long-reach optical access networks: A survey of research challenges, demonstrations, and bandwidth assignment mechanisms

Long-Reach optical access is a promising proposal for future access networks. This technology can enable broadband access for a large number of customers in the access/metro area, while decreasing capital and operational expenditures for the network operator. First, the paper reviews the evolutionary path of access networks and shows the drivers from technology and business perspectives for high bandwidth and low cost. A variety of research challenges in this field is reviewed, from optical components in the physical layer to the control and management issues in the upper layers. We discuss the requisites for optical sources, optical amplifiers, and optical receivers when used in networks with high transmission rate (10 Gbps) and large power attenuation (due to large split, transmission over 100 km and beyond, and propagation), and the key topological structures that allow to guarantee physical protection (tree-and-branch, ring-and-spur). Then, some relevant demonstrations of Long-Reach Optical Access Networks developed worldwide by different research institutes are presented. Finally, Dynamic Bandwidth Allocation (DBA) algorithms that allow to mitigate the effect of the increased control-plane delay in an extended-reach network are investigated.

Operating Penalties in Single-Fiber Operation 10-Gb/s, 1024-Way Split, 110-km Long-Reach Optical Access Networks

We report for the first time optical signal-to-noise penalties which lead to performance degradations in single-fiber long-reach optical access networks when compared to identical dual-fiber systems. A simplified architecture, with reduced optical amplifier count compared to previous work, for single-fiber operation of a symmetrical 10-Gb/s, 1024-way split, 110-km long-reach optical access network is presented and demonstrated. In addition, a possible solution to remove the optical signal-to-noise penalty is suggested