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Increasing mobile traffic and smart devices require continuous expansion of optical access network capacity and easy optical connectivity for residential, business, and mobile services. A high-speed TDM-PON system with high power budget is an attractive solution to accommodate explosive mobile traffic since multiple remote nodes with simple optical power splitters could easily provide optical connections anywhere in an optical distributed network. Thus, both high speed per wavelength and high-power budget are desirable in the TDM-PON system. We demonstrate a TDM-PON system with 50 Gb/s/λ with PAM4 and 35-dB power budget in the entire O-band by simply operating a booster SOA in the saturation region. In addition, a dynamic range of 50 Gb/s PAM4 receiver higher than 15 dB is demonstrated to support loud-soft ratio. We also successfully demonstrate error-free transmission of 50 Gb/s TDM-PON system by utilizing an OLT line-card and an ONU board.

To meet the latency and bandwidth requirements of 5G mobile services and next-generation residential/business services, we present high speed and low-latency passive optical network (PON) enabled by time controlled-tactile optical access (TIC-TOC) technology. The TIC-TOC technology could support bandwidth-intensive as well as low-latency services for 5G mobile network by using channel bonding and low-latency oriented dynamic bandwidth allocation (DBA). In order to confirm the technical feasibility of TIC-TOC, FPGA-based OLT and multi-speed ONU prototypes are implemented. We experimentally demonstrate the real-time packet transmission up to 50 Gb/s without packet loss during 48-hour through the channel bonding in a single optical distribution network (ODN) with 20 km reach and 1:64 split ratio. Less than 400 μs latency for 5G mobile services is also demonstrated. Furthermore, we confirm that total throughput could be expanded up to 100 Gb/s by adding more channels.

We review TDM-PON based optical access for 5G and tactile internet applications, and introduce recent feasibility studies based on high-capacity and low latency TDM-PON. Lessons learned from the tactile internet testbed are also discussed.

We review optical access technologies for tactile internet accommodating bandwidth intensive as well as low-latency services such as smart factory, remote robot control and AR/VR. Recent feasibility demonstration of tactile internet testbed is also introduced.

We present a cost-effective photonics-based THz wireless delivery system using a directly modulated distributed feedback laser diode (DFB-LD). A DFB-LD with non-return to zero (NRZ) modulation up to 25 Gbps and a uni-traveling-carrier photodiode (UTC-PD) with a horn antenna is employed to transmit a THz wave into free space in the photonics-based THz signal transmitter. A Schottky barrier diode (SBD) with a horn antenna is used to directly detect the THz wave from free space at the THz signal receiver. To achieve the best bit error rate performance, we varied the optimal THz carrier frequency in a photonics-based THz wireless delivery system. After THz carrier frequency optimization, bit error rates were measured by varying THz link operating conditions, such as the data rate, photocurrent of UTC-PD, and wireless transmission distance. We successfully transmitted a 25 Gb/s NRZ signal over 1.6 and 2.2 m wireless transmission distances before and after managing the adiabatic chirp characteristic of directly modulated DFB-LD using the laser-to-filter detuning effect, respectively, while satisfying the 7% hard decision-forward error correction (HD-FEC) threshold ( 3 . 4 × 1 0 − 3 ).

Current radio access networks (RANs) need to evolve to handle diverse service requirements coming from the growing number of connected devices and increasing data rates for the upcoming 5G era. Incremental improvements on traditional distributed RANs cannot satisfy these requirements, so the novel and disruptive concept of a cloud RAN (CRAN) has been proposed to decouple digital units (DUs) and radio units (RUs) of base stations (BSs), and centralize DUs into a central office, where virtualization and cloud computing technologies are leveraged to move DUs into the cloud. However, separating RUs and DUs requires low-latency and high-bandwidth connectivity links, called "fronthaul," as opposed to traditional backhaul links. Hence, design of the 5G transport network, that is, the part of the network that carries mobile data traffic between BSs and the core network and data centers, is key to meet the new 5G mobile service requirements and effectively transport the fronthaul traffic. Today, consensus is yet to be achieved on how the fronthaul traffic will be transported between RUs and DUs, and how virtualization of network resources will occur from a radio network segment to the centralized baseband processing units. In this article, we present a new 5G architecture, called virtualized cloud radio access network (V-CRAN), moving toward a cell-less 5G network architecture. We leverage the concept of a virtualized BS (V-BS) that can be optimally formed by exploiting several enabling technologies such as software defined radio (SDR) and coordinated multipoint (CoMP) transmission/reception. A V-BS can be formed on a per-cell basis or per-user basis by allocating virtualized resources on demand. For the fronthaul solution, our approach exploits the passive optical network (PON), where a wavelength can be dynamically assigned and shared to form a virtualized passive optical network (VPON). Several use cases of the V-CRAN are presented to show how network architecture evolution can enhance system throughput, energy efficiency, and mobility management.

We review optical access and transport technologies for 5G and beyond, and introduce recent feasibility demonstration of NG-EPON prototype supporting channel-bonding and low-latency dynamic bandwidth allocation technologies.

In recent years, the increasing traffic demand in radio access networks (RANs) has led to considerable growth in the number of base stations (BSs), posing a serious scalability issue, including the energy consumption of BSs. Optical-access-enabled Cloud-RAN (CRAN) has been recently proposed as a next-generation access network. In CRAN, the digital unit (DU) of a conventional cell site is separated from the radio unit (RU) and moved to the “cloud” (DU cloud) for centralized signal processing and management. Each DU/RU pair exchanges bandwidth-intensive digitized baseband signals through an optical access network (fronthaul). Time-wavelength division multiplexing (TWDM) passive optical network (PON) is a promising fronthaul solution due to its low energy consumption and high capacity. In this paper, we propose and leverage the concept of a virtual base station (VBS), which is dynamically formed for each cell by assigning virtualized network resources, i.e., a virtualized fronthaul link connecting the DU and RU, and virtualized functional entities performing baseband processing in DU cloud. We formulate and solve the VBS formation (VF) optimization problem using an integer linear program (ILP). We propose novel energy-saving schemes exploiting VF for both the network planning stage and traffic engineering stage. Extensive simulations show that CRAN with our proposed VF schemes achieves significant energy savings compared to traditional RAN and CRAN without VF.

© 2016 Sil-Gu Mun et al. 9 http://dx.doi.org/10.4218/etrij.16.0115.0044 We demonstrate a timeand wavelength-division multiplexed passive optical network system employing a vertical-cavity surface-emitting laser array–based optical line terminal transceiver and a tunable bidirectional optical subassembly–based optical network terminal transceiver. A packet error–free operation is achieved after a 40 km single-mode fiber bidirectional transmission. We also discuss an arrayed waveguide grating, a photo detector array based on complementary metal–oxide– semiconductor photonics technologies, and low-cost key devices for deployment in access networks.

A large incoherent crosstalk (IC) caused by amplified spontaneous emission (ASE) noise power from Txdisabled optical network units and a differential...

We successfully demonstrate the multi-channel 50G-EPON system using dynamic MPRS channel bonding and coordinated DBA in real-time. We also verify the packet throughput of 40-Gb/s and 16-Gb/s in down/upstream direction without packet drop through envelope frame transmission.

We review next generation passive optical network for enabling low latency and high bandwidth services. We present recent results on next-generation PON prototype of 100G-EPON based on channel bonded 100 Gb/s MAC, PON transceivers with 25 Gb/s APD-ROSAs.

We demonstrated a link budget improved 2×25 Gb/s WDM/TDM-PON by using O-band SOA with an assist light and FEC. When the assist light is used to the SOA, gain-saturation induced crosstalk of SOA was successfully mitigated. 50G-Ethernet PON traffic was transmitted over 20-km reach and 256-split.

Bandwidth requirements of both wireless and wired clients in access networks continue to increase rapidly, primarily due to the growth of video traffic. Application awareness can be utilized in access networks to optimize quality of experience (QoE) of end clients. In this study, we utilize information at the client-side application (e.g., video resolution) to achieve superior resource allocation that improves user QoE. We emphasize optimizing QoE of the system rather than quality of service (QoS), as user satisfaction directly relies on QoE and optimizing QoS does not necessarily optimize QoE, as shown in this study. We propose application-aware resource-allocation schemes on an Ethernet passive optical network (EPON), which supports wireless (utilizing orthogonal frequency division multiple access) and wired clients running video-conference applications. Numerical results show that the application-aware resource-allocation schemes improve QoE for video-conference applications for wired and wireless clients., Comment: Journal of Optical Communications and Networking, 2018

We report multilane-based real-time 100G-PON with dynamic channel bonding and low-latency DBA. Packet throughput of 80-Gb/s in downstream and 32-Gb/s in upstream with multi-speed ONUs on the distance 20-km and a 1:16 splitter are also demonstrated.

As bandwidth requirements of access networks continue to increase rapidly, especially due to the growth of streaming traffic, the need for resolving bandwidth contention among competing users and applications becomes more compelling. The proposed Software-Defined Ethernet Passive Optical Network (EPON) architecture utilizes an application-level feedback from the client side (for video users) to the network through a Software-Defined-Network (SDN) controller to achieve better client-and-service-level differentiation in the downstream direction of an EPON access network Numerical results obtained from simulation experiments demonstrate that the proposed architecture with downstream resource allocation for video streaming applications considerably reduce video stalls and increase video buffer level at the client applications leading to better Quality of Experience (QoE) for users along with better client-and-service-level differentiation.

We experimentally demonstrate multilane-based 50-Gb/s EPON system using O-band wavelength bands and RS(255,223) code. The packet throughput of 40-Gb/s and 16-Gbp/s at a downstream and upstream direction is presented on 20-km reach with 1:64 split ratios.

We reviews optical access technologies for 5G mobile communication networks such as mobile data compression, high-speed passive optical network (PON), and analog radio over fiber (RoF) technologies. Recent feasibility studies for future optical access network with optical mobile convergence are discussed.

We firstly propose and demonstrate the 50-Gb/s multilane EPON that can accommodate 25G-EPON ONUs and 50G-EPON ONUs in the legacy ODN. For this, we use two wavelength pairs within O-band which assigned 1309/1270-nm and 1295/1330-nm to each lane, respectively. We also design MAC control that operates the discovery process with multilane-controllable GATE/REPORT frame via lane 0. We confirm that 50-Gb/s multilane EPON satisfy a loss-free for 1010 packets at the throughput of 40-Gb/s at downstream and 16-Gb/s at upstream with the RS(255,223)-based FEC at the distance of 20 km and 1:32 splitter.

Recently, the IEEE 802.3 Ethernet Working Group has classified three architectures for the nextgeneration 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 awavelength. Existing dynamic bandwidth and wavelength allocation (DBWA) schemes for conventional EPON can be applied to MSD-PON and SSDPON, 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 ofWA-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, onWA-PON latency and packet loss ratio, and we evaluate the energy efficiency gain of the modified DBWA scheme.

Time- and wavelength-division multiplexed passive optical network allows wavelength sharing by optical network units (ONUs) in a time-division multiplexing fashion. When ONUs are lightly loaded, they can share fewer wavelengths to reduce energy consumption. In such a dynamic system, the configuration of wavelength sharing should adapt to the traffic changes for energy saving and load balancing (which affects the quality of service). However, going from one configuration to another is nontrivial, as it usually involves wavelength reassignment and potential service disruptions. The optimization and algorithm design have to account for such reconfiguration (along with other aspects). In this study, we have developed optimization models and online algorithms that incorporate the reconfiguration dimension. Various underlying tradeoffs (e.g., energy saving versus reconfiguration and load balancing versus reconfiguration) are investigated for both static planning and dynamic operations.

We propose and demonstrate an efficient power-saving optical network unit (ONU) based on upstream traffic monitoring for 10-Gb/s wavelength division multiplexed passive optical networks (WDM-PONs). The power-saving mode controller uses a -processor and traffic monitoring modules followed by the proposed power-saving processes to operate the sleep mode ONU. The power consumption of the ONU is effectively reduced from 19.3 W to 6.4 W when no traffic from the users is detected. In addition, we design a power-saving mechanism based on a cyclic sleep mode operation to allow a connectivity check between the optical line terminal and ONU. Our calculation results show that the WDM-PON ONU reduces the power consumption by around 60% using the proposed mechanism.

We proposed and demonstrated high efficient pre-spectrum sliced seed lights (PS-SL) for serving low-cost seeded wavelength division multiplexing passive optical network (WDM–PON). The PS-SLs reused backward amplified spontaneous emission light which were generated by an Erbium doped fiber amplifier (EDFA) to improve output characteristics. The power, flatness and bandwidth of seed signal from the proposed PS-SL were sufficient to serve multiple seeded WDM–PON OLTs. We experimentally demonstrated the feasibility of the PS-SL with multiple seeded WDM–PONs over 20 km transmission. In addition, the PS-SL was tolerated to these ranges of environmental conditions since no data error was observed after 48 h. We anticipated a considerable reduction in the seed light cost per channel for multiple WDM–PONs because the seed light cost was shared by multiple WDM–PON OLTs.

To alleviate the back-reflection induced interferometric crosstalk in a loop-back WDM-PON based on RSOA, we propose the use of off-the-shelf single mode operated laser with intentional optical feedback as a seeding source. For adjusting the external optical feedback quantity, we could effectively broaden the spectral linewidth of single mode operated laser output. We also experimentally demonstrated that our proposed method could enhance the up- and down-stream transmission performances under relatively lower signal to crosstalk ratio.

We demonstrate a real-time 25-Gb/s PON prototype with ethernet-PON MAC/PHY, O-band transmitter, and cost-effective APD receivers. With applying parasitic inductance and capacitance reduction, the frequency response of 25-Gb/s APD ROSA with TO46-pacakge is improved to support high receiver sensitivity around -25 dBm at the BER of 10(-3). The 30 dB power budget of 25 Gb/s downstream is achieved at the BER of 10(-3). With long-term ethernet packet transmission, 25 Gigabit and 10 Gigabit ethernet traffics are successfully transmitted through the 20-km SMF over 14 hour's observation window. Furthermore, QoS and bandwidth re-assignment function of the 25-Gb/s PON prototype are successfully demonstrated with respect to residential, business and mobile backhaul services in ONUs. (C) 2016 Optical Society of America

To effectively schedule transmissions in NG-EPON, Hybrid-PON is further classified into MSD-PON, SSD-PON, and WA-PON depending on their different access architectures, viz. how a group of ONUs share the assigned wavelength channels. The architectures for these three Hybrid-PONs were introduced by the IEEE 802.3 Ethernet Working Group in 2015. In this study, we first propose to apply some existing dynamic bandwidth allocation (DBA) schemes in the cases of MSD-PON and SSD-PON. Then, since WA-PON is a new hybrid multiplexing architecture and previous DBA schemes cannot exploit its flexibility of wavelength assignment and sharing, we develop the optimization model and also provide a novel DBA scheme for WA-PON. Then, we compare the performance of these hybrid PONs by simulation in terms of average delay and packet drop ratio. We analyze the influence of increasing buffer size for each ONU in WA-PON and show how the flexibility of WA-PON can impact the performance. We find that WA-PON can reduce the drop ratio compared with SSD-PON at low offered load, and has smaller average delay than MSD-PON, which suggest that WA-PON can tolerate heavier traffic and performs the best among three Hybrid-PON architectures.

To meet challenging 5G capacity requirements, operators are densifying their cellular networks by deploying additional small cells to cover hot spots, and such an increase in the number and density of cells may result in excessive numbers of handovers. In this study, we propose a handover reduction mechanism implemented in a cloud radio access network (CRAN) by exploiting the high capacity of an optical access network serving as a “fronthaul.” CRAN has been proposed as a 5G radio access network architecture, where the digital unit (DU) of a conventional base station (BS) is separated from the radio unit (RU) and moved to the “cloud” (DU-cloud) for better mobility management and cost saving. Separating RUs and DUs requires a low-latency and high-bandwidth 5G transport network to handle “fronthaul” traffic, for which optical access is an excellent choice. Here, we present a new 5G architecture, called virtualized-CRAN (V-CRAN), moving toward a cell-less 5G mobile network architecture. We leverage the concept of a “virtualized-BS” (V-BS) that can be formed by exploiting several enabling technologies such as software-defined radio and coordinated multi-point transmission/reception. A V-BS can be formed on a per-user basis by allocating virtualized resources on demand so that common signals can be jointly transmitted from multiple RUs to the user without triggering handover. We first model the handover reduction optimization problem for a scenario where future mobility information is known, and then propose a suite of algorithms for a scenario where future information is unknown. Simulation results show that V-CRAN can enhance the throughput of users at the cell-edge, as well as significantly reduce the number of handovers, handover delay, and failure rate.

We demonstrate a linear bus wavelength-reused gigabit wavelength-division multiplexing passive optical network (WDM-PON) with multiple optical add-drop nodes. A commercially available reflective semiconductor optical amplifier-based WDM-PON has a sufficient power budget to provide multiple optical add/drop nodes in 16 WDM channels. Sixteen 1.25 Gb/s WDM channels are successfully transmitted over 20 km of single-mode fiber with four optical add/drop multiplexers, even with 32 dB reflection and chromatic dispersion in the link.

Colorless gigabit wavelength-division-multiplexing (WDM)/time-division-multiplexing (TDM) hybrid passive optical network (PON) using a remote protocol terminator is proposed and experimentally demonstrated. The system consists of reflective semiconductor optical amplifier-based WDM-PON and a legacy TDM-PON, combined with a simple and efficient remote node structure in order to provide high-speed fiber-to-the-home service to a large area with a high population density. The demonstrated system can support 512 subscribers with a single feeder fiber. The performance and feasibility of the system were evaluated by transmitting gigabit per second data including the effects of Rayleigh backscattering and 20 km attenuation. The system has been used by Korea Telecom to provide commercial services in Gwangju, Korea, since March 2009, after successfully passing through the benchmark test. This is the first commercial deployment of a WDM/TDM hybrid PON. It can accommodate field-deployed TDM-PON link without any modification and extend the maximum total reach of PON link by the use of remote protocol termination. Number of subscribers and the allocated bandwidth to the subscribers can be designed by simply changing the splitting ratio.

We demonstrate four conventional TDM PONs with symmetric 2.5-Gb/s line rate and extended reach, sharing a common infrastructure. A hybrid SOA-Raman amplifier provides 150-nm bidirectional gain over the PONs' downstream and upstream CWDM wavelength plan.

In recent years, the increasing traffic demand in radio access networks (RAN) has led to considerable growth of the number of base stations (BS), posing a serious scalability issue with respect to the energy consumption of BSs. Optical-access-enabled Cloud RAN (CRAN) has been recently proposed as a next-generation access network, where the digital unit (DU) of a conventional cell site is separated from the radio unit (RU), by an optical access network (fronthaul), and moved to the “cloud” (DU pool) for centralized signal processing and management. Time-Wavelength Division Multiplexing (TWDM) Passive Optical Network (PON) is a promising fronthaul solution due to its low energy consumption and high capacity. In this study, we propose the concept of Virtual Base Station (VBS), which is dynamically formed for each cell by assigning virtualized network resources, including i) a virtualized PON link connecting the DU and RU and ii) virtualized functional entities performing baseband processing in DU pool. We propose a novel energy-saving scheme exploiting VBS formation for CRAN and compare its performance with the optimal results of an Integer Linear Program for VBS formation optimization problem. Numerical evaluation shows that CRAN with VBS formation achieves significant energy savings compared to traditional RAN and CRAN without VBS formation.

We study an SDN-enabled EPON architecture that utilizes application information from clients to achieve superior upstream resource allocation. This leads to better quality of experience of video-conferencing clients which are high consumers of upstream bandwidth.