Next-generation Access Networks Research Articles

Flexible 2 × 2 multiple access visible light communication system based on an integrated parallel GaN/InGaN micro-photodetector array module

In recent studies, visible light communication (VLC) has been predicted to be a prospective technique in the future 6G communication systems. To suit the trend of exponentially growing connectivity, researchers have intensively studied techniques that enable multiple access (MA) in VLC systems, such as the MIMO system based on LED devices to support potential applications in the Internet of Things (IoT) or edge computing in the next-generation access network. However, their transmission rate is limited due to the intrinsic bandwidth of LED. Unfortunately, the majority of visible light laser communication (VLLC) research with beyond 10 Gb/s data rates concentrates on point-to-point links, or using discrete photodetector (PD) devices instead of an integrated array PD. In this paper, we demonstrated an integrated PD array device fabricated with a Si-substrated GaN/InGaN multiple-quantum-well (MQW) structure, which has a 4×4 array of 50 μm×50 μm micro-PD units with a common cathode and anode. This single-integrated array successfully provides access for two different transmitters simultaneously in the experiment, implementing a 2×2 MIMO-VLLC link at 405 nm. The highest data rate achieved is 13.2 Gb/s, and the corresponding net data rate (NDR) achieved is 12.27 Gb/s after deducing the FEC overhead, using 2.2 GHz bandwidth and superposed PAM signals. Furthermore, we assess the Huffman-coded coding scheme, which brings a fine-grain adjustment in access capacity and enhances the overall data throughput when the user signal power varies drastically due to distance, weather, or other challenges in the channel condition. As far as we know, this is the first demonstration of multiple visible light laser source access based on a single integrated GaN/InGaN receiver module.

The Power Quality of the distribution networks and its impact on the Telecommunication Next Generation Access Network

The paper deals with the Power Quality of the electrical distribution network and its impact on the new telecommunication networks. In particular, in the frame of the deployment of the Next Generation Access Network (NGAN) in the Fiber To The Cabinet (FTTCab) architecture, the impact of severe voltage dips and micro interruptions on the most important Information and Communications Technology (ICT) devices has been evaluated experimentally by Telecom Italia, defining in particular a sort of customized voltage dips immunity area for its telecommunications network equipment (TLC). On the base of these experimental results RSE has performed statistical analyses on voltage dips occurring outside this area which could be responsible in theory for the telecommunication devices reboot. The analyses are based on the data provided by the MV distribution network monitoring system QuEEN in the assumption that MV dips could be totally transferred to the LV network where the telecommunication cabinets are connected. A short analysis of voltage dips propagation from the medium voltage MV to the low voltage LV networks has been performed, on a few measurements sites at disposal in order to confirm this assumption.

Low-cost, large-coverage, and high-flexibility coherent PON for next-generation access networks: advances, challenges, and prospects [Invited

Low-cost, large-coverage, and high-flexibility coherent PON for next-generation access networks: advances, challenges, and prospects [Invited

Spectrally-Sliced Coherent Receiver Utilizing a Gain-Switched Optical Frequency Comb

The spectrally-sliced coherent receiver is an attractive solution for future optical access network applications where cost is a sensitive factor, as it enables reduced bandwidth of the analog front-end components and analog-to-digital convertors when compared to a conventional intradyne coherent receiver. In a proof-of-concept experiment, we demonstrate a single-polarization 50 Gb/s QPSK C-band transmission experiment over 40 km of standard (G.652) fiber using receiver bandwidths as low as 6.25 GHz and also utilize an array of local oscillator lines derived from an injection locked gain-switched optical frequency comb, which can be realized as a compact photonic integrated circuit. This paper also analyses the influence of optical frequency comb properties on the quality of the reconstructed signal. The critical parameters considered in this study include comb power and flatness, mutual comb line coherence, and the comb line suppression ratio after demultiplexing the comb lines. We have shown that with practically achievable comb parameter values, the receiver can operate with less than a 1 dB sensitivity penalty compared to a conventional intradyne receiver. The scheme has the potential to provide a low-cost coherent receiver solution for next-generation access networks.

A Method for the Design of Bicomplex Orthogonal DSP Algorithms for Applications in Intelligent Radio Access Networks

In this paper, a new method for designing orthogonal bicomplex digital signal processing (DSP) algorithms is developed. In contrast to those previously reported on, the method proposed is universal, since it is not affected by the order or the type of the real digital processing algorithm employed as a prototype. The method is based on a transformation starting with either real or complex orthogonal DSP algorithms represented in the z-domain, and transforming them into orthogonal bicomplex algorithms. The proposed new method is applied in the design of bilinear orthogonal bicomplex DSP systems with a canonical number of elements, the main advantage of which is that the order of the digital system is reduced by a factor of four. As well as being canonical, the orthogonal bicomplex digital systems are also symmetrical structures, as a result of which they offer parallelism and subsequent unification. It is experimentally shown that bicomplex orthogonal DSP algorithms acquire the properties of the initial algorithm prototype, irrespective of whether it is real or complex. Since the new design method is universally applicable, it can be used to develop bicomplex orthogonal digital algorithms of any order and type. Being simple, canonical, and symmetrical—and, thus, leading to lower equipment cost, reduced complexity, and higher energy efficiency—these structures may well be appropriate for the enhancement of the implementation of intelligent algorithms in next-generation radio access networks.

Coherent Passive Optical Networks: Why, When, and How

While the capacity of the next-generation access network is expected to be 100 Gb/s and beyond, coherent optics is going to be a logical choice for the physical layer as the currently used intensity-modulation/ direct-detection technology will fail to meet the required power budget of such high line-rate systems. In this article, we present an overview of necessities, timeframe, and technological challenges for the future passive optical network utilizing coherent technology.

Network modeling approaches for calculating wholesale NGA prices: A full comparison based on the Greek fixed broadband market

According to the European Commission Recommendation for setting copper and fiber wholesale prices where cost orientation is imposed as a remedy, National Regulatory Authorities (NRAs) should adopt a Bottom-UP Long-Run Incremental Cost Plus (BU LRIC+) costing methodology that estimates the current cost that a hypothetical efficient operator would incur to build a modern efficient Next Generation Access (NGA) network. The starting point of modeling an efficient operator investing in NGA networks is the network modeling approach. In this paper, we compare the most widely adopted network modeling approaches in terms of wholesale fiber-to-the-home (FTTH) prices. In particular, the modified scorched node approach is compared to the extreme cases of the scorched node and the scorched earth approaches. The comparison between the aforementioned scenarios sheds light on the impact of each approach on the wholesale FTTH prices. The main finding of this paper is that the scorched earth approach leads to a maximum of 10% reduction in the short-term access prices compared to the most inefficient scorched node approach, whereas further extending its optimizations by optimizing the number of central offices, both the short-term and long-term wholesale price reductions are quite significant (more than 20%) regardless of service speeds. Consequently, NRAs should consider a geographically differentiated modeling approach when regulating the wholesale market by adjusting the level of scorching in each area and network segment according to the investment plans of telecom operators. An appropriate variation of the modeled network operator's efficiency is expected to more accurately represent the costs of a reasonably efficient operator based on the real market conditions and a forward-looking perspective. These findings provide valuable information to both network operators and telecom regulators.

Performance Analysis of a Full-Duplex TWDM-PON Using OFDM Modulation with Red LED Visible Light Communication System

Today’s access networks are in high demand to fulfill the high bandwidth requirement because of extensive improvement in high transmission rate applications for cloud computing, big data analytics, and other next-generation 5G smart applications. In this work, the symmetrical and bidirectional time and wavelength division multiplexing-passive optical network (TWDM-PON) system is proposed and demonstrated. Orthogonal frequency division multiplexing (OFDM) with 4-level quadrature amplitude modulation is used for downstream and upstream transmission. Also, 625 nm red light-emitting diode is utilized for visible light communication (VLC) using a wireless link to encourage the economic high transmission rate fiber/VLC optical network. The TWDM-PON employing OFDM with the VLC system has been analysed for downstream and upstream channels for variable fiber-wireless link range. Additionally, the impact of a high transmission rate and usage of digital signal processing (DSP) unit to reduce losses due to fiber nonlinearity effects in the proposed link has been investigated. The results show that the maximum faithful wireless and wired range for the proposed system is 140 m and 60 km respectively at 20 Gbps to attain the minimum 3.8 × 10−3 BER. The decrease in error vector magnitude (EVM%) by almost 52% with the use of DSP in the proposed system provides a high transmission rate of 200 Gbps in the proposed link. Further, comparative performance of the proposed system with previous latest works in literature reveals a superior performance of the proposed link. The proposed TWDM-PON system provides a next-generation access network from rural areas to urban areas.

Energy-Efficient Frame Aggregation Scheme in IoT Over Fiber-Wireless Networks

With the tremendous growth of traffic demand caused by the conventional service and emerging Internet-of-Things (IoT) applications, it is vitally challenging to support seamlessly access for billions of IoT devices along with existing Internet service. Fiber-Wireless (FiWi) access networks is an ideal solution for the next-generation access networks to support both IoT and conventional service. One of the main challenges faced by the design of an FiWi access network is the high energy consumption due to low utilization of optical network units (ONUs) and high control overhead of data transmission. In this article, An adaptive frame aggregation scheme with load transfer is proposed to reduce the energy consumption in FiWi. By evaluating the quality of wireless channel, the proposed scheme adaptively adjusts the length of the aggregated frame to reduce the energy consumption caused by the frequent preemption of wireless channel and the numerous retransmission of data frames resulted by poor channel quality. In the optical backhaul, according to the delay requirements of services with different priorities, the proposed scheme calculates the optimal frame length for each queue and performs load transfer among ONUs to dynamically distribute network load and maximize the sleep rate of ONUs for energy saving. Simulation results and theoretical analysis both unanimously show that the proposed scheme achieves significant amounts of energy saving, while preserving delay performance of various services.

Assessing fifteen years of State Aid for broadband in the European Union: A quantitative analysis

In this paper, we document how public funds, or State Aid, have been used to support the deployment of broadband infrastructure in Europe since 2003. Our descriptive analysis relies on a unique data set on all the broadband measures notified to the European Commission by Member States between 2003 and 2018. We identify two waves of State Aid for broadband: one for the deployment of basic broadband, and a more recent one for the roll out of next-generation access networks. The use of State Aid is very heterogeneous across Member States, with a few large countries representing the bulk of the cases. The objective of most plans is to expand broadband coverage. The typical project relies mainly on public funds, and involves a direct grant, an open tender, and a contract for 3–5 years. Access obligations are imposed on networks deployed with State Aid, using a benchmarking approach in most cases. Finally, we show that notifications are associated with a relatively high level of broadband coverage in notifying countries, suggesting that public investment is taking over from private investment.

Investigating the intertwining impact of wholesale access pricing and the commitment to net neutrality principle on European next-generation access networks private investment plans: An options-game application for capturing market players' competitive interactions

Whilst the deployment of next generation access networks (NGANs) is undoubtedly beneficial to the economy, new legal developments in the United States (US) regarding the issue of net neutrality (NN) pose a new challenge not only to policy makers but to telecommunication providers as well, that could justify a fresh approach when assessing NGANs investments. In particular, the Federal Communications Commission (FCC) subverted extant NN rules in the US and if the European Union (EU) decides to follow a similar deregulatory path in the future it could change the way telecommunications providers on both sides of the Atlantic lay down their optical-fibre network infrastructure investment plans. For instance, if traffic prioritization is allowed then diversification of revenue sources can be achieved by charging customers for privileged data delivery to their premises. Currently, NGANs roll-out throughout EU is an ongoing process in a setting whereby access regulation in the form of network element unbundling is already imposed. As a result, these legal developments form a new context within which it makes sense to assess the role of NGANs wholesale access pricing in tandem with the degree of commitment to NN rules so as to i) determine their combinatorial impact on private telecommunications operators' financial figures and ii) capture their competitive interactions. Towards this end, an important aspect of particular value to market players (i.e. incumbents and competitive providers – CPs), and policy makers (i.e. National Regulatory Authorities – NRAs) that this article aims to examine is how to employ the option-game (OG) analysis, that reflects the intersection of game theory (GT) and real options (ROs), to model the competitive interactions between participants in a particular competition game set-up by means of deriving possible Nash-equilibrium (NE) outcomes within a regulatory setting part of which is the commitment or non-commitment to the NN principle. This, hybrid, evaluation tool is applied on top of a conventional discounted cash flow (DCF) techno-economic analysis assessment of an NGAN investment opportunity.

Energy-Efficient Decentralized Framework for the Integration of Fog With Optical Access Networks

The increasing numbers of broadband users and the corresponding rapid expansion of access networks have been putting more pressure on improving their energy efficiency to reduce both their operating costs and carbon footprint. At the center are passive optical networks (PONs), with them being one of the leading broadband technologies of today. Although they are considered to be the most energy-efficient among wired access technologies, their power consumption is still considerably high and is expected to increase over the next few years. As a result, many energy conservation frameworks have been proposed for PONs that are all centralized-based. In this paper, we propose a novel PON energy-conservation framework that is, for the first time, decentralized-based. Not only does the proposed framework aim to provide better network performance while conserving energy, but it also supports novel cloudlet placements for integrating fog computing with PONs by utilizing edge-to-edge communications. The framework is therefore designed to meet the requirements of next-generation access networks by addressing three main challenges; conserving energy, achieving high network performance, and supporting fog computing.

Mitigation of Pattern-Dependent Effect in SOA at O-Band by Using DSP

Semiconductor optical amplifier (SOA) is regarded as a promising candidate to amplify the optical signal in next-generation access network, especially for O-band signal transmission. However, the SOA-based system suffers from the pattern-dependent effect due to its gain saturation. Compared to digital signal processing (DSP) at receiver, DSP in the transmitter can reduce implementation complexity, which is attractive for the multi-user system. In this paper, we propose three methods to mitigate the pattern-dependent effect in SOA and compare their performance based on: 1) look-up-table (LUT) considering pattern-dependent effect, 2) pre-distortion without considering pattern-dependent effect, 3) probabilistic shaping (PS). The performance of three mitigation methods is investigated in an intensity modulation with direct detection (IM/DD) 4-ary pulse-amplitude-modulation (PAM-4) transmission system at O-band. Our research results show that all these schemes can improve the receiver dynamic range of PAM-4 signals at 50 Gbit/s and 100 Gbit/s. Moreover, PS and LUT can also improve the receiver dynamic range of 75-Gbit/s PAM-8 signals.

Long-reach Optical Access (LROA): A Cost-effective Promising Approach

To compensate the decrease in its revenue, most telecom operators have adopted similar strategy which is to provide faster Internet with low cost to its customers. Studies suggested that providing faster Internet with low cost can be achieved by reducing the cost of building next-generation access network. Among the various technologies introduced for next-generation access, long-reach optical access LROA is considered the largest candidate. This is due to the anticipated cost effectiveness of this technology. In LROA, more users can be supported over a common optical component (e.g., a transmitter, a fiber, or probably both), i.e., small number of entities is employed in the access network for service provisioning, which is considered as an improvement in the cost-sharing concept. Our objective in this paper is to verify the cost-effectiveness of this technology. To this end, a statistical-based cost comparison was conducted. The comparison was between the currently deployed passive optical networks (PONs), i.e., the Broad band PON (B-PON [G. 983]), the Ethernet PON (E-PON [IEEE802.3ah]), and the gigabit PON (G-PON [ITU-T G. 984]) and one of the LROA architectures proposed in the literature. The comparison process confirmed that the LROA requires less cost and cost per subscriber as compared with the currently deployed PONs.

Are Internet users in Slovenia willing to pay for fast broadband and what drives them to migrate?

The European Union (EU) member states are faced with a significant gap between availability of high-speed broadband and the share of households subscribed to such Internet access. This paper investigates the determinants of Internet users’ willingness to pay (WTP) for next-generation access (NGA) in Slovenia. Following the EU Digital Agenda target whereby all households should have Internet access of at least 30 Mbps by 2020, the WTP for an Internet speed of 30 Mbps is analysed. The results show that characteristics relating to the current use of Internet services and characteristics of Internet users both play an important role in explaining the WTP for NGA In particular, the presence of a student or pupil in the household, household income, subscription to mobile broadband and the quality of Internet services positively influence the WTP decision, while respondents that are employed or are already subscribed to fibre have lower WTP The results of our analysis may help Internet service providers and policymakers identify remedies which can reduce the demand gap for NGA networks.

Anatomy of a public-private partnership: Hold-up and regulatory commitment in Ultrafast Broadband

In recent years, the preference for purely private funding and ownership of telecommunications networks has given way to a ‘new wisdom’ that some form of public funding is now likely necessary if faster and more capacious next generation access (NGA) networks are to be constructed in a timely fashion for the majority of the population. Policy-makers are charged with deciding how that public investment will take place. One approach is via Public-Private Partnerships (PPPs), where public and private actors collaborate in UFB (Ultrafast Fibre Broadband) investment, construction and operation. However, the body of analysis of PPPs in NGA networks to guide policy-makers is scant.By using the concept of regulatory commitment, the paper compares the experiences gained in a hold-up situation in PPPs in other infrastructures (e.g. roading) with the UFB context. A case study of New Zealand's Ultrafast Fibre Broadband Initiative is used to draw new insights for government purchasers and regulatory agencies. In comparing the different forms of PPPs, the paper shows that UFB PPPs reverse the typical direction of financing and ownership observed in roading PPPs. Financing and asset ownership are separated in UFB PPPs, increasing the potential for misalignment of incentives and the likelihood that the public party can use its legislative powers to alter regulatory settings after the PPP contract is signed, and thereby hold up the private party once existing network assets are sunk. Whilst the government instigating the PPP may not be inclined to act opportunistically, a successive government facing different political priorities does not face the same incentives. To the extent that the private party can anticipate this risk, it should structure the initial agreement to ensure that the public party is penalised if such an event occurs (i.e. an automatic right to favourable renegotiation or payment of compensation). Such terms will discourage opportunism, so that the project benefits from time-consistent alignment of incentives and objectives.

A Comparative Analysis of Selected National and Regional Investment Initiatives That Seek to Achieve Broadband Expansion by Deploying NGA Networks

Abstract Expectations about higher economic growth and the ever-increasing demand for higher bandwidth are driving the worldwide deployment of Next-Generation Access (NGA) networks. The paths followed to achieve this goal markedly vary, however, across different countries. This article offers a comparison of a handful of leading NGA deployments that rely on different investment models. We study the broadband national initiatives of New Zealand and Australia and a group of selected regional NGA deployments in Europe. While New Zealand's approach partially relies on a public–private partnership model of investment, Australia's National Broadband Network is a wholly government-funded initiative and the European local initiatives in Sweden, Spain, the Netherlands, and Portugal use a range of mixed models of investment. We use a common technology–policy–market framework that allows for a clear mapping of the incentives, goals, and actions of those involved in network deployment. Our main interest is the identification of the drivers for investment as well as the description of main risk factors in each case. By applying this framework to those selected deployment cases our work draws relevant conclusions about the impact of investment decisions on performance criteria such as coverage and uptake.

A Comparative Analysis of Selected National and Regional Investment Initiatives That Seek to Achieve Broadband Expansion by Deploying NGA Networks

Abstract Expectations about higher economic growth and the ever-increasing demand for higher bandwidth are driving the worldwide deployment of Next-Generation Access (NGA) networks. The paths followed to achieve this goal markedly vary, however, across different countries. This article offers a comparison of a handful of leading NGA deployments that rely on different investment models. We study the broadband national initiatives of New Zealand and Australia and a group of selected regional NGA deployments in Europe. While New Zealand's approach partially relies on a public–private partnership model of investment, Australia's National Broadband Network is a wholly government-funded initiative and the European local initiatives in Sweden, Spain, the Netherlands, and Portugal use a range of mixed models of investment. We use a common technology–policy–market framework that allows for a clear mapping of the incentives, goals, and actions of those involved in network deployment. Our main interest is the identification of the drivers for investment as well as the description of main risk factors in each case. By applying this framework to those selected deployment cases our work draws relevant conclusions about the impact of investment decisions on performance criteria such as coverage and uptake.

MDM transmission of CAP-16 signals over 1.1- km anti-bending trench-assisted elliptical-core few-mode fiber in passive optical networks.

Mode-division multiplexing passive optical network (MDM-PON) is a promising scheme for next-generation access networks to further increase the transmission capacity and number of end-customers. In this paper, we propose and experimentally demonstrate the implementation of MDM-PON architecture with the carrier-less amplitude/phase (CAP) modulation signals and two effectively separated spatial modes multiplexing transmission in an elliptical-core few-mode fiber (EC-FMF). The trench-assisted EC-FMF features favorable anti-bending performance with negligible power variations and stable mode intensity profiles under extreme bending conditions. Two spatial modes carrying CAP-16 signals for four users with net data rate of 5 Gb/s per user in the downstream transmission over 1.1-km EC-FMF is demonstrated. The measured mode crosstalk including mode (de)multiplexing and 1.1-km EC-FMF transmission is less than -18 dB and multiple input multiple output (MIMO) technique is not used in the experiment for simplicity. The measured optical signal-to-noise ratio (OSNR) penalties for the downstream transmission without or with crosstalk at a bit-error rate (BER) of 3.8x10-3 (7% forward error correction (FEC) threshold) are less than 1.8 dB and 3.1 dB, respectively. Larger transmission capacity and more users are expected when further employing higher dimension CAP signals and EC-FMF supporting more separable spatial modes.

A Frequency Reuse-Based Design for Flexible and Scalable Passive Optical Networks (PONs)

The accelerated growth in the bandwidth demand emphasizes the necessity to evolve from the currently deployed gigabit-class passive optical networks (PONs) to the next-generation optical access networks (NG-OANs). Different architectures were proposed in the literature in order to create a NG-OAN that is able to fulfilling the aforementioned goal. In this paper, a time-division multiplexing (TDM)/dense wavelength-division multiplexing (DWDM) scheme was proposed. The proposed scheme is sought to satisfy the current and future anticipated bandwidth demands. The architecture we proposed was able to allow different bit rate optical line terminals OLTs to use the same frequency band, and transmit their services over a 24 km shared feeder to 16 passive remote terminals (PRTs) with 16 ONU group for each. Each group can accommodate up to 16 ONU, total of 256 ONU/PRT, resulting in overall system capacity 4096 ONU. The architecture also allows the independent-upgradeability for each optical network terminal ONU.