Next-generation Access Networks Research Articles

Field Measurement and Analysis of Long-Reach and High-Splitting-Ratio 10G-EPON With Optical Amplifier in Central Office

It is important to economize the infrastructure of the access network and enhance its profitability because it represents the greatest part of network infrastructure cost. As 10G-EPON can be cost-effectively shared among various access services, it is one of the strong candidates to reduce the infrastructure cost of the next-generation access network. To further enhance cost effectiveness, it is useful to improve the acceptable link budget of access systems by using optical amplifiers (OAs), which can increase the splitting ratios and extend the reachable distance of the system. In this paper, we demonstrate an $N$ :1 redundant 10G-EPON system with dual-rate central-office-set-type semiconductor optical amplifier (CO-SOA). Our 10G-EPON system reduces OPEX and CAPEX due to its extended reachable distance and elimination of intermediate offices while keeping its system reliability with the $N$ :1 protection system. Moreover, we also develop a method for estimating the total reachable distance of 10G-EPON systems with OAs in order to quantitatively evaluate the effect of extending reachable distance on various combinations of splitting ratio based on the results of actual demonstrations. Analyses of field measurement results clarify that the proposed system has sufficient design flexibility so as to satisfy the subscriber distribution requirements as regards the factors of splitting ratio and reachable distance. The results indicate that the $N$ :1 optical subscriber unit protection with CO-SOAs is a promising approach to practical 10G-EPON systems that are cost effective and reliable.

Flexible tunable optical transceiver based on field-programmable gate array for time and wavelength-division multiplexed passive optical network systems

Time- and wavelength-division multiplexed passive optical networks (TWDM-PONs) have been selected by the full services access network community as the most suitable technology for next-generation optical access networks. A key technology in TWDM-PON is the colorless optical network unit transceiver. This paper proposes a flexible, tunable optical transceiver that uses directly modulated tunable lasers. Using a field-programmable gate array (FPGA), programmable reconfigurations and testing capabilities can be embedded into the transceiver in order to implement wavelength control, signal generation, pre-emphasis for upstream, and a bit error rate (BER) test for the downstream. To ensure high-quality signal generation at different bitrates, impedance matching between the laser driver circuit and the laser diodes is optimized. Using the proposed transceiver, three-section-distributed Bragg reflector tunable lasers at or below 2.5 Gb/s direct modulation through a 40-km standard mode fiber transmission were successfully implemented.

Power Budget of Ultra-Dense Virtual-Carrier-Assisted DD MB-OFDM Next-Generation PON

An ultra-dense multi-band orthogonal frequency division multiplexing (MB-OFDM) passive optical network (PON) with a dedicated band capacity per user of 2.5 or 10 Gb/s is demonstrated experimentally. A band spacing of 6.25 GHz and a low-cost virtual carrier-assisted direct-detection (DD) scheme are employed. The proposed MB-OFDM PON shows a great potential in the context of next-generation optical access networks due to the low receiver bandwidth required, low-cost implementation, and high granularity, flexibility, and scalability provided. The power budget evaluated from the experimental results shows that the virtual carrier-assisted DD MB-OFDM solution is more suited to short-reach PONs. For a PON reach of 20 km and a band capacity of 2.5 Gb/s, the proposed network supports 128 users. For a band capacity of 10 Gb/s, the network supports 32 users in a PON with reach of 10 km.

Energy-Efficient Virtual Base Station Formation in Optical-Access-Enabled Cloud-RAN

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.

A Full-Duplex PON with Hybrid 64/16/4QAM OFDM Downlink and Hybrid 16/8/QPSK OFDM Uplink

In the context of next-generation optical access networks beyond 10 G, for high SE and flexible dynamic bandwidth allocation (DBA), the scheme of hybrid 64/16/4QAM-OFDM signal for downlink transmission and hybrid 16/8/QPSK-OFDM signal for uplink transmission is successfully proposed and experimentally presented in a full-duplex PON based on OFDM system. Here, for the uplink, in order to unit management of the optical line terminal (OLT) and reduce cost, the optical source functioned as the optical subcarrier at optical network units (ONUs) is from OLT in the central station. Moreover, there is an external cavity laser (ECL) with center frequency of 193.2 THz not only employed as optical modulated signal but also acted as LO signal. Our simulation results show that bit error ratio (BER) under hardware detection forward error correction has been successfully gained after 20 km of SSMF transmission. It is observed that the receiver sensitivity of multilevel PSK (M-PSK) is obviously larger than that of the M-QAM in this measurement scheme.

Performance evaluation of asynchronous multi‐carrier code division multiple access for next‐generation long‐reach fibre optic access networks

In this study, the authors evaluate the performance of asynchronous optical multi-carrier code division multiple access (MC-CDMA) for intensity modulated/direct detection systems to be used in next-generation optical access networks. The proposed system employs Gold sequence in frequency-domain to provide asynchronous resource sharing. In long-reach passive optical networks, fibre impairments degradation to the performance of ordinary optical CDMA can be avoided by frequency-domain digital compensation methods in the proposed MC-CDMA. In comparison with orthogonal frequency division multiple access, peak-to-average power ratio in the proposed MC-CDMA is reduced and asynchronous resource sharing is achieved. The performance of the proposed optical MC-CDMA system is analytically evaluated by driving closed-form equations for signal-to-interference plus noise ratio and bit error rate (BER) performances. Furthermore, the simulation results are provided in terms of BER against signal-to-noise ratio in one case and the number of users in another, conditioned on the modulation levels. Finally, the analytical formulation of BER is verified with the help of simulation results.

Demonstration of hybrid orbital angular momentum multiplexing and time-division multiplexing passive optical network.

Mode-division multiplexing passive optical network (MDM-PON) is a promising scheme for next-generation access networks to further increase fiber transmission capacity. In this paper, we demonstrate the proof-of-concept experiment of hybrid mode-division multiplexing (MDM) and time-division multiplexing (TDM) PON architecture by exploiting orbital angular momentum (OAM) modes. Bidirectional transmissions with 2.5-Gbaud 4-level pulse amplitude modulation (PAM-4) downstream and 2-Gbaud on-off keying (OOK) upstream are demonstrated in the experiment. The observed optical signal-to-noise ratio (OSNR) penalties for downstream and upstream transmissions at a bit-error rate (BER) of 2 × 10(-3) are less than 2.0 dB and 3.0 dB, respectively.

Optimal location planning of relay-based next generation wireless access networks

Use of relays is considered one of the most effective ways for capacity enhancement and coverage extension in next-generation broadband wireless access networks (BWAN). The paper investigates the location planning problem in BWANs, aiming at an optimal deployment of relay stations and base stations to enhance capacity. We develop formulations in mixed integer linear programming to effectively capture various planning policies that govern relay and base station placement. Case studies are conducted to verify the effectiveness of the proposed formulations. We show that the same traffic demand can be satisfied with up to 73 % fewer relay stations with a slight (6 %) decrease in the overall network capacity, compared with our benchmark. Based on the developed formulations, we introduce a maximin objective function to properly distribute excess bandwidth to all subscriber stations rather than assigning it to a single one, which surprisingly leads to a significant gain in the rate allocated to each subscriber station.

Polarization multiplexing of two MIMO RoF signals and one baseband signal over a single wavelength

Next-generation (NG) access networks require simultaneous provision of wired and wireless services and high data rates to meet the large demands of mobility and multiple services. In this paper, we propose a novel spectral efficient radio over fiber (RoF) scheme to simultaneously provide two spatially multiplexed multiple input multiple output (MIMO) wireless signals with a baseband (BB) wired signal in one wavelength using a centralized light source. The proposed scheme can be applicable to wavelength division multiplexed passive optical networks (WDM-PONs). The BB signal is modulated at a low extinction ratio (ER). The modulated light is re-used to modulate two MIMO signals that have the same carrier frequency that is combined optically using polarization-division-multiplexing (PDM). The data rate for each MIMO stream was 1.25Gb/s, and the data rate was 2.5Gb/s for the BB signal. Error free performance with a bit error rate (BER) of 10−9 was achieved for all three signals after 20km and 60km through single mode fiber (SMF) for 16-QAM and 4-QAM for the MIMO signals, respectively.

Fixed Access Network Sharing

Fixed broadband network deployments are moving inexorably to the use of Next Generation Access (NGA) technologies and architectures. These NGA deployments involve building fiber infrastructure increasingly closer to the customer in order to increase the proportion of fiber on the customer’s access connection (Fibre-To-The-Home/Building/Door/Cabinet… i.e. FTTx). This increases the speed of services that can be sold and will be increasingly required to meet the demands of new generations of video services as we evolve from HDTV to “Ultra-HD TV” with 4k and 8k lines of video resolution. However, building fiber access networks is a costly endeavor. It requires significant capital in order to cover any significant geographic coverage. Hence many companies are forming partnerships and joint-ventures in order to share the NGA network construction costs. One form of such a partnership involves two companies agreeing to each build to cover a certain geographic area and then “cross-selling” NGA products to each other in order to access customers within their partner’s footprint (NGA coverage area). This is tantamount to a bi-lateral wholesale partnership.The concept of Fixed Access Network Sharing (FANS) is to address the possibility of sharing infrastructure with a high degree of flexibility for all network operators involved. By providing greater configuration control over the NGA network infrastructure, the service provider has a greater ability to define the network and hence to define their product capabilities at the active layer. This gives the service provider partners greater product development autonomy plus the ability to differentiate from each other at the active network layer.

Upstream WDM-PON transmission scheme based on PDM-OOK modulation and digital coherent detection with dual-modulus algorithm.

Wavelength-division-multiplexing passive optical network (WDM-PON) is a promising architecture for next-generation access networks because of its large bandwidth, protocol transparency and scalability. In this paper, we propose a cost-effective, high-speed upstream WDM-PON scheme adopting polarization division multiplexed (PDM) on-off keying (OOK) modulation at the optical network unit (ONU) and digital coherent/self-coherent detection with a novel blind dual-modulus equalization algorithm at the optical line terminal (OLT). As such, the upstream capacity can be directly enhanced at low ONU expenditure, and receiver sensitivity as well as power budget can be also improved. Enabled by the scheme, 40-Gb/s upstream transmission in 80-km WDM-PON is experimentally demonstrated.

Virtualized security at the network edge: a user-centric approach

The current device-centric protection model against security threats has serious limitations. On one hand, the proliferation of user terminals such as smartphones, tablets, notebooks, smart TVs, game consoles, and desktop computers makes it extremely difficult to achieve the same level of protection regardless of the device used. On the other hand, when various users share devices (e.g., parents and kids using the same devices at home), the setup of distinct security profiles, policies, and protection rules for the different users of a terminal is far from trivial. In light of this, this article advocates for a paradigm shift in user protection. In our model, protection is decoupled from users' terminals, and it is provided by the access network through a trusted virtual domain. Each trusted virtual domain provides unified and homogeneous security for a single user irrespective of the terminal employed. We describe a user-centric model where nontechnically savvy users can define their own profiles and protection rules in an intuitive way. We show that our model can harness the virtualization power offered by next-generation access networks, especially from network functions virtualization in the points of presence at the edge of telecom operators. We also analyze the distinctive features of our model, and the challenges faced based on the experience gained in the development of a proof of concept.

Economic replicability tests for next-generation access networks

This paper discusses the relevant cost standard for the economic replicability test for Next-Generation Access (NGA) networks, described in the “Recommendation on consistent non-discrimination obligations and costing methodologies” adopted by the European Commission. According to the Recommendation, in order to reconcile investment and competition, wholesale prices should have nonlinear characteristics and only partly vary by the number of accesses. It demonstrates that a cost standard for the economic replicability test, which implies fully fixed and variable cost recovery for the access seeker, including the total wholesale price, would be incompatible with the economics of NGA networks and that such a test would deter NGA investment. Therefore, the cost standard should include only the variable part of the wholesale price. However, this paper underlines that during a transition phase, until competitors have secured access to NGA infrastructure, a second temporary test called the “competition migration test” should be added to ensure incumbent NGA retail prices do not foreclose efficient copper-based entrants. The two proposed tests surpass the limits of the “ladder of investment” theory by including the “business migration effect” developed by Bourreau, Cambini, and Dogan (2012).

Analytical Analysis of In-Band Crosstalk, Out-of-Band Crosstalk and GVD-Based Power Penalties in DWDM and TDM/DWDM-PONS

In addition to the ever-increasing demand for broader bandwidth per user, which results from the continuous development of new bandwidth-hungry services and applications, the consequent upgrade from the currently deployed Time-Division Multiplexing Passive Optical Networks (TDM-PONs) to Next-Generation Optical Access Networks (NG-OANs) has become inevitable. Different architectures for creating a NG-OAN have been proposed in the literature. Among those architectures, the DWDM and TDM/DWDM-Based OANs are very promising candidates. They were mainly proposed to exploit the large wavelength counts available in the fibre (its virtual unlimited bandwidth) to achieve a significant increase in the system capacity. Moreover, they allow coexistence in an open access environment among different network operators. In this study, we first analyze the impact of in-band crosstalk, out-of-band crosstalk to evaluate the performance of the Arrayed Waveguide Grating (AWG). The reason to focus on the AWG is due to this optical device is used almost in all DWDM and TDM/WDM-PONs. We then turn our attention to analyze the impact of group velocity dispersion GVD to estimate the maximum allowable bit rate for optical transmission without the need for using a Dispersion Management Technique (DMT) and/or a Forward Error Correction Technique (FECT). The analysis was performed using Matlab software (The Math works, Inc., Natick, MA, USA) and confirms that the in-band crosstalk has a stronger effect than the out-of-band crosstalk because its noise floor is reached at a lower crosstalk noise and with fewer crosstalk components. The in-band crosstalk noise should be kept below -37 dB and -34 dB to maintain a power penalty of less than 1 dB if 15 and 7 in-band crosstalk components are considered, respectively. The out-of-band crosstalk noise should be kept below -20.3 dB and -17.18 dB to maintain a power penalty of less than 1 dB if 240 and 56 out-of-band crosstalk components are considered, respectively. It was observed that the GVD noise floor is reached at a shorter fiber length as the bit rate increases and it was confirmed that a significant improvement in which the GVD noise floor is reached at longer fiber can be achieved if an externally modulated, small spectral-width source is used when a bit rate of 622 Mbps, 1 Gps, or 2.5 Gbps is used. However, a dispersion management technique becomes necessary if the bit rate increases to 10 Gbps or more.

New RoF-PON architecture using polarization multiplexed wireless MIMO signals for NG-PON

Next-generation access networks require provision of wireless services and high data rate to meet the huge demands for mobility and multiple services. Moreover, reusing the currently deployed optical distribution networks (ODNs) is highly beneficial and cost effective for providing the new high data rate wireless demands. In this paper, bidirectional radio over fiber passive optical network (RoF-PON) capable of handling multiple-input–multiple-output (MIMO) streams at low cost, high spectral efficiency and backward compatibility with currently deployed PON, is proposed. To the best of our knowledge, all the existing RoF MIMO solutions have not considered compatibility with currently deployed ODNs. Eight laser diodes (LDs) at the central office (CO) are enough for the whole system, instead of having LD or optical transmitter at each remote antenna unit (RAU), which makes a colorless and cost-effective RAU. Twenty four wavelengths are generated using optical comb technique. Each two 16-QAM MIMO signals that have the same carrier frequency in the downstream (DS) transmission are optically combined using polarization-division-multiplexing (PDM), where each two upstream (US) MIMO signals are time division multiplexed. The PDM configuration doubles spectral efficiency with a power penalty of only 1.5dB. The proposed architecture is a bidirectional asymmetric RoF-PON with total 40/10Gb/s for DS/US transmission. Even after transmission over 20km SMF and splitting ratio of 32, acceptable transmission performance and widely separated constellation diagrams for the 16-QAM signals are achieved, with bit error rate (BER) of 10−6 for DS signals and 10−3 for the US signals which can be reduced down to 10−6 by using forward error correction (FEC).

Ultra-Dense, Single-Wavelength DFT-Spread OFDMA PON With Laserless 1.2 Gb/s ONU Ready for Silicon Photonics Integration

We introduce an ultra-dense network architecture designed for silicon photonics at the optical network unit (ONU). This network relies on only 3.333 GSa/s and 417 MSa/s converters at the OLT and ONU, respectively, and offers up to 12 Gbit/s of symmetric traffic in a single 12.5-GHz optical channel. Multiple access and lowest processing speeds at the ONU are enabled by choosing 10 DFT-spread OFDM subbands. We demonstrate this FDMA network architecture in a proof-of-principle experiment with up to eight 300-MBd 16QAM subbands offering a bidirectional data rate of 9.6 Gb/s. Real-time signal processing is realized for downstream transmission. Finally, we shortly address future improvements of this network architecture by employing integrated silicon photonics and analog signal processing to enable fine FDM for next-generation access networks.

A unified framework for open access regulation of telecommunications infrastructure: Review of the economic literature and policy guidelines

The concept of open access (OA) plays a central role in the ongoing academic and political debate on the appropriate regulatory framework for next-generation access networks in Europe. However, clear policy conclusions on the effect of OA regulation were usually precluded by a fundamental lack in common understanding what actually defines an OA policy and along which dimensions of OA regulation can be structured. This paper attempts to reconcile these diverse views by offering a definition and a conceptual framework by which OA endeavors can be identified and uniquely classified. The framework encompasses, among others, mandated OA regulation of vertically integrated firms, public-sector participation, co-investments, and OA in the context of vertical separation. Along this framework, the extant economic literature is surveyed with regard to aspects of competition and social welfare, investment and innovation, as well as practical and legal issues. Based on these insights, a policy guideline is developed that shall assist policy makers in identifying the appropriate OA scenario for the regulation of telecommunications infrastructure.

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.

Fiber-wireless (FiWi) access network: Performance evaluation and scalability analysis of the physical layer

The fiber-wireless (FiWi) access network is a prestigious architecture for next generation (NG) access network. NG access networks are proposed to provide high data rate, broadband multiple services, scalable bandwidth, and flexible communication for manifold wireless end-users (WEUs). In this paper, the FiWi access network is designed based on a wavelengths division multiplexing/time division multiplexing passive optical network (WDM/TDM PON) at the optical backhaul with data rate of 2.5Gb/s and wireless fidelity-worldwide interoperability for microwave access (WiFi–WiMAX) technologies at the wireless front-end along a 50m–5km wireless links with data rate of 54–30Mb/s, respectively. The performance of the optical backhaul and the wireless front-end, in the proposed FiWi access network, has been evaluated in terms of bit error rate (BER), error vector magnitude (EVM), and signal-to-noise ratio (SNR) of the physical (PHY) layer. The scalability of the optical backhaul based on maximum split ratio of 1/32 for each wavelength channel and a fiber length of 24km from the central office (CO) to the access point (AP) is analyzed with bit error rate (BER) of 10−9.

Unbundling in Current Broadband and Next-Generation Ultra-Broadband Access Networks

This article overviews the methods that are currently under investigation for implementing multi-operator open-access/shared-access techniques in next-generation access ultra-broadband architectures, starting from the traditional “unbundling-of-the-local-loop” techniques implemented in legacy twisted-pair digital subscriber line access networks. A straightforward replication of these copper-based unbundling-of-the-local-loop techniques is usually not feasible on next-generation access networks, including fiber-to-the-home point-to-multipoint passive optical networks. To investigate this issue, the article first gives a concise description of traditional copper-based unbundling-of-the-local-loop solutions, then focalizes on both next-generation access hybrid fiber–copper digital subscriber line fiber-to-the-cabinet scenarios and on fiber to the home by accounting for the mix of regulatory and technological reasons driving the next-generation access migration path, focusing mostly on the European situation.