Future Access Networks Research Articles

Energy efficient flexible hybrid wavelength division multiplexing-time division multiplexing passive optical network with pay as you grow deployment

A flexible hybrid wavelength division multiplexing-time division multiplexing passive optical network architecture that allows dual rate signals to be sent at 1 and 10 Gbps to each optical networking unit depending upon the traffic load is proposed. The proposed design allows dynamic wavelength allocation with pay-as-you-grow deployment capability. This architecture is capable of providing up to 40 Gbps of equal data rates to all optical distribution networks (ODNs) and up to 70 Gbps of a asymmetrical data rate to the specific ODN. The proposed design handles broadcasting capability with simultaneous point-to-point transmission, which further reduces energy consumption. In this architecture, each module sends a wavelength to each ODN, thus making the architecture fully flexible; this flexibility allows network providers to use only required OLT components and switch off others. The design is also reliable to any module or TRx failure and provides services without any service disruption. Dynamic wavelength allocation and pay-as-you-grow deployment support network extensibility and bandwidth scalability to handle future generation access networks.

Chirp-based direct phase modulation of VCSELs for cost-effective transceivers.

A 2.5 Gb/s differential binary phase-shift keying (DPSK) transmitter based on direct phase modulation of a vertical cavity surface emitting lasers (VCSEL) using its own chirp is proposed. The VCSEL, which has a wavelength of 1539.84 nm, has been characterized both statically and dynamically. The sensitivity of a single photodiode heterodyne receiver using the proposed 2.5 Gb/s VCSEL transmitter is -39.5 dBm. Thus, this transmitter is an extremely cost-effective solution for future access networks.

Design, implementation, and evaluation of an XG-PON module for the ns-3 network simulator

10-gigabit-capable Passive Optical Network (XG-PON), one of the latest standards of optical access networks, is regarded as one of the key technologies for future Internet access networks. This paper presents the design and evaluation of our XG-PON module for the ns-3 network simulator. This module is designed and implemented with the aim to provide a standards-compliant, configurable, and extensible module that can simulate XG-PON with reasonable speed and support a wide range of research topics. These include analyzing and improving the performance of XG-PON, studying the interactions between XG-PON and the upper-layer protocols, and investigating its integration with various wireless networks. In this paper, we discuss its design principles, describe the implementation details, and present an extensive evaluation on both functionality and performance.

Mobility Scenarios into Future Wireless Access Network

The rapid growth of smart devices demands an enhanced throughput for network connection sustainability during mobility. However, traditional wireless network architecture suffers from mobility management issues. In order to resolve the traditional mobility management issues, we propose a novel architecture for future wireless access network based on software-defined network (SDN) by using the advantage of network function virtualization (NFV). In this paper, network selection approach (NSA) has been introduced for mobility management that comprises of acquiring the information of the underlying networking devices through the OpenFlow controller, percepts the current network behavior and later the selection of an appropriate action or network. Furthermore, mobility-related scenarios and use cases to analyze the implementation aspects of the proposed architecture are provided. The simulation results confirm that the proposed scenarios have obtained a seamless mobility with enhanced throughput at minimum packet loss as compared to the existing IEEE 802.11 wireless network.

Performance Analysis of Survivable Hybrid Wireless Optical Broadband Access Networks

The ever increasing needs in internet connectivity leads to the demands for reliable high capacity networks. The future access networks will aimed to satisfy the end user needs through its large bandwidth, higher mobility, best QoS and wide area coverage. Wireless Optical Broadband Access Network (WOBAN) is a compromised solution which has flexible Wireless mesh network as its front end and robust bandwidth efficient Optical network as its back end. If a network element is failed in front end then the traffic will be rerouted in another path and provides reliable unthreaded connectivity. In case of single segment failure all optical network units (ONU)will be disconnected from the Optical line terminal (OLT) results huge data losses. In existing system optimizing backup ONU deployment scheme (OBOF) supports the survivability of WOBAN. The operational efficiency of WOBAN is improved by Automated Failure Deduction and Rerouting Algorithm (AFDRR) during single segment failure based on least congested routes. Implementations of AFDRR is performed in various wireless technologies like WiFi(802.11), WiMAX(802.16) and UMTS. Data packets are send from sender node to the receiver node and QoS parameters like throughput, end to end delay, packet delivery ratio,energy and path switching time are measured.

Handover Delay Estimation Method for IMS-Based Systems with Heterogeneous Access Networks

IP multimedia subsystem (IMS) is an architectural framework designed to merge the Internet and cellular networks, as such users can have access to the current and future services available over the Internet with their mobile devices anytime and virtually everywhere at affordable charges and faster rates, but heterogeneity of access networks in IMS-based systems makes handover process to be a critical issue, especially when moving from one access network to another access network with different technology, hence there is a need to devise a simple approach to estimate handover delay when moving to any access network. This paper proposes a simple method to estimate handover delay for IMS-based systems with heterogeneous access networks. The proposed method can be used to estimate handover delay for current and future access networks, but for illustration purpose, in the paper two access networks were considered, i.e. UMTS and WLAN. Numerical analysis conducted in the paper has shown that handover process to UMTS access network tends to be much longer than that of WLAN access network.

Self-seeded quantum-dash laser based 5 m-128 Gb/s indoor free-space optical communication: erratum

We demonstrate an indoor 5 m free-space optical wireless coherent communication in mid L-band (1606.7 nm) by employing a tunable self-seeded InAs/InGaAlAs/InP quantum-dash (Qdash) laser as a subcarrier generator for 128 Gb/s dual-polarization quadrature phase shift keying (DP-QPSK) modulation signal. The bare Qdash laser diode displays ∼6 nm self-locked Fabry–Perot mode tunability with ∼30 dB side mode suppression ratio (SMSR) and ∼10 dBm mode power across the tuning range, thus encompassing ∼10 modes with an achievable capacity of 1.28 Tb/s (10×128 Gb/s) and potentially qualifying the source requirements for future access networks.

Multiple Channel Interference Cancellation of Digital Filter Multiple Access PONs

By making use of the digital signal processing (DSP) based software-reconfigurable digital orthogonal filtering, digital filter multiple access passive optical networks (DFMA PONs) have demonstrated great potential for offering excellent backward compatibility with existing PONs and supporting future cloud access networks. However, intensity modulation and direct detection (IMDD) DFMA PONs suffer from imperfect channel orthogonality-induced cross-channel interference. In this paper, a DFMA channel interference cancellation (DCIC) technique is, for the first time, proposed and extensively investigated, to significantly improve the downstream and upstream performance of the IMDD DFMA PONs. A comprehensive DCIC theoretical model is developed, and through fitting with experimental measurements, the developed theoretical model is rigorously verified and a set of accurate transceiver/system parameters is identified. It is shown that DCIC increases the aggregated upstream signal transmission capacity by a factor of > 2 and extends the differential optical network unit (ONU) launch power dynamic range by approximately 14 dB. Such significant performance improvements are achieved after just one iteration. Other salient DCIC advantages include ONU count-independent low DSP complexity, small latency and transparency to signal modulation format, signal bit rate, and initial system operation conditions.

Coherent Access: A Review

In this paper, we will address the benefits of the coherent detection in future optical access networks. The scarcity of the optical spectrum, the required flexibility, and constant evolution of requirements highlight the effectiveness of coherent techniques toward the future passive optical networks (PON). A set of architectures for coherent optical access networks will be presented and the key attributes of each scenario will be investigated. In addition, as a basis to decrease the cost of the local oscillator (LO) at customer side, we experimentally investigate the possibility of using a low-cost laser as LO with real-time detection of a Nyquist-shaped differential quadrature phase-shift keying (DQPSK) signal using simple 8-bit digital signal processing (DSP) on a field-programmable gate array. Moreover, we experimentally derive a set of optimized parameters and their impact on the network operation for coherent ultradense wavelength-division multiplexing (UDWDM) systems. The balance between the number of channels, power budget, and dynamic power range will be evaluated. Furthermore, we demonstrate a reconfigurable real-time receiver DSP for future flexible UDWDM-PON systems applying the DQPSK and D8PSK modulation formats. By reviewing some of the motivations for this technology, such as flexibility, spectral efficiency, as well as compatibility with software-defined networking, we show that this technology is approaching the required maturity.

Monolithic Integration on InP of a DML and a Ring Resonator for Future Access Networks

The future technology migration in access networks compels the development of key innovative transmitters operating at 10 Gb/s around 1550 nm and capable of transmitting data in extended reach passive optical networks (>60 km). A laser modulated directly appears to be a low cost and a simple solution to address these needs. However, the extinction ratio and the distance of transmission are limited by frequency chirping inherent to high bit rate modulation at 1550 nm. In this letter, we demonstrate the monolithic integration of a directly modulated lasers and a ring resonator (RR) and show the possibility to engineer the RR with specific frequency modulation efficiency. The ring is used as an optical eye reshaper, which enables the increase of the extinction ratio above 9 dB. Transmissions up to 65 km with 5.8 dBm of modulated optical power coupled into the fiber are demonstrated, proving the feasibility of our transmitter for the next generation passive optical network stage 2

Simple and reconfigured single-sideband OFDM RoF system.

We propose a simple and reconfigured dispersion-tolerant single sideband (SSB) orthogonal frequency division multiplexing (OFDM) radio over fiber (RoF) system enabled by digital signal processing (DSP), one in-phase/quadrature (I/Q) modulator and direct-detection. The generated radio frequency (RF) is based on DSP and the frequency can be flexibly adjusted, which can be employed in the future software-defined radio access network (RAN). Based on our proposed system, we have experimentally demonstrated 16-ary quadrature amplitude modulation (16QAM) 21.87-Gb/s 21-GHz and 38-GHz SSB-OFDM RoF signal generation and transmission over 80-km single-mode fiber (SMF), respectively.

Design and implementation of flexible TWDM-PON with PtP WDM overlay based on WSS for next-generation optical access networks

Aiming at the increasing demand of the diversification services and flexible bandwidth allocation of the future access networks, a flexible passive optical network (PON) scheme combining time and wavelength division multiplexing (TWDM) with point-to-point wavelength division multiplexing (PtP WDM) overlay is proposed for the next-generation optical access networks in this paper. A novel software-defined optical distribution network (ODN) structure is designed based on wavelength selective switches (WSS), which can implement wavelength and bandwidth dynamical allocations and suits for the bursty traffic. The experimental results reveal that the TWDM-PON can provide 40 Gb/s downstream and 10 Gb/s upstream data transmission, while the PtP WDM-PON can support 10 GHz point-to-point dedicated bandwidth as the overlay complement system. The wavelengths of the TWDM-PON and PtP WDM-PON are allocated dynamically based on WSS, which verifies the feasibility of the proposed structure.

A Numerical Framework for the Analysis of Handoff Delay Component in Proxy NEMO Environment

Network Mobility Basic Support Protocol (NEMO-BSP), the existing IETF standard for mobile network support, signifies an important portion for future heterogeneous wireless access networks. The reason is to provide continuous Internet connectivity during movement of Mobile Router (MR) in NEMO. This paper conducted a quantitative analysis on the handoff delay component of NEMO-BSP as well as its existing enhancements, i.e., Fast NEMO (F-NEMO) handoffs, and an Extension of F-NEMO (EF-NEMO), using the numerical framework. The mathematical scenario includes two access routers, one local home agent and up to 20 MRs that interrelate by two different wireless access networks are mainly WiFi and WiMAX. The analysis offers quantitative outcomes of the performance enhancements achieved via the proposed improvements concerning handoff delay gain, packet loss, and packet loss ratio. The numerical results assist in understanding the influence of link switching delay, mobility rate, and radius on the handoff delay gain, packet loss, and packet loss ratio. The results of this analysis will also be aided to pick an appropriate mobility management scheme for Proxy NEMO environment.

Performance study of DMT transmission for next generation passive optical network

Discrete multi-tone (DMT) based passive optical network (PON) is a subject of great interest for recent research works, due to its high spectral efficiency, high flexibility and high tolerance to the fiber chromatic dispersion. In this paper, we investigate the transmission performance of DMT transmission for next generation PON, including the optimization of modulation index and the power fading of double sideband (DSB) induced by chromatic dispersion. A new single sideband (SSB) DMT modulation based on a dual-driver Mach-Zehnder modulator (DDMZM) is also presented, which can eliminate the power fading. The simulation results show that 4×25Gb/s DSB DMT-PON combining with wavelength division multiplexing (WDM) and the single wavelength 100Gb/s SSB-DMT are both promising candidates for future access network.

Fronthaul network design for radio access network virtualization from a CAPEX/OPEX perspective

With the increase of mobile traffic demand and the need to reduce expenses to handle this demand, a novel solution, known as Cloud Radio Access Network (C-RAN), has been proposed for future radio access network. This solution involves virtualizing base stations and centralizing processing resources into a baseband processing unit (BBU) pool. C-RAN also helps fully deploying cooperative schemes used in LTE and LTE-Advanced. In this paper, we analyze C-RAN cost structure. Then, unlike previous works, we mathematically formulate cell-BBU pool assignment, taking into account fronthaul network expenditure. Two optimization models are proposed for two different architectures. We then use these formulations to develop solutions to our problem, which optimize the C-RAN costs subject to demand constraints. Through extensive experiments, cost efficiency of C-RAN architecture is discussed and the effect of different parameters is analyzed. We also derive conditions where utilizing C-RAN architecture can help cost savings.

Investigation of broadband digital predistortion for broadband radio over fiber transmission systems

In future broadband cloud radio access networks (C-RAN), front-haul transmission systems play a significant role in performance and cost of C-RAN. Broadband and high linearity radio over fiber (RoF) transmission systems are considered a promising solution for the front-haul. Digital linearization is one possible solution for RoF front-haul. In this paper, we investigate RF domain digital predistortion (DPD) linearization for broadband RoF front-haul. The implemented DPD is first investigated in 2.4GHz WiFi over fiber transmission systems at 36Mb/s, and more than 8-dB and 5.6-dB improvements of error vector magnitude (EVM) are achieved in back to back (BTB) and after 10km single mode fiber (SMF) transmission. Further, both WiFi and ultra wide band (UWB) wireless signals are transmitted together, in which the DPD has linearization bandwidth of 2.4GHz. It is shown that the implemented DPD leads to EVM improvements of 4.5-dB (BTB) and 3.1-dB (10km SMF) for the WiFi signal, and 4.6-dB (BTB) and 4-dB (10km SMF) for the broadband UWB signal.

Joint Scheduling and Beamforming Coordination in Cloud Radio Access Networks With QoS Guarantees

The cloud radio access network (C-RAN) is a promising architecture for future radio access networks (RANs) due to its advantages in cost efficiency, flexibility, and utilization efficiency. To fully reap these benefits, this paper focuses on joint optimization of user grouping, virtual base station (VBS) clustering, and transmit beamforming in C-RAN downlink networks for maximizing the system utility, subject to the diverse quality-of-service (QoS) requirements of users and the power constraints of distributed remote radio heads (RRHs). To tackle the high computational complexity in solving the nonconvex combinatorial optimization problem, a two-stage solution is proposed. Specifically, a dynamic user-centric scheduling algorithm is developed to form user groups and cluster RRHs into VBSs by exploiting the nonuniform distribution of users. Then, an iterative transmit beamformer optimization algorithm is devised to coordinate the transmit beamforming among the VBSs to mitigate the intracell and intercell interference, hence further enhancing the overall system utility. Evaluation results demonstrate that the proposed algorithm achieves significant performance gain over various reference algorithms in terms of system utility, system throughput, and energy efficiency.

Power Depletion and Crosstalk Induced by Stimulated Raman Scattering in WDM Fronthaul

The power depletion and crosstalk induced by stimulated Raman scattering in wavelength division multiplexing-based mobile fronthaul are investigated by simulation and experiment for the first time to the best of our knowledge. The simulation results show that the maximum power depletion is 1.7 dB in the case of 40-km fiber transmission with four fronthaul wavelength pairs. However, for the future hybrid fiber and radio access network, where the whole $\text{C}\,+\,\text{L}$ wavebands may be employed, the power depletion will be increased to 11 dB. Meanwhile, in order to verify the simulation, we conducted an experiment with four fronthaul wavelength pairs. The measured power depletion is consistent with the simulation results. As for the Raman crosstalk, the experimental results indicate that it varies from the fiber lengths and has the low-pass characteristic. These results provide a valuable reference for the wavelength allocation in the future hybrid fiber and radio access network.

Time division multiplexed orbital angular momentum access system

We propose and experimentally demonstrate time division multiplexed orbital angular momentum (OAM) access system to increase transmission capacity and spectral efficiency. In this system, data carried on different time tributaries share the same OAM mode. Multiple time division multiplexed OAM modes are multiplexed to realize two-dimensional (time dimension and OAM dimension) multiplexing. Therefore, the capacity and spectral efficiency of the access system will increase. The orthogonality between optical time division multiplexing (OTDM) and OAM techniques is also verified in our experiment. In a proof-of-concept experiment, 2×5-Gbps return-to-zero signal over OAM mode +4 is transmitted and investigated. The bit error ratio performance after transmission in this system can be smaller than 1×10−9. Results show that the proposed time division multiplexed OAM access system is suitable for future broadband access network.

N∶1 Protection Design for Minimizing OLTs in Resilient Dual-Homed Long-Reach Passive Optical Network

Long-reach passive optical networks (LR-PONs) prove to be a suitable candidate for future broadband access networks. The longer reach of the feeder fiber in a LR-PON enables us to consolidate a large number of end users. The longer reach also eliminates a degree of electronic processing by eliminating the metro network and connecting the local exchanges (or the central offices) directly to a consolidated metro/core (MC) node. However, longer reach makes the feeder fiber more vulnerable to failures, and therefore, for resiliency purposes, a dual-homed architecture is proposed. For the usual case of 1 + 1 protection, the dual-homed secondary MC node would contain duplicate resources that would take over in the event of the failure of any of the individual working optical line terminals (OLTs) or the entire primary MC node in the case of a catastrophe. In this work we propose an Nl1 protection mechanism to reduce backup OLTs in a resilient dual-homed LR-PON deployment. We model the problem as an integer linear program and solve it for Irish and UK network deployments. Our results show that the percentage of backup OLTs can be reduced by 6 times for Ireland and by 4 times for the UK compared to a 1 + 1 protection deployment scenario.