Flexible TDMA/WDMA passive optical network: Energy efficient next-generation optical access solution

Access networks must further advance to address the intensification of the requirements of growing speeds and the usage of Internet applications, and time and wavelength division multiple access (TDMA/WDMA) based passive optical networks (TWDM-PONs) have been widely considered as one of the evolutionary steps of next-generation optical access (NGOA) networks. TWDM-PON combines the flexibility of TDMA with an increased capacity offered by the use of a WDM layer. Moreover, it offers interesting and challenging avenues to minimize energy consumption: especially, with current access networks consuming about 80% of the energy consumed in the Internet. Along with other efforts, reducing energy consumption of central offices is conspicuous as it directly minimizes the operational expenditures of network providers. In this paper, we explore the new paradigms to conserve energy at the central offices in TWDM-PONs. By extensive simulations, we evaluate the possible energy savings in the various flavors of TWDM-PON. Based on the findings, we propose a new architectural flavor of TWDM-PON and benchmark the architecture for cost, power consumption and reach. We also propose a novel energy saving scheme for the proposed architecture and evaluate the impact of the proposed algorithm on energy savings by extensive simulations.     

SUCCESS: a next-generation hybrid WDM/TDM optical access network architecture

In this paper, the authors propose a next-generation hybrid WDM/TDM optical access network architecture called Stanford University aCCESS or SUCCESS. This architecture provides practical migration steps from current-generation time-division multiplexing (TDM)-passive optical network (PONs) to future WDM optical access networks. The architecture is backward compatible for users on existing TDM-PONs, while simultaneously capable of providing upgraded high-bandwidth services to new users on DWDM-PONs through advanced WDM techniques. The SUCCESS architecture is based on a collector ring and several distribution stars connecting the CO and the users. A semipassive configuration of the Remote Nodes (RNs) enables protection and restoration, making the network resilient to power failures. A novel design of the OLT and DWDM-PON ONUs minimizes the system cost considerably: 1) tunable lasers and receivers at the OLT are shared by all ONUs on the network to reduce the transceiver count and 2) the fast tunable lasers not only generate downstream data traffic but also provide DWDM-PON ONUs with optical CW bursts for their upstream data transmission. Results from an experimental system testbed support the feasibility of the proposed SUCCESS architecture. Also, simulation results of the first SUCCESS DWDM-PON MAC protocol verify that it can efficiently provide bidirectional transmission between the OLT and ONUs over multiple wavelengths with a small number of tunable transmitters and receivers.     

Evolution toward the next-generation core optical network

With high-bandwidth and on-demand applications continuing to emerge, next-generation core optical networks will require significant improvements in capacity, configurability, and resiliency. These advancements need to be achieved with architectures and technologies that are scalable with respect to network cost, size, and power requirements. To investigate the limitations of extending today's solutions to meet these goals, a North American backbone network with a tenfold growth in traffic is modeled. The results of this paper illuminate at least three areas that will potentially require innovative solutions, namely 1) transmission modulation formats, 2) switching granularity, and 3) edge traffic grooming. In addition to probing issues related to increased capacity, configurability is also examined, mainly in the context of switching architectures. Advanced network protection is discussed as well, at a high level. A central theme is how to harness the trend of optics scaling better than electronics. Throughout this paper, potential advancements in architecture and technology are enumerated to serve as a foundation for the research needed to attain the goals of next-generation core networks.     

A WDM-based optical access network for wide-area gigabit access services

This article proposes and demonstrates a WDM-based access network that directly connects end users over a wide area to the center node and provides guaranteed full-duplex Gigabit Ethernet access services to each of over 100 users. The center node employs an optical carrier supply module that generates not only the optical carriers for the downstream signals but also those for the upstream signals. The latter are supplied to optical network units (ONUs) at users' homes/buildings via the network. Since the ONUs simply modulate the optical carriers supplied from the center node via the network, they are wavelength-independent.     

光接入网技术研究

文章介绍了宽带光纤接入网系统和其中的几种主流接入方式，并详细比较了几种接入技术在应用上的优缺点，最后给出了建议和展望。     

A bandwidth scalable OFDM passive optical network for future access network

In order to reduce the cost for delivering the ever increasing broadband services, network providers need to simplify their network architectures and have a better control of the bandwidth. In this article, we propose a simple and cost-effective bandwidth scalable passive optical network (PON) based on orthogonal frequency division multiplexing (BSOFDM-PON). We report performance analysis in terms of the signal-to-noise ratio (SNR), bit-error-rate (BER), and error vector magnitude (EVM) of a PON system accommodating 32 optical network units (ONUs). Our simulations have successfully demonstrated that throughputs of 35.5 and 53.2 Gbps can be achieved using 16 and 64 QAM, respectively, within a total distance ranging from 20 to 30 km. It gives throughputs of 1.10 and 1.66 Gbps per ONU.     

SUCCESS-HPON: A next-generation optical access architecture for smooth migration from TDM-PON to WDM-PON

Optical access networks are considered to be a definite solution to the problem of upgrading current congested access networks to ones capable of delivering future broadband integrated services. However, the high deployment and maintenance cost of traditional point-to-point architectures is a major economic barrier. Current TDM-PON architectures are economically feasible, but bandwidth-limited. In this article we first discuss the possible role of WDM in access networks and investigate the associated issues. We then present the Stanford University Access Hybrid WDM/TDM Passive Optical Network (SUCCESS-HPON), a next-generation hybrid WDM/TDM optical access architecture that focuses on providing a smooth migration path from current TDM-PONs to future WDM-PONs. The first testbed for this architecture is described, along with the experimental results obtained, including feasibility of bidirectional transmission on the same wavelength on the same fiber for access networks and ONU modulation of upstream data on continuous waves provided by the OLT, eliminating the need for tunable components at the ONUs. The development of a second testbed and the issues it will address, including the implementability of the SUCCESS-HPON MAC protocol and scheduling algorithms, are also described.     

A novel self-surviving architecture for next-generation OFDM passive optical network supporting colorless ONUs

In this paper, we propose a novel self-surviving architecture for next-generation orthogonal frequency division multiplexing (OFDM) passive optical network (PON) supporting colorless optical network units. The proposed scheme can protect distribution and feeder fiber simultaneously. Two different frequency bands are used in this proposed system for paratactic OFDM-PON. The disrupt signals can be restored via the fiber links of the neighboring OFDM-PON without special protecting fibers. We analytically and experimentally study the receiver sensitivity to downstream 10 Gb/s OFDM signals and upstream 2.5 Gb/s NRZ signals. The proposed architecture is designed mainly for next-generation PON systems.     

ATM access through a passive optical network

A system is described that transports asynchronous transfer mode (ATM) cells through a passive optical local network. It distributes a 155.52 Mbit/s ATM stream to 64 customer ends, synchronising return cells to interleave at the exchange end. A variant to the Orwell protocol is used for bandwidth control.<>     

Smart OLT equipment of optical access network

A distributed architecture of optical line terminal(OLT) equipment is proposed for response to national bandwidth acceleration requirements and for future smooth evolution to 50G passive optical network(PON). This architecture moves the forwarding function of the control board to each service board to improve the switching capacity and performance of the system. The traditional control boards of centralized architecture OLT equipment have exchange and traffic processing function, and every servi...     

FM subcarrier fiber optical transmission system design and itsapplication in next-generation wireless access

This paper presents a design method of optical frequency modulation (FM) subcarrier (with super carrier) transmission modem. The nonideal link characteristics, including laser chirping, fiber dispersion, voltage controlled oscillator (VCO) phase noise, relative intensity noise (RIN), and equivalent network model of laser diode of such a system that may bring about signal distortion are discussed first. We then propose a hierarchical methods to establish the system equivalent model. Finally this FM modem is applied to a GSM wireless system, in which multichannel signals are transmitted over fiber between radio port and basestation, and system performance is appraised by its dynamic range. It is found that optical FM subcarrier (with super carrier) transmission technique can improve the system dynamic range, compared with the intensity modulated direct detection (IMDD) method, and this is a economical and efficient method     

基于并行排队策略的天基光网络接入选择算法

针对卫星光网络接入选择算法不够灵活高效的问 题,研究了天基光网络中基于并行排队策略(PQS,parallel queuing strategy)的 动态在线式接入选择算法。分析接入选择问题的约束条件并建立数学模型,在 排队模型的基础上增加动 态优先级策略dps(dynamic priority strategy),实现不同优先级任务的区分服务;通过引 入时间敏感因子实现对不同优先级任务等待 时延区分度的调节,避免低优先级任务一直被高优先级任务抢占的问题;通过增加PQS使调 度 方案得到全局优化,缩短任务等待时延。仿真结果表明,本文算法将等待时延降低 30%左右,有效提升了接入调度的灵活和高效性。     

高生存性光接入网结构分析

从网络结构方面对光接入网生存性进行了研究,在对各种网络接入结构生存性初期分析的基础上,利用共享链路组(SRLG)的概念定量分析了各种接入拓扑结构的网络生存性,表明了星型环接入网结构在网络生存性方面较现行各种网络结构的优越性;提出了改进的网络生存率计算算法,利用分层计算和等价归并结合的方式,减少了计算量,提高了计算效率,尤其在总故障数目多的情况下可以大大减少计算时间,快速计算网络生存率.     

波分复用无源光接人网

介绍了波分复用无源光接入网(WDMPON)的系统结构,对下行传输和上行传输中的关键技术进行了探讨,分析比较了PSPON和WDMPON的一般特性及其优缺点.     

MPCP based active optical access network with PLZT high-speed optical switch

An active optical access network architecture with our newly developed PLZT ((Pb,La)(Zr,Ti)O₃) high-speed optical switch is introduced, with a view to realizing the next-generation high capacity scalable access network. This system is developed based on the latest IEEE standard of PON (10G-EPON; IEEE802.3av) in consideration of the coordination with future high capacity PON. PLZT high-speed optical switches are able to switch an optical signal at nano-second speed (<5-10 ns). Generally, the merits of using optical switches are increasing the number of subscribers and transmission distance easily, preventing malicious ONUs from interfacing with the communication between OLT and the other ONUs, realizing fast fiber and OLT protection/restoration and providing various services by controlling optical switches dynamically. This paper focuses on two key technologies; a PLZT optical switch and a new discovery process for active optical access network based on MPCP defined at IEEE802.3. A major challenge in designing active optical access network is supporting the discovery process of MPCP because it does not offer broadcast transmission unlike the regular PON. We propose here a new discovery process; it has been tested successfully in an implementation of our proposed system.     

A framework design for the next-generation radio access system

Extensive use of the Internet and huge demands for multimedia services via portable devices require the development of packet-based radio access systems with high transmission efficiency. Advanced radio transmission technologies have recently been proposed to achieve this challenging task. However, few researches have been reported on the design of an integrated system that can efficiently exploit the advantages of these transmission technologies. This paper considers the design of a packet-based cellular system for next-generation radio access. We propose a novel system framework that can incorporate various advanced transmission technologies such as link adaptation, opportunistic packet scheduling, channel coding, and multiantenna techniques. For efficient use of these technologies together, we first investigate the interoperability between these technologies by proposing a so-called cause and effect analysis. Based on this investigation, we design a differentiated-segments-based orthogonal frequency-division multiplexing system, called DiffSeg, to accommodate heterogeneous operating conditions in a seamless manner. Simulation results show that the proposed DiffSeg system can provide a nearly optimum performance with flexible configuration in a wide range of wireless channel conditions.     

Optical power budget enhancement in next-generation DDO-OFDM-based optical access networks using square root module

A passive optical network based on orthogonal frequency division multiplexing (OFDM-PON) gives improved performance for high speed optical access network due to its greater resistance to fiber dispersion and higher bandwidth efficiency. In optical fiber communication, chromatic dispersion (CD) is a linear distortion in fiber, but it is converted into nonlinear distortion due to square-law characteristic of photo diode detector at the receiver side resulting in degradation of performance. To compensate for this nonlinear distortion, we proposed to use a linearized receiver circuit with square root module (SRM) device which can improve the performance of system in terms of CD tolerance. In this paper, we have analytically analyzed the performance of OFDM-PON system with and without SRM device for direct-detection optical OFDM-PON (DDO-OFDM-PON) system. At BER of \(10^{-3}\), which is the limit of forward error correction, there is 11.1 and 13.5 dB improvement in optical budget with SRM for downstream and upstream direction, respectively, as compared to conventional DDO-OFDM-PON system.     

A comprehensive study on next-generation optical grooming switches

This paper investigates the characteristics and performance of different optical grooming switches, i.e., optical cross-connects (OXCs) capable of traffic grooming, under a dynamic traffic environment. We present four optical grooming-OXC architectures, namely, single-hop grooming OXC, multihop partial-grooming OXC, multihop full-grooming OXC, and light-tree-based source-node grooming OXC. After exploring their grooming capabilities, we propose three grooming schemes and two corresponding algorithms, grooming using auxiliary graph and grooming using light-tree. Through the algorithms, we evaluate the performance of different optical grooming OXCs in a dynamic traffic environment under different connection bandwidth-granularity distributions. Our investigation uncovers the following results: (1) the multihop full-grooming OXC can achieve the best network performance, but it may encounter cost and scalability constraints; (2) by using significantly less low-granularity electronic processing and intelligent traffic-grooming algorithms, the multihop partial-grooming OXC shows reasonable network performance and, hence, can be viewed as a cost-effective alternative when a network node does not require full-grooming capability; (3) the single-hop grooming OXC may cause a large amount of capacity waste and lead to poor network performance; and (4) through its multicast capability, a light-tree-based source-node grooming OXC can significantly out-perform the performance of a single-hop grooming OXC in terms of network throughput and network resource efficiency. From our results, we also observe that the connection bandwidth-granularity distribution has a large impact on network throughput and network resource efficiency and, therefore, should be carefully considered for network design and traffic provisioning.     

浅谈光接入网技术及其应用

简要描述了接入网的基本概念及其在现代通信中的重要性。以光接入网为例,着重介绍了当前热门的几种光接入网技术,包括内置SDH接入,光用户环路、混合光纤/同轴接入、ATM技术为基础的无源光网络等,阐明了光接入网的发展前景。