An input traffic allocation strategy and an efficient transmission technique for collisions-free WDM ring MANs

This paper presents a wavelength division multiplexing multi-ring architecture with a separate control wavelength for metropolitan area networks. We study the critical problem of low fiber bandwidth utilization that many access ring protocols introduce, especially at high load conditions. In our study this problem is effectively faced by: (1) applying an efficient slotted access algorithm to avoid both data wavelengths and receiver collisions, (2) introducing a number of buffers at each node to effectively allocate the incoming traffic into them, and (3) applying an efficient algorithm for buffer selection for transmission that combines the priority criteria of packet age and receiver collisions avoidance. In this way, we obtain maximum fiber bandwidth utilization. Especially, our aim is to achieve not only significant throughput enhancement, but also essential dropping probability and total delay reduction. Also, the number of transmission buffers per node is investigated in order to manage maximum throughput improvement, while considering the financial cost. Finally, a discrete-event simulation model based on Poisson statistics is developed for the performance measures evaluation.     

A new 'constant-amplitude' architecture for MQAM transmission

Constant-amplitude transmitter architectures offer high amplification efficiencies by using one or more nonlinear amplifiers. In this article, we propose one new such architecture, dubbed DbPSK, for efficient MQAM transmission. The proposed architecture decomposes the MQAM constellation into two pseudo-MPSK constellations that are independently amplified, with high efficiency nonlinear amplifiers, then combined to generate the original MQAM signal amplified. We show that the proposed architecture provides interesting performance in terms of power, efficiency and linearity for any MQAM signal transmission and we discuss its implementation aspects. This architecture can be considered as an improvement of the NLA-QAM architecture used in satellite applications.     

Fault-tolerant architecture with dynamic wavelength and bandwidth allocation scheme in WDM-EPON

This study proposes a novel cost-based fault-tolerant WDM-EPON (CFT-WDM-EPON) to provide overall protection. It only equips a backup feeder fiber to recover the system failure. Additionally, a prediction-based fair wavelength and bandwidth allocation (PFWBA) scheme is proposed to enhance the differentiated services for WDM-EPON based on dynamic wavelength allocation (DWA) and prediction-based fair excessive bandwidth reallocation (PFEBR) from our previous work. PFEBR involves an early-DBA mechanism, which improves prediction accuracy by delaying report messages of unstable traffic optical network units (ONUs), and assigns linear estimation credit to predict the arrival of traffic during waiting time. DWA can operate in coordination with an unstable degree list to allocate the available time of wavelength precisely. Simulation results show that the proposed PFWBA scheme outperforms WDM IPACT-ST and DWBA3 in terms of packet delay, jitter performance, throughput, wasted bandwidth, gain ratio of bandwidth, and packet loss.

A new architecture for transmission of MPEG-4 video on MPLS networks

Due to insufficient network bandwidth on the Internet, multimedia-oriented applications are still not popular. Traffic on the Internet often causes congestion in routers. Therefore, the Internet must overcome these challenges and bottlenecks to provide more multimedia-oriented applications. We study the transmission of MPEG-4-based video traffic in MPLS networks, and propose a better architecture, called actively reserved bandwidth architecture, for improving CR-LDP in MPLS networks. The architecture is designed to overcome the bottleneck of router in MPLS networks. This approach is beneficial to the transmission of MPEG-4-based video traffic.     

An AWG-based WDM-PON architecture employing WDM/TDMA transmission for upstream traffic with dynamic bandwidth allocation

In this article, we examine a candidate architecture for wavelength-division multiplexed passive optical networks (WDM-PONs) employing multiple stages of arrayed-waveguide gratings (AWGs). The network architecture provides efficient bandwidth utilization by using WDM for downstream transmission and by combining WDM with time-division multiple access (TDMA) for upstream transmission. In such WDM-PONs, collisions may occur among upstream data packets transmitted simultaneously from different optical networking units (ONUs) sharing the same wavelength. The proposed MAC protocol avoids such collisions using a request/permit-based multipoint control protocol, and employs a dynamic TDMA-based bandwidth allocation scheme for upstream traffic, called minimum-guaranteed maximum request first (MG-MRF), ensuring a reasonable fairness among the ONUs. The entire MAC protocol is simulated using OPNET and its performance is evaluated in terms of queuing delay and bandwidth utilization under uniform as well as non-uniform traffic distributions. The simulation results demonstrate that the proposed bandwidth allocation scheme (MG-MRF) is able to provide high bandwidth utilization with a moderately low delay in presence of non-uniform traffic demands from ONUs.     

构建可运营、可管理、可盈利的新型宽带城域网——上海网通如何实现宽带网络的盈利

电信的寒冬来临之后，国内的大小运营商熄灭了圈地的热火，将主要精力放在发展驻地用户。其中，酒店用户因其投入成本低、资金回报高、流动性大等优点，已成为运营商竞相投资的热点。上海网通凭借其敏锐的洞察力，看到了这个市场的巨大潜力，从2001年上海APEC会议开始投资酒店，到2002年，已经陆陆续续投资了近20家高档商务酒店。宽带运营管理需要有效的手段，其中最主要的是采用北京城市热点资讯有限公司的Dr.COM宽带计费运营管理系统，来帮助上海网通实现与酒营管理系统，来帮助上海网通实现与酒店的利益分成，上海网通已经从一个简单…     

OMAC: A new access control architecture for overlay multicast communications

Multicast communications concern the transfer of data among multiple users. Multicast communications can be provided at the network layer—an example is IP multicast—or at the application layer, also called overlay multicast. An important issue in multicast communications is to control how different users—senders, receivers, and delivery nodes—access the transmitted data as well as the network resources. Many researchers have proposed solutions addressing access control in IP multicast. However, little attention has been paid to overlay multicast. In this paper, we investigate the access control issues in overlay multicast and present OMAC: a new solution to address these issues. OMAC provides access control for senders, receivers, and delivery nodes in overlay multicast. The proposed architecture, which is based on symmetric key cryptosystem, centralizes the authentication process in one server whereas it distributes the authorization process among the delivery nodes. Moreover, delivery nodes are utilized as a buffer zone between end systems and the authentication server, making it less exposed to malicious end systems. To evaluate our work, we have used simulation to compare the performance of OMAC against previous solutions. Results of the simulation show that OMAC outperforms previous multicast access control schemes. Copyright © 2010 John Wiley & Sons, Ltd.     

Novel wavelength and bandwidth allocation algorithms for WDM EPON with QoS support

Ethernet passive optical networks (EPONs) have been considered as the one of the most promising candidates for next-generation access networks. However, the EPON architecture although cost effective is bandwidth limited and quality of service (QoS) support is still a major concern. In this paper, we propose a cost-efficient wavelength division multiplexing (WDM) EPON architecture. We present two wavelength and bandwidth allocation algorithms with full QoS support to fulfill all requirements of new application and services in a converged triple play network. We analyze and compare the presented models and algorithms in terms of delay, jitter, queue occupancy, throughput and overall system performance. We conduct detailed simulation experiments to study the performance and validate the effectiveness of the proposed architecture and algorithms.     

A new rate control scheme for H.263 video transmission

In some image/video applications, the variable bit rate image/video bitstream will be transmitted over a constant bit rate transmission channel, in which a channel buffer is employed. In this study, a new rate control scheme for H.263 video transmission is proposed. Three proposed techniques include: preprocessing the INTRA coded macroblock (MB) incorporated the just-noticeable-distortion (JND) concept, constructing a bit estimation model in the frequency domain (instead of the bit estimation model in the spatial domain employed in Test Model Near-term version 11 (TMN11)), and adjusting quantization parameter (QP) for each MB by a Lagrangian optimization strategy.In the proposed approach, the target number of bits for a video frame is first obtained by using a simple rate control procedure for the frame layer. The proposed JND preprocessing is applied on all the INTRA coded MBs so that the number of coded bits for a scene changed frame will decrease, without any perceptual loss. Within the MB layer, instead of the bit estimation model in the spatial domain employed in TMN11, a bit estimation model in the frequency domain, directly depending on discrete cosine transform coefficients, is proposed. Then the Lagrange multiplier is used to determine the optimal QP for each MB. The resulting QP and number of coded bits of the current MB are fed backward to update the parameters of the bit estimation model.Based on the simulation results obtained in this study, the proposed approach can meet the target bit rate more accurately, keep a lower channel buffer fullness (delay), and have a larger average frame rate than TMN11, whereas the peak signal-to-noise ratio value and the processing time of the proposed approach are “approximately” as good as that of TMN11.     

C-RAN架构中适用于干扰消除的资源分配机制

针对在C-RAN( Clean-Radio Access Network)架构无线网络中的干扰消除机制会带来背景噪声放大的问题,利用C-RAN架构网络的集中式处理,从而可以对全网络系统求解干扰。在定义网络背景噪声放大因子的基础上,将网络中背景噪声放大的最小化问题建立为以资源分配集合为可行空间、以最小化背景噪声放大因子为目标函数的最优化数学模型,并给出了利用遗传算法进行求解的方法,在此基础上设计了资源分配的机制。对该机制的仿真结果表明：将此机制应用到C-RAN构架网络中,能有效降低误码率,提升网络中用户公平性和吞吐量。     

Energy-efficient dynamic wavelength and bandwidth allocation algorithm with delay constraint for time and wavelength division multiplexed passive optical networks

Based on offline scheduling and node modular design,an energy-efficient dynamic wavelength and bandwidth allocation algorithm with the delay constraint (EE-DWBA-DC) was proposed.Optical line terminal (OLT) and optical network units (ONU) were considered to save energy.Under the constraint of packet delay,the number of active wavelengths could be reduced as much as possible and the length of polling cycle was increased.At the same time,the uplink and downlink transmission time of OLT and ONU were concentrated to reduce the state conversion times and extend its low-power duration.In addition,the high energy consumption voids of channels were attempted to be minimized.The simulation results verify that the proposed algorithm can reduce the energy consumption of OLT and ONU and the total energy consumption of the whole network under the premise of guaranteeing packet delay constraints.     

A new architecture and a new metric for lightwave networks

The notion of a logically routed network was developed to overcome the bottlenecks encountered during the design of a large purely optical network. In the last few years, researchers have proposed the use of torus. Perfect shuffle, hypercube, de Bruijn graph, Kautz graph, and Cayley graph as an overlay structure on top of a purely optical network. All these networks have regular structures. Although regular structures have many virtues, it is often difficult in a realistic setting to meet these stringent structural requirements. In this paper, we propose generalized multimesh (GM), a semiregular structure, as an alternate to the proposed architectures. In terms of simplicity of interconnection and routing, this architecture is comparable to the torus network. However, the new architecture exhibits significantly superior topological properties to the torus. For example, whereas a two-dimensional (2-D) torus with N nodes has a diameter of Θ(N^0.5), a generalized multimesh network with the same number of nodes and links has a diameter of Θ(N^0.25). In this paper, we also introduce a new metric, flow number, that can be used to evaluate topologies for optical networks. For optical networks, a topology with a smaller flow number is preferable, as it is an indicator of the number of wavelengths necessary for full connectivity. We show that the flow numbers of a 2-D torus, a multimesh, and a de Bruijn network, are Θ(N^1.5), Θ(N^1.25), and Θ(N log N), respectively, where N is the number of nodes in the network. The advantage of the generalized multimesh over the de Bruijn network lies in the bet that, unlike the de Bruijn network, this network can be constructed for any number of nodes and is incrementally expandable     

A heuristic wavelength assignment algorithm for multihop WDMnetworks with wavelength routing and wavelength re-use

Presents a heuristic algorithm for effectively assigning a limited number of wavelengths among the access stations of a multihop network wherein the physical medium consists of optical fiber segments which interconnect wavelength-selective optical switches. Such a physical medium permits the limited number of wavelengths to be re-used among the various fiber links, thereby offering very high aggregate capacity. Although the optical connectivity among the access station can be altered by changing the states of the various optical switches, the resulting optical connectivity pattern is constrained by the limitation imposed at the physical level. The authors also study two routing schemes, used to route requests for virtual connections. The heuristic is tested on a realistic traffic model, and the call blocking performance of new requests for virtual connections is studied through extensive simulations and compared against the blocking performance of an ideal infinite capacity centralized switch (lowest possible call blocking caused exclusively by congestion on the finite capacity user input/output links, never by the switch fabric itself). Surprisingly, the authors find that, for a wide range of parameters, the blocking performance of the lightwave network is almost the same as that of the ideal centralized switch. From these results, they conclude that the heuristic algorithm is effective and the routing scheme is efficient     

A green radio resource allocation scheme for LTE-A downlink systems with CoMP transmission

In this paper, we propose a green radio resource allocation (GRRA) scheme for LTE-advanced downlink systems with coordinated multi-point (CoMP) transmission to support multimedia traffic. The GRRA scheme defines a green radio utility function, which is composed of the required transmission power, assigned modulation order, and the number of coordinated transmission nodes. By maximizing this utility function, the GRRA scheme can effectively save transmission power, enhance spectrum efficiency, and guarantee quality-of-service requirements. The simulation results show that when the traffic load intensity is greater than 0.7, the GRRA scheme can save transmission power by more than 33.9 and 40.1 %, as compared with the conventional adaptive radio resource allocation (ARRA) scheme (Tsai et al. in IEEE Trans Wireless Commun 7(5):1734–1743, 2008) with CoMP and the utility-based radio resource allocation (URRA) scheme (Katoozian et al. in IEEE Trans Wireless Commun 8(1):66–71, 2009) with CoMP, respectively. Besides, it enhances the system throughput by approximately 5.5 % and improves Jain’s fairness index for best effort users by more than 155 % over these two ARRA and URRA schemes.     

A new architecture for non-linear analogue-digital conversion

A modified architecture is proposed for the non-linear analogue-digital conversion of a transducer response. It is proved that by making use of a dual-slope A/D converter and by changing the clock frequency fed to the A/D converter during the deintegration period and blocking some of the pulses during this period, a nonlinear A/D conversion can be achieved. This method was used to linearize a Pt-PtRh thermocouple response and excellent results were obtained. Further, it is proved that the frequency change depends only on the maximum slope of the transducer response that is to be corrected.     

An end-to-end transmission architecture for the remote control of robots over IP networks

Teleoperation via the Internet is attracting more and more attention from both academia and industry. Physical interaction with remote environments over IP networks, however, poses many technical challenges that are still outstanding, such as time delay, limited bandwidth, and unreliable transmission. To deal with these problems, the majority of current work is concentrated on developing advanced remote control algorithms or interface techniques whereas data transmission between the human operator and the remote robot through the Internet is often treated as a given condition. This paper describes a novel data transmission architecture, for which the core is the trinomial transport protocol, to facilitate the remote control of Internet robots. The trinomial protocol is analyzed theoretically and its advantages over other existing protocols are verified by simulation and experimental studies.     

A novel receiver architecture for single-carrier transmission over time-varying channels

In this paper, we present a single-carrier transceiver for rapidly time-varying channels, where the equalization step is implemented in the frequency domain. When the channel abides with both fast fading and severe inter-block interference, our equalizer relies on a band approximation of the frequency-domain channel matrix to maintain low complexity. We will show that the band approximation error can be associated in the time domain to a critically-sampled complex exponential basis expansion modeling error. Based on this property, we propose a novel receiver architecture that extends the original data model by inserting zeros at the receiver. The resulting effective channel can be characterized by an oversampled complex exponential basis expansion model, which has a considerably reduced modeling error compared to the critically-sampled one. In other words, the band assumption that is essential to the equalizer will be made more accurate and thus the equalization performance can be improved.     

WDM EPON中的动态波长带宽分配算法

基于WDM EPON系统结构和已有波长带宽分配算法(DWBA)的不足,提出了一种结合流量预测与预分配机制的动态波长带宽分配算法--DWBPA.仿真表明在不同网络负载情况下,该算法不仅保证了波长带宽分配的公平性,而且能够满足高优先级业务的延时要求.     

一种具有平顶陡边响应的长波长光探测器

在PIN型光探测器的基础上制备了一种适用于波分复用系统的具有平顶陡边响应的长波长光探测器。利用低压金属有机化学气相沉积(LP-MOCVD)设备在GaAs衬底上二次外延生长了具有台阶结构的GaAs/AlGaAs滤波腔和InP基PIN光探测器。高质量的GaAs/InP异质外延采用了低温缓冲层生长工艺;具有台阶结构的Fabry-Pérot(F-P)滤波腔采用了纳米量级台阶的制备方法。通过理论计算优化了实现平顶陡边光谱响应特性的器件结构;并通过实验成功制备出了具有平顶陡边响应性能的光探测器,器件的工作波长位于1 549nm,峰值量子效率大于25%,0.5dB光谱响应线宽为3.9nm,3dB光谱响应线宽为4.2nm,响应速率达到17GHz。     

A new approach for routing and wavelength assignment for permanent and reliable wavelength paths in wide all-optical WDM networks

This article proposes a new approach for routing and wavelength assignment (RWA) for permanent and reliable wavelength paths (WP) in wide all-optical WDM networks with wavelength continuity constraint. Given a number of available wavelengths on each optical fiber, for each simple link failure of the network, we seek to maximize the number of satisfied requests for connections. This is known as RWAP problem. In our algorithm, called RWA with Minimum Loaded Link for Permanent and Reliable wavelength paths (MLL-PR), routing is based on the search for the optimal path while trying to minimize the maximum load on the links of the network in order to minimize the maximum link capacity and then minimize the number of dropped lightpaths after any link failure. The wavelength assignment is based on a graph coloring method using tabu-search. A series of experiments using two well-known networks (ARPANET and NSFNET) have been carried out in order to evaluate the performance of our approach, in terms of the number of blocked demands, for different failure scenarios. Generally, our results are better than those provided by the current solving approaches taken as reference.