共查询到20条相似文献,搜索用时 468 毫秒
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Considering the influence of more random atmospheric turbulence,worse pointing errors and highly dynamic link on the transmission performance of mobile multiple-input multiple-output(MIMO)free space optics(FSO)communication systems,this paper establishes a channel model for the mobile platform.Based on the combination of Alamouti space-time code and time hopping ultra-wide band(TH-UWB)communications,a novel repetition space-time coding(RSTC)method for mobile 2×2 free-space optical communications with pulse position modulation(PPM)is developed.In particular,two decoding methods of equal gain combining(EGC)maximum likelihood detection(MLD)and correlation matrix detection(CMD)are derived.When a quasi-static fading and weak turbulence channel model are considered,simulation results show that whether the channel state information(CSI)is known or not,the coding system demonstrates more significant performance of the symbol error rate(SER)than the uncoding.In other words,transmitting diversity can be achieved while conveying the information only through the time delays of the modulated signals transmitted from different antennas.CMD has almost the same effect of signal combining with maximal ratio combining(MRC).However,when the channel correlation increases,SER performance of the coding 2×2 system degrades significantly. 相似文献
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The problem of lightpath topology design (LTD) and traffic routing over the lightpaths for wavelength-routed optical backbone networks has been investigated extensively in the past using heuristic as well as linear-programming based approaches. Sensitivity of such long-haul backbones to physical-layer impairments is required to be adequately addressed during LTD phase to improve overall performance. For optical communication using wavelength-division multiplexing (WDM) over a long-haul fiber backbone, four-wave mixing (FWM) may become one of the significant transmission impairments. Intrinsically, for a WDM-based wavelength-routed network with wavelengths assigned using equally-spaced channels, the generated FWM components are found to remain more crowded at the center of the fiber transmission window. Using this observation, we propose an LTD scheme employing a unique wavelength assignment (WA) technique, wherein long lightpaths (traversing through a larger number of fiber links) are allocated wavelengths at the either edges of the fiber transmission window whereas short lightpaths (consisting of fewer fiber links) are placed in the middle of the transmission window, thereby reducing the FWM crosstalk for long lightpaths. Since long lightpaths comprise of large numbers of fiber links and intermediate nodes, they experience large amplified spontaneous emission (ASE) noise and switch crosstalk. Therefore, by using the proposed WA technique, long lightpaths while suffering from more ASE noise and switch crosstalk get subjected to lesser FWM crosstalk leading to a more uniform distribution of overall optical signal-to-noise ratio for all the lightpaths across the network. Analysis of our results indicates that the proposed FWM-aware LTD scheme with the novel WA technique can achieve similar congestion levels (of lightpaths) and bandwidth utilization efficiency without any need of additional network resources as compared with the existing FWM-unaware LTD schemes. 相似文献
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Hwang Jong-Gyu Jung Jae-Il Park Yong-Jin Bae Jung-Hyun Song Hyun-Su Kim Sung-Un 《Photonic Network Communications》2004,8(3):319-334
A major challenge in next generation Internet (NGI) backbone networks based on dense-wavelength division multiplexing (DWDM) is the provision of guaranteed quality-of-service (QoS) for a wide variety of multimedia applications. This paper proposes a new routing algorithm called multi-wavelength minimum interference path routing (MW-MIPR) to provide more reliable QoS guarantees by consideration of the potential future network's congestion status. This improves wavelength utilization by choosing a route that does not interfere too much with potential future connection requests. Moreover, we introduce a differentiated routing and wavelength assignment (RWA) mechanism combined with recovery strategy and the proposed MW-MIPR algorithm based on the differentiated service model in the NGI. Simulation results show that the proposed MW-MIPR algorithm achieves a smaller blocking probability than dynamic routing (DR) that yields the best performance among previous RWA algorithms. And we prove that a differentiated RWA combined with a recovery capability together with the proposed routing scheme provides satisfied QoS assurance for each service class in terms of signal quality and survivability. 相似文献
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In-band crosstalk has been widely considered as a major transmission impairment that significantly impacts the bit error rate (BER) performance of lightpaths in circuit-switched all-optical wavelength-routed networks. Such crosstalk usually occurs when multiple wavelengths pass through an optical crossconnect node, and the magnitude of the crosstalk is largely dependent on the wavelengths assigned to the lightpaths. Traditional wavelength assignment (WA) schemes pay little regard to the physical layer quality of service (QoS), and hence cannot provide optimized network performance in practical networks with imperfect physical transmission media. In this paper, we first present our categorization of in-band crosstalk based on the location of crosstalk generation, then we propose two QoS-friendly WA approaches, one of which selects the wavelength based on the estimated BERs, and the other based on the weighted crosstalk number counting. The two approaches have different computation complexities. Numerical results show that both approaches can significantly improve the BER blocking rate by suppressing the created in-band crosstalk, but the BER-based approach generally gives the better performance at the price of more extensive computation.This work was supported in part by DARPA Grants #N66001-00-1-8949 and #66001-01-1-8932 (co-funded by NSA). 相似文献
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Dong Mei Shan Kee Chaing Chua Mohan G. Minh Hoang Phunq 《Communications, IEEE Transactions on》2008,56(10):1694-1704
Optical burst switching (OBS) is a promising technique for wavelength division multiplexing (WDM) networks. In practice, wavelength converters (WCs) are either absent or only sparsely deployed in WDM networks due to economic and technical limitations. Thus, wavelength assignment is expected to be an important component of OBS networks. In this paper, an offline wavelength assignment scheme in OBS networks without wavelength conversion capability is proposed. The key idea of the scheme is to decide the wavelength searching order of each traffic connection at edge nodes according to the wavelength priorities determined by the calculated burst loss probabilities on different wavelengths. Simulation results indicate that the proposed scheme can reduce the network-wide burst loss probability significantly compared with other schemes. It is also illustrated that the performance of the proposed scheme can be further enhanced by a larger number of wavelengths per link and a reasonable delay bound at edge nodes. 相似文献
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E. Salvadori V.S. Chava A. Zanardi D. Siracusa G. Galimberti A. Tanzi G. Martinelli O. Gerstel 《Optical Switching and Networking》2013,10(1):3-15
In transparent optical networks, physical layer impairments (PLIs) incurred by non-ideal optical transmission media accumulate along an optical path, and the overall effect determines the optical feasibility of the lightpaths. In addition, transparent optical networks suffer from inefficient wavelength utilization, as a connection request may be rejected because of non-availability of a common wavelength on all the links along the chosen route. To increase optical reach, resource utilization, and average call acceptance ratio (and hence revenues), network operators are resort to translucent optical networks. In these networks a limited number of regenerators are placed at a selected set of nodes. In this scenario development of an optical control plane which is aware of PLIs, location and number of regenerators, is of paramount importance for on-demand lightpath provisioning. In this paper, we propose a novel approach of constructing a reachability graph of the physical network considering PLIs and regenerators. If there is no transparent path in the physical network, we route the connections with multiple transparent segments on the reachability graph. We propose efficient mechanisms and corresponding GMPLS protocol extensions for impairment and regenerator aware routing and wavelength assignment (IRA-RWA) in translucent optical networks. The simulation results suggest that our proposed approach together with LSP stitching signaling mechanism is feasible to implement and close to deployment. 相似文献
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This paper proposes and evaluates a four-wave mixing (FWM) aware evolutionary programming algorithm for dynamically setting
up lightpaths in an optical wavelength division multiplexed network (WDM network). The proposed algorithm also considers the
effect of amplified spontaneous emission noise (ASE noise) on a lightpath during propagation of the optical signal from any
source to the intended destination. As crosstalk due to FWM and ASE noise are two transmission impairments that degrade the
quality of optical signal even at low to medium data rates, it is mandatory for an algorithm for dynamic routing and wavelength
assignment in a WDM network to consider the effect of these two impairments on the lightpath to be established. The distinguishing
feature of the proposed algorithm is that it is based on an initial population of a single individual and uses a fitness function
that is expressed in terms of the number of hops, path cost, variance contributions due to FWM crosstalk, amplifier noise,
and different beat noises at the receiver. The performance of a newly introduced FWM aware priority-based wavelength assignment
technique is compared with few of the existing wavelength assignment techniques in the present work. 相似文献
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Anwar Al-Yatama 《Photonic Network Communications》2014,27(1):34-46
One of the most important performance measurements in wavelength-division multiplexing (WDM) networks is the call blocking probability. In this paper, we present an approximate analytical method to evaluate the blocking probabilities in survivable WDM networks with dynamically arriving connection requests. Our approach utilizes the wavelength independence whereby WDM network can be regarded as an aggregation of disjoint single wavelength sub-networks with a common physical topology. In each single wavelength sub-network, we derive the calculation of the blocking probability from an exact analysis. We assume dedicated protection with fixed routing and either first-fit or random wavelength assignment. Simulation results demonstrate the accuracy of the proposed method. 相似文献
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A quasi-static routing scheme called path switching for large-scale ATM packet switch systems is proposed. Previously the Clos network has been used as the model for many large-scale ATM switch architectures, in which the most difficult issue is path and bandwidth assignment for each connection request. The static routing scheme, such as multirate circuit switching, does not fully exploit the statistical multiplexing gain. In contrast, the dynamic routing scheme, such as straight matching, requires slot-by-slot computation of route assignment. Path switching is a compromise of these two routing schemes. It uses a predetermined periodical connection pattern in the central stage, look-ahead selection in the input stage, and output queueing in the last stage. The scheduling of path switching consists of capacity assignment and route assignment. The capacity assignment is constrained by the quality of service of connection requests. The route assignment is based on the timespace interleaving of the coloring of bipartite multigraphs. We show that path switching can handle multirate and multimedia traffic effectively in the Clos network 相似文献
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In this paper, a novel fuzzy dynamic routing and wavelength assignment technique is proposed for a wavelength division multiplexing optical network to achieve the best quality of network transmission. This paper proposes a novel quality of service aware fuzzy logic controlled dynamic routing and wavelength assignment algorithm (QoS-FDRWA), where the optimum path is chosen by a fuzzy rule-based inference system. The proposed fuzzy routing technique incorporates optical network transmission attributes such as latency, physical length of the link, data packet loss, number of hops, and wavelength availability status in the path. 相似文献
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Hai‐Han Lu Wen‐Shing Tsai Tzu‐Shen Chien Shih‐Hung Chen Yu‐Chieh Chi Che‐Wei Liao 《ETRI Journal》2007,29(2):162-168
A new scheme for bi‐directional HDTV/Gigabit Ethernet/CATV transmission over a hybrid dense‐wavelength‐division‐multiplexing passive optical network (DWDM‐PON) is proposed and demonstrated. It is based on injection‐locked vertical‐cavity surface‐emitting lasers and distributed‐feedback laser diodes as transmitters. Services with 129 HDTV channels, a 1.25 Gbps Gigabit Ethernet connection, and 77 CATV channels are successfully demonstrated over 40 km single‐mode fiber links. Good performance of bit error rate, carrier‐to‐noise ratio, composite second order, and composite triple beat is achieved in our proposed bidirectional DWDM‐PON. 相似文献
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《Optical Fiber Technology》2007,13(3):191-197
We consider the routing and wavelength assignment (RWA) problem on wavelength division multiplexing (WDM) networks without wavelength conversion. When the physical network and required connections are given, RWA is the problem to select a suitable path and wavelength among the many possible choices for each connection such that no two paths using the same wavelength pass through the same link. In WDM optical networks, there is need to maximize the number of connections established and to minimize the blocking probability using limited resources. This paper presents efficient RWA strategies, which minimizes the blocking probability. Simulation results show that the performance of the proposed strategies is much better than the existing strategy. 相似文献
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We study a class of all-optical networks using wavelength-division multiplexing (WDM) and wavelength routing, in which a connection between a pair of nodes in the network is assigned a path and a wavelength on that path. Moreover, on the links of that path no other connection can share the assigned wavelength. Using a generalized reduced load approximation scheme we calculate the blocking probabilities for the optical network model for two routing schemes: fixed routing and least loaded routing 相似文献
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光虚拟专用网(OVPN)是光网络的主要服务模式之一,OVPN的生存性是其业务得以开展的前提和基础。首先对虚拟专用网的概念作一介绍,随后对OVPN生存性的问题进行了分析,在此基础之上给出了OVPN生存性的基本模型,最后讨论了三种不同的OVPN生存性路由方案,并对其性能进行了分析和对比。 相似文献
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This paper shows a new scheme which improves the crosstalk performance of large optical multi/demultiplexers, a key component in wavelength division multiplexing (WDM) systems. This scheme uses arrayed waveguide gratings (AWG's) of various sizes and requires no additional equipment. It is well known that a large multi/demultiplexer can be constructed by cascading small multi/demultiplexers. We have studied the impact of the number and size of AWG stages on crosstalk performance. This paper proves that to obtain a multistage multi/demultiplexer with minimum crosstalk, the total channel number of each AWG stage must be minimized. For example, cascading 10-channel AWG's and 11-channel AWG's improves the crosstalk performance of a 110-channel multi/demultiplexer by about 7.5 dB. Furthermore, the crosstalk performance degradation due to fabrication error is theoretically investigated taking channel bandwidth into account. Optimum design parameters of multistage AWG's are introduced: When the AWG suppression ratio is 30 dB and the ratio of channel bandwidth to channel spacing is about 0.24, the degradation in crosstalk performance due to fabrication error is minimized. The tradeoff between the crosstalk performance and the efficiency in terms of hardware and wavelength are also discussed. It is discovered that this simple scheme can yield a crosstalk-free WDM router. Crosstalk reduction obtained by this scheme allows the realization of flexible multiwavelength networks based on wavelength routing 相似文献
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We have developed a new layered-routing approach to address the problem of all-optical multicast over wavelength-routed wavelength
division multiplexing (WDM) networks. We model the WDM network as a collection of wavelength layers with sparse light- splitting
(LS) and wavelength conversion (WC) capabilities. We apply the degree constraint technique to solve the problem. The approach
is capable of completing multicast routing and wavelength assignment (MCRWA) in one step. We propose two generic frameworks
to facilitate heuristic development. Any heuristic that is derived from either Prim’s or Kruskal’s algorithm can be easily
imported to solve the MCRWA problem. One example is given for each framework to demonstrate heuristic development. Extensive
simulations were carried out to measure the performance of heuristics developed from the frameworks. The results show that
the STRIGENT scheme is suitable for hardware design and it is advisable to deploy light splitters and wavelength converters
to the same node for better performance. 相似文献
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A new all-optical access-metro network interface based on optical burst switching (OBS) is proposed. A hybrid wavelength-division multiplexing/time-division multiplexing (WDM/TDM) access architecture with reflective optical network units (ONUs), an arrayed-waveguide-grating outside plant, and a tunable laser stack at the optical line terminal (OLT) is presented as a solution for the passive optical network. By means of OBS and a dynamic bandwidth allocation (DBA) protocol, which polls the ONUs, the available access bandwidth is managed. All the network intelligence and costly equipment is located at the OLT, where the DBA module is centrally implemented, providing quality of service (QoS). To scale this access network, an optical cross connect (OXC) is then used to attain a large number of ONUs by the same OLT. The hybrid WDM/TDM structure is also extended toward the metropolitan area network (MAN) by introducing the concept of OBS multiplexer (OBS-M). The network element OBS-M bridges the MAN and access networks by offering all-optical cross connection, wavelength conversion, and data signaling. The proposed innovative OBS-M node yields a full optical data network, interfacing access and metro with a geographically distributed access control. The resulting novel access-metro architectures are nonblocking and, with an improved signaling, provide QoS, scalability, and very low latency. Finally, numerical analysis and simulations demonstrate the traffic performance of the proposed access scheme and all-optical access-metro interface and architectures 相似文献