共查询到20条相似文献,搜索用时 0 毫秒
1.
Free-Space Optical Communications 总被引:6,自引:0,他引:6
With recent successes of laboratory, inatmosphere, and space demonstrations of free-space optical communications, there is no doubt that the technology is ready for operational deployment. While these successes have shown that there are no laws of physics against such systems, their estimated system costs are still much too high for serious considerations. Two types of development can reduce the cost dramatically. The first is via the improvement of physical-link communication efficiency by an order of magnitude using photon-counting receivers for vacuum channels, system complexity, weight, and power for space systems can be greatly reduced. The second is through the use of coherent systems in links where clear-air turbulence impairs communication efficiency, and in multiple access applications where coherent processing can reduce the level of interference, significant reduction in system costs can be realized 相似文献
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由于在性能和复杂度之间的良好折中,软信息辅助硬判决译码近年来受到了光通信领域的高度关注,其中包括了软信息辅助比特标记(Soft-Aided Bit-Marking,SABM)算法.为了易于硬件实现,本文基于阶梯码(Staircase Code,SCC)提出了一种改进型SABM算法(improved SABM,iSABM),称为iSABM-SCC.iSABM-SCC利用信道软信息,通过两个可信度阈值将硬判决输出比特标记为三种可信度等级,用以辅助硬判决译码识别译码错误和扩展纠错能力,达到提升阶梯码性能的目的.在受大气湍流影响的自由空间光通信中的仿真表明,iSABM-SCC性能显著优于标准SCC和RS码.以强湍流信道为例,码率为0.75的iSABM-SCC在4-PAM调制下较标准SCC产生的性能增益可达4.37 dB,在8-PAM调制下较RS码产生的性能增益可达11.06 dB. 相似文献
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Autonomous Reconfiguration in Free-Space Optical Sensor Networks 总被引:1,自引:0,他引:1
《Selected Areas in Communications, IEEE Journal on》2005,23(8):1556-1563
This research focuses on the physical and logical control and reconfigurability of network topologies through intelligent and dynamic rearrangement of nodes in an optical wireless sensor network. We address high data rate sensor networks (e.g., infrastructure monitoring; surveillance), which consist of gigabit per second, narrow beam, free-space optical links between fixed and/or mobile nodes. In our approach, the seamless operation of such networks requires maintenance of wireless link connectivity and quality and at all times, amidst, for example, changing atmospheric, and traffic and platform conditions. This is achieved by dynamic reconfiguration through topology control. We address the problem of dynamic formulation of topologies, which contain only two transceivers per communications node or switch. The task of reconfiguration requires the formation of a biconnected graph or a ring topology. The problem is similar to the traveling salesman problem and is NP complete. We address the mixed integer programming formulation of this problem, and show that it does not scale even for a small network. We then focus on heuristics for dynamic, autonomous reconfiguration. Using simulations, we investigate tradeoff between solution quality and computational time. We also investigate the effectiveness of these dynamic reconfiguration heuristics compared to fixed, degraded topologies. 相似文献
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Free-space optical communications (FSO) propagated over a clear atmosphere suffers from irradiance fluctuation caused by small but random atmospheric temperature fluctuations. This results in decreased signal-to-noise ratio (SNR) and consequently impaired performance. In this paper, the error performance of the FSO using a subcarrier intensity modulation (SIM) based on a binary phase shift keying (BPSK) scheme in a clear but turbulent atmosphere is presented. To evaluate the system error performance in turbulence regimes from weak to strong, the probability density function (pdf) of the received irradiance after traversing the atmosphere is modelled using the gamma-gamma distribution while the negative exponential distribution is used to model turbulence in the saturation region and beyond. The effect of turbulence induced irradiance fluctuation is mitigated using spatial diversity at the receiver. With reference to the single photodetector case, up to 12 dB gain in the electrical SNR is predicted with two direct detection PIN photodetectors in strong atmospheric turbulence. 相似文献
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Sangwoo Lee Mohsen Kavehrad 《International Journal of Wireless Information Networks》2009,16(4):185-196
This paper is about signal processing techniques for airborne free-space optical (FSO) wireless communications through clouds.
FSO channel is known to be accompanied by multi-scattering, which causes severe intersymbol interference. Unlike traditional
FSO systems relying on optical signal processing devices, this research paper investigates the feasibility of digital signal
processing schemes applied to FSO. By having a channel shortening equalizer (CSE or TEQ for time equalization) at the transmitter
and a Viterbi equalizer at the receiver, reliable communication at low-to-mid level optical thickness values is shown to be
feasible. We also propose how existing TEQ algorithms can be modified to fit into TEQ-in-transmitter configurations. Performance
is evaluated in BER, and compared with conventional equalizations. 相似文献
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天气的影响会导致自由空间光通信系统性能恶化。利用Mie理论和两种雨滴谱分布模型,计算了不同降雨量下大气激光传输的衰减;根据Kim和AlNaboulsi模型计算了激光在不同能见度下的衰减。研究了降雨和雾气对自由空间光通信系统性能的影响,分析了不同降雨量时降雨和雾气天气条件下传输距离与误码率的关系以及发射功率与误码率的关系。结果表明,降雨量不同会影响通信距离;雾天衰减比雨天衰减更为严重,通信距离变短,为保证系统正常工作,可以适当加大发射功率。 相似文献
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In polarization-encoded free-space quantum communications, a transmitter on a satellite and a receiver in a ground station each have a respective polarization zero direction, by which they encode and decode every polarization quantum bit required for a quantum communication protocol. In order to complete the protocol, the ground-based receiver needs to track and compensate for the polarization zero direction of the satellite-based transmitter. Expressions satisfied by amplitudes of the s-polarization component and the p-polarization component are derived based on a two-mirror model, and a condition satisfied by the reflection coefficients of the two mirrors is given. A polarization tracking principle is analyzed for satellite-to-ground quantum communications, and quantum key encoding and decoding principles based on polarization tracking are given. A half-wave-plate-based dynamic polarization-basis compensation scheme is proposed in this paper, and this scheme is proved to be suitable for satellite-to-ground and intersatellite quantum communications. 相似文献
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《Communications Magazine, IEEE》2008,46(7):134-135
This issue of the Optical Communications series features five articles that address developments in several segments of the optical communications network. 相似文献
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《Optical Fiber Technology》2014,20(5):501-512
Network coding (NC) integrated into Passive Optical Networks (PONs) is regarded as a promising solution to achieve higher throughput and energy efficiency. To efficiently support multimedia traffic under this new transmission mode, novel NC-based hybrid scheduling mechanisms for Next-generation PONs (NG-PONs) including energy management, time slot management, resource allocation, and Quality-of-Service (QoS) scheduling are proposed in this paper. First, we design an energy-saving scheme that is based on Bidirectional Centric Scheduling (BCS) to reduce the energy consumption of both the Optical Line Terminal (OLT) and Optical Network Units (ONUs). Next, we propose an intra-ONU scheduling and an inter-ONU scheduling scheme, which takes NC into account to support service differentiation and QoS assurance. The presented simulation results show that BCS achieves higher energy efficiency under low traffic loads, clearly outperforming the alternative NC-based Upstream Centric Scheduling (UCS) scheme. Furthermore, BCS is shown to provide better QoS assurance. 相似文献
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The recent trend in optical networks is switching packets directly in the optical domain. The aim is to benefit from both packet flexibility and optical transparency. In this article, we review current optical architectures that try to reconcile these two requirements. We discuss the challenges encountered in these new architectures and their respective niches. To meet the requirements of next-generation high-speed optical networks, we also propose a new solution based on the distribution of the aggregation process in the network. The feasibility of this scheme and the benefit that it provides over existing solutions are analyzed in this article. 相似文献
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在综合分析研究零散、有限的公开文献资料基础上,主要通过光纤通信系统在外军(美军)C4I系统中的具体应用实例来说明它的发展和现场应用情况。文中着重介绍战场上光纤通信系统、战术通信系统集成,军用机载、舰载C4I光纤通信设备、技术体制和标准;论述了光纤宽带综合数字航空信息交换网(B-IDAIEN)对实现光纤智能舱与光纤智能蒙皮的作用;还涉及到光纤制导导弹的应用和开发情况。这些例子较为详实地反映了光纤通信在外军军用通信中的重要地位和作用 相似文献
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《Communications Magazine, IEEE》2009,47(10):36-38
This feature topic on military communications includes five articles that deal primarily with wireless tactical networks, covering topics ranging from security to software defined radio design and mobile ad hoc networks (MANETs) for covert battlefield operations. 相似文献
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随着Blu-ray视频记录格式的出现,终端用户可在单个光盘上记录、重写和回放至少2h的数字高清晰度电视(HDTV)节目或13h以上的标准视频图像信息。然而,当前的Blu—ray系统仅受到热衷于家庭HDTV人士的青睐。若想扩大其市场并得到广大消费者的认可,必须降低成本费用。 相似文献
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Estimators motivated by the minimum mean-square estimation (MMSE) criterion are presented for the estimation of the optical signal intensity in free-space optical (FSO) communication systems impaired by atmospheric-induced scintillation. Joint parameter estimators for the estimation of signal intensities across a photodetector array are investigated. Three scenarios are considered. First, it is assumed that the received signal is detected using a p-i-n photodiode array and that the receiver operates under a shot-noise-limited condition. In the second scenario, the received signal is detected using an APD array and the receiver operates under a shot-noise-limited condition. In the third scenario, the received signal is detected using an APD array, but the receiver is impaired by thermal noise as well as shot noise. The mean primary electron count received by the APD is assumed to be large enough to justify the Gaussian approximation. The optical channel is modeled using a log-normal distribution with correlated random signal intensities across the array. With the aid of simulation, it is shown that the proposed estimators outperform the maximum-likelihood estimators for small scintillation indices while providing a performance similar to the maximum a posteriori estimator. 相似文献
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OFDM for Optical Communications 总被引:12,自引:0,他引:12
《Lightwave Technology, Journal of》2009,27(3):189-204
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下一代光接入网EPON 总被引:14,自引:0,他引:14
现在,以太网无源光网络(EPON)技术已经走向市场,并被视为下一代接入网的最佳候选技术,它代表了低成本、高带宽以太网设备与低成本光纤网的融合。从推出EPSON技术的背景、基本要领、要解决的主要问题、标准进展情况和市场分析等方面对EPSON加以阐述。 相似文献