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1.
Optical wireless communication (OWC) is gaining acceptance in an increasing number of sectors of science and industry, owing to its unique combination of features: extremely high bandwidth, rapid deployment time, license- and tariff-free bandwidth allocation, and low power consumption, weight, and size. However, the major drawback of OWC in terrestrial applications is the threat of downtime caused by adverse weather conditions, such as fog and haze. Several researchers have proposed and developed communication systems that use far-IR radiation to mitigate weather effects. In this study we analyze the performance of a short-distance terrestrial OWC system as a function of wavelength. A mathematical model for OWC link performance is derived. Using this model, we perform a simulation of our system under different weather conditions. From the results of our calculations, the improvement of link availability for 10 microm compared with 0.785-1.55 microm for a distance of 1-km propagation is 0.2% (99.6-99.8%). This modest improvement should be considered relative to the complexity and cost of quantum cascade laser transmitters and far-IR receivers. 相似文献
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It is well-known that the performance of the relay-based decode-and-forward (DF) cooperative networks outperforms the performance of the amplify-and-forward cooperative networks. However, this performance improvement is accomplished at the expense of adding more signal processing complexity (precoding/decoding) at each relay node. In this study, the authors tackle this signal processing complexity issue by proposing a Jacket-based fast method for reducing the precoding/decoding complexity in terms of time computation. Jacket transforms have shown to find applications in signal processing and coding theory. Jacket transforms are defined to be n x n matrices A = (ajk) over a field F with the property AA† = n/n, where A† is the transpose matrix of the element-wise inverse of A, that is, A† = (a-1kj,/sub>), which generalise Hadamard transforms and centre weighted Hadamard transforms. In particular, exploiting the Jacket transform properties, the authors propose a new eigenvalue decomposition (EVD) method with application in precoding and decoding of distributive multi-input multi-output channels in relay-based DF cooperative wireless networks in which the transmission is based on using single-symbol decodable space-time block codes. The authors show that the proposed Jacket-based method of EVD has significant reduction in its computational time as compared to the conventional-based EVD method. Performance in terms of computational time reduction is evaluated quantitatively through mathematical analysis and numerical results. 相似文献
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This paper describes a method to control capacity of a multi-type heat pump system. Because indoor units are interconnected, alteration of the heating or cooling setting of one indoor unit can influence the performance of the other indoor units. Proportional-integral (PI) controllers were used to assess system performance, and the PI controllers’ gain values were optimized by using a genetic algorithm. A system model was established following a system identification optimization process, and a pseudo random binary sequence was selected as the system identification input signal. A multi-input multi-output (MIMO) controller was more effective in reducing such cross-coupling effects than a single-input single-output (SISO) controller. The temperature at the secondary fluid outlet in the condenser and the saturation pressure at the evaporator were selected as the control variables in the MIMO controller. The experimental results showed that an optimized MIMO controller could reduce overshoot by up to 40% compared with the results using a SISO controller. 相似文献
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There is an increasing demand for transdermal high-data-rate communication for use with in-body devices, such as pacemakers, smart prostheses, neural signals processors at the brain interface, and cameras acting as artificial eyes as well as for collecting signals generated within the human body. Prominent requirements of these communication systems include (1) wireless modality, (2) noise immunity and (3) ultra-low-power consumption for the in-body device. Today, the common wireless methods for transdermal communication are based on communication at radio frequencies, electrical induction, or acoustic waves. In this paper, we will explore another alternative to these methods--optical wireless communication (OWC)--for which modulated light carries the information. The main advantages of OWC in transdermal communication, by comparison to the other methods, are the high data rates and immunity to external interference availed, which combine to make it a promising technology for next-generation systems. In this paper, we present a mathematical model and experimental results of measurements from direct link and retroreflection link configurations with Gallus gallus domesticus derma as the transdermal channel. The main conclusion from this work is that an OWC link is an attractive communication solution in medical applications. For a modulating retroreflective link to become a competitive solution in comparison with a direct link, low-energy-consumption modulating retroreflectors should be developed. 相似文献
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Beam width and transmitter power adaptive to tracking system performance for free-space optical communication 总被引:3,自引:0,他引:3
The basic free-space optical communication system includes at least two satellites. To communicate between them, the transmitter satellite must track the beacon of the receiver satellite and point the information optical beam in its direction. Optical tracking and pointing systems for free space suffer during tracking from high-amplitude vibration because of background radiation from interstellar objects such as the Sun, Moon, Earth, and stars in the tracking field of view or the mechanical impact from satellite internal and external sources. The vibrations of beam pointing increase the bit error rate and jam communication between the two satellites. One way to overcome this problem is to increase the satellite receiver beacon power. However, this solution requires increased power consumption and weight, both of which are disadvantageous in satellite development. Considering these facts, we derive a mathematical model of a communication system that adapts optimally the transmitter beam width and the transmitted power to the tracking system performance. Based on this model, we investigate the performance of a communication system with discrete element optical phased array transmitter telescope gain. An example for a practical communication system between a Low Earth Orbit Satellite and a Geostationary Earth Orbit Satellite is presented. From the results of this research it can be seen that a four-element adaptive transmitter telescope is sufficient to compensate for vibration amplitude doubling. The benefits of the proposed model are less required transmitter power and improved communication system performance. 相似文献
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The application of coherent detection to indoor optical free-space communications is considered here. Analytical expressions are derived for a wide line-of-sight (W-LOS) optical link which determine the coverage area and the required photo-detection area given different binary digital transmission schemes and a given bit rate. The coverage area is maximised for systems using both metal-semiconductor-metal (MSM) and PIN photo-detectors. Results show that MSM photo-detectors, due to their inherently lower capacitance per unit photo-detection area, result in a greater coverage area than their PIN counterparts. To demonstrate the viability of implementing coherent detection indoors, a 200 Mb/s LOS optical link which uses coherent detection is also reported. 相似文献
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X Liu 《Applied optics》2012,51(19):4463-4468
It has been important to optimize the transmitter power in wireless optical communication systems. The conventional approach was based on the reciprocal Pareto model. In this paper, the investigation is extended to a more general scenario where the instantaneous signal-to-noise ratio follows the log-square-Ricean distribution. Accordingly, the optimization model is established. The conventional model thus becomes a special case of the new model. It is shown that the new model can be analytically solved. The sample solutions clearly show how the optima of transmitter power change when the log-square-Ricean profile changes. These results would provide useful guidelines to system design. 相似文献
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DC-OFDM超宽带无线通信系统 总被引:1,自引:0,他引:1
对高速超宽带(UWB)无线通信技术进行了研究,提出了双载波-正交频分复用(DC-OFDM)UWB系统方案,包括频带划分方案、帧结构和发射端系统方案以及参考接收机方案,给出了方案的计算机仿真结果和硬件实验结果.DC-OFDM UWB方案采用独创的双载波结构,降低了对射频和基带关键电路硬件实现的要求,获得了频域分集效果,提高了频谱使用灵活性.硬件实验系统的无线传输速率达到110 Mbps,传输距离为10m,信号发射功率小于0.1mW. 相似文献
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Performance improvement of optical wireless communication through fog with a decision feedback equalizer 总被引:3,自引:0,他引:3
Aharonovich M Arnon S 《Journal of the Optical Society of America. A, Optics, image science, and vision》2005,22(8):1646-1654
Optical wireless communication (OWC) systems use the atmosphere as a propagation medium. However, a common problem is that from time to time moderate cloud and fog emerge between the receiver and the transmitter. These adverse weather conditions impose temporal broadening and power loss on the optical signal, which reduces the digital signal-to-noise ratio (DSNR), produces significant intersymbol interference (ISI), and degrades the communication system's bit error rate (BER) and throughput. We propose and investigate the use of a combined adaptive bandwidth mechanism and decision feedback equalizer (DFE) to mitigate these atmospheric multipath effects. Based on theoretical analysis and simulations of DSNR penalties, BER, and optimum system bandwidths, we show that a DFE improves the outdoor OWC system immunity to ISI in foggy weather while maintaining high throughput and desired low BER. 相似文献
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Shohet G Zalevsky Z Marom E 《Journal of the Optical Society of America. A, Optics, image science, and vision》2007,24(1):179-187
Optical bandpass tunable filters are key elements for dense WDM optical communication systems. Recently, a realization of optical linear transformation using a spatial diffraction optical system was presented and theoretically analyzed [J. Opt. Soc. Am. A21, 732 (2004)]. We present an optical bandpass tunable filter based on this optical system and a spatial light modulator. The mathematical analysis and additional computer simulations for testing the filter's basic parameters using the Fresnel diffraction theory are presented. Some newly obtained laboratory experimental results of the device in the optical visible spectrum will be shown. 相似文献
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Performance of optical wireless communication (OWC) systems can be optimised using constant optical power transmission in conjunction with forward error control coding. A new family of constant power error correcting codes using multiple pulse position modulation optical transmission are introduced. This doubly featured technique may extend the capability of many difficult wireless optical links beyond their existing barriers and may enable a higher error performance for OWC networks. The potential and design of look-up table codes are investigated. The Monte Carlo methods provide supportive data for the performance and code word search. 相似文献
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Optical wireless communication has been the subject of much research in recent years because of the increasing interest in laser satellite-ground links and urban optical wireless communication. The major sources of performance degradation have been identified as the spatial, angular, and temporal spread of the propagating beam when the propagation channel is multiscattering, resulting in reduced power reception and intersignal interference, as well as turbulence-induced scintillations and noise due to receiver circuitry and background illumination. However, coherence effects due to multipath interference caused by a scattering propagation channel do not appear to have been treated in detail in the scientific literature. We attempt a theoretical analysis of coherence interference in optical wireless communication through scattering channels and try to quantify the resultant performance degradation for different media. We conclude that coherence interference is discernible in optical wireless communication through scattering channels and is highly dependent on the microscopic nature of the propagation medium. 相似文献
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Hadjinicolaou M.G. Nilavalan R. Itagaki T. Voskarides S.C. Pattichis C.S. Schizas A.N. 《Communications, IET》2009,3(8):1284-1296
For the first time, a complete wireless and mobile emergency TeleOrthoPaedics system with field trials and expert opinion is presented. The system enables doctors in a remote area to obtain a second opinion from doctors in the hospital using secured wireless telecommunication networks. Doctors can exchange securely medical images and video as well as other important data, and thus perform remote consultations, fast and accurately using a user friendly interface, via a reliable and secure telemedicine system of low cost. The quality of the transmitted compressed (JPEG2000) images was measured using different metrics and doctors opinions. The results have shown that all metrics were within acceptable limits. The performance of the system was evaluated successfully under different wireless communication links based on real data. 相似文献
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Polishuk A Arnon S 《Journal of the Optical Society of America. A, Optics, image science, and vision》2004,21(7):1307-1315
We derive a model that optimizes the performance of a laser satellite communication link with an optical preamplifier in the presence of random jitter in the transmitter-receiver line of sight. The system utilizes a transceiver containing a single telescope with a circulator. The telescope is used for both transmitting and receiving and thus reduces communication terminal dimensions and weight. The optimization model was derived under the assumption that the dominant noise source was amplifier spontaneous-emission noise. It is shown that, given the required bit-error rate (BER) and the rms random pointing jitter, an optimal transceiver gain exists that minimizes transmitted power. We investigate the effect of the amplifier spontaneous-emission noise on the optimal transmitted power and gain by performing an optimization procedure for various combinations of amplifier gain and noise figure. We demonstrate that the amplifier noise figure determines the optimal transmitted power needed to achieve the desired BER but does not affect the optimal transceiver telescope gain. Our numerical example shows that for a BER of 10(-9), doubling the amplifier noise figure results in an 80% increase in minimal transmitted power for a rms pointing jitter of 0.44 microrad. 相似文献