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121.
A. M. Bck D. C. Carpenter A. P. Gallois 《International Journal of Satellite Communications and Networking》1990,8(2):111-115
The requirement for a model of FM-TV spectra in the planning procedure of satellite communication systems is introduced. Based on long-term measurements of live TV channels, statistical properties of video spectra are examined and probability distributions for the luminance and chrominance components are proposed. The spectrum of the frequency-modulated signal is then derived, and signal distortion due to bandlimiting is calculated. Adjacent and cochannel interference effects are also investigated, with example cases illustrating influences of subcarrier loading and energy dispersion. The proposed model, which describes FM-TV spectra in terms of random variables, makes it possible to examine relative effects of system parameters, and will, therefore, be of benefit in the planning of new satellite services. 相似文献
122.
陈如明 《电信工程技术与标准化》2000,(5):5-10
本文论述了当前全球无线通信发展中的六大新走势,即市场走势规模化,网络走势全球化,业务走势数据化,技术走势宽带化,接入走势普遍化以及知识走势经济化。 相似文献
123.
S. V. Pappu 《Optics & Laser Technology》1989,21(5)
A state-of-the-art review on holographic optical elements (HOE) is presented in two parts. In Part I a conceptual overview and an assessment of the current status on the design of HOE have been included. It is pointed out that HOE development based on the use of squeezed light, speckle, non-linear recording, comparative studies between optics and communication approaches, are some of the promising directions for future research in this vital area of photonics. 相似文献
124.
本文概述了军用光纤通信元器件及系统研制和开发近况;分析了军用环境对通信系统及元器件的要求;着重介绍了美国海、陆、空三军对光纤在军事上应用的开发计划;阐述了军用市场及投资情况并对市场发展趋势作了预测。 相似文献
125.
Ahmed El Shafie Tamer Khattab Amr El‐Keyi Mohamed Nafie 《Wireless Communications and Mobile Computing》2016,16(2):166-176
In this paper, we consider a cognitive scenario where an energy harvesting secondary user shares the spectrum with a primary user. The secondary source helps the primary source in delivering its undelivered packets during periods of silence of the primary source. The primary source has a queue for storing its data packets, whereas the secondary source has two data queues: a queue for storing its own packets and the other for storing the fraction of the undelivered primary packets accepted for relaying. The secondary source is assumed to be a battery‐based node, which harvests energy packets from the environment. In addition to its data queues, the secondary user has an energy queue to store the harvested energy packets. The secondary energy packets are used for primary packets decoding and data packets transmission. More specifically, if the secondary energy queue is empty, the secondary source can neither help the primary source nor transmit a packet from the data queues. The energy queue is modeled as a discrete‐time queue with Markov arrival and service processes. Because of the interaction of the queues, we provide inner and outer bounds on the stability region of the proposed system. We investigate the impact of the energy arrival rate on the stability region. Numerical results show the significant gain of cooperation.Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
126.
Location‐based distributed caching for device‐to‐device communications underlaying cellular networks
Aiqing Zhang Lei Wang Liang Zhou 《Wireless Communications and Mobile Computing》2016,16(13):1859-1875
Device‐to‐device (D2D) communications have been viewed as a promising data offloading solution in cellular networks because of the explosive growth of multimedia applications. Because of the nature of distributed device location, distributed caching becomes an important function of D2D communications. By taking advantage of the caching capacity of the device, in this work, we explore the device storage and file frequent reuse to realize distributed content dissemination, that is, storing contents in mobile devices (named helpers). Specifically, we first investigate the average and lower bound of helper amount by dividing the network into small areas where the nodes are within each other's communication radius. Then, optimal helper amount is derived based on average helper amount and network topology. Subsequently, a location‐based distributed helper selection scheme for distributed caching is proposed based on the given optimal helper amount. In particular, nodes are selected as helpers according to their locations and degrees, and contents are placed in the manner for maximizing total user utility. Extensive simulation results demonstrate the factors that affect the optimal helper amount and the total user utility. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
127.
多天线技术是目前无线通信领域最主要突破之一,在此主要论述了多天线技术的原理和多天线技术的不同实现方法,并讨论了多天线技术在LTE系统中的应用。 相似文献
128.
宽带无线通信系统在应急指挥系统的应用分析 总被引:1,自引:0,他引:1
本文依据处理突发事件时应急指挥系统的特点,对基于该系统的宽带无线通信系统的频率选择、接入方式、功能特点等进行分析研究. 相似文献
129.
130.
优化卫星通信技术研究 总被引:2,自引:2,他引:0
卫星通信相关的费用包括固定投资和运行费用,从卫星通信经济学的角度出发,优化卫星通信可以节省成本。首先介绍了VSAT卫星通信网的网络拓扑及组网方式;其次从卫星通信的调制及编码技术两个方面分别对卫星通信进行优化,重点对格状编码调制、LDPC码、Turbo码与级联码编码技术、载波迭加技术进行了研究,并分别指出了各自的优点;最后对优化卫星通信技术的应用前景进行讨论。 相似文献