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本文对微波副载波用电视群信号调频的光纤传输中的信噪比平衡问题进行了分析,推导出VSB-AM信号在解调后的信噪比表达式,引入了信噪比恶化系数的概念.为了实现多路VSB-AM信号间的信噪比的平衡,相应的微波副载波频偏应有确定的比例关系. 相似文献
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本文研究了采用光纤微波副载波复用技术对多路电视信号进行长距离中继传输的基本限制和主要技术。分析了在电继传输时,PAL—D制电视传输频道数限制及微波副载波的最佳频带。讨论了单模光纤色散和衰耗特性对光系统的要求。给出了由光波层、微波层、电视层共三个层次组成的系统单元的方案。并对系统单元做了一些基本实验。 相似文献
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本文提出一个新的多路复用微波副载波星形网络。该网络总共只使用两个激光器作为每个用户外差探测的信号和本振光源。每个激光器功率通过一个无源星形网络分配给位于不同地方的每个用户。该网络使用微波副载波复用和外差探测,每个用户使用一个Mach-Zehnder相位调制器用微波副载波调制光信号。使用电调谐选择副载波信道。本文研究表明网络容量可以支持80个用户。所有用户只分享二个激光器提供的光,可以大大减小网络的复杂性和成本,因此该网络很容易被用户所接受。 相似文献
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微波设备中的副载波分盘包括副载波调制盘和副载波解调盘.这两类盘数量大,故障率高,检修任务重.传统的办法是利用转接板在微波架上进行"在线"检修.但这样做操作起来不方便,且影响设备的正常运行,不利于播出安全.因此,笔者设计了如下的副载波分盘检修台. 相似文献
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介绍了一种便携台式射频微波副载波复用的光通信系统,其特点是体积小、性能稳定、适用范围广、复用接口多、用户数多等等。文中就系统内各单元的组件及特点作了描述,最后给出了系统部分实验结果。 相似文献
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卫星电视与地面微波传输参数的差异及其接收设备替代的几个问题湘西自治州广播电视局刘崇尧卫星电视信号与地面微波信号都是由视频、声音副载波组成的基带对载波调频再发射出去的微波信号。目前,卫星电视接收设备第一中频与1.4GHz微波频率基本吻合,所以在某些情况... 相似文献
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为了研究多脉冲视频累积提高激光回波探测信噪比的途径的有效性,以噪声的统计特性为基础,理论分析了多脉冲视频累积提高激光回波探测信噪比的基本原理,并通过数值仿真和实验验证了视频累积提高激光探测信噪比的可行性。结果表明,当脉冲累积数N较小时,通过多脉冲视频累积可以提高激光回波探测的信噪比N1/2倍,与视频累积结论一致;但当N大于一定值之后,由于系统带宽、A/D转换精度和采样率等因素的影响,使信噪比随累积脉冲数的变化明显偏离了N1/2指数规律。该研究为进一步通过多脉冲视频积累探测改善激光回波探测的信噪比,实现强噪声背景下的弱信号检测提供了理论和实验基础,对提高半导体激光测距系统的探测能力有着直接的指导意义。 相似文献
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Methods used to characterize the degradation of symbol error rate (SER) vs. carrier-to-noise ratio (C/N) performance of several different components of systems that broadcast digital video signals are presented. The techniques are based on repetitively sampling and then digitizing the IQ constellation at baseband. Mathematically different levels of noise calculated relative to the carrier are added to the digitized constellation. Examination of the resulting distributions of noise versus error thresholds allows the estimation of SER vs. C/N in the absence of any error correction in the receiver. The effects of IF bandwidth and transmit and receive filters are also taken into account. The estimated SER vs. C/N can be plotted and compared to the theoretical SER vs. C/N for the modulation format, IF bandwidth, and transmit and receive filters in the system under test 相似文献
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The paper presents a rather new approach of electrooptic modulation of light suitable for coherence multiplexingN transmission channels. A parallel array ofN electrooptic multiplexers powered by multimode semiconductor lasers is used for imprinting the signals on light simultaneously. It is shown that the electrooptic multiplexers have to generate optical time delays whose optimal values are ruled by the sequence1/2N cdot delta f, 1/N cdot delta f, 3/2N cdot delta f , etc., wheredelta f is the intermodal separation of the laser longitudinal modes. The performance of the system is discussed in terms of crosstalk, number of possible channels, and signal power. The demonstration of the method is reported in the area of optical communications with the transmission of base-band video signals. 相似文献
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国内外许多公司都在开发有关MPEG-4视频标准的产品,最具代表意义的即是数字视频录像机(DVR)。为了缩短开发周期,这里介绍基于嵌入式Linux操作系统,应用专用音视频编解码芯片AT2042实现数字视频录像机功能,该系统实现MPEG-4视频标准高级框架的编解码器,并在此基础上添加数字硬盘的功能,例如编码存储、解码播放、快进、快退和暂停等功能。最后给出系统的实际运行的测试结果。该系统已实现对视频数据的编、解码,且实现MPEG-4/MPEG-2/MPEG-1 H.263视频标准,并已成为成型产品推向市场。 相似文献
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在三网融合的大环境下,德清广电在拓展宽带业务的同时大力发展IP增值业务,承接了德清县党政高清视频会议系统,该高清视频会议系统以1个主会场和N个分会场为载体,实现各个会场之间的双向音视频传送,达到面对面视频会议的需求。 相似文献
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全数字视频对讲系统音视频信号的采集、编解码等信号处理是分别进行的,信号在传输过程中将产生不同的延时,这就导致在视频通话过程中出现唇音不同步的现象.提出一种基于非介入式测量技术的全数字视频对讲系统的唇音同步测试方法,适用于对音视频同步性能要求较高的实时全数字视频对讲系统,且不受通信接口、传输协议、加密通信技术等限制. 相似文献
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Harmonic broadcasting for video-on-demand service 总被引:5,自引:0,他引:5
Li-Shen Juhn Li-Ming Tseng 《Broadcasting, IEEE Transactions on》1997,43(3):268-271
Using conventional broadcasting, if we want to support a 120-minute popular movie every 10 minutes, we need 12 video channels. Assuming the set-top box at the client end can buffer portions of the playing video on a disk, pyramid broadcasting schemes can reduce the bandwidth requirements to 5.7 channels. We present a new scheme which only needs 3.2 channels. For a movie with length D minutes, if we want to reduce the viewer waiting time to D/N minutes, we only need to allocate H(N) video channels to broadcast the movie periodically, where H(N) is the harmonic number of N, H(N)=1+1/2+…+1/N. In order to support video-on-demand service for a popular movie, the new scheme greatly reduces the bandwidth requirements 相似文献
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Internal business networks are expected to present an economic area of application for broad-band communications. A star network with switches optimized for various services is envisaged. An asynchronous switch for video in square wave frequency modulation (SWFM) format can provide a practical solution for full bandwidth switched video services. A transmission scheme is described which combines a SWFM video service together with synchronous PCM data and voice services, asynchronous data up to 9.6 kbauds and network clocks at both 2 MHz and 160 kHz for ISDN, so that all services destined for one terminal site may be transmitted in binary format on cable or fiber. An experimental link is described which provides up to 10 Mbit/s data capacity together with the video service. The hardware is constructed with 74HC family CMOS. An analysis of the effects of data modulation on video quality is given. Measurements of video S/N and distortion are reported. Measured bit-error rate in a 64 kbit/s data channel is reported. The measurements relate to a coaxial cable link with link lengths from 200 to 400 meters. 相似文献
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H.264/AVC是由国际电信联盟(ITU)和国际标准化组织(ISO)共同制定的新一代视频编码标准,首先指出目前采用其他标准设计视频监控系统的不足,介绍和分析H.264/AVC采用的新编码技术,最后根据视频监控系统的特点,主要讨论H.264/AVC在视频监控应用中涉及的关键技术,包括SP/SI帧技术和分层编码技术。 相似文献
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对噪声不敏感的视频同步分离 总被引:2,自引:0,他引:2
介绍数字视频处理中时钟发生器同步锁相的必要性。分析同步不稳对图像处理的影响。在大背景噪声下,提取同步信号的方案。实验表明,在极低估噪比下,可以使数字系统稳定同步。 相似文献