面向未来的无线光通讯

目前的最后一公里宽带接入解决方案是光纤和无线技术。光纤以可靠性及高带宽著称,但作为最终解决方案,实施起来却很困难、缓慢并且花费高昂。无线技术虽然提供了快速安装和比光纤低廉的价格,但带宽却非常有限。同时,无线传输不安全并且需要昂贵的频率执照。无线光通讯的出现弥补了两者应用     

如何为光纤水平布线系统选择最好的介质？

越来越多的用户开始趋向于在网络的水平布线中采用光纤产品，实现光纤到桌面，甚至连接到无线接入点。对更高带宽的需求推动了光纤水平布线系统的安装。     

光纤无线电系统中的新型探测法研究

光纤无线电系统利用光载波携带毫米波信号在中心站和基站之间构成上行和下行传输链路,能够满足宽带无线接入系统的需求.利用光外差的方法产生毫米波信号是光载毫米波最简单和直接的方式.分析了在光纤无线电系统中利用光纤布拉格光栅从可调谐激光器中反射出两束相位近似相等的相干光,采用平衡探测产生了毫米波信号,降低了相位噪声和强度噪声对产生的毫米波信号的影响.     

浅析局域网中的几种传输介质

介绍了同轴电缆、双绞线、光纤和无线介质,为学习局域网中的传输介质提供了良好的帮助。     

无线MMX技术在MPEG-4中的应用

无线MMX(Wireless MMX Technology)是用来提高移动多媒体计算性能的技术。针对无线视频通信的应用，研究了采用无线MMX来实现MPEG-4视频编解码的技术；通过对无线MMX体系结构和指令特点的分析，从指令优化和算法优化两方面给出了MPEG-4编解码器优化的关键策略。经过优化的编解码器可很好地满足无线视频通信要求。     

基于分布式光纤技术的煤矿巷道顶板监测系统

当前巷道顶板变形监测方式为基于井下工业环网的在线实时监测,采用电子式和光纤光栅式的位移传感器并以无线方式连接,存在有较多监测盲点、误差较大、依靠连续供电等问题。针对上述问题,设计了一种基于分布式光纤技术的煤矿巷道顶板监测系统。该系统以布里渊光时域反射计(BOTDR)作为数据采集和分析的核心监测工具,采用5 mm钢绞线光纤作为感测光纤,以锚杆、锚索为固定点布设光缆,通过顶板光纤的应变变化来监测顶板变形状况,实现了对煤矿巷道顶板的实时在线分布式监测。现场应用结果表明,光纤应变变化能够实时准确地反映顶板变形情况,基于光纤应变的顶板监测结果与顶板离层仪监测结果、十字法观测结果一致。用光纤应变表征顶板变形程度消除了人为因素和断电等影响,保证了监测结果的客观性,这种长距离、耐腐蚀、抗干扰、无需供电的分布式光纤应变监测方式为煤矿提供了一种全新的巷道监测手段。     

基于OCDMA系统的光纤光栅频谱特性分析

该文研究了光纤布拉格光栅阵列的反射谱,分析了几种不同的切趾函数对旁瓣的影响。讨论了啁啾光栅的反射谱性能,结论表明了啁啾系数和折射率调制深度是影响啁啾光栅反射谱特性的主要因素,通过切趾技术可以改善啁啾光栅的性能,使其适用于OCDMA系统。重点分析了相移超结构光纤光栅(SSFBG)的原理,并设计出了一种码长31的gold码SSFBG编解码器,仿真了其反射谱曲线。     

基于光纤接入家庭无线局域网的探析

随着信息技术的发展以及人们对信息的需求,家庭各成员共享Internet连接显得尤为重要,并且无线局域网的优越灵活性和便捷性在网络应用中发挥着举足轻重的作用,该文以光纤接入家庭无线局域网为例,分析家庭无线局域网的优缺点和常见故障的分析,并提出安全措施。     

清华同方紧盯“最后一公里”

目前我国在社区宽带接入“最后一公里”采用的大多是10兆以太网光纤技术,需要进行光纤的铺设,价格比较昂贵,而且实施起来工期较长。而相比之下,如果使用无线技术接入则具有更为强大的优势:不需要布线,只需在社区内建设一个与骨     

超分辨率扫描成像系统图像无损压缩算法研究

针对光纤耦合的超分辨率扫描成像系统因传输的数据量过大而导致的丢帧现象,引入无损压缩技术对耦合的图像数据进行压缩传输。系统采用可逆的整数小波变换和集合树分裂算法组成的无损压缩方案,并根据耦合成像的特性,对耦合图像进行分割处理,以满足系统对压缩效率的要求。图像的平均压缩比达到了2.3,传输的波特率降到200 Mbps,目前系统提供的256 Mbps的带宽已经完全满足需求。实验结果表明,无损压缩编解码器的引入,降低了光纤耦合系统对传输带宽的要求,并保证了图像的完全重构。     

用于高密度信息存储的RLL(4,11)编码设计

在分析现有光盘调制码的基础上，提出了一种3／8码率的游程长度受限码RLL(4，11)编码，比现有的EFM调制码的代码密度高出9．4％，并为这种编码设计了相应的编码器．在编码器设计中，提出了一种试探性的算法对状态图进行简化，将状态数降至14个，从而大大简化了编码和解码过程．还分析了这种编码的解码方法及其块解码器的窗口大小，估计了预期值的上限．由于这一编码在抑制直流成分上的不足，对应用此编码的系统进行了界定，最后给出了这个新编码的适用领域．     

基于Hi3510设计与实现视音频编解码器

针对数字视频监控领域的需求,研究开发了一种基于Hi3510的嵌入式视音频编解码器。提出了编解码系统的总体设计方案。给出基于Hi3510的系统硬件设计方案,包括:CPU、D/A、实时时钟、以太网接口和电源等5个模块。给出基于嵌入式操作系统的应用软件设计方案,重点是采集、编码、传输和控制等4个类的设计。基于上述方案实现了视音频编解码器系统。测试结果表明,这种编解码器用于数字视频监控,提高了系统的稳定性和可靠性,可以满足远程多用户网络视频监控的需要。     

Communication Scheduling and Remote Estimation With Adversarial Intervention

We study a communication scheduling and remote estimation problem within a worst-case scenario that involves a strategic adversary. Specially, a remote sensing system consisting of a sensor, an encoder and a decoder is configured to observe, transmit, and recover a discrete time stochastic process. At each time step, the sensor makes an observation on the state variable of the stochastic process. The sensor is constrained by the number of transmissions over the time horizon, and thus it needs to decide whether to transmit its observation or not after making each measurement. If the sensor decides to transmit, it sends the observation to the encoder, who then encodes and transmits the observation to the decoder. Otherwise, the sensor and the encoder maintain silence. The decoder is required to generate a real-time estimate on the state variable. The sensor, the encoder, and the decoder collaborate to minimize the sum of the communication cost for the sensor, the encoding cost for the encoder, and the estimation error for the decoder. There is also a jammer interfering with the communication between the encoder and the decoder, by injecting an additive channel noise to the communication channel. The jammer is charged for the jamming power and is rewarded for the estimation error generated by the decoder, and it aims to minimize its net cost. We consider a feedback Stackelberg game with the sensor, the encoder, and the decoder as the composite leader, and the jammer as the follower. Under some technical assumptions, we obtain a feedback Stackelberg solution, which is threshold based for the scheduler, and piecewise affine for the encoder and the decoder. We also generate numerical results to demonstrate the performance of the remote sensing system under the feedback Stackelberg solution.      

三值光计算机编码器与解码器原理的实验研究

用普通分离元件(偏振片、液晶、透镜、分光镜)完成了一位三值光信号的编码与解码实验。实验证实了三值光计算机编码器与解码器原理的正确性和可行性。该实验为实现三值光计算机其他核心部件的实验奠定了基础。     

三代移动通信变速率语音编解码AMR-WB+算法优化

首先简要介绍了AMR-WB+语音压缩算法的基本原理,描述了AMR-WB+编解码流程;然后通过两类优化策略对AMR-WB+算法进行优化;最后给出了优化前后编解码复杂度比较,并对结果进行了分析。     

一种Turbo乘积码编译码器的设计与实现

分析了Turbo乘积码的线性编码和基于Chase算法的软输入软输出迭代译码方法,讨论了硬件可实现的低延迟编码器、译码器应具有的结构特点,并采用此方法设计了1个长度为1024bit、码率66％的Turbo乘积码。该编码器工作时钟和输入数据速率相同,译码器则需要3倍于输入数据速率的时钟,译码器理论吞吐率可达60Mb／s。实测结果表明,其性能和仿真值相差不大于0．4dB。     

数字水印信道分类及其信道容量分析

在数字水印理论模型研究过程中,将数字水印系统看作一种通信系统,将信道的概念引入数字水印系统,形成数字水印信道,通过对水印信道容量的研究来指导数字水印系统中嵌入算法及攻击算法的设计。基于带边信息的水印信道模型,根据水印编码方和水印译码方是否知道水印的边信息(即信道状态信息),该文将数字水印信道归纳为4类：编译码双方都不知道边信息的水印信道,仅编码方知道边信息的水印信道,编码方和译码双方都知道边信息的水印信道,仅译码方知道边信息的水印信道。对相应的水印信道容量进行了分类讨论,结果证明,这一类含水印强度因子的水印信道容量是水印强度因子的单调函数。     

A novel weight initialization with adaptive hyper-parameters for deep semantic segmentation

The semantic segmentation process divides an image into its constituent objects and background by assigning a corresponding class label to each pixel in the image. Semantic segmentation is an important area in computer vision with wide practical applications. The contemporary semantic segmentation approaches are primarily based on two types of deep neural networks architectures i.e., symmetric and asymmetric networks. Both types of networks consist of several layers of neurons which are arranged in two sections called encoder and decoder. The encoder section receives the input image and the decoder section outputs the segmented image. However, both sections in symmetric networks have the same number of layers and the number of neurons in an encoder layer is the same as that of the corresponding layer in the decoder section but asymmetric networks do not strictly follow such one-one correspondence between encoder and decoder layers. At the moment, SegNet and ESNet are the two leading state-of-the-art symmetric encoder-decoder deep neural network architectures. However, both architectures require extensive training for good generalization and need several hundred epochs for convergence. This paper aims to improve the convergence and enhance network generalization by introducing two novelties into the network training process. The first novelty is a weight initialization method and the second contribution is an adaptive mechanism for dynamic layer learning rate adjustment in training loop. The proposed initialization technique uses transfer learning to initialize the encoder section of the network, but for initialization of decoder section, the weights of the encoder section layers are copied to the corresponding layers of the decoder section. The second contribution of the paper is an adaptive layer learning rate method, wherein the learning rates of the encoder layers are updated based on a metric representing the difference between the probability distributions of the input images and encoder weights. Likewise, the learning rates of the decoder layers are updated based on the difference between the probability distributions of the output labels and decoder weights. Intensive empirical validation of the proposed approach shows significant improvement in terms of faster convergence and generalization.

     

BCH编译码器在NANDFlash控制器中的应用研究

针对空间应用对固态存储器中ECC校验在计算速度和纠错能力上的要求,提出了一种应用在NANDFlash控制器中的高速并行BCH编译码器。文中采用了一种独特的译码器架构,并改进了计算伴随式的算法,先利用编码电路计算出伴随多项式,再利用译码电路计算出伴随式。与直接计算出伴随式的译码器相比,虽然译码时间略有增加,但却能明显减少资源的占用量。结合采用其他一些节省资源和提高运行速度的措施,使该译码器的设计更适应空间应用的需要。     

Joint optimization of continuity and quality for streaming video

This paper aims to reduce the amount of prebuffering required to ensure a maximum video continuity in streaming. Current approaches do this by slowing the playout frame rate of the decoder, this is known as adaptive media playout (AMP). However, doing this introduces playout distortion to the viewers as the video is played slower than its natural playout rate. We approach this by proposing a frame rate control scheme that jointly adjusts the encoder frame generation rate of the encoder and the playout frame rate of the decoder. In addition to using AMP to improve video continuity, we also allow the encoder to increase the encoder frame generation rate. This means the encoder will be sending more frames to the decoder to quickly increase the number of frames available at the playback buffer, thus lowering the chance of buffer underflow which causes discontinuity in video playback. At the same time, the increase in the number of frames at the playback buffer may mean that the decoder does not need to use AMP to delay the playback, thus lowering the playback distortion. However, the increase in encoder frame generation rate comes at a price because frame quality will need to decrease in order to meet the constraint on available network bandwidth. This implies that the scheme needs to find the optimal trade-off between frame quality, playout distortion and video continuity. To do that, we characterize the frame rate control problem using Lyapunov optimization. We then systematically derive the optimization policies. We also show that these policies can be decoupled into separate encoder and decoder optimization policies, thus allowing for a distributed implementation. Simulation results show significant reductions in the prebuffering requirements over a scheme that perform no frame rate control and lower playout distortions compared to the AMP schemes, while exhibiting a modest drop in frame quality.