WDM PON光信道分配方法的研究

在WDM PON中,为了使各ONU能通过多个光信道传输数据分组,在ONU需配置可调谐光发射器,而调谐时间的长短不仅与光发射器的成本密切相关,而且对网络吞吐率、时延等参数有较大影响.通过调整光信道分配方法,当光发射器具有较长调谐时间的情况下,使网络参数获得较大改善.     

GPS矢量跟踪建模与抗干扰性能分析

对GPS矢量跟踪环路的抗干扰性能进行了深入讨论。建立了矢量延迟锁定环及矢量频率锁定环的系统模型及带宽模型,分析说明了矢量跟踪环路能够自适应调整噪声带宽,从而适应不同强度的干扰环境;结合环路内的测量误差,计算得到矢量跟踪环路的干信比容限,确定了复杂环境中矢量跟踪环路的抗干扰性能。通过与标量跟踪的比较分析表明,GPS矢量跟踪具有更强的抗干扰能力。     

灵巧弹药感应装定系统基带码型特征分析及应用研究

为满足灵巧弹药大数据量、高速率、高可靠性的装定需求,实现灵巧弹药的数据装定,针对感应装定系统的信道特性,从能量传输有效性、功率谱与带宽、码元同步误差对误码率的影响3个方面, 对单极性不归零码、单极性归零码、密勒码、曼彻斯特码、传号反转码、变形密勒码6种数字基带码型进行理论分析、仿真和实验室试验。仿真与试验结果表明：低电平间隙因子为0.3的变形密勒码具有很好的能量传输有效性、较为丰富的时钟定时信息和较低的误码率,适合选做发送信道的基带码型;曼彻斯特码是一种自同步相位编码,具有丰富的时钟定时信息、较低的误码率,适合选做反馈信道的基带码型;实验室试验结果与理论仿真结果具有一致性。     

基于反馈重传的网络信道编码多播研究

在无线网络中,采用现用机制(ARQ)带宽利用率并不是很高。针对这种情况,提出了一种将网络编码思想融入到重传机制中的方式———NC-ARQ,来提高单跳无线网络(例如WiMAX、WLAN等)的带宽利用率。此外,高误比特率下,在NC-ARQ基础上将网络编码与信道编码结合,即NC-HARQ,可以进一步改善无线网络的带宽利用率。分析了在传统反馈重传机制和信道编码中加入网络编码后,多播网络带宽利用率的增益。理论和仿真都证明了加入网络编码后,反馈重传机制的带宽利用率能得到较大改善。     

On Handoff Performance for an Integrated Voice/Data Cellular System

One of the key challenges in the design of bandwidth allocation policies for a multi-services mobile cellular network is to guarantee the potentially different Quality of Service (QoS) requirement from diverse applications, while at the same to ensure that the scarce bandwidth be utilized efficiently. Complete Sharing (CS) and Dynamic Partition (DP) schemes have been shown as viable techniques for managing the bandwidth. However, there has been no study that compares their respective performance, which is the focus of this paper. Specifically, in this paper, through both analysis and simulation, we demonstrate that both schemes can achieve comparable performance by proper manipulation of control parameters. The tradeoff is that DP scheme can more easily achieve the target QoS requirement, at the expense of some over-provisioning, thus can potentially lead to less channel efficiency when comparing to a CS based scheme.     

一种具有超远寄生阻带的带阻滤波器的设计

本文介绍了一款具有超远寄生阻带的紧凑型带阻滤波器。在传统的带阻滤波器设计方法基础上,本文通过谐 振腔加载电容来实现小型化,并且在电容圆盘上挖槽实现了超远的寄生阻带。首先设计一款具有超远寄生阻带的单腔, 之后将几个这种单腔串联起来构成了带阻滤波器。为了阐述设计过程,设计了一款中心频率为2.35GHz、相对带宽 4.2%、寄生阻带大于12.5GHz 的带阻滤波器,其过渡带为100MHz,阻带抑制大于40dB。     

谈开口箱

通过分析开口箱的有关问题,引导出开口箱名称的来由和两种工作原理;介绍了开口箱的设计、制作、材料和结构,以及开口箱的3种调整方法和各自的特点;最后介绍了开口箱的阻抗曲线与Q值和听感的关系。     

有限脉冲响应理论在交错滤波器设计中的应用

利用数字信号处理理论,设计不等带宽晶体型交错滤波器。运用琼斯矩阵理论计算晶体型交错滤波器的光谱透射率表达式, 在此基础上利用数字信号处理中的Z变换方法对其进行简化, 使其满足有限脉冲响应（FIR）表达式, 继而利用数字信号处理中的FIR理论设计不等带宽型交错滤波器。其中晶体和检偏器的偏角根据系统光谱透射率的表达式反向推解求出。设计了窄口和宽口输出谱3 dB处带宽比为1∶2的50 GHz不等带宽交错滤波器, 并给出了宽口和窄口输出光谱在0.5 dB处带宽宽度、隔离度和陡度的各组参数; 比较了在同种阶数下运用不同FIR设计所得的结果, 分析了不同方法对于输出透射光谱波形特性的优缺点。     

Performance evaluation of TCP under dynamic allocation scheme for down‐link transmission rate in W‐CDMA systems

IMT‐2000 has attracted much attention as the Next Generation Mobile Communication System. IMT‐2000 can provide high‐bit‐rate data communication service, so that a great number of packets conveyed by TCP (transmission control protocol) can be transmitted over a wireless link. W‐CDMA, standardized in 3GPP (which standardizes IMT‐2000), allows dynamically allocating transmission rates to flow over a wireless link in response to a changing FER for each flow, which is thought to be essential for a next generation mobile communication system. Therefore, in this paper, we study the characteristics of the dynamic allocation scheme when TCP flows share a wireless link, and, in particular, we focus on the throughput performance of these TCP flows. First, we use simulations to examine the effectiveness of the dynamically allocating down‐link transmission rate for TCP flows in response to changing the frame error rate (FER). Through the simulation results, we will show how it can improve the total throughput performance of TCP flows. Furthermore, we can obtain an effective way to allocate transmission rates to flows with different FERs in order to achieve high total throughput. Finally, we will deal with a case of multiple flows from a fixed host to a mobile host. In actual networks, this often happens. In this case, we will show that the total throughput of TCP flows degrades less than in the single‐flow case, even when the FER is high. Copyright © 2004 John Wiley & Sons, Ltd.     

梯度折射率塑料光纤上的波分复用数据传输试验研究

首先介绍了梯度折射率塑料光纤的制造方法和性能;其次阐述了在梯度折射率塑料光纤上进行波分复用数据传输试验的最新研究成果。