一种基于 PI 控制的数字低压差稳压器高速可调节模型

数字低压差线性稳压器由于可以在低电源电压下工作而被广泛使用。在数字低压差线性稳压器中,其利用模数转换器和积分器进行稳压操作。但是当负载出现瞬态电压变化,其稳定时间将会很长。在PI控制系统中,积分系数大的电路建立时间很短,会产生过冲,然后输出才会稳定。积分系数小的模型输出可以直接稳定,但是建立时间太长。提出了一种高速可调节电路模型,目的是利用电压传感器和时间数字转换器(TDC),并在电路中加入2种不同积分系数的积分器。首先利用电压传感器和时间数字转换技术(TDCT)实现模数转换以得到数字信号。随后判断数字信号与基准电压,在误差很大时,控制电路选择大积分系数,输出到PI控制;误差小时,控制电路选择小的积分系数,这样可以使电路结合不同积分系数电路的优点,从而达到同时缩短电路建立时间和稳定时间的目的。     

用RSVP-TE实现的ASON信令

描述怎样运用信令协议RSVP-TE实现自动交换光网络中动态地建立、删除连接的要求。仿真实现了前向资源预留(FRP)和后向资源预留(BRP)两种不同的信令方案,并收集了阻塞率(BR)、控制信道带宽(CCB: control channel bandwidth)及连接建立时间(CST: connection setup time)等相关统计量,比较了这两种方案的性能,发现在相同的仿真环境以及相同网络负载的情况下,后向资源预留的阻塞率性能优于前向资源预留,同时后向资源预留的连接建立时间以及使用的控制信道带宽都大于前向资源预留。     

Optimization of SIP Session Setup Delay for VoIP in 3G Wireless Networks

Wireless networks beyond 2G aim at supporting real-time applications such as VoIP. Before a user can start a VoIP session, the end-user terminal has to establish the session using signaling protocols such as H.323 and session initiation protocol (SIP) in order to negotiate media parameters. The time interval to perform the session setup is called the session setup time. It can be affected by the quality of the wireless link, measured in terms of frame error rate (FER), which can result in retransmissions of packets lost and can lengthen the session setup time. Therefore, such protocols should have a session setup time optimized against loss. One way to do so is by choosing the appropriate retransmission timer and the underlying protocols. In this paper, we focus on SIP session setup delay and propose optimizing it using an adaptive retransmission timer. We also evaluate SIP session setup performances with various underlying protocols (transport control protocol (TCP), user datagram protocol (UDP), radio link protocols (RLPs)) as a function of the FER. For 19.2 Kbps channel, the SIP session setup time can be up to 6.12s with UDP and 7s with TCP when the FER is up to 10 percent. The use of RLP (1, 2, 3) and RLP (1, 1, 1, 1, 1, 1) puts the session setup time down to 3.4s under UDP and 4s under TCP for the same FER and the same channel bandwidth. We also compare SIP and H.323 performances using an adaptive retransmission timer: SIP outperforms H.323, especially for a FER higher than 2 percent.     

Hot small-signal S-parameter measurements of power transistors operating under large-signal conditions in a load-pull environment for the study of nonlinear parametric interactions

This paper presents a setup that enables wide-band (in-band and out-of-band) measurements of hot small-signal S-parameters of nonlinear devices driven by a large-signal single tone (namely, the pump signal). A load-pull characterization is performed at the pump frequency (F/sub 0/), while hot small-signal S-parameters are measured with a perturbating signal at a frequency (f) by the use of a probe tone. Basically, the frequency of the probe tone is swept over a wide bandwidth (at the present time from 300 MHz up to F/sub 0//2). A higher frequency range, from near dc to KF/sub 0/, will be implemented in a similar manner. The measurement setup reported here is applied to on-wafer measurements of S-band HBTs. Hot small-signal S-parameter measurements versus large-signal load impedance and pump level will be shown. An application to the prediction of parametric oscillations will be demonstrated. A parametric oscillation predicted at 373 MHz is confirmed by spectrum measurements.     

On-call processing delay in high speed networks

In future BISDN networks, significant burdens will be placed on the processing elements in the network since call routing and admission policies will be more computationally intensive than those in present day networks. Thus, the bottleneck in future networks is likely to shift from the communication links to the processing elements. The delays at these elements are influenced by their processing capacity and factors such as; routing algorithms, propagation delays, admission control functions, and network topology. The goal of this paper is to characterize the behavior of these factors on the call setup time and accepted call throughput. This behavior is examined for three sequential routing schemes and two flooding routing schemes under various network parameters and different forms of admission control. The results of our study indicate that processing capacity and the admission control function can affect the call setup time and accepted call throughput significantly while propagation delay does not affect these performance measures significantly     

Factors affecting call setup time

The difference between call setup time and post dialling time is given. The factors affecting setup time (delay) are presented. Some of these factors depend on the network itself and the others on the behaviour of customers. The importance of call setup time in the future due to new ways of using the network are discussed.     

边沿触发器亚稳态现象的实验观测

在跨时钟域数据传输中,常因违反触发器的建立时间和保持时间要求而产生亚稳态现象,导致数据误码。为对亚稳态发生过程进行直观观测,利用所搭建的亚稳态观测平台,在建立时间区域对TTL维持阻塞型集成边沿触发器74LS74芯片和CMOS传输门型集成边沿触发器74HC74芯片分别进行了误码测试。测试结果表明,两芯片性能接近,在建立时间0.9～1.6ns区间存在0%～100%误码过渡带,能观测亚稳态过程的直观波形。测试过程中,发现触发器输入电平上跳变时,误码率在以上区间存在稳定的单调变化曲线。当触发器输入电平下跳变时,误码率会从0%瞬变到100%,实验未观测到过渡带。输入下跳变时,当延迟参量单向递增或递减时,瞬变区域不一样,存在回差现象。     

THz time domain monostatic radar cross section measurement of metallic plates and dihedrons

THz Radar Cross Section(RCS) measurement setup based on THz Time Domain Spectroscopy (TDS) is built to provide large scaled targets test ability in recent years. As calibrations, the metal plates and dihedrons are used in our experiments. The measurements are performed in a monostatic terahertz time-domain setup. The author proposed time domain and frequency domain calibration methods for angular RCS of calibrations, comparing the measurements with the theory to verify the ability of the time domain measurement setup.     

ASTN中连接建立时间问题分析

对基于SDH的ASTN中的连接建立时间进行了仿真,发现了采用泊松业务模型时,业务量越大,平均连接建立时间越小的问题,并进行了分析和研究。表明了连接建立时间的减少主要是由建立连接成功的业务平均路由长度变短造成的。     

Designing a CORBA-based high performance open programmablesignaling system for ATM switching platforms

ATM switching platforms are well suited for transporting multimedia streams with quality-of-service (QOS) requirements. This paper describes the system design of a high performance connection management system for xbind, a flexible open programmable signaling system for ATM switching platforms. The latency and throughput of call processing is improved by caching, message aggregation, and processing of requests in parallel. Using a set of general purpose UNIX work stations, we are able to attain a maximum throughput of close to 600000 call operations/h (setup and delete) with an average call setup time of 85 ms. With a low traffic load of 3600 call operations/h, an average call setup latency of 11 ms can be obtained. The system is adaptive. By adjusting various control parameters, the connection manager(s) can be dynamically configured to trade off between throughput and call setup time     

A layered broadband switching architecture with physical or virtualpath configurations

The authors describe a multilayer connection control architecture for broadband communications. A graph framework is introduced to describe network layers of network design, path configurations, dynamic call routing, burst switching, and asynchronous transfer mode (ATM) cell switching. These hierarchical layers of switching are performed at decreasing time scales, respectively. Switching at the higher layer is performed to reduce blocking at the next smaller time scale. A layered notion of equivalent bandwidth for satisfying layered grade-of-service parameters is introduced for making connections at these time scales. The authors then focus on the path configuration layer. Two path setup methods, namely, physical and virtual path setup, are described. Mathematical programs minimizing path bandwidth usage subject to meeting grade-of-service requirements are formulated for both methods. The relative merits of these methods are compared. In one example, physical path setup is shown to require roughly 50% more bandwidth than virtual path setup     

Improved EDF-based management of the setup of connections in opaque and transparent optical networks

The need to support the diverse quality-of-service (QoS) requirements of the ever-emerging Internet applications is a major challenge for optical network operators. This paper tackles such a challenge through the definition of a QoS-aware optical connection setup management scheme. The proposed scheme utilizes the Earliest Deadline First (EDF) queueing discipline to schedule the setup of optical connections that cannot be established due to lack of optical resources. The EDF-based approach aims at minimizing blocking probability while realizing QoS differentiation. Blocking probability reduction is realized through the insertion of blocked connection requests into a queue giving them thus a second chance with respect to network access. QoS differentiation on the other hand is achieved as follows. The blocked connection requests are ranked in the EDF queue according to their connection setup requirements, which are viewed as deadlines during connection setup. In this way, pending connection requests having shorter setup time requirements are guaranteed to experience better QoS compared to the ones having longer setup time requirements. The performance of the EDF-based strategy is analyzed through extensive simulations in the context of both opaque and transparent NSFNET network topologies. The reported results show that the proposed strategy yields remarkable reduction in terms of blocking probability while effecting QoS differentiation.     

An integrated routing and admission control mechanism for real‐time multicast connection establishment

There are two major difficulties in real‐time multicast connection setup. One is the design of an efficient distributed routing algorithm which optimizes the network cost of routing trees under the real‐time constraints. The other is the integration of routing with admission control into one single phase of operations. This paper presents a real‐time multicast connection setup mechanism, which integrates multicast routing with real‐time admission control. The proposed mechanism performs the real‐time admission tests on a cost optimal tree (COT) and a shortest path tree (SPT) in parallel, aiming at optimizing network cost of the routing tree under real‐time constraints. It has the following important features: (1) it is fully distributed; (2) it achieves sub‐optimal network cost of routing trees; (3) it takes less time and less network messages for a connection setup. Copyright © 2001 John Wiley & Sons, Ltd.     

Provisioning QoS in inter-domain traffic engineering

This work describes an architectural framework that allows inter-domain Traffic Engineering Label Switched Paths (TE-LSPs) with guaranteed quality of service (QoS) to be setup. Such TE-LSPs, called EQ-links, are setup by coordinating path computation elements (PCEs) of neighboring autonomous systems (ASs) along a pre-determined inter-AS path, computed through cooperative interaction between pairs of neighboring ASs. After defining the architectural requirements for the framework, we describe and analyze the Inter-AS Path Computation Protocol (IA-PCP), which computes an interdomain path at the AS level, i.e., selecting a sequence of ASs to the destination, based on a loose source routing approach. The results of the IA-PCP computations are then fed to the PCEs for complete path computation. The proposed architecture has been actually implemented within the testbed of the EuQoS project, which is aimed at enabling end-to-end QoS in the Internet. We report results related to the setup time of EQ-links, measured in the pan-European testbed of the EuQoS project, showing that path computation and setup takes an affordable time overhead.     

VSS based session setup mechanism in IMS

This paper proposes a novel session setup mechanism in IMS (IP Multimedia Subsystem) by introducing the functional entity termed VSS (Visitor Subscriber Server) which is used to provide registration and location management. The new mechanism aims at improving session setup procedure by a betterment of location management in IMS. Through the use of two-tier subscriber information database constituted by the HSS (Home Subscriber Server) and the VSS, the new mechanism seperates the registration procedure and location management from the S-CSCF (Serving-Call’Session Control Function), and makes them be handled by the VSS. At the same time, the new mechanism updates the signaling procedure of registration and session setup. With VSS based location management, the cost of registeration and session setup procedure as well as the delay of session setup procedure become lower. The cost and delay functions of the new session setup mechanism as well as the cost function of new registeration are deduced. Then, simulations and analysis verify that the performance of this new mechanism gets the benefit in cost and time.     

A new modular design for test and application PCBs of SAW RF filters to ensure precisely predictable filter characteristics

This paper presents the design of an optimized test and application setup for surface acoustic wave (SAW) RF filters. These structures have been investigated, including the test devices, by simulation techniques based on full-wave methods and common SAW simulation methods. In this paper, the simulation technique will be explained in detail, focusing on the interfaces of the simulation models. Parasitic electromagnetic effects in the test and application setup will be analyzed by simulation and measurement. This paper demonstrates the possibility of accurate performance prediction of SAW RF filters using specially designed test setups in the measurement and an optimized application environment, e.g., in mobile phones. Modular parts for such test setups and the application environment are discussed.     

A new approach for optical colored image compression using the JPEG standards

Image compression consists in reducing information volume representing an image. Elimination of redundancies and non-pertinent information enables memory space minimization and thus faster data transmission. The present work aims to improve the quality of the compressed image while minimizing the time required for compression by using the principle of coherent optics. We present an optical adaptation of the method of JPEG compression technique for binary, gray-level and color images. Illustrative simulations will be given at the end to validate our architecture and to evaluate the performance on different types of images (binary, gray and color). An optical implementation setup is proposed and validated experimentally.     

一种用于波长路由光网络的分布式快速波长预留协议

波长预留协议用于在光通道建立过程中预留和配置波长.目前已有的波长预留协议都把协议设计的目标定为降低网络阻塞率,没有一种协议设计把目标定为缩短光通道的建立时间和简化协议处理过程.然而更短的建立时间和更小的协议复杂度对于未来极其动态的光网络却是非常重要的.提出了一种新颖的用于波长路由光网络的分布式快速波长预留协议-目的端预留协议,它在保证网络阻塞率可以接受的前提下,不仅可以降低连接建立时间,还可以减少控制节点处理器需要处理的信令消息数量.仿真结果证明了这一点.     

Finite-point method for efficient timing characterization of sequential elements

Timing characterization of sequential elements, such as latches and flip-flops, is one of the critical steps for timing closure in the pipelined design. Traditional characterization of setup and hold time constraints is computationally intensive, due to the demand on high accuracy in monitoring the operation failure. To improve the efficiency, this work proposes a finite-point based method for the characterization of setup and hold time constraints. The finite-point method identifies several critical data points in the non-linear curve of timing characteristics, and abstracts the essential setup/hold information from them. Moreover, compact models are derived for each point, further reducing the computation cost. The proposed method is general for all sequential elements in the standard cell library. It is comprehensively validated using benchmark circuits at 45 nm node. Experimental results demonstrate approximately 25× reduction in characterization time, with the prediction error in setup and hold time within 9% of FO₄ nominal delay, as compared to that of SPICE simulation results.     

A programmable NMOS DRAM controller for microcomputer systems with dual-port memory and error checking and correction

An NMOS DRAM controller for use in microcomputer systems based on the iAPX-86 and iAPX-286 microprocessor families or on the Multibus system bus is described. The controller provides complete support for dual-port memories and memories with error checking and correction. The controller has programmable attributes for configuring it to the particular requirements of the system. The controller uses parallel arbitration to minimize arbitration delay. A memory cycle will start on the same clock edge that samples a command if the cycle has been previously enabled. Novel logic and circuit design techniques have been used to achieve 16 MHz operation, 20 ns input setup time, and 35 ns output delay time.