Electronic Implementation of Multirate Sigma-Delta Modulators Using CMOS Technologies

Multirating has been recently proposed to reduce the frequency rate of the first integrator(s) of a single-loop, or the first stage(s) of a cascade, Sigma-Delta modulator (SDM). This is a promising technique for the design of high speed, low-power modulators, as the first integrator (or stage) in the chain primarily determines the performances of the modulator, as well as its power consumption. This paper presents the first implementation of a 2nd-order multirate SDM, showing different circuit solutions. The experimental results obtained with a prototype in a standard 0.6 μm CMOS technology shows that different clock rates can be selected for each integrator of a SDM. Alfredo Pérez Vega-Leal was born in Seville, Spain. He received the Telecommunications Engineering and Ph.D. degrees from the University of Seville, Seville, Spain, in 1998 and 2003, respectively. Since 1995, he has been with the Department of Electronic Engineering, School of Engineering, University of Seville, as research student and became an Associate Professor in 1999. His research interests are related to low-voltage low-power analog circuit design, A/D and D/A conversion. Francisco Colodro was born in Peal de Becerro (Jaén), Spain, in 1968. He received the Ingeniero de Telecomunicación degree from the University of Vigo, Vigo, Spain, in 1992, and the Ph.D. degree from the University of Sevilla, Sevilla, Spain, in 1997. In 1992 he joined the Department of Electronics Engineering, University of Sevilla, where he is currently and Associate Professor. His research interests are in the architectural study of Σ Δ modulators, the implementation of ADCs based on Σ Δ modulators, and application of electronic circuits and systems to communication. Marta Laguna was born in Seville, Spain. She received the Telecommunications Engineering degree from the University of Seville in 2002. She is currently working toward the Ph.D. degree. Her doctoral work focuses on the design of continuous-time sigma-delta modulators. Since 2001, she has been with the Department of Electronic Engineering, School of Engineering, University of Seville, as research student and became an assistant teacher in 2004. Her research interests are high-speed analog-to-digital converters and sigma-delta modulators. Antonio Torralba (M'89–SM'02) was born in Sevilla, Spain, in 1960. He received the electrical engineering and Ph.D. degrees from the University of Sevilla in 1983, and 1985, respectively. Since 1983 he has been with the Department of Electronics Engineering, School of Engineering, University of Sevilla, where he has been Associate Professor in 1987, and Full Professor since 1996, leading a research group on mixed signal design. In 1999 he made a short stay at the Department of Electrical Engineering, NMSU, and he is presently in the Department of Electrical Engineering, TAMU for a Sabbatical stay. His interests include low-voltage analog circuits and systems, analog to digital conversion, Σ Δ modulators, and electronic circuits and systems with application to control and communication. In these fields he has published around 40 journal papers and more than 100 conference papers, and he holds 2 international patents.     

The Medium Time Metric: High Throughput Route Selection in Multi-rate Ad Hoc Wireless Networks

Modern wireless devices, such as those that implement the 802.11abg standards, utilize multiple transmission rates in order to accommodate a wide range of channel conditions. The use of multiple rates presents a significantly more complex challenge to ad hoc routing protocols than the traditional single rate model. The hop count routing metric, which is traditionally used in single rate networks, is sub-optimal in multi-rate networks as it tends to select short paths composed of maximum length links. In a multi-rate network, these long distance links operate at the slowest available rate, thus achieving low effective throughput and reduced reliability due to the low signal levels. In this work we explore the lower level medium access control and physical phenomena that affect routing decisions in multi-rate ad hoc networks. We provide simulation results which illustrate the impact of these phenomena on effective throughput and show how the traditional minimum hop routing strategy is inappropriate for multi-rate networks. As an alternative, we present the Medium Time Metric (MTM) which avoids using the long range links often selected by shortest path routing in favor of shorter, higher throughput, more reliable links. Our experimental results with 802.11 g radios show that the Medium Time Metric achieves significantly higher throughput then alternative metrics. We observed up to 17 times more end-to-end TCP throughput than when the Min Hop or ETX metrics were used. Baruch Awerbuch is currently a professor at the Computer Science Dept. at Johns Hopkins University. His current Research interests include: Security, Online Algorithms, Distributed and Peer-to-Peer Systems, Recommendation Systems, and Wireless Networks. Baruch Awerbuch has published more than 100 papers in journals and refereed conferences in the general area of design and analysis of online algorithms, combinatorial and network optimization, distributed algorithms, learning, fault tolerance, network architecture, and others. Baruch Awerbuch is a co-director of the JHU Center for Networks and distributed systems http://www.cnds.jhu.edu. He is supervising the Archipelago project http://www.cnds.jhu.edu/archipelago whose goal is developing WiFi (IEEE 802.11 based) multi-hop wireless network based on novel rerouting algorithms. Dr. Awerbuch served as a member of the Editorial Board for Journal of Algorithms, Wireless Networks and Interconnection Networks. He was a program chair of the 1995 ACM Conference on Wireless Computing & Communication and a member of the program committees of the 2004 ACM Mobihoc, as well as PC member ACM PODC Principles of Distributed Computing (PODC) Conference in 1989 and of the Annual ACM STOC (Symposium on Theory of Computing) Conference in 1990 and 1991. Web: http://www.cs.jhu.edu/~baruch David Holmer received his B.S. in electrical engineering and MSE in computer science from the Johns Hopkins University in 2001 and 2002. He is now a Ph.D. candidate in the Department of Computer Science at Johns Hopkins University, and a research assistant in the Wireless Communication Group. The theme of his research is the development of deployable high performance ad hoc networking technology. As a result, his interests span many aspects of wireless networking including: routing, medium access control, physical layer properties and simulation, security, and energy efficiency. Herbert Rubens is a Ph.D. candidate in the Computer Science Department at the Johns Hopkins University (JHU) in Baltimore, Maryland. He is a member of the Wireless Communication Group, and specializes in multi-hop ad hoc protocol design. He has designed innovative mechanisms allowing power efficiency, high scalability, and efficient resource allocation in wireless networks. He obtained his B.Sc. and Masters Degree in computer science from Johns Hopkins University in 2001 and 2002 respectively. His research interests include ad hoc routing, medium access control, network security, and distributed algorithms.     

通信系统中自适应回波抵消的一种新方法

语音分组传输系统的出现，对回波抵消技术提出了新的挑战。在回波抵消中一个关键的问题是需要快速有效地估计延迟时间。基于直接计算输入信号互相关函数的延迟估计方法，在实际应用中回波消除性能差，运算量大。为此提出了基于混合模型的延时估计方法，对输入信号进行带通滤波和降低抽样率抽样，使其具有白噪声特性，然后快速计算互相关函数的估计值。理论分析和实验结果证明新的延迟估计方法有很好的回波消除性能和较少的运算量，在实际通信系统中有较好的应用前景。     

多速率语音芯片AMBE-2020的开发和应用

AMBE-2020是由DVSI公司推出的高性能多速率语音编码、解码芯片，它的语音算法采用专利的AMBE语音压缩技术。该芯片能在较低的速率下实现全双工、高质量的语音通信，并且操作简单、编码速率可变、功耗小等优点。介绍了AMBE-2020芯片，并建立了一个简单的语音压缩系统的应用实例。     

一种用于3G系统中复杂背景噪声环境下的话音激活检测算法

本文讨论了一种新的应用在3G自适应多速率系统中复杂背景噪声环境下的话音激活检测算法。这种算法基于谱估计理论和周期信号检测方法,应用一个IIR滤波器组把输入窄带语音信号分面九个频带,进而估计每个频带的语音信号和背景噪声的电平,结合基音和音调检测,在区分语音和移动环境中的大多数背景噪声对表现得足够健壮,最后,基于欧洲电信标准委员会建议的3G平台对这种算法进行了仿真评估,并就其健壮性从主客观两个方面进行了分析。     

新的多速率多播拥塞控制方案

提出了一种新的基于数据包束探测(packet-bunch probe)和TCP吞吐量公式的多速率多播拥塞控制方案PTMCC(packet-bunch probe and TCP-formula based multicast congestion control)。这种接收端驱动的拥塞控制,采用数据包束来探测网络的可用带宽,利用TCP吞吐量公式得到TCP友好速率,并采用了新的速率调节算法。仿真实验表明,PTMCC在收敛性、灵敏性以及TCP友好性上具有较好的性能。     

基于GC5016的并行多通道接收机研究

给出了并行多通道接收机方案,以多速率信号处理理论为基础,采用了宽带中频带通采样的软件无线电架构。使用TI的数字上/下变频转换器GC5016作为接收机的核心芯片,主要介绍了GC5016的结构和功能,及其作为数字下变频器的使用,重点对CIC和PFIR两种滤波器在抽取重采样和滤波整型中的作用进行了理论分析和仿真研究。CPLD作为主要的外围器件,产生配置时序,在上位机的控制下完成重配置功能。设计大量采用可编程器件,具有较高的集成度、灵活性和广泛的应用前景。     

一种新的多速率多播拥塞控制策略

本文提出了一种新的多速率多播拥塞控制策略,以满足分层多播接收者的可用带宽异构性。这种接收方驱动的拥塞控制策略,能够根据网络情况变化动态地调整分层的数量及层速率,运用最优层速率分配算法来满足接收者的可用带宽异构性,接收者的可用带宽可以用根据TCP友好经验公式计算出。仿真实验表明,该算法在TCP友好性上有良好的性能,同时它可以明显提高系统的吞吐量。     

Adaptive threshold control for auto-rate fallback algorithm in IEEE 802.11 multi-rate WLANs

The IEEE 802.11 standard supports multiple rates for data transmission in the physical layer. Nowadays, to improve network performance, a rate adaptation scheme called auto-rate fallback (ARF) is widely adopted in practice. However, ARF scheme suffers performance degradation in multiple contending nodes environments. In this article, we propose a novel rate adaptation scheme called ARF with adaptive threshold control. In multiple contending nodes environment, the proposed scheme can effectively mitigate the frame collision effect on rate adaptation decision by adaptively adjusting rate-up and rate-down threshold according to the current collision level. Simulation results show that the proposed scheme can achieve significantly higher throughput than the other existing rate adaptation schemes. Furthermore, the simulation results also demonstrate that the proposed scheme can effectively respond to the varying channel condition.     

多速率调制解调器设计与实现

现代通信系统中多种信息速率并存,多速率兼容成为一个突出的问题.基于直接序列扩频（DS-SS）和卷积编码技术,提出了一种可以满足多速率兼容的调制解调器实现方法,通过选择不同长度的伪随机序列或者卷积编码,不同的信息速率占用相同的传输带宽.对扩频、解扩以及卷积码的编码和解码部分进行了较为详细的论述,给出了关键模块的原理和实现方法,对使用此调制解调器的通信系统进行了测试,并给出了测试数据.