DPLL implementation in carrier acquisition and tracking for burst DS-CDMA receivers

INTRODUCTIONDS CDMAtechniquesplayanimportantroleincurrentHFCnetworksandwirelesscommuni cationsystems (Chungetal.,1993;Gaudenzietal.,1996 ;Viterbi,1997) .CrucialtotheDS CDMAsystemispropercodeandcarriersyn chronization .Literatureoncodesynchronizationisabun…     

DPLL implementation in carrier acquistion and tracking for burst DS-CDMA receivers

This paper presents the architectures, algorithms, and implementation considerations of the digital phase locked loop (DPLL) used for burst-mode packet DS-CDMA receivers. As we know, carrier offset is a rather challenging problem in CDMA system. According to different applications, different DPLL forms should be adopted to correct different maximum carrier offset in CDMA systems. One classical DPLL and two novel DPLL forms are discussed in the paper. The acquisition range of carrier offset can be widened by using the two novel DPLL forms without any performance degradation such as longer acquisition time or larger variance of the phase error. The maximum acquisition range is 1/(4T), whereT is the symbol period. The design can be implemented by FPGA directly. Project (No. 60002003) supported by the National Natural Science Foundation of China     

Performance of a novel carrier frequency offset estimation algorithm for OFDM-based WLANs

INTRODUCTION Orthogonal frequency division multiplexing (OFDM) has been treated as the key transmission method in Wireless Local Area Networks (WLANs) based on IEEE802.11a protocol (IEEE Standard 802.11a- 1999). However, the sensitivity of the scheme to the frequency offset limits its development. Moose (1994) proposed maximum likelihood esti-mation for the carrier frequency offset by using two different received symbols, but the limitation of this method is that the acquisition r…     

A high performance frequency offset estimator for OFDM

INTRODUCTION Orthogonal frequency division multiplexing (OFDM) has become a promising technology for future wireless communication systems (Kim et al., 2003; 3GPP TSG-RAN-1.TR, 2004) due to its ability to transform a wideband frequency selective channel to a set of parallel flat-fading narrow-band channels, which substantially simplifies the channel equaliza- tion problem. However, a critical weakness of OFDM is its sensitivity to carrier frequency offset (CFO) since it can only t…     

一种应用于DRM/DAB频率综合器的宽带低相位噪声LC压控振荡器(英文)

介绍了一种应用于DRM/DAB频率综合器的宽带低相位噪声低功耗的CMOS压控振荡器.为了获得宽工作频带和大调谐范围,在LC谐振腔里并联一个开关控制的电容阵列.所设计的压控振荡器应用中芯国际的0.18μm RF CMOS工艺进行了流片实现.包括测试驱动电路和焊盘,整个芯片面积为750μm×560μm.测试结果表明,该压控振荡器的调谐范围为44.6%,振荡频率范围为2.27～3.57GHz.其相位噪声在频偏为1MHz时为-122.22dBc/Hz.在1.8V的电源电压下,其核心的功耗为6.16mW.     

GPS软件接收机的构建及其精频捕获算法的实现

介绍了一种GPS软件接收机的设计方法.该设计采用软件无线电设计理念,主要包括前端模块、捕获模块、跟踪模块、同步模块、导航解算模块以及其他辅助模块.捕获模块采用基于圆周相关的捕获算法,通过FFT(快速傅立叶变换)分别作用于输入信号和本地码信号将运算变换到频域内处理.该算法可得到C/A码起始相位和分辨率为1 kHz的载波频率信号,但此载波频率精细度差,不能直接用于跟踪环路.为提高载波频率分辨率,采用基于相位关系计算的精频估计算法.实验表明应用精频捕获算法得到的载波精频估计误差在几赫兹以内,可直接用于后续跟踪环路.     

应用于低中频Zigbee收发机的5-GHz恒定带宽频率综合器（英文）

设计并实现了一个应用于ZigBee收发机的全集成整数N频率综合器.频率综合器中采用了稳定环路带宽技术,使频率综合器的环路带宽在压控振荡器（VCO）的整个输出频率范围内恒定不变,从而维持了频率综合器的相位噪声最优值与环路稳定性.频率综合器的同相与正交信号（IQ）由VCO输出端的除2分频器产生.该频率综合器采用0.18μm RF CMOS工艺技术制造,芯片面积约1.7mm2.频率综合器采用在晶圆测试的方式进行了测试.在1.8V电源电压下,频率综合器不包括输出缓冲所消耗的总功率为28.8mW.频率综合器在2.405GHz载波1及3MHz频偏处测得相位噪声分别为-110和-122dBc/Hz.频率综合器在2MHz频偏处测得的参考杂散为-48.2dBc.测得的建立时间约为160μs.     

Simulation of dual transponder carrier ranging measurements

The most dominant error source for microwave ranging is the frequency instability of the oscillator that generates the carrier phase signal. The oscillator noise is very difficult to filter due to its extremely low frequency. A dual transponder carrier ranging method can effectively minimize the oscillator noise by combing the reference phase and the to-and-fro measurement phase from the same single oscillator. This method does not require an accurate time tagging system, since it extracts phases on the same satellite. This paper analyzes the dual transponder carrier ranging system by simulation of the phase measurements with comprehensive error models. Both frequency domain and time domain noise transfer characteristics were simulated to compare them with dual one-way ranging. The simulation results in the two domains conformed to each other and demonstrated that a high level of accuracy can also be achieved by use of the dual transponder carder ranging system, with relatively simple instruments.     

使用试错法加快扩频通信伪随机码捕获

An optimun search algorithm for the coherent acquisition in direct-sequence spread-spectrum （DSSS） receivers is proposed and analyzed in this paper. The system consists of two major parts： a phase region estimator and a phase alignment detector. We use an auxiliary sequence to correlate the incoming signal in the phase region estimator. Since the cross-correlation value between the auxiliary sequence and the incoming PN signal has linear magnitude, and can provide the direction for the phase updating, an optimum search algorithm, try and error method, can be adopted to obtain the phase region information of the incoming signal. The mean acquisition time is derived through the signal flow graph theory. The time is compared with that of the conventional serial search scheme, and the results show that the proposed scheme can achieve coarse acquisition significantly faster than the conventional scheme.     

第三代移动通信中的一种新型AFC算法

在无线移动通信中 ,接收机的本地振荡频率和载波频率之间往往存在较大的频率偏差 ,AFC用于克服此频偏 .传统的AFC采用了模拟环路滤波器 ,因此只能工作在连续的输入信号模式 ,而不能工作于间断导频的W CDMA系统中 .本文对此提出了新的AFC算法 :用最大似然方法估计衰落信道 ,得到间断导频信道的幅度和相位 ,并在一个时隙中进行最大比合并 ,从而得到一个判决变量 .最后用这些变量调节本地振荡频率 ,以跟踪载波频率 .仿真结果显示这种新的AFC算法是可靠而有效的 .     

应用于无线传感网频率合成器的0.5V低电压鉴频鉴相器设计

基于0.13μm CMOS技术设计了一个应用于无线传感网频率合成器、电源电压为0.5 V的鉴频鉴相器.它的功能是比较输入信号的频率和相位差,并输出一个与该差值成比例的电压.因电源电压是0.5 V,所以该电路采用低阈值晶体管.为了增大相位误差的检测范围和提高最大工作频率,该电路采用了脉冲锁存的结构.当输入信号频率为2 M...     

The benefit of being naïve and knowing it: the unfavourable impact of perceived context familiarity on learning in complex problem solving tasks

Previous research has found that embedding a problem into a familiar context does not necessarily confer an advantage over a novel context in the acquisition of new knowledge about a complex, dynamic system. In fact, it has been shown that a semantically familiar context can be detrimental to knowledge acquisition. This has been described as the “semantic effect” (Beckmann, Learning and complex problem solving, Bonn, Holos, 1994). The aim of this study was to test two competing explanations that might account for the semantic effect: goal adoption versus assumptions. Participants were asked to learn about the causal structure of a linear system presented on a computer containing three outputs by changing three inputs through goal free exploration. Across four conditions the level of familiarity was experimentally varied through the use of different variable labels. There was no evidence that goal adoption can account for poor knowledge acquisition under familiar conditions. Rather, it appears that a semantically familiar problem context invites a high number of a priori assumptions regarding the interdependency of system variables. These assumptions tend not to be systematically tested during the knowledge acquisition phase. The lack of systematicity in testing a priori assumptions is the main barrier to the acquisition of new knowledge. The semantic effect is in fact an effect of untested presumptions. Implications for research in problem solving, knowledge acquisition and the design of computer-based learning environments are discussed.     

基于CC2530的水环境监测系统设计

为了解决有线水环境监测系统布线难、成本高、监测范围受限等问题,文章设计了一种基于CC2530的无线传感器网络系统对水环境进行实时监测.该系统以Zigbee CC2530芯片和CDMA模块为核心,利用分布在监测水域的各传感器节点采集数据,数据经zigbee无线网络传至中心节点,再通过CDMA模块传给远程数据管理中心,中心管理人员可利用监控平台方便观察水质状况,及时采取应对措施.通过在汉江流域湖北襄阳市一桥至二桥段布置50个传感器节点和10个中心节点对其水质进行监测,监测结果表明该系统能够实现水环境多种参数的实时采集和可靠传输,通过监控中心可以方便地对各个参数进行实时监控.     

基于CDMA/GPRS的DF1协议通讯驱动的开发

以AB DF1串口控制协议为例,说明了利用CDMA/GPRS DTU传输串口数据和组建无线远程控制系统(SCADA)的基本方法.对系统组建所涉及的软硬件环境进行了介绍,并详细描述了DF1控制协议的分析过程和将其与DTU开发包集成以实现新的通讯驱动的原理.通过此类原理,我们可以实现在统一的软件构架下,通过加载所需的通讯驱动,与包含不同用户设备的RTU进行通讯,而这样的RTU,均是采用DTU为其通讯手段.     

大学任务型外语教学中“学得”与“习得”的整合

美国语言学家克拉申在其语言习得理论中提出了“学得”与“习得”的概念。通过比较分析可阐明“学得”与“习得”是两种具有不同特点的学习方式,且在不同的学习环境中具有各自的优势。在大学任务型外语教学中,我们要努力创造各种条件将两者有机地整合起来,充分发挥其整体优势,以提高学生的自主学习能力和课堂教学效率。     

认知理论应用于情态动词教学的方法与原则

情态动词是情态系统最为核心的表达形式,也是各种语言实现情态意义最为重要的方式与载体。已有研究发现,不同母语背景学习者在情态动词习得上都存在不同程度的问题。其原因有二:一是情态动词具有多义性,其意义会随着语境的改变而改变,情态动词的多义性造成了自身的复杂性;二是受传统教学方法的影响。文章以认知教学法为基础,以范畴化理论与心理空间理论为例来探讨认知理论应用于情态动词教学的方法与原则。与传统教学方法相比,认知方法只能作为一种补充,在教学实践中不能完全替代传统教学方法。     

MIMO-QAM系统载波频偏估计

本文在分析MIMO-QAM系统可行性的基础上,提出了一种频偏估计算法,并进行了仿真。该算法利用帧同步序列,优化系统资源配置。仿真结果表明,本文提出的算法是可行的,具有较高的精度和实用价值。     

Improved DOA Estimation Algorithm with Sensor Array Perturbations for CDMA System

An improved direction of arrival (DOA) estimation algorithm with sensor gain and phase uncerlatinties for synchronous code divison multiple access(CDMA) system with decorrelator is presented,Through decorrelating processing DOAs of the desired users cna be estimated independently and all other resolved signal interferences are eliminated,Emphasis is directed to applications in which sensor gain and phase are pertubed that often happen actually, It is shown that improved DOA estimation can be achieved for decoupled signals by gain and phase pre-estimation procedures.     

Evaluation of virtual microscopy in medical histology teaching

Histology stands as a major discipline in the life science curricula, and the practice of teaching it is based on theoretical didactic strategies along with practical training. Traditionally, students achieve practical competence in this subject by learning optical microscopy. Today, students can use newer information and communication technologies in the study of digital microscopic images. A virtual microscopy program was recently introduced at Ghent University. Since little empirical evidence is available concerning the impact of virtual microscopy (VM) versus optical microscopy (OM) on the acquisition of histology knowledge, this study was set up in the Faculty of Medicine and Health Sciences. A pretest‐post test and cross‐over design was adopted. In the first phase, the experiment yielded two groups in a total population of 199 students, Group 1 performing the practical sessions with OM versus Group 2 performing the same sessions with VM. In the second phase, the research subjects switched conditions. The prior knowledge level of all research subjects was assessed with a pretest. Knowledge acquisition was measured with a post test after each phase (T1 and T2). Analysis of covariance was carried out to study the differential gain in knowledge at T1 and T2, considering the possible differences in prior knowledge at the start of the study. The results pointed to non‐significant differences at T1 and at T2. This supports the assumption that the acquisition of the histology knowledge is independent of the microscopy representation mode (VM versus OM) of the learning material. The conclusion that VM is equivalent to OM offers new directions in view of ongoing innovations in medical education technology. Anat Sci Educ 6: 307–315. © 2013 American Association of Anatomists.     

Efficient timing and frequency offset estimation scheme for OFDM systems

A new training symbol weighted by pseudo-noise(PN) sequence is designed and an efficient timing and fre quency offset estimation scheme for orthogonal frequency division multiplcxing(OFDM)systems is proposed.The timing synchronization is accomplished by using the piecewise symmetric conjugate of the primitive training symbol and the good autocorrelation of PN weighted factor.The frequency synchronization is finished by utilizing the training symbol whose PN weighted factor is removed after the timing synchronization.Compared with conventional schemes,the proposed scheme can achieve a smaller mean square error and provide a wider frequency acquisition range.