Pilot power minimization with coverage and locatability constraints in CDMA systems

Position location (PL) of a UE requesting E-911 services should be provided by wireless communication service providers, according to the Federal Communications Commission (FCC) regulations. Raising pilot power fraction can improve the system locatability, while it may also cause pilot pollution and increase interference to UEs in neighboring cells. In this letter we find the optimal pilot power allocation subject to coverage and locatability constraints. The results have shown that with new localization techniques such as idle period downlink (IPDL) and cumulative virtual blanking (CVB), the coverage and locatability constraints can be satisfied without requiring long integration time and large pilot power fraction.     

Fast acquisition clock and data recovery circuit with low jitter

This paper presents a half-rate clock and data recovery circuit (CDR)that combines the fast acquisition of a phase selection (PS) delay-locked loop (DLL) with the low jitter of a phase-locked loop (PLL). The PLL acquisition time improves considerably with use of a phase frequency magnitude detector(PFMD) that feeds back an estimate of the magnitude of the frequency difference in addition to the sign. Measurements in 0.5/spl mu/m CMOS technology show operation up to 700 Mb/s, a 7% acquisition range, an initial acquisition time of 8 bit times with jitter of 30% bit time, and jitter of 16 ps after the PLL acquires lock. With a phase frequency detector (PFD), the PLL locks in about 700 ns from an initial frequency difference of 7%. Measurements using a PFMD show the 700 ns PLL acquisition time is reduced on average by about a factor of 5 to 140 ns from an initial 7% frequency difference. The power dissipation is 300mW.     

Jamming sensor networks: attack and defense strategies

Wireless sensor networks are built upon a shared medium that makes it easy for adversaries to conduct radio interference, or jamming, attacks that effectively cause a denial of service of either transmission or reception functionalities. These attacks can easily be accomplished by an adversary by either bypassing MAC-layer protocols or emitting a radio signal targeted at jamming a particular channel. In this article we survey different jamming attacks that may be employed against a sensor network. In order to cope with the problem of jamming, we discuss a two-phase strategy involving the diagnosis of the attack, followed by a suitable defense strategy. We highlight the challenges associated with detecting jamming. To cope with jamming, we propose two different but complementary approaches. One approach is to simply retreat from the interferer which may be accomplished by either spectral evasion (channel surfing) or spatial evasion (spatial retreats). The second approach aims to compete more actively with the interferer by adjusting resources, such as power levels and communication coding, to achieve communication in the presence of the jammer.     

Generation of low jitter and discrete tunable dual-wavelength optical pulses at arbitrary repetition rates

Recently there is an increasing interest in generatingshort optical pulses with lowti ming jitter and tuneablemulti-wavelength due toitsi mportant applicationin op-tical ti me division multiplexed(OTDM),wavelength di-vision multiplexed(WDM)systems,and opt…     

考虑耦合器附加相移光纤环形腔精细度计算

从理论上导出了考虑耦合损耗引起的附加相移后光纤环形腔的带阻输出特性。分析表明 ,附加相移对环形腔谐振频率的影响可以忽略 ,对腔内光强的其它频率特性没有影响。但使输出特性中的谐振峰出现不对称 ,计算结果证明谐振峰半功率全宽较之不考虑损耗引起的附加相移时增大 ,精细度由此而有所下降 ,附加相移越大 ,精细度下降越多。     

利用80C31单片机串行口实现多个LED显示的一种简单方法

介绍利用80C31单片机串行口、廉价的74HC164和74HC244集成实现多个LED显示的一种简单方法,利用该方法设计的多路LED显示系统具有硬件结构简单、软件编程容易和价格低廉的特点。     

Mobile and Multicast IP Services in PACS: System Architecture, Prototype, and Performance

Traditionally, wireless cellular communication systems have been engineered for voice. With the explosive growth of Internet applications and users, there is an increasing demand on providing Internet services to mobile users based on the voice-oriented cellular networks. However, Internet services add a set of radically different requirements on to the cellular wireless networks, because the nature of communication is very different from voice. It is a challenge to develop an adequate network architecture and necessary systems components to meet those requirements.This paper describes our experience on developing Internet services, in particular, mobile and multicast IP services, in PACS (Personal Access Communication Systems). Our major contributions are five-fold: (i) PACS system architecture that provides wireless Internet and Intranet access by augmenting the voice network with IP routers and backbone links to connect to the Internet; (ii) simplified design of RPCU (Radio Port Controller Unit) for easy service maintenance and migration to future IP standards such as IPv6; (iii) native PACS multicast to efficiently support dynamic IP multicast and MBone connectivity; (iv) optimization and incorporation of Mobile IP into PACS handoff mechanism to efficiently support roaming within a PACS network as well as global mobility between PACS networks and the Internet; (v) successful prototype design of the new architecture and services verified by extensive performance measurements of IP applications. Our design experience and measurement results demonstrate that it is highly feasible to seamlessly integrate the PACS networks into the Internet with global IP mobility and IP multicast services.     

EEG complexity as a measure of depth of anesthesia for patients

A new approach for quantifying the relationship between brain activity patterns and depth of anesthesia (DOA) is presented by analyzing the spatio-temporal patterns in the electroencephalogram (EEG) using Lempel-Ziv complexity analysis. Twenty-seven patients undergoing vascular surgery were studied under general anesthesia with sevoflurane, isoflurane, propofol, or desflurane. The EEG was recorded continuously during the procedure and patients' anesthesia states were assessed according to the responsiveness component of the observer's assessment of alertness/sedation (OAA/S) score. An OAA/S score of zero or one was considered asleep and two or greater was considered awake. Complexity of the EEG was quantitatively estimated by the measure C(n), whose performance in discriminating awake and asleep states was analyzed by statistics for different anesthetic techniques and different patient populations. Compared with other measures, such as approximate entropy, spectral entropy, and median frequency, C(n) not only demonstrates better performance (93% accuracy) across all of the patients, but also is an easier algorithm to implement for real-time use. The study shows that C(n) is a very useful and promising EEG-derived parameter for characterizing the (DOA) under clinical situations.     

二元光学技术在激光成像雷达扫描器上的应用

激光扫描技术是在巡航导弹制导中应用的CO2激光成像雷达的关键技术之一.研制了圆盘型反射式位相计算全息光栅扫描器,扫描角度范围为10°×2°,分辨率为64点/行,衍射效率为27.6%.结合CO2激光成像雷达的特点及目前对二元光学技术理论和加工工艺的研究,提出:目前的二元光学技术,特别是多重掩模蚀刻工艺的发展,可使计算全息光栅扫描器成为解决CO2激光成像雷达扫描技术的有效途径.