High-resolution angle-of-arrival measurement of the mobile radiochannel

The accurate planning of microcellular mobile radio networks requires a thorough understanding of the mechanisms that govern radio wave propagation in urban environments. Combined measurements of time delays and angles-of-arrival (AoAs), both in azimuth and elevation, of individual multipath contributions are expected to he very helpful in the validation and improvement of existing ray-tracing propagation models. To this end, we have applied the uniform circular array (UCA)-MUSIC angular superresolution algorithm to complex impulse response measurement data obtained from a synthetic uniform circular array. Beamspace processing and forward/backward averaging were applied to cope with strongly correlated signals. The presented experimental results show that our approach is capable of identifying the dominant multipaths in actual mobile propagation environments     

On the systematic measurement errors of correlative mobile radiochannel sounders

We show that measurements of time-varying mobile radio channels obtained with uncalibrated correlative channel sounders are affected by four different types of systematic errors (commutation, pulse-compression, aliasing, and misinterpretation error). We analyze these errors and provide upper error bounds that are formulated in terms of channel and sounder parameters. Based on these error bounds, we provide guidelines for a judicious choice of important sounder parameters. Computer simulations using a simple two-path channel illustrate our theoretical results. Finally, we show how our results can be used to assess the accuracy of measured channel data     

Joint clock recovery and baseband combining for the diversity radiochannel

Multipath fading is one of the major impairments encountered in terrestrial digital radio. A common countermeasure to limit the outage time due to multipath is the space diversity technique, which takes its effectiveness from the low correlation between the field samples of two well separated antennas. A very simple and effective blind receiver is proposed for the diversity radio channel. The novelty of the present study is the application of the constant modulus algorithm to joint clock recovery and baseband combining. The effectiveness of our proposal relies upon the synergic action of clock recovery and adaptive baseband combining, which allows optimal equalization of the two-ray diversity channel     

利用智能手机测量噪声的问题分析

一般的噪声测量都需要专业声级计,普通消费者一般不会购买声级计,为了能让普通人都能够了解周围的噪声情况,提出了一种利用手机进行噪声测量的方法,从手机测量噪声的原理分析了智能手机测量噪声的可行性,在测量有代表性手机的频率响应和级线性范围等基本性能的基础上,分析了手机测量噪声存在的问题.     

虚拟网址转换--实现移动互联网的新技术

虚拟网址转换(Virtual NetworkAddress Translation，VNAT)技术是应用于动态IP互连的崭新技术。VNAT能使双方在漫游时仍保持连接状态，适用于从个人通信终端到服务器的各种设备，其最大的优点在于不用对现有设备及协议作任何改动。当两个端点(endpoint)建立连接之后，VNAT用虚拟地址替换物理地址，同时建立从虚拟地址到物理地址的映射。传送层协议看到的只是连接双方的虚拟地址，而不用考虑低层物理地址的变化。这样，当任一端点改变其物理地址时，VNAT更新映射信息，而虚拟地址保持不变使连接得以保持。VNAT技术的体系结构VNAT…     

Multipath distortion of differentially encoded GMSK with 2-bdifferential detection in bandlimited frequency-selective mobile radiochannel

Error performance of Gaussian minimum-shift keying (GMSK) with 2-b differential detection in a frequency-selective mobile radio channel is analyzed. The two-wave model using two Rayleigh waves with constant group time-delay is adopted to describe a frequency-selective mobile radio channel. The Gaussian-type bandpass filter is introduced as a receiving filter to demonstrate the effects of band limitation at the receiver. A preferable receiving bandwidth in the frequency-selective mobile channel is also discussed. It is shown that the preferable receiving bandwidth is almost that obtained in an additive Gaussian noise channel since the magnitude of the interfering (or delayed) wave is relatively small. It is hardly affected by the maximum Doppler frequency and remains almost constant for the various parameters, e.g. average carrier-to-noise power ratio     

Diversity techniques for mobile radio reception

After discussing the nature of the electromagnetic field in urban environments, and the use of diversity techniques in fading media, the paper presents a survey of these techniques as applied to mobile radio, with emphasis on systems designed for analogue communication. It includes a unified approach to systems based on the double-heterodyne phase-stripper principle. The discussion is not restricted to present-day receivers only, but includes considerations which may apply in future designs.     

Digital modulation techniques for mobile and personal communicationsystems

The paper describes in detail various digital modulation techniques for mobile and personal communication systems. Among others, these include π/4-shift quadrature phase-shift keying (QPSK), used in the second generation digital cellular mobile systems in North America and Japan, and Gaussian minimum-shift keying (GMSK), employed in the GSM system in Europe. It then briefly discusses the current research activities in modulation schemes for future systems     

Escrow techniques for mobile sales and inventory applications

We address the design of architectures and protocols for providing mobile users with integrated Personal Information Services and Applications (PISA), such as personalized news and financial information, and mobile database access. We present a system architecture for delivery of PISA based on replicated distributed servers connected to users via a personal communications services (PCS) network. The PISA architecture partitions the geographical coverage area into service areas, analogous to PCS registration areas, each of which is served by a single local server. When a user moves from one service area to another, the service is provided by the new local server. This is accomplished by a service handoff, analogous to a PCS call handoff, which entails some context information transfer from the old to the new server. We focus on the mobile sales and inventory application as an example of a PISA with a well‐defined market segment. We design a database management protocol for supporting both mobile and stationary salespersons. Our design uses the site‐transaction escrow method, thus allowing faster responses to mobile clients, minimizing the amount of context information which must be transferred during a service handoff, and allowing mobile clients to operate in disconnected mode by escrowing items on their local disks. We develop a formal model for reasoning about site‐transaction escrow, and develop a scheme for performing dynamic resource reconfiguration which avoids the need for time‐consuming and costly database synchronization operations (i.e., a two‐phase commit) when the mobile sales transaction completes. A further refinement to the scheme avoids an n‐way two‐phase commit during resource reconfiguration operations, replacing it with several simpler two‐phase commits. This revised version was published online in July 2006 with corrections to the Cover Date.     

Self-phasing antenna array techniques for mobile communicationsapplications

This paper provides a summary of the basic concepts of retrodirective antenna arrays. Originally this class of antenna was developed in the 1960s for direct satellite-to-ground transmission of high-power microwave energy. The explosive growth of mobile communications has, in the authors' opinion, reopened the debate for alternative applications of retrodirective array techniques. Advances in microstrip antenna design coupled with the availability of integrated circuit amplifier and mixer components permit minimum-complexity retrodirective antenna arrays to be constructed. Several different planar retrodirective antenna architectures are presented and their basic operational characteristics given. A novel application for co-operating retrodirective antennas in a duplex communication link with inherent space division multiple access capability is also described. Finally some of the operational parameters which could ultimately limit the performance of this class of antenna are discussed     

移动电源综合性能测量技术分析

通过对移动电源重要性能及参数的分析,提出了针对每项性能及参数的测量方法?采用这些测量方法可以达到对移动电源综合性能的评估目的?其中电性能参数中输出电压?放电性能?转换效率的测量,可以分析得到移动电源输出电压值?输出容量值能否满足要求?安全性能中过充电保护?过放电保护?短路保护?发热?防火的测量来检查移动电源能否符合安全要求,以保证使用人员的安全?环境适应性和电磁兼容性参数的测量用以保证移动电源处于非常态环境时的性能能否满足要求?     

车载移动立体测量系统检校及精度分析

车载移动立体测量系统可以用于快速、准确的高精度数据采集和三维建模。针对车载移动立体测量检校问题,设计了一套高精度的车载移动立体测量系统检校方法,建立了检校的数学模型,并进行了试验,分析了检校前后车载移动立体测量系统的测量精度差异。实验证明,本文研究的车载移动立体测量系统检校方法能有效地提高系统测量精度。     

Comparing viewing and filtering techniques for mobile urban exploration

The exploration of the immediate surroundings through mobile location-aware devices is starting to become an everyday urban activity. Due to the increasing amount of available geo-referenced information, advanced viewing and filtering techniques need to be investigated as a complementation to simple present-day 2D-map presentations. This article examines both well-established techniques (2D map, list view, category view) and advanced concepts (3D map, tag cloud) regarding their support of mobile urban exploration. In a field study, 26 participants used an experimental multi-view prototype for viewing and filtering tasks on a route through an urban environment. The results show that content-based views may provide similarly good support for viewing the content as spatial interfaces. Furthermore, the experiment provides evidence that the advantages of content-based filtering techniques are increasingly preferred to spatial ones in regard to the amount of available information.     

Wave techniques for noise modeling and measurement

The noise wave approach is applied to analysis, modeling, and measurement applications. Methods are presented for the calculation of component and network noise wave correlation matrices. Embedding calculations, relations to two-port figures-of-merit, and transformations to traditional representations are discussed. Simple expressions are derived for MESFET and HEMT noise wave parameters based on a linear equivalent circuit. A noise wave measurement technique is presented and experimentally compared with the conventional method     

Co-channel interference measurement method for mobile communication

A new method of measuring co-channel interference for mobile communication systems is proposed. In this method, the carrier envelope is sampled, and signal-carrier-to-interference-carrier ratio (CIR) is calculated by signal processing. The circuits for measurement are composed of an envelope detector, an analog-to-digital converter, and a microcomputer. Theoretical and experimental evaluations of measurement errors are examined, and the method is proved to be promising. Using this method, the signal-to-interference ratio of up to 20 dB is measured, within 2 dB error for fading frequency of less than 80 Hz.     

Theoretical analysis and measurement results of vegetation effectson path loss for mobile cellular communication systems

This paper reports on studies of propagation in an urban forested park area to investigate the statistical nature of the time fading for frequencies ranging from 0.9 GHz to 1.8 GHz, as well as to examine the range dependence and the base station height gain. Measurements of the received signal over 30 s intervals for a stationary mobile were used to construct the distribution functions for the fading. In most cases, the distribution could be approximated by a Rician distribution, whose K-factor was found to depend on transmitter height     

Electrical techniques for the measurement of deep states

When point defects, either intrinsic (such as vacancies or interstitials) or extrinsic (most impurities with the exception of shallow donors or acceptors) are introduced into a semiconductor, they can result in the occurrence of ‘deep states’. These are electronic levels that are not normally ionized at room temperature, but can affect both carrier concentrations and minority carrier lifetime. The purpose of this review is to provide an outline of the techniques that are commonly used to characterize deep defect states in terms of their electrical properties.     

High-frequency measurement techniques for magnetic cores

Conventional techniques and new techniques based on digitizing instruments for making high-frequency B-versus-H loop and core-loss measurements on magnetic cores are presented and compared. Potential sources of measurement errors and their magnitudes, limitations imposed by the instrumentation, and thermal considerations are discussed. Circuits suitable for high-frequency sine-wave or square-wave core excitation are also discussed. The utility of such measurements is illustrated with sample data     

Spread slotted ALOHA techniques for mobile and personal satellitecommunication systems

The objective is to develop a general theoretical framework for a class of spread slotted ALOHA (SSA) systems. The contributions include: modeling of a generalized spread slotted ALOHA (SSA) system; derivation of computationally efficient closed form expressions for the SSA system throughput and delay taking into account receiver complexity; and presentation of numerical results to validate the derivation as well as to substantiate the superior performance of the proposed scheme. The results demonstrate that SSA schemes offer significant improvements in terms of throughput, delay, and network stability against excessive loading at very acceptable levels of receiver implementation complexities. Also, SSA is found to be highly robust to errors in the time of arrivals and eliminates the need for a guard time