A pilot-based dynamic channel assignment scheme for wireless access TDMA/FDMA systems

We propose a control architecture for implementing a dynamic channel assignment (DCA) algorithm which optimizes two-way channel quality in a TDMA portable radio system. Computer simulations are used to evaluate the performance of this DCA method. A common control frequency, which is frame-synchronized among base stations, provides (1) beacons for portables to locate base stations and obtain DCA information, (2) broadcast channels for system and alerting information, and (3) pilot signals to permit portables to evaluate downlink interference. This allows low-complexity radio ports and portables to mutually select channels to avoid interference and avoid creating excessive interference. Results from computer simulations demonstrate the good spectrum efficiency of this method and its potential for handling nonuniform traffic demand. This work is targeted toward understanding the implications to local exchange networks of wireless system alternatives that could provide access to those networks.A preliminary work with the same title was presented at the Second International Conference on Universal Personal Communications, October 12–15, 1993, Ottawa, Canada.     

An efficient location cache scheme for three‐level database architecture in PCS networks

Recently, hierarchical architecture for location databases has been proposed in order to accommodate the growing number of personal communication systems users. With the three‐level hierarchical database architecture, which is compatible with the current cellular mobile systems, newly developed additional databases, including the regional location database (RLR), are positioned between the HLR and the VLRs. We propose an efficient cache scheme, the double T‐thresholds location cache scheme, which could reduce the network and database costs to lookup a portable using the three‐level architecture. This scheme extends the existing T‐threshold location cache scheme, which is effective only under the two‐level architecture of location databases currently adopted by IS‐41 and GSM. The idea behind our proposed scheme is to use two pieces of cache information, VLR and RLR, which serve the called portables. These two pieces are required in order to exploit not only the locality of a registration area (RA), but also the locality of a regional registration area (RRA), a wide area covered by the RLR. We also use two threshold values in order to determine whether the two pieces are obsolete. In order to model the RRA residence time, the branching Erlang‐∞ distribution is introduced. The cost analysis presented in this paper shows that the double T‐thresholds location cache scheme significantly reduces the network and database costs for most patterns of portables. Copyright © 2001 John Wiley & Sons, Ltd.     

Implicit deregistration in a PCS network

Registration/deregistration is required in a PCS network when a portable moves between registration areas. Several schemes were proposed to deregister a portable after it moves out of a registration area (RA). A simple scheme called implicit deregistration totally eliminates network traffic due to deregistration. However, this scheme may delete valid registration records. Thus, the size of a registration database must be sufficiently large to ensure low probability that a valid registration record is deleted. This paper describes an analytic model to determine the size k of the registration database for an RA in the implicit deregistration scheme. If the expected number of portables in an RA is N, then our study indicates that good performance can be achieved if k≃5N     

Deregistration strategies for PCS networks

This paper studies three deregistration strategies (explicit, implicit, and timeout (TO) deregistration) for personal communication service (PCS) networks to determine the network conditions under which each strategy, gives the best performance. Two performance measures are considered: (1) the probability α that a portable cannot register (and receive service) and (2) the number of deregistration messages sent in a strategy. For the same database size, α is smaller for explicit deregistration (ED) than it is for TO or implicit deregistration (ID). On the other hand, ID does not create any deregistration message traffic. With an appropriate TO period, the deregistration message traffic for TO deregistration is much smaller than the traffic for ED. Suppose that there are N portables in a registration area (RA) on the average. To ensure that α<10^-3 our study indicates that if the database size is larger than 4N, then the implicit scheme should be selected (to eliminate deregistration traffic). If the database size is smaller than 1.5 N, then the explicit scheme should be selected. Otherwise, the TO scheme should be selected to achieve the best performance     

小型无线光通信终端大视场扫描捕获光学天线设计

针对小型、轻量化光通信终端,设计了一种大视场扫描捕获方案,并对该方案中所涉及的光学天线进行了详细研究。这种扫描捕获方案将MEMS反射镜作为伺服控制机构,进行天线指向控制;光学天线采用收发共口径体制,能够将MEMS反射镜的指向范围扩大3倍,且全视场畸变控制在了0.7%以内;最后对这种捕获方案的通信链路功率进行了核算,功率余量4.6 dB,较为充足。本文所提出的方案体小质轻,是无线激光通信领域中较为独特的形式,在无人机、单兵的应急建链、通信中具备良好的应用前景。     

Performance evaluation of non-linear transmit power amplifiers forNorth American digital cellular portables

This paper discusses the system performance degradation resulting from using a non-linear transmit power amplifier (PA) in a North American digital cellular (NADC) portable radio. The NADC portables require a linear power amplifier for the spectrally efficient linear modulation scheme, π/4-DQPSK. It is well known that these PA's can exhibit non-linear characteristics that degrade system performance. System degradation is measured using bit error rate (BER) as the figure of merit. The PA is modeled by its AM-AM and AM-PM characteristics; the receiver architecture contains the simple, yet robust, differential detector. Simulation results are presented for additive white Gaussian noise (AWGN), Rayleigh fading, and frequency selective fading environments, and compared to results for a truly linear PA. In addition, PA spectral regrowth is discussed as well as the potential use of a linearization technique to compensate for the PA effects     

The cellular environment of lightweight handheld portables

The European cellular environment is described, and the types of cellular environments that are able to support lightweight handheld portables are addressed. Microcellular structures are considered, covering propagation measurements, rapid handover, interfacing with local area networks, and highway microcells with an overlaying macrocell. Narrowband transmission of subband-coded speech by 16-level QAM and high-bit-rate transmission are discussed. Picocells, i.e., very small areas or volumes that might encompass an office, a house and its immediate environment, or a hot spot that provides high-capacity communication, are considered     

基于语音卡系统的技术实现

计算机电话集成技术(CTI)的应用,特别是基于语音卡的应用越来越广泛。语音卡监视系统的开发,需要COM组件的背景;编程驱动可以采用状态轮询、线程函数或消息机制,使用数据库、多线程、消息映射等多项技术。通过介绍基于语音卡系统的开发过程,详细阐述系统实现的相关技术,对采用语音卡进行的各种开发以及相关项目的开发具有普遍的指导意义。     

Modeling techniques for large-scale PCS networks

There has been rapid growth in the demand for mobile communications that has led to intensive research and development of complex PCS (personal communication services) networks. Capacity planning and performance modeling are necessary to maintain a high quality of service to the PCS subscriber while minimizing costs. Effective and practical performance models for large-scale PCS networks are available. Two new performance models are presented in this article which can be solved using analytical techniques. The first is the so-called portable population model, based on the flow equivalent assumption (the rate of portables into a cell equals the rate of portables out of the cell). The model provides the steady-state portable population distribution in a cell that is independent of the portable residual time distribution, which can be used by simulations to reduce the necessary execution time by reaching the steady state more rapidly. Additionally, this model can be used to study the blocking probability of a low (portable) mobility PCS network and the performance of portable deregistration strategies. The second model is the so-called portable movement model which can be used to study location tracking and handoff algorithms. The model assumes that the arriving calls to a portable form a Poisson process, and portable residual times have a general distribution. This model can be used to study location-tracking algorithms and handoff algorithms. It is shown that under some assumptions, the analytic techniques are consistent with the simulation model     

An energy efficient middleware for an ad-hoc AAL wireless sensor network

DIA (Dispositivo Inteligente de Alarma, in Spanish) is an AAL (Ambient Assisted Living) system that allows to infer a potential dangerous action of an elderly person living alone at home. This inference is obtained by a specific sensorisation with sensor nodes (portables and fixes) and a reasoning layer embedded in a PC that learns of the users behaviour patterns and advices when actual one differs significantly of the normal patterns. In AAL systems, energy is a limited resource therefore sensor devices need to be properly managed to conserve energy. In this paper, we introduce the design and implementation of innovative and specific mechanisms at the sensory layer middleware which is capable of, first to discriminate spurious motion detections assuming that these signals do not resemble the patterns of real motion detections and, second to reduce the dynamics of messages by a sensor signal processing in order to compress the whole information in one single event. The middleware achieves power saving by modifying the raw information from sensors and adapting it to the predefined semantic of the reasoning layer. It manages the important task of data processing from sensors (raw information), and transfers the pre-processed information into the top layer of reasoning in a more energy efficient way. We also address the trade-off between reducing power consumption and reducing delay for incoming data. We present results from experiments using our implementation of these mechanisms at the middleware that comprises from node firmware to the PC driver. The number of messages of the proposed method with respect to the raw data is reduced by approximately 98.5%. The resources used in the PIR signal processing is reduced by approximately 85%. The resulting delay introduced is small (10–19 s) but system dynamics is slow enough to avoid contextualisation errors or reduction of system performance. We consider these results as very satisfactory.     

IFRS: An Indexed Face Recognition System Based on Face Recognition and RFID Technologies

Access control systems are in contact with humans in everyday life, it is used in buildings, smartphones, cars, and IoT. Access control systems became an active research area. The performance of an access control system is specified by its speed and accuracy. Biometric systems are powerful access control systems which use humans’ biological or physiological properties to provide access to the restricted data or area. From all of the many biometric system types, the face recognition system is the only type that is delivering the automatic property. Moreover, it is the most acceptable type of biometric systems to the humans. The main challenges in the face recognition system are the degradation of the speed and accuracy when the system database grew bigger. This is because the face recognition system is an identification system that adopts a one to many (1:M) relationship. As a result, there is a need to develop a system with one to one (1:1) relationship, which is a challenging process. Motivated by such challenge, this paper proposes a system called Indexed Face Recognition System (IFRS) which is based on the combination of face recognition technology and Radio Frequency Identification technology. IFRS uses Local Binary Pattern Histogram as a feature vector and Haar-cascade classifier for the face detection. Moreover, the system is enhanced with three pre-processing methods namely: Bilateral filter, Histogram Equalization, and applying Tan and Triggs’ algorithm. In addition, IFRS performs an image normalization processes before and after Face Detection phase to enhance images quality, these process are: Color Conversion and Image Cropping and Resizing. Two experiments were done. The first experiment was done on 400 images with 40 subjects (10 images per subject). The second experiment was done on 210 collected images for 21 subjects (10 images per subject) from University students as a real-life case study. The practical results demonstrates that 4?×?4 image divisions gives better results than 8?×?8 image divisions as far as recognition time, database access time, and storage capacity are concerned. The practical results show that IFRS can reach an accuracy of 100% with a very little amount of time delay that is negligible.     

Engineering workstations-what the vendors wrought

Increasingly powerful workstations recently unveiled by manufacturers are surveyed. The power did not just go into desktop or deskside units, but into portables as well. Central processing units (CPUs) operating at 33 MHz were commonplace, and 40 and 50 MHz chips were not unusual. In most cases, the manufacturers introduced multiple units to their families of machines     

嵌入式操作系统UC/OS-II的内核实现

介绍一种源代码公开的嵌入式操作系统UC／0S—Ⅱ，由美国人JEAN J．LABR0SSE编写。程序主要用C语言编写，已在全世界流传，可以移植到多种CPU平台上，有许多成功的应用。     

Call performance for a PCS network

It is well known that, due to the mobility of a portable and limited channel availability, calls of portables may not be completed due to being blocked or terminated during the call initiation or the handover process. The characteristics of the call-completion and call-holding times for both a complete call and an incomplete call are of critical importance for establishing the actual billing process in the PCS network. We derive the call-completion probability (hence, call-dropping probability) and the effective call-holding time distributions for complete/incomplete calls with a general cell-residence time and a general call-holding time are analyzed, and general computable formulas are obtained. We show that when call-holding times are Erlang distributed, easy-to-compute formulas for the probability of a call completion and the expected effective call-holding times for both a complete call and an incomplete call can be derived     

Integrated browsing and querying for image databases

The image database system El Niño uses a new interaction model that aims to overcome the problem of the semantic gap where the meaning that the user has in mind for an image is at a higher semantic level than the features on which the database operates. To solve this problem, we replaced the usual query paradigm with a more active exploration process and developed an interface based on these premises     

基于脉冲重复间隔的活动雷达库关联算法

电子支援侦察系统具有对战场环境中活动雷达进行跟踪、监视的功能,上述功能是通过将雷达脉冲序列与活动雷达库中的记录进行关联实现的。文中提出了一种基于生物信息学中动态规划思想的关联算法,该算法通过提取雷达脉冲序列脉冲重复间隔变化规律,并将此作为识别特征对雷达批数据进行关联,仿真说明了该算法即使在有脉冲丢失和干扰脉冲的情况下仍具有较好的处理效果。     

基于半导体生产管理的数据仓库技术

描述了计算机集成制造(CIM)系统的体系结构及主要功能，提出了一种改进现有数据库管理系统的新型数据仓库设计技术。通过把在线事务处理数据库(OLTP)选择性地增量备份到一个临时的缓存(Cache)数据库，把Cache数据库中的数据增量提取到操作数据存储(ODS)数据仓库中，客户端通过水晶报表服务器或微软OLAP服务器，可直接访问ODS数据库中面向主题集成的各种事实型数据。通过Cache数据库，避免了OLTP数据库与ODS数据库的直接链接，减小了ODS数据仓库数据组合与计算对OLTP数据库的性能影响，最大限度地提升了OLTP数据库的效率，满足了生产线对OLTP数据库的高性能要求。     

Call blocking performance of distributed algorithms for dynamicchannel allocation in microcells

We determine the call blocking performance of channel-allocation algorithms where every channel is available for use in every cell and where decisions are made by mobiles/portables based only on local observations. Using a novel Erlang-B approximation method, together with simulation, we demonstrate that even the simplest algorithm, the timid, compares favorably with impractical, centrally administered fixed channel allocation. Our results suggest that an aggressive algorithm, that is, one requiring call reconfigurations, could provide a substantially reduced blocking probability. We also present some algorithms which take major steps toward achieving the excellent blocking performance of the hypothetical aggressive algorithm but having the stability of the timid algorithm     

Adapting laptops to data acquisition

It is explained how portable computers, which lack expansion slots, can instead be made to accept medium-speed data through their parallel ports. The advantages of portables are recalled, and methods for attaching data acquisition instruments to personal computers are reviewed. The ability of the parallel port to serve as a data acquisition interface capable of performance substantially above that of the RS-232 serial interface is discussed. The issue of building versus buying a parallel port adapter is considered