Spectrum Challenges and Solutions by Cognitive Radio: An Overview

This paper provides an overview of major problems that are confronting wireless communication with regard to spectrum use in general i.e. by all sectors, government, private, other telecom service providers and military communication. It is commonly believed that there is a crisis of spectrum availability due to tremendous growth in the wireless based systems and the evolution of the radio communication technologies. In fact, there is no shortage of radio spectrum, only a dearth of affordable communications infrastructure. There is potential to make considerably better usage of the radio-spectrum. There are many areas of the radio spectrum which are not fully utilized. Cognitive radios (CR) have been proposed as a way to reuse this underutilized spectrum in an opportunistic manner. A CR is an autonomous unit in a communications environment that senses its environment, tracks changes, and reacts upon its findings and frequently exchanges information with the networks. We show the how the radio frequency is being managed in India and what India is doing to face the challenges to improve the spectrum management. The radio Communication Assembly of ITU is also studying the plan for implementation of CR systems including technical and regulatory issues.

CDMA Mobile System Overview: Introduction,Background, and System Concepts

The CDMA Mobile System (CMS) has been developed by Electronics and Telecommunications Research Institute (ETRI) and fieldtested for commercial ser- vice deployment in Korea. The project was started in 1989 and completed in 1995 with the CMS commercial test. During the course of development, there had been active technical cooperation with Qualcomm, Inc. and Korean manufacturers. The CMS adopted the basic CDMA concepts conforming to Korean CDMA system which was derived from IS-95. The CMS functions are allocated to subsystems by considering efficiency and expandability. The CMS consists of mobile stations and the infrastructure which is composed of base stations, mobile exchanges and home location register/authentication center. The commercial field tests performed both in Taejon and Seoul have indicated that the CMS capacity is 10 to 15 times larger than that of AMPS. This paper overviews the development history, system characteristics, architecture and test results.     

大容量、智能化光传输系统：机遇、挑战与应对策略

分析了长距大容量、智能化光传输系统的五大关键技术：单波超400 Gbit/s、波段扩展、空分复用（SDM）、光层操作维护管理（OAM）和备用路径性能检测技术,并从学术研究、业界标准化动态等方面介绍了这些技术的进展。针对光传输系统技术发展趋势,从硬件、软件两个层面讨论了光通信的发展机遇和面临的挑战。基于中兴通讯光网络智能化平台框架,并结合中兴通讯在大容量、高速相干光通信方面的研究与产品开发工作实际,介绍了4个典型案例：灵活调制与光域均衡相结合来有效减少滤波代价、C+L波段扩展助力单波400 Gbit/s长距传输、高频光标签实现在线光性能监测、光探针和全局功率分析算法（GPA）确保备用路径快速可靠恢复。基于这些技术的产品化,中兴通讯将持续为客户创造价值,为用户提供更好的网络服务体验。     

软件定义边界SDP:概念、技术及应用研究综述

随着云计算、容器技术、软件定义网络等新技术不断发展,带来了一系列新的安全挑战,如身份验证,访问控制,数据隐私和数据完整性等。软件定义边界SDP的提出为网络安全模型提供了一种新的解决思路,该模型与VPN最大的区别在于需要先验证用户身份并验证设备才能建立连接。简要描述SDP体系结构,关键技术及应用场景,并对相关产品进行简单对比,结果表明SDP作为一种安全模型可以动态保护访问安全。     

Resource Allocation Schemes in D2D Communications: Overview,Classification, and Challenges

Device-to-Device (D2D) communications is predicted to be a major part of 5G wireless communications due to its benefits such as flexible connectivity and unloading of traffic burden off the cellular networks. However, interference scenarios in D2D communications are usually more complicated than conventional wireless communications, e.g., spectrum reuse is commonly involved in D2D communications, especially when it works as an underlay. Therefore, how to coordinate the challenges of significant interference with the demand of higher data rates under the constraints of efficient energy consumption and spectrum utilization has become a haunting problem in our way to the ideal performance of wireless communications system. The solution resides in multiple resource allocation techniques in D2D communications as each of them attempts to solve or optimize one or several essential elements in the system. In this paper, a survey of resource allocation schemes in D2D communications is presented. We discuss the optimization classification including objectives, constraints, problem types and solutions. This paper also highlights system characteristics. Finally, future research challenges are outlined.     

无线网状网络的安全性：挑战和解决方案

Wireless mesh network is a new emerging field with its potential applications in extremely unpredictable and dynamic environments. However, it is particularly vulnerable due to its features of open medium, dynamic changing topology, cooperative routing algorithms. The article surveys the state of the art in security for wireless mesh networks. Firstly, we analyze various possible threats to security in wireless mesh networks. Secondly, we introduce some representative solutions to these threats, including solutions to the problems of key management, secure network routing, and intrusion detection. We also provide a comparison and discussion of their respective merits and drawbacks, and propose some improvements for these drawbacks. Finally, we also discuss the remaining challenges in the area.     

呼叫中心简介及解决方案

介绍了CTI技术和呼叫中心的发展现状和未来趋势，并通过实例分析，提出了呼叫中心的解决方案。     

电容器测试的挑战与方案

电容器广泛用于旁路、耦合、滤波和隧道电子电路.这些器件的制造商和用户都需要分析器件的电容值、额定电压、温度系数和泄漏电阻作为质量检查.本文详细介绍了电容器的测试技术.     

Multipath Ghosts in Through-the-Wall Radar Imaging: Challenges and Solutions

In through-the-wall radar imaging (TWRI), the presence of front and side walls causes multipath propagation, which creates fake targets called multipath ghosts. They populate the scene and reduce the probability of correct target detection, classification, and localization. In modern TWRI, specular multipath exploitation has received considerable attention for reducing the effects of multipath ghosts. However, this exploitation is challenged by the requirements of the reflecting geometry, which is not always available. Currently, the demand for a high radar image resolution dictates the use of a large aperture and wide bandwidth. This results in a large amount of data. To tackle this problem, compressive sensing (CS) is applied to TWRI. With CS, only a fraction of the data are used to produce a high-quality image, provided that the scene is sparse. However, owing to multipath ghosts, the scene sparsity is highly deteriorated; hence, the performance of the CS algorithms is compromised. This paper presents and discusses the adverse effects of multipath ghosts in TWRI. It describes the physical formation of ghosts, their challenges, and existing suppression techniques.     

Physical Layer Security for MmWave Communications:Challenges and Solutions

The mmWave communication is a promising technique to enable human commutation and a large number of machine-type communications of massive data from various non-cellphone devices like Internet of Things(IoT) devices, autonomous vehicles and remotely controlled robots. For this reason, information security, in terms of the confidentiality, integrity and availability(CIA), becomes more important in the mmWave communication than ever since. The physical layer security(PLS), which is based on the in...     

TCP Variants for Mobile Adhoc Networks: Challenges and Solutions

Wireless Personal Communications - Transmission Control Protocol (TCP) provides connection oriented and reliable transport layer services. Mobile Adhoc Networks (MANETs) are autonomous and...     

细线条自动光学检查所面临的挑战及解决方法

制作高密度互连衬底依靠细线条印刷电路板技术,这种技术带来了非常严格的类似线间距变窄到50～15μm时的成品率问题。几何图形、形状、材料和表面抛光有关的细线条面板对光学检查提出了新的挑战,需要新的方法来保证可靠的检查。这种挑战是由生产因素产生的,例如导体线条的高宽比、在半添加加工中电镀线条的拱形顶部、有光泽或半透明的薄片和嵌入式无源元件等。其他的挑战来自物理和光学极限,即对于非常小的细线条缺陷需要达到很高的放大倍率才能查出。     

Android平台的安全挑战及应对措施

文章分析了当前Android平台所面临的安全威胁,介绍了时下针对Android平台的几种主要的恶意行为,包括恶意吸费、隐私窃取等。文章对于Android平台安全问题的产生原因进行了说明和分析,并提出了相应的解决方案和应对措施。     

对网络设备测试的挑战和解决方案

对基于SoC系统芯片的网络设备进行测试，测试行为因许多交互因素正在变得越来越复杂，这是因为对每一个性能或子系统单独地测试并不能保证系统正确的运行，而对所有可能存在的因素的综合测试几乎是很难实现的。本文将描述导致作者得出上述结论的一些原因。指出怎样在制造中测试网络设备，以及所用的测试方法。网络设备测试的挑战在论证测试网络设备的正常运行是一项具有挑战性的工作之前，值得一提的是甚至对正常运行的界定都简直是一件难事。考虑到设备作为具有高级 QoS (服务质量)和过滤功能的交换机 / 路由器,除了实现IEEE 标准和IE…     

On Routing in Multichannel Wireless Mesh Networks: Challenges and Solutions

Wireless mesh networks have emerged as a promising solution to providing cost-effective last-mile connectivity. Employing multiple channels is shown to be an effective approach to overcoming the problem of capacity degradation in multihop wireless networks. However, existing routing schemes that are designed for single-channel multihop wireless networks may lead to inefficient routing paths in multichannel WMNs. To fully exploit the capacity gain due to multiple channels, one must consider the availability of multiple channels and distribute traffic load among channels as well as among nodes in routing algorithms. In this article we focus on the routing problem in multichannel WMNs. We highlight the challenges in designing routing algorithms for multichannel WMNs and examine existing routing metrics that are designed for multichannel WMNs, along with a simulation-based performance study. We also address some open research issues related to routing in multichannel WMNs.     

Cybersecurity Issues in Wireless Sensor Networks: Current Challenges and Solutions

The spectrum is a scarce resource and shall be used efficiently. It is observed that fixed spectrum allocation techniques, currently in use, may not be able to accommodate increased number of users trying simultaneously to access the network. Researches suggest that this problem of spectrum scarcity can be addressed by cognitive radio networks; which permits the dynamic use of spectrum. One of the basic requirements of dynamic spectrum access in cognitive radio network is spectrum handoff. There is an associated issue with frequent spectrum handoffs and that is of the ping-pong ect. The ping-pong ect is caused due to the motion of mobile users between the adjacent cells, thus, initiating unnecessary spectrum handoffs. The purpose of this study is to develop and analyse a system that has the ability to perform cient decision about the execution of spectrum handoffs and in turn reduce the chances of ping-pong ect. Therefore, a fuzzy logic based system has been developed in a cognitive radio WLAN and UMTS environment and handoff is investigated between primary and secondary users. Our proposed hybrid system uses a two-stage fuzzy logic controller to reduce the number of ping-pong handoffs. In the rst stage, the system is designed to control the power of SU and to avoid any interference to PU. In the second stage, the system is designed to take the decision to execute handoff.

     

New Challenges for Integrated Circuit Solutions

Integrated circuit solutions have been one of the enabling technologies, contributing to the success of wireless communications. As the focus of the new generation is moving towards higher bandwidths and new services and applications, challenges for the integrated circuit solutions are ever growing. Development focus has shifted from component design and optimization towards significant system oriented content captured both in the hardware platform and supporting software. This integrated approach challenges existing development models, and affects other disciplines related to wireless system development. This paper explores major challenges for integrated circuit solutions emerging from the system-oriented approach.     

城市光无线通信网络中的问题及其解决方案

在短距离通信中,城市光无线通信(urban optical wireless communication,UOWC)网络可以提供很高的传输速率,因而越来越受到关注.UOWC的终端包括一个光发射机和一个光接收机,它们通常安装在相距几百米的大厦的顶端.UOWC具有几个显著的优点:使用简单、重量轻便、容量巨大,而且它无需向政府相关部门交纳频率使用许可费.UOWC目前还存在一些问题,比如:在恶劣的天气中或大楼摆动时它的通信性能非常差.本文提出了克服这些缺点的一些方法.     

城市光无线通信网络中的问题及其解决方案

由于城市光无线通信(UOWC)在短距离通信中可以提供很高的传输速率，所以越来越受到关注。UOWC的终端包括一个光发射机和一个光接收机，它们通常安装在相距几百米的大厦的顶端。UOWC具有几个显著的优点：使用简单、小型轻便、容量巨大，而且无需交纳许可费。但是UOWC目前还存在一些问题，比如在恶劣的天气中或大楼摆动时它的通信性能就会非常差。文中提出了一些克服这些缺点的方法。