WiMAX接入核心网络中的数据通道技术

近几年来，无线通信技术飞速发展，宽带技术无线化是宽带通信发展的趋势。作为一种宽带无线技术，WiMAX因其传输速率快、传输距离远、具有QoS保障、安全性能好等优点，在“最后一公里”接入技术中占据非常重要的地位。在WiMAX接入核心网络中，数据通道技术就是完成基站、网关间的数据传输，是基站和网关中一个不可缺少的功能模块。详细介绍了数据通道的建立、修改和删除过程以及在几种典型场景中的应用。     

Adaptive Empirical Path Loss Prediction Models for Indoor WLAN

This paper presents robust empirical path loss models to characterize indoor propagation for access point (AP) deployed at different heights. The proposed models are developed with wireless local area network infrastructure at 2.4 GHz. The models are backed by extensive received signal strength (RSS) measurements acquired in line of sight and obstructed line of sight regions. The models are developed for two conditions, viz; quasi realistic and realistic RSS measurements. The quasi realistic measurements are taken after suppressing human intervention and electrical interferences to minimum. While the realistic RSS measurements are made in presence of all the human interventions and electrical interferences. The shadow fading component for both quasi realistic and realistic conditions is statistically modeled with the dependency on AP height. The proposed technique can be applied with higher confidence level to the buildings with similar construction features where RSS measurements are made upon. The results reveal that the performance of the proposed propagation models is significantly higher than the existing International Telecommunication Union-path loss model. The results also demonstrate that the realistic path loss model is more robust than the quasi realistic model.     

Analytical Models for Architecture-Based Software Reliability Prediction: A Unification Framework

Traditional approaches to software reliability modeling are black box-based; that is, the software system is considered as a whole, and only its interactions with the outside world are modeled without looking into its internal structure. The black box approach is adequate to characterize the reliability of monolithic, custom, built-to-specification software applications. However, with the widespread use of object oriented systems design & development, the use of component-based software development is on the rise. Software systems are developed in a heterogeneous (multiple teams in different environments) fashion, and hence it may be inappropriate to model the overall failure process of such systems using one of the several software reliability growth models (black box approach). Predicting the reliability of a software system based on its architecture, and the failure behavior of its components, is thus essential. Most of the research efforts in predicting the reliability of a software system based on its architecture have been focused on developing analytical or state-based models. However, the development of state-based models has been mostly ad hoc with little or no effort devoted towards establishing a unifying framework which compares & contrasts these models. Also, to the best of our knowledge, no attempt has been made to offer an insight into how these models might be applied to real software applications. This paper proposes a unifying framework for state-based models for architecture-based software reliability prediction. The state-based models we consider are the ones in which application architecture is represented either as a discrete time Markov chain (DTMC), or a continuous time Markov chain (CTMC). We illustrate the DTMC-based, and CTMC-based models using examples. A detailed discussion of how the parameters of each model may be estimated, and the life cycle phases when the model may be applied is also provided     

A Framework for Cognitive WiMAX With Frequency Agility

Cognitive radios have the ability to sense the radio spectrum environment and to switch dynamically to available frequency ranges. Mobile WiMax is an emerging wireless networking standard that could potentially benefit from cognitive radio technology. We develop a framework for applying cognitive radio technology to mobile WiMax networks to increase capacity and simplify network operations. In the proposed cognitive WiMax architecture, base stations are equipped with sensitive detectors and assign channels to subscriber stations dynamically based on spectrum availability. Power control is employed to increase frequency reuse in conjunction with spectrum sensing. Using computer simulation, we evaluate the performance of ldquocognitive channel assignmentrdquo relative to conventional dynamic channel assignment. Our numerical results show that cognitive radios can substantially increase the capacity of emerging WiMax networks by exploiting inherent spectrum hole opportunities. The key performance parameters determining the achievable capacity of cognitive WiMax networks are the detection and interference range, which depend in turn on characteristics of the radio propagation environment.     

WiMAX网络的自适应切换算法

宽带无线通信由于载频的不断提高使得覆盖网络的半径越来越小,切换将变的更加频繁。针对不同移动用户,提出了一种基于移动速度的自适应切换算法,在切换过程中目标基站通过自适应的调整切换的延时时间来提高切换质量,降低了切换的掉话率。仿真表明,该策略可以有效降低切换掉话率,得到了一个比较完善的切换机制,可广泛用于将来宽带无线通信融合网络的切换中。     

网络流量预测中的时间序列模型比较研究

网络流量预测在新一代网络协议设计、网络管理与诊断、设计高性能路由器等方面都具有重要意义.目前通常采用ARMA和FARIMA时序模型对网络流量序列进行拟合与预测,但没有对时间尺度的大小与模型选择的关系进行研究.本文对实际网络流量在不同时间尺度(毫秒、秒、分)下进行了流量预测建模并对预测性能进行比较,分析表明使用时序模型进行流量预测时,大时间尺度(分)流量预测较小时间尺度(毫秒、秒)具有更小的预测误差.并且,对于小时间尺度上的自相似流量序列,自相似模型FARIMA并没有较其他时序模型有更好的预测性能.     

WiMAX无线网络规划方法

随着宽带无线接入技术的发展,WiMAX无线网络的应用越来越广泛,因此WiMAX网络的规划方法和手段受到越来越多的重视.本文讨论了 WiMAX无线网络在规划中引入的新问题,介绍了WiMAX无线网络规划流程和方法,阐述了规划中需重点考虑的问题.     

WiMAX体系结构和应用

介绍了以IEEE802.16标准为基础的无线城域网技术WiMAX的发展过程,分析了无线城域网体系结构,包括物理层技术特点、MAC层的QoS保证机制,并对WiMAX的几种典型应用进行了分析.     

WiMAX网络规划策略研究

随着WiMAX无线网络应用的不断增加,WiMAX大规模组网中．无线网络规划方法的重要性日益突出。根据WiMAX无线通信技术的现状,文中给出了WiMAX无线网络规划的一般流程．并对其中覆盖预测、容量预测及频率规划等重要问题进行了阐述。     

WiMAX Network for Capacity and Coverage Assessment

This article represents the system performance and its operation stability of a fixed worldwide interoperability for microwave access network operating with point to multipoint technology. It provides broadband access in fixed locations for mixed environments in Greater Noida, UP, India. The Field measurement for its capacity and coverage are recorded simultaneously to optimize a network by raising customer premises equipment (CPE) antenna height. This process is not going to alter any technical parameters of a network. CPE antenna is a directional antenna facing towards base station to achieve optimum LOS reception. The net changes in RSS 10–17 dBm, DTR 512–1.8 Mbps, path loss exponent 0.5–0.9 and standard deviation of 1.2–2.3 were observed by raising CPE antenna height of 2–5 m above the prescribed height. The path loss exponents for different environments are obtained using least squares method based on measured data by MatLab statistics tool. Standard deviations of signal strength variability with distance are derived. Real coverage of a network is presented based upon path loss exponent and standard deviation. Our result suggest that, raising the height of CPE antenna can reduce transmitted power, there for reducing overall maintenance cost and system interference in future.     

提升4G无线网扩容方案准确度研究

随着不限量套餐的推进,4G网络用户和业务节节攀升,4G小区扩容需求激增,4G网络首次面临大规模容量冲击。而此前,由于4G网络一直处于规模覆盖提升阶段,只对局部已发生的容量需求进行零星补充。随着扩容规模性增长,零星补充扩容已无法满足需求,并将逐渐影响到4G网络用户感知。因此4G网络中,需同时精准预测用户数、业务需求带宽、网络承载效率和网络负载门限才能确保扩容准确率。     

移动WiMAX无线网络规划

讨论移动WiMAX无线网络规划流程和方法，阐述规划中需要考虑的重要问题。     

WiMAX网络规划研究

分析了影响WiMAX网络规划的主要因素,阐述了规划所遵循的基本原则,并分别从前期调研、初步规划和详细规划方面详细介绍了WiMAX网络规划的流程。     

基于神经网络模型的网络流量预测综述

网络流量预测技术可以帮助运营商准确预估网络的使用情况,合理分配并高效利用网络资源,以满足日益增长且多样化的用户需求。大量研究表明,神经网络的预测性能高于其他经典预测方法,在网络流量预测中的应用潜力巨大。总结网络流量预测的一些关键因素和预测误差评判方法,重点介绍近年提出的可用于预测的神经网络模型原理、相关预测方法及其属性比较,旨在为包括流量在内的各种网络参数预测技术的学术研究与实际应用提供可借鉴的方法和手段。     

移动WiMAX的组网方式研究及性能仿真

本文从目前常见的移动网组网方式和频率复用方式出发,重点分析了在不同频率复用方式下网络性能的优劣,并通过系统仿真,量化地比较不同组网方式下网络覆盖和小区吞吐量的差异,从而为移动WiMAX的规划建设提出具有指导意义的建议.     

WiMAX无线网络规划

本文结合WiMAX的技术特性,主要探讨了IEEE802.16d和802.16e无线网络的覆盖、容量和频率规划特点,并分析了WiMAX的系统干扰,为运营商的网络建设提供了参考与建议。     

基于WiMAX网络的入网技术研究

WiMAX是一种基于标准的技术，具有标准化、技术成熟、传输速度快、覆盖范围广、良好的抗雨衰性能、扩容性强，组网灵活的优点，已成为当前运营商宽带城域网建设“最后一公里”理想的无线接入手段。文章给出了WiMAX网络详细的入网过程，包括网络发现与选择、鉴权注册、业务流和数据通道的建立，并给出了WiMAXN络的自举过程及每个过程中详细的通信流程图。     

基于神经网络的传播预测模型浅析

传播预测模型是网络规划和频谱资源合理利用的基础。在分析了现有模型不足的基础上,介绍了人工神经网络的结构及其传播预测模型的构建,并对该模型进行了改进,提出了应用反向传播(Back-Propagation,BP)神经网络的混合传播模型。人工神经网络具有良好的非线性逼近能力和泛化能力,非常适用于特定地区传播损耗的预测。通过对试验数据的分析处理,验证了此方法能够更真实地反映该区域的无线电波传播环境,得到更高的预测准确度。     

太阳能电池组件过程功率测试准确性提高的研究

主要研究提高晶体硅太阳能电池组件功率测试准确性的方法。通过优化测量环境、测量仪器设置等因素,功率测量准确性能够得到有效提高,这些方法在组件生产中的应用对质量保障非常有利。     

WIRELESS BROADBAND ACCESS: WIMAX AND BEYOND - A Secure and Service-Oriented Network Control Framework for WiMAX Networks

WiMAX, worldwide interoperability for microwave access, is an emerging wireless communication system that can provide broadband access with large-scale coverage. As a cost-effective solution, multihop communication is becoming more and more important to WiMAX systems. To successfully deploy multihop WiMAX networks, security is one of the major challenges that must be addressed. Another crucial issue is how to support different services and applications in WiMAX networks. Since WiMAX is a relatively new standard, very little work has been presented in the literature. In this article we propose a secure and service-oriented network control framework for WiMAX networks. In the design of this framework we consider both the security requirements of the communications and the requirements of potential WiMAX applications that have not been fully addressed previously in the network layer design. The proposed framework consists of two basic components: a service-aware control framework and a unified routing scheme. Besides the design of the framework, we further study a number of key enabling technologies that are important to a practical WiMAX network. Our study can provide a guideline for the design of a more secure and practical WiMAX network