Impact of secondary user mobility on spectrum handoff under generalized residual time distributions in cognitive radio networks

Cognitive Radio is an emerging technology to accommodate the growing demand for wireless technology via dynamic spectrum access to enhance spectrum efficiency. Spectrum handoff is an important component of Cognitive Radio technology for practical implementation of radio frequency access strategy and better utilization of spectrum in both primary and secondary networks. The probability of spectrum handoff and expected number of spectrum handoffs are key parameters in performance analysis and design of the cognitive radio network. This work presents an analytical model to evaluate the impact of secondary users’ mobility on intra-cell spectrum handoff considering primary users’ activity model in a cognitive radio network. A standard form of intra-cell spectrum handoff probability and expected number of intra-cell spectrum handoffs are derived for complete call duration of a non-stationary secondary user. The probability and expected number of intra-cell spectrum handoffs of a post inter-cell handoff call are also derived for generalized residual time distributions of call holding time and spectrum holes. A detailed analysis of these performance measuring metrics is presented under the impact of departure rate and cell crossing rate of secondary users. The accuracy of the derived analytical result is validated by Monte-Carlo simulation of the model.     

不同推荐系统输入的聚类实现

论文在分析推荐输入瓶颈问题的基础上,借助社区思想实现了显式评分输入的用户聚类,解决了评分矩阵稀疏的问题;借助用户兴趣度的定义,实现了隐式浏览输入的用户聚类,解决了用户兴趣度不易获取的问题．论文的研究立足于推荐系统的输入,通过聚类分析,为推荐算法的研究奠定了理论基础．     

Maximum product of effective channel gains: an innovative user selection algorithm for downlink multi‐user multiple input and multiple output

Recently, zero‐forcing beamforming has been widely used for multiple‐input and multiple‐output broadcast channels, because it could provide suboptimal capacity with low complexity. To increase the sum data rate, a good user selection algorithm is attractive. In this paper, a new user selection algorithm named maximum product of effective channel gains is presented. The proposed algorithm is described mathematically, and the lower bound of the sum capacity is demonstrated to be proportional to the product of effective channel gains. Our simulation results show that maximum product of effective channel gains can achieve higher sum rate compared with the classical algorithm, semi‐orthogonal user selection, with the same complexity order, especially when the signal‐to‐noise ratio is high; in addition, the complexity of the proposed algorithm is superior to minimum of the Frobenius norm of the pseudo‐inverse algorithm. Meanwhile, the number of users that can be served simultaneously is equal to the number of transmission antennas, which is the maximum performance that can be achieved.Copyright © 2012 John Wiley & Sons, Ltd.     

电信运营商网络与信息系统安全管控技术探讨

本文详细阐述了在3G和全业务形势下,电信运营商新型网络与信息系统安全管控方案、创新技术、解决的问题、技术难点、系统部署等内容,提高安全管控对网络与信息系统的安全保障水平和运维效率。     

基于IOS环境的应用软件交互设计策略

以苹果公司App Store销售平台上所发布的移动App应用的人机交互界面设计为例,从产品交互设计角度,提出一种相对实用、高效的移动App应用图形用户界面（GUI）的设计策略。该设计策略更适应移动App应用的商业生存法则。     

简易量化分析方法在网优策略中的应用

作为全球少数几个超大本地网之一,近年来,上海地区移动通信网络情况日益复杂,在话音业务中的客户感知和运营商网络指标之间存在着一定程度的差异.为了改善客户最终体验,需要优化网络综合质量.在对网络优化目标原则进行了研究之后,提出了一种简易的网优策略量化分析方法,定义了一系列场景采用量化算法对比分析,寻找在安全、成本、容量上的...     

基于网络负载的动态资费奖励业务经验分享

移动通信的市场竞争日趋激烈,运营商在面临同质化竞争、资费不断下降、收入增长平缓的同时,也受困于网络资源使用严重不均衡的问题。本文介绍了爱立信通过动态资费奖励业务帮助运营商有效改善这些问题的内容。     

嵌入式实时操作系统中系统调用方法的设计与实现

在高安全性的实时操作系统中支持两种运行形态:系统态和用户态。核心OS运行在系统态,应用运行在用户态。为有效保护核心OS的安全,用户态的应用通过系统调用的方式调用核心OS提供的功能接口。笔者在深入研究系统调用的基础上,设计并实现了一种系统调用方法。通过在某嵌入式实时操作系统中的实现,证明该方法是安全的、可行的、有效的。     

省级电信运营商Cache系统建设方案探讨

通过建设Cache系统,可以靠近用户提供电信服务,提升用户体验.本文分析比较了Cache系统的三种用户引导模式,结合电信运营商的网络部署现状,探讨了Cache系统的网络部署方案以及运营思路等,对省级电信运营商Cache系统的建设具有重要的借鉴意义.     

User pairing schemes for capacity maximization in non‐orthogonal multiple access systems

This paper addresses the issues related with conventional near–far user pairing in non‐orthogonal multiple access. Performance effects of near–far pairing on regions with negligible channel gain differences between users are investigated. These regions occur when pairing is performed between cell center and cell edge users, thus leaving the cell mid users to be either paired with each other or kept unpaired. Pairing these mid users with each other causes successive interference cancelation (SIC) performance degradation resulting in capacity reduction for these users. On the other hand, leaving these mid users unpaired perfectly avoids the SIC issue but makes these users unable to benefit from the capacity gains provided by non‐orthogonal multiple access. Therefore, two user pairing strategies have been proposed that can provide capacity gains to almost all the users by accommodating them in pairs, while avoiding or minimizing the mid users pairing problem. A generalized M‐users pairing scheme is also proposed. Simulations have been performed to investigate the performance of proposed schemes for both perfect and imperfect SIC receiver scenarios in comparison with conventional pairing where the mid users are kept paired with each other. Simulation results show that proposed schemes achieve high capacity gains, especially when imperfect SIC is considered. Copyright © 2016 John Wiley & Sons, Ltd.