Time-frequency channel modeling and estimation of multi-carrier spread spectrum communication systems

In wireless communications, the channel is typically modeled as a random, linear, time-varying system that spreads the transmitted signal in both time and frequency due to multi-path propagation and Doppler effects. Estimated channel parameters allow system designers to develop coherent receivers that increase the system performance. In this paper, we show how time-frequency analysis can be used to model and estimate the time-varying channel of a multi-carrier spread spectrum (MCSS) system using a complex quadratic sequence as the spreading code. We will show that for this spreading code, the effects of time delays and Doppler frequency shifts, caused by the mobility of environment objects, can be combined and represented effectively as time shifts. The discrete evolutionary transform (DET), as a time-frequency analysis method, enables us to estimate the effective time shifts via a spreading function and to use them to equalize the channel. Using the effective time shifts, the time-varying channel can be represented simply as linear-time invariant system by embedding the Doppler shifts that characterize the time-varying channel into effective time shifts. The channel parameters are used to estimate the data bit sent. To illustrate the performance of the proposed method we perform several simulations with different levels of channel noise, jammer interference, and Doppler frequency shifts.     

The relationship of service failure severity, service recovery justice and perceived switching costs with customer loyalty in the context of e-tailing

Given that e-tailing service failure is inevitable, a better understanding of how service failure and recovery affect customer loyalty represents an important topic for academics and practitioners. This study explores the relationship of service failure severity, service recovery justice (i.e., interactional justice, procedural justice, and distributive justice), and perceived switching costs with customer loyalty; as well, the moderating relationship of service recovery justice and perceived switching costs on the link between service failure severity and customer loyalty in the context of e-tailing are investigated. Data collected from 221 useful respondents are tested against the research model using the partial least squares (PLS) approach. The results indicate that service failure severity, interactional justice, procedural justice and perceived switching costs have a significant relationship with customer loyalty, and that interactional justice can mitigate the negative relationship between service failure severity and customer loyalty. These findings provide several important theoretical and practical implications in terms of e-tailing service failure and recovery.     

论科研创新中的网络非正式交流及相关资源

就科学研究、知识创新而言 ,信息交流过程的网络化将成为一种趋势。本文着重论述的是 :网络非正式交流与非稳定性信息资源的关系 ;网络的媒介优势导致科学交流中结构模式的变化 ;以及对网络信息流变、知识环境营造的观念认识和开发研究。     

浅谈中小企业内部控制框架的构建

中小企业在我国国民经济中占有重要的地位,然而却没有针对中小企业的内部控制框架。本文从内部控制理论的发展演变过程入手,阐述了中小企业内部控制的目标及现状,认为中小企业内部控制框架应定位于内部控制结构模式,条件成熟后,向内部控制要素框架模式过渡,最后,阐明了中小企业内部框架构建中应注意的问题。     

On the value of project safeguards: Embedding real options in complex products and systems

This study defines a project safeguard as the design and physical development work needed to ensure, or enhance, the embedding of a real option in complex products and systems (CoPS). Safeguards operationalize optionlike strategic thinking at implementation. I examine safeguarding investments through an in-depth multiple-case study of 12 options embedded across 5 projects encompassed by an airport expansion programme. This includes options to phase out delivery (stage-option), grow capacity (growth-option), and switch operational regime (switch-option). Passive safeguards only involve design work, whereas active safeguards involve both design and physical execution. The analysis shows how the confluence between the uncertainty of option exercising and the modularity of the relevant functional elements in relation to the CoPS architecture affects the attractiveness of safeguarding. High uncertainty makes safeguarding less attractive as it can lead to sunk costs that may not pay off over the CoPS operating life. Conversely, high modularity increases the attractiveness of safeguarding because (1) safeguards can be limited to marginal investments at the interfaces between the functional elements with other CoPS subsystems, and (2) the stability of modular design rules increases the likelihood that safeguards remain valid over time. Safeguards build options into integrative CoPS. This flexibility and redundancy makes them resilient to change stemming from option exercising if uncertainties resolve favourably in the future.     

论高职院校辅导员的思考力、执行力和掌控力

学生的特点决定高职院校必须严格管理,思考力、执行力和掌控力是高职院校管理中提高辅导员管理水平的三项重要能力.本文简要阐述了思考力、执行力和掌控力对班级建设和发展的重要性以及提升改善思考力、执行力和掌控力的基本对策.