Semi-Markov multistate modeling of the land mobile propagation channel for geostationary satellites

This paper describes a new semi-Markov propagation channel model for land mobile satellite systems using geostationary satellites. The multistate model switches between propagation states representing line-of-sight, shadowing, or blockage of the signal. The duration of times spent in each state follow probability distributions recommended by the radiocommunication sector of the International Telecommunication Union (ITU-R). The actual parameters to be used with the ITU-R distributions were modified and fitted to observed data. The open-area state durations follow a power-law distribution, while the state durations for both the shadowed and the blocked states follow a lognormal distribution. Parameters for both two- and three-state models are extracted from an L-band measurement campaign performed by Inmarsat in the United Kingdom. Propagation channel models characterizing the fading within the open, shadowed, or blocked propagation states are described as well. The semi-Markov models represent an improvement over the more commonly used Markov models where the duration in each state follows an exponential distribution. The new model enables more accurate prediction and simulation of system performance and availability.     

西安鼓楼历史街区保护与发展

本文是中挪合作项目，它以生态、文化和社会可持续发展原理为基础，探讨城市的保护与更新。以西安鼓楼历史街区、西安回民区中的一部分作为示范区。本文从城市对规划挑战与需要、文化遗产价值及其在规划中的冲突、城市地区的文化遗产评估的概念、示范设计途径、街道设计、分析结论六方面进行了阐述。