Traffic Models and Blocking Probabilities for Two-Fold and Three-Fold SDMA Communication Systems

Spectrum efficiency is a constant challenge in the design of wireless networks. Space-division-multiple-access (SDMA) is a promising approach to achieve higher spectral efficiency which reuses bandwidth via multiplexing signals based on their spatial signature. Several different studies have shown that SDMA can effectively improve system capacity in a mobile environment. In this paper, we present a new Markov chain traffic model for a duplicate-at-last (DL) approach [IEE Proceedings on Communication 146 (1999) 303] in two-fold and three-fold SDMA systems. Simplified blocking probability formulations for two-fold and three-fold SDMA are also derived. Simulations based on a common method of spatial separation check for channel allocation in SDMA are presented to evaluate the probability of successfully creating two-fold and three-fold SDMA channels. The simulation, as well as analytical, results indicate that the SDMA system can reduce the blocking probability of the calls and result in more traffic loading than a traditional cellular system. The results also show that our simplified approaches not only can reduce the computational complexity, but can also accurate approximate two-fold and three-fold SDMA performance. Wen-Jye Huang received the B.S. degree in electrical engineering from Tatung Institute of Technology, Taipei, Taiwan, in 1991, the M.S. degree in electrical engineering from Ohio University, Athens, OH, in 1997, and the Ph.D. degree in electrical engineering from The Pennsylvania State University, University Park, PA, in 2001. Since 2002, he joined the Department of Electrical Engineering, Chang Gung University, Kwei-San, Tao-Yuan, Taiwan, as an assistant professor. His research activities include smart antenna, SDMA, and MC-CDMA techniques. John F. Doherty received the B.S. degree (with honors) in engineering science from the College of Staten Island, City University of New York, in 1982, the M.Eng. degree in electrical engineering from Stevens Institute of Technology, Hoboken, NJ, in 1985, and the Ph.D. degree in electrical engineering from Rutgers University, New Brunswick, NJ, in 1990. He was an integrated circuit reliability engineer with IBM, from 1982 to 1984. From 1985 to 1988, he was member of the technical staff at AT&T Bell Laboratories, working in sonar signal processing. In 1990, he joined the Electrical and Computer Engineering Department, Iowa State University, Ames, as an assistant professor and Harpole Entair fellow. He is currently an associate professor of electrical engineering with The Pennsylvania State University, University Park. His current research activities include interference rejection in wireless communication systems, spatial-division multiple-access techniques, and radar target detection techniques. He is a former AFOSR summer faculty research fellow at the Rome Laboratory, Rome, NY, and an Army Research Office Young Investigator.     

移动软交换核心技术研究

由于软交换技术与移动核心网络技术的结合具有众多的优越性,已成为研究热点.为此文章对下一代移动核心网的相关技术标准、组网结构、服务质量、网管、业务等进行了阐述,并分析了下一代移动核心网络的关键技术、演进步骤、所能开展的业务以及未来网络如何融合等问题.     

Delay-on-Demand: A Signaling Protocol to Reduce Blocking Probability in Optical Burst-Switching Networks

Optical burst switching (OBS) is emerging as one promising switching paradigm for the next generation optical networks. To support multiple services in burst-switching networks, the OBS paradigm should support some quality-of-service (QoS) provisioning. A major design issue in such networks is to reduce the blocking probability of the bursts arising due to resource contention at the intermediate core router. In this paper, we propose a signaling protocol which we call ‘Delay-on-Demand’ (OBS-DoD), to reduce blocking probability and support QoS in optical burst-switching networks. The proposed scheme guarantees that at least one of the bursts succeeds depending on its priority, propagation delay from the ingress router, and the burst-size when contention occurs at the core router. For this, we use a control packet to delay, in case of a contention, the transmission of bursts at the ingress router. We compare the performance of our proposal, by simulation, with an earlier proposed scheme, and show that the proposed OBS-DoD outperforms the earlier scheme in reducing the blocking probability. For simulation, we generated bursty traffic using an M/Pareto distribution.     

On large minimal blocking sets in PG(2,q)

The size of large minimal blocking sets is bounded by the Bruen–Thas upper bound. The bound is sharp when q is a square. Here the bound is improved if q is a non‐square. On the other hand, we present some constructions of reasonably large minimal blocking sets in planes of non‐prime order. The construction can be regarded as a generalization of Buekenhout's construction of unitals. For example, if q is a cube, then our construction gives minimal blocking sets of size q^4/3 + 1 or q^4/3 + 2. Density results for the spectrum of minimal blocking sets in Galois planes of non‐prime order is also presented. The most attractive case is when q is a square, where we show that there is a minimal blocking set for any size from the interval . © 2004 Wiley Periodicals, Inc. J Combin Designs 13: 25–41, 2005.     

Product form stationary distributions for queueing networks with blocking and rerouting

In this paper we study Markovian queueing networks in which the service and the routing characteristics have a particular form which leads to a product form stationary distribution for the number of customers in the various queues of the network. We show that if certain transitions are prohibited due to blocking conditions, then the form of the stationary distribution is preserved under a certain rerouting protocol. Several examples are presented which illustrate the wide applicability of the model. This revised version was published online in June 2006 with corrections to the Cover Date.     

小灵通应急通信系统的工程建模与仿真

应用Matlab语言GUI工具,建立了小灵通(PAS)应急通信系统的工程实施模型.功能包括:建立了小灵通通信系统的统计模型;对应急服务区固定网络通信指标分析;对有应急任务时,现场通信情况预先模拟,以确定工程施行过程中应急通信设备数量等的投入;还设计了模拟通信工作环境的电子地图,以直观地显示通信现场情况等.系统模型的建立为小灵通应急通信任务的高效运行提供了必要的保障.     

Time-varying many-server finite-queues in tandem: Comparing blocking mechanisms via fluid models

This paper focuses on the mechanism of Blocking Before Service (BBS), in time-varying many-server queues in tandem. BBS arises in telecommunication networks, production lines and healthcare systems. We model a stochastic tandem network under BBS and develop its corresponding fluid limit, which includes reflection due to jobs lost. Comparing our fluid model against simulation shows that the model is accurate and effective. This gives rise to design/operational insights regarding network throughput, under both BBS and BAS (Blocking After Service).     

船舶遇险报警通信设备使用策略

介绍了新航天测量船在航天工程中的重要作用,简述了各种船载通信设备的配备和功能。针对船载通信设备的特点,具体阐述了船载遇险报警通信设备的作用。特别是总结了在船舶遇险时,根据通信设备无线电波的覆盖范围和船舶所在的海区,对遇险报警设备进行正确使用的策略,以保障遇险报警及时而有效。最后举例说明了船舶在三大洋航行时,某点位发生遇险时,船舶如何求救的措施。     

基于排队理论的信道分配算法研究

针对蜂窝移动通信系统,基于排队理论提出了一种信道分配方案。该方案将信道分为2部分:语音信道和数据保护信道。预留数据保护信道用于补偿数据丢包率,同时对语音业务设置FIFO排队缓冲器,切换呼叫优先占用缓冲器以确保切换优先。当语音信道空闲时,数据业务可以占用语音信道,一旦有语音呼叫请求到来且无可用语音信道,数据业务应释放占用的语音信道,在数据缓存器中排队等待。仿真结果表明该方案不仅降低了新增呼叫阻塞率和切换掉话率,而且提升了数据业务的性能。     

看涨期权契约与看跌期权契约对比分析研究

在面临相同随机市场需求的情况下,本文对期权契约中的看涨期权与看跌期权契约进行了对比分析,以期为决策者在实际采购活动中选择不同类型的期权契约时提供决策依据。通过模型建立与求解分析,本文得出了销售商接受期权契约时,契约参数需要满足的条件及相应的订购策略;并进一步得出了两种期权契约下,供应链达到协调状态时的具体条件,分析了此时契约参数对供销双方利润的影响,继而给出了两种期权契约的适用范围以及供销双方的契约选择偏好。在此基础上,本文还给出了不同期权契约下,供销双方各自利润均不低于其自身保留利润时契约参数的取值范围,并证明了两种期权契约均可有效提高销售商的利润水平。最后,本文通过算例对上述结论进行了验证。