基于动态定价的帧聚合策略(英文)

Frame aggregation is a wireless link optimization mechanism that aims to reduce transmission overheads by sending multiple frames as the payload of a single MAC frame. It is considered as one of the most efficient methods to improve the wireless channel utilization and the throughput of wireless networks.The static assignment of frame aggregation parameters can result in delay penalties due to variations in traffic type. We propose a frame aggregation scheme which is based on dynamic pricing and queue scheduling for a multitraffic scenario. The scheme adopts a dynamic differential pricing scheme for different types of traffic. Meanwhile, it polls buffer queues in accordance with the optimal aggregation weight factors to maximise the network revenue.Simulation results indicate that the proposed frame aggregation scheme can effectively improve the network revenue and the average throughput, while guaranteeing the delay requirements of all types of traffic.     

EEFA:高能效的IEEE 802.11N帧聚合调度算法(英文)

Packet size is restricted due to the error-prone wireless channel which drops the network energy utilization.Furthermore,the frequent packet retransmissions also lead to energy waste.In order to improve the energy efficiency of wireless networks and save the energy of wireless devices,EEFA(Energy Efficiency Frame Aggregation),a frame aggregation based energy-efficient scheduling algorithm for IEEE 802.1 In wireless network,is proposed.EEFA changes the size of aggregated frame dynamically according to the frame error rate,so as to ensure the data transmission and retransmissions completed during the TXOP and reduce energy consumption of channel contention.NS2simulation results show that EEFA algorithm achieves better performance than the original frame-aggregation algorithm.     

一种采用两级缓冲调度区分业务的帧聚合策略

帧聚合是改善无线MAC(Media Access Control)协议信道利用率,提高频谱效率的有效手段之一。该文针对多业务场景,采用两级缓冲区调度策略,按照不同聚合权重因子对各队列轮询聚合。根据各个队列的包超时紧迫因子动态调整各队列的聚合权重,以满足各QoS等级业务的时延限制。该文还将排队论模型引入到帧聚合策略的性能分析中,建立了系统的数学分析模型,定量分析了主要性能参数与系统负载的关系。通过与IEEE 802.11n标准中定义的两层帧聚合策略比较表明,该文提出的帧聚合策略的性能优于IEEE 802.11n两层帧聚合策略。     

通信星座综合性能优化(英文)

In order to attain better communications performance rather than just expand coverage and save system cost,criteria related to the communications quality and capacity are extracted and revised to build an integrated performance metric system which aims to effectively guide the satellite communications constellation design.These performance metrics together with the system cost serve as the multiple objectives whilst the coverage requirement is regarded as the basic constraint in the optimization of the cons...     

cdma定位业务探讨(下)

５定位服务质量定位服务质量是ＬＣＳ客户向ＭＰＣ提交定位请求时 ,向ＭＰＣ描述所需服务质量的一组属性。ＰＱｏＳ属性包括响应时间、水平精度、垂直精度、优先级和位置信息保留时间。不同的ＰＱｏＳ可以满足不同业务对精度、响应时间和优先级等的不同需要。５．１精度精度包括水平精度和垂直精度。ＭＰＣ应当尽可能满足ＬＣＳ客户提出的精度要求 ,对精度要求取决于业务类型 ,有的只对水平精度要求 ,有的可能还有垂直精度的要求 ,如美国紧急服务要求在采用基于移动台的定位技术时 ,精度小于５０ｍ的占６７ % ,小于１５０ｍ占９５ % ,对于一…     

通用组帧规程(GFP)帧同步性能研究

通用组帧规程(GFP)是一种具有实现简单和低开销特点的新型数据链路协议,其帧同步采用基于帧标头循环冗余校验(CRC)的多个帧搜捕器方案。采用状态转移法对其帧同步性能进行研究,并给出计算和数值分析结果。针对该方案帧失步平均持续时间过长的缺点,提出了一种GFP帧同步机制的改进方案。理论分析和计算结果表明,此方案可以有效降低GFP帧同步的失步平均持续时间,改善GFP帧同步系统的性能。     

突发业务环境下CBR业务性能的实验分析

CBR业务是一类极为重要的实时业务,能否有效地传递这类业务关系到从现有网络向ATM的过渡,因此CBR业务的服务质量是一个值得研究的重要课题。本文利用计算机仿真的方法,全面地分析了突发业务环境下,影响CBR业务服务质量的各种因素,指出复接器占有率、缓冲区容量、背景强度、背景流的自相关特征对CBR业务的时延及时延抖动有很大的影响,尤其是背景流具有长时相关性时,CBR业务的服务质量将严重恶化,必须设法加以控制。     

突发业务环境下CBR业务性能的实验分析

ＣＢＲ业务是一类极为重要的实时业务,能否有效地传递这类业务关系到从现有网络向ＡＴＭ的过渡,因此ＣＢＲ业务的服务质量是一个值得研究的重要课题,本文利用计算机仿真的方法,全面地分析了突发业务环境下,影响ＣＢＲ业务服务质量的各种因素,指出复接器占有率,缓冲区容量,背景强度,背景流的自相关物征对ＣＢＲ业务的是延及时抖动有很大的影响,尤其是背景流具有长时相关性时,ＣＢＲ业务是服务质量将严重恶化,必须设法加以     

中高层大气瑞利多普勒测风激光雷达性能分析(英文)

设计了基于Fabry-Perot(FP)标准具的中高层大气(20~60 km)多普勒测风激光雷达(DWL)系统。介绍了激光雷达的多普勒测风基本原理;根据探测指标分别给出了DWL的发射机、接收机、发射接收光学和风场反演等子系统方案,重点对接收机的参数进行了详细的设计与分析;最后对全系统的信号信噪比、探测偏差进行了理论模拟。得出的结论为:当脉冲累计时间为5 min(15 000 shots)时,该系统在晚上60 km高度处的探测偏差为3.6 m/s。     

电信业务处理系统业务需求分析(下)

文章在分析了中国电信的目前业务处理的系统现状的基础上,提出了新的电信业务处理系统的定位、宗旨和设计思想,详细说明了信息的组织方式。并分析了新的竞争形势下电信业务处理系统的业务需求、功能要求、统计查询要求和接口要求。     

Performance Analysis of S-MAC Protocol under Unsaturated Conditions

In this letter, we present a new analytical model that accurately evaluates the throughput, service delay and energy consumption of S-MAC protocol. Our model takes into account the impact of several factors together, including periodic listen and sleep cycle, various incoming traffic loads, the backoff mechanism in S-MAC protocol, the queueing behavior at the MAC layer, and the non-independent nature of service delay distributions of nodes. Simulations show that our analytical results are highly accurate.     

Delay Performance Analysis and Evaluation of IEEE 802.11e EDCA in Finite Load Conditions

The paper presents an analytical model for the performance evaluation of IEEE 802.11e EDCA scheme under finite load conditions on the basis of various instances of delay metric (i.e., media access delay, queuing delay and total delay). The simulation results show that the analytical estimated instances of the delay metric are almost accurate. The paper exhibits that concerning the delay of serving classes, EDCA compared to the conventional DCF, favors high priority classes against low priority ones, while almost does not affect the behavior of medium ones. Dimitris Vassis was born in Ioannina, Greece, in 1978. He received the Diploma in Electrical and Computing Engineering and the MBA in Techno-economic Systems both from the National Technical University of Athens (NTUA), Greece, in 2001 and 2004 respectively. Currently, he is a Ph.D. student in the University of the Aegean, Department of Information and Communication Systems Engineering. His research interests are in the fields of performance evaluation and performance analysis of wireless access networks. George Kormentzas is currently lecturer in the University of the Aegean, Department of Information and Communication Systems Engineering. He was born in Athens, Greece on 1973. He received the Diploma in Electrical and Computer Engineering and the Ph.D. in Computer Science both from the National Technical University of Athens (NTUA), Greece, in 1995 and 2000, respectively. From 2000 to 2002, he was a research associate with the Institute of Informatics & Telecommunications of the Greek National Center for Scientific Research “Demokritos”. His research interests are in the fields of traffic analysis, network control, resource management and quality of service in broadband networks. He has published extensively in the fields above, in international scientific journals, edited books and conference proceedings. He is a member of pronounced professional societies, an active reviewer and guest editor for several journals and conferences and EU-evaluator for Marie Curie Actions. George Kormentzas has participated in a number of national and international research projects, serving in some instances as the project's technical representative for University of Aegean and/or as WP leader and/or as the project's Technical Manager.     

Performance analysis of IEEE 802.11ah wireless local area network under the restricted access window‐based mechanism

IEEE 802.11ah is an approved amendment to IEEE 802.11 wireless local area network (WLAN) standard to support growing demand for machine‐to‐machine (M2M) applications. To enable an efficient scheme for accessing the channel by a large number of stations (STAs) within the coverage of an access point, 802.11ah has developed a novel mechanism known as Restrictred Access Window (RAW). Here, a group of STAs attempts channel access during their designated RAW slot by following the carrier sense multiple access‐collission avoidance (CSMA‐CA)‐based enhanced distributed channel access (EDCA) mechanism. In this paper, we develop an analytical model for finding the nonsaturation/saturation throughput of 802.11ah WLAN under the RAW‐based channel access mechanism. We describe an analytical model for finding the average frame delay as well. The impact of the number of STAs and number of groups on network throughput and average delay are presented. We establish that the RAW mechanism can improve the throughput while the average frame delay gets reduced. The analytical results are validated by extensive simulation studies.     

An efficient admission control for IEEE 802.11 networks based on throughput analyses of (un)saturated channel

This paper presents a novel analytical model and an efficient admission control (AC) algorithm for IEEE 802.11 distributed coordinated function access mechanism. In contrast to the previous approaches, both saturated and unsaturated states of network are analyzed and the impacts of error‐frame rate and retransmission limit are also taken into account based on an improved Markov chain model. Thus, the network resources can be efficiently utilized. Taking the throughput difference between saturated and unsaturated states as the residual bandwidth, an efficient AC algorithm is designed to utilize the network resources effectively. Extensive simulation data match our analytical results and demonstrate that the AC algorithm is efficient and can make the effective utilization of network resources. Copyright © 2008 John Wiley & Sons, Ltd.     

基于控制帧改进的速率自适应算法

针对目前经典的IEEE 802.11速率自适应算法进行分析研究,提出了在基于接收端的自适应速率算法(RBAR)和机遇式自适应速率算法(OAR)基础上根据信道质量对控制帧采用速率自适应从而减少控制帧开销的改进机制,以提高网络资源的利用率和系统的吞吐量。采用NS2网络仿真工具仿真验证其吞吐量,并与经典算法吞吐量进行对比。仿真结果表明,根据对于控制帧采用速率自适应,可以有效提高系统吞吐量和网络资源的利用率,性能优于传统经典的速率自适应算法。     

Shear‐Induced Aggregation of Mammalian Synovial Fluid Components under Boundary Lubrication Conditions

The lubricating and structural properties of different mammalian synovial fluids in thin films undergoing shear between two mica surfaces are studied in detail using a surface force apparatus (SFA). A 10–13 nm thick film of synovial components (proteins, lipids, and polymers) adsorbs on the mica surfaces in less than an hour of incubation time, and induces a strong repulsion between the surfaces that prevents them from coming into contact. Upon shearing, the structure of the confined synovial fluid changes dramatically when sheared above a “critical” shear rate of about 2 s^?1 (corresponding to approximately 40 nm s^?1). Above this critical shear rate and up to at least 70 μm s^?1, the proteins and biopolymers in the fluid gradually aggregate to form a homogenous gel layer on each mica surface. As shearing continues, the gel layer gradually breaks up into discrete/individual gel particles that can roll in the contact keeping the sheared surfaces far apart even under high compressive loads (pressure P ≈ 20 MPa). These particles eventually become elongated and finally behave as roller bearings. This mechanism is consistently observed for three mammalian synovial fluids and two types of surfaces suggesting that it actually occurs in articular joints and prostetic implants in vivo. The implications of these findings for joints and prosthetic implants structure and lubrication are discussed; in particular the formation and function of the lamina splendens.     

Performance benchmarking of wireless Web servers

The advent of mobile computers and wireless networks enables the deployment of wireless Web servers and clients in short-lived ad hoc network environments, such as classroom area networks. The purpose of this paper is to benchmark the performance capabilities of wireless Web servers in such an environment. Network traffic measurements are conducted on an in-building IEEE 802.11b wireless ad hoc network, using a wireless-enabled Apache Web server, several wireless clients, and a wireless network traffic analyzer. The experiments focus on the HTTP transaction rate and end-to-end throughput achievable in such an ad hoc network environment, and the impacts of factors such as Web object size, number of clients, and persistent HTTP connections. The results show that the wireless network bottleneck manifests itself in several ways: inefficient HTTP performance, client-side packet losses, server-side packet losses, network thrashing, and unfairness among Web clients. Persistent HTTP connections offer up to 350% improvement in HTTP transaction rate and user-level throughput, while also improving fairness for mobile clients accessing content from a wireless Web server.     

分布式MIMO-OFDM系统帧同步性能分析

多入多出-正交频分复用(MIMO-OFDM)技术是下一代宽带无线通信系统的核心技术之一,它对定时同步(包含帧同步和符号同步)性能非常敏感,而分布式天线系统是未来通信系统的开放式架构,这种架构使得帧同步的实现更加困难,且算法更加复杂,因此,急需提出性能分析方法来指导帧同步算法的设计.本文为分布式MIMO-OFDM系统的帧同步提出了一种准确的性能分析方法,从帧同步度量函数的统计特征出发,将信号在主信号方向角上进行正交分解,提出了高斯性能分析方法,利用正态分布的3σ原则,推导出了正确帧同步概率的求解方法.最后将提出的性能分析方法应用到不同发射天线数目以及目前已经提出的几种算法进行分析和对比,验证了该方法的准确性和有效性.     

OFDM解调器在若干干扰样式下的性能分析

OFDM技术在无线通信中应用日益广泛。本文基于OFDM系统接收端信号流程，依次分析了高斯白噪声（AWGN）、单音、多音、扫频、转发等干扰样式下OFDM解调器的性能。根据分析结果认为，OFDM技术抗人为干扰能力方面，需要和其他抗干扰技术结合使用。