Path-Loss Characteristics of Urban Wireless Channels

Wireless channel data was collected in Cambridge, Massachusetts for diverse propagation environments over distances ranging from tens of meters to several kilometers using mobile 2.4-GHz transmitters and receivers. The 20-MHz bandwidth signals from eight individually movable van-top antennas were Nyquist sampled simultaneously with 12-bit accuracy. Although path-loss variance for any given link length within single residential/urban neighborhoods was large, single streets typically exhibited path-loss, ${rm L}({rm dB})=-10log_{10}({rm P}_{r}/{rm P}_{t})cong 10alphalog_{10}{rm r}+{rm C}$, where P is the received or transmitted power, r the link-length, $alpha$ the street-dependent path-loss coefficient, and C the loss incurred at street intersections. Measurements yielded $alphacong 1.5+3.2betapm 0.27$ for $2≪alpha≪5$ ; $beta$ is the fraction of the street length having a building gap on either side. Experiments over links as short as 100 meters indicate a 10-dB advantage in estimating path loss for this model compared to optimal linear estimators based on link length alone. Measured air-to-ground links were well modeled by $alpha=2$ for the elevated LOS path, and by stochastic log-normal attenuation for the ground-level scattering environment. These models permit path-loss predictions based on readily accessible environmental parameters, and lead to efficient nodal placement strategies for full urban coverage.      

Relay Multi-hop Communications for Next Generation Mobile Networks: Investigation of Path-Loss Models

In next generation communication systems, a multi-hop scheme, in which stations between a mobile terminal and a base station relay signal transmissions, seems a promising ap-proach for wide-area coverage and system capacity enhancement. Another prospective benefit for multi-hop scheme is the reduction of transmission power for a link. This reduction is expected by splitting the transmission into a series of hops using the other mobile stations as repeaters which provide a gain from receiver (Rx) to transmitter (Tx). In this way, the transmission power is expected to become less due to the non-linear nature of the path loss. In this work, different path loss models are examined for multi-hop communication systems. Direct communication and the multi-hop communication cases are compared according to different path loss models. The question of how path loss changes by splitting the transmission into a series of sub-paths is also investigated. The investigations show that it is not possible to reduce the path losses except for some cases thus the transmit power. On the other hand using the multi-hop scheme makes possible to increase the coverage area of the network and also reduce the dead spots in the cell.     

无线网络中的移动模型

移动ad hoc网络(MANET)是指不依赖于固定设备,而由一组无线节点通过自组织而形成的网络.移动性是MANET最主要的特性之一,对网络的性能产生极大的影响.该文主要介绍了MANET中常见的移动模型,并简要分析了他们的主要特点和适用环境.     

多信道无线Mesh网络的性能研究

在无线Mesh网络中使用多信道可以减少碰撞和干扰,提高系统吞吐量.本文先介绍无线Mesh网络,然后介绍多信道在无线Mesh网络中的应用,分析了几种常用的多信道MAC协议.接着着重阐述了多信道无线Mesh网络所面临的问题与挑战,对信道分配、路由选择和隐蔽终端这3个主要问题进行分析,并对其研究设计方向进行了展望.     

Impact of Interference on Multi-Hop Wireless Network Performance

In this paper, we address the following question: given a specific placement of wireless nodes in physical space and a specific traffic workload, what is the maximum throughput that can be supported by the resulting network? Unlike previous work that has focused on computing asymptotic performance bounds under assumptions of homogeneity or randomness in the network topology and/or workload, we work with any given network and workload specified as inputs.A key issue impacting performance is wireless interference between neighboring nodes. We model such interference using a conflict graph, and present methods for computing upper and lower bounds on the optimal throughput for the given network and workload. To compute these bounds, we assume that packet transmissions at the individual nodes can be finely controlled and carefully scheduled by an omniscient and omnipotent central entity, which is unrealistic. Nevertheless, using ns-2 simulations, we show that the routes derived from our analysis often yield noticeably better throughput than the default shortest path routes even in the presence of uncoordinated packet transmissions and MAC contention. This suggests that there is opportunity for achieving throughput gains by employing an interference-aware routing protocol.     

Wireless Network Simulation – Your Window on Future Network Performance

The paper describes three relevant perspectives on current wireless simulation practices. In order to obtain the key challenges for future network simulations, the characteristics of “beyond 3G” networks are described, including their impact on simulation.Erik Fledderus (1970) received a PhD in Applied Mathematics in 1997, after which he started working at KPN Research, which merged with TNO in January 2003. He developed the basis for UMTS radio network planning at KPN, and initiated in 2000 a European project proposal, Momentum, in the area of UMTS radio planning and simulation, with 7 partners from Germany and Pottugal. Erik acted as project leader and co-ordinator from 2001-2003. Also at the end of 2000 he initiated together with Eindhoven University of Technology, Agere Systems and Philips Research a research proposal in the area of antenna arrays and MIMO in WLAN and UMTS. One of the results of this project~lies at the basis for the 802.11n-proposal by Agere/Philips.Since March 1st 2003, Erik is part-time professor at Eindhoven University of Technology in the field of Wireless Communication Networks.Within TNO he is senior strategist, program manager of the program Future ICT Architectures, and leading in the knowledge management regarding radio and mobile network technology, and strategist on mobile/wireless technology in general.     

改进无线网络TCP性能的研究

对采用TCP协议传输数据的实现过程及其在无线网络中可能遇到的问题进行了描述。对因无线信道误码率较高和频繁切换而导致网络性能下降的问题,提出了无线链路层快速重传技术改善网络性能的有效措施,并研究了在无线网络中链路层快速重传技术对无线TCP数据传输的影响。仿真表明链路层快速重传可以有效地改善无线TCP的性能,进一步提高了网络利用率和吞吐量。     

Nakagami衰落信道下合作分集的无线家庭网络性能分析

提出在未来无线家庭网中采用合作分集的思想,通信时利用处于空闲状态的终端用户对所发送信息进行中继发送,保证整个网络误码率性能、中断概率以及发送功率达到最佳折衷.在Nakagami平衰落信道条件下研究了再生中继和非再生中继两种合作方式下的中断概率和误码率性能,给出误码率和中断概率的解析表达式,并用matlaab进行仿真,仿真结果表明,在低信噪比条件下再生中继大大优于非再生中继方式,但高信噪比条件下两者性能接近.     

Efficient Wireless Network Simulations with Detailed Propagation Models

Accurate simulation of wireless networks requires realistic models of the channel propagation medium. The widely used free space model is computationally efficient but ignores many attenuation components which affect wireless signal propagation. This paper describes the impact of the accuracy of the wireless channel model on the accuracy of the results and on the execution time of large-scale network models. It then introduces means to reduce the runtime execution when deploying such detailed propagation models.     

无线网络中iSCSI性能的研究

在介绍和分析标准iSCSI协议体系结构的基础上,给出了在iSCSI会话中通过建立多个虚拟TCP连接且在无线局域网中的iSCSI层采用并行工作机制的优化方法,并对其性能进行了理论分析和实验测试.结果表明,与标准iSCSI相比,在无线网络中使用多连接TCP能有效的改善iSCSI协议的存储性能.     

3G无线网络性能评价KPI体系研究

本文从UTRAN(UMTS terrestrial radio access network,陆地无线接入网)的技术特征出发,在分析考虑GSM、GPRS无线网络的KPI(key performance indicator,关键性能指标)体系的基础之上,给出了UTRAN的KPI体系的选取原则与方法,提出了UTRAN的KPI体系.     

干扰管理——提升无线通信网络性能的核心技术

文章阐述了无线通信网络干扰管理的实现方法,该方法通过对干扰进行多维建模,利用多种干扰管理技术,并结合资源管理手段,最终实现干扰的智能动态联合管理.干扰管理作为提升无线网络性能的核心技术,将成为缓解资源供需矛盾、有效规避或利用干扰、实现通信系统和网络性能持续改进的重要手段.     

无线信道干扰概率对网络性能影响分析

通过对无线网络中信道受干扰程度的研究,提出无线信道干扰概率思想,依据干扰概率得到无线信道的通断特性及干扰等级,进而分析无线信道干扰概率与系统可靠度和业务传输成功率等性能指标的关系。利用OPNET工具构建无线网络和算法模型,仿真分析干扰概率对网络性能的影响,为设计无线网络抗干扰路由协议、提高无线网络抗干扰性能提供理论基础。     

蜂窝移动网中基于MMPP业务输入模型的系统性能分析

文章针对现有的以Poisson过程作为输入业务流模型分析系统性能的不足,提出采用马尔可夫调制泊松过程(MMPP)作为输入业务流来分析系统的呼叫阻塞率和掉话率.数值和仿真结果表明,MMPP能够较好的对蜂窝移动网中的业务输入流近似建摸,它考虑了业务流本身的相关特性和突发特性,可以更加准确的用于分析系统性能.     

Performance Analysis of Wireless Network Coding via Percolation

In order to investigate the effect of net- work connectivity on the performance of wireless network coding, we introduce percolation theory to construct the system model of multi-hop wireless network for asymp- totic connectivity. Concretely, we proposed a normaliza- tion algorithm for random network to layer the nodes of the largest connected component in multi-hop wireless net- work, and derived the theoretical conditions of percola- tion occurrence for the normalized hierarchical network of the largest connected component. Furthermore, accord- ing to the critical threshold of percolation phenomenon, we derived the performance of wireless network coding for the largest connected component. The mean delay and throughput were quantified in terms of network coding parameters such as coding window size, transmission ra- dius, and node density. These conclusions clarify the ef- fective performance of wireless network coding for random network, and will contribute to the evaluation of optimal performance of wireless network coding.     

ALA2在无线网络中的性能分析

对于信道资源有限的无线通信网络,如何尽可能地提高信道利用率是首先要考虑的问题;而对于话音等实时业务,如何保证其服务质量也是一个非常关键的问题。为了有效地解决这两个问题,ITU－T和ATM论坛制订了AAL2适配标准。在该适配标准中有一个称为“Timer-CU”的参数,用于为信元传递的端到端时延提供保证,但在AAL2标准文档中并没有讨论如何设置参数。通过分析这一参数对网络和端到端时延的影,为如何合理设置这一参数值提供了一定的依据。     

基于WLAN的Mesh网络和PMP网络性能比较

无线Mesh网络是一种高速率、高容量的分布式网络，是一种新型的可以解决“最后一英里”瓶颈问题的网络。介绍了无线Mesh网络的结构、特点和应用，分析了DSR路由协议，研完了在DSR路由协议下，基于WLAN的无线Mesh网络的性能，比较了在负栽相同的情况下，基于DSR的Mesh网络和与其具有可比性的PMP网络的性能，得到在同等负载的情况下，Mesh网络的性能优于PMP网络的结论。     

Dynamic Multi-hop Clustering in a Wireless Sensor Network: Performance Improvement

A cluster-based model is preferable in wireless sensor network due to its ability to reduce energy consumption. However, managing the nodes inside the cluster in a dynamic environment is an open challenge. Selecting the cluster heads (CHs) is a cumbersome process that greatly affects the network performance. Although there are several studies that propose CH selection methods, most of them are not appropriate for a dynamic clustering environment. To avoid this problem, several methods were proposed based on intelligent algorithms such as fuzzy logic, genetic algorithm (GA), and neural networks. However, these algorithms work better within a single-hop clustering model framework, and the network lifetime constitutes a big issue in case of multi-hop clustering environments. This paper introduces a new CH selection method based on GA for both single-hop and the multi-hop cluster models. The proposed method is designed to meet the requirements of dynamic environments by electing the CH based on six main features, namely, (1) the remaining energy, (2) the consumed energy, (3) the number of nearby neighbors, (4) the energy aware distance, (5) the node vulnerability, and (6) the degree of mobility. We shall see how the corresponding results show that the proposed algorithm greatly extends the network lifetime.     

无线网络中TCP拥塞控制算法的性能分析

根据无线网络中存在随机数据包丢失的特定情况,对TCP拥塞控制算法在无线网络中的性能进行了分析。理论分析和仿真结果表明,随着无线链路中随机数据包丢失概率的增加,TCP拥塞控制算法将导致无线网络性能的严重下降。