Blocking probability and channel assignment in wireless networks

We consider a multi-hop wireless network with a connection-oriented traffic model and multiple transmission channels that can be spatially re-used. In such a network the blocking probability of a call that makes a channel request depends on (a) the channel assignment scheme and (b) the transmission radius of the nodes which affects the network link structure. In this work, we study these two aspects for simple wireless networks. Specifically, we develop blocking probability analysis for a wireless line and grid network and explore the tradeoff between transmission radius and blocking probability for multi-hop calls. We show that for a line network a larger transmission radius can substantially reduce the blocking probability of calls, while for a grid network with a more dense node topology using a smaller transmission radius is better. We then, investigate various channel assignment schemes and present a novel non-rearranging channel assignment algorithm for multi-hop calls in a general network. Our algorithm efficiently incorporates spatial channel re-use and significantly reduces call blocking probability when compared to other algorithms.     

Lifetime evaluation in energy‐efficient rectangular ad hoc wireless networks

Ad hoc wireless network nodes are typically battery‐powered, therefore energy limit is one of the critical constraints of ad hoc wireless networks' development. This paper evaluates the network lifetime of a rectangular network model that achieves energy efficiency by optimizing the node radio range based on the geographical adaptive fidelity (GAF) topology management protocol (Proceedings of ACMMobil'01, July 2001; 70–84). We derive the optimal transmission range of nodes and analyze both static and dynamic traffic scenarios in both equal‐grid and adjustable‐grid rectangular GAF models, where the results show that the adjustable‐grid model saves 78.1% energy in comparison with the minimum energy consumption of equal‐grid model. The impact of node density on both equal‐grid and adjustable‐grid models is investigated to achieve grid‐lifetime balance among all grids to optimize the entire network lifetime. The lifetime estimation results show that without node density control the adjustable‐grid model prolongs the entire network lifetime by a factor of 4.2 compared with the equal‐grid model. Furthermore, the adjustable‐grid model with node density control is able to prolong the entire network lifetime by a factor of 6 compared with the equal‐grid model. Copyright © 2010 John Wiley & Sons, Ltd.     

一种提高IEEE 802.11吞吐量和公平性的自适应优化算法

该文提出了一种针对IEEE 802.11 DCF网络增强其吞吐量和公平性性能的自适应优化算法,算法基于网络节点侦听信道得到的网络状态信息进行竞争发送的自适应调整以获得最优的网络性能,称之为CSCC(Channel Sensing Contention Control)算法。算法采用了对节点的信道接入请求以概率参数P_T进行过滤的方法控制节点竞争接入信道的激烈程度,其主要特点在于在优化调整过程中不需要进行计算复杂的网络节点数量估计,并且可以在不同网络状态下围绕始终确定的优化目标进行参数优化调整。仿真实验结果表明,算法能够适应不同节点数量和不同数据大小的网络进行自适应的网络优化调整,并获得了系统吞吐量、碰撞概率、延迟、延迟抖动、公平性等多方面的性能改善。     

认知网络主用户吞吐量受限下的传输半径分析与仿真

该文针对认知无线电中认知用户对主用户接收机造成的并发通信干扰问题,采用信息论的观点,在主用户吞吐量门限和主用户通信中断概率的限制条件下,首先分析了认知用户对主用户接收机的干扰功率,并引用马尔科夫不等式,推导出主用户传输半径范围,同时数值分析表明:在其他条件一定时,主用户平均吞吐量、认知用户接入数目和主用户传输半径之间是相互量化制约的关系。其次,改进开发了一个基于中断概率的认知无线电网络仿真平台,分析了在不同认知用户密度下,主用户吞吐量和传输半径之间的实际作用关系,验证了所提模型的合理性和正确性。     

Critical connectivity phenomena in multihop radio models

The percolation of a broadcast in a multihop radio network modeled by a spatial Poisson process is studied. The effect of station density and transmission radius on the extent of broadcast percolation is examined. For broadcast percolation in one spatial dimension, analytical expressions for the average extent of percolation are derived. A model for two-dimensional spatial percolation is presented along with related simulation results. The results suggest that in optimizing transmission radius as a function of communication performance measures, the choice of radius may be bounded from below by the need to maintain a desired network connectivity. The connectivity constraint can be relaxed to some extent in certain non-Poisson spatial models     

水下光无线传感器网络的连接性分析与定位技术

针对水下光无线传感器网络(UOWSN)节点的传输范围受限和间歇性连接的问题,利用多跳通信扩大传输范围来增强网络连接性,提出一种网络节点定位算法.首先,将UOWSN建模为三维(3D)随机缩放模型图,并根据网络节点数、通信范围以及光发散角推导了该模型下网络节点的连接性概率表达式;然后,利用接收信号强度(RSS)定位算法修正...     

Performance Study of Large-Scale Video Streaming Services in Highly Heterogeneous Environment

To support large-scale Video-on-Demand (VoD) services in a heterogeneous network environment, either a replication or layering approach can be deployed to adapt the client bandwidth requirements. With the aid of the broadcasting and caching techniques, it has been proved that the overall performance of the system can be enhanced. In this paper, we explore the impact on the broadcasting schemes coupled with proxy caching and develop an analytical model to evaluate the system performance in a highly heterogeneous network environment. We develop guidelines for resources allocation, transmission strategies as well as caching schemes under different system configurations. The model can assist system designers to study various design options as well as perform system dimensioning. Moreover, a systematic comparison between replication and layering is performed. From the results, it can be seen that the system performance of layering is better than that of replication when the environment is highly heterogeneous even if the layering overhead is higher than 25%. In addition, it is found that the system blocking probability can be further reduced by exploring the broadcast capability of the network if the proxy server cannot store all the popular videos.     

On the Probability of K-hop Connection in Wireless Sensor Networks

Considering a wireless sensor network whose sensors are randomly and independently distributed in a bounded area according to a homogeneous Poisson process with intensity p and each sensor has a uniform transmission radius of r_o, an important problem is to obtain the probability that two random sensors separated by a known distance x are k hop neighbors for some positive integer k. In this letter, we give a recursive analytical equation for computing this probability. The analytical solution is validated by simulations.     

Outage Probability in Full Spectrum Reuse Cellular Systems with Discontinuous Transmission

Co-channel interference has a very strong impact on the performance of cellular mobile radio systems; a performance measure to evaluate its effect is the outage probability. This work presents an analytical general formula for the outage probability evaluation in full spectrum reuse cellular systems with discontinuous transmission. In particular, both Nakagami and Rician fading along with log-normal shadowing have been considered in the signal propagation model. In addition, the discontinuous transmission strategy is considered. The results are applied to the throughput evaluation of a packet cellular radio network based on the slotted Aloha protocol.     

Transmission Range Effects on AODV Multicast Communication

As laptop computers begin to dominate the marketplace, wireless adapters with varying bandwidth and range capabilities are being developed by hardware vendors. To provide multihop communication between these computers, ad hoc mobile networking is receiving increasing research interest. While increasing a node's transmission range allows fewer hops between a source and destination and enhances overall network connectivity, it also increases the probability of collisions and reduces the effective bandwidth seen at individual nodes. To enable formation of multihop ad hoc networks, a routing protocol is needed to provide the communication and route finding capability in these networks. The Ad hoc On-Demand Distance Vector Routing protocol (AODV) has been designed to provide both unicast and multicast communication in ad hoc mobile networks. Because AODV uses broadcast to transmit multicast data packets between nodes, the transmission range plays a key role in determining the performance of AODV. This paper studies the effects of transmission range on AODV's multicast performance by examining the results achieved at varying transmission ranges and network configurations.     

Optimal transmission ranges and code rates for frequency-hop packetradio networks

We consider a frequency-hopping multihop packet radio network using M-ary frequency-shift keying modulation in a Rayleigh fading environment. Each node transmits packets using an extended (n, k) Reed-Solomon code and the slotted ALOHA channel access protocol. For this network, we determine the optimum transmission range, optimum code rate, and optimum slotted ALOHA transmission probability to be used by each node in the network. Tradeoffs in choosing the transmission range and code rate, and the spectral efficiency of the network are captured in a new performance measure, information efficiency, which is analogous to expected forward progress. Maximizing the information efficiency yields the optimum desired network parameters     

On the robustness of space-time coding techniques based on a general space-time covariance model

The robustness of space-time coding techniques for wireless channels that exhibit both temporal and spatial correlation is investigated. A general space-time covariance model is developed and employed to evaluate the exact pairwise error probability for space-time block codes. The expressions developed for the pairwise error probability are used in conjunction with the union bound to determine an upper bound for the probability of a block error. The block error probability is evaluated for several space-time codes and for wireless channels that exhibit varying degrees of spatial and temporal correlation. Numerical results are presented for a two-dimensional Gaussian scatterer model which has been shown to be consistent with recent field measurements of wireless channels. The results demonstrate that the best-case wireless channel is uncorrelated in both space and time. Correlation between transmission paths, due to insufficient spacing of the transmit antennas or scatterers located in close proximity to the mobile, can result in a significant performance degradation. The conditions that result in uncorrelated transmission paths are quantified in terms of the effective scattering radius and the spacing of the transmit and receive antennas.     

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。     

Performance Analysis of Multi-Fiber WDM Network with Limited-Range Wavelength Conversion

Wavelength routed optical networks have emerged as a technology that can effectively utilize the enormous bandwidth of the optical fiber. Wavelength conversion technology and wavelength converters play an important role in enhancing fiber utilization and in reducing the overall call blocking probability of the network. In this paper, we develop a new analytical model to calculate the average blocking probability in multi-fiber link networks using limited range wavelength conversion. Based on the results obtained, we conclude that the proposed analytical model is simple and yet can effectively analyze the impact of wavelength conversion ranges and number of fibers on network performance. Also a new heuristic approach for placement of wavelength converters to reduce blocking probabilities is explored. Finally, we analyze network performance with the proposed scheme. It can be observed from numerical simulations that limited range converters placed at a few nodes can provide almost the same blocking probability as full range wavelength converters placed at all the nodes. We also show that being equipped with a multi-fiber per-link has the same effect as being equipped with the capability of limited range wavelength conversion. So a multi-fiber per-link network using limited range wavelength conversion has similar blocking performance as a full wavelength convertible network. Since a multi-fiber network using limited range wavelength conversion could use fewer converters than a single-fiber network using limited range wavelength conversion and because wavelength converters are today more expensive than fiber equipment, a multi-fiber network in condition with limited range wavelength conversion is less costly than a single fiber network using only limited range wavelength conversion. Thus, multi-fiber per-link network using limited range wavelength conversion is currently a more practical method for all optical WDM networks. Simulation studies carried out on a 14-node NSFNET, a 10-node CERNET (China Education and Research Network), and a 9-node regular mesh network validate the analysis.     

基于TDMA起伏追踪机制的LTE网络数据传输优化算法

针对当前LTE网络数据传输优化算法对信道转移判断效率低、带宽占用率高、难以提升数据传输质量等不足,提出了一种新的LTE网络数据传输优化算法.基于时分多址(TDMA)控制技术,结合马尔科夫信道转移模型优化了信道带宽偏移轨迹;通过获取激发态-非激发态信道转移概率构建了起伏追踪机制,对信道转移时的起伏特性进行筛选.仿真结果表明:与当前LTE网络数据传输中常用的混频载波带通过滤算法、窄带噪声调整自适应过滤算法相比,所提算法进行数据传输所需的带宽最低,而数据传输质量更高,信道传输性能更好.     

Partner selection strategies in cooperative wireless networks with optimal power distribution

There have been several results that illustrate the best performance that a network can get through cooperation of relay nodes. For practical purposes, not all nodes in the network should be involved at the same time in every transmission. Therefore, optimal partner selection protocols in cooperative wireless networks are believed to be the first important thing that should be paid attention to. This problem in our article is considered in the context of regenerative nodes and non-altruistic cooperation （no pure relay exists; all nodes have their own data to transmit）. For each transmission, the protocol must provide the user （source node） a ＇best partner＇ （relay node） to cooperate with （for network simplicity and less transmission signals here, assume that each user has only one cooperative node）. A criterion is essentially needed when defining what a ＇best partner＇ is; in this article, two factors, i.e, the successful transmission probability and the transmission power, are considered. Three optimal partner selection strategies with different goals are proposed and analyzed respectively. The simulation results show that these are all supposed to be good tradeoffs between power consumption and transmission performance.     

基于预警优先级的ZigBee传感网络MAC层退避算法

针对无线传感器网络中有预警信息的高优先级数据包需要尽快传输,且IEEE 802.15.4协议本身不支持任何优先级传输机制的情况,提出了一种基于预警优先级的非时隙CSMA/CA自适应调整阶梯退避算法,并建立了离散时间马尔可夫分析模型,比较分析了网络中不同优先级节点的信道接入概率、网络吞吐量和传输延时,仿真结果表明,本文改进的自适应调整阶梯退避机制对提高无线传感器网络中高优先级数据包的实时传输性能具有积极的作用。     

Relay Placement for Coverage Extension in Cellular Wireless Networks Under Composite Fading Model

In relay-assisted cellular networks, mobile stations are connected to base station through two or more single-hop communication links, where the intermediate nodes act as relay stations (RSs). The focus of this paper is on two-hop relay assisted cellular networks, where optimal relay placement is a crucial issue for achieving maximum extension of the cell coverage. However, the location of RS has significant impact on signal-to-interference plus noise ratio (i.e., SINR) and outage probability experienced on the access and backhaul links. Moreover, the frequency re-use factor also has significant influence on the SINR. In this paper, we develop analytical models for computing the SINR and outage probability performance of a two-hop relay assisted cellular network for both downlink (DL) as well as uplink (UL) transmission scenarios, considering the impact of path loss, shadowing, Nakagami fading and co-channel interference. We then investigate optimal placement of RS while satisfying the required criterion on probability of correct decoding, initially by considering the DL scenario alone and then by considering both DL and UL scenarios jointly. Through extensive evaluations, we report the impact of realistic propagation models on outage probability, optimal relay position and the cell coverage radius. Further, the model can be used to find the impact of co-channel re-use factor on optimal relay positioning in two-hop cellular networks.     

无线双通道网络话音业务信道接入性能分析

无线双通道网络能够有效解决战术环境下码分组网数目过小造成的码分资源浪费问题。混合业务传输环境下,实时话音业务信道接入性能是衡量无线双通道网络性能的关键指标之一。通过使用一种理想的固定时分信道带宽分配方案,在保障话音业务传输实时性的条件下,分别从单跳网络拓扑和多跳网络拓扑结构给出了双通道网络可用信道数目。使用基于优先权的混合业务多服务台离散时间排队模型分析了双通道网络的话音业务平均数目、呼叫阻塞概率、平均网络吞吐量和信道利用率等性能。数值计算结果证明：相比传统网络,双通道网络在混合业务高负载条件下能够容纳更多的话音业务并具有更低的呼叫阻塞概率。     

Design of a Symmetric CPW-Fed Patch Antenna for WLAN/WIMAX Applications Using ANN

The upper bound capacity based on the SINR model is a very important parameter when evaluating the performance of the multi-hop wireless ad hoc networks. In this paper, a new upper bound capacity algorithm is proposed. Firstly, we analyzed the classical physics SINR model over the Rayleigh fading channels to establish the relationship between density of nodes and path outage probability. Then, we developed the closed-form expression of the upper bound transmission capacity based on the Weber model for the random networks. Finally, we evaluated effects of parameters in the communication range, density, SINR threshold and fading factors, and consequently transmission capacity of the network by sensitivity analysis. The numerical simulation showed that the optimum density of nodes was existed to obtain the upper bound transmission capacity. The capacity increased firstly and then decreased over the density of nodes increasing. It affected by channel fading factor and communication range sensitively.