The effect of contention in CSMA networks: Model and fairness protocol

Multi-hop wireless networks using Carrier Sense Multiple Access (CSMA) suffer from various forms of unfairness. A majority of the existing work focuses on fairness issues due to hidden terminals and the impact on backoff mechanisms. This paper focuses on a more fundamental form of unfairness that arises due to unequal contention opportunities at a node; some nodes rarely observe an idle channel since two or more interferers can transmit together. Contention unfairness is unrelated to hidden terminals. The paper analyzes the impact of contention and provides insight into developing solutions for contention unfairness. We first develop a model-from first principles-for contention in IEEE 802.11 networks. The accuracy of the model is validated through simulations and the results show that such unfairness is a common phenomenon. Based on the insights gained from the model, we propose and evaluate distributed schemes that reduce the effect of unfairness due to contention. We show that contention unfairness occurs frequently in general scenarios. Simulation results indicate that the proposed protocols improve the overall system performance by providing greater fairness with a small reduction in throughput.     

异构无线传感器网络中异构节点的部署与优化

在无线传感器网络中适当地部署少量的异构传感器节点能够有效地延长网络寿命,提高网络的可靠性.本文主要研究无线传感器网络中异构节点的部署问题,提出了基于选址问题的异构节点部署算法,以优化无线传感器网络中异构节点的数量和位置.与其它算法相比,该算法对无线传感器网络的拓扑结构没有特定的要求,可以支持随机部署或人工部署的各种传感器网络,最后还给出了该算法的仿真测试结果.     

基于虚拟积分激励的内容部署方法

移动自组织网络是个多跳无线网络,依靠节点间的合作和转发增强网络的性能,若将内容部署在网络中适合的位置可以极大地减少节点获取数据的成本,提高网络的性能. 由于节点是理性的,在没有利益驱动的情况下,节点难以与其他节点合作进行内容部署. 本文将虚拟积分激励的方法用于此类内容部署问题中,激励节点相互合作进行内容部署工作,从而提高网络性能和降低网络成本. 实验结果表明,本文的激励方法可以有效地减少内容部署成本.     

Contention based scheduling for femtocell access points in a densely deployed network environment

The proliferation of new data intensive devices has caused an enormous burden on wireless systems. A femtocell network is a promising new technology developed to meet these demands. Since each femtocell network consists of uncoordinated subnetworks that work independently, the interference between subnetworks can result in a significant degradation of the overall network capacity. In this paper, we address the interference problem between uncoordinated femtocell access points (FAPs) and propose a distributed FAP scheduling scheme in a densely deployed femtocell network where FAPs interfere with each other. In contrast to previous works that have focused on dynamic power and frequency management, our approach focuses on time sharing through FAP contention. Depending on the outcome of contention, our method selects a winning FAP to be the sole user of the next time frame. The approach operates in a fully distributed manner with help from mobile nodes (MNs). To implement this scheme, we develop a new synchronous frame structure, which uses special common control channels. Through simulations, we observe that the proposed scheme doubles the network capacity compared to the legacy non-contending scheme, and could serve as the basis for future standards on femtocell networks.     

基于时间部署的无线传感器网络密钥管理方案

提出一种基于时间部署的随机密钥管理方案.该方案采用了特殊的两级随机密钥预分配和清除机制以及按时间顺序的成组部署方法:每个传感器节点从多个密钥池中随机选择密钥并在一定条件下删除相关的密钥;所有传感器节点被组织成部署组并按时间顺序被部署到网络中.与经典的随机密钥管理方案相比,该方案在为成对密钥的生成提供了较高的节点连通度的同时,提高了节点资源利用率并且增强了网络抵抗节点受损攻击的能力.     

Simple,extensible and flexible random key predistribution schemes for wireless sensor networks using reusable key pools

Sensor nodes are tiny, low-power, computationally limited and battery constrained electromechanical devices. A sensor node contains a sensing unit and a wireless communication unit. Sensor nodes are deployed over a field for sensing an event data in the environment and transfer it towards a base station over its wireless channel. In a typical application, vast amount of sensor nodes are deployed over a field which constitute a sensor network. Sensor nodes must be customized for a specific sensor network application before the deployment. This customization is needed not only for underlying networking application, but also for security related configurations. Random key predistribution mechanisms have been proposed to provide security for wireless sensor networks. In the literature, there are well known random key predistribution schemes. Some of these schemes are secure, but quite complex to apply in real-world applications due to their node-based customization requirements, while some other are easily applicable but they do not offer reasonable security. In this paper, we propose random key predistribution schemes for wireless sensor networks that provide varying ranges of security. The proposed schemes are easily applicable in real world scenarios due to their simplicity and relaxed node customization requirements. In this respect, our schemes provide a tradeoff. Moreover, our proposed schemes show a good extensibility property. We assume prior deployment knowledge. We examine performance of our schemes and compare them with well known random key predistribution schemes.     

无线Mesh网络中基于最小权有限支配集的网关部署算法研究

无线Mesh网络中网关是网络性能的瓶颈,网关部署至关重要。本文对无线Mesh网络中网关QoS性能进行分析,提出基于最小权有限支配集,以部署费用为贪心策略的贪婪算法(Greedy_LDSC),该算法用贪心法提高了网关的性价比。同时,提出了基于最小权有限支配集改进的贪婪算法(Greedy_LDSI),以降低网关的部署费用。仿真实验表明,从网关性价比方面来看,Greedy_LDSC算法的网关性价比之和比基于最小权有限支配集的网关部署算法(GREEDY_LDS)要高;从网关部署费用方面来看,Greedy_LDSI算法的网关部署费用比GREEDY_LDS算法会低。     

DGA: Distributed geographic-sensing addressing method for linear-zone internet of things

Several applications of Internet of Things (IoT) have hundreds of nodes, and the expansibility and flexibility of the network can be greatly improved if the nodes can address themselves automatically and dynamically.Existing nodes addressing methods are mainly based on the logical relationships between nodes and routers. In this paper, the automatic geographic-sensing addressing method is studied for end-node (sensor/actuator) without satellite positioning device (such as global positioning system or Beidou system) for the application of IoT deployed in a linear area. The nodes ID is determined by its geographical location, which is very important for location-based routing and transmitting strategies. First, a sniffer method is designed to realize automatic addressing in an ideal state. Then, according to the actual application scenario, two distributed ID estimation algorithms based on received signal strength indicator(RSSI) and ranging are proposed. Through the deployment of LoRa-2.4 GHz wireless node for testing, results show that when the deployment distance between nodes is greater than twice the ranging error, the reliability of our algorithm can be guaranteed.     

High-speed backhaul networks: Myth or reality?

Wireless technology promises a realization of the long-standing vision of ubiquitous high-speed Internet access. WiFi-based wireless mesh networks that provide user access and wireless data transport over a multi-hop backhaul network are a promising incarnation of the above vision. However, while WiFi is successfully used to provide user connectivity via access points, we note that currently deployed wireless mesh networks show a dismal performance and lack mechanisms in the backhaul to provide an efficient and fair data transport over multiple hops. To assess the capabilities and the limitations of wireless backhaul networks, we are currently building MagNets, a next-generation wireless mesh network in the city of Berlin. Using MagNets, this paper provides insight on how to plan and design efficient wireless backhaul networks by describing the work breakdown and the lessons learned from the design and deployment process. Then, we perform a comprehensive performance evaluation to investigate the impact of a wide range of parameters to shed light on the potential and limitations of wireless backhaul networks.     

Random key predistribution for wireless sensor networks using deployment knowledge

We consider a key distribution scheme for wireless sensor networks which uses deployment knowledge. Deployment is modeled as a grid of hexagonal clusters, into centers of which the sensor nodes are dropped according to a given probability distribution (e.g. a Gaussian one). We consider sensor connectivity in a random intersection graph model, instead of the more commonly used in literature G(n, p) graph model. While the latter is easier to analyze, the former is much more suitable to modeling sensor network key distribution. We provide analytical, asymptotic results showing how to pick parameters (key pool size |S|, the number of chosen keys d) depending on the number of deployed nodes in order to assure global connectivity of the network, and estimate the diameter of the network for the given parameters.     

Can the current generation of wireless mesh networks compete with cellular voice?

Wireless mesh networks are being deployed to provide broadband wireless connectivity to city-wide hotspots. The typical architecture in these deployments thus far is a single-radio architecture: mesh nodes carry only one radio, which is used both to receive the traffic from the clients and to relay this traffic through the mesh to the wired Internet gateway.In this paper, we study the performance of a representative single-radio mesh network both in a live setup and in a laboratory environment. We characterize the performance of different applications (e.g. VoIP), and study some key challenges of mesh networks such as the fairness in bandwidth allocation and hidden node terminal. Finally, we compare the results of the study with traditional cellular networks, and discuss various options to enhance the performance of wireless mesh networks in the future.     

SafeMesh: A wireless mesh network routing protocol for incident area communications

Reliable broadband communication is becoming increasingly important during disaster recovery and emergency response operations. In situations where infrastructure-based communication is not available or has been disrupted, an Incident Area Network needs to be dynamically deployed, i.e. a temporary network that provides communication services for efficient crisis management at an incident site. Wireless Mesh Networks (WMNs) are multi-hop wireless networks with self-healing and self-configuring capabilities. These features, combined with the ability to provide wireless broadband connectivity at a comparably low cost, make WMNs a promising technology for incident management communications. This paper specifically focuses on hybrid WMNs, which allow both mobile client devices as well as dedicated infrastructure nodes to form the network and provide routing and forwarding functionality. Hybrid WMNs are the most generic and most flexible type of mesh networks and are ideally suited to meet the requirements of incident area communications. However, current wireless mesh and ad-hoc routing protocols do not perform well in hybrid WMN, and are not able to establish stable and high throughput communication paths. One of the key reasons for this is their inability to exploit the typical high degree of heterogeneity in hybrid WMNs. SafeMesh, the routing protocol presented in this paper, addresses the limitations of current mesh and ad-hoc routing protocols in the context of hybrid WMNs. SafeMesh is based on the well-known AODV routing protocol, and implements a number of modifications and extensions that significantly improve its performance in hybrid WMNs. This is demonstrated via an extensive set of simulation results. We further show the practicality of the protocol through a prototype implementation and provide performance results obtained from a small-scale testbed deployment.     

无线自组网络中TCP流公平性的分析与改进

研究了TCP(transmission control protocol)流在多跳无线自组网络中的公平性问题,发现IEEE802.11DCF协议在此环境下会导致严重的不公平性,即部分节点垄断了网络带宽而其他节点被饿死.首先,通过仿真分析了产生TCP流不公平性的原因,指出其根源在于MAC(media access and control)协议的不公平性,同时,TCP的超时机制加剧了不公平性的产生;然后,利用概率模型定量分析了TCP不公平性与MAC协议参数之间的关系,发现TCP流的公平性与TCP报文长度直接相关,并且增加MAC协议初始竞争窗口的大小能够有效提高公平性.据此,提出了一种根据TCP报文长度动态调节初始回退窗口大小的自适应回退MAC协议改进算法.理论分析和仿真表明,该算法在很大程度上可以有效缓解不公平性问题的产生,并且不会引起网络吞吐量的严重降低.     

Mesh-Mon: A multi-radio mesh monitoring and management system

Mesh networks are a potential solution for providing communication infrastructure in an emergency. They can be rapidly deployed by first responders in the wake of a major disaster to augment an existing wireless or wired network. We imagine a mesh node with multiple radios embedded in each emergency vehicle arriving at the site to form the backbone of a mobile wireless mesh. The ability of such a mesh network to monitor itself, diagnose faults and anticipate problems are essential features for its sustainable operation. Typical SNMP-based centralized solutions introduce a single point of failure and are unsuitable for managing such a network. Mesh-Mon is a decentralized monitoring and management system designed for such a mobile, rapidly deployed, unplanned mesh network and works independently of the underlying mesh routing protocol. Mesh-Mon nodes are designed to actively cooperate and use localized algorithms to predict, detect, diagnose and resolve network problems in a scalable manner. Mesh-Mon is independent of the underlying routing protocol and can operate even if the mesh routing protocol completely fails. One novel aspect of our approach is that we employ mobile users of the mesh, running software called Mesh-Mon-Ami, to ferry management packets between physically-disconnected partitions in a delay-tolerant-network manner. The main contributions of this paper are the design, implementation and evaluation of a comprehensive monitoring and management architecture that helps a network administrator proactively identify, diagnose and resolve a range of issues that can occur in a dynamic mesh network. In experiments on Dart-Mesh, our 16-node indoor mesh testbed, we found Mesh-Mon to be effective in quickly diagnosing and resolving a variety of problems with high accuracy, without adding significant management overhead.     

A generalization of the 0-1 principle for sorting

The traditional zero-one principle for sorting networks states that “if a network with n input lines sorts alln² binary sequences into nondecreasing order, then it will sort any arbitrary sequence of n numbers into nondecreasing order”. We generalize this to the situation when a network sorts almost all binary sequences and relate it to the behavior of the sorting network on arbitrary inputs. We also present an application to mesh sorting.     

基于地址空间的树型网络地址分配

无线传感器网络(WSN)是由大量部署在监测区域内的微型传感器节点通过无线通信方式组成的一个多跳、自组织的网络。分布式的环境感知能力和简单灵活的部署方式,使得WSN成为影响人们日常生活的重要因素;并且随着微电子技术和通信技术的不断发展,WSN已被广泛应用于国防军事、环境监测、医疗健康、智能家居和工业制造等领域。ZigBee是一种支持低速率传输、低功耗、安全可靠的面向可用产品及应用的无线个人局域网的全球标准,与蓝牙、Wi-Fi等其他无线个人局域网标准不同,其提供了低功耗的无线树状和网状网络,可以支持上千个无线传感器设备在网络中使用。ZigBee技术的分布式地址分配机制(Distributed Address Assignment Mechanism,DAAM)中存在网络孤立节点,这种情况导致闲置地址无法使用,且造成了资源浪费。针对这一问题,提出了一种新的树型网络地址分配和路由算法(Address Assignment Algorithm for Tree Network,AAN),在保持与原有协议兼容的基础上通过协调器节点对网络进行维护和控制,各节点根据算法设定的步骤依次进行地址空间分配。该算法可以减少网络中的闲置地址空间及网络中的孤立节点数,优化网络拓扑结构,减少建立与维护路由表所需的时间与存储空间。仿真实验结果表明,所提算法在地址分配成功率、孤立节点数以及网络深度方面优于DAAM算法。     

一种新的队列管理机制在无线Mesh网络中的应用

在无线Mesh网络中,对于传输距离不同的数据流存在严重的不公平性问题,同时物理位置不同的AP之间也存在着同样问题。为保证网络公平性,提出改进MAC层机制和引入缓存管理的联合解决方案。在分析了无线Mesh网络空间不公平性的基础上,通过改进MAC层中竞争窗口,引入缓存管理算法,得到一种新的队列管理方案IQMA（Improving Queue Management Algorithm）。仿真结果表明,新的方案改善了节点间的不公平性问题和长跳流歧视问题,提高了网络资源利用率。     

随机部署的无线传感器网络的负载平衡

从结构的角度来研究在大规模随机部署时所形成的无线传感器网络的数据流负载平衡。通过统计分析邻居节点数目来分析其对无线传感器网络的数据流负载平衡的影响,发现在大规模随机部署时节点的邻居节点数目近似服从正态分布,其成因在于边缘效应。仿真实验发现节点通信半径的增大比部署密度的增大更不利于负载平衡。     

Load-aware routing in mesh networks: Models, algorithms and experimentation

In this paper we consider wireless mesh networks (WMNs) used to share the Internet connectivity of sparsely deployed fixed lines with heterogeneous capacity, ranging from ISP-owned high-speed links to subscriber-owned low-speed connections. If traffic is routed in the mesh without considering the load distribution and the bandwidth of Internet connections, some gateways may rapidly get overloaded because they are selected by too many mesh nodes. This may cause a significant reduction of the overall network capacity. To address this issue, in this paper we first develop a queuing network model that predicts the residual capacity of network paths, and identifies network bottlenecks. By taking advantage of this model, we design a novel Load-Aware Route Selection algorithm, named LARS, which improves the network capacity by allocating network paths to upstream Internet flows so as to ensure a more balanced utilization of wireless network resources and gateways’ Internet connections. Using simulations and a prototype implementation, we show that the LARS scheme significantly outperforms the shortest-path first routing protocol using a contention-aware routing metric, providing up to 240% throughput improvement in some network scenarios.     

一种基于分簇的分布式无线传感器网络拓扑控制算法研究

拓扑控制是无线传感器网络的一个重要研究方向。无线传感器网络中一般节点数量大,分布范围广泛且不规则,难以进行集中式控制。本文提出了一种基于分簇的分布式无线传感器网络拓扑控制(CDTC)算法。利用分簇思想将网络划分为可重叠的簇,簇内各节点按照局部最小生成树算法思想确定邻居关系,调整发送功率,生成合适的网络拓扑。仿真实验证明运行CDTC算法后,网络中节点平均发送功率明显减少,平均节点度较低,节点间干扰较少。