End-to-end protocols for Cognitive Radio Ad Hoc Networks: An evaluation study

Cognitive radio ad hoc networks (CRAHNs) constitute a viable solution to solve the current problems of inefficiency in the spectrum allocation, and to deploy highly reconfigurable and self-organizing wireless networks. Cognitive radio (CR) devices are envisaged to utilize the spectrum in an opportunistic way by dynamically accessing different licensed portions of the spectrum. To this aim, most of the recent research has mainly focused on devising spectrum sensing and sharing algorithms at the link layer, so that CR devices can operate without interfering with the transmissions of other licensed users, also called primary users (PUs). However, it is also important to consider the impact of such schemes on the higher layers of the protocol stack, in order to provide efficient end-to-end data delivery. At present, routing and transport layer protocols constitute an important yet not deeply investigated area of research over CRAHNs. This paper provides three main contributions on the modeling and performance evaluation of end-to-end protocols (e.g. routing and transport layer protocols) for CRAHNs. First, we describe NS2-CRAHN, an extension of the NS-2 simulator, which is designed to support realistic simulation of CRAHNs. NS2-CRAHN contains an accurate yet flexible modeling of the activities of PUs and of the cognitive cycle implemented by each CR user. Second, we analyze the impact of CRAHNs characteristics over the route formation process, by considering different routing metrics and route discovery algorithms. Finally, we study TCP performance over CRAHNs, by considering the impact of three factors on different TCP variants: (i) spectrum sensing cycle, (ii) interference from PUs and (iii) channel heterogeneity. Simulation results highlight the differences of CRAHNs with traditional ad hoc networks and provide useful directions for the design of novel end-to-end protocols for CRAHNs.     

Opportunistic medium access control for maximizing packet delivery rate in dynamic access networks

One of the key challenges to enabling efficient cognitive radio (CR) communications is how to perform opportunistic medium access control (MAC) that maximizes spectrum efficiency. Several CRN MAC protocols have been designed assuming relatively static primary radio (PR) channels with average idle durations largely exceed CR transmission times. For such CR environment, typical multichannel MAC protocols, which select the best quality channel, perform reasonably well. However, when such mechanism is employed in a CRN that coexists with highly dynamic licensed PR networks (PRNs), where PR channel idle durations are comparable to CR transmission times, the forced-termination rate for CR transmission can significantly increase, leading to a reduction in network throughput. To reduce the forced-termination rate, many MAC protocols have been proposed to account for the dynamic time-varying nature of PR channels by requiring communicating CR users to consistently perform channel switching according to PR activities. However, such channel-switching strategy introduces significant overhead and latency, which negatively affect network throughput. Hence, in this paper, we propose a probabilistic channel quality- and availability-aware CRN MAC. Our protocol uses a novel channel assignment mechanism that attempts at maximizing the packet success probability of each transmission and hence avoids the significant overhead and latency of channel switching. Simulation results show that by being quality- and availability-aware, our protocol provides better spectrum utilization by decreasing the forced-termination rate and improving network throughput.     

节点度估计和静态博弈转发策略的Ad Hoc网络路由协议

针对Ad Hoc网络路由发现过程中广播路由请求分组导致的广播风暴问题，提出了一种基于节点度估计和静态博弈转发策略的Ad Hoc网络路由协议NGRP.NGRP考虑边界影响，采用分段函数的思想将网络场景分为中心、边和角区域，分别估算网络中节点在不同区域的节点度，避免了周期性广播Hello消息获取节点度导致的开销；NGRP路由请求分组的转发采用静态博弈转发策略，利用节点度估算参与转发路由请求分组的节点数量，将转发和不转发作为策略集合，设计效益函数，通过纳什均衡获得节点转发路由请求分组的转发概率，从而减少了路由请求分组广播过程中产生的大量的冗余、竞争和冲突，提高了路由发现过程中路由请求分组的广播效率.运用NS-2对协议的性能进行大量的仿真，结果表明：NGRP的分组投递率、路由开销、MAC层路由开销和吞吐率这4项指标明显优于AODV+FDG，AODV with Hello和AODV without Hello协议.     

基于虚拟信道多路径融合认知无线网络路由算法

针对认知无线网络中频谱的动态性、时变性、多样性以及节点移动性, 提出了一种基于虚拟信道的多路径融合认知无线网络路由算法. 在路由建立过程中, 为解决源节点与目的节点信道同步问题, 源节点在公共控制信道上广播添加虚拟信道的路由请求, 在当前所处信道为虚拟信道的节点中转发. 目的节点对多条路径通过信道切换进行融合, 以规避主用户的活动区域, 减少路径跳数, 提高链路的稳定性. 在路由维护阶段, 通过卡尔曼滤波对节点移动速度进行预测, 在链路断裂之前启动路由修复. 最后通过NS2中CRCN Simulator仿真结果表明, 该算法在链路通信的稳定性、分组投递率、吞吐量、端到端时延等方面有明显的改善, 提高了网络的整体性能.     

基于认知的多信道无线mesh网络路由协议研究

在多信道无线mesh网络中,路由选择与频谱可用性之间的相互依赖性很强,这就要求设计路由协议时要充分考虑信道的选择。传统的路由协议不能很好地适用于多信道无线mesh网络,因此提出了一种基于认知无线电的无线mesh网络路由协议,其中每个节点配置两个网络接口,路由选择与信道选择同时进行,通过冲突避免的设计,充分利用了多信道的优势。仿真结果表明,相对于传统路由协议,提出的路由协议能大大提高网络的吞吐量。     

一种基于地理位置的启发式Ad Hoc路由协议

近几年地理Ad Hoc路由以其独立选路由、避免泛洪以及有良好的可扩展性和适应性而得到快速发展。地理路由面临一个由贪婪方式转发而失败的本地最小问题,该文提出了一种启发式的地理位置辅助路由协议AGAR,利用启发函数对获得位置信息进行路径优化,克服了平面路由算法解决本地最小问题所带来的复杂性。仿真结果表明,该协议能有效地降低网络中扩展节点数目,具有较高的包投递率和较低的端到端延迟。     

一种改进的基于位置信息的AdHoc路由协议

近几年地理Ad Hoc路由以其独立选路由、避免泛洪以及有良好的可扩展性和适应性而得到快速发展。地理路由面临一个由贪婪方式转发而失败的本地最小问题,该文根据提出的启发式的地理位置辅助路由协议AGAR进行改进,主要是对本地最小问题造成的三角环路以及最短路径查找方面做出改善,仿真结果表明,改进后的算法有较好的投包率和较低的开销。     

An adaptive and QoS-based spectrum awareness framework for CR networks

The Cognitive Radio (CR) networks have the capability to be aware of the licensed spectrum and to solve the inefficient usage of the vacant bands in an opportunistic manner. Thus, a spectrum awareness framework must be designed by considering the spectrum availability, the Primary User (PU) interference avoidance and the heterogeneous Quality of Service (QoS) requirements of CR users (CrUs). Considering these challenges, the main contribution of this paper is to design a complete framework for the spectral awareness in CR networks achieving higher spectrum utilization and fairness. Specifically, a PU Presence Map (PuM) is built for the PU interference avoidance. The QoS requirements of CR users are classified using a Request Map, ReM. An admission control is proposed to stabilize the heterogeneous QoS requirements according to PuM and ReM. Moreover, the adaptiveness of the framework is provided by continuous monitoring of the spectrum against dynamic variations. The simulations demonstrate that the proposed spectrum awareness framework maximizes the available spectrum utilization while maintaining the fairness.     

一种新型面向频谱高利用率的认知MAC协议

认知无线电是无线访问领域出现的新技术,目的在于大幅度提高无线频谱的使用.其基本思想是:次用户(非授权用户)在不干扰主用户(授权用户)的条件下允许使用授权频谱.提出一种新的基于独占模式的认知MAC协议.在该协议中,次用户被划分为若干不重叠的组,每个组使用特定的拍卖算法来对其需要租用的信道进行投标.实验表明,这种新协议能够最大化利用频谱资源,并且保证信道在组间分配的公平性和动态性.     

采用Hull树的贪婪地理位置路由算法的设计

地理位置路由算法是指借助节点获得的地理位置信息进行无线传感网络中的路由发现与数据转发工作。本文提出一种基于Hull树的贪婪地理位置路由算法——Greedy Hull Tree Geographic Routing(GHTGR)。通过图形学中凸包的概念,在网络初始阶段分布式地在各节点上建立Hull树以探查网络局部拓扑结构;同时在数据分组的路由转发阶段,通过Hull树内的搜索,寻找下一跳转发节点,完成数据分组的转发传输。通过仿真实验表明,与现有地理位置路由算法相比,该算法能够正确地寻找数据转发路径,有效地减少网络能耗,提高网络传输性能。     

用于多跳无线传感器网络的能量有效数据转发协议

为了增加无线传感器网络的寿命,必须尽可能地节省节点的能量.节省能量最显著的方法就是在节点不参与数据传输时,使其无线模块处于睡眠状态.本文提出了一种适用于无线传感器网络的可靠、能量有效的数据传输（REEGF）协议.此协议通过使网络节点的唤醒模块工作于周期性的侦听/睡眠方式,当节点有数据业务时,利用节点的唤醒模块把节点的一跳邻居节点同步唤醒,确保数据被及时、可靠地发送.通过采用类似于RTS/CTS的控制信息交换方式和发送忙音, REEGF协议有效地避免了数据传输的隐藏和暴露终端问题.基于节点的位置, REEGF协议采用竞争的方式,选取朝着目标SINK节点前进距离最大的邻节点,作为中转接收节点,实现了路由、MAC和拓扑管理的有机结合,节省了节点的资源.分析表明,在网络节点密度适度的情况下, REEGF协议的可靠性、能量消耗和链路建立时延显著地优于文[8]提出的GeRaF协议.     

大规模认知无线电网络的时延分析

时延作为无线网络的最基本的性能之一,对网络信息分发、路由协议设计、节点部署等都具有重要意义。与传统的无线网络不同,认知无线电网络的频谱资源具有动态变化性,该特性会对网络时延产生极大的影响。因此,如何对动态频谱环境下的大规模认知无线电网络进行时延分析,是一项很具挑战性的课题。为此,首先对动态频谱环境进行建模,将认知用户的频谱接入过程建模为一个连续时间的马尔可夫链,并建立认知用户的生存函数来量化授权用户活动以及信道数量对频谱环境的影响;其次,将上述模型与首次通过渗流理论结合起来,研究了大规模认知无线电网络时延的伸缩规律,并获取了更为精确的时延与距离比的上限值。理论分析及仿真结果表明,动态频谱环境与密度一样会对时延产生极大影响。研究结论对认知无线电网络的设计具有重要的指导意义。     

Intelligent multicast routing for multimedia over cognitive radio networks: a probabilistic approach

Cognitive radio (CR) technology has been demonstrated as one of the key technologies that can provide the needed spectrum bands for supporting the emerging spectrum-hungry multimedia applications and services in next-generation wireless networks. Multicast routing technique plays a significant role in most of wireless networks that require multimedia data dissemination to a group of destinations through single-hop or multi-hop communication. Performing multimedia multicasting over CR networks can significantly improve the quality of multimedia transmissions by effectively exploiting the available spectrum, reducing network traffic and minimizing communication cost. An important challenge in this domain is how to perform a multi-cast transmissions over multiple hops in a dynamically varying CR environment while maintaining high-quality received video streaming to all multi-case CR receivers without affecting the performance of legacy primary radio networks (PRNs). In this paper, we investigate the problem of multicast multimedia streaming in multi-hop CR networks (CRNs). Specifically, we propose an intelligent multicast routing protocol for multi-hop ad hoc CRNs that can effectively support multimedia streaming. The proposed protocol consists of path selection and channel assignment phases for the different multi-cast receivers. It is based on the shortest path tree (SPT) that implements the expected transmission count metric (ETX). The channel selection is based on the ETX, which is a function of the probability of success (POS) over the different channels that depends on the channel-quality and availability. Simulation results verify the significant improvement achieved by the proposed protocol compared to other existing multicast routing protocols under different network conditions.

     

A qualitative comparison evaluation of the greedy forwarding strategies in Mobile Ad Hoc Network

The Mobile Ad Hoc Network (MANET) is wireless network which provides communication among wireless mobile hosts without the need of any standing network infrastructure. In such networks, and to facilitate communication between participating nodes, every node has to offer routing services. Routing in MANET is responsible for selecting and forwarding packets along optimal paths. Finding an optimal route is a crucial task in MANET where routes tend to be multi-hop. Many routing protocols have been proposed in literature. However, few of them are efficient when the network is sparse and highly dynamic. Position-based routing and forwarding provides the opportunity for improving the efficiency and performance of the existing MANET routing strategies. This research work presents an extensive overview of geographic forwarding techniques in MANET. In particular, it focuses on the presentation of the basic operation mode of geographic forwarding, which is greedy forwarding. Meanwhile, this research work presents a qualitative evaluation of the most current and popular greedy forwarding strategies used with position based routing protocols. Furthermore, the findings have been used to conclude the most appropriate unicast forwarding policy for future research efforts.     

A secure alternate path routing in sensor networks

This paper presents a secure alternate path routing in sensor networks. Our alternate path scheme makes the routing protocol resilient in the presence of malicious nodes that launch selective forwarding attacks. SeRINS (a Secure alternate path Routing IN Sensor networks) detects and isolates the compromised nodes, which try to inject inconsistent routing information, from the network by neighbor report system. In neighbor report system, a node’s route advertisement is verified by its surrounding neighbor nodes so that the suspect node is reported to the base station and is excluded from the network. Simulation experiments show that SeRINS is resilient in the presence of several compromised nodes which launch selective forwarding attacks, and robust by excluding the compromised nodes which inject inconsistent routing information from the network.     

UWSNs中基于深度的抑制空洞路由优化算法

针对传统的水下无线传感器网络(UWSNs)的位置路由存在路由空洞问题,提出了基于深度的抑制空洞路由(DSVR)的UWSNs路由协议.DSVR协议通过融合跳数、物理距离和邻居数多个指标决策路由.为了提高通信可靠和缓解路由空洞,DSVR协议选择具有最小跳数路径、最少邻居数的节点作为下一跳转发节点.同时,DSVR协议利用定时器抑制冗余数据包.仿真结果表明:提出的DSVR协议能有效地提高数据包传递率,并降低端到端传输时延以及能耗.     

Scoped Bellman-Ford Geographic Routing for Large Dynamic Wireless Sensor Networks

Routing is a fundamental problem in wireless sensor networks. Most previous routing protocols are challenged when used in large dynamic networks as they suffer from either poor scalability or the void problem. In this paper,we propose a new geographic routing protocol,SBFR(Scoped Bellman-Ford Routing),for large dynamic wireless sensor networks. The basic idea is that each node keeps a view scope of the network by computing distance vectors using the distributed BellmanFord method,and maintains a cost for routing to the sink. When forwarding a packet,a node picks the node with minimum cost in its routing table as a temporary landmark. While achieving good scalability,it also solves the void problem in an efficient manner through the combination of Bellman-Ford routing and cost-based geographic routing. Analytical and simulation results show that SBFR outperforms other routing protocols not only because of its robustness and scalability but also its practicality and simplicity.     

基于最短时延的认知无线电网络安全路由算法

针对认知无线电网络可用频谱动态变化和路由过程中出现的安全问题,提出将最短数据传输时延和高安全等级路由作为选路标准,设计了一种跨层路由选择算法。算法通过优化转发节点个数和各转发节点接收、发送数据信道来减少数据传输时延。通过选择具有高安全级别的转发节点来保证路由的安全性。理论分析表明算法是高效和可行的。它的时间复杂度是O(N2),其中N是拓扑图中节点的个数。     

无线传感器网络的安全地理位置跨层协议

许多无线传感器网络(WSN)协议设计过程中,没有考虑到安全问题。提出一种安全地理位置跨层协议(Secure Geo-graphic Integrated Protocol,SGIP)。在安全协议的设计过程中,同时考虑了安全引导过程。首先改进了基于位置的密钥引导方案,使其不但充分利用地理信息,而且可以同时为广播包和单播包加密,并且转发区域内所有节点都与源节点有共享密钥。在此基础上,采用基于MAC层竞争的地理路由选择算法,并对不同数据包采用不同的加密方式,设计了安全的路由/MAC跨层协议。分析表明协议具有很好的安全性能,并且开销较小。     

基于受限等效时延的传感器网络路由协议

实时需求是传感器网络应用于时间敏感领域的一个重要议题.提出一种新颖的受限等效时延（CED）的概念,把端到端的时延需求划分成路径上每段链路的CED的总和.每个节点可以根据CED独立选择下一跳节点,因此简化了路由寻找过程.仿真结果表明这种路由协议在保证高连通率的前提下可以提供较低的能量消耗和较短的端到端时延.