An adjusted K‐medoids clustering algorithm for effective stability in vehicular ad hoc networks

Recently, the routing problem in vehicular ad hoc networks is one of the most vital research. Despite the variety of the proposed approaches and the development of communications technologies, the routing problem in VANET suffers from the high speed of vehicles and the repetitive failures in communications. In this paper, we adjusted the well‐known K‐medoids clustering algorithm to improve the network stability and to increase the lifetime of all established links. First, the number of clusters and the initial cluster heads will not be selected randomly as usual, but based on mathematical formula considering the environment size and the available transmission ranges. Then the assignment of nodes to clusters in both k‐medoids phases will be carried out according to several metrics including direction, relative speed, and proximity. To the best of our knowledge, our proposed model is the first that introduces the new metric named “node disconnection frequency.” This metric prevents nodes with volatile and suspicious behavior to be elected as a new CH. This screening ensures that the new CH retains its property as long as possible and thus increases the network stability. Empirical results confirm that in addition to the convergence speed that characterizes our adjusted K‐medoids clustering algorithm (AKCA), the proposed model achieves more stability and robustness when compared with most recent approaches designed for the same objective.     

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.     

A tree-based address configuration for a MANET

This paper proposes an address configuration scheme for a MANET. In this paper, the tree-based architecture and the algorithm of constructing a MANET are presented. In this architecture, a proxy node can assign a unique address for neighbor new nodes, so the address configuration task is distributed around all proxy nodes. The transmission of control packets is controlled within one-hop scope, so the cost is reduced and the delay is shortened. Through this architecture, the address resources released by failed nodes can be automatically reclaimed for reuse, so a proxy node has always the sufficient address space for assignment. In order to ensure the uniqueness of a node’s address, the paper also proposes the MANET merging and partitioning algorithms. Finally, this paper evaluates the performance metrics of both the proposed scheme and the existing schemes, and the results show that the proposed scheme reduces the address configuration cost and shortens the address configuration delay.     

Joint Power Control with Inter-Link Interference Prediction for Wireless Ad Hoc CDMA Networks

In the last fewyears there has been quite anin-terest in the ad hoc(self-organizing)networks basedon code division multiple access(CDMA)tech-niques[1].Thefocus of this paperisto work on powercontrol algorithms for ad hoc CDMA networks.As-suming that thereis a receive node that receivendif-ferent signals transmitted fromnneighbor transmitnodes throughnchannels that are assigned in oneti me slot and using different spread codes.In order to meet signal-to-interference-ratio(SIR)requirement,th…     

机载网络MAC协议研究综述

随着航空通信应用的不断深化、无线自组织网络研究的迅猛发展,机载网络介质访问控制（MAC）协议的研究已成为新的研究热点。首先总结和分析了机载网络MAC协议设计的应用需求,进而重点从信道接入方式角度综述了机载网络的基于竞争类MAC协议、基于调度类MAC协议、混合类MAC协议和跨层协议设计等四类MAC协议的研究进展,最后对比分析了各类典型协议的特点、性能和适用范围,并给出了需要进一步重点研究的问题,以期为从事该方面研究的人员提供参考。     

VANET路由协议设计时的网络容量仿真分析

针对车载自组网中节点移动速度快、拓扑变化频繁以及无线信道质量不稳定的特点,提出了此类网络的路由协议必须综合考虑业务需求、网络能力以及自组网本身的特点等因素的设计思想。分析了承载业务分为低速率的导频信道和高速率的业务信道对传输速率的不同要求,研究了在选择路由协议时的网络容量上、下限问题。仿真实验结果表明,节点的可行吞吐量的上下限将随着无线电波衰减系数和节点带宽的增大而增大。在车载自组网路由协议设计时需要考虑这种关系,从而提高节点的可行吞吐量。     

A novel Intrusion Detection System for Vehicular Ad Hoc Networks (VANETs) based on differences of traffic flow and position

Vehicle ad hoc networks (VANETs) have attracted great interests from both industry and academia, but a number of issues, particularly security, have not been readily addressed. Intrusion Detection System (IDS) as one of the most important approaches to protect network security has been studied adequately in previous literatures. However, the performance of IDSs still needs to be improved to adapt the scenario of VANETs which are very fast moving and highly dynamic. In this paper, we propose a novel IDS that is able to be appropriately used in the wireless and dynamic networks, like VANETs. It mainly contains a novel feature extraction algorithm and a classifier based on an improved growing hierarchical self-organizing map (I-GHSOM) for IDS in VANETs. The proposed feature extraction algorithm is used to quickly extract distinct features from vehicle messages for IDS’s training and test. In the proposed algorithm, two key features including the differences of traffic flow and of position are extracted. The former feature is calculated according to the range of the distance between vehicles, while both a voting filter mechanism and a semi-cooperative mechanism are designed to get the latter feature. Furthermore, in the I-GHSOM-based classifier, for quickly attaining precise classification results, two novel mechanisms (relabeling and recalculating mechanisms) are proposed to relabel the units of GHSOM and check whether the balance of GHSOM structure is broken or not. Simulation results show that the proposed IDS is better than others in the measurement of accuracy, stability, processing efficiency and message scales.     

面向Ad Hoc网络的无证书认证组密钥协商协议

安全和效率是影响无证书认证组密钥协商协议能否在Ad Hoc网络中得到实际应用的两个关键因素。针对这两个关键因素，以提高Ad Hoc网络安全组通信的安全性和效率为目标，提出一个无证书认证组密钥协商协议，基于椭圆曲线密码体制（ECC）点乘运算实现无配对的无证书认证组密钥协商和身份认证；并使用Huffman密钥树优化通信轮数，以降低计算量和通信量，提高组密钥协商效率。安全分析和性能分析表明，与现有基于无证书的组密钥协商协议相比，所提方案在组密钥协商时具有较高的效率和安全性，可以满足资源受限条件下组密钥建立以及组成员变动带来的密钥更新问题。     

Clairvoyance: A framework to integrate shared displays and mobile computing devices

Supporting formal and informal meetings with digital information and ubiquitous software systems every day becomes increasingly mandatory. These meetings require that the integration of devices participating in the meeting and the information flow among them should be done as seamless as possible to avoid jeopardizing the natural interactions among participants. Trying to contribute to address such a challenge, this article presents a framework that allows devices integration and smooth information flow. This framework, named Clairvoyance, particularly integrates mobile computing devices and large-screen TVs through a mobile ad hoc network, and thus it eases the implementation of shared displays intended to be used in formal and informal meetings. Clairvoyance provides a set of services through an API, which can be used to develop ubiquitous applications that support meetings in particular scenarios. The preliminary evaluation of this framework considered its usage to implement a ubiquitous system that supports social meetings among friends or relatives. According to developers, the framework is easy to use and it provided all required services for such an application. The solution obtained was then utilized by end-users in simulated meetings. The evaluation results indicate that the Clairvoyance services were suitable to support the informal meetings, and that the devices integration and information flow were transparent for the end-users.     

一种适用于多跳Ad Hoc网络的增强型协作多址接入协议

 针对多跳Ad Hoc网络提出一种增强型协作多址接入协议.该协议联合考虑数据传输速率和隐藏终端对协作网络性能的影响,通过优化协议的握手规则和协同节点的选择策略,从而在不引入开销的条件下,有效提高了网络的饱和吞吐量并降低了业务的接入时延.另外,基于对节点行为及其所处状态概率的分析,本文建立了协作多址协议在多跳Ad Hoc网络中的饱和吞吐量分析模型,并给出相应的理论分析结果.最后,通过在多跳Ad Hoc网络中的大量仿真,评估了所提增强型协作多址接入协议和分析模型的性能.仿真结果表明:相对于已有的协作多址协议该协议能够有效提高网络的饱和吞吐量.此外,仿真结果和理论分析结果能够很好的匹配,从而也证明了分析模型的正确性和有效性.