Robust mobility adaptive clustering scheme with support for geographic routing for vehicular ad hoc networks

There are a number of critical problems related to road safety in intelligent transportation systems (ITS) caused by increased vehicle usage, urbanisation, population growth and density, and faster rates of movements of goods and people. It is envisaged that vehicular ad hoc networks (VANETs) will bring about a substantial change to the way our road transport operates to improving road safety and traffic congestion. A major challenge in VANETs is to provide real-time transfer of information between vehicles within a highly mobile environment. The authors propose a new clustering scheme named robust mobility adaptive clustering (RMAC) to strategically enable and manage highly dynamic VANETs for future ITS. It employs a novel node precedence algorithm to adaptively identify the nearby 1-hop neighbours and select optimal clusterheads based on relative node mobility metrics of speed, locations and direction of travel. Furthermore, the zone of interest concept is introduced for optimised approach to the network structure such that each vehicular node maintains a neighbour table of nodes, beyond its communications range, that reflects the frequent changes on the network and provides prior knowledge of neighbours as they travel into new neighbourhoods. RMAC predominantly employs more reliable unicast control packets and supports geographic routing by providing accurate neighbour information crucial when making routing decisions in multi-hop geographic routing. It is shown by simulations that RMAC on IEEE802.11 ad hoc WLAN protocol is very effective in a highly dynamic VANETs environment, being robust on link failures, and having very high cluster residence times compared to the well known distributed mobility clustering scheme.     

Link stability and mobility in ad hoc wireless networks

The fact that ad hoc networks are required to support mobility of individual network nodes results in problems arising when routing data. These problems include route loss, poor longevity of established routes and asymmetric communications links. Mobility of nodes also increases the control traffic overhead and affects the performance of the protocol. Mobility can, however, be exploited to improve route longevity when establishing the route. In some situations, the source of information is not available (e.g. GPS information in the underground), hence protocols relying on this information will fail to operate correctly. In such situations, alternative `self-content' information should be available to perform the needed task of routing. Three novel schemes that make use of such information, the heading direction angle, to provide a mechanism for establishing and maintaining robust and long-lived routes are presented. The results show that these schemes reduce the overhead and increase the route longevity when compared with the AODV protocol. The schemes described can operate as a standalone mechanism or can be adopted by other routing protocols in order to improve their performance.     

Randomised and distributed methods for reliable peer-to-peer data communication in wireless ad hoc networks

Peer-to-peer (P2P) communications have attracted a great deal of attention from the network research community in recent years. However, due to the fundamental limitations of wireless environments, providing reliable data availability for P2P applications over wireless ad hoc networks is still a major challenge. To address the problem, a distributed and randomised scheme based on self-avoiding walks is proposed. The scheme concatenates disparate network layers, with the goal of recovering from routing failures that disrupt P2P data accessibility. In addition, a probabilistic approach is presented that explores the tradeoffs between several system parameters. Some new analysis tools, such as path coupling, are utilised which provide a better understanding of the system's operations. That the proposed concepts and techniques make a significant contribution to the design of effective and efficient P2P applications in wireless ad hoc networks is believed.     

Sea trials of an underwater, ad hoc, acoustic network with stationary assets

The diverse roles of deployable underwater assets have increased the need for ad hoc networking capability. This capability is defined as the ability to form acoustic communication links by deploying assets in a non-deterministic manner, without depending on a priori route and positioning information. Each asset represents a node in the network, and can act as a data source, sink or router, and initiates, stores or relays data, respectively. Data packets may be hopped over a few nodes before arriving at the designated destination. This ad hoc network consists of two main layers: the medium access control (MAC) layer to resolve node contention, and the ad hoc routing layer to manage routing information. In the MAC layer, both random access and timedivision protocols are applied. The protocol in the routing layer is responsible for route setup and route maintenance. This concept of multiple-hop, ad hoc networking was implemented during sea trials conducted in Portland Harbour, UK, involving up to six nodes. The trial was designed with the aim of gaining application experience in ad hoc network deployment and in assessing the performance of the protocols in a real operating environment. The emphasis was on modem integration, and the stability and reliability of packet transport. The trial results and their subsequent analysis demonstrated the robustness of the network in performing ad hoc routing and resolving node contention in a realistic and acoustically challenging environment.     

A comparative QoS survey of mobile ad hoc network routing protocols

A mobile ad hoc network (MANET) is a wireless, dynamic, infrastructure-less, self-organized, multi-hop, and decentralized network. Each node in MANET can act as a router as well as a work station. Many routing protocols have been developed to increase the efficiency of MANET. The primary objective of this paper is a detailed QoS comparison of reactive (AODV), proactive (DSDV), and hybrid (ZRP) routing protocols of MANET in order to find which routing protocol works best in a particular network scenario. The analysis was made for TCP-based traffic patterns. The performance differentials were analyzed on the basis of normalized routing overhead, packet loss, packet delivery ratio, control packets, end-to-end delay, packet received, and packet sent with a variation of nodes density and mobility. The results were obtained using the NS-2 simulator.     

On physical layer-oriented routing with power control in ad hoc wireless networks

Routing in ad hoc wireless networks does not simply consist in finding a route with shortest length (as in wired networks with virtually error-free communication links), but it requires the creation of a stable and good quality communication route to avoid any unnecessary packet loss. In this paper,we discuss physical layer-oriented routing in ad hoc wireless networks, and we analyse the potential advantages of combining the use of power control (PC) with the chosen routing strategy. More precisely, we propose a modified ad hoc on-demand distance vector (MAODV) routing protocol, with and without PC, derived from the AODV-routing protocol by considering the bit error rate at the end of a multi-hop path as the metric to be minimised for route selection. In other words, we consider routing with a physical layer-oriented quality of service criterion, and we analyse the system performance in scenarios with either strong line-of-sight (LOS) or shadowed communications. Although in a scenario with strong LOS communications there are a few cases where the MAODV-PC protocol offers the best performance, in the presence of shadowed communications the proposed physical layer-oriented strategy is not attractive.     

Directional routing protocols for ad-hoc networks

A directional routing approach for multihop ad-hoc networks, is presented which has been applied to two on-demand routing protocols: namely dynamic source routing (DSR) and ad-hoc on-demand distance vector routing (AODV). Both DSR-based and AODV-based directional routing protocols are designed to balance the tradeoff between co-channel interferences from nodes hops away and the total power consumed by all the nodes. In order to select the best route, three metrics are considered in the route discovery process. They consist of hop count, power budget and overlaps between adjacent beams. By exploiting the direction of directional antennas, both routing protocols are capable of reducing overlaps between beams of the nodes along the route, thus eliminating interference. Arbitrary networks and random networks are considered in the simulations. The results show considerable performance gains for transmission of real-time traffic over ad hoc networks.     

Epidemic algorithms for reliable and efficient information dissemination in vehicular

Vehicular ad hoc networks (VANET), which are created by vehicles equipped with short- and mediumrange wireless communication, have an array of important applications in intelligent transport systems. Many of these applications require reliable, bandwidth-efficient dissemination of traffic and road information via ad hoc network technology. This is a difficult task since inter-vehicular networks often lack continuous end-to-end connectivity and are characterised by large variations in node density. A new epidemic algorithm for information dissemination in highly dynamic and intermittently connected VANET is introduced. It is shown through realistic simulations in highway traffic that the proposed algorithm is capable of reliable and efficient information dissemination in VANET in the face of frequent network fragmentation and large density variations.     

Source selection routing algorithms in integrated cellular networks

Integrated cellular networks (ICNs) are normally constructed by adding ad hoc overlay on cellular networks to solve the latter's flexibility and capacity expansion problems. In such networks, routing plays a critical role in finding a route to divert congested traffic from a congested cell to another less crowded cell. Much work has been conducted on routing protocols in ICNs, whereas no dedicated work has been found for an important aspect of routing, namely source selection. The process of a source selection can be an algorithm that is designed for selecting a proper pseudo- source to release its occupying channel to a blocked mobile user. Consequently, this pseudo-source diverts its ongoing call to another cell by using a free channel in a neighbour cell via a relaying route. Based on an introduction of a representative ICN infrastructure, three source selection algorithms are proposed. Both numerical analysis and evaluation results are presented, which show the efficiency of the algorithms and their different abilities in adapting to different network situations, such as traffic density and cell capacity.     

Compatibility of TCP Reno and TCP Vegas in wireless ad hoc networks

Previous work has shown that TCP (transmission control protocol) Vegas outperforms the more widely deployed TCP Reno in both wired and wireless networks. It was also shown that when both TCP variants coexist on the same wired links, Reno dominates because of its more aggressive behaviour. This paper examines for the first time the compatibility between Reno and Vegas in wireless IEEE 802.11 ad hoc networks. It is shown that Vegas generally dominates in the heterogeneous Reno/Vegas network scenario; a startling result that is inconsistent with what is seen in wired networks. It is shown that the wireless ad hoc network environment does not reward the aggressive behaviour of Reno. On the other hand, Vegas, with its more accurate yet more conservative mechanisms, is able to capture most of the bandwidth. This is found to be true when using the on-demand routing protocols of dynamic source routing (DSR) or ad hoc on-demand distance vector (AODV): the failure of a node to reach a next-hop node because of media access control (MAC)-sublayer repeated collisions is reported to the routing protocol, which then declares a route error that impacts Reno in a more serious way than Vegas. When the table-driven routing protocol destination-sequenced distance vector (DSDV) is used, Reno and Vegas share the network bandwidth in a fairer manner. Generally, fairness in this environment can be improved by reducing the TCP maximum window size.     

基于模糊预测机制的QoS路由

由于有线网络的QoS选路算法不能直接用于自组网,基于预测机制,提出了一个时间约束的最小代价分布QoS路由协议.研究了模糊控制技术的使用,对每种度量,定义了相应的模糊隶属度函数用于预测一个更稳定的链路,实现了一个模糊推理规则库以产生每种链路的模糊代价.通过仿真,比较了基于最短路的QoS和基于洪泛机制的稳定路由QOS,结果表明,基于预测机制的QOS选路的平均呼叫有高的接收率.     

A load-balanced routing method for large-scale mesh multiprocessors

Research on message routing in large-scale mesh multiprocessors usually focuses on routing in light traffic. Studies employ simple routing methods that are not load-balanced but do not need route initiation before message transmission. In non-light and/or non-uniform input traffic situations, maximum bandwidth utilization and average latency of such routing methods can be poor due to congestion caused by unbalanced load in global mesh regions. Existing load-balanced routing methods applied in mobile ad hoc mesh networks require route initiation before message transmission, which is not acceptable in mesh multiprocessors. In this research, we designed a load-balanced hierarchical mesh-routing method without route initiation. We organize a large-scale mesh into a virtually structured hierarchical mesh structure. Global mesh routing can thus be transformed into a number of load-balanced routing subtasks at levels of hierarchical submesh regions. In such a structure, we designed periodical hierarchical traffic state polling and distribution with very low overhead. We developed two congestion-avoidance routing methods for load-balanced routing at levels of submesh regions with polled traffic states. Experimental results show that maximum bandwidth utilization and average latency in non-light and/or non-uniform input traffic situations can be improved significantly in comparison with ordinary mesh multiprocessor routing methods.     

Ad hoc网络中一种跨层流量分配算法——CLATA

针对ad hoc网络各协议层的功能都相互关联的特点,提出了一种在ad hoc网络中基于网络平均时延最小的跨层自适应流量分配算法（CLATA）。该算法将网络层自适应流量分配信息传递给媒体接入控制（MAC）层,以改进MAC层中的冲突退避算法,实现网络平均时延最小化,提高网络的利用率。仿真实验结果表明,该算法可以动态调整链路之间的流量,并具有快速的自适应性,优化网络资源的利用。     

ACO–EEOLSR: enhanced energy model based link stability routing protocol in mobile ad hoc networks

A mobile ad hoc network (MANET) has abundant mobile nodes that are free to communicate independently in many locations. Many existing energy models address the inadequacy of resources based on Ad hoc On-demand Multipath Distance Vector and Optimized Link State Protocol (OLSP) routing protocols for MANET along with various parameters. The architecture of energy-efficient routing mechanisms is a challenging problem in a MANET. In this work, a novel energy-aware routing model is introduced for MANET comprising an ant colony optimization (ACO) enhanced approach to energy-efficient-optimized link state routing (named ACO–EEOLSR). Initially, the route discovery is progressed by means of neighbor estimation and also with the authentication of link stability. Parameters such as energy, distance, and hop count are employed as willingness nodes, where both the energy and distance are entrenched through the OLSP. Consequently, the hop count is applied via the ACO system that is beneficial for link stability. After the acceptance of an acknowledgement, the hop count is authorized for further performance analysis. This approach increases the Quality of Service and also uses less energy compared to other energy models. The accomplished simulation upshot depicts that the ACO–EEOLSR outperforms the EEOLSR scheme with respect to the performance metrics of energy consumption, packet delivery ratio, total remaining time, average network lifetime, and a variance of energy.     

MAC-layer channel utilisation enhancements for wireless mesh networks

The authors focus on a wireless mesh network, that is, an ad hoc IEEE 802.11-based network whose nodes are either user devices or Access Points providing access to the mesh network or to the Internet. By relying on some work done within the IEEE 802.11s TG, the network nodes can use one control channel and one or more data channels, each on separate frequencies. Then, some problems related to channel access are identified and a MAC scheme is proposed that specifically addresses the problem of hidden terminals and the problem of coexisting control and data traffic on different frequency channels. An analytical model of the MAC scheme is presented and validated by using the Omnet++ simulator. Through the developed model, we show that our solution achieves very good performance both in regular and in very fragmented mesh topologies, and it significantly outperforms the standard 802.11 solution.     

自组网中一种基于跨层负载感知的蚁群优化路由协议

将蚁群优化和跨层优化方法结合起来,提出了一种基于跨层负载感知和蚁群优化的路由协议(CLAOR)。协议将整个路径中各节点MAC层的总平均估计时延和节点队列缓存的占用情况结合起来,共同作为路由选择和路由调整的重要度量标准进行按需路由发现和维护,通过拥塞节点丢弃蚂蚁分组以及借助部分兼具蚂蚁功能的数据分组实现正常路由表的维护等方法,减少了控制开销,增加了算法的可扩展性,较好地解决了自组网中现有基于蚁群优化的路由协议中普遍存在的拥塞问题、捷径问题和引入的路由开销问题。仿真结果表明,CLAOR在分组成功递交率、路由开销以及端到端平均时延等方面具有优良性能,能很好地实现网络中的业务流负载均衡。     

Mobile IP handoffs among multiple internet gateways in mobile ad hoc networks

In a mobile ad hoc network (MANET) with multiple Internet gateways, efficient management of mobile IP functionality supporting seamless data services is a major challenge. The inadequacy of existing mobile IP schemes applicable to MANETs motivated the search for more efficient gateway discovery/handoff schemes. A solution for mobile IP-based gateway discovery/handoff in dynamic source routing (DSR)-based MANET is formulated. Enhanced mobile IP protocol suitable for MANET environment, i.e. the mobile IP registration controller, is designed. In particular, one of the most significant contributions deals with the mobile IP handoff triggering mechanism which is adaptively assisted by the DSR route maintenance mechanism. Simulation results are provided to support the idea.     

Jamming-based medium access control with dynamic priority adjustment in wireless ad-hoc networks

The paper presents a jamming-based MAC with dynamic priority adjustment (JMDPA) for multimedia services in wireless ad hoc networks. The proposed scheme differentiates multimedia traffic into classes with different priority levels. A mobile node is prioritised in frame transmissions by issuing a precalculated length of jamming noise: the one with the longest jamming length can win the frame transmission. The winner immediately broadcasts its current priority level (local priority) to update the global priorities of all the neighbouring nodes. The global priority is used as a contention baseline, which prevents any node with a local priority lower than the baseline from participating in the next contention. One of the innovative designs in the proposed scheme is right, in that the priority of a mobile node can be dynamically adjusted according to network conditions so that any possible starvation of low-priority traffic or any ineffective contention of high-priority traffic can be avoided. A multidimensional Markov model, together with the scalability analysis, is introduced to evaluate the performance of the proposed JMDPA. The analytical results provide very useful guidelines to tune the QoS parameters for supporting prioritised multimedia traffic in wireless ad hoc networks     

Using link layer throughput maximisation in ad hoc network routing algorithms

This paper studies link layer throughput maximisation for mobile ad hoc network routing algorithms. We analyse the transmission rates and take into account the interference effects to propose a theoretical model of throughput maximisation called Throughput Aware Link Selection (TALS). TALS can easily be infused into other routing protocols. Simulations show performances increases when compared with other methods. The results demonstrate that TALS helps to increase network throughput.     

一种新的基于移动预测的MANET路由协议

移动自组网是一种由一系列可以自由移动的节点主机聚集而成的一个临时性动态网络。它没有固定基站，也没有作为控制管理中心的节点主机，由于其拓扑的动态性，其路由协议与其他传统网络有很大的区别。为了能更有效地移动自组网中实现数据的传送，本文提出了一种基于移动预测下的MANET路由协议，该协议综合考虑了传输路径的延时和稳定性，选择在延时限制下平均拥有最稳特性的传输路径，模拟结果表明，这种方法比基于移动预测量稳路径路由协议的传输时延要短，传送成功概率要高，而控制开销却相关不大。