Wireless community networks

An open standard IEEE 802.11 wireless local area networking technology provides an inexpensive and easy way to share bandwidth among multiple users. Such technology makes it possible to implement ad hoc wireless community networks using fixed wireless nodes rather than conventional base. A rural ad hoc network forwards packets from one wireless node to another to route data to a limited number of Internet gateways. A wireless community network uses two types of links between nodes. Point-to-multipoint links use omnidirectional antennas, while point-to-point links employ unidirectional antennas.     

On-Demand Medium Access in Multihop Wireless Networks with Multiple Beam Smart Antennas

The paper presents a detailed discussion of various issues involved in designing a medium access control (MAC) protocol for multihop wireless networks with nodes employing multiple beam smart antennas. Multiple beam smart antennas can form several beams simultaneously and can initiate concurrent transmissions or receptions .in them, thereby increasing the throughput of the bottleneck nodes. Traditional on-demand MAC protocols for omnidirectional and single beam directional antennas based on the IEEE 802.11 distributed coordination function (DCF) mechanism cannot take advantage of this unique capability of multiple beam antennas as they do not facilitate concurrent transmissions or receptions by a node. This paper introduces a novel protocol, hybrid MAC (HMAC), which enables concurrent packet reception (CPR) and concurrent packet transmission (CPT) at a node equipped with multiple beam antennas and is backward compatible with IEEE 802.11 DCF. Simulation results show the superior performance of HMAC in most ad hoc scenarios. Moreover, in some sample topologies, the throughput of HMAC is close to the theoretical maximum. The paper also presents a wireless mesh network architecture with heterogeneous antenna technologies and illustrates the advantages of employing multiple beam smart antennas and HMAC in such networks.     

Efficient Broadcasting Using Network Coding and Directional Antennas in MANETs

In this paper, we consider the issue of efficient broadcasting in mobile ad hoc networks (MANETs) using network coding and directional antennas. Network coding-based broadcasting focuses on reducing the number of transmissions each forwarding node performs in the multiple source/multiple message broadcast application, where each forwarding node combines some of the received messages for transmission. With the help of network coding, the total number of transmissions can be reduced compared to broadcasting using the same forwarding nodes without coding. We exploit the usage of directional antennas to network coding-based broadcasting to further reduce energy consumption. A node equipped with directional antennas can divide the omnidirectional transmission range into several sectors and turn some of them on for transmission. In the proposed scheme using a directional antenna, forwarding nodes selected locally only need to transmit broadcast messages, original or coded, to restricted sectors. We also study two extensions. The first extension applies network coding to both dynamic and static forwarding node selection approaches. In the second extension, we design two approaches for the single source/single message issue in the network coding-based broadcast application. Performance analysis via simulations on the proposed algorithms using a custom simulator and ns2 is presented.     

基于自适应波束天线的局部优化拓扑控制算法

拓扑控制有助于提高ad hoc网络的性能,采用定向天线的自组网拓扑控制比全向天线网络更为复杂。基于自适应波束定向天线模型提出一种局部区域优化的拓扑控制算法。该算法利用分簇的思想将网络划分为可重叠的多个区域,区域内节点采用最小生成树（MST）的思想确定邻居关系,通过调整节点发射功率,改变天线波束的朝向、宽度和增益来构建拓扑。算法减小了节点的平均度数,降低了节点的发射功率,从而降低节点能耗,减少了节点间干扰,提高了网络吞吐量,仿真结果表明,算法显著提高了网络性能。     

LODMAC: Location Oriented Directional MAC protocol for FANETs

Flying Ad Hoc Network (FANET) is a novel mobile ad hoc network type where the communicating nodes are Unmanned Aerial Vehicles (UAVs). FANETs promise many new ways for both civilian and military applications. Today, traditional omnidirectional antennas are deployed on UAV nodes which result in reduced spatial reuse and limited network capacity. Alternatively, deployment of directional antennas can significantly increase the capacity, spatial reuse and communication range of FANETs. In addition, being aware of the exact locations of the neighboring nodes in a FANET is vital especially for directional ad hoc multi-UAV scenarios. In this paper, we present a novel MAC protocol, LODMAC (Location Oriented Directional MAC), which incorporates the utilization of directional antennas and location estimation of the neighboring nodes within the MAC layer. By defining a new Busy to Send (BTS) packet along with the Request to Send (RTS) and Clear to Send (CTS) packets, LODMAC effectively addresses the well known directional deafness problem. In terms of throughput, utilization, average network delay and fairness, LODMAC protocol outperforms the well-known DMAC (Directional MAC) protocol which puts LODMAC to be a robust mile-stone for the on-coming FANET MAC protocols.     

移动Ad Hoc网络路由协议的性能分析与比较

移动Ad Hoe网络是由一组无线移动主机组成的一个没有任何建立好的基础设施或集中管理设备的临时网络.网络拓扑易变、带宽、能源有限是移动Ad Hoe网络的主要特点.分析表驱动路由协议DSDV和按需路由协议DSR、AODV和TO-RA,并利用NS2软件进行了仿真实验,通过改变节点的暂停时间和移动速度这两个参数来比较这两个参数对这四种协议性能的影响.仿真结果表明,按需路由协议在分组投递率、端到端的平均时延、路由开销方面都表现出较好的性能.但同时结合表驱动路由协议的特点,为进一步在综合考虑以上两类路由协议特点的基础上研究新的路由协议提供很好的参考.     

A lightweight anonymous routing protocol without public key en/decryptions for wireless ad hoc networks

More attention should be paid to anonymous routing protocols in secure wireless ad hoc networks. However, as far as we know, only a few papers on secure routing protocols have addressed both issues of anonymity and efficiency. Most recent protocols adopted public key Infrastructure (PKI) solutions to ensure the anonymity and security of route constructing mechanisms. Since PKI solution requires huge and expensive infrastructure with complex computations and the resource constraints of small ad hoc devices; a two-layer authentication protocol with anonymous routing (TAPAR) is proposed in this paper. TAPAR does not adopt public key computations to provide secure and anonymous communications between source and destination nodes over wireless ad hoc networks. Moreover, TAPAR accomplishes mutual authentication, session key agreement, and forward secrecy among communicating nodes; along with integration of non-PKI techniques into the routing protocol allowing the source node to anonymously interact with the destination node through a number of intermediate nodes. Without adopting PKI en/decryptions, our proposed TAPAR can be efficiently implemented on small ad hoc devices while at least reducing the computational overhead of participating nodes in TAPAR by 21.75%. Our protocol is certainly favorable when compared with other related protocols.     

无线自组网中一种高效的路由协议

无线自组网与传统的有线网不同,它由一些可移动的结点组成,这些结点的带宽、计算能力和能量都受到一定限制。针对这种网络,研究者们提出了按需路由协议,这些协议非常适合无线自组网这种拓扑结构,但是由于缺乏对全局拓扑和结点移动性的了解,可能达不到最优。因此提出了一种高效的路由协议ERNC,该协议基于已提出的SHORT路由协议[13],并对以前所提出的NAOR协议[14]进行了扩展,即利用网络编码技术来进一步提高路由协议的性能。最后,使用NS-2模拟器来评估ERNC的性能,结果显示ERNC在分组投递率和平均端到端时延等方面获得了比已有协议更好的性能。     

WSN中基于混合天线的PEGASIS改进算法*

针对无线传感器网络面积大、节点传输距离远的特点而导致能量消耗过快容易死亡的问题,引入定向天线,设计了基于混合天线的高能效收集路由协议(EEMC)。通过定义距离阈值,在区域内构造多条短链,短链通过链头收集链内节点数据后直接与基站通信。距离阈值根据链路位置和节点死亡情况长链系数有所变化,短链间采用全向天线传输数据,链头节点通过定向天线向远处的基站发送数据。仿真结果表明,该算法大大减缓了第一个死亡节点到来的时间,节省了每轮的网络能耗。     

AHBP: An efficient broadcast protocol for mobile Ad hoc networks

Broadcast is an important operation in many netowkr protocols.It is utilized to discover routes to unknown nodes in mobile ad hoc networks(MANETs) and is the key factor in scaling on -demand routing protocols to large networks.This paper presents the Ad Hoc Broadcast Protocol(AHBP)and its performance is discussed.In the protocol,messages,are only rebroadcast by broadcast relay gateways that constitute a connected dominating set of the network.AHBP can efficiently reduce the redundant messages which make flookding-like protocols perform badly in large dense networks.Simulations are conducted to determine the performance characteristics of the protocol.The simulation results have shown excellent reduction of broadcast redundancy with AHBP.It also contributes to a reduced level of broadcast collision and congestion.     

The role of congestion in probabilistic broadcasting for ubiquitous wireless multi-hop networks through mediation analysis

Broadcast schemes play an important role in the performance of mobile ad hoc networks, which are a clear example of ubiquitous wireless multi-hop networks where nodes collaborate in a distributed way. They are widely used as a dissemination mechanism and as a part of the discovery phase of routing protocols. The simple flooding algorithm is the usual mechanism employed in mobile ad hoc networks, but its inefficiency has been demonstrated in congested scenarios due to the high number of collisions and contentions. However, these problems can be partially alleviated by using a probabilistic broadcast approach in which every node forwards the incoming packets according to a certain forwarding probability. In this paper, we use a simple probabilistic broadcast protocol to evaluate the effects of congestion on the performance of broadcasting in ad hoc networks through a mediation analysis. We hypothesize that the congestion mediates in the relationship between the forwarding probability (independent variable) and the output metric (dependent variable). We consider several output metrics according to the application of the broadcasting protocol such as reachability, broadcasting delay, packet delivery fraction and end to end delay. The simulation results show the existence of the mediating effects and how such effects may be counterbalanced depending on the target use of the probabilistic broadcast scheme.     

高能量节点驱动的按需距离矢量路由协议

无线自组织网络中的按需距离矢量路由协议(AODV)没有考虑到能量消耗的均衡性和网络生命期的问题。针对AODV的这一缺点,提出了一种高能量节点驱动的AODV协议(HN-AODV)。此协议将高能量节点驱动的策略应用于按需路由发现过程,尽量选择能量较高的节点来承担转发任务,以此来平衡网络能耗。仿真结果显示,HN-AODV在基本不降低数据传输性能的前提下,显著提高了网络生命周期。这种高能量节点驱动的方案同样可以运用在其它类似的反应式路由协议中。     

Performance analysis of broadcast protocols in ad hoc networks based on self-pruning

Self-pruning is an effective scheme for efficient broadcasting in ad hoc wireless networks. In a self-pruning broadcast protocol, a node may not forward a broadcast packet if a certain self-pruning condition is satisfied based on the neighborhood information. In a static network with an ideal MAC layer, only a subset of nodes forward the broadcast packet and still guarantee the complete network delivery. Various protocols have been proposed with different self-pruning conditions. Recently, a generic self-pruning protocol was proposed by Wu and Dai (2003), which combines the strength of previous conditions and is more effective. In this paper, we first propose an enhanced version of the generic protocol, which is more elegant in interpreting existing protocols and has a simpler correctness proof. Then, we evaluate the performance of the family of self-pruning protocols under various network situations with ns2. The objective is to observe the efficiency and reliability of these protocols as a function of network density, congestion, and mobility, and provide a guideline of implementation in the "real world". Our performance analysis reveals that the protocol reliability is barely affected by packet collision. However, most self-pruning protocols suffer from low delivery ratio in highly mobile networks. We further explore various techniques that improve the delivery ratio and show that both high efficiency and reliability can be achieved in highly mobile networks.     

按需式ad hoc移动网络路由协议的研究进展

Ad hoc移动网络是一种完全由移动主机构成的网络，网络拓扑易变，带宽，能源有限是ad hoc移动网络的主要特点，针对这些特点，目前设计的ad hoc路由协议大多采用按需查找方式，该文介绍了这方面研究的最新进展，对几种典型的按需路由协议进行了说明，分析和综合比较，文中分析了目前协议存在的一些问题并提出了相应的改进方法，最后指出了下一步研究方向。     

A Polynomial Time Solution to Minimum Forwarding Set Problem in Wireless Networks under Unit Disk Coverage Model

Network-wide broadcast (simply broadcast) is a frequently used operation in wireless ad hoc networks (WANETs). One promising practical approach for energy-efficient broadcast is to use localized algorithms to minimize the number of nodes involved in the propagation of the broadcast messages. In this context, the minimum forwarding set problem (MFSP) (also known as multipoint relay (MPR) problem) has received a considerable attention in the research community. Even though the general form of the problem is shown to be NP-complete, the complexity of the problem has not been known under the practical application context of ad hoc networks. In this paper, we present a polynomial time algorithm to solve the MFSP for wireless network under unit disk coverage model. We prove the existence of some geometrical properties for the problem and then propose a polynomial time algorithm to build an optimal solution based on these properties. To the best of our knowledge, our algorithm is the first polynomial time solution to the MFSP under the unit disk coverage model. We believe that the work presented in this paper will have an impact on the design and development of new algorithms for several wireless network applications including energy-efficient multicast, broadcast, and topology control protocols for WANETs and sensor networks.     

Towards estimating lifetime of ad hoc wireless networks

Ad hoc wireless networks possess highly constrained energy resources. The available energy resources should thus be used efficiently, in order to satisfy the requirements. Hence, the protocols at all the layers of the protocol stack should be energy aware and energy efficient. However, all the existing protocols are not energy aware and perform poorly in the presence of a limited power source. Even the energy aware protocols proposed for ad hoc networks do not consider all the characteristics of the underlying batteries. Hence, they fail to efficiently utilize the available energy. There also exist a few protocols, which, though battery unaware, unknowingly prove to be energy efficient. Thus, a mechanism is required to measure the efficiency of the protocols of ad hoc networks, in terms of the network lifetime. To the best of our knowledge, there has been no reported work till date for analyzing the lifetime of the ad hoc networks for various protocols.The protocols at all the layers of the protocol stack together decide the discharge of the battery source of a node. However, assuming that only the MAC protocols decide the battery performance, we focus on measuring the energy efficiency of MAC protocols. This paper primarily provides a novel generalized analytical model for estimating lifetime of ad hoc networks, in the presence of the following two kinds of MAC protocols: (i) reservation-based TDMA protocols and (ii) a specific class of CSMA protocols that try to follow a pattern, such as a round-robin scheduling, for packet transmission. Our model uses discrete-time Markov chain with probabilistic recovery to model the batteries of the ad hoc nodes. We found that our analytical model accurately estimates the lifetime of the network for various MAC protocols. We prove through analytical and simulation studies that energy awareness is crucial in deciding the performance of the MAC protocols for both homogeneous and heterogeneous ad hoc wireless networks.     

基于功率优化的Ad hoc网络定向媒质接入控制

由于无线Ad hoc网络是一种由移动终端组成、网络拓扑结构动态变化的对等、自组织、多跳网络,使得传输带宽、传输功率成为具有挑战性的任务之一。分析了目前通常采用的信道接入技术(如：全向天线;CSMA／CA和洪泛)及存在的问题;在此基础上,为保证有效利用传输带宽,提高功率利用率,给出了用于定向天线的MAC的解决方案(简称DMAC)。节点通过虚拟载波侦听来重定向,实现定向传输,使功率得到优化。     

Repetition-based cooperative broadcasting for vehicular ad-hoc networks

In vehicular ad hoc networks, most of critical applications involved with safety rely on reliable broadcast communications with low latency. Recently, repetition-based protocols have been proposed to meet the requirements of timeliness and reliability for broadcasting. In these protocols, a sender repeatedly retransmits the broadcast message during the lifetime of the message. However, existing protocols face serious problems such as deterioration of the signal quality caused by wireless fading. In particular, since excessive repetitions might cause network congestion and waste channel resources, reliability of broadcasting should be achieved with as small a number of repetitions as possible. In this paper, we therefore propose a novel repetition-based broadcast protocol which exploits a cooperative diversity technique (called RB-CD) making a small number of repetitions robust for wireless fading. To support this cooperative diversity, neighboring nodes transmit the same message almost simultaneously (that is, using the same repetition pattern for each other) in order to form a virtual antenna array. The virtual antenna array achieves a diversity gain at the receivers. In the RB-CD protocol, the virtual antenna array consists of the source and some of its neighbors (called relays) which participate in repeating the transmission of a broadcast message. In addition, a new distributed relay selection algorithm is introduced in the RB-CD protocol. From the ns-2 simulation results, we verified that RB-CD provides a more reliable broadcasting service due to its capability of exploiting cooperative diversity.     

多跳无线移动Ad Hoc网络路由协议的研究分析

无线移动Ad Hoe网络(MANET)作为可移动分布式多跳无线网络，没有预先确定的网络拓扑或网络基础设施以及集中控制．为了在如此的网络中促进通信，路由协议主要用于在节点之间发现路径．Ad Hoe网络路由协议的主要目的是网络拓扑的动态变化、任意两个节点之间建立一个使得通信总费用和带宽消费最少的正确和有效的通信路径．描述了设计移动Ad Hoe网络路由协议所面临的问题以及对它们的评价，详细比较了七种典型无线移动AdHoe网络路由协议的特性和功能，即DSDV，CGSR，WRP，AODV，DSR，TORA和ABR，为进一步的研究提出了新的课题．     

An on-demand routing protocol for improving channel use efficiency in multichannel ad hoc networks

In wireless ad hoc networks, end-to-end delivery over network is a critical concern for routing protocols. The capacity of routing protocols is constrained by the intra-flow interference introduced by adjacent nodes on the same path, and inter-flow interference generated by nodes from neighboring paths. In this paper, we develop an on-demand routing protocol M-AODV-R that solves the channel assignment, reuse and routing problem jointly. The proposed channel reuse scheme and channel assignment scheme can enhance channel reuse rate. This cross-layer design approach can significantly improve the performance of multichannel ad hoc networks over existing routing protocols. Simulation results show that the proposed routing M-AODV-R can effectively increase throughput and reduce delay, as compared to AODV protocol.