An End-to-End Bandwidth Allocation Algorithm for Ad Hoc Networks

Bandwidth-guaranteed QoS service in ad hoc networks is a challenging task due to several factors such as the absence of the central control, the dynamic network topology, the hidden terminal problem and the multihop routing property. An end-to-end bandwidth allocation algorithm was proposed in [Lin and Liu, 15] to support the QoS service in ad hoc networks. However, without exploring the global resource information along the route, the performance of that algorithm is quite limited. In addition, it also incurs significant control overhead. We develop a new algorithm for end-to-end bandwidth calculation and assignment in ad hoc networks which utilizes the global resource information along the route to determine the available end-to-end bandwidth. Our method also employs the topology-transparent scheduling technology to reduce the control overhead. The proposed algorithm can be efficiently utilized in a distributed manner. Both theoretical analysis and simulation results show that our end-to-end bandwidth allocation scheme can significantly improve the network capacity compared with the existing method.     

Multicast Communication in Ad Hoc Networks with Directional Antennas

This paper investigates the benefits and impacts of using directional antennas for multicast communications in ad hoc networks. In terms of signal reception, directional antennas have shown considerable improvement in the performance of all aspects over omni-directional antennas, especially over dense networks with heavy traffic load. In addition, we have found that transmitting multicast packets directionally to known neighboring group members or forwarders can help reduce the average end-to-end packet delay and increase the overall throughput. However, directional transmission of unacknowledged data transfers may result in lower performance in terms of packet delivery ratio than omni-directional transmission in any carrier sensing MAC protocols under moderate load due to the effect from the hidden terminal problem. Both analytical results and simulation results, as well as an acknowledgment mechanism to improve the successful delivery rate of multicast data packets, are presented. Prepared through collaborative participation in the Communications and Networks Consortium sponsored by the U.S. Army Research Laboratory under the Collaborative Technology Alliance Program, Cooperative Agreement DAAD19-01-2-0011. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation thereon.     

Asymptotic Connectivity in Wireless Ad Hoc Networks Using Directional Antennas

Connectivity is a crucial issue in wireless ad hoc networks (WANETs). Gupta and Kumar have shown that in WANETs using omnidirectional antennas, the critical transmission range to achieve asymptotic connectivity is $O(sqrt{log n/n})$ if $n$ nodes are uniformly and independently distributed in a disk of unit area. In this paper, we investigate the connectivity problem when directional antennas are used. We first assume that each node in the network randomly beamforms in one beam direction. We find that there also exists a critical transmission range for a WANET to achieve asymptotic connectivity, which corresponds to a critical transmission power (CTP). Since CTP is dependent on the directional antenna pattern, the number of beams, and the propagation environment, we then formulate a non-linear programming problem to minimize the CTP. We show that when directional antennas use the optimal antenna pattern, the CTP in a WANET using directional antennas at both transmitter and receiver is smaller than that when either transmitter or receiver uses directional antenna and is further smaller than that when only omnidirectional antennas are used. Moreover, we revisit the connectivity problem assuming that two neighboring nodes using directional antennas can be guaranteed to beamform to each other to carry out the transmission. A smaller critical transmission range than that in the previous case is found, which implies smaller CTP.      

Receiver-Oriented Multiple Access in Ad Hoc Networks with Directional Antennas

Directional antennas can adaptively select radio signals of interest in specific directions, while filtering out unwanted interference from other directions. A couple of medium access protocols based on random access schemes have been proposed for networks with directional antennas, using the omnidirectional mode for the transmission or reception of control packets in order to establish directional links. We propose a distributed receiver-oriented multiple access (ROMA) scheduling protocol, capable of utilizing multi-beam forming directional antennas in ad hoc networks. Unlike random access schemes that use on-demand handshakes or signal scanning to resolve communication targets, ROMA computes a link activation schedule in each time slot using two-hop topology information. It is shown that significant improvements on network throughput and delay can be achieved by exploiting the multi-beam forming capability of directional antennas in both transmission and reception. The performance of ROMA is studied by simulation, and compared with a well-know static scheduling scheme that is based on global topology information.     

End-to-End Link Reliable Energy Efficient Multipath Routing for Mobile Ad Hoc Networks

Among the many multipath routing protocols, the AOMDV is widely used in highly dynamic ad hoc networks because of its generic feature. Since the communicating nodes in AOMDV are prone to link failures and route breaks due to the selection of multiple routes between any source and destination pair based on minimal hop count which does not ensure end-to-end reliable data transmission. To overcome such problems, we propose a novel node disjoint multipath routing protocol called End-to-End Link Reliable Energy Efficient Multipath Routing (E2E-LREEMR) protocol by extending AOMDV. The E2E-LREEMR finds multiple link reliable energy efficient paths between any source and destination pair for data transmission using two metrics such as Path-Link Quality Estimator and Path-Node Energy Estimator. We evaluate the performance of E2E-LREEMR protocol using NS 2.34 with varying network flows under random way-point mobility model and compare it with AOMDV routing protocol in terms of Quality of Service metrics. When there is a hike in network flows, the E2E-LREEMR reduces 30.43 % of average end-to-end delay, 29.44 % of routing overhead, 32.65 % of packet loss ratio, 18.79 % of normalized routing overhead and 12.87 % of energy consumption. It also increases rather 10.26 % of packet delivery ratio and 6.96 % of throughput than AOMDV routing protocol.     

Exploiting In-Zone Broadcasts for Cache Sharing in Mobile Ad Hoc Networks

The problem of cache sharing for supporting data access in mobile ad hoc networks is studied in this paper. The key to this problem is to discover a requested data item in an efficient manner. In the paper, we propose two caching protocols, IXP and DPIP, which distinguish themselves from the existing ones in that they fully exploit in-zone broadcasts to facilitate cache sharing operation. In particular, the DPIP protocol offers an implicit index push property, which is highly useful for enhancing cache hit ratio in the neighborhood of a data requester node. Moreover, our protocols also exploit the broadcasts to facilitate the design of a simple but efficient count-based cache replacement scheme. Performance study shows that the proposed protocols can significantly improve the performance of data access in a mobile ad hoc network.     

Energy-Efficient Routing Algorithms Using Directional Antennas for Mobile Ad Hoc Networks

Power consumption is an important issue in the wireless ad hoc networking environment. In this paper, we present several energy-efficient routing algorithms using directional antennas for wireless ad hoc networks. These algorithms are simple to implement and are distributed and can be applied to mobile environments. We evaluate how directional antennas improve system throughput. We study the influence of the battery recovery effect and mobility on the network throughput during a network lifetime. We also present an algorithm that exploits the broadcast nature of the wireless communication environment to improve end-to-end bit error performance for a Rayleigh fading channel.     

A Cross-Layer Framework for Exploiting Virtual MISO Links in Mobile Ad Hoc Networks

Space-time communications can help combat fading and, hence, can significantly increase the capacity of ad hoc networks. Cooperative diversity or virtual antenna arrays facilitate spatio-temporal communications without actually requiring the deployment of physical antenna arrays. Virtual MISO entails the simultaneous transmission of appropriately encoded information by multiple nodes to effectively emulate a transmission on an antenna array. We present a novel multilayer approach for exploiting virtual MISO links in ad hoc networks. The approach spans the physical, medium access control and routing layers, and provides 1) a significant improvement in the end-to-end performance in terms of throughput and delay and 2) robustness to mobility and interference-induced link failures. The key physical layer property that we exploit is an increased transmission range due to achieved diversity gain. Except for space-time signal processing capabilities, our design does not require any additional hardware. We perform extensive simulations to quantify the benefits of our approach using virtual MISO links. As compared to using only SISO links, we achieve an increase of up to 150 percent in terms of the end-to-end throughput and a decrease of up to 75 percent in the incurred end-to-end delay. Our results also demonstrate a reduction in the route discovery attempts due to link failures by up to 60 percent, a direct consequence of the robustness that our approach provides to link failures     

基于定向天线的移动自组网路由协议研究

同等功耗下,定向天线能够产生更高的增益,提供更大的传输范围,提高网络的空间复用度和吞吐量,天线选择的方向性又降低了邻近结点之间的相互干扰,采用定向天线能够给移动自组网带来潜在性能的提高。对基于定向天线的移动自组网路由协议进行研究,简单介绍了定向天线,总结了引入定向天线产生的路由问题,对现有的一些典型定向路由协议进行了分类、介绍和比较,最后对引入定向天线带来的好处进行了分析。     

基于自适应波束天线自组网的能量效率拓扑控制

 针对自适应波束定向天线自组网,运用样方统计法推导自组网高概率连通的关键传输半径和邻居数K,提出一种基于邻居数的分布式拓扑控算法DK-Neigh,构建结点出度等于(或略小于)K的有向连通拓扑图.仿真结果表明:DK-Neigh可以保证网络连通率大于96%;当天线波束宽度小于60时,DK-Neigh的结点节能比全向天线K-Neigh算法提高15%.DK-Neigh在保证网络高概率连通的同时减少结点能耗,提高网络能量效率.     

CDR-MAC: A Protocol for Full Exploitation of Directional Antennas in Ad Hoc Wireless Networks

In this paper, we propose a new Medium Access Control (MAC) protocol for full exploitation of directional antennas in wireless networks. The protocol introduces a circular directional transmission of the Request To Send (RTS) control packet, spreading around a station information about the intended communication. The stations that receive the directional RTS, using a simple scheme of tracking the neighbors' directions, defer their transmission toward the beams that could harm the ongoing communication. In this way, the proposed protocol takes advantage of the benefits of directional transmissions as the increase of spatial reuse and of coverage range. Additionally, it reduces the hidden-terminal problem, as well as the deafness problem, two main factors for the decrease of the efficiency of directional transmissions in ad hoc networks. The performance evaluation of the protocol shows that it offers a significant improvement in static, as well as mobile, scenarios, as compared to the performance of the proposed protocols that use omnidirectional or directional transmissions.     

自组网内的延迟限制QoS路由算法研究

介绍了自组网内的延迟限制 ＱｏＳ（Ｑｕａｌｉｔｙ－ｏｆ－Ｓｅｒｖｉｃｅ）路由算法，并对它进行了仿真。该算法可在网络状态信息不精确的情况下，同时并行寻找多条路径，以优化路径选择。当节点移动、离开、加入时，引入容错机制，以便于路径保持。通过仿真可以看出，该算法在适度的寻路代价下，可以得到较高的呼叫接收率。     

无线特定网络--Ad Hoc网络

Ad Hoc网络是一种没有固定结构的无线移动网络。介绍了移动Ad Hoc网络（MANETs)的主特点和与传统有线分组交换网相比的特性,讨论了应用于Ad Hoc网络的路由机制和所需面临的问题。     

Tone Dual‐Channel MAC Protocol with Directional Antennas for Mobile Ad Hoc Networks

The directional medium access control (MAC) protocol improves the throughput of mobile ad hoc networks but has a deafness problem and requires location information for neighboring nodes. In the dual‐channel directional MAC protocol [12], the use of omnidirectional packets does not require the exact location of destination node. In this letter, we propose a tone dual‐channel MAC protocol with directional antennas to improve the throughput of mobile ad hoc networks. In the proposed MAC protocol, we use a directional CTS and an out‐of‐band directional DATA tone with a new blocking algorithm to improve the spatial reuse. We confirm the throughput performance of the proposed MAC protocol by computer simulations using the Qualnet simulator.     

Improving Transport Layer Performance in Multihop Ad Hoc Networks by Exploiting MAC Layer Information

The traditional TCP congestion control mechanism encounters a number of new problems and suffers a poor performance when the IEEE 802.11 MAC protocol is used in multihop ad hoc networks. Many of the problems result from medium contention at the MAC layer. In this paper, we first illustrate that severe medium contention and congestion are intimately coupled, and TCP's congestion control algorithm becomes too coarse in its granularity, causing throughput instability and excessively long delay. Further, we illustrate TCP's severe unfairness problem due to the medium contention and the tradeoff between aggregate throughput and fairness. Then, based on the novel use of channel busyness ratio, a more accurate metric to characterize the network utilization and congestion status, we propose a new wireless congestion control protocol (WCCP) to efficiently and fairly support the transport service in multihop ad hoc networks. In this protocol, each forwarding node along a traffic flow exercises the inter-node and intra-node fair resource allocation and determines the MAC layer feedback accordingly. The end-to-end feedback, which is ultimately determined by the bottleneck node along the flow, is carried back to the source to control its sending rate. Extensive simulations show that WCCP significantly outperforms traditional TCP in terms of channel utilization, delay, and fairness, and eliminates the starvation problem     

Understanding and Exploiting the Trade-Offs between Broadcasting and Multicasting in Mobile Ad Hoc Networks

We find that current group communications protocols are far from "one size fits all", they are typically geared toward and optimized for particular scenarios. Multicasting, in general, works well if the density of group members is sparse and in low mobility; broadcasting, in contrast, works well with a high density of group members and in high mobility. Due to the dynamics of the network, one strategy may be preferable to the other at different times and in different localized regions. In this paper, we first quantify the trade-offs between broadcasting and multicasting and evaluate the suitability of a strategy in various scenarios of deployment. Based on the lessons learned, we design a protocol that adapts in response to the dynamics of the network. We named our protocol Fireworks. Fireworks is a hybrid two-tier multicast/broadcast protocol that provides efficient and lightweight multicast dissemination and self-adapts in response to variations in the density and distribution of group members to provide efficient performance. Fireworks creates pockets of broadcast distribution in areas with many members, while it creates and maintains a multicast backbone to interconnect these dense pockets. Fireworks offers packet delivery statistics comparable to that of a pure multicast scheme but with significantly lower overheads. We also show that Fireworks has a lower level of degrading influence on the performance of coexisting unicast sessions than either traditional multicast or broadcast methods     

Delay and Capacity Trade-Offs in Mobile Ad Hoc Networks: A Global Perspective

Since the original work of Grossglauser and Tse, which showed that mobility can increase the capacity of an ad hoc network, there has been a lot of interest in characterizing the delay-capacity relationship in ad hoc networks. Various mobility models have been studied in the literature, and the delay-capacity relationships under those models have been characterized. The results indicate that there are trade-offs between the delay and capacity, and that the nature of these trade-offs is strongly influenced by the choice of the mobility model. Some questions that arise are: (i) How representative are these mobility models studied in the literature? (ii) Can the delay-capacity relationship be significantly different under some other "reasonable" mobility model? (iii) What sort of delay-capacity trade-off are we likely to see in a real world scenario? In this paper, we take the first step toward answering some of these questions. In particular, we analyze, among others, the mobility models studied in recent related works, under a unified framework. We relate the nature of delay-capacity trade-off to the nature of node motion, thereby providing a better understanding of the delay-capacity relationship in ad hoc networks in comparison to earlier works.     

Explicit Multicasting for Mobile Ad Hoc Networks

In this paper we propose an explicit multicast routing protocol for mobile ad hoc networks (MANETs). Explicit multicasting differs from common approaches by listing destination addresses in data packet headers. Using the explicit destination information, the multicast routing protocol can avoid the overhead of employing its own route construction and maintenance mechanisms by taking advantage of unicast routing table. Our protocol – termed Differential Destination Multicast (DDM) – is an explicit multicast routing protocol specifically designed for MANET environment. Unlike other MANET multicasting protocols, instead of distributing membership control throughout the network, DDM concentrates this authority at the data sources (i.e. senders) thereby giving sources knowledge of group membership. In addition, differentially-encoded, variable-length destination headers are inserted in data packets which are used in combination with unicast routing tables to forward multicast packets towards multicast receivers. Instead of requiring that multicast forwarding state to be stored in all participating nodes, this approach also provides the option of stateless multicasting. Each node independently has the choice of caching forwarding state or having its upstream neighbor to insert this state into self-routed data packets, or some combination thereof. The protocol is best suited for use with small multicast groups operating in dynamic MANET environment.     

Ad Hoc网络中QoS技术研究

服务质量保障是Ad Hoc网络环境中的一个复杂的急需解决的问题。首先论述了Ad Hoc网络的网络协议模型、QoS服务模型、QoS路由以及QoS保障策略等方面的问题,然后对其进行了综合分析,在此基础上,给出了Ad Hoc网络中不同层次的QoS路由方案以及其未来的研究方向。