Location‐Aided Routing (LAR) in mobile ad hoc networks

A mobile ad hoc network consists of wireless hosts that may move often. Movement of hosts results in a change in routes, requiring some mechanism for determining new routes. Several routing protocols have already been proposed for ad hoc networks. This paper suggests an approach to utilize location information (for instance, obtained using the global positioning system) to improve performance of routing protocols for ad hoc networks. By using location information, the proposed Location‐Aided Routing (LAR) protocols limit the search for a new route to a smaller “request zone” of the ad hoc network. This results in a significant reduction in the number of routing messages. We present two algorithms to determine the request zone, and also suggest potential optimizations to our algorithms. This revised version was published online in July 2006 with corrections to the Cover Date.     

Privacy preservation in secure group communications for?vehicular ad hoc networks

Secure communications for vehicular ad hoc networks (VANETs) have become an important research issue these years. Many protocols for secure vehicle-to-vehicle communications and vehicle-to-infrastructure communications have been proposed, yet fewer protocols are concerned with secure group communications for VANETs. Of those existing protocols for group communications, some of them form a group of vehicles based on geographical regions and provide broadcasting to the group members with or without message confidentiality. The others allow secure vehicle-to-vehicle communications within a group with session keys, but they do not preserve user privacy for communicating parties within the group. In this paper, we propose a novel group communication scheme for vehicular networks, in which a group is formed by a set of related vehicles of the same purpose, such as a platoon of recreational vehicles targeted for the same tourist spot. The scheme not only offers efficient and secure group communications but also provides privacy preservation for vehicle-to-vehicle communications within a group. Security analysis is given to demonstrate the robustness of the proposed scheme.     

Providing reliable and fault tolerant broadcast delivery in mobile ad‐hoc networks

Mobile adhoc networks are making a new class of mobile applications feasible. They benefit from the fast deployment and reconfiguration of the networks, are mainly characterized by the need to support manytomany interaction schema within groups of cooperating mobile hosts and are likely to use replication of data objects to achieve performances and high data availability. This strong group orientation requires specialized solutions that combine adaptation to the fully mobile environment and provide the adequate level of fault tolerance. In this paper, we present the reliable broadcast protocol that has been purposely designed for mobile adhoc networks. The reliable broadcast service ensures that all the hosts in the network deliver the same set of messages to the upper layer. It represents the building block to obtain higher broadcast and multicast services with stronger guarantees and is an efficient and reliable alternative to flooding. The protocol is constructed on top of the wireless MAC protocol, which in turn sits over the clustering protocol. It provides an exactly once message delivery semantics and tolerates communication failures and host mobility. Temporary disconnections and network partitions are also tolerated under the assumption that they are eventually repaired, as specified by a Liveness property. The termination of the protocol is proved and complexity and performance analyses are also provided.     

How is the capacity of ad hoc networks improved with directional antennas?

The capacity of wireless ad hoc networks is constrained by the interference caused by the neighboring nodes. Gupta and Kumar have shown that the throughput for such networks is only Θ bits per second per node in a unit area domain when omnidirectional antennas are used [1]. In this paper we investigate the capacity of ad hoc wireless networks using directional antennas. Using directional antennas reduces the interference area caused by each node, thus increases the capacity of the network. We will give an expression for the capacity gain and we argue that in the limit, when the beam-width goes to zero the wireless network behaves like the wired network. In our analysis we consider both arbitrary networks and random networks where nodes are assumed to be static. We have also analyzed hybrid beamform patterns that are a mix of omnidirectional/directional and a better model of real directional antennas. Simulations are conducted for validation of our analytical results. Su Yi received the B.S. and M.S degrees in automation from Tsinghua University, China, in 1998 and 2001, respectively. She received her Ph.D. degree in electrical engineering from Rensselaer Polytechnic Institute, in December 2005. Her research interests include various topics in wireless ad hoc networks, including capacity of wireless networks, error control coding, and multimedia communications over wireless. Yong Pei is currently a tenure-track assistant professor in the Computer Science and Engineering Department, Wright State University, Dayton, OH. Previously he was a visiting assistant professor in the Electrical and Computer Engineering Department, University of Miami, Coral Gables, FL. He received his B.S. degree in electrical power engineering from Tsinghua University, Beijing, in 1996, and M.S. and Ph.D. degrees in electrical engineering from Rensselaer Polytechnic Institute, Troy, NY, in 1999 and 2002, respectively. His research interests include information theory, wireless communication systems and networks, and image/video compression and communications. He is a member of IEEE and ACM. Shivkumar Kalyanaraman is an Associate Professor at the Department of Electrical, Computer and Systems Engineering at Rensselaer Polytechnic Institute in Troy, NY. He received a B.Tech degree from the Indian institute of Technology, Madras, India in July 1993, followed by M.S. and Ph.D. degrees in computer and Information Sciences at the Ohio State University in 1994 and 1997 respectively. His research interests are in network traffic management topics such as congestion control, reliability, connectionless traffic engineering, quality of service (QoS), last-mile community wireless networks, low-cost free-space-optical networks, automated network management using online simulation, multicast, multimedia networking, and performance analysis. His special interest lies in developing the interdisciplinary connections between network architecture and fields like control theory, economics, scalable simulation technologies, video compression and optoelectronics. He is a member of ACM and IEEE. Babak Azimi-Sadjadi received his B.Sc. from Sharif University of Technology in 1989, his M.Sc. from Tehran University in 1992, and his Ph.D. from the University of Maryland at College Park in 2001 all in Electrical Engineering. He is currently with Intelligent Automation Inc. where he is a Senior Research Scientist He also has a joint appointment with the department of Electrical, Systems, and Computer Engineering of Rensselaer Polytechnic Institute where he is a research assistant professor. His research interests include, nonlinear filtering, networked control systems, and wireless networks.     

ARMS-EGR—Adaptive ranking and mobile sink-enabled energy-efficient geographic routing protocol in flying ad hoc networks

Unmanned aerial vehicles (UAVs) have become widespread because of their involvement in a variety of applications. The task of designing the energy-efficient routing between UAVs has been considered a matter of great interest due to the inherent challenges of controlling the dynamics exhibited by UAVs. Energy limitations are considered the main limitations of UAVs. This research paper proposes a novel routing protocol, adaptive ranking and mobile sink (MS)-enabled energy-efficient geographic routing (ARMS-EGR) for flying ad hoc networks. In ARMS-EGR, the whole network is partitioned into cells. The cell contains cell members (CM) and cell heads (CHs). The CH works as a cluster head. Additionally, two MSs have been used to collect data captured by CM. Multihop communication on the network leads to an increase in traffic and consumes the energy of the UAVs located near the base station (BS). MSs are used for power distribution and load balancing across the network. Adaptive ranking of forwarder UAVs and CHs is performed during intracell and intercell multihop communication, respectively, using adaptive ranking. A cell with one-hop communication can directly send packets to the MS, but the ARMS-EGR routing protocol has been proposed for multihop communication. The proposed approach is simulated in NS-2.35 software. The results show that end-to-end latency and power consumption during packet transmission are greatly minimized. ARMS-EGR also demonstrates improvements in message success rates, number of alive nodes, and packet delivery ratio, making ARMS-EGR particularly suitable for flying ad hoc networks (FANETs).     

The hop count shift problem and its impacts on protocol design in wireless ad hoc networks

The hop count information has been exploited in the design of networking protocols in wireless ad hoc multi-hop networks. The hop count setup process normally assumes a perfect disk communication model and uses a simple controlled flooding approach. However, the practical communication model may not be such a disk communication model but time-varying and lossy. Sometimes transmissions can be successful beyond the nominal transmission range, i.e., the radius of such a disk model. The defacto hop count which are setup via time-varying and lossy radio channels may be different from the one based on the disk communication model. This paper introduces the hop count shift problem in realistic radio channels and investigates its impacts, via extensive simulations, on some representative hop count based protocols. Our simulation results suggest that these protocols’ performance generally suffers from the hop count shift problem, and the degradation is dependent on how the practical communication model deviates from the disk communication model. We also propose a strategy to combat the hop count shift problem and conduct simulations to show its effectiveness. The study of this paper necessitates reexaminations for the design of new hop count setup mechanism and the hop count based networking protocols.     

Interference aware routing for mobile ad hoc networks based on node＇s sending and receiving capabilities

How to efficiently build routes among nodes is increasing important for mobile ad hoc networks （MANETs）. This paper puts forward an interference aware routing protocol called Interference aware cross layer routing protocol （IA-CLR） for MANETs based on the IEEE 802.11 medium access layer （MAC）. By defining the node＇s sending and receiving capabilities, IA-CLR can indicate the interference strength of the link in a real and comprehensive way. Further more, in order to choose the route with minimum bottleneck link interference, a new routing metric is proposed by combining the MAC layer and the network layer for cross layer design. Simulation results show that IA-CLR can significantly improve the performances of network such as the average end-to-end delay, the packets loss ratio and the throughput.     

Simulation‐based performance evaluation of routing protocols for mobile ad hoc networks

In this paper we evaluate several routing protocols for mobile, wireless, ad hoc networks via packetlevel simulations. The ad hoc networks are multihop wireless networks with dynamically changing network connectivity owing to mobility. The protocol suite includes several routing protocols specifically designed for ad hoc routing, as well as more traditional protocols, such as link state and distance vector, used for dynamic networks. Performance is evaluated with respect to fraction of packets delivered, endtoend delay, and routing load for a given traffic and mobility model. Both small (30 nodes) and medium sized (60 nodes) networks are used. It is observed that the new generation of ondemand routing protocols use much lower routing load, especially with small number of peertopeer conversations. However, the traditional link state and distance vector protocols provide, in general, better packet delivery and endtoend delay performance.     

Fault-tolerant routing in adversarial mobile ad hoc networks: an efficient route estimation scheme for non-stationary environments

Designing routing schemes that would successfully operate in the presence of adversarial environments in Mobile Ad Hoc Networks (MANETs) is a challenging issue. In this paper, we discuss fault-tolerant routing schemes operating in a network with malfunctioning nodes. Most existing MANET protocols were postulated considering scenarios where all the mobile nodes in the ad hoc network function properly, and in an idealistic manner. However, adversarial environments are common in MANET environments, and misbehaving nodes certainly degrade the performance of these routing protocols. The need for fault tolerant routing protocols was identified to address routing in adversarial environments in the presence of faulty nodes by exploring redundancy-based strategies in networks. It turns out that since the nodes are mobile, the random variables encountered are non-stationary, implying that estimation methods for stationary variables are inadequate. Consequently, in this paper, we present a new fault-tolerant routing scheme that invokes a stochastic learning-based weak estimation procedure to enhance a route estimation phase, which, in turn, is then incorporated in a route selection phase. We are not aware of any reported method that utilizes non-traditional estimates to achieve the ranking of the possible paths. The scheme, which has been rigorously tested by simulation, has been shown to be superior to the existing algorithms.     

Dynamic framework with adaptive contention window and multipath routing for video-streaming services over mobile ad hoc networks

The number of portable electronic devices capable of maintaining wireless communications increases day by day. Such mobile nodes may easily self-configure to form a Mobile Ad Hoc Network (MANET) without the help of any established infrastructure. As the number of mobile devices grows, the demand of multimedia services such as video-streaming from these networks is foreseen to increase as well. This paper presents a proposal which seeks to improve the experience of the end users in such environment. The proposal is called dCW-MMDSR (dynamic Contention Window-Multipath Multimedia Dynamic Source Routing), a cross-layer multipath routing protocol which includes techniques to achieve a dynamic assignment of the Contention Window of the IEEE 802.11e MAC level. In addition, it includes multipath routing suitable for layered coded video to improve the performance of the service. The operation is simple and suitable for low capacity wireless devices. Simulations show the benefits under different scenarios.     

Cloud service performance evaluation: status,challenges, and opportunities – a survey from the system modeling perspective

With rapid advancement of Cloud computing and networking technologies, a wide spectrum of Cloud services have been developed by various providers and utilized by numerous organizations as indispensable ingredients of their information systems. Cloud service performance has a significant impact on performance of the future information infrastructure. Thorough evaluation on Cloud service performance is crucial and beneficial to both service providers and consumers; thus forming an active research area. Some key technologies for Cloud computing, such as virtualization and the Service-Oriented Architecture (SOA), bring in special challenges to service performance evaluation. A tremendous amount of effort has been put by the research community to address these challenges and exciting progress has been made. Among the work on Cloud performance analysis, evaluation approaches developed with a system modeling perspective play an important role. However, related works have been reported in different sections of the literature; thus lacking a big picture that shows the latest status of this area. The objectives of this article is to present a survey that reflects the state of the art of Cloud service performance evaluation from the system modeling perspective. This articles also examines open issues and challenges to the surveyed evaluation approaches and identifies possible opportunities for future research in this important field.     

Bracketing or reinforcing? Socio-economic status,network power,and online deliberation

The extent to which the deliberative scenario brackets socio-economic inequalities (i.e., functioning as an ideal public sphere) has been long-debating. This study empirically addresses this question in the online setting. We test whether offline advantages (i.e., economic and cultural capitals) can be translated into power in online deliberation and how their dynamic relations further influence interlocutors’ deliberation experience (i.e., perceived procedural fairness and validity claim). Power is conceptualized as network power, including prestige (indegree), leadership (outdegree), and brokering power (betweenness). A national sample of Singaporeans participated in a three-week online deliberation, and network power is measured based on the web log. The participants answered a two-wave (i.e., pre- and post-deliberation) survey to indicate individual attributes. Structural equation modeling finds that online deliberation brackets as well as reinforces offline status. Economic capital is suppressed while cultural capital translates into network power, which further influences interlocutors’ evaluation of the deliberation.     

English–Korean speech translation corpus (EnKoST-C): Construction procedure and evaluation results

We present an English–Korean speech translation corpus, named EnKoST-C. End-to-end model training for speech translation tasks often suffers from a lack of parallel data, such as speech data in the source language and equivalent text data in the target language. Most available public speech translation corpora were developed for European languages, and there is currently no public corpus for English–Korean end-to-end speech translation. Thus, we created an EnKoST-C centered on TED Talks. In this process, we enhance the sentence alignment approach using the subtitle time information and bilingual sentence embedding information. As a result, we built a 559-h English–Korean speech translation corpus. The proposed sentence alignment approach showed excellent performance of 0.96 f-measure score. We also show the baseline performance of an English–Korean speech translation model trained with EnKoST-C. The EnKoST-C is freely available on a Korean government open data hub site.     

Cross-layer protocol design and optimization for delay/fault-tolerant mobile sensor networks (dft-msn?s)

While extensive studies have been carried out in the past several years for many sensor applications, the main approach for sensor networking cannot be applied to the sceonarios with extremely low and intermittent connectivity, dubbed the Delay/Fault-Tolerant Mobile Sensor Network (DFT-MSN). Without end-to-end connections due to sparse network density and sensor node mobility, routing in DFT-MSN becomes localized and ties closely to medium access control, which naturally calls for merging Layer 3 and Layer 2 protocols in order to reduce overhead and improve network efficiency. Due to the unique characteristics of DFT-MSN, the communication links exist only with certain probabilities and become the scarcest resource. At the same time, the sensor nodes in DFT-MSN have very limited battery power like those in other sensor networks. Clearly, there is a tradeoff between link utilization and energy efficiency. In order to address the trade-off, we develop a cross-layer data delivery protocol for DFT-MSN, which includes two phases, i.e., the asynchronous phase and the synchronous phase. In the first phase, the sender contacts its neighbors to identify a set of appropriate receivers. Since no central control exists, the communication in the first phase is contention-based. In the second phase, the sender gains channel control and multicasts its data message to the receivers. Furthermore, several optimization issues in these two phases are identified, with solutions provided to reduce the collision probability and to balance between link utilization. Our results show that the proposed cross-layer data delivery protocol for DFT-MSN achieves a high message delivery ratio with low energy consumption and an acceptable delay.     

A new channel, power and rate assignment algorithm for?multi-radio wireless mesh networks

Endowing mesh routers with multiple radios is a recent solution to improve the performance of wireless mesh networks. The consequent problem to assign channels to radios has been recently investigated and its relation to the routing problem has been revealed. The joint channel assignment and routing problem has been shown to be NP-complete and hence mainly heuristics have been proposed. However, such heuristics consider wireless links just like wired links, whereas disregarding their peculiar features. In this paper, we consider the impact of tuning the transmission power and rate of the wireless links on the efficiency of the channel assignment. Then, we present a channel, power and rate assignment heuristic and compare its performance to previously proposed algorithms.     

MPEG-4: Why,what, how and when?

The MPEG-4 Version 1 standard has been recently finalized. Since MPEG-4 adopted an object-based audiovisual representation model with hyperlinking and interaction capabilities and supports both natural and synthetic content, it is expected that this standard will become the information coding playground for future multimedia applications. This paper intends to give an overview on the MPEG-4 motivations, objectives, achievements, process and workplan, providing a stimulating starting point for more detailed reading.     

Computer Architecture, Supercomputer,and over-clock(上)

时间回到十七年前,当年我还是一个中学三年级的学生。某天,又到了上历史课的时候了。我的历史老师是个用心的好老师,除了上课之外,她也会和学生说说家常,谈一些人生的经验。不过,到了现在,我印象最深的是那天她说了一句很有意思的话。她说:“我今天本来不舒服,但想到各位求知若渴的眼神,让我不得不打起精神来为各位好好地上课……”     

International Workshop on Ware Proagation,Scattering and Emission (WPSE''''03): Theory, Experiments, Numerical Simulation and Inversion

International Workshop on Ware Proagation,Scattering and Emission (WPSE'03): Theory, Experiments, Numerical Simulation and Inversion