This paper describes a self-organizing, multihop, mobile radio network, which relies on a code division access scheme for multimedia support. In the proposed network architecture, nodes are organized into nonoverlapping clusters. The clusters are independently controlled and are dynamically reconfigured as nodes move. This network architecture has three main advantages. First, it provides spatial reuse of the bandwidth due to node clustering. Secondly, bandwidth can be shared or reserved in a controlled fashion in each cluster. Finally, the cluster algorithm is robust in the face of topological changes caused by node motion, node failure and node insertion/removal. Simulation shows that this architecture provides an efficient, stable infrastructure for the integration of different types of traffic in a dynamic radio network. 1.

Connected dominating set (CDS) has been proposed as virtual backbone or spine of wireless ad hoc networks. Three distributed approximation algorithms have been proposed in the literature for minimum CDS.

Personal communications and mobile computing will require a wireless network infrastructure which is fast deployable, possibly multihop, and capable of multimedia service support. The first infrastructure of this type was the Packet Radio Network (PRNET), developed in the 70's to address the battlefield and disaster recovery communication requirements. PRNET was totally asynchronous and was based on a completely distributed architecture. It handled datagram traffic reasonably well, but did not offer efficient multimedia support. Recently, under the WAMIS and Glomo ARPA programs several mobile, multimedia, multihop (M 3 ) wireless network architectures have been developed, which assume some form of synchronous, time division infrastructure. The synchronous time frame leads to efficient multimedia support implementations. However, it introduces more complexity and is less robust in the face of mobility and channel fading. In this paper, we examine the impact of synchronization on wirel...

Abstract—Connected dominating set (CDS) has been proposed as virtual backbone or spine of wireless ad hoc networks. Three distributed approximation algorithms have been proposed in the literature for minimum CDS. In this paper, we first reinvestigate their performances. None of these algorithms have constant approximation factors. Thus these algorithms can not guarantee to generate; a CDS of small size. Their message complexities canbeashighasO n 2, and their time complexities may also be as large as O n 2; and O n 3. We then present our own distributed algorithm that outperforms the existing algorithms. This algorithm has an approximation factor of at most 8, O (n) time complexity and O (n log n) message complexity. By establishing the (n log n) lower bound on the message complexity of any distributed algorithm for nontrivial CDS, our algorithm is thus message-optimal.

This paper presents on-demand routing scalability improvements achieved using a "passive" clustering. Any on demand routing typically requires some form of flooding. Clustering can dramatically reduce transmission overhead during flooding. In fact, by using clustering, we restrict the set of forwarding nodes during flood search and thus reduce the energy cost and traffic overhead of routing in dynamic traffic and topology environments. However existing "active" clustering mechanisms require periodic refresh of neighborhood information and tend to introduce quite a large amount of communication maintenance overhead. In this paper, we introduce a passive clustering scheme which is mostly supported/maintained by user data packets instead of explicit control packets. The passive scheme is consistent with the on-demand routing philosophy. Simulation results show significant performance improvements when passive clustering is used. 1. INTRODUCTION Clustering in wireless ad hoc network has ...

During the past few years, distributed wireless sensor networks have been the focus of considerable research for both military and civil applications. Sensors are generally constrained in on-board energy supply therefore efficient management of the network is crucial to extend the life of the system. Sensors ’ energy cannot support long haul communication to reach a remote command site, thus they require multi-tier architecture to forward data. An efficient way to enhance the lifetime of the system is to partition the network into distinct clusters with a high-energy node called gateway as cluster-head. Failures are inevitable in sensor networks due to the inhospitable environment and unattended deployment. However, failures in higher level of hierarchy e.g. cluster-head cause more damage to the system because they also limit accessibility to the nodes that are under their supervision. In this paper we propose an efficient mechanism to recover sensors from a failed cluster. Our approach avoids a full-scale re-clustering and does not require deployment of redundant gateways.

In this study we investigate the interaction between TCP and MAC layer in a wireless multi-hop network. This type of network has traditionally found applications in the military (automated battlefield), law enforcement (search and rescue) and disaster recovery (flood, earthquake), where there is no fixed wired infrastructure. More recently, wireless "ad-hoc" multi-hop networks have been proposed for nomadic computing applications. Key requirements in all the above applications are reliable data transfer and congestion control, features that are generally supported by TCP. Unfortunately, TCP performs on wireless in a much less predictable way than on wired protocols. Using simulation, we provide new insight into two critical problems of TCP over wireless multi-hop. The first is the conflict between data packets and ACKs, which causes TCP performance to degrade for window sizes greater than 1 packet. The second is the interaction between MAC and TCP layer backoff timers which causes severe unfairness and capture conditions. In the paper, we identify these problems in several representative simulation runs on various topologies and traffic patterns and indicate possible remedies to improve TCP efficiency over a wireless multi-hop network. 1.

An ad hoc network is a fast deployable selfconfiguring wireless network characterized by node mobility, dynamic topology structure, unreliable media and limited power supply. Nodes in an ad hoc network must cooperate and carry out a distributed routing protocol in order to make multi-hop communications possible. On Demand Routing is one of the most popular routing styles in ad hoc networks. In On Demand Routing, “flooding ” is used to find a feasible route from source to destination. The function of flooding is to deliver a packet from one source to every other node in the system. Conventional flooding can be very costly in On Demand networks in terms of network

Mobile ad hoc networks (MANET) are becoming an integral part of the ubiquitous computing and communication environment, providing new infrastructure for multimedia applications such as video phone, multimedia-on-demand, and others. In order to access multimedia information in MANET, Quality of Service (QoS) needs to be considered, such as high success rate to access multimedia data, bounded end-to-end delay, and others. In this paper, we present a data accessibility service for a group of mobile users to access desired data with high success rate. This accessibility service is only possible if we utilize advanced data advertising, lookup and replication services, as well as a novel predictive location-based QoS routing protocol in an integrated fashion. Using cross-layer design, we illustrate how the QoS routing protocol assists data advertising, lookup and replication services to achieve high data access success rate. Simulation results have shown that our design is successful in a dynamic MANET.

A Mobile Ad Hoc Network (MANET) is usually assumed to be homogeneous, where each mobile node shares the same radio capacity. However, a homogeneous ad hoc network suffers from poor scalability. Recent research has demonstrated its performance bottleneck through both theoretical analysis and simulation experiments and testbed measurements. This is further exacerbated by heavy routing overhead of ad hoc routing protocols when the network size is large. In this paper, we present a design methodology to build a hierarchical large-scale ad hoc network using different types of radio capabilities at different layers. In such a structure, nodes are first dynamically grouped into multi-hop clusters. Each group elects a cluster-head to be a backbone node (BN). Then higher-level links are established to connect the BNs into a backbone network. Following this method recursively, a multilevel hierarchical network can be established. Three critical issues are addressed in this paper. We first analyze the optimal number of BNs for a layer in theory. Then, we propose a stable and light overhead clustering scheme to deploy the BNs. Finally LANMAR routing is extended to operate the physical hierarchy efficiently. We show that the Hierarchical LANMAR (H-LANMAR) can incorporate and efficiently utilize backbone links to reach remote destinations (thus reducing the hop distance). Simulation results using GloMoSim confirm that our proposed schemes achieve good performance.