Showing papers by "Xiaoyan Hong published in 2001"

A Mobility framework for ad hoc wireless networks

Abstract: Mobility management in ad hoc wireless networks faces many challenges. Mobility constantly causes the network topology to change. In order to keep accurate routes, the routing protocols must dynamically readjust to such changes. Thus, routing update traffic overhead is significantly high. Different mobility patterns have in general different impact on a specific network protocol or application. Consequently the network performance will be strongly influenced by the nature of the mobility pattern. In the past, mobility models were rather casually used to evaluate network performance under different routing protocols. Here, we propose a universal mobility framework, Mobility Vector Model, which can be used for recreating the various mobility patterns produced in different applications. Case studies on optimal transmission range as a function of mobility and on network performance under various mobility models are presented in the paper. Simulation results show that excessively large transmission range will not improve network performance significantly because of the increased collisions. There is an optimal range between 1.5 - 2 times the mean node distance for free space channel. Also, simulation results show that different mobility models will have different impact on the network performance for a variety of routing protocols (AODV, DSR, FSR). When choosing routing protocols for ad hoc network applications, performance studies under multiple mobility models are recommended. The Mobility Vector model can provide a realistic and flexible framework for reproducing various models.

A Mobility Framework for Ad Hoc Wireless Networks

Abstract: Mobility management in ad hoc wireless networks faces many challenges. Mobility constantly causes the network topology to change. In order to keep accurate routes, the routing protocols must dynamically readjust to such changes. Thus, routing update traffic overhead is significantly high. Different mobility patterns have in general different impact on a specific network protocol or application. Consequently the network performance will be strongly influenced by the nature of the mobility pattern. In the past, mobility models were rather casually used to evaluate network performance under different routing protocols. Here, we propose a universal mobility framework, Mobility Vector Model, which can be used for recreating the various mobility patterns produced in different applications. Case studies on optimal transmission range as a function of mobility and on network performance under various mobility models are presented in the paper. Simulation results show that excessively large transmission range will not improve network performance significantly because of the increased collisions. There is an optimal range between 1.5 - 2 times the mean node distance for free space channel. Also, simulation results show that different mobility models will have different impact on the network performance for a variety of routing protocols (AODV, DSR, FSR). When choosing routing protocols for ad hoc network applications, performance studies under multiple mobility models are recommended. The Mobility Vector model can provide a realistic and flexible framework for reproducing various models.

Landmark routing in large wireless battlefield networks using UAVs

Abstract: In the future automated battle field communications will be supported in part by a hierarchical wireless network that includes: ad hoc ground radio subnets; point to point wireless long haul backbone, and; unmanned aerial vehicles (UAVs). In such a hierarchical network, nodes are generally partitioned into groups. Each group has one or more backbone nodes that provide access points to the backbone network and to UAVs. Communications between groups can thus utilize links at higher level. A critical protocol in the operation of such a large mobile network is routing. Previous research of UAV based systems has generally assumed the use of a hierarchical routing scheme, for example, extended hierarchical state routing (EHSR). However, a hierarchical scheme like EHSR has some limitations. In this paper, we extend landmark ad hoc routing (LANMAR) to a hierarchical structure with backbone nodes, high quality backbone links and UAVs. We show that the basic LANMAR scheme can be extended to incorporate backbone and UAV links. We will also show how backbone links and UAV links are automatically discovered by the LANMAR routing algorithm and are used effectively to reach remote destinations (thus reducing the hop distance). In other words, our scheme will combine the benefits of "flat" LANMAR routing and physical network hierarchy, without suffering of the intrinsic EHSR limitations.

The Mars sensor network: efficient, energy aware communications

Abstract: Data centric sensor networks will play an important role in planetary explorations. In the future JPL envisions sending in-situ missions with distributed instruments and sensors capable to cooperate autonomously and to collect scientific measurements (gases, chemicals, temperature, etc.). A lander or a rover functioning as a base station collects measurements and relays aggregated results to an orbiter. The wireless, multi-hop communication network connecting instruments (sensors) and the rover is functionally similar to the packet radio networks used in other ad hoc networking environments (e.g., automated battlefield, civilian emergencies, group networking, etc.). Thus, it can exploit some of the protocols developed for the latter. This paper proposes a poll-reply scheme in collecting the sensor data. Investigations of this model show an uneven distribution of energy consumption among nodes especially those close to base station. As the energy conservation and the network lifetime are critical issues for these small energy constrained sensor nodes, our paper further presents a clustering assisted, energy aware polling model. Using the passive clustering protocol, the approach provides an efficient forwarding mesh and results in more evenly distributed energy consumption without introducing extra control messages to the network. The network lifetime is prolonged while maintaining connectivity and satisfying latency constraints.

Contradictory relationship between Hurst parameter and queueing performance (extended version)

Abstract: Long Range Dependent (LRD) network traffic does not behave like the traffic generated by the Poisson model or other Markovian models. From the network performance point of view, the main difference is that LRD traffic increases queueing delays due to its burstiness over many time scales. LRD behavior has been observed in different types and sizes of networks, for different applications (e.g., WWW) and different traffic aggregations. Since LRD behaviour is not rare nor isolated, accurate characterization of LRD traffic is very important in order to predict performance and to allocate network resources. The Hurst parameter is commonly used to quantify the degree of LRD and the burstiness of the traffic. In this paper we investigate the validity and effectiveness of the Hurst parameter. To this end, we analyze the UCLA Computer Science Department network traffic traces and compute their Hurst parameters. Queueing simulation is used to study the impact of LRD and to determine if the Hurst parameter accurately describes such LRD. Our results show that the Hurst parameter is not by itself an accurate predictor of the queueing performance for a given LRD traffic trace.

Design of multilevel heterogeneous ad-hoc wireless networks with UAVs

Abstract: Multi-Layer Ad Hoc Wireless Networks with UAVs is an ideal infrastructure to establish a rapidly deployable wireless communication system any time any where in the world for military applications. In this paper, we review the research we have done so far for our heterogeneous solution. First of all, we proposed the infrastructure of Multi-level Heterogeneous Ad-Hoc Wireless Network with UAVs. Second, we developed a new MAC layer protocol, Centralized Intelligent Channel Assigned Multiple Access (C-ICAMA), for ground mobile backbone nodes to access UAV. Third, we extended HSR (Hierarchical State Routing) to this Multi-Level Heterogeneous Ad-Hoc Wireless Network. Due to the intrinsic limitations of Extended HSR, we extended the Landmark Ad Hoc Routing (LANMAR) as our forth step. Security is a critical issue for mobile ad-hoc wireless networks, especially for military applications. We developed an embedded distributed security protocol and integrated with this heterogeneous hierarchical ad hoc wireless networks in our fifth step. Therefore, the hierarchical multi-layer approach is the most desirable approach to achieve routing scalability in multi-hop wireless networks.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.