Guangyu Pei

A group mobility model for ad hoc wireless networks

In this paper, we present a survey of various mobility models in both cellular networks and multi-hop networks. We show that group motion occurs frequently in ad hoc networks, and introduce a novel group mobility model Reference Point Group Mobility (RPGM) to represent the relationship among mobile hosts. RPGM can be readily applied to many existing applications. Moreover, by proper choice of parameters, RPGM can be used to model several mobility models which were previously proposed. One of the main themes of this paper is to investigate the impact of the mobility model on the performance of a specific network protocol or application. To this end, we have applied our RPGM model to two different network protocol scenarios, clustering and routing, and have evaluated network performance under different mobility patterns and for different protocol implementations. As expected, the results indicate that different mobility patterns affect the various protocols in different ways. In particular, the ranking of routing algorithms is influenced by the choice of mobility pattern.

Scalable routing strategies for ad hoc wireless networks

We consider a large population of mobile stations that are interconnected by a multihop wireless network. The applications of this wireless infrastructure range from ad hoc networking (e.g., collaborative, distributed computing) to disaster recovery (e.g., fire, flood, earthquake), law enforcement (e.g., crowd control, search-and-rescue), and military (automated battlefield). Key characteristics of this system are the large number of users, their mobility, and the need to operate without the support of a fixed (wired or wireless) infrastructure. The last feature sets this system apart from existing cellular systems and in fact makes its design much more challenging. In this environment, we investigate routing strategies that scale well to large populations and can handle mobility. In addition, we address the need to support multimedia communications, with low latency requirements for interactive traffic and quality-of-service (QoS) support for real-time streams (voice/video). In the wireless routing area, several schemes have already been proposed and implemented (e.g., hierarchical routing, on-demand routing, etc.). We introduce two new schemes-fisheye state routing (FSR) and hierarchical state routing (HSR)-which offer some competitive advantages over the existing schemes. We compare the performance of existing and proposed schemes via simulation.

Fisheye state routing: a routing scheme for ad hoc wireless networks

This paper presents a novel routing protocol for wireless ad hoc networks-fisheye state routing (FSR). FSR introduces the notion of multi-level fisheye scope to reduce routing update overhead in large networks. Nodes exchange link state entries with their neighbors with a frequency which depends on distance to destination. From link state entries, nodes construct the topology map of the entire network and compute optimal routes. Simulation experiments show that FSR is a simple, efficient and scalable routing solution in a mobile, ad hoc environment.

A Mobility Framework for Ad Hoc Wireless Networks

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.

C-ICAMA, a centralized intelligent channel assigned multiple access for multi-layer ad-hoc wireless networks with UAVs

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 tactical environment, information traffic is quite asymmetric. Ground fighting units are information consumers and receive far more data than they transmit. The up-link is used for sending requests for information and some networking configuration overhead with a few kilobits, while the down-link is used to return the data requested with megabits size (e.g. multimedia file of images and charts). Centralized intelligent channel assigned multiple access (C-ICAMA) is a MAC layer protocol proposed for ground backbone nodes to access UAV (unmanned aerial vehicle) to solve the highly asymmetric data traffic in this tactical environment. With its intelligent scheduling algorithm, it can dynamically allocate bandwidth for up-link and downlink to fit the instantaneous status of asymmetric traffic. The results of C-ICAMA is very promising, due to the dynamic bandwidth allocation of asymmetric up-link and down-link, the access delay is tremendously reduced.

Mobility management for hierarchical wireless networks

In this paper, we consider the mobility management in large, hierarchically organized multihop wireless networks. The examples of such networks range from battlefield networks, emergency disaster relief and law enforcement etc. We present a novel network addressing architecture to accommodate mobility using a “Home Agent” concept akin to mobile IP. We distinguish between the “physical” routing hierarchy (dictated by geographical relationships between nodes) and “logical” hierarchy of subnets in which the members move as a group (e.g., company, brigade, battalion in the battlefield). The performance of the mobility management scheme is investigated through simulation.

The Mars sensor network: efficient, energy aware communications

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.

Ad Hoc, Wireless, Mobile Networks: The Role of Performance Modeling and Evaluation

Consider a networking environment in which the users are mobile, the topology changes, CDMA provides multiple channels, the bandwidth of a given link is unpredictable and possibly very low, the error rates are extremely high and variable, major interference occurs when multiple transmissions take place over (possibly different) links on the same or different codes, real-time multimedia traffic must be supported as well as datagram traffic, there is no stable communication infrastructure, and there is no central control! This is the network environment (often referred to as “Ad Hoc Wireless Network”) which we are addressing in this chapter.