Ching-Chuan Chiang

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.

On-demand multicast routing protocol

This paper presents a novel multicast routing protocol for mobile ad hoc wireless networks. The protocol, termed ODMRP (on-demand multicast routing protocol), is a mesh-based, rather than a conventional tree-based multicast scheme and uses a forwarding group concept (only a subset of nodes forwards the multicast packets via scoped flooding). It applies on-demand procedures to dynamically build routes and maintain multicast group membership. ODMRP is well suited for ad hoc wireless networks with mobile hosts where bandwidth is limited, topology changes frequently, and power is constrained. We evaluate ODMRPs scalability and performance via simulation.

Routing and multicast in multihop, mobile wireless networks

In this paper we present a multicast protocol which builds upon a cluster based wireless network infrastructure. First, we introduce the network infrastructure which includes several innovative features such as: minimum change cluster formation; dynamic priority token access protocol, and distributed hierarchical routing. Then, for this infrastructure we propose a multicast protocol which is inspired by the core based tree approach developed for the Internet. We show that the multicast protocol is robust to mobility, has low bandwidth overhead and latency, scales well with membership group size, and can be generalized to other wireless infrastructures.

Tree multicast strategies in mobile, multishop wireless networks

Tree multicast is a well established concept in wired networks. Two versions, per‐source tree multicast (e.g., DVMRP) and shared tree multicast (e.g., Core Based Tree), account for the majority of the wireline implementations. In this paper, we extend the tree multicast concept to wireless, mobile, multihop networks for applications ranging from ad hoc networking to disaster recovery and battlefield. The main challenge in wireless, mobile networks is the rapidly changing environment. We address this issue in our design by: (a) using “soft state” (b) assigning different roles to nodes depending on their mobility (2‐level mobility model); (c) proposing an adaptive scheme which combines shared tree and per‐source tree benefits, and (d) dynamically relocating the shared tree Rendezvous Point (RP). A detailed wireless simulation model is used to evaluate various multicast schemes. The results show that per‐source trees perform better in heavy loads because of the more efficient traffic distribution; while shared trees are more robust to mobility and are more scalable to large network sizes. The adaptive tree multicast scheme, a hybrid between shared tree and per‐source tree, combines the advantages of both and performs consistently well across all load and mobility scenarios. The main contributions of this study are: the use of a 2‐level mobility model to improve the stability of the shared tree, the development of a hybrid, adaptive per‐source and shared tree scheme, and the dynamic relocation of the RP in the shared tree.

Parallel simulation environment for mobile wireless networks

A parallel simulator has been designed for the evaluation of wireless, multihop, mobile networks. This paper describes the process of porting the simulator from a sequential to a parallel environment. Parallelization is critical in large radio networks, where the complexity of radio propagation models, channel access schemes and interference patterns makes sequential simulation very time consuming - in the order of several hours for 100 nodes experiments. With parallel execution, speedups of up to tenfold have been observed on a 16 processor SP/2, making large net work simulations viable.