Chih-Che Lin

The design and implementation of the NCTUns 1.0 network simulator

This paper presents the design and implementation of the NCTUns 1.0 network simulator, which is a high-fidelity and extensible network simulator capable of simulating both wired and wireless IP networks. By using an enhanced simulation methodology, a new simulation engine architecture, and a distributed and open-system architecture, the NCTUns 1.0 network simulator is much more powerful than its predecessor--the Harvard network simulator, which was released to the public in 1999. The NCTUns 1.0 network simulator consists of many components. In this paper, we will present the design and implementation of these components and their interactions in detail.

NCTUns 5.0: A Network Simulator for IEEE 802.11(p) and 1609 Wireless Vehicular Network Researches

NCTUns is a novel network simulator and emulator that has many unique features over traditional network simulators and emulators. It is an open-source software running on Linux and is being used by many researchers in the world. According to the NCTUns official Web site (http://NSL.csie.nctu.edu.tw/nctuns.html), as of June 1, 2008, more than 11,546 people from 124 countries have registered and downloaded this software and these numbers are still fast increasing. In its 5.0 release, NCTUns provides a complete implementation of the IEEE 802.11(p)/1609 standards defined for wireless vehicular networks. In this paper, we present the capabilities of NCTUns 5.0 focusing on its uses for IEEE 802.11(p)/1609 wireless vehicular network researches.

A Practical Routing Protocol for Vehicle-formed Mobile Ad Hoc Networks on the Roads

An IVC (Inter-vehicle communication) network is a type of mobile ad hoc networks (MANET) in which high-speed vehicles send, receive, and forward packets via other vehicles on the roads. An IVC network can provide useful applications in future Intelligent Transportation Systems. However, due to frequent network topology changes, a routing path in an IVC network breaks easily. As such, a routing protocol proposed for general MANET (e.g., AODV) performs poorly in IVC networks. To address this problem, we designed and implemented an intelligent flooding-based routing protocol and conducted several field trials to evaluate its performance on the roads. Results obtained from field trials show that (1) our protocol outperforms AODV significantly on IVC networks, and (2) our protocol can make many useful services such as email, ftp, web, video conferencing, and video broadcasting applicable on IVC networks for vehicle users.

The design and implementation of the NCTUns network simulation engine

Abstract NCTUns is a network simulator running on Linux. It has several unique advantages over traditional network simulators. This paper presents the novel design and implementation of its simulation engine. This paper focuses on how to combine the kernel re-entering and discrete-event simulation methodologies to execute simulations quickly. The performance and scalability of NCTUns are also presented and discussed.

Improving the Channel Utilization of IEEE 802.11p/1609 Networks

The IEEE 802.11p/1609 standards specify a suite of communication protocols for vehicular communication networks. A new operational mode, called theWAVE (Wireless Access in Vehicular Environments) mode, is defined to enable communication among high-speed vehicles or between a vehicle and a roadside infrastructure network. In the WAVE mode, a mobile/stationary station uses a combined FDMA/TDMA channel access scheme to switch its channel between the control channel and a service channel every 50 ms. The primary purpose of this design is to detect new services announced by other stations. However, if a station would like to use all of its service channel bandwidth to transmit a large volume of data to another station, switching back to the control channel every 50 ms without doing anything useful only unnecessarily reduces the maximum possible transmission throughput by a half. To overcome this problem, in this paper we propose an improved channel access scheme to allow a station to stay on a service channel as long as it requires before returning to the control channel. Our simulation results show that the proposed scheme significantly improves the service channel utilization under various network conditions.

Improving the Performances of Distributed Coordinated Scheduling in IEEE 802.16 Mesh Networks

The IEEE 802.16 mesh network is a promising next-generation wireless backbone network. In such a network, setting the holdoff time for nodes is essential to achieving good performances of medium-access-control-layer scheduling. In this paper, we propose a two-phase holdoff time setting scheme to improve network utilization. Both static and dynamic approaches of this scheme are proposed, and their performances are compared against those of the original schemes. Our simulation results show that both approaches significantly increase the utilization of the control-plane bandwidth and decrease the time required to establish data schedules. In addition, both approaches provide efficient and fair scheduling for IEEE 802.16 mesh networks and generate good application performances.

Evaluating and improving the TCP/UDP performances of IEEE 802.11(p)/1609 networks

The IEEE 802.11(p)/1609 standard is an emerging technology for vehicular communication networks. It amends the IEEE 802.11-2007 standard and defines a new WAVE operational mode for vehicular environments. The WAVE mode utilizes a combined FDMA/TDMA scheme to manage network bandwidth. In this mode, a node must periodically switch its frequency channel between two different channels over time. Such a design may result in bandwidth wastage due to the residual time caused by channel switching. In this paper, we propose two easy-to-implement schemes to mitigate this problem and compare their TCP/UDP performances with those of the original scheme. Our simulation results provide many insights into the operations of these schemes on IEEE 802.11(p)/1609 networks and show that the proposed schemes always outperform the original scheme.

NCTUns 6.0: A Simulator for Advanced Wireless Vehicular Network Research

NCTUns is a novel network simulator/emulator that has many unique features over traditional network simulators/emulators. It runs on Linux and many papers/projects have used it for wireless vehicular network research. According to the NCTUns website (http://NSL.csie.nctu.edu.tw/nctuns.html), as of December 24, 2009, more than 16,164 people from 137 countries in the world have registered and downloaded this software since its first public release on November 1, 2002. In its 6.0 release, NCTUns adds new supports for large-scale microscopic wireless vehicular network (WVN) simulation. In this paper, we introduce the important capabilities of NCTUns 6.0 for wireless vehicular network research.

A Vehicle Collision Warning System Employing Vehicle-To-Infrastructure Communications

Road safety has become an important issue and gained much attention for many years. To avoid vehicle collisions on the roads, researchers have proposed various collision warning systems (CWS) using different technologies. Compared with CWS using other technologies, a radio-based CWS is more capable of avoiding collisions in off-sight scenarios (such as the four corners of an intersection). Most existing radio-based CWSs operate using vehicle-to-vehicle communications. However, in such CWSs, high mobility of moving vehicles easily results in message collisions and link breakage, impairing the reliability of these CWSs. An alternative is employing vehicle-to-infrastructure communication to build CWSs. In this paper, we propose a radio-based CWS employing vehicle-to-infrastructure communications. Our simulation results show that the proposed CWS can effectively reduce the number of vehicle collisions without degrading the traffic throughput of a road network.

Improving the Data Scheduling Efficiency of the IEEE 802.16(d) Mesh Network

In an IEEE 802.16(d) (WiMAX) mesh network, network bandwidth can be managed by either the centralized scheduling (CS) mode or the distributed scheduling (DS) mode. Compared with the CS mode, the DS mode provides a larger bandwidth capacity and is more scalable. However, because the DS mode uses an on-demand three-way handshake procedure to establish data schedules, the network quality experienced by application programs may fluctuate drastically. To address this problem, in this paper we propose three schemes to improve the data scheduling efficiency of the DS mode of the IEEE 802.16(d) mesh network. Our simulation results show that network performances and qualities experienced by application programs are significantly improved under our schemes.