Wen-Tsuen Chen

On the Automated Generation of Program Test Data

Software validation through testing will continue to be a very important tool for ensuring correctness of large scale software systems. Automation of testing tools can greatly enhance their power and reduce testing cost. In this paper, techniques for automated test data generation are discussed. Given a program graph, a set of paths are identified to satisfy some given testing criteria. When a path or a program segment is specified, symbolic execution is used for generating input constraints which define a set of inputs for executing this path or segment. Problems encountered in symbolic execution are discussed. A new approach for resolving array reference ambiguities and a procedure for generating test inputs satisfying input constraints are proposed. References to arrays are recorded in a table. during symbolic execution and ambiguities are resolved when test data are generated to evaluate the subscript expressions. The implementation of a test data generator for Fortran programs incorporating these techniques is also described.

Secure broadcasting using the secure lock

The authors discuss secure broadcasting, effected by means of a secure lock, on broadcast channels, such as satellite, radio, etc. This lock is implemented by using the Chinese Remainder theorem (CRT). The secure lock offers the following advantages: only one copy of the ciphertext is sent; the deciphering operation is efficient; and the number of secret keys held by each user is minimized. Protocols for secure broadcasting using the secure lock, based on the public-key cryptosystem as well as the private-key cryptosystem, are presented. >

Active application oriented vertical handoff in next-generation wireless networks

The coexistence of heterogeneous wireless networks providing service anywhere at anytime is an inevitable trend in the development of next-generation wireless data networks. Vertical handoff is the switching of the mobile terminal (MT) among different types of wireless networks. How and when to carry out vertical handoff directly affects the performance and quality of network services. In this paper, we propose a novel vertical handoff scheme in which the MT can request and initiate the handoff actively, contrary to other schemes where the MTs participate passively during the handoff process. Our active application oriented scheme provides an efficient interface management for multi-interface MTs to reduce the power consumption caused by unnecessary interface activation. By treating the application running in the MT as the main vertical handoff decision factor, the proposed scheme is able to switch the MT at the right time to the most suitable network to minimize the waste of network resources. Finally, simulation results are presented to show the improved performance over passive schemes.

Architecture for mobility and QoS support in all-IP wireless networks

Mobility management and quality-of-service (QoS) provisioning are the important tasks on the future development of wireless networks. The high host mobility makes these tasks more challenging. In this paper, we propose an architecture which supports both mobility and QoS management in Internet protocol (IP)-based wireless networks. In mobility management, the fast handoff, which the packets are forwarded in advance to the neighboring locations where a mobile node (MN) may move to, is provided to reduce the service disruption. Also, the fast location lookup, which the routing information about a MN is replicated to some routers, is provided to avoid the triangular routing problem incurred by the protocol of mobile IP. In QoS provisioning, we enable the end-to-end QoS guarantee by using the resource reservation protocol (RSVP) signaling. In particular, the RSVP aggregation technique is used to avoid the scalability problem. Also, the technique of passive resource reservation is used to reduce the influence of host mobility on the resource reservation delay. We emphasize the integration of mobility and QoS management in the architecture design. A performance analysis is given to justify the benefits of our proposed architecture.

The strongly connecting problem on multihop packet radio networks

The problem of strongly connecting a multihop packet radio network by using a minimal total amount of transmission power is investigated. This problem is shown to be NP-complete. An approximation algorithm with the same computational complexity as that of finding a minimum spanning tree is given. It is also shown that the approximation algorithm can find a solution no greater than twice that of the optimal solution. Experimental results show that the approximation solution may be close to the optimal solution. >

Integrating mobile IP with ad hoc networks

Extending traditional IEEE 802.11-based access points to incorporate the flexibility of mobile ad hoc networks would help make the dream of ubiquitous broadband wireless access a reality. The authors discuss several issues related to integrating the mobile Internet protocol with Manets.

RSVP mobility support: a signaling protocol for integrated services Internet with mobile hosts

The resource reservation mechanism is essential for QoS provisioning in integrated services networks. The resource reservation protocol (RSVP) is a receiver oriented resource reservation protocol, and an Internet standard approved by the Internet Engineering Task Force (IETF). However, the RSVP designed for the fixed network has been facing a great challenge owing to the participation of wireless networks. In this paper, we describe a new signaling protocol for mobile hosts to reserve resources in the integrated services Internet. Under our approach, we extend the RSVP model based on IP multicast to support mobile hosts. The mobility of a host is modeled as a transition in multicast group membership. Provision of QoS in wireless networks is more complex than in wired networks due to user mobility. To overcome the mobility impact on service guarantees, mobile hosts need to make resource reservation in advance at the locations it may visit during the lifetime of the connections. These locations become the leaves of the multicast tree in our design. To obtain more efficient use of scarce wireless bandwidth, we propose the extended reservation model. A mobile proxy in a cell is required to manage resource reservations and other mobility related tasks on behalf of mobile hosts. The mobility impacts on packet delay, bandwidth utilization and packet loss rate are investigated via simulations.

An efficient multipolling mechanism for IEEE 802.11 wireless LANs

To expand support for applications with QoS requirements in wireless local area networks (WLANs), the 802.11 E Task Group was formed to enhance the current IEEE 802.11 Medium Access Control (MAC) protocol. The multipolling mechanism was discussed in the task group, but some problems remain unsolved. In this paper, we show a design of the multipolling mechanism with the advantages of high channel utilization and low implementation overhead. In our proposed mechanism, wireless stations use a priority-based contention scheme to coordinate in themselves the transmission order on the channel. Moreover, we propose a polling schedule mechanism for our proposed multipoll to serve real-time traffic with constant and variable bit rates. The bounded delay requirement of the real-time traffic can be satisfied in our scheduling model. We establish an admission test to estimate the system capacity and to determine whether a new connection can be accepted. We study the performance of our proposed mechanism analytically, as well as through simulated experiments. The results show that the proposed mechanism is more efficient than the one discussed in the IEEE 802.11 E task group.

A novel code assignment scheme for W-CDMA systems

The third-generation wideband CDMA (W-CDMA) systems support the relative higher and variable bit rate transmissions for applications with various quality-of-service (QoS) requirements. Code assignment and reassignment schemes in W-CDMA are essential, with the aim of boosting utilization of codes. A dynamic code assignment scheme (DCA) is proposed for traffic with various QoS classes introduced by Universal Mobile Telecommunication System (UMTS). From the simulation results, the proposed DCA can reduce the new call blocking probability and thus improve the system utilization for W-CDMA.

Design and Implementation of a Real Time Video Surveillance System with Wireless Sensor Networks

One important goal of surveillance systems is to collect information about the behavior and position of interested targets in the sensing environment. These systems can be applied to many applications, such as fire emergency, surveillance system, and smart home. Recently, surveillance systems combining wireless sensor networks with video cameras have become more and more popular. In traditional video surveillance systems, the system performance and cost is proportional to the number of deployed video camera. In this paper, we propose a real time video surveillance system consisting of many low cost sensors and a few wireless video cameras. The system allows a group of cooperating sensor devices to detect and track mobile objects and to report their positions to the sink node in the wireless sensor network. Then, the sink node uses the IP cameras deployed in the sensing area to record these events and display the present situations. We also propose a camera control scheme to initialize the coverage distribution of cameras and support the inter-task handoff operations between cameras. We have implemented the proposed system with 16 sensor nodes and two IP cameras, and evaluated the system performance. The result shows that our surveillance system is adaptable to variant environments and provides real time information of the monitored environment.