Hsu-Chun Yen

Bio: Hsu-Chun Yen is an academic researcher from National Taiwan University. The author has contributed to research in topics: Petri net & Decidability. The author has an hindex of 23, co-authored 141 publications receiving 1769 citations. Previous affiliations of Hsu-Chun Yen include University of Iowa & Kainan University.

Quality-of-service provisioning system for multimedia transmission in IEEE 802.11 wireless lans.

Abstract: In this paper, we propose a polling with non-preemptive priority based access control scheme for the IEEE 802.11 protocol. Under such a scheme, modifying the DCF access method in the contention period supports multiple levels of priorities such that user mobility can be supported in wireless LANs. The proposed transmitpermission policy and adaptive bandwidth allocation scheme derive sufficient conditions such that all the timebounded traffic sources satisfy their time constraints to provide various QoS (quality-of-service) guarantees in the contention free period while maintaining efficient bandwidth utilization at the same time. In addition, our proposed scheme is provably optimal for voice traffic, minimizing the average waiting time for voice over IP packets. In addition to theoretical analysis, simulations are conducted to evaluate the performance of the proposed scheme. As it turns out, our design indeed provides a good performance in the IEEE 802.11 wireless LANs environment.

A unified approach for deciding the existence of certain Petri net paths

Abstract: In this paper, we develop a unified approach for deriving complexity results for a number of Petri net problems. We first define a class of formulas for paths in Petri nets. We then show that the satisfiability problem for our formulas is EXPSPACE complete. Since a wide range of Petri net problems can be reduced to the satisfiability problem in a straightforward manner, our approach offers an umbrella under which many Petri net Problems can be shown to be solvable in EXPSPACE.

Quality-of-service provisioning system for multimedia transmission in IEEE 802.11 wireless LANs

Abstract: IEEE 802.11, the standard of wireless local area networks (WLANs), allows the coexistence of asynchronous and time-bounded traffic using the distributed coordination function (DCF) and point coordination function (PCF) modes of operations, respectively. In spite of its increasing popularity in real-world applications, the protocol suffers from the lack of any priority and access control policy to cope with various types of multimedia traffic, as well as user mobility. To expand support for applications with quality-of-service (QoS) requirements, the 802.11E task group was formed to enhance the original IEEE 802.11 medium access control (MAC) protocol. However, the problem of choosing the right set of MAC parameters and QoS mechanism to provide predictable QoS in IEEE 802.11 networks remains unsolved. In this paper, we propose a polling with nonpreemptive priority-based access control scheme for the IEEE 802.11 protocol. Under such a scheme, modifying the DCF access method in the contention period supports multiple levels of priorities such that user handoff calls can be supported in wireless LANs. The proposed transmit-permission policy and adaptive bandwidth allocation scheme derive sufficient conditions such that all the time-bounded traffic sources satisfy their time constraints to provide various QoS guarantees in the contention free period, while maintaining efficient bandwidth utilization at the same time. In addition, our proposed scheme is provably optimal for voice traffic in that it gives minimum average waiting time for voice packets. In addition to theoretical analysis, simulations are conducted to evaluate the performance of the proposed scheme. As it turns out, our design indeed provides a good performance in the IEEE 802.11 WLAN's environment, and can be easily incorporated into the hybrid coordination function (HCF) access scheme in the IEEE 802.11e standard.

Mental map preserving graph drawing using simulated annealing

Abstract: Information visualization has attracted much attention in recent years in many fields of science and engineering. In many applications, graphs are 'dynamic' in the sense that changes are constantly applied to a graph to reflect the evolution of the system behaviour represented by the graph. In the past, the concept of the so-called "mental map" has largely been ignored. Users often have to spend a lot of time relearning the redrawn graphs. This paper proposes an effective way to release the user from such kind of a distasteful job by maintaining a high degree of the "mental map" for general graphs when graphs are redrawn. Our experimental results suggest this new approach to be promising.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Spiking Neural P Systems

Abstract: This paper proposes a way to incorporate the idea of spiking neurons into the area of membrane computing, and to this aim we introduce a class of neural-like P systems which we call spiking neural P systems (in short, SN P systems). In these devices, the time (when the neurons fire and/or spike) plays an essential role. For instance, the result of a computation is the time between the moments when a specified neuron spikes. Seen as number computing devices, SN P systems are shown to be computationally complete (both in the generating and accepting modes, in the latter case also when restricting to deterministic systems). If the number of spikes present in the system is bounded, then the power of SN P systems falls drastically, and we get a characterization of semilinear sets. A series of research topics and open problems are formulated.

On the synthesis of discrete controllers for timed systems

Abstract: This paper presents algorithms for the automatic synthesis of real-time controllers by finding a winning strategy for certain games defined by the timed-automata of Alur and Dill. In such games, the outcome depends on the players' actions as well as on their timing. We believe that these results will pave the way for the application of program synthesis techniques to the construction of real-time embedded systems from their specifications.

Reasoning about systems with many processes

Abstract: Methods are given for automatically verifying temporal properties of concurrent systems containing an arbitrary number of finite-state processes that communicate using CCS actions. TWo models of systems are considered. Systems in the first model consist of a unique control process and an arbitrary number of user processes with identical definitions. For this model, a decision procedure to check whether all the executions of a process satisfy a given specification is presented. This algorithm runs in time double exponential in the sizes of the control and the user process definitions. It is also proven that it is decidable whether all the fair executions of a process satisfy a given specification. The second model is a special case of the first. In this model, all the processes have identical definitions. For this model, an efficient decision procedure is presented that checks if every execution of a process satisfies a given temporal logic specification. This algorithm runs in time polynomial in the size of the process definition. It is shown how to verify certain global properties such as mutual exclusion and absence of deadlocks. Finally, it is shown how these decision procedures can be used to reason about certain systems with a communication network.